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transcript
Chapter 2
DETAILS OF APPARATUS
AND CHARACTERIZATION TECHNIQUES
2.1. Introduction
Naphthalocyanines are novel Phthalocyanine type materials widely used in
the area of thin film active devices for optoelectronic applications. Though the study
of thin film phenomena coupled with organic semiconductors dates back well over a
century, significant applications regarding those lasted only for two decades. Today
thin film science is projected to be one of the major processing techniques to
fabricate electronic, optical and magnetic data storage devices, fuel cells and solar
cells. Latest developments in thin film technology reside in the nano solar cell
fabrications and thin film batteries for nano markets. The growing needs for different
types of thin films ensure suitable deposition techniques, potential materials and apt
coating substrates. Modern electronics choose organic semiconductors as active
layers from their inorganic counter parts due to the favourable electrical properties.
Physical Vapour Deposition (PVD) is one of the best methods for sublimation at low
temperature without undergoing decomposition for organic semiconductors,
especially phthalo and naphthalocyanines. In this research work, efforts have been
taken to fabricate (metal free, Zinc and Vanadyl) Tert-Butyl substituted 2,3
naphthalocyanines thin films using PVD technique onto glass substrate. By varying
different factors like thin film thickness, post deposition air and vacuum annealing
and by heating substrate; the basic electrical, optical, structural and surface
morphological properties are studied. As a part of application level study, we
irradiate respective thin films with different dosage of gamma rays and study the
defect level conduction mechanism to show their use in the field of dosimeteric
sensors and sources. This chapter briefly describes the PVD technique employed for
TTBNc thin film fabrication and the theory behind different characterization
techniques like D.C. electrical conductivity, UV-Visible spectroscopy, X-ray
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diffractogram (XRD), Scanning Electron Microscopy (SEM) and Atomic Force
Microscopy (AFM).
2.2. Thin film deposition techniques
Organic thin films with high structural order are required to implement the
novel electronic and optical application that have been proposed for devices based
on small conjugated molecules. Among the candidates for technologies such as large
area and mechanically flexible organic electronics, naphthalocyanines stand out for
relatively high field effect mobility and their ability to form ordered thin films on
various types of substrates. Much of the physical phenomena associated with bulky
naphthalocyanines are well known. However, this cannot be said about
Naphthalocyanine thin films. Thin film active materials, defined by dimensions on
the order of microns, give relatively new research output apart from their bulky
counter parts; still they have some scientific infancy [1, 2]. Structures could be
designed to interact and be built at the micron level using different thin film
fabrication technology which comes under three major headings:
1. physical methods
2. chemical methods and
3. sputtering
Each of the above mentioned methods can be used to prepare thin films
from a variety of materials like metals, semiconductors, insulators or dielectrics
and each of them has its own advantages and disadvantages [3]. From here,
onwards we restrict our discussion only thermal evaporation method which we have
employed to prepare thin films for the present study.
2.3. Thermal evaporation
Among the most widely acceptable techniques for thin film deposition,
thermal evaporation method is a versatile and flexible one for producing deposits
of organic semiconductors. Basically it involves three steps, boiling or subliming
of source to form its vapour, transport of the vapour from the source to the
substrate and condensation of the vapour on the substrate. The basic physics of the
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process contains elements of thermodynamics, kinetic theory of gases and
condensation phenomena [4].
Solid materials are sublimed under high vacuum when heated to
sufficiently high temperature [5]. The condensation of the vapour on to a cooler
substrate yields thin solid films. This method has the following advantages.
1. Impurity concentration in the film is minimum.
2. Material boils at lower temperature under vacuum.
3. Growth can be effectively controlled.
4. Mean free path of the vapour atom is considerably larger at low pressure
and hence a sharp pattern of the film is obtained.
5. Wide variety of substrates.
The evaporation rate and hence the condensation have wide limits, depending
upon the purity of source material used. Characteristics of the prepared films are
determined by parameters such as temperature, type of substrate, deposition rate and
residual atmosphere. All these parameters can be controlled in the thermal evaporation
method. More than that, single evaporation can give films of different thicknesses. We
have used here molybdenum boats and tungsten baskets for evaporation of materials.
Film of high purity can readily be produced with a minimum of interfering conditions.
The nature and properties of evaporated thin films depend on factors as shown below.
1. Nature and Pressure of residual gases.
2. Vapour beam intensity.
3. Nature and conditions of substrate.
4. Temperature of vapour source and velocity of impinging molecule.
5. Material contamination from vapour source.
2.4. Vacuum coating unit
The type of vacuum equipment needed obviously depends on the desired
purity of the film. Detailed reviews on various types of vacuum systems and their
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ultimate pressures are given by Holland [2], Carewell [6] Dushaman [7] and Roth [8].
The vacuum system employed to deposit and characterize thin film in the present
work contains an assortment of pumps, tubes, valves and gauges to establish and
measure the required reduced pressure as shown in Figure 2.1. Basically the
vacuum system “Hind Hivac” vacuum coating unit model No. 12A4D consists of
0.4m diffusion pump backed up by oil sealed rotary pump. Ultimate pressure
obtained in a 0.3m diameter steel bell jar is of the order of 8×10-6mbar. It has
setups of electron beam evaporation and flash evaporation. Most of the evaporation
is carried out at a pressure of (1-2)×10-5Torr. The pressure measurement in the
system is done by means of Pirani and Penning Gauges (6 and 7 in Figure 2.1)
provided with the system. The Pirani gauge model Hind Hivac-A 6 STM is used to
measure vacuum in the range 0.5×10-3Torr. The Penning gauge model STM 4 is
used to measure vacuum in the range 10-2 to 10-6Torr in two ranges with instant
range – charger provided by a toggle switch.
Figure 2.1 Schematic diagram of a vacuum coating unit with
1. bell jar 2. diffusion pump
3. rotary pump 4. control panel
5. L. T control 6. pirani gauge
7. penning gauge
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The system is accompanied by a digital thickness monitor model number
DTM-101 having a temperature controller cum monitor to show the interior dom
temperature (30oC) at the time of coating and a display setting to show the rate of
coating. A schematic diagram showing vacuum chamber with thickness monitor is
given in Figure 2.2.
Figure 2.2 Schematic diagram of vacuum chamber and DTM: Substrate -1,
Shutter-2, Quartz crystal-3, Molybdenum boat-4, Oscillator -5, DTM- 6.
2.5. Purity of materials
If the evaporant is contaminated, the deposited thin film gets
contaminated. Usually high purity materials are used in this work. The source
materials used in the present study are originally procured from Aldrich Co.Inc.
WI., USA. The purity of materials is further checked with CHNS (Carbon-
Hydrogen-Nitrogen-Sulphur) analysis. The contents along with the rated purity
are given in the Table 2.1.
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Table 2.1 Percentage of Carbon, Hydrogen, Nitrogen and Sulphur in the source materials along with the rated purity
Material C% H% N% S% Total% Rated%
TTBNc 69.73 13.19 14.07 0.002 96.99 97
ZnTTBNc 71.69 01.94 10.28 0.004 83.91 84
VTTBNc 69.49 04.57 09.87 0.007 83.94 84
The rated purity for metal free matches while metal bearing TTBNc shows
a deviation from Sigma product informations; those are 97%, 90% and 95%
respectively for TTBNc, ZnTTBNc and VTTBNc compounds. Here it may be
taken that remaining 6% going to Zinc percentage purity for ZnTTBNc and nearly
10-11% contributed for V=O (Vanadium double bonded with Oxygen) molecule in
VTTBNc.
2.6. Substrate cleaning A wide variety of cleaning procedures are available to develop good quality
thin films. Highly polished and thoroughly cleaned glass substrates are used here
for deposition of films. First, the substrates are cleaned using liquid detergent.
Then it is kept in dilute nitric acid for some time. After this, the substrates are
cleaned using distilled water. Then the substrates are agitated in acetone. Finally
the substrates are dried in hot air.
2.7. Thin film preparation Thin films are evaporated on to clean glass substrates using thermal
evaporation method. Thermal evaporation is a simple method in which the material
is created in a vapour form by means of resistive heating. On heating a material in
vacuum, sublimation takes place and the atoms are transported and get deposited
on to pre cleaned substrates held at suitable distance at desired temperatures. The
material for deposition is supported on a source which is heated to produce desired
vapour pressure. The requirements for the source are that it should have a low vapour
pressure at the deposition temperature and should not react with the evaporant. The
shape of the source is designed and fabricated in such a way to hold the evaporant
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material [9]. The semiconductor is evaporated using Molybdenum boat and Tungsten
baskets as the source for coating electrodes. The unit is operated at 10V/100A ratings
of the step down transformer.
2.8. Thickness measurements
Average thickness measurement for all the thin films coated at a time is
made by digital thickness monitor along with the coating unit. For accuracy,
different methods are employed in deposited thin film for thickness measurements
[10]. In our laboratory, optical techniques are used for reconfirmation of thickness
measurement. This technique is used for both opaque and transparent thin films.
The basic principle behind this technique is the interference of two or more beams
of light reflected or transmitted from the bottom and top of the film the thickness
of which is to be measured. The condition for maxima in reflection will be the
condition for minima in transmission and vice versa.
For opaque films, sharp step-down to substrate plane must be first
generated either by a deposition through a mask or by subsequent etching. For
practical purposes the fringes formed are classified as the two cases of multiple
beam interferometry. They are Fizeau fringes of equal thickness and FECO fringes.
We have used Tolansky’s multiple beam interference method for the determination
of the thickness of thin film.
2.8.1. Tolansky’s multiple beam Fizeau fringe method
Figure 2.3 shows the schematic representation of Fizeau fringes produced
by multiple beam interference. The technique can be employed when the film to be
studied remains stable in vacuum and can be coated with highly reflective layer
[11]. The film is deposited on the glass substrate. A sharp shadowing with sharp
masks during deposition produces edge on the film. The film is then coated with a
highly reflecting silver layer. A second glass plate with a silver coated surface and
having some percentage of transmission is lowered on to the glass substrate and the
whole system is illuminated with a parallel beam of monochromatic light of
wavelength (λ=5893Ao) from a sodium vapour lamp.
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Figure 2.3 Schematic representation of the multiple beam interference method a) Fringe pattern b) Arrangement and c) Sample with step
At a small distance between two glass plates, when the cover glass is tilted
slightly, multiple beam interference fringes are shifted by a distance ‘x’. In the
region of sharp edge, the fringes are shifted by a distance ‘∆x’ [12]. A shift ‘∆x’ in
‘x’ correspond to a thickness step of λ/2 and the thickness of the film is given by,
T =
∆x
x
2
λ (2.8.1.1)
One of the varying parameters for thin films is its thickness and it gets
varied by placing the glass substrate on different positions inside the evacuated
chamber or by coating the thin films for different thickness by fixing all other
varying parameters like internal pressure, substrate temperature, primary and
secondary current and density. Thickness variation may result in the variation of
electrical, optical, structural and surface morphological output of semiconducting
thin films.
2.9. Sample annealing The samples are annealed in a specially designed furnace to change their
properties. It consists of a coil of Kanthal (AI grade temperature range 1150 -
13500C). Figure 2.4 shows the experimental set up for sample annealing. To avoid
heat loss, it is surrounded by a thick package of fire brick silica whose working
temperature is 11000C and the melting point is 17100C. The width of the heating
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element is about 20cm. The filament is also covered with sillmate (Al2O3 - SiO2)
tube, maximum working temperature is 15000C and melting point is 17100C.
Figure 2.4 Photograph of the furnace and temperature controller
It helps to provide uniform heating region at the centre of the tube. In
addition, it avoids any thermal shock during the annealing process. The
temperature of the heater is controlled and recorded by a digital temperature
controller cum recorder. Apart from air annealing, vacuum annealing is also done
on thin films by placing them inside an evacuated chamber in complete darkness
due to photosensitivity of Naphthalocyanines. A rough vacuum of 10-3mbar is
created inside the chamber using an external rotary pump. Temperature variation is
done on thin films under vacuum using a Chromel-Alumel thermocouple placed in
close proximity of the samples.
2.10. Substrate heating Substrate heating can be done within the set up of the coating unit by
connecting Substrate Heating (SH) controller to the substrate holder in evacuated
chamber. The internal settings like placing of copper constantan thermocouple over
the substrate to control the suitable substrate temperature. The voltage variation in
SH controller, is needed to create suitable temperature. For example, inorder to
create 100οC in the substrate holder, we have to suitably adjust the SH controller
voltage to 40V A.C. with which it shows a maximum variation of ±5οC. At that
time there is a change in the primary current to 2.5µA and secondary current to
55µA without changing the base pressure (1×10-5mbar).
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2.11. Gamma ray irradiation Gamma chamber- 5000, a compact self shielded 60Co irradiator is used in
the present study to irradiate gamma rays to thin film samples to study high energy
ray impact on thin films. Gamma chamber is highly applicable in phthalo-
naphthalocyanine research applications that require irradiation materials with
ionizing radiations of varying doses. By fixing the density of materials to unity,
present dose rate is fixed in gamma chamber. For the apparatus, the dose rate
decreases 1.1% Gray/month. Due to the decrease of dose rate, the same apparatus
requires different time periods for creating a suitable irradiation dosage at different
time periods. Presently, we find the dose rate to be 1284.99Gray/hour. So, for the
irradiation of 500Gray gamma ray on thin film samples we require 23minutes
20seconds, for 1000Gray irradiation it needs 46minutes 41seconds and 1500 Gray
irradiation takes 1hour, 10minutes and 2seconds.
2.12. Characterization techniques Micro and nano structures, crystallinity, impurity content, chemical
composition, surface morphology, application of light and electromagnetic field
etc. influence various properties of thin films. The characterization of thin film
micro structure is necessary for improving of the performance quality of various
devices. The above mentioned favourable factors strongly depend on thin film
thickness, substrate heating, post deposition air and vacuum annealing, high energy
electromagnetic beam irradiation, choice of substrates and conditions of thin film
preparations. Some of the important film properties and characterization
techniques are as follows.
2.12.1 Conductivity measurements
The electrical conductivity measurements are carried out in a conductivity
cell. The cell consists of a thick walled cylindrical chamber with a bottom flange
and four side tubes made of stainless steel. Three side tubes are closed air tight
with glass windows and are used in spectroscopic studies. The remaining side tube
is connected to a rotary vacuum pump and the chamber can be evacuated to low
pressure of 10-3mbar. The inner tube is made of stainless steel pipe which has been
welded to a large copper finger. The liquid nitrogen cavity and the heater coil help
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the sample to attain the required temperature very quickly. The outer enclosure is
made leak proof by using an ‘O’ ring which rests inside the groove on the flanges.
A sample holder fixed at the copper finger can hold the film with the help of
screws. The outer surface of the copper finger is covered with mica sheets and the
heating coil is wound over it. The electrical leads are taken out through Teflon
insulation. A D.C. power supply is used to heat the heater coil. The electrical
leakage current through the mount is by-passed to earth by grounding the inner
tube. The leads of the electrodes are taken out using Bi Noded Circuit (BNC)
connector. A Chromel-Alumel thermocouple in contact with the sample senses the
temperature. Temperature of the sample in the cell can be varied from liquid
nitrogen temperature to 400 0C.
Electrical conductivity measurements are carried out using Keithley
programmable electrometer model No.617. It is a highly sensitive instrument
designed to measure voltage, current, charge and resistance. The very high input
resistance, low input offset current and sensitivity allows accurate measurements.
The measuring range is in between 10µV and 200V for voltage measurements,
0.1pA and 20mA in the current mode and 10fC and 20nC in coulomb mode. The
resistance can be measured in two modes; (i) constant current mode and (ii)
constant voltage mode. Due to the high input resistance, a resistance as high as
200GΩ can be measured in the constant current mode. Using constant voltage
mode, resistance as high as 1016Ω can be measured. In this mode the measured
resistance is automatically calculated from the applied voltage. The model 617 has
a built in voltage source which can be used to apply a current I, through the
unknown resistance R. The insulation resistance is then automatically calculated by
the instrument as R =V/ I, where I is the current through the resistance and V is the
programmed voltage. The voltage can be programmed between -102.35V and +
102.4V in steps of 50mV and the maximum measurable output current is 2mA.
The instrument is capable of an internal 100 point data store and that can be used
to login a series of readings. The fill rate of data store can be set to specific
intervals according to the experimental conditions. The photograph of
experimental set up used to measure the electrical properties and analyse the
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device characteristics is given in Figure 2.5. The four probe technique was not
satisfactory for apparently high resistivity films because the order of magnitude of
the film [13].
Figure 2.5 Photograph of electrical conductivity experimental set up
The longitudinal structure of thin film with silver coated on two sides as in
Figure 2.6 is used as source for measuring the conductivity by two probe analysis.
Figure 2.6 Longitudinal structure of thin film
2.12.2 U.V- Visible Spectrophotometer
CARY 5000 (Version No. 1.09) has been used to record the optical
absorbance of the films in the UV-Visible and in NIR region. It is a double beam
system employing a static beam splitting half mirror which sends the light beam
from the monochromator through the sample and the reference substrate equally.
Semiconductor film
1cm 1cm 1cm 0.5m 0.5m
1cm
4cm
Thick Ag film Glass substrate
Glass substrate
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The light sources are either Deuterium lamp or Halogen lamp. The Deuterium
lamp produces wavelength starting from 200nm. The halogen lamp produces
wavelength up to 3100nm. Switching wavelength of light source can be set to any
value with in the range of 295 to 364nm. The lamps can be automatically
interchanged according to the wavelength needed. All the optical elements except
the light source are isolated from the external atmosphere by the window plate so
as to make the set up dust free. The slit width of the monochromator is fixed at
2nm. The collimated beam is allowed to split by the half mirror into the sample
and the reference beam. Two voltages are produced by the detector which is
proportional to the light intensities of the reference and sample beams respectively.
These two voltages are amplified and fed to the electrical system. The photograph
of CARY 5000 (Version No. 1.09) double beam mode spectrophotometer is as
shown in Figure 2.7.
Figure 2.7 Photograph of CARY 5000 double beam mode spectrophotometer
The optical behaviour of a material is generally used to determine its
optical constants, refractive index (n) and extinction coefficient (k). Films are ideal
specimens for reflectance, transmittance and interferometric measurement. The
methods are generally classified into (1) Reflection method, (2) Reflection and
Transmission method and (3) Interferometric method. Out of these three methods,
Reflectance method is used to determine the optical constants of the films in this
work.
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2.12.3 X-ray Diffractometer
The diffraction of X-rays by micro crystals in powder and film results from
a scattering process mainly due to electrons of corresponding atoms without
change in wavelength (λ). The intensities of diffracted beams are determined by
the positions of the atoms within the unit cell. So, by measuring the intensities of
the diffracted beams, idea about the atomic positions can be obtained. The velocity
of propagation of X-rays in vacuum is found to be same as that of electromagnetic
radiations and they exhibit dual nature. In the phenomena of refraction,
interference, diffraction and polarization, X- radiation acts as waves, giving
thereby to λ a real significance. But in the phenomena of photoelectric effect,
Compton effect, the appearance of sharp spectral lines and a definite short
wavelength limit of continuous spectrum, the energy of X-radiation appears to
propagate in quanta defined by the values of hν. When a monochromatic beam of
X-radiations having a wavelength (λ) falls upon the atoms in the Bragg plane, a
wavelet of scattered radiations spreads out from each atom in all directions.
Siemens-EQBCL015 X-ray Diffractometer (Model No. D5005) is used for the X-
ray diffraction of both powder and thin film samples and the schematic diagram for
Siemens-D5005 model is given in Figure 2.8.
Figure 2.8 Schematic diagram for Siemens- D 5005 model X-ray Diffractometer
Since X-rays are much more penetrating than ordinary light, it is essential
to consider the reflection at several such layers. At each layer there is a partial
reflection and the X-ray beam will be completely absorbed after penetrating a large
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number of layers. Now these reflected wavelets will reinforce themselves only
when they meet in the same face, the condition for which is that the path difference
between two such rays must be an integral multiple of wavelength. Thus the
condition for diffraction is
θλ sin2dn = (2.12.3.1)
Where d is the distance between adjacent planes in the crystal and θ is the
glancing angle, n is the order of reflection and λ is the wavelength of the incident
X-radiation. This characterization is used as a very important tool for the
identification of phases and crystallographic plane of grain growth. From the XRD
data, we attempt to calculate the mean crystalline size, dislocation density and
structural strain from the θ value and full width at half maximum (FWHM) of the
diffraction peak [14].
2.12.4. Scanning electron microscope
Scanning electron microscopy (SEM) is one of the most versatile and
useful instruments which provide morphologic and topographic information about
the surfaces of solids that is usually necessary in understanding the behaviour of
surfaces. It provides better depth of focusing and details than by the conventional
techniques. The surface with a rough topography can be examined. It is possible to
have a three dimensional view of the surface. In addition, in-situ observation of
surface morphology changes during oxidation of the specimen is also possible.
In a scanning electron microscope, the surface of a solid sample is scanned
in a raster pattern with a beam of energetic electrons. The back scattered and
secondary electrons produced from the surface in this process serve as the basis of
scanning electron microscopy. The secondaries are formed by the interaction of the
primary electron beam with the loosely bound electron of the surface atoms and
their emission is very much sensitive to the incident beam direction and the
topography of the surface atoms. The contrast depends on the rate of secondary
electron yields and the incident angle of the primary beam to the surface element.
When the electron beam scans the specimen surface, there will be a change in the
secondary electron emission according to the surface texture. In the present study,
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SEM is taken using the instrument JEOL/EO (Model No. JSM- 6390) and the
schematic diagram is shown in Figure 2.9.
Figure 2.9 Block diagram of JEOL-JSM- 6390 SEM instrument
From the SEM image, the surface morphology of thin film sample and the
average grain size for nano particle identification is well interpreted [15, 16, 17].
2.12.5 Atomic force microscope
Thin film surfaces can be topographically imaged to an atomic level
resolution by making use of a microscopic technique like Atomic force microscopy
(AFM). The principle of AFM is simple: a tip of nanometer scale sharpness is
mechanically contacted with the surface to probe the morphology. High instrument
resolution is obtained using a very sharp Silicon Nitride probe. The sample is
mounted under the probe and it is moved in X, Y and Z directions by a ceramic
piezo-scanner. The tip is mounted on the edge of an elastic cantilever (100-200µm)
of low spring constant to keep the probe in contact with surface. Deflection of the
tip along Z axis, due to different height on the surface of the sample, is monitored
by an optical laser. With all this information, it is possible to obtain a 3D scan of
the surface. Property-sensitive imaging modes can also be performed simultaneous
to topographic imaging. Tip chemistry can be modified for controlled studies of
probe-sample interaction. Many of the essential experimental features of AFM
parallel to those of Scanning Tunnelling Microscope (STM).
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There are three basic modes of operation associated with AFM such as Non
contact AFM (NC-AFM), Contact AFM and tapping mode. In the non- contact
AFM mode, the cantilever is located tens to hundreds of angstroms from the
specimen surface. To prevent the surface contact, a stiff cantilever is used resulting
in low tip- specimen forces of ~ 10-12N. NC-AFM has the ability to probe soft or
elastic materials and minimization of both surface contamination and tip
degradation. Normally, the spatial resolution of AFM is poor than that of STM.
But with sharp probe tips, a stiff cantilever, and operation in ultra vacuum, atomic
resolutions have been readily imaged by it.
In contact AFM mode, also known as the repulsive mode, the tip actually
makes physical contact with the surface, and force in the range of 10-6 to 10-8N is
typically generated. The block diagram for a general contact mode AFM is shown
in Figure 2.10. It grasps clear topological evidence apart from the former type.
Tapping mode is having both the advantage of NC-AFM and Contact type. It
sweeps through the surface touching at regular intervals.
Figure 2.10 Block diagram for contact mode atomic force microscopy
Here we employ Veeco 3-D nanoscope in contact mode to take the topological
image of thin films and the photograph is as shown in Figure 2.11.
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Figure 2.11 Photograph of Veeco 3-D Nanoscope with contact mode AFM
The Nanoscope III-D AFM is primarily used to study the topography of
semiconductor surfaces and other materials. It can operate in contact mode (where the
tip is in continuous physical contact with the probed surface) or in tapping mode.
Tapping Mode AFM, the most commonly used of all AFM modes, is a patented
technique (Veeco Instruments) that maps topography by lightly tapping the surface with
an oscillating probe tip. The cantilever oscillation amplitude changes with sample
surface topography, and the topography image is obtained by monitoring these changes
and closing the Z feedback loop to minimize them. This eliminates shear forces which
can occur in contact mode and so minimizes the damage to soft samples. The Multi
Mode system features multiple scanners that permit the user to tailor the system for
individual research. Scanners with large scan ranges up to 120µm in the X-Y plane, and
a Z range up to 5µm, as well as high-resolution scanners with 0.4mm X-Y plane and
submicron Z range are available [18, 19]. The instrument can also perform scanning
capacitance measurements. The Nanoscope IIIa controller provides 16-bit resolution on
all three axes, with three independent 16-bit Digital-to-Analogue Converters (DACs) in
X and Y for control of the scan pattern, scaling, and offset [20]. The III-D Nanoscope
image analysis and presentation software contains powerful algorithms for the
measurement and presentation of the research results including: cross sectional analysis,
roughness measurement, grain size analysis, depth analysis, power spectral density,
histogram analysis, bearing measurement and fractal analysis [21].
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