Dr Ajit Kulkarni

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)