CHARACTERISATION OF Ge10Se80Te10
CHALCOGENIDE GLASS
SUBMITTED BY
DIVYA NARAYANAN
Master of Technology
INTERNATIONAL SCHOOL OF PHOTONICS,COCHIN UNIVERSITY OF
SCIENCE AND TECHNOLOGY
WORK CARRIED OUT AT
INTERNATIONAL SCHOOL OF PHOTONICS
COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY
KOCHI –682 022
December 2014
COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY
INTERNATIONAL SCHOOL OF PHOTONICS
KOCHI –682 022
CERTIFICATE
This is to certify that the Project report entitled “CHARACTERISATION OF
Ge10Se80Te10 CHALCOGENIDE GLASS” submitted by DIVYA NARAYANAN
is a bonafide record of the project done under my supervision.
Dr.Sheenu Thomas
Supervising guide
Associate Professor
International School of Photonics,CUSAT
ACKNOWLEDGEMENT
Firstly I thank Lord almighty for guiding me in every step on my way to the completion
of this project.
This project would not have been successfully materialized, had it not been for the
several people who have helped me. I am extremely indebted to Ms Ajina.C for her valuable
support throughout the work.
I am extremely grateful to Dr.M.KAILASNATH (Director ,Intetnational School of
Photonics,CUSAT) for his valuable support and guidance.
I also thank Dr.Sheenu Thomas, my project guide for her valuable guidance in choosing
the topic, progress of my work and preparation of project report.
I sincerely thank all my friends and classmates who in one way or the other have helped
me in this work.
I truly admire my family for their constant encouragement and enduring support which was
inevitable for the success of all my ventures.
Divya Narayanan
ABSTRACT
Here the chalcogenide glass Ge10Se80Te10 was synthesized. Thin film , nanocolloid and filim
from nanocolloid were prepared.. The nanocolloid was prepared by mixing the powdered sample
in solutions like butylamine, diethyl amine, ethanol amine and ethylyne diamine The film from
nanocolloid was prepared by spin coating. The properties were evaluated for the bulk , thin film
nanocolloid,spin coated film of Ge10Se80Te10. The studies include absorption, transmission,
nonlinear, photoinduced etc. An application of the sample was also evaluated ie Temperature
sensor.
Table of Contents
1) INTRODUCTION................................................................................................................. 1
1.1 Chalcogens ....................................................................................... 1
1.2 Chalcogenide Glass .......................................................................... 2
1.3 Recent Trends inChalcogenide Glass.............................................. 4
1.4 Properties of Chalcogenide Glass ..................................................... 8
1.4.1 Structural Property .......................................................................................... 8
1.4.2 Electrical Properties & Electronic Band Structutre .................................... 10
1.4.3 Thermal Properties ......................................................................................... 12
1.4.4 Optical Properties ........................................................................................... 13
1.5 Applications .................................................................................... 18
2) MATERIALS & METHODS ............................................................................................. 20
2.1 Preparation Techniques ................................................................. 20
2.2 GeSeTe ... ........................................................................................ 20
2.3 Experimental Tools& Techniques used for ChG ......................... 20
2.3.1 Structural Characterisation ........................................................................... 20
2.3.2 Optical Characterisation ................................................................................ 23
2.3.3 Photodarkening Experiment .......................................................................... 27
3) BULK GLASS ..................................................................................................................... 29
3.1 Preparation…… ............................................................................. 29
3.2 Studies on bulk sample .................................................................. 30
3.2.1 XRD ................................................................................................................ 30
3.2.2 Absorption ....................................................................................................... 31
3.3 Conclusion ................................................................................................... 33
4) THIN FILM ........................................................................................................................ 34
4.1 Preparation…… ............................................................................. 34
4.2 Studies on thin film ........................................................................ 36
4.2.1 EDAX ............................................................................................................... 36
4.2.2 Absorption ....................................................................................................... 37
4.2.3 Transmission ................................................................................................... 39
4.2.4 Photodarkening Experiment ..................................................................... 40
4.2.5 Nonlinear studies ......................................................................................... 50
4.3 Conclusion………………………………………………………54
5)NANOCOLLOID…………………………………………………………………………..55
5.1 Experiment on A………………………………………………………………55
5.1.1 Absorption…………………………………………………………………………..56
5.1.2 Nonlinear studies………………………………………………………………….57
5.2 Experiment on B………………………………………………………………58
5.2.1 Absorption…………………………………………………………………………..58
5.2.2 Nonlinear studies……………………………………………………………………59
5.3 Experiment on Cand D ……………………………………………………….55
5.4 Experiment on E………………………………………………………………60
5.4.1 Absorption…………………………………………………………………………..60
5.4.2 Nonlinear studies…………………………………………………………………..61
5.5 Experiment on F………………………………………………………………64
5.5.1 Absorption…………………………………………………………………………..64
5.6 Experiment on G………………………………………………………………65
5.6.1 Absorption…………………………………………………………………………..65
5.6.2 Nonlinear studies…………………………………………………………………..66
5.7 Conclusion…………………………………………………………………………….69
6 ) SPIN COATING………………………………………………………………………...70
6.1 Experiment on E………………………………………………………………71
6.1.1 Absorption…………………………………………………………………………..71
6.1.3 Transmission………………………………………………………………………...74
6.1.3 Nonlinear studies……………………………………………………………………75
6.2 Experiment on F………………………………………………………………75
6.2.1 Absorption…………………………………………………………………………..75
6.2.3 Transmission………………………………………………………………………...78
6.2.3 Nonlinear studies……………………………………………………………………80
6.3 Experiment on G………………………………………………………………81
6.3.1 Absorption…………………………………………………………………………..81
6.3.3 Transmission………………………………………………………………………...84
6.3.3 Nonlinear studies……………………………………………………………………86
6.4 Conclusion……………………………………………………………………………..87
7) Temperature sensor using GeSeTe glass……………………………………………88
7.1 Absorption after 0 degree celsius……………………………………………………..88
7.2 Absorption after 5 degree celsius……………………………………………………..89
7.3 Absorption after 15 degree celsius……………………………………………………..91
7.4 Absorption after 35 degree celsius……………………………………………………..92
7.5 Absorption after 55 degree celsius……………………………………………………..93
7.6 Absorption after 75 degree celsius……………………………………………………..94
7.7 Absorption after 100 degree celsius……………………………………………………..95
8) CONCLUSION .................................................................................................................. 98
9) REFERENCES ................................................................................................................. 100
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INTRODUCTION
1.1 CHALCOGENS
The chalcogens are the chemical elements in group 16 of the periodic table. This group is
also known as oxygen family. The members of this group show increasing metal character as
the atomic number increases.
It consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and
the radioactive element polonium (Po). The synthetic element livermorium (Lv) is predicted
to be a chalcogen as well. Often, oxygen is treated separately from the other chalcogens,
sometimes even excluded from the scope of the term "chalcogen" altogether, due to its very
different chemical behavior from sulfur, selenium, tellurium, and polonium. The word
"chalcogen" is derived from a combination of the Greek word khalkόs (χαλκός) principally
meaning copper (the term was also used for bronze/brass, any metal in the poetic
sense, ore or coin), and the Latinised Greek word genēs, meaning born or produced.
Sulfur has been known since antiquity, and oxygen was recognized as an element in the 18th
century. Selenium, tellurium and polonium were discovered in the 19th century, and
livermorium in 2000. All of the chalcogens have six valence electrons, leaving them two
electrons short of a full outer shell. Their most common oxidation states are −2, +2, +4, and
+6. They have relatively low atomic radii, especially the lighter ones.
Lighter chalcogens are typically nontoxic in their elemental form, and are often critical to
life, while the heavier chalcogens are typicallytoxic. All of the chalcogens have some role in
biological functions, either as a nutrient or a toxin. The lighter chalcogens, such as oxygen
and sulfur, are rarely toxic and usually helpful in their pure form. Selenium is an important
nutrient but is also commonly toxic. Tellurium often has unpleasant effects (although some
organisms can use it), and polonium is always extremely harmful, both in its chemical
toxicity and its radioactivity.
Sulfur has more than 20 allotropes, oxygen has nine, selenium has at least five, polonium has
two, and only one crystal structure of tellurium has so far been discovered. There are
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numerous organic chalcogen compounds. Not counting oxygen, organic sulfur compounds
are generally the most common, followed by organic selenium compounds and organic
tellurium compounds. This trend also occurs with chalcogen pnictides and compounds
containing chalcogens and carbon group elements.
Oxygen is generally extracted from air and sulfur is extracted from oil and natural gas.
Selenium and tellurium are produced as byproducts of copper refining. Polonium and
livermorium are most available in particle accelerators. The primary use of elemental oxygen
is in steelmaking. Sulfur is mostly converted into sulfuric acid, which is heavily used in the
chemical industry. Selenium's most common application is glassmaking. Tellurium
compounds are mostly used in optical disks, electronic devices, and solar cells. Some of
polonium's applications are due to its radioactivity.
FIGURE 1.1- PERIODIC TABLE
1.2 CHALCOGENIDE GLASSES
Chalcogenide glasses (ChG) belong to an important class of amorphous solids which contain
at least one chalcogen element(sulphur, selenium and tellurium) as a major constituent.An
amorphous solid is defined as any solid that shows a short range order molecular structure or
medium range order but does not show any long range order. Glass, an amorphous solid is
defined in American Society for Testing and Materials as ‘an inorganic product of fusion
which has been cooled to a rigid condition without crystallization. Glass formation is possible
in a system of any composition provided that it contains sufficient ‘network
modifier’.Network modifiers produce three dimensional random network of strong bonds in a
system. Glass is an isotropic material, where as crystalline materials are generally
anisotropic. Like all glasses ChG‘s exhibit a glass transition temperature, a fact which
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becomes very important for the processing of bulk glasses into thin film and fiber form as
required for most applications.Chalcogenide glasses have certain unique properties that make
them of interest compared to other materials for optoelectronic applications. Their good
infrared transparency (as shown in Figure1.2), high refractive index, photosensitivity,
amenability to doping and alloying, low phonon energy and compatibility with low
temperature processing make them smart materials for optical integration. Moreover,due to
their amorphous nature, chalcogenide glasses do not need to be grown on single crystalline
substrates and can potentially be incorporated within the interconnect levels of a CMOS chip.
This backend compatibility minimizes the need for dedicated processing facilities,which
reduces fabrication costs and leverages the existing and welldeveloped semiconductor
technologies. Many of the unique properties of ChG are a direct result of low phonon energy
associated with this material resulting from the heaviness of the chalcogen nuclei.ChG with
heavier nuclei and weaker bonding have lower vibrational frequency and thus lower phonon
energies.
FIGURE 1.2-Optical transmission of three families of chalcogenide glass
compared to silica and fluride glass
The historical development of ChG as optical materials in infrared systems began with the
rediscovery of arsenic trisulfide glass.Development of the glass as a practical optical material
was continued by W. A. Fraser and J. Jerger in 1953 at Servo Corporation. Jerger, Billian,
and Sherwood extended their investigation of arsenic glasses containing selenium and
tellurium,and later adding germanium as a third constituent. Research in this fascinating area
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of chalcogenides glasses gained its momentum in with the discovery that ChG’s behave like
intrinsic semiconductors by Kolomiets. Later on Eaton, Ovshinsky and Pearson observed
their semiconductor properties and switching phenomenon. The discovery of switching and
memory effects in ChG was a turning point which attracted many researches to the world of
amorphous chalcogenide semiconductors.
The chalcogenide glasses share two common properties that have a profound impact on
their interaction with light; their electronic structure and their phonon vibrations.
Electronically, the chalcogenide glasses behave as semiconductors. They have a bandgap, and
consequently they are transparent to a certain range of wavelengths of light. The disorder of
the network creates localized electronic states that extend into the forbidden bandgap. These
states have a significant effect on the electrical and optical properties of the chalcogenide
glasses. The transparent window extends far into the infrared because the infrared side of the
transparent region is determined by the phonon energy of the material. The presence of large,
heavy atoms shifts the phonons to lower energy and therefore longer wavelengths. The low
phonon energy makes the chalcogenide glasses attractive as infrared optical materials.
1.3 RECENT TRENDS IN CHALCOGENIDE GLASSES
Device applications using ChG usually require the glass to be processed into either fiber or
thin film form. Conventionally,chalcogenide films are deposited using physical vapour
deposition (PVD) techniques such as thermal evaporation, pulsed laser deposition or
sputtering from the bulk melt quenched . These methods suffer from several shortcomings
which intermittently confine their use. They are in general limited to largely two dimensional
surfaces and require high-vacuum processing and sometimes difficult target preparation in
the case of laser deposition and sputtering. Another impediment, particularly for thermal
evaporation, is the observation that the resulting film often has a different composition
(stoichiometry) from that of the parent glass target, or is inhomogeneous in thickness, owing
to differential volatility in multi-component materials. A common solution to this problem is
solution-based coating methods. Solution-based coating methods offer a prospective pathway
to overcome these limitations by controlling the chemical composition of the solution phase
and hence the chemistry of the film with high accuracy. Solution casting method offers
higher production rate, simpler processing and opportunity to incorporate other materials like
metals, semiconductors, nano particles, polymers etc.
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1.3.1 Chalcogenide glass as nanomaterial
Nano colloids of chalcogenide glass have gained a lot of interest in the research field
recently. Understanding the chemical stability of the glasses, and finding the suitable solvent
for making solutions is very important in nano colloid preparations. Laser ablation method
was employed for the preparation of aqueous As2S3 colloidal solution by R A Ganeev et al.
Their investigation of nonlinear-optical parameters on the prepared nano colloids showed the
non linear refractive index to be -7.5 *10 -18 m 2W -1 and nonlinear absorption coefficient to
be 1 cmGW1.Eventhough the samples showed good optical non linearity, the ageing occurs
in the solution due to spontaneous nanoparticles clusterization. So in order to avoid this
ageing, stabilizer have to be added.Another method for the preparation of chalcogenide nano
colloid was by reorganisation of dissolution of As2S3 in liquid ammonia by Berzelius and
Bineau. Then onwards a lot of structural and optical studies were carried out on chalcogenide
nano colloid prepared by dissolution in different solvents like ethylenediamine,
nbutylamine,n-propylamine, diethylamine, triethylamine and other organic solvents. Even
though attempts to understand the mechanism of dissolution of chalcogenides in amines and
the existence of chalcogenide clusters with dimensions of several nanometres were reported
earlier, factors such as the use of suitable solvent for bulk glass dissolution solubility and
solution viscosity have only been studied recently by Song et al. G.C. Chern and I.Lauks had
made important contribution in the area of nano colloid chalcogenide glass like As2S2,
As2Te3, As2Te3 and Ge-Se. The proposed dissolution product of As2S3 and Ge23Sb7S70 in
amine solvent is as given in Figure 1.3.
FIGURE 1.3-Structure of dissolution products
Thin films prepared from nano colloid Ge 23S 7S 70 ChG are reported to be of promising
optical properties. Shanshan Song et al. have shown that photo-responsive nano colloid ChG
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can be used for tuning quantum cascade (QC) lasers. The photosensitivity of the cladded
chalcogenide layer is utilized for tuning of over 30 nm, by deep-etched distributed Bragg
gratings in cladding layer. ChG based QC lasers offers high power and room temperature
operation making them a promising choice for trace-gas detection in the mid-infrared where
the spectroscopic fingerprints of majority atmospheric trace gas are found. Recently in 2010
Chalcogenide opal and inverse opal photonic crystals were successfully fabricated from nano
colloid As 30S 70 chalcogenide glass by Tomas Kohoutek et al. The fabricated photonic
structures from nano colloid As 30S70 and silica as shown in Figure 1.4, are proposed for
designing novel flexible colloidal crystal laser devices, photonic waveguides and chemical
sensors.
FIGURE 1.4 –Photonic Structures
1.3.2 Chalcogenide/Polymer Composite Filim
Presently, great interest has been devoted to the fabrication of new materials suitable for
photonics applications. Among these, the amorphous chalcogenide structures are of
considerable interest due to their effectiveness in nonlinear optical characteristics. The
Quantum wave stacks (QWS) devices based on high refractive index chalcogenides and low
refractive index polymers seem to be promising for applications challenging favourable
performance ratio. There exist certain challenges associated with the use of chalcogenide
glasses in integrated optics like toxicity, durability, large coefficient of thermal expansion
(CTE) etc. This can be overcome by making composite films using chalcogenide glass and
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polymer. As it was shown by many authors it is reasonable to combine the properties of
these two groups of materials by getting nano-composites from polymers and ChG for
optimization of the sensitive parameters, simplification of the technology of fabrication,
improving the stability of the registration media, solving problems related to ecological
outputs etc. Tomas Kohoutek recently fabricated Ge-Se/Polystyren (PS) dielectric and
Au/Ge-Se/PS /dielectric reflectors from amorphous chalcogenide and polymer films with the
optical reflectivity (R) higher than R > 99 % near λ ~1550 nm using low-temperature and
inexpensive deposition techniques. Thin polymer films anchored to ChG are widely used for
modulation of the surface properties and for fabrication of versatile adaptive surfaces capable
of responding to changes in the environment. Diffractive structures by holographic and e-
beam recording technologies were recently reported by
Andriesh et al using rare-earth-doped chalcogenide glasses and polymer nanocomposite.
1.3.3 Chalcogenide glass fiber
Optical fibers need low-phonon-energy materials which exhibit excellent resistance to
moisture corrosion and good glassforming ability. The only vitreous materials that
accomplish these requirements are glasses based on sulphur, selenium, or
tellurium.Chalcogenides fibers and ChG fibers doped with rare earths have been studied for
active applications in the near- and mid-IR. The low phonon energy of chalcogenide glasses
activates many mid-IR transitions for rare-earth ions that are usually absent in materials with
higher phonon energies. Arsenic trisulfide glasses suffer from poor rare-earth solubility and
shows signs of crystallization coinciding with the temperature for fiber-drawing. Ge–As–Ga–
Sb–S glass doped with neodymium chalcogenide fibers exhibited an optical amplification at
1.083 μm with a maximum internal gain of 6.8dB achieved for a pump power of 180 mW.
ChG fibers find application in all optical switches and fiber lasers. Holey fibers based on Ga-
La-S glasses chalcogenide glasses are recently demonstrated. In these structures, the holes
generate a low effective index in the cladding and permit light guiding in the solid core by
internal reflection at the core-clad interface. Review on chalcogenide holey fibers by J.Trolès
et al. says holey fibers possess the potential3for new applications in the fields of high
nonlinear optics and largemode-area propagation together with single-mode operation at all
wavelengths.
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1.4 Properties of chalcogenide glasses
1.4.1 Structural property
The atomic structure and related properties in chalcogenide glasses depend upon preparation
methods and history after preparation. This prehistory dependence is common in all
nonequilibrium glass systems. Various experimental techniques like Xray,neutron, electron
diffractions, the anomalous x-ray scattering, the molecular vibrational (IR and Raman)
spectra, the Electron Spin Resonance (ESR), the Nuclear Magnetic Resonance (NMR) and
the Extended X-ray Absorption Fine Structure (EXAFS) are used to probe the microscopic
structures of ChG.Amorphous chalcogenide materials are reported to have a disordered
structure even though the disorder in the structure of an amorphous material is not complete
on the atomic scale. ChG lacks a long range periodic ordering of the constituent atoms.
Chemical ordering has a significant effect on the control of the atomic correlation in these
glassy solids. This is particularly important if one approaches from the nonstoichiometric to
the stoichiometric compositions. The chemical bonding between atoms, which result in the
short-range order, is responsible for most of the properties of amorphous materials. The
semiconducting property of chalcogenide glasses is, however, a direct consequence of the
covalent bonding existing in these materials. In chalcogenide glasses the covalent bonded
atoms are arranged in an open network with order extending up to the third or fourth nearest
neighbours. So chalcogenide glasses are also referred to as network glasses. Various
structural models5 have been developed for amorphous materials depending upon their
chemical nature. The Continuous Random Network (CRN) or Zachariasen model was
developed for directional bonding, present in covalent solids. Another model Random Close
Packing (RCP) or Bernal model was developed for non-directional bonding present in
metallic solids. The Random Coil (RC) [Flory model] deals with one dimensional bonding
present in polymers.The CRN model suggested for amorphous semiconductors is based on
certain features of these materials like directional nature of bondings, well-defined SRO (the
bond length and bond angle) and the topological constraints. The main drawback of the CRN
model is that it assumes that all constituent atoms satisfy their valence requirements (8-N),
where N is the valency. Hence, the structural defects such as dangling bonds, voids etc. are
not taken into account.The Random Close Packed (RCP) model is applicable for non-
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directional bonding present in metallic solids providing a satisfactory model for the structure
of amorphous metals. Like the CRN model and RCP model, Random Coil model, is
essentially a homogeneous single-phase model. This model is widely applied to one-
dimensional bonding present in polymers.To understand the chemical ordering and structural
model consider the simple case of binary alloy Ax B100-x. The atoms A and B,say belongs to
the 'a' and 'b' groups of the periodic table, respectively.There are two models to count the
fraction of A-A, A-B and B-B bonds by assuming that all atoms satisfy the (8-N) rule. These
are the Random Covalent Network (RCN) model and the Chemically Ordered Network
(CON) model. The RCN considers these bond distributions as purely statistical and neglects
the relative bond energies i.e. in random. The fraction of these bonds depends upon their
coordination numbers (8-a), (8-b) and the concentration x.Therefore it gives A-A, A-B and B-
B bonds at all the concentrations except at x = 0 and 1. Where as the CON model considers
thepreferential ordering i.e. the heteropolar A-B bonds are more preferred entities. Thus, this
model predicts a chemically ordered phase at critical composition Xc = Ya/(Ya + Yb) (the
coordination of the A and B atoms are Ya = 8 - a and Yb = 8 - b respectively). The structural
controversy is less for selenium.
1.4.2 Electrical properties and electronic band structure
Structural defects play an important role in electrical properties than the role of impurities in
ChG. The band of the states existing near the centre of the gap arise from specific defect
characteristics of the material like dangling bonds, interstitals etc.Thus the band structure of
the ChG specifically defines its property.Density of states (DOS) diagram is used to explain
or predict the properties of a material in the band theory. It denotes the number of electron
states per unit energy per electron a material will have at an energy level and it is used
successfully to describe many of the characteristic found in a crystalline solids. Band theory
for amorphous materials was first explained by Mott by extending the band theory of
crystalline materials. Mott suggested that the spatial fluctuations in the potential caused by
the configurational disorder in amorphous materials could lead to the formation of localized
states based on Anderson's localization principle. The diagram of the DOS for crystalline and
the modification of it for amorphous materials by Mott is given in figure.
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(a) (b)
FIGURE 1.5:-(a)-DOS of crystalline semiconductor (b)DOS models proposed by MOTT
for amorphous semiconductor
These localized states do not occupy all the energy states in the band but it form a tail above
and below the band. An electron in a localized state will not diffuse at zero temperature to
other allowed states with corresponding potential fluctuations. Several models have been
proposed for the band structure of amorphous semiconductors using the concept of localised
states in band tails. The first diagrammatic representation of the band structure of amorphous
semiconductor was given by Cohen and is referred to as the Cohen-Fritzsche-Ovshinsky
(CFO) model. This model suggests that the tail states extend across the gap in a structure-less
distribution. The bandpicture of CFO model is shown in Figure 1.6. The relevant features of
this model are 1) continuous tailing of the localized states, which is so high that they overlap
in the middle of the gap. Thus some of the normally filled valence band tails would be at a
higher energy than then normally empty conduction tails. Obviously, a redistribution of
charge carriers must take place.Thus electrons transfer takes place from the high lying
valence band tails to the low-lying conduction band tails. Hence, there is a deep electron trap
above and below the E F which is shown in Figure 1.6 a. This model predicts the existence of
the average mobility gap between the valence and conduction bands. There is a finite density
of these states g (E F) at EF. If g(E F)> g (Ec), it would make materials to be metallic
otherwise they would remain as semiconductors. The existence of high density of g (E F)
turns materials into undopable ones.The band picture of model proposed by Marshall and
Owen is given in Figure 1.6.b. The main difference between the CFO and the David Mott
(DM) model is the origin of deep traps in the middle of the gap.There is also another model
proposed by Emin called Small polaron model. Emin suggested that the extra free carriers in
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some amorphous semiconductor may enter as a self trapped (small polaron) state as a result
of the surrounding atomic lattice. All of the chalcogenide glasses appear to share a common
electronic band structure. The chalcogen atoms all have six valence electrons in an
s2p4configuration. The two half-filled p shells participate in the formation of covalent bonds,
so the chalcogen atoms are normally two fold coordinated. The valence band of chalcogenide
glasses consists of states from the p bonding (σ) and loan pair ( LP) orbitals.The LP electrons
have higher energy than the bonding electrons, so the full LP band forms the top of the
valence band. The conduction band is formed by the antibonding (σ*) band. The LP band
falls between the σ and σ* bands, so the bandgap is about half of the bonding-antibonding
splitting energy. Because the electrical properties are determined by the LP band, these
chalcogenide glasses are called lone-pair semiconductors.
FIGURE 1.6: (a)-DOS Models by CFO (b)-DOS model by Marshell and Owen
1.4.3 Thermal properties
Glass transition, crystallisation and melting temperatures,along with the coefficient of
thermal expansion, thermal diffusivity etc are the thermal properties associated with
chalcogenide glass. The glass transition temperature of ChG is related to the
magnitude of cohesive forces within the network and these forces must be overcomed
to allow atom movement. Thermal conductivity is critical to many electronic devices.
Thermal conductivity, of a material results from transport of energy via electrons or
via lattice vibrations(phonons). The total thermal conductivity is the sum of both.
Thermal conductivity is related to phonon mean free path. Phonon mean free path in
ChG is considerably shorter and correspondingly thermal conductivity is less.
Thermal diffusivity (TD) has a major role in switching exhibited by a chalcogenide
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glass. TD decides the rate at which heat can be dissipated away from the conducting
channel. It has been recently pointed out that there is a strong correlation between the
thermal diffusivity and the switching behaviour of chalcogenide glasses. ChG with
low thermal diffusivity are likely to exhibit memory behaviour and those with higher
values of thermal diffusivity may show threshold-type switching. Consequently, the
measurement of thermal diffusivity of switching glasses is important for identifying
suitable materials for phase change memory applications. Like optical absorption
coefficient, thermal diffusivity is unique for each material and is often ideal over
conductivity measurements due to its insensitivity to radiative heat losses as the latter
involves heat fluxes that are difficult to control.
1.4.4 Optical properties
Chalcogenide glasses are promising candidates for photonic applications due to their
attractive optical properties, such as high refractive index, high photosensitivity and large
optical nonlinearity.The investigation of the optical properties of chalcogenide glasses is of
considerable interest and affords critical information about the electronic band structure,
optical transitions and relaxation mechanisms. The optical and electrical properties of
chalcogenide glasses are generally much less sensitive to non stoichiometry and the presence
of impurities is less sensitive than crystalline semiconductors.
1.4.4.1Absorption spectroscopy
The typical absorption spectra of chalcogenide glass is shown in Figure 1.9. In amorphous
semiconductors, the optical absorption edge spectra generally contain three distinct
region2,15: A)High absorption region (α=104 cm-1) ,which involves the optical transition
between valence band and conduction band and determines the optical bandgap, B) Spectral
region with α=10 2-10 4 cm is called Urbach’s exponential tail (In this region most of the
optical transitions take place between localized tail states and extended band states) andC)
The region α ≥ 10 2 cm -1 involves low energy absorption and originates from defects and
impurities.
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FIGURE 1.8-ABSORPTION CURVE
1.4.4.3 Photoinduced properties
The photoinduced phenomena exhibited in ChG can be grouped into three categories: the
photon mode, in which the photoelectronic excitation directly induces atomic structural
changes;the photothermal mode, in which photoelectronic excitation induces some structural
changes with the aid of thermal activation; and the heat mode, in which the temperature rise
induced by optical absorption is essential. Interestingly, these three kinds of phenomena are
likely to appear in sulfides, selenides, and tellurides,respectively. The photon effects are of
particular interest from the viewpoint of fundamental science and modern applications.One of
the interesting properties of the chalcogenide materials is their sensitivity to the action of
light and other electromagnetic radiations.Therefore, many effects discovered in
chalcogenide disordered materials are3based on the action of light. Some of the important
photoinduced effects are photo-darkening, photo-bleaching, photo-plastic effect, photo-
induced fluidity, photo-induced ductility, optomechanical effect, polarization dependent
photoplastic, light-stimulated interdiffusion effect, photoexpansion,photocontraction,
athermal photo-induced transformation effect,photo-induced amorphisation effect, laser-
induced suppression of photocrystallization, photoinduced softening and hardening effect,
photoamplified oxidation effect, photo-dissolution, photo-doping effects,
photopolymerization effect, photo-anisotropy effect, photo-induced dichroism,photoinduced
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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scattering of light, photo-elastic birefringence effect,switching(Ovshinsky) effect,
photoluminescence etc. Many types of photosensitive processes observed in the chalcogenide
glasses are accompanied by changes in the optical constants, i.e., changes in the electronic
band gap, refractive index and optical absorption coefficient. These light-induced changes are
favoured in chalcogenide glasses due to their structural flexibility (low coordination of
chalcogens) and also due to their high-lying lone-pair p states in their valence bands.
Annealing chalcogenide glasses can affect the photoinduced changes, in particular
irreversible effects occur in as-deposited films, while reversible effects occur in well-
annealed films as well as bulk glasses. Changes in local atomic structure are observed on
illumination with light having photon energy near the optical band gap of the chalcogenide.
(a) PHOTODARKENING
In chalcogenide glasses the photodarkening (PD) process refers to a shift of the optical
absorption edge to lower energies upon the application of light whose energy is near that of
the band gap. All chalcogenide glasses appear to exhibit the PD process to varying degrees.
The role of specific defects in the photodarkening process has yet to be established because a
microscopic description of this effect does not exist yet.
(b) PHOTOLUMNISENCE
The defect states in the band-gap of ChG are expected to play an important role in the
occurrence of most of the photo-induced phenomena, since the defects are considered to alter
their charge conditions or their mutual interactions by trapping photo-excited carriers. To
investigate these gap-states, photoluminescence (PL) measurement is an effective tool since
their spectra provide detailed information on the relaxation process of photo-excited
electron–hole pairs.
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1.4.4.4 OPTICAL NONLINEARITY
Different techniques, such as two-photon absorption spectroscopy, degenerate four wave
mixing (DFWM), Z-scan, thirdharmonic generation (THG) and optical Kerr shutter (OKS)
have been used to measure the non-linear refractive index as well as the nonlinear absorption
coefficient of chalcogenide materials. Spectral dependence of different nonlinear parameters
like two-photon absorption (β) and intensity-dependent refractive index (n2) on linear
absorption and refractive index for an ideal amorphous semiconductor is shown in Figure 1.9
refractive index n 0, two-photon absorption β, and intensity-dependent refractive index n2 in
an ideal amorphous semiconductor with energy gap Eg. J.S. Sanghera et al. have compared
the nonlinear optical properties of these chalcogenide glasses in both bulk and fiber form.The
first investigations of the non-linear absorption of nanosecond laser pulses with hν <Eg in
ChG were reported by Lisitsa et al.. The dynamics of such induced absorption with
subpicosecond and picosecond time resolution have been investigated by Fork, Shank
etal.and by Ackley, Tauc et al . These authors showed that as a result of strong excitation of
ChG with excitation energy less than bandgap,an additional induced absorption appears,
which exhibits maximum amplitude during the excitation pulse and relaxes with several time
constants. This kind of photo-induced absorption (when hν is far from the absorption edge
Eg) appears only at strong laser excitation of ChG. The mechanisms of two-photon (or two-
step) absorption and of the carrier localization and redistribution on states in the gap were
proposed to explain the photo-induced absorption in ChG. In telecommunications based
applications, chalcogenide glasses stand out because they exhibit third-order optical
nonlinearities (Kerr,Raman and Brillouin) between two to three orders of magnitude greater
than silica.Microscopically, the nonlinear terms arise through several mechanisms such as
electronic, atomic (including molecular motions), electrostatic, and thermal processes.
Among these, the electronic process can provide the fastest response with nano second and
lower time scales, which will be needed for optical information technologies. The nonlinear
absorptions usually exhibited in amorphous semiconductors are shown in Figure 1.10.
Nonlinear absorption refers to the change in transmittance of a material as a function of
intensity or fluence.
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FIGURE 1.9-SPECTRAL DEPENDENCE
(a) (b) (c) (d)
FIGURE 1.10-(a)-One photon absorption (b) Two photo absorption (c) Two step
absorption via midgap state (c)Raman scattering process in a semiconductor
Many reports indicate that a two-photon absorption process is responsible for the optical non-
linearities observed in chalcogenide glasses. Studying on the spectral dependence of
absorption using a tunable source, showed that two-photon and two-step absorption occurs in
As2S3, and the two-photon absorption spectrum appeared to vary exponentially with energy.
This exponential form implies that the two photon process is resonantly enhanced by the gap
states which cause the weak absorption tail found in this glass.
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1.5 APPLICATIONS
Much more must be learned about the structure-property relationships in chalcogenide
glasses before we know the true potential for these glasses. Chalcogenide glasses have been
studied as promising integrated optics materials since early 1970. The IR transparency of
chalcogenide glasses (ChGs) leads to a wide variety5 of optical applications as shown in
Figure 1.11. Chalcogenide glasses have the potential to be the basis for future optical
computers, much as silicon is the basis for today’s microprocessors and computer memories.
Any optical microcircuit will require passive devices such as waveguides and gratings to
control the flow of optical information between the active elements. These elements can be
fabricated in a chalcogenide glass by several methods including photodarkening and
photodoping. Grating can be recorded on chalcogenide bulk and thin films. The
photosensitive response of the chalcogenide glasses can be used to produce high-resolution
images and photolithographic resists16. High-speed optical switching has been demonstrated
with chalcogenide glasses. Demultiplexing signals of 50 Gbit/s was achieved and the system
has the potential to exceed 100 Gbit/s operations. Infrared fibers based on ChG are of great
technological importance for communication, imaging, remote sensing and laser power
delivery. ChG fibers find application in the various fields due to their high
bandgap,longwavelength multiphonon edge and low optical attenuation. They are also
chemically stable in air and can be drawn into long core-clad fibers.They also have the
potential to permit new applications that are unachievable with current infrared materials.
The ChG find application in different fields as shown in Figure 1.11.
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FIGURE 1.11-APPLICATION OF CHALCOGENIDE GLASSES
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2.MATERIALS AND METHODS
2.1 PREPARATION TECHNIQUES
The methods used for preparation of bulk glass,thin filim and nanocolloid is discussed in
detail in preceeding chapters.
2.2 GeSeTe
The Ge-Se-Te system forms a stable glass. The properties of this glass shows that it is
similar to many other chalcogenide glasses with respect to infrared transmission and
semiconducting electrical behavior. The composition GeSeTe does not lie close to other well
investigated regions of glass-forming composition, and so a more thorough study of GeSeTe
glass was made. Here Ge10Se80Te10 composition is studied.
2.3 EXPERIMENTAL TOOLS AND TECHNIQUES USED FOR
CHARACTERISATION OF ChG GLASSES
In this section the structural, thermal and optical characterization and the tools used for
characterizing chalcogenide based materials are included.
2.3.1 STRUCTURAL CHARACTERISATION
The structural characterization of the investigated samples of chalcogenide glass was done
using X -Ray diffraction technique,Scanning electron microscopy.
(a) X-Ray DIFFRACTION( XRD)
Macroscopically, the distinction between crystalline solids and non crystalline solids can be
made just by observation. The crystals have definite shapes which reflect the regular atomic
arrangement in the atomic scales for example the cubic faces of common salt and glasses on
the other hand have curved surfaces. Microscopically, the distinction can be made using X-
ray diffraction (XRD). It is a rapid analytical technique primarily used for phase
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identification of a crystalline material and can provide information on unit cell dimensions.
The analyzed material is finely ground, homogenized,and average bulk composition is
determined. Hence it is also called the powder diffraction method. Max von Laue, in 1912,
discovered that crystalline substances act as three-dimensional diffraction gratings for X-ray
wavelengths similar to the spacing of planes in a crystal lattice. X-ray diffraction is now a
common technique for the study of crystal structures and atomic spacing. X-ray diffraction is
based on constructive interference of monochromatic X-rays and a crystalline sample. The
interaction of the incident rays with the sample produces constructive interference (and a
diffracted ray) when conditions satisfy Bragg's Law (nλ=2d sin θ). This law relates the
wavelength of electromagnetic radiation to the diffraction angle and the lattice spacing in a
crystalline sample. These diffracted X-rays are then detected, processed and counted. By
scanning the sample through a range of 2θ angles, all possible diffraction directions of the
lattice should be attained due to the random orientation of the powdered material. Conversion
of the diffraction peaks to d-spacings allows identification of the mineral because each
mineral has a set of unique d-spacings. If a material does not show this diffraction peaks it
proves that the material is not a crystal and must be non crystalline.We have used the Bruker
AXS D8 Advance diffractometer whose source of X rays is Cu, Wavelength 1.5406 A°.
(b) Scanning Electron Microscopy(SEM)
Surface imaging of the chalcogenide nano clusters in the spin coated thin films are studied
using Scanning electron microscope(JEOL Model JSM - 6390LV) equipped with EDS (JEOL
Model JED –2300) for the qualitative elemental analysis.
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2.3.2 OPTICAL CHARACTERISATION
(a) Absorption,reflection,transmission measurement
JASCO V-570 UV/VIS/NIR Spectrophotometer was used for the absorption, transmission
and reflectance measurements of the samples. The spectrometer consist of Optical system33:
single monochromatic, UV/ VIS region 1200 lines/ mm plane grating, NIR region: 300 lines/
nm plane grating, Czenry –Turner mount double beam type Resolution: 0.1 nm (UV/ VIS
region) 0.5 nm (NIR region).Wavelength range: 200 nm to 2200 nm. The beam from the light
source is converged and enters the monochromator. It is dispersed by the grating in the
monochromator and the light passes out through the exit slit. This light is split into two light
paths by a sector mirror,one incident on the sample to be measured and the other on the
reference sample such as solvent. The light that has passed through the sample or reference
sample is incident on the photomultiplier tube and PbS photoconductive cell which are the
detectors. In the reflectance measurement the set up has to be changed.The Model SLM-468
single reflection attachment is designed to measure the relative reflectance of sample using
the forward reflected light from the aluminum-deposited plane mirror as reference. It permits
the measurement of the reflectance of metal deposited film,metal plating etc. The wavelength
range is 220 nm to 2200 nm with a beam port diameter of 7 mm and angle of incidence
approximately 5º.
(b) Optical absorption spectroscopy of amorphous semiconductors
Absorption spectroscopy of the materials investigated in this thesis was studied using Jasco
V570 spectrophotometer. The typical absorption spectrum of chalcogenide glass is shown in
Figure 2.5. In amorphous semiconductors, the optical absorption edge spectra generally
contain three distinct region:
(A) High absorption region (α=104 cm-1), which involves the optical transition between
valence band and conduction band6which determines the optical bandgap. The
absorption coefficient in this region is given by
α hυ=B(hυ-Eg)p ( 2.1)
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where Eg is the optical bandgap and B is a constant related to band tailing parameter. In the
above equation, p=1/2 for a direct allowed transition=3/2 for a direct forbidden transition,
p=2 for an indirect allowed transition and p=3 for an indirect forbidden transition.
FIGURE 2.1-ABSORPTION CURVE OF CHALCOGENIDE GLASSES
(B) Spectral region with α=102-104 cm-1 is called Urbach’s exponential tail region in
which absorption depends exponentially on photon energy 36and is given by
α hυ= αo exp(hυ/Ee) ( 2.2)
where αo is a constant and Ee is interpreted as band tailing width of localized states, which
generally represents the degree of disorder in amorphous semiconductors. In this region most
of the optical transitions take place between localized tail states and extended band states.
(C) The region with α ≥ 102 cm-1 involves low energy absorption and originates from defects
and impurities.
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(a)Analysis of Transmission Spectra of thin films using Swanepoels method
Basically, the amount of light that gets transmitted through a thin film material depends on
the amount of reflection and absorption that takes place along the light path. The transmission
spectrum which depends on the material will have two distinctive features, it will either have
interference fringes or it will not. The schematic representation of behaviour of light passing
through the material is shown in Figure 2.2.
FIGURE 2.2-Schematic diagram of light passing through thin film
The optical constants can be measured by examining the transmission through a thin film
deposited on a transparent glass or other (e.g. sapphire) substrate. Figure 2.3 shows a
spectrum taken from a thin film on glass substrate. Swanepoel has critically reviewed how a
single transmission spectrum as shown in figure can be used to extract the optical constants
of a thin film.
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FIGURE 2.3- Transmission spectra showing interference fringes
The refractive index of the thin film with uniform thickness can be calculated from the two
envelopes, TM (λ) and Tm(λ), by considering the extremes of the interference fringes.
Maxima T M= Ax/(B-Cx+Dx 2) (2.3)
Minima T m= Ax/(B+Cx+Dx 2) (2.4)
Subtracting the reciprocal of above first equation 2.3 from second equation 2.4 yields an
expression that is independent of the absorbance, x
(1/T m)-(1/T M)=2C/A (2.5)
Where A =16n2s (2.6)
C=2(n2-1)(n2-s) (2.7)
Rearranging for n
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In this equation, s is the refractive index of glass substrate and its values are obtained from
transmission spectra of substrate Ts,using the relation.
In the region of weak and medium absorption, where α≠0,transmittance decreases mainly due
to the effect of absorption coefficient, α and Eq.(2.9) modifies to
where TM and Tm are the transmission maximum and corresponding minimum at a certain
wavelength .
If n1 and n2 are refractive indices of two adjacent maxima or two adjacent minima at
wavelengths λ1 and λ2, respectively, then the thickness d1 of the film is given by
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2.3.3 PHOTODARKENING EXPERIMENT
Photoinduced darkening experiments were done on the thin films using the experimental set
up as shown in Figure 2.4. Photoinduced studies were carried out using above band gap and
near band gap laser sources. We have used 30mW DPSS(532nm) to study the
photosensitivity of the unannealed films. The laser power was made stable during exposure to
avoid significant uncertainty in the total supplied energy. The laser beam was expanded using
a plano-concave lens and collimated with a second plano-convex lens. The absorbance
spectra of the film at normal incident condition in the spectral range 200–2200 nm were
recorded by a double beam UV–VIS–NIR spectrophotometer (Jasco V570) after and before
exposure. All the measurements were executed at room temperature and the samples were
kept in the dark between experiments.
FIGURE 2.4-Photodarkening experiment
2.3.4 Z-SCAN for analyzing nonlinear properties of the sample
Z-scan technique introduced by Sheik Bahae is a single beam method for measuring the sign
and magnitude of nonlinear refractive index that has a sensitivity compared to interferometric
methods. It provides direct measurement of nonlinear absorption coefficient.Previous
measurements of nonlinear refraction have used a variety of techniques including nonlinear
interferometry, degenerate four wave mixing, nearly degenerate three wave mixing, ellipse
rotation and beam distortion measurements. The first three methods namely nonlinear
interferometry and wave mixing are potentially sensitive techniques, but all require complex
experimental apparatus. The propagation of laser beam inside such a material and the ensuing
self refraction can be studied using the z-scan technique. Thus it enables one to determine the
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third order nonlinear properties of solids, ordinary liquids, and liquid crystals. The
experimental set up for single beam z-scan technique is given in Figure 2.5. In the ordinary
single beam configuration, the transmittance of the sample is measured, as the sample is
moved along the direction of the focussed guassian beam. A laser beam propagating through
a nonlinear medium will experience both amplitude and phase variation. If transmitted light is
measured through an aperture placed in the far field with respect to focal region, the
technique is called closed aperture z-scan. In this case, the transmitted light is sensitive to
both nonlinear absorption and nonlinear refraction. In a closed aperture z-scan experiment,
phase distortion suffered by the beam while propagating through the nonlinear medium is
converted into corresponding amplitude variations. On the other hand, if transmitted light is
measured without an aperture, the mode of measurement is referred to as open aperture z-
scan. In this case, the output is sensitive only to nonlinear absorption. Closed and open
aperture z-scan graphs are always normalized to linear transmittancei.e., transmittance at
large values of |z|.Closed and open aperture z-scan methods yield the real part and imaginary
part of nonlinear susceptibility χ(3) respectively. Usually closed aperture z-scan data is
divided by open aperture data to cancel the effect of nonlinear absorption contained in the
closed aperture measurements. The new graph, called divided z-scan,contains information on
nonlinear refraction alone.
FIG 2.5-ZCAN TECHNIQUE
An important requirement in the z-scan measurement is that,it is assumed that the sample
thickness is much less than Rayleigh’s range z0 (diffraction length of the beam [z0=k ω0/2,
where k is the wave vector and ω0 is the beam waist radius. The beam waist radius ω0 is
given by ω0=fλ/D, where f is the focal length of the lens used, λ is the wavelength of the
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source and D is the beam radius at the lens. This is essential to ensure that the beam profile
does not vary appreciably inside the sample because z-scan technique is highly sensitive to
the profile of the beam and also to the thickness of the sample. Any deviation from gaussian
profile of the beam and also from thin sample approximation will give rise to erroneous
results.
2.3.4.1 Open aperture ZScan
Non linear absorption of a sample is manifested in the open aperture z- Scan measurement. If
the sample is having nonlinear absorption such as two photon absorption (TPA), it is
manifested in the measurement as a transmission minimum at the focal point.Otherwise if the
sample is a saturable absorber, the transmission increases with increase in incident intensity
and results in transmission maximum at the focal region. In the case of an open aperture z-
scan, the aperture as shown in Figure 2.5 is absent. In the absence of an aperture the
transmitted light measured by the detector is sensitive only to intensity variations.
Hence,phase variations of the beam are not taken into consideration
2.3.4.2 Closed aperture ZScan
The basis of closed aperture z-scan is the self refraction and self phase modulation effects.
The technique relies on the transmittance measurement of a nonlinear medium through a
finite aperture in the far field as a function of the sample position z with respect to the focal
plane using a single gaussian beam in a tight focus geometry.Consider, for instance, a
material with a negative nonlinear refraction and thickness smaller than the diffraction length
of the focused beam being positioned at various points along the z-axis. This assumption
implies that the sample acts as a thin lens of variable focal length due to the change in
refractive index at each position ( n = n0 + n2 I ).
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3.BULK GLASS
3.1 PREPARATION
Bulk glasses were prepared using melt quenching method. Melt quenching technique was the
only method used for the preparation of bulk glasses before the development of chemical
vapour deposition and sol gel technique. One of the important features of the melt quenching
technique is the high flexibility of geometry and composition and the advantage of obtaining
materials of large size in comparison to other methods. The doping or codoping of active ions
or transition metals are quiet easy using this method. This method can be used for the
preparation of silicate, borate,phosphate, oxide or non oxide systems. One of the main
disadvantages of this method is the lack of ultra high purity as compared to other chemical
methods. In order to avoid contamination, the crucibles made of noble metals can be used.
Melt quenching method applied for chalcogenide glass preparation is as follows. This method
is based on the fusion of raw materials in to a viscous solid, followed by forming in to a
shape and quenching to a glass. The electronic grade (5N purity) constituent elements are
weighed in proportion to their atomic weight percentages. The raw materials used in the
present study are Ge, Se,Te. For each composition approximately around 4gm of material is
transferred to clean quartz ampoules of 8 mm diameter and 8cm length. The ampoule is then
evacuated at a pressure of 10-3 m bar for half an hour and then flame sealed at this vacuum
using oxygen -indane flame torch. Precleaning and evacuating helps to avoid the presence of
impurities. The ampoule is then placed in a rocking and rotating furnace as shown in Figure
3.1.
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FIGURE 3.1-Rocking and rotating furnace
The furnace can attain a maximum temperature of 1100ºC. The temperature controller in this
unit is C961 Blind Temperature Controller with single thermocouple or RTD input and one
relay output with user specific control action and relay logic. Before keeping the ampoule, the
furnace can be programmed to the desired temperature. The samples presented in this thesis
are prepared at a temperature of 1050ºC. In order to homogenize the melt continuous rotation
and rocking in an interval of 1hour is given. The melt is then rapidly quenched to ice cold
water. The samples are then taken out from the sealed ampoules by dipping it in Hydrofluoric
acid (HF) solution. HF solution etches the quartz ampoule leaving the bulk glass.
3.2 STUDIES ON BULK Ge 10Se 80Te 10
3.2.2 XRD
XRD is explained in the previous section.
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FIGURE 3.1-XRD of Ge10Se80Te10
The absence of sharp peaks prove that the prepared sample is amorphous in nature.
3.2.2 Absorption
Absorption spectroscopy is studied using Jasco V570 spectrophotometer.The specifications
of which are given in previous chapter.The absorbance corresponding to wavelength from
200-2200nm is taken.
Ge Se Te SAIF COCHIN BRUKER D8 Cochin Uni
Operations: Smooth 0.150 | Background 0.214,1.000 | Import
File: SAIFXR140821A-01(GeSeTe).raw - Step: 0.020 ° - Step time: 65.6 s - WL1: 1.5406 - kA2 Ratio: 0.5 - Generator kV: 40 kV - Generator mA: 35 mA - Type: 2Th/Th locked
Lin
(C
ounts
)
0
1000
2000
3000
4000
5000
6000
7000
8000
2-Theta - Scale
3 10 20 30 40 50 60 70 80
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200 400 600 800 1000 1200
-2
-1
0
1
2
3
4A
bso
rba
nce
Wavelength(nm)
B
FIGURE 3.2 –ABSORPTION SPECTRUM OF BULK Ge 10 Se 80Te 10
This graph can be modified to get bandgap of the glass. The energy hv vs ( αhv)1/2 graph is
extrapolated to X-axis and point is noted from which the bandgap of the bulk material is
calculated.
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1 2 3
1.5
2.0
2.5
3.0
3.5
4.0(
ah
v)^
1/2
( cm
-1e
V)
Energy(eV)
BANDGAP GRAPH
FIGURE 3.3-Bandgap graph
The bandgap is found to be 1.22 eV by this method.
3.3 Conclusion
1) X-ray diffraction studies conducted on the bulk sample show no prominent peaks
which reveals the amorphous nature of the samples .
2) Optical bandgap determined by UV-Vis-NIR spectroscopy is found to be 1.22eV
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4.THIN FILM
4.1 PREPARATION
Thin film preparation can be based on physical deposition or chemical deposition.
Depositions that happen because of a chemical reaction are Chemical Vapour Deposition
(CVD), Electrodeposition, Epitaxy, Thermal oxidation etc and depositions that happen
because of a physical reaction are Physical Vapour Deposition, Evaporation, Sputtering and
Casting. The vapour deposition methods such as thermal evaporation, sputtering and
chemical vapour deposition methods can yield amorphous thin films deposited on a substrate.
Here thermal evaporation technique is used.
4.1.1 Thermal Vapourisation
It is perhaps the simplest vapour deposition technique which involves resistive or electron
beam heating in vacuum of a reservoir containing the material to be evaporated. The melt so
produced then evaporates and the vapour is condensed on to a substrate, forming a thin film.
In chalcogenide glass the deposition of the film at the oblique incidence may result to
structural inhomogeneity which may lead to formation of columnar growth morphology for
the films.The making of an amorphous chalcogenide thin film by thermal evaporation in
vacuum coating unit is done in the following way. The unit used for coating is India High
Vacuum pumps (12A4-D). Firstly, bulk sample is weighed and 0.39g loaded in tungsten boat
in the system as shown in Figure 4.1. After this the bell jar is closed and the system pumped
down to around 2*10-5 torr through a diffusion pump. At this level of air pressure, the entire
environment inside the deposition chamber is free of impurities and the sample is ready for
deposition.The chamber is evacuated by INDVAC Diffpak pump Model 114D abd backed by
250 liters per minute, doublestage, direct driven,Rotary vacuum pump, ModelIVP.
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FIGURE 4.1-BELL JAR IN THERMAL EVAPORATION UNIT
With the shutter in the closed position, the temperature of the substrate is set to the desired
level heated till the sample loaded starts to evaporate. The heating element in the system is
conal sheated nichrome having a power rating of 500 watts, 120 V to 140V. Once the
evaporation rate is stabilized and the substrate reaches its desired temperature, the vapour is
allowed to come into contact with the substrate. The rate of evaporation is maintained to be
10A0/s. The evaporation rate as well as the film thickness can be controlled using a quartz
crystal in Digital thickness Monitor Model-CTM-200 attached to the bell jar. When the
desired thickness is reached, theshutter is closed. The amorphous film is maintained at the
substrate temperature until the boat and the chamber is cooled down to a level suitable for the
film to be removed from the system.
FIGURE 4.2-Ge10Se80Te10
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4.2 STUDIES ON Ge 10Se 80Te 10
4.2.1 EDAX
To confirm the composition of the elements in the sample EDAX spectra have been taken.
Table 4.1 compares the atomic percentage of components obtained from EDAX analysis with
respect to the nominal composition. Figure 4.3 shows EDAX spectra of Ge10Se80Te10 thin
film.
Element Mass% Atom%
Ge 3.81 4.36
Se 81.98 86.37
Te 14.21 9.27
Table 4.1-EDAX of the thin film
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The EDAX image is
FIGURE 4.3-EDAX of thin film
4.2.2 ABSORPTION SPECTRUM
Absorption spectroscopy is studied using Jasco V570 spectrophotometer. The specifications
of which are given in previous chapter. The absorbance corresponding to wavelength from
200-2200nm is taken.
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0 500 1000 1500 2000 2500
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Absorbance spectrum
FIGURE 4.4-ABSORBANCE SPECTRUM OF THIN FILM Ge 10 Se 80Te10
This graph can be modified to get bandgap of the glass. The wavelength is known so we plot
the energy hv in xaxis and ( αhv)^1/2 in yaxis. The graph is extrapolated to xaxis and point is
noted,this is the bandgap of the bulk material.
1 2 3
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
( a
hv)^
1/2
(cm
-1e
V)
Energy(eV)
FIGURE 4.5- ( αhv)^1/2 Vs energy graph
The bandgap is obtained from the graph is 1.478 eV.
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4.2.3 TRANSMISSION SPECTRUM
The transmission spectrum of the sample fabricated obtained from a spectrometer is as shown
in Figure 4.4. The plot shows fringes due to interference at various wavelengths. A
continuously oscillating maxima and minima at different wavelengths confirm the optical
homogeneity of deposited thin films. Optical transmission is very complex functions and
strongly depend on the absorption coefficient. Various optical parameters are calculated for
the prepared thin film as given in Chapter 2 using a straight forward method proposed by
Swanepoel, which is based on the use of extrema’s of the interference fringes of the
transmittance spectrum.
0 500 1000 1500 2000 2500
0
20
40
60
80
100
Tra
nsm
itta
nce
(a.u
)
Wavelength(nm)
Figure 4.6-Transmission spectra of Ge 10Se 80Te10
Using Swapnoel’s method the refractive index is found at wavelength 917.02nm is 2.84 and
that at 1045.32nm is 2.75. These values are obtained by using eqns(2.3 to 2.11). Now by
using eqn 2.12 we get the thickness of film to be 3.55µm. The variation of refractive index
(n) with wavelength for the thin film is shown in Figure 4.7. The decrease in refractive index
with wavelength shows the normal dispersion behavior of the material.
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WAVELENGTH(nm) REFRACTIVE INDEX
917.02 2.84
1045.32 2.75
1237.50 2.68
1529.10 2.66
2013.44 2.42
800 1000 1200 1400 1600 1800 2000 2200
2.4
2.5
2.6
2.7
2.8
2.9
refr
active
in
de
x
wavelength (nm)
refractive index
FIGURE 4.7-Variation of refractive index with wavelength
4.2.4 Photoinduced darkening
Chalcogenide glasses when exposed to above- and near bandgap light, absorption coefficient
over a broad range of frequencies increases. The amount of increase depends on the
wavelength of the inducing light, the duration of exposure and the intensity of the light. The
photodarkening process involves a shift of the optical absorption edge to lower energy and an
increase in the band tail absorption. The absorption change is permanent and can only be
removed by annealing the glass at a temperature near its glass transition temperature. Because
the optical changes can be removed this is known as reversible photodarkening. Reversible
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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photodarkening has been observed in bulk glasses and well as in thin films. The
photodarkening can be induced with above-bandgap or below-bandgap light, so long as the
light has sufficient energy to excite electrons from the LP band. The index of refraction of the
glass also changes with photodarkening. The associated index change may prove useful for
the fabrication of optical structures in bulk glasses and in thin films.
EXPERIMENTAL SETUP:-
The photodarkening experiment was arranged as shown in Figure.4.6. Diode pumped solid
state laser (DPSS) of 532nm is used to study the photosensitivity of the films. The laser
power was made stable during exposure to avoid significant uncertainty in the total supplied
energy. The laser beam was expanded using a plano-concave lens and collimated with a
second plano-convex lens. The transmittance and absorption spectra of films at normal
incident condition in the spectral range 200–2200 nm were recorded by a double beam UV-
VIS-NIR spectrophotometer (Jasco V 570).
FIGURE 4.8-SETUP FOR PHOTODARKENING EXPERIMENT
There will not be any change to the thickness of the film. In order to study the kinetics
involved in the photoinduced process, time dependence of bandgap of the sample on laser
irradiation was made. The sample were irradiated at different time intervals and the
absorption and transmission spectra were recorded using double beam UV-VIS-NIR
spectrophotometer (Jasco V 570) at each interval.
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(a) ABSORPTION SPECTRUM
The sample were irradiated for 5 minutes,10 minutes,20 minutes,30 minutes and 60
minutes. The absorption at each interval was taken using spectrometer mentioned
above.
0 500 1000 1500 2000 2500
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Absorbance spectrum
Figure 4.9-Absorption spectrum without illumination
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0 500 1000 1500 2000 2500
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 4.10-Absorbance spectrum at 5minute illumination
With the help of absorption spectrum
0 500 1000 1500 2000 2500
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Ab
so
rba
nce
(cm
-1)
wavelength(nm)
Figure 4.11-Absorption spectrum after 10min illumination
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0 500 1000 1500 2000 2500
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 4.12-Absorption spectrum after 20min illumination
0 500 1000 1500 2000 2500
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
B
Figure 4.13-Absorption spectrum after 30min illumination
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0 500 1000 1500 2000 2500
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5A
bso
rba
nce
(a.u
)
Wavelength(nm)
FIGURE 4.14-Absorption spectrum after 60min illumination
From the absorption spectrum the hv Vs ( αhv)1/2 graph is plotted corresponding to each
interval.They are given below.
1 2 3
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
( a
hv)^
1/2
(cm
-1e
V)
Energy(eV)
FIGURE 4.15- hv Vs ( αhv)1/2 without illumination
The bandgap found by this method is 1.478 eV.
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1 2 3
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
( a
hv)^
1/2
(cm
-1e
V)1
/2
hv(eV)
FIGURE 4.16- hv Vs ( αhv)1/2 with 5 minutes illumination
The bandgap obtained is 1.472 eV.
1 2 3
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
( a
hv)^
1/2
(cm
-1e
V)1
/2
Energy(eV)
FIGURE 4.17- hv Vs ( αhv)1/2 with 10 minutes illumination
The bandgap obtained is 1.472 eV.
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1 2 3
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
( a
hv)^
1/2
(cm
-1e
V)
Energy(eV)
FIGURE 4.18- hv Vs ( αhv)1/2 with 20 minutes illumination
The bandgap obtained is 1.466eV.
1 2 3
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
( a
hv)^
1/2
(cm
-1e
V)
Energy(eV)
FIGURE 4.19- hv Vs ( αhv)1/2 with 30 minutes illumination
The bandgap obtained is 1.466 eV.
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1 2 3
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0 (
ah
v)^
1/2
(c
m-1
eV
)1/2
Energy(eV)
FIGURE4.20- hv Vs ( αhv)1/2 with 60 minutes illumination
The bandgap obtained is 1.461 eV.
Although darkenening in films has attracted attention for its possible applications in optical
memory elements, the mechanism causing the change in optical gap remains unclear. One of
the possible mechanism can be due to the dissociation of the bonds or bonding rearrangement
leading to large absorption of light ie, illumination above the band gap alters the bonstatistics
resulting in the randomness of the bond distribution and the creation of defect states which
leads to an increase in disorder. As discussed earlier the bandgap decreases with increase in
exposure.The above values are tabulated in the Table 4.2 given below:
EXPOSURE TIME BANDGAP(eV)
0 MINUTES 1.478
5 MINUTES 1.472
10 MINUTES 1.472
20 MINUTES 1.466
30MINUTES 1.466
60 MINUTES 1.461
Table 4.2-Bandgap variation with exposure time
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Figure 4.22 shows the plot of Bandgap variation with exposure time
0 10 20 30 40 50 60
1.460
1.465
1.470
1.475
1.480
Ba
nd
ga
p (
eV
)
Time (minutes)
Figure 4.22-Bandgap variation with exposure time
The photodarkening effects induced by Diode pumped solid state laser (DPSS) of was very
small hence the photo induced experiment was repeated with He-Ne laser of 635nm
wavelength . The results are tabulated below.
EXPOSURE TIME BANDGAP
0 minute 1.48
5 minutes 1.47
10 minutes 1.41
20 minutes 1.29
30 minutes 1.24
45 minutes 1.21
Table 4.3-Bandgap variation with exposure time
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0 10 20 30 40 50
1.20
1.25
1.30
1.35
1.40
1.45
1.50
BA
ND
GA
P(e
V)
EXPOSURE TIME(MINUTES)
Figure 4.23-Variation of bandgap with exposure time
Studies show that photoinduced effects on thin film is higher for He-Ne laser than Diode
Pumped Solid State Laser. The difference in the magnitude of photodarkening can be due to
the difference in effective penetration depth.
4.2.5 Nonlinear studies
Z-Scan is used for studying the nonlinear properties. Z-scan technique introduced by Sheik
Bahae is a single beam method for measuring the sign and magnitude of nonlinear refractive
index that has a sensitivity compared to interferometric methods. It provides direct
measurement of nonlinear absorption coefficient. Previous measurements of nonlinear
refraction have used a variety of techniques including nonlinear interferometry, degenerate
four wave mixing, nearly degenerate three wave mixing, ellipse rotation and beam distortion
measurements. The first three methods namely nonlinear interferometry and wave mixing are
potentially sensitive techniques, but all require complex experimental apparatus. The
propagation of laser beam inside such a material and the ensuing self refraction can be
studied using the z-scan technique. Thus it enables one to determine the third order nonlinear
properties of solids, ordinary liquids, and liquid crystals. The experimental set up for single
beam z-scan technique is given in Figure 2.5. In the ordinary single beam configuration, the
transmittance of the sample is measured, as the sample is moved along the direction of the
focussed guassian beam. A laser beam propagating through a nonlinear medium will
experience both amplitude and phase variation. If transmitted light is measured through an
aperture placed in the far field with respect to focal region, the technique is called closed
aperture z-scan. In this case, the transmitted light is sensitive to both nonlinear absorption and
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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nonlinear refraction. In a closed aperture zscan experiment, phase distortion suffered by the
beam while propagating through the nonlinear medium is converted into corresponding
amplitude variations. On the other hand, if transmitted light is measured without an aperture,
the mode of measurement is referred to as open aperture z-scan. In this case, the output is
sensitive only to nonlinear absorption. Closed and open aperture z-scan graphs are always
normalized to linear transmittance i.e., transmittance at large values of |z|.Closed and open
aperture z-scan methods yield the real part and imaginary part of nonlinear susceptibility χ(3)
respectively.Usually closed aperture z-scan data is divided by open aperture data to cancel the
effect of nonlinear absorption contained in the closed aperture measurements. The new graph,
called divided z-scan,contains information on nonlinear refraction alone.
Figure 4.25-Z –Scan setup
An important requirement in the z-scan measurement is that,it is assumed that the sample
thickness is much less than Rayleigh’s range z0 (diffraction length of the beam [z0=k ω0/2,
where k is the wave vector and ω0 is the beam waist radius. The beam waist radius ω0 is
given by ω0=fλ/D, where f is the focal length of the lens used, λ is the wavelength of the
source and D is the beam radius at the lens. This is essential to ensure that the beam profile
does not vary appreciably inside the sample because z-scan technique is highly sensitive to
the profile of the beam and also to the thickness of the sample. Any deviation from gaussian
profile of the beam and also from thin sample approximation will give rise to erroneous
results.
The nonlinear studies are done at 120 µJand 77 µJ.Both open and closed Z-Scan are done.
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Figure 4.26-Open aperture Z-Scan of thin film at 120 µJ
Figure 4.27-Open aperture Z-Scan of thin film at 77µJ
The curve shows that the sample exihibits saturable absorption. When the absorption cross-
section from excited state is smaller than that from the ground state, the transmission of the
system will be increased when the system is pumped with high intensity laser beam. This
process is called saturable absorption. if the sample is a saturable absorber, transmission
increases with increase in incident intensity and results in a transmission maximum at the
focal region.The nonlinear absorption coefficient and imaginary part of nonlinear
susceptibility χ(3) can be found out by following equations.
L eff=1-exp(-(αl))/α (4.1)
-6 -5 -4 -3 -2 -1 0 1 2 30
50
100
150
200
250
z(cm)
Norm
alis
ed T
ransm
itta
nce(a
.u)
-6 -5 -4 -3 -2 -1 0 1 2 30
50
100
150
200
250
300
z(cm)
Norm
alis
ed T
ransm
itta
nce(a
.u)
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β=q/I0Leff (4.2)
α=absorption at 532 nm
l=cuvette thickness
β=nonlinear absorption coefficient
q=First value obtaines from matlab program
I0=E0/Power Width*Area (4.3)
Power width(z)=7 ns
Area=π*ω02 (4.4)
ω0= fλ/D, (4.5)
f=focal length=20cm
D=radius of aperture=6mm
Im(χ(3)=n02C2β/240π2 ω (4.6)
From the calculations above the nonlinear absorption coefficient and imaginary parts of
susceptibility are tabulated below.
E0(µJ) 77 120
β(m/W)(10-10) -4.4814 -2.699
Im(χ(3) (e.s.u)(10-11) -3.4277 -2.06437
The nonlinear absorption coefficient and imaginary part of the susceptibility decrease with
the energy. The measured value of β for the samples decreases with increasing input intensity
due to the removal of an appreciable fraction of photocarriers from the ground state.
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4.3 Conclusion
1) EDAX spectra show that the thin film does not have the same composition as that of bulk
sample.
2) The bandgap calculated for the thin film was 1.474 eV which is different from bulk
sample.
3) Studies show that a low power radiation is sufficient enough to provide a shift in the
absorption edge. This mechanism in Ge10Se80Te10 glasses can be used to realize continuous
wave laser written waveguide and for fabricating photosensitive optical components for
various applications. The photo induced effect was more prominent for He-Ne laser of 635
nm wavelength.
4) Nonlinear absorption coefficient and imaginary part of susceptibility was calculated and
nonlinear studies show that these samples exihibit saturable absorption. The third order
susceptibility, Im(χ(3) is of interest because of its importance in applications such as
nonlinear propagation in fibers, fast optical switching, self-focusing, damage in optical
materials and optical limiting in semiconductors. Saturable absorbers are useful in laser
cavities. The key parameters for a saturable absorber are its wavelength range (where it
absorbs), its dynamic response (how fast it recovers), and its saturation intensity and fluence
(at what intensity or pulse energy it saturates). They are commonly used for passive Q-
switching. However, saturable absorbers are also useful for purposes of nonlinear filtering
outside laser resonators, e.g. for cleaning up pulse shapes, and in optical signal processing.
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5. NANOCOLLOID
The finely grounded powder is mixed in different solutions and all the solutions are kept for
many months. Some got partially dissolved and some did not show any sign of
dissolution.The prepared solutions are as follows.
A-0.0275g of powdered sample is mixed in 50ml of butyl amine
B-0.0275g of powdered sample is mixed in 50ml of diethyl amine
C-0.051g of powdered sample is mixed in 50ml of ethanol amine
D-0.0272g of powdered sample is mixed in 30ml of ethanol amine
E-0.014g of powdered sample is mixed in 30 ml of ethanol amine
F-0.0272g of powdered sample in 30ml of ethanol amine
G-0.025g of powdered sample is mixed in 30ml of ethylyne diamine
For every sample absorption and nonlinear effects are studied
5.1 Experiments on A
A is kept nearly for 3 months and it showed colour change.Considering this as a sign of
dissolution the studies are carried out.
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FIGURE 5.1-Powdered sample in butyl amine
5.1.1 Absorption
0 500 1000 1500 2000 2500
-3
-2
-1
0
1
2
3
4
5
6
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
B
Figure 5.2-Absorbance of sample in butylamine
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0 1 2 3 4 5 6 7
0
1
2
3
4
5(
ah
v)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 5.3-- hv Vs ( αhv)^1/2 graph of A
The bandgap of prepared solution is found to be 2.21eV.
5.1.2 Nonlinear studies
The nonlinear studies of A is carried out.Z Scan is carried out . Z-Scan is explained in the
previous chapter in detail.The studies are carried out 43-47 µJ and 104 µJ.The curve didn’t fit
for both open and closed Z-Scan. The sample did not mix properly in butyl amine and hence
the coefficients could not be found out
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5.2 Experiments on B
The sample was kept for 8 months and it showed only partial dissolution.
5.2.1 Absorption
0 500 1000 1500 2000 2500
-2
-1
0
1
2
3
4
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 5.4-Absorbance of sample in diethylamine
To find the bandgap the another graph is plotted.
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2 3 4 5 6 7
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0(
ah
v)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 5.5-- hv Vs ( αhv)^1/2 graph of B
The bandgap is determined to be 2.289 eV.
5.2.2 Nonlinear studies
The nonlinear studies of B is carried out.Z Scan is carried out . ZScan is explained in the
previous chapter in detail. The studies are carried out 43-47 uJ and 104 uJ.The curve didn’t fit
for both open and closed ZScan.
The sample didn’t mix properly in butyl amine.So the coefficients could not be found out
5.3 Experiments on C and D
The samples did not mix in the solutions.
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5.4 Experiments on E
5.4.1 Absorption
0 500 1000 1500 2000 2500
-2
-1
0
1
2
3
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 5.6-Absorbance of sample in E
0 1 2 3 4 5 6 7
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
( a
hv)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 5.7-- hv Vs ( αhv)^1/2 graph of E
The bandgap was found to be 2.97eV.
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5.4.2 Nonlinear Studies
The experiments are carried out at 70 and 100 µJ. Both open aperture and closed aperture Z-
Scans were undertaken.
Figure 5.8-Open aperture Z-Scan at 70µJ
Figure 5.9-Open aperture Z-Scan at 100µJ
The sample exihibits reverse saturable absorption. When the absorption cross-section from
excited state is larger than that from the ground state, the transmission of the system will be
less under intense laser fields. This process is called reverse saturable absorption. The reverse
saturable absorption, which is generally associated with a large cross section of absorption
from excited levels, brings about optical limiting effects in colloidal solutions. In
semiconductor materials the optical limiting is governed by two photon absorption as
observed in the present studies. An important parameter in the optical limiting phenomena is
-4 -3 -2 -1 0 1 2 3 4 50.4
0.5
0.6
0.7
0.8
0.9
1
1.1
z(cm)
Norm
alis
ed T
ransm
itta
nce(a
.u)
-4 -3 -2 -1 0 1 2 3 4 50.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
z(cm)
Norm
alis
ed t
ransm
itta
nce(a
.u)
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the limiting threshold. It is obvious that lower the optical limiting threshold, better the
efficiency of optical limiting material.
The β and Im(χ(3) decreases with increase in E0. The experimental data shows best fit for two
photon absorption confirming that TPA may be the basic mechanism involved in thenonlinear
absorption process. Possibility of higher order nonlinear processes such as free carrier
absorption contributing to induced absorption cannot be ruled out. The measured value of β
for the samples decreases with increasing input intensity due to the removal of an appreciable
fraction of photocarriers from the ground state. Thus when the incident intensity exceeds the
saturation intensity, the nonlinear absorption coefficient of the medium decreases.
The closed aperture Z Scan was also carried out to get real part of susceptibility.
The nonlinear refractive index n2 is given by the relation
n2=C n0λΔϕ0/80π2 I0Leff (5.1)
Re(χ(3)= n0 n2/3π (5.2)
E0(µJ) 70 100
β(m/W)(10-10) 1.488 1.178
Im(χ(3) (e.s.u)(10-12) 4.1898 3.75
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Figure 5.10-Closed aperture Z-Scan at 100µJ
The curve didnot fit at 70µJ.The calculations were done for 100 µJ.
n2=-7.6046*10-11
Re(χ(3)=-1.307*10-11
Here the real part is larger than imaginary part which shows that nonlinear refraction is more
than absorption.
-4 -3 -2 -1 0 1 2 3 40
0.5
1
1.5
2
2.5
3
3.5
z(cm)
No
rma
lise
d T
ransm
itta
nce
(a.u
)
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5.5 Experiments on F
5.5.1 Absorption
0 500 1000 1500 2000 2500
-2
-1
0
1
2
3
4
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 5.11-Absorbance of sample in F
0 1 2 3 4 5 6 7
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
( a
hv)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 5.12-- hv Vs ( αhv)1/2 graph of F
The bandgap is 1.786 eV.
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5.6 Experiments on G
5.6.1 Absorption
0 500 1000 1500 2000 2500
-3
-2
-1
0
1
2
3
4
5
6
Ab
so
rba
nce
Wavelength(nm)
Figure 5.13-Absorbance of sample G
The bandgap can be calculated from below graph
.
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0 1 2 3 4 5 6 7
0
1
2
3
4
5(
ah
v)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 5.14-- hv Vs ( αhv)^1/2 graph of G
The bandgap is 1.91348 eV
5.6.2 Nonlinear Studies
Figure 5.15-Open aperture Z-Scan at 70µJ
-4 -3 -2 -1 0 1 2 3 4 50.4
0.5
0.6
0.7
0.8
0.9
1
1.1
z(cm)
No
rma
lise
d T
ransm
itta
nce
(a.u
)
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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Figure 5.16-Open aperture Z-Scan at 100µj
The sample exihibits reverse saturable absorption. When the absorption cross-section from
excited state is larger than that from the ground state, the transmission of the system will be
less under intense laser fields. This process is called reverse saturable absorption.
The β and Im(χ(3) decreases with increase in E0. The experimental data shows best fit for two
photon absorption confirming that TPA may be the basic mechanism involved in thenonlinear
absorption process. Possibility of higher order nonlinear processes such as free carrier
absorption contributing to induced absorption cannot be ruled out. The measured value of β
for the samples decreases with increasing input intensity due to the removal of an appreciable
fraction of photocarriers from the ground state. Thus when the incident intensity exceeds the
saturation intensity, the nonlinear absorption coefficient of the medium decreases.
The closed aperture results are
-4 -3 -2 -1 0 1 2 3 4 50.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
z(cm)
No
rma
lise
d T
ransm
itta
nce
(a.u
)
E0(µJ) 70 100
β(m/W)(10-10) 1.462 1.107
Im(χ(3) (e.s.u)(10-12) 4.219 3.194
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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Figure 5.17-Closed aperture Z-Scan at 70µJ
Figure 5.18-Closed aperture Z-Scan at 100µJ
-5 -4 -3 -2 -1 0 1 2 3 40
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
z/z0
Norm
alis
ed T
ransm
itta
nce
-4 -3 -2 -1 0 1 2 3 4-1
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
4
z/z0
Norm
alis
ed T
ransm
itta
nce(a
.u)
E0(µJ) 70 100
n2 (10-10) -1.15587 -1.53
Re(χ(3) (e.s.u)(10-11) -2.0113 -2.663
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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5.7 Conclusion
Investigations on the nanocolloids prepared show that it takes a long time for dissolution
and some solutions were highly unstable. Sample A,B shows large bandgap compared to
bulk samples. Samples C and D were not completely dissolved. On exposure to light it was
seen that the sample F and solvent got separated and hence nonlinear properties could not be
evaluated..F has the bandgap somewhat near to bulk.The dissolution was complete for F and
G only.Rest all other showed partial dissolution.The sample E and F exihibits reverse
saturable absorption and the nonlinear absorption coefficient and imaginary part of
susceptibility increases when the energy is increased.For sample E nonlinear refraction is
more than absorption. From closed aperture z-scan nonlinear refractive index can be found
out.Nonlinear index of refraction is the change in refractive index or the spatial distribution
of the refractive index of a medium due to the presence of optical waves and has generated
significant and technological interest. It has been utilized for a variety of applications such as
nonlinear spectroscopy, correcting optical distortions, optical switching, optical logic gates,
optical data processing, optical communications, optical limiting, passive laser mode-locking,
wave guide switches and modulators. The nonlinear studies show that materials are
promising candidates for light-emitting devices, optoelectronic devices and optical limiters
for the development of nonlinear optical devices with a relatively small limiting threshold.
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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6. Spin coating
SPIN 150-v3 was used for spin coating the films. Spin Coating involves the acceleration of a
liquid puddle on a rotating substrate .In this technique the coating material is deposited in the
center of the substrate either manually or by a robotic arm. The physics behind spin coating
involve a balance between centrifugal forces controlled by spin speed and viscous forces
which are determined by solvent viscosity. Some variable process parameters involved in
spin coating are Solution viscosity, Solid content, Angular speed and Spin Time.
Figure 6.1-Spin coating
Here the nanocolloids explained in the previous chapter are coated into films. The
nanocolloids D,E and F are coated into films.
Composite film preparation
2 grams of polyvinyl alcohol is mixed in 18ml of hotwater. It is continuously stirred till the
sample mixed properly.Polyvinyl alcohol and sample are mixed. Then this mixture is coated
using spin coating technique. Then the properties of the coated filims are studied.
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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6.1 Experiment on E
1ml polyvinyl alcohol and 1ml E are mixed. Two films film 1 and film 2 are prepared from
the mixture.
Absorption,transmission and nonlinear studies are conducted for each film.
.
6.1.1 Absorption
0 500 1000 1500 2000 2500
-0.4
-0.3
-0.2
-0.1
0.0
0.1
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 6.2-Absorption spectrum of spin coated filim from E (film1)
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
0.0
0.1
0.2
0.3
0.4
0.5
( a
hv)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 6.3- hv Vs ( αhv)1/2 graph of film1
The bandgap is found to be 1.335eV.
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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0 500 1000 1500 2000 2500
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 6.4-Absorption of film2
2 3 4 5 6 7
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
( a
hv)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 6.5- hv Vs ( αhv)1/2 graph of film2
The bandgap is found to be 2.0874 eV
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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6.1.2 Transmission spectrum
0 500 1000 1500 2000 2500
80
100
120
140
160
180
200
220
240
Tra
nsm
itta
nce
(a.u
)
Wavelength(nm)
Figure 6.6-Transmission spectrum of film1
The maxima and minimas are not obtained.So the thickness cannot be calculated.
0 500 1000 1500 2000 2500
70
75
80
85
90
95
100
105
Tra
nsm
itta
nce
(a.u
)
Wavelength(nm)
Figure 6.7- Transmission spectrum of film2
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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The maxima and minimas are not obtained.So the thickness cannot be calculated.
6.1.2 Nonlinear Studies
The studies are carried out for film1 and film2 but the curves didn’t fit.The studies are carried
out 100uJ.
6.2 Experiment on F
1ml of pva and 1 ml of F taken and mixed. Three films film 1 ,film 2,film 3 are prepared at
600rpm,1000rpm and 1500rpm.
6.2.1 Absorption
0 500 1000 1500 2000 2500
0.55
0.60
0.65
0.70
0.75
0.80
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 6.8-Absorption of film1
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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0 1 2 3 4 5 6 7
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2(
ah
v)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 6.9- hv Vs ( αhv)1/2 graph of film1
The bandgap is 0.275 eV
0 500 1000 1500 2000 2500
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0.12
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 6.10-Absorption of film 2
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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1 2 3 4 5 6 7
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
( a
hv)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 6.11- hv Vs ( αhv)1/2 graph of film 2
The bandgap is 1.391 eV
0 500 1000 1500 2000 2500
0.92
0.94
0.96
0.98
1.00
1.02
1.04
1.06
1.08
1.10
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 6.12-Absorption of film 3
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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0 1 2 3 4 5 6 7
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6(
ah
v)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 6.13- hv Vs ( αhv)1/2 graph of film 3
The bandgap is 0.4 eV
6.2.2 Transmission
0 500 1000 1500 2000 2500
16
18
20
22
24
26
28
Tra
nsm
itta
nce
(a.u
)
Wavength(nm)
Figure 6.14-Transmission spectrum of film1
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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The maxima and minimas are not obtained.So the thickness cannot be calculated.
0 500 1000 1500 2000 2500
80
85
90
95
100
105
Tra
nsm
itta
nce
(a.u
)
Wavength(nm)
Figure 6.15-Transmission spectrum of film 2
The maxima and minimas are not obtained.So the thickness cannot be calculated.
0 500 1000 1500 2000 2500
8.0
8.5
9.0
9.5
10.0
10.5
11.0
11.5
Tra
nsm
itta
nce
(a.u
)
Wavelength(nm)
Figure 6.16-Transmission spectrum of film 3
The maxima and minimas are not obtained.So the thickness cannot be calculated.
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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6.2.2 Nonlinear Studies
Experiments are conducted for film 1.
Figure 6.17-Open aperture ZScan at 44µJ
Figure 6.18-Open aperture ZScan at 110µJ
-5 -4 -3 -2 -1 0 1 2 3 40.8
0.85
0.9
0.95
1
1.05
1.1
1.15
z(cm)
No
rma
lise
d T
ransm
itta
nce
(a.u
)
-4 -3 -2 -1 0 1 2 3 4 5
0.7
0.8
0.9
1
1.1
1.2
1.3
z(cm)
Norm
alis
ed T
ransm
itta
nce(a
.u)
E0(µJ) 44 110
β(m/W)(10-11) 9.52 6.6762
Im(χ(3) (e.s.u)(10-12) 2.29816 1.611664
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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The sample exihibits reverse saturable absorption. The β and Im(χ(3) decreases with increase
in E0.
6.3 Experiment on G
1ml of pva and 2 ml of G taken and mixed.
6.3.1 Absorption
0 500 1000 1500 2000 2500
0.85
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 6.19-Absorption of film1
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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0 1 2 3 4 5 6 7
0.5
1.0
1.5
2.0
2.5
( a
hv)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 6.20- hv Vs ( αhv)1/2 graph of film1
The bandgap is 0.3897 eV.
0 500 1000 1500 2000 2500
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 6.21-Absorption of film 2
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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0 1 2 3 4 5 6 7
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5(
ah
v)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 6.22- hv Vs ( αhv)1/2 graph of film 2
The bandgap is 0.5486eV
0 500 1000 1500 2000 2500
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 6.23-Absorption of film 3
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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0 1 2 3 4 5 6 7
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
( a
hv)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 6.24- hv Vs ( αhv)1/2 graph of film 3
The bandgap is 0.3847 eV
6.3.2 Transmission
0 500 1000 1500 2000 2500
6
7
8
9
10
11
12
13
14
Tra
nsm
itta
nce
(a.u
)
Wavelength(nm)
Figure 6.25-Transmission spectrum of film1
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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0 500 1000 1500 2000 2500
0
10
20
30
40
50
60
70
80
Tra
nsm
itta
nce
(a.u
)
Wavelength(nm)
Figure 6.26-Transmission spectrum of film 2
The maxima and minimas are not obtained.So the thickness cannot be calculated.
0 500 1000 1500 2000 2500
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Tra
nsm
itta
nce
(a.u
)
Wavelength(nm)
Figure 6.27-Transmission spectrum of film 3
The maxima and minimas are not obtained.So the thickness cannot be calculated.
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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6.3.3 Nonlinear Studies
Experiments are performed for film 3.
Figure 6.28-Open aperture ZScan at 44µJ
Figure 6.29-Open aperture ZScan at 110µJ
At 44µJ saturable absorption is obtained ,as the energy is increased reverse saturable
absorption is obtained.
-4 -3 -2 -1 0 1 2 3 4 50.98
1
1.02
1.04
1.06
1.08
1.1
1.12
1.14
z(cm)
Norm
alis
ed T
ransm
itta
nce
-3 -2 -1 0 1 2 3 4 5 6-0.2
0
0.2
0.4
0.6
0.8
1
1.2
z(cm)
Norm
alis
ed T
ransm
itta
nce
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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6.4 Conclusion
The transmission spectrum of films did not have maxima and minima so the thickness of the
filim cannot be obtained. One film coated from E showed bandgap near the bulk sample ie
1.335 eV. The nonlinear studies are done but the coefficients could not be evaluated as the
graph did not fit . The films coated from G shows large bandgap variation from the bulk.One
filim coated from F exihibits bandgap 1.391eV ie near bulk bandgap. All other shows large
variation. Nonlinear effects are studied for film 1 coated from F and film 3 coated from G. G
shows a transition from saturable absorption reverse saturable absorption when the energy is
increased. F exihibits reverse saturable absorption. The nonlinear absorption coefficient and
imaginary part of susceptibility increases when the energy is increased. Nonlinear optical
characterisation of the films studied by the z-scan technique shows reverses saturable
absorption(except filim from G at 100µJ )which makes it useful for optical limiting
applications. Thus depending the nano colloid solution used for the fabrication of nano
composite films, varying nonlinear response can be obtained,enabling a pathway to new
materials for optoelectronic devices.
E0(µJ) 44 110
β(m/W) -3.4636*10-11 1.11*10-10
Im(χ(3) (e.s.u) -8.3698*10-13 2.298*10-10
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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7. Temperature sensor using GeSeTe glass
There are numerous applications for chalcogenide glass as discussed in chapter 1. One of its
application is discussed here. The glass sample can be used as an active medium for a
temperature sensor. The investigations are done in prepared sample glass.Here thin film of
the sample is used. The bulk sample is coated as thin film by a vacuum coating unit as
discussed earlier. The thin film is heated at different temperature using a heater and the
temperature is noted by a thermometer. The absorption at each temperature is taken by
JASCO-V spectrometer from which bandgap is found out. The glass transition temperature
of this sample is 150 degree Celsius. The experiment is conducted over a range of 0-100
degree Celsius temperature.
7.1 Absorption at 0 degree celsius
0 500 1000 1500 2000 2500
0
1
2
3
4
5
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 7.1-Absorption at degree Celsius
For finding the band gap ,graph is plotted as shown below.
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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0 1 2 3 4 5 6 7
0
1
2
3
4
5
6(
ah
v)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
FIGURE7.2- hv Vs ( αhv)1/2 without heating
The bandgap is found to be 1.445 eV.
7.2 Absorption after 5 degrees heating
The thin filim is heated and temperature is noted by a thermometer.The heating was stopped
when the sample attained 5 degree Celsius.Then absorption was taken using JASCO-V
spectrometer from which the bandgap was calculated using hv Vs ( αhv)1/2 graph.The
procedure is same for all the temperatures.
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0 500 1000 1500 2000 2500
0
1
2
3
4
5A
bso
rba
nce
(a.u
)
Wavelength(nm)
Figure 7.3-Absorption at 5 degree
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
( a
hv)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 7.4- hv Vs ( αhv)1/2 after 5 degree heating
The bandgap is 1.39 eV.
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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7.3 Absorption after 15 degree heating
0 500 1000 1500 2000 2500
0
1
2
3
4
5
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 7.5-Absorption after 15 degree heating
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
( a
hv)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 7.6- hv Vs ( αhv)1/2 after 15 degree heating
The bandgap is found to be 1.336 eV
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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7.4 Absorption after 35 degree heating
0 500 1000 1500 2000 2500
0
1
2
3
4
5
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 7.7-Absorption at 35 degree
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
( a
hv)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 7.8- hv Vs ( αhv)1/2 after 35 degree heating
The bangap is found to be 1.245 eV
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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7.5 Absorption after 55 degree heating
0 500 1000 1500 2000 2500
0
1
2
3
4
5
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 7.9-Absorption at 55 degree
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
( a
hv)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 7.10- hv Vs ( αhv)^1/2 after 55 degree heating
The bandgap is found to be 1.118eV.
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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7.5 Absorption after 75 degree heating
0 500 1000 1500 2000 2500
0
1
2
3
4
5
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 7.11-Absorption at 75 degree
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
( a
hv)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 7.12- hv Vs ( αhv)^1/2 after 75 degree heating
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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The bandgap is 0.8617 eV
7.5 Absorption after 100 degree heating
0 500 1000 1500 2000 2500
0
1
2
3
4
5
Ab
so
rba
nce
(a.u
)
Wavelength(nm)
Figure 7.13-Absorption at 100 degree
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
( a
hv)^
1/2
(c
m-1
eV
)^1
/2
Energy(eV)
Figure 7.14- hv Vs ( αhv)^1/2 after 100 degree heating
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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The bandgap is 0.573 eV.
Temperature(degree Celsius) Bandgap(eV)
0 1.445
5 1.389
15 1.336
35 1.245
55 1.118
75 0.862
100 0.537
Table 7.1-Bandgap variation with temperature
0 20 40 60 80 100
0.6
0.8
1.0
1.2
1.4
1.6
Ba
nd
ga
p(e
V)
Temperature(degree Celsius)
Figure 7.15-Bandgap variation with temperature
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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The glass transition temperature of this sample is 150 degree Celsius. A quasi linear
behaviour below transition temperature is exhibited for these glasses which is similar to the
studies already reported “ On the Application of Chalcogenide Glasses in Temperature
Sensors”(M. Shpotyuk, D. Chalyy, O. Shpotyuk, M. Iovu, A. Andriesh4, M. Vakiv and S.
Ubizskii).
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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8. CONCLUSION
Ge10Se80Te10 sample was prepared by melt quench technique. The sample was charecterised
in 4 different forms ie bulk glass, thin film, nanocolloid and spin coated nanocolloid film. X-
ray diffraction studies conducted on the bulk sample show no prominent peaks which
reveals the amorphous nature of the samples . Optical bandgap determined by UV-Vis-NIR
spectroscopy is found to be 1.22eV. The bulk glass is not used as such for application
purpose. Device applications using ChG usually require the glass to be processed into either
fiber or thin film form. Thin film was coated using India High Vacuum pumps (12A4-D).
EDAX spectra show that the thin film does not have the same composition as that of bulk
sample. The bandgap calculated for the thin film was 1.474 eV which is different from bulk
sample. The photo induced effects was prominent for He-Ne laser of 635 nm than diode
pumped solid state laser of 532 nm. Nonlinear absorption coefficient and imaginary part of
susceptibility was calculated and nonlinear studies show that these samples exihibit
saturable absorption. Nano colloids of chalcogenide glass have gained a lot of interest in the
research field recently. Understanding the chemical stability of the glasses, and finding the
suitable solvent for making solutions is very important in nano colloid preparations. 7
different samples are prepared by using solvents like butylamine,diethylamine,ethanol amine
and ethylyne diamine. They were named A, B, C. D, E, F and G. The absorption and
transmission taken for all except C and D. The nonlinear optical properties are evaluated for
E and G. E and G showed reverse saturable absorption so it can be used for optical limiters.
Due to the difficulty in dissolution the concentration dependence could not be evaluated. The
samples E, F, G were mixed with polyvinyl alcohol and coated to film using spin coating.
The transmission spectrum of films did not have maxima and minima so the thickness of the
film cannot be obtained. The absorption spectrum of all films taken and the bandgap is found
out. Nonlinear effects are studied for film 1 coated from F and film 3 coated from G. G shows
a transition from saturable absorption to reverse saturable absorption when the energy is
increased. F exihibits reverse saturable absorption. So this can be used as optical limiters.
Among thin film, nanocolloid and spin coated film, thin film has bandgap near to the bulk.
The thin film can be used as saturable absorber and nanocolloid and film coated from F can
be used as reverse saturable absorber. Nonlinear absorption coefficient is maximum for the
thin film compared to others. The spin coated film is cheaper compared to thin film. One of
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
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the application of sample was evaluated. The glass sample can be used as an active medium
for a temperature sensor. A quasi linear behaviour below transition temperature is exhibited
for these glasses which is similar to the studies already reported.
CHARACTERISATION OF Ge Se Te CHALCOGENIDE GLASS
International School of Photonics Page 100
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