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Characterisation Tools for Nano @ IITB
Ajit KulkarniI. I. T.-Bombay
Why this talk here?• Process may be based on a recipe – if it does not
work, what next?• Or a new process is developed, how do you
develop an understanding of the process?• Characterise the product, a material.• What do we mean by characterisation?• More difficult to define the question than to answer
it• So once again…what is Characterisation?
Charcterisation of the UNKNOWN……material
• Characterisation is the study of structure (including microstructure) and composition (including trace level).
• Charcterisation makes use of one or more structure, composition-property correlation previously established.
• Is it a catch-22 problem?– Or is it the limitation
Characterisation of Materials - composition, structure, microstructure,
mapping
• Philosophy– No characterisation is complete or absolute– Characterisation is not a goal unto itself.– Time, cost and need determine the
methodology of characterisation along with its limitations.
– One has to look for ‘IT’ to see it. One may see ‘IT’ if ‘IT is there. ‘IT’ can’t be seen if you don’t look for ‘IT’ even if it is there. One may not see ‘IT’ even if ‘IT’ is there, because it depends on how you look for ‘IT’.
Analysis - Probes and Signals
What can be learnt from these signals?
photons
ions
electrons
EMISSION
TRANSMISSION
Interaction with material
EXCITATION
• bonding geometry of molecules
• physical topography
• chemical composition
• chemical structure
• atomic structure
• electronic state
Probes and volume of interaction
Volume of interaction depends on nature of probe (photon / electrons / ion) and its penetrability), sample(density), the way, the signal spreads laterally in the sample (scattering).
Ultimately, this determines, lateral resolution and depth resolution for the analysis. Operating parameters of the instrument (acceleration voltage) alters energy of electrons and hence depth of interaction volume.
In a scanning electron microscope, spot size or cross section of e-beam limits lateral resolution .
In transmission electron microscope, the wavelength and the energy spread limits resolution.
Of course, the instrument may set an upper limit. (aberrations)
In ESCA, the escape depth of electrons determines the depth resolution.
Analytical Techniques – a comparison
Analytical Technique Signal Measured Elemental Range Depth Resolution Surface info.
SIMS Secondary Ions H-U 5-30 Å Chemical composition
Chemical structure
TOF-SIMS Secondary Ions H-U, Large Organic 2000 Å (Scanning Mode) Adsorbate bonding
Molecules / Cluster Ions
TEM Transmitted Electrons X-Rays Na-U EDX N/A
FE-SEM, EDX Backscattered or Na-U 1 - 5 micrometres
Secondary Electrons and X-Rays
ISS Ions H- U monolayer atomic structure
(ion scattering spectroscopy) chemical composition
AES/SAM Auger Electrons Li-U 2-30nm chemical composition
(Auger electron spectroscopy, scanning Auger microscopy)
ESCA/XPS Photoelectrons Li-U 5 - 30nm chemical composition
(electron spectroscopy for chemical analysis, X-ray photoelectron spectroscopy) chemical structure
RAIRS IR photons organic, some inorganics monolayer Adsorbate bonding
(reflection-absorption infra-red spectroscopy)
STM - solid surfaces upper most atoms physical topography
(scanning tunnelling microscopy)
Analytical Technique Signal Measured Elemental Range Depth Resolution surface info,
Sample size, nature and the need for standards
In TEM, ~3 mm diameter sample of a few hundred Å thick is studied. Does it represent the ‘bulk’. What is the effect of this sampling procedure?
Surface and bulk analysis ? What you see on the surface need not represent bulk. ESCA / Auger looks at a few nanometer thick layers only. EDAX may look at signal averaged over a depth of one micron. Even exposure to air may add / modify the surface.
Signal from one constituent may get altered by another constituent – interference Even microstructure can alter signal strength.Matrix effects – make things difficult to quantify Nearly identical standards are needed. Convenient for quality control in a plant. How about an R&D lab?Some times analysis of each sample is a research project.
Some jargons to remember
Signal to noise ratioBackground correctionSpectral resolution (can be Mass resolution)SensitivityLimit of detectionRange of measurementsCalibrationInterference and Matrix effectReference or standard
No single technique can offer a universal solution.
Probe-material interaction –an example… X- ray as a probe
X-rays in photoelectrons out
Sample Surface Layer
Binding energy (eV) = photon energy - kinetic energy - work function BE (eV) = hν - KE – ΦMeasuring (signal) electron intensity and energy will give quantitative and qualitative information
Ev
Ef
KE
BEvalence band
corelevels
photon
After Photoemission……
X-ray Fluorescence or Auger electron emissionXRF/ EDAX / WDS / Electron probe micro analyser/AES
Fluorescence yield
Analytical tools based on above fundaes
• Fluorescence X-rays (XRF)
• Diffracted X-rays (XRD)
• Emitted Electron (AES)
• Photoelectron (XPS)
X-ray Fluorescence Spectroscopy
Emitted X-rays can be used to analyse the atom that is emitting
QualitativelyandQuantitatively
Triggering emission – signal it can be X-rays, electrons, Ions
XRFEDS / WDS in SEM / EPMA/ TEM / STEMIon probe microanalysis
In X-ray fluorescence measurements, intensity of characteristic radiation emitted by analyte atom is measured
Intensity of X-rays is a function of incoming signal intensityabsorption cross sectionFluorescence yieldconcentration of atoms in targetself absorptionMatrix effect
when it is measured the Signal measured is a function of
Detector characteristicsCollection geometry
…Matrix effect
A sample with a surface of size 1 cm2 - this will have ~ 1015 atoms in
the surface layer. In order to detect the presence of impurity atoms
present at the 1 % level, a technique must be sensitive to ca. 1013
atoms. Contrast this with a spectroscopic technique used to
analyse a 1 cm3 bulk liquid sample i.e. a sample of ca. 1022
molecules. The detection of 1013 molecules in this sample would
require 1 ppb (one part-per-billion) sensitivity - very few techniques
can provide anything like this level of sensitivity. Selectivity to
surface atoms.
Surface and Bulk Analysis – constraints
• Penetration depth of the X-ray radiation is 102-103 nm.
• Surface sensitivity arises from the short distance the photoelectrons can travel in the solid before suffering inelastic scattering.
Surface Sensitivity of XPS
d
Photoelectrons outX-rays in
d = 3
• The average distance from the surface a photoelectron can travel without energy loss is defined as the inelastic mean free pathlength (IMFP), .
• Sampling depth, d, defined as the average distance from the surface for which 95% of photoelectrons are detected, d = 3.
Surface Sensitivity of XPS
‘universal curve’
X-ray Photoelectron spectroscopy is...
Surface sensitive - photoelectron signal from first 1-10 layers of atoms and molecules.Quantitative.Provides insight into the chemical state of the element. Sensitive - detection limit ~0.1 atomic %.
Able to detect all elements except H and He.• Nondestructive analysis.
TiN
SiO2
Si
Si 2p region as a function of depth from the surface
• Si 2p region shows chemical environment of the Si atoms.
Depth Profile through a TiN/SiO2 thin film on Si.
Tools for better vision-microscopy
• Transmission Electron Microscope-CM200
• FEGTEM-JEM2100F
• CryoTEM*-
• FEGSEM- J7600F
• ESEM*-
• IR microscope –
• Confocal Laser Scanning microscope*
Sophisticated Analytical Instrument Facility
Instrument Details :Make : PHILIPS
Model: CM200Specification : Operating voltages : 20-200kv Resolution :2.4 Å
Materials Science/Metallugy biological Science
Nanotechnology
Ceramics
Pharmaceuticals
Semiconductors
Applications :
TEM images are formed using transmitted electrons (instead of the visible light) which can produce magnification details up to 1,000,000x with resolution better than 10 Å. Further more the analysis of the X-ray produced by the interaction between the accelerated electrons with the sample allows determining the elemental composition of the sample with high spatial resolution.
Electron beam can be raster scanned over the sample and any signal generated can be measured as a function of beam position. .. Mapping of sample for Composition, morphology etc. (STEM)
TEM
Centre for Research in Nanotechnology & Science (CRNTS)
27
Field emission gun
Higher brightness, 100 times greater than LaB6 gun
Higher coherency
Higher energy resolution, 0.7 to 0.8eV
Higher resolution, increased contrast – lattice imaging
STEM mode, EDS, 2Kx2K camera
On the anvil a new HRTEM (JEM 2100F)
JSM-7600F FEG SEM Scanning electron Microscope
☆High resolution
☆High stability
☆High productivity
Features of JEOL JSM 7600F
• Designed for Nano sciences
• In-Lens FE GUN
• Aperture angle optimizing lens
• Gentle Beam mode
• Specimen Airlock
Why you need low kV20kV 5kV
15kV 3kV
Resolution of JSM-7600F
15kV 1kV
Specimen: Evaporated gold on carbon
Platinum catalyst on carbon 15kV, x500,000
Ultra High Resolution by JSM-7600F
Composition and mapping
X-ray Fluorescence Spectrometer – Philips 400W
Secondary Ion Mass Spectrometer- Phi-NanoTOF
Induction Coupled Plasma Atomic Emission Spectrometer-
Laser ablation-ICP Mass Spectrometer
EDS and WDS in electron microscopes (STEM, SEM)
ESCA*
PHI nanoTOF TOF-SIMS
Secondary Ion Trajectories in TRIFT Analyzer
Ga+, Aun+
Cs+, C60+
Pre-Spectrometer Blanker
SED
Detector
Angular AcceptanceDiaphragm
ESA 1
ESA 2ESA 3
Energy Slit for Metastable Ion Rejection
Post-SpectrometerBlanker
Sam
ple
User selectable angular acceptance diaphragm
Total Secondary Ion Image Aluminum Ion Image Silicon Ion Image
Superior TRIFT Analyzer ImagingLMIG FIB cut and TOF-SIMS Images
Only a PHI TRIFT analyzer can collect ions from the top surface and the perpendicular face of the
FIB cut
representative ofreflectron performance
representative ofTRIFT performance
The TRIFT analyzer is able to efficiently
collect the secondary ions that are emitted at
oblique angles (i.e. ions emitted more
parallel to the substrate surface).
The ability to collect obliquely-emitted
secondary ions results in unequalled imaging
performance.
Oblique angular direction due to extraction field lines curving from the substrate over the In particle.
10m 10m
100m 100m
SiC Fiber
Tire Chord
TRIFT Adjustable Solid Angle of Acceptance Wide Collection Angle for Superior Imaging Narrow Collection Angle for Best Mass Resolution
“Turn Key” Charge NeutralizationPatented dual beam charge
compensation has been used for many years on PHI XPS instruments.
The dual beam charge compensation method has proven successful at “turn key” insulator analysis.
The dual beam method allows electron energies below 10eV to be used, reducing sample damage.
Inert gas ion energies (≤10eV) are below the damage threshold.
Effective neutralization enables insulator imaging at higher magnifications.
Sample Platen
Analytical Ion Beam
Low-energyElectron Beam
Insulating Sample
Low-energyIon Beam
(B)
Sample Platen
Analytical Ion Beam
Low-energyElectron Beam
Insulating Sample++- - - - - - - - - - - - - - - - - - - - - - -
(A)
Negative chargesurrounding
analytical zonerepels electrons.
“Turn Key” Charge Neutralization
42.9 43.0 43.1 43.20
20
40
60
80
100
Tot
al C
ount
s (0
.000
4 am
u bi
n)
m/m = 2,000
Ga+ dose = 2x1011 ions/cm2
raster size = 250 m43 m/z of PET
Improper charge neutralization.
42.9 43.0 43.1 43.20
200
400
600
800
1000
1200
Tot
al C
ount
s (0
.000
4 am
u bi
n)
m/m > 9,000
Ga+ dose = 2x1011 ions/cm2
raster size = 250 m43 m/z of PET
m/z
CH3Si
C2H3O
C3H7Proper charge neutralization.
Sample: bulk PET
“Turn Key” Charge Neutralization
28.95 29.00 29.05 29.100
1000
2000
3000
4000
5000
To
tal C
ou
nts
(0
.00
02
am
u b
in)
m/m > 8,000 @ 29m/z
3mm thick polypropylene (PP)100m x 100m raster area10 minute acquisition
C2H5+
Generation of 3D Isosurfaces and Cross-
Section ImagesY
Z
SiSi
Chemical and Biological tools
Nuclear Magnetic Resonance Spectrometer
Electron pin Resonance Spectrometer
FTIR spectrometer
Fluorescence Spectrometer
CHSN analyser
FACS Cell sorter
Fluorescence Microscope
Tissue culture laboratory
Other Materials- Characterisation tools
Thermogravimetry, Differential Thermal analyser
Differential Scanning calorimeter
Image analyser with Optical Microscope –polariser, DIC etc
Confocal Laser Raman Spectrometer – Photoluminescence Spectrometer
Dynamic Light scattering- particle size analyser
Zeta Potential measuring unit
Centre for Research in Nanotechnology & Science (CRNTS)
Instrument Details :
The CHNS(O) Analyzer find utility in determining the percentages of Carbon, Hydrogen, Nitrogen, Sulphur and Oxygen of organic compounds, based on the principle of "Dumas method" which involves the complete and instantaneous oxidation of the sample by "flash combustion". The combustion products are separated by a chromatographic column and detected by the thermal conductivity detector (T.C.D.), which gives an output signal proportional to the concentration of the individual components of the mixture.
Make : Thermo finnigan, Italy
Model : FLASH EA 1112 series
Specification : Estimation of CHN/CHNS/O in percentage level to high concentration level.
Instrument Details :
Electron Spin resonance spectroscopy is based on the absorption of microwave radiation by an unpaired electron when it is exposed to a strong magnetic field. Species that contain unpaired electrons (namely free radicals, odd-electron molecules, transition metal complexes, rare earth ions, etc.) can therefore be detected by ESR.
Make : VARIAN, USA
Model: E-112 ESR Spectrometer
Specification : X-band microwave frequency (9.5 GHz)
Electron Spin Resonance, ESR, is a powerful non-destructive and non-intrusive analytical method. ESR yields meaningful structural information even from ongoing chemical or physical processes, without influencing the process itself. It is the ideal technique to complement other analytical methods in a wide range of application areas.
Molecular structure
Crystal structure
Reaction kinetics
Valence electron wave functions
Molecular motion
Relaxation properties
Electron transport
Crystal / ligand fields
Reaction mechanisms etc.
Applications :
Centre for Research in Nanotechnology & Science (CRNTS)
Instrument Details :
Infrared Spectroscopy gives information on the vibrational and rotational modes of motion of a molecule and hence an important technique for identification and characterisation of a substance.. The Infrared spectrum of an organic compound provides a unique fingerprint, which is readily distinguished from the absorption patterns of all other compounds; only optical isomers absorb in exactly the same way. Hence FTIR is an important technique for identification and characterization of a substance.
Make : Nicolet Instruments Corporation, USA
Model: MAGNA 550
Specification : Range - 4000 cm-1 to 50 cm-1
Chemistry & Chemical Engineering
Polymer & Rubber Industries
Forensic Labs
Pharmaceutical Labs
Food Industries
Agriculture
Petroleum
Industries Nanotechnology
Applications :
Centre for Research in Nanotechnology & Science (CRNTS)
Sophisticated Analytical Instrument Facility
Instrument Details :
Specification :
5mm Autoswitchable probe with PFG (1H/ 13C/ 31P/ 19F) 5mm Dual Broad Band probe with PFG for Multinuclear NMR
(13C, 15N, 27Al, 31P, 29Si, 77Se, 119Sn, 125Te, 199Hg, 51V, 7Li etc.)
Nuclei with non-zero spins, when placed in a strong magnetic field precess at specific orientations with respect to the applied magnetic field. When appropriate energy is supplied in the form of radio frequency, these nuclei flip to a higher energy state. The energy absorbed during this transition is a function of nucleus type and its chemical environment in the molecule The excited nuclei are allowed to precess freely and come back to their equilibrium positions. During this process an electric signal is induced in a suitably placed RF coil. This signal which is monitored with respect to time is called free induction decay (FID). The FID, which is in time domain gives its equivalent frequency domain signal on Fourier transformation. A plot of the absorption frequency versus the intensity of the absorption constitutes the NMR spectrum.
Make : VARIAN, USA
Model: Mercury Plus 300MHz NMR SPECTROMETER
Instrument Details :
X-ray generator:
4 KW with 60 KV, 125 mA (in steps). The generator is solid state based on 'Switch Mode Power Supply' design to respond fast the changes sought in X - Ray tube power.
Make : PHILLIPS (now, PANAlytical, The Spectris Technology, The Netherlands)Model: PW 2404
Specification: X-Ray tube with Rh target.
Centre for Research in Nanotechnology & Science (CRNTS)