Chapter 5
Materials Characterization
Lecture 1
Dr. Alagiriswamy A A (PhD., PDF)
Dept. of Physics and Nanotechnology
SRM University Main Campus,
Ktr., SRM Nagar,
Chennai, Tamilnadu
5. Characterization Techniques
• 5.1 X-ray Diffraction (XRD)
• 5.5 Neutron diffraction (ND)
• 5.3 Electron diffraction (ED)
• 5.4 X-ray fluorescence methods (XRF)
• 5.5 Infrared Spectroscopy (IRS)
• 5.6 Fourier Transform infrared spectroscopy (FTIR)
• 5.7 Surface Raman spectroscopy (SRS)
• 5.8 Ultraviolet-visible spectroscopy (UVS)
• 5.9 Thermogravimetric analysis (TGA)
• 5.10 Differential scanning calorimetric analysis (DSC)
• 5.11 Differential thermal analysis (DTA)
Characterization of Solid Samples
Bulk
elemental
composition
Dissolution step
Direct solid analysis
Atomic
absorption
ICP spectrometry
Electron. microscope
ICP mass spect.
CHN analyser
Structural Properties
Surface phenomena
IR spectrom.
Dynamic SIMS.
UV-Vis spectrom
Static SIMS
XRD/FESEM
SEM/FESEM
TEM./HRTEM
SEM-EDX
XPS/SAM
dilatometry.
AFM
Excitation
Source
Sample
Detector
Why do you characterize??
Materials Characterization
Materials
Characterization has
several main aspects
Accurately measuring
the physical and
chemical properties of
materials
Providing local
microscopy
Accurately measuring
(determining) the
structure of a material
- atomic level structure
- microscopic level
structures
Background
A slight history
X-rays were discovered by W.C. Röentgen in 1895, and led to several uses
X-ray radiography is used for creating images of light-opaque materials relies on
the relationship between density of materials and absorption of xrays. Applications include a variety of medical and industrial applications.
X-ray fluorescence spectrometry relies on characteristic secondary radiation
emitted by materials when excited by a high-energy x-ray source and is used
primarily to determine amounts of particular elements in materials.
X-ray crystallography relies on the dual wave/particle nature of x-rays to discover
information about the structure of crystalline materials
More of interest, owing to the facts:X-rays rays – a primer
X-rays: high energy (1 to 100 keV), short wavelength
(1 nm to 0.05 nm) electromagnetic radiation
Brehmstrahlung (or Continuum) Radiation: German for “breaking radiation”, noise that appears
in the spectra due to deceleration of electrons as they strike the anode of the X-ray tube
High energy + strong dependence on atomic number make X-rays a valuable (medical) diagnostic tool
X-ray wavelengths are similar to the spacing of atoms in matter –not far
off from the size scale of nanostructured solids
non-destructive/a well-established scientific basis/mathematical
analytics
relatively simple demands on equipment and experimental
technique
X-rays can be scattered by electrons in a solid
There is “life” beyond Bragg’s Law (Growing Reliance On
Nanoscale Materials)
Light and matter exhibit wave-particle duality
Relation between wave and particle properties
E  h
p
h

given by the de Broglie relations
Evidence for
particle
properties of
light
,
Photoelectric
effect, Compton
scattering
Evidence for
wave properties
of matter
Electron
diffraction,
interference of
matter waves
(electrons,
neutrons, He
atoms, C60
molecules)
x  p  / 2
x
Heisenberg uncertainty principle limits
y  p y  / 2
simultaneous knowledge of conjugate
Variables. This is because of intrinsic nature
z  p z  / 2
Scattering by One Electron
Oscillation direction
of the electron
X-ray beam
The scattered energy
(intensity) is:

Electron
Electric vector of
The incident beam
2
1 e  2
I el  I 0 2  2  sin 
r  mc 
2
10
Scattering by Two Electrons
p
q
 2
s0
r

1
s
The phase difference of wave
2 with respect to wave 1 is:

2r  (s 0  s)

 2 r  S
S  s  s0
2
1
S  2 s sin 

2 sin 

Let the magnitudes of s0 and s = 1/λ
Diffracted beams 1 and 2 have the same magnitude,
but differ in phase because of the path difference p +
q
1
1
How about scattering by
• an atom
• a row of atoms,
• a plane of atoms
• A unit cell
• A crystal
t=4
t=5
t=6
t=7
(r)
t=3
t=2
t=1
2a.S t=0
t=8
+r
nucleus
-r
(-r)
April 9, 2015
12
Single molecule diffraction?
The scattering by a single electron is weak, but not too weak:
 A crystal amplifies “the” signal by summing up the
amplitudes from ~1024 electrons;

Don’t you even need crystals rather than looking
at single electron diffraction pattern????
The Laue method is mainly used to determine the orientation of large single
crystals while radiation is reflected from, or transmitted through a fixed crystal.
The diffracted beams form arrays of spots, that lie on curves on the film.
The Bragg angle is fixed for every set of planes in the crystal. Each set of planes
picks out and diffracts the particular wavelength from the white radiation that
satisfies the Bragg law for the values of d and θ involved.
For every set of crystal planes, by chance, one or more
crystals will be in the correct orientation to give the
correct Bragg angle to satisfy Bragg's equation. Every crystal
plane is thus capable of diffraction. Each diffraction line is
made up of a large number of small spots, each from a
separate crystal. Each spot is so small as to give the
appearance of a continuous line
Neutron diffraction
= h/p; = 2.860 / E1/2
•Fast moving neutrons, slow, thermal, resonance neutrons, cold,
•Atomic nuclei could scatter neutrons, and emit beta particles
Electron diffraction
Davisson and Germer's discovery of
electron diffraction
Lack of surface
sensitivity
X-ray Fluorescence (XRF) Methods
Instrumentation
1. X-ray fluorescence system
utilizing an analyzing crystal
The filtered primary x-rays from the
tube hits the sample and produce the
fluorescence radiation characteristic
of the elements in the sample.
This radiation passes through a
collimator
and
the
relative
wavelengths are separated by the
diffracting crystal.
The intensity of each wavelength is
determined and recorded as the
synchronized detector rotates in an
arc around the analyzing crystal.
Schematic diagram of an X-ray fluorescence
system utilizing an analyzing crystal
What’s the point?
We utilize the x-rays produced by the electron microprobe for many research
applications.
There are other techniques, similar in some ways, that are worth discussing, that
utilize x-rays for secondary x-ray fluorescence. Two in particular are:
XRF (X-Ray Fluorescence), where x-rays from a sealed tube are used to produce xrays by secondary fluorescence in samples of interest (traditionally a macrotechnique)
Synchrotron Radiation, where electrons are accelerated in ~10s-100s meters diameter
rings, and then made to produce highly focused beams of extremely intense x-rays or
light, which are then fed into many different types of experiments.
The benefits of secondary x-ray fluorescence include very low detection limits (10s of
ppm easy in 10 seconds, no backgrounds)
XRF - Features
Energy
dispersive
X-ray
fluorescence
technology (ED-XRF) provides one of the
simplest, most accurate and most economic
analytical methods for the determination of
the chemical composition of many types of
materials. It is non-destructive and reliable,
requires
no,
or
very
little,
sample
preparation and is suitable for solid, liquid
and powdered samples. It can be used for a
wide range of elements, from sodium (11)
to uranium (92), and provides detection
limits at the sub-ppm level; it can also
measure concentrations of up to 100%
easily and simultaneously
X-ray Attenuation
X-ray
T
A
R
G
E
T
characteristic
(Compton)
(Rayleigh)

The basics of XRF are very similar to those of EPMA—we are dealing with
characteristic x-rays and continuum x-rays— with the exception that we are
doing secondary fluorescence : x-ray spectroscopy of our samples using x-rays
coming out of a sealed tube to excite the atoms in our specimen.

The big difference is that
•
there is NO continuum generated in the sample (x-rays can’t generate the
Bremsstrahlung), and
•
we are using BOTH characteristic x-rays of the sealed tube target (e.g., Cr, Cu,
Mo, Rh) AND continuum x-rays to generate the characteristic x-rays of the
atoms in the sample.

XRF has been a bulk analytical tool (grind up 50-100 grams of your rock or
sample to analyze), though recently people are developing “micro XRF” to focus
the beam on a ~100 mm spot.
XRF spectrometer
(including marketed new)
An XRF spectrometer is
very similar to an electron
microprobe: just replace
the electron gun with an xray tube located very close
to the specimen; both the
characteristic
and
the
continuum x-rays cause
(secondary) fluorescence of
the specimen, and the
resulting x-rays are focused
using collimators in either
WDS (crystal + counter)
or EDS
(solid
state
detector) mode .
Detector Principles
A detector is composed of a non-conducting
or semi-conducting material between two
charged electrodes.
X-ray radiation ionizes the detector material
causing
it
to
become
conductive,
momentarily.
The newly freed electrons are accelerated
toward the detector anode to produce an
output pulse.
In ionized semiconductor produces electronhole pairs, the number of pairs produced is
proportional to the X-ray photon energy
n
where :
n
E
e
E
e
= number of electron-hole pairs produced
= X-ray photon energy
= 3.8ev for Si at LN2 temper atures
Si(Li) Detector
Window
FET
Super-Cooled Cryostat
Si(Li)
crystal
Pre-Amplifier
Dewar
filled with
LN2
Cooling: LN2 or Peltier
Window: Beryllium or Polymer
Counts Rates: 3,000 – 50,000 cps
Resolution: 120-170 eV at Mn K-alpha
Spectral Comparison - Au
Si(Li) Detector
Si PIN Diode Detector
10 vs. 14 Karat
10 vs. 14 Karat
Concentration
Quantitative Analysis
Thursday, April 09, 2015