unitoperation Flashcards
1
Q
What is mechanism of XPS(X-ray photoelectron spectroscopy)
A
x-ray beam incidents on solid surface –> emit photoelectron owing to photoelectric effect –> kinetic energies analyzed–> X-ray photoemission spectroscopy provides elemental information and information about the chemical bond through the kinetic enerfy of the detected electrons
2
Q
How is depth profiling performed?
A
combining a sequence of ion gun etch cycles with XPS analysis;
Ar source with controlled E (100V 5000V)–> surface etched by rastering an ion beam over a square or rectangular area of the sample; atomic concetration and/or oxidation state of certain element as a dunction of depth can be obtained
3
Q
What is angle-resolved XPS?
A
Angle resolved X-ray photoelectron spectroscopy (ARXPS) is a technique to
control the detection depth of a sample by changing the sample tilt angle with
reference to the analyzer.
4
Q
Is XPS a small-area or large-area analytical technique compared to
AES?
A
Smallest analytical area for XPS: -10 mum diameter
5
Q
Is XPS suitable for insulators?
A
Yes. For non conducting materials,
Strengths and Weaknesses
Strengths:
Non-destructive for surface studies
Surface sensitive technique (top 10 nm)
Chemical state identification on surfaces
Identification of all elements except for H and He
Quantitative analysis, including chemical state differences
Applicable for a wide variety of materials, including non conducting
samples (paper, plastics, and glass)
Depth profiling with matrix-level concentrations (atomic %)
Weaknesses:
Expensive equipment and maintenance costs
Detection limits typically ~ 0.1% atomic
Smallest analytical area ~ 10 mm diameter
Samples must be ultra high vacuum compatible
Samples that decompose under X-ray irradiation cannot be studied
6
Q
What kind of applications are most suitable for XPS?
A
Ultra high vacuum compatible,
stable under x-ray irradiation with small diameter (-10mm)
7
Q
How are Auger electrons produced?
A
k
8
Q
Why is AES surface sensitive?
A
l
9
Q
How is depth profiling performed?
A
m
10
Q
Explain the differences between AES and EDS.
A
n
11
Q
What kinds of problems are best tackled by AES?
A
v
12
Q
electrical conductivity
A
current density : : 𝐽 =
𝐼/𝐴= −𝑛𝑣𝑑𝑒
= 𝐸/𝜌= 𝜎𝐸
𝜌 is the resistivity and 𝜎 is the conductivity
Drift velocity due to the electric field:
𝑣𝑑 = −𝑒𝐸𝜏/𝑚= −𝜇𝐸e conductivity 𝜎 = 𝑛𝑒𝜇
resistivity 𝜌 = 1/𝑛e𝜇
13
Q
drude model
A
classically treated the microscope behaviour of electron;
free electron model
kinetic theory : assuming the microdcope behacior of electrons in a solid may be treated classically:
Assumption:
1. matter consists of light negativelt charged e- ( mobile) & heavt static postively charged ions
2. neglecting e- e- & e- ions interactions (free electron)
3. probability of an e- suffering a collision in short time dt : 𝑑𝑡/𝜏, where 𝜏 :the mean free
time between collisions
1/𝜏: electron
scattering rate( avg rate of collision)
14
Q
Drude conductivity
A
scatterings of e- by ions --> resistance J = -envd = 𝜎𝐄 𝑣𝑑 = − 𝑒𝐄𝜏/𝑚 = −𝜇E --> J = e^2 n 𝜏/m *E DC conudctivity: σ= 𝑛𝑒^2𝜏/𝑚 = ne𝜇
15
Q
thckness independent rou –> sheet resistance
A
Rs =𝜌 / 𝑡 [om/m^2]
𝑅 = 𝑅𝑠 𝐿/W
16
Q
Resistivity: 4 pint probe
A
The four point probe is commonly used to
determine the resistivity of semiconductor
samples (wafers)
The outer 2 probes are connected to a current
source
The two inner probes are high impedance
voltage sensors
The sample thickness 𝛿 is assumed to be
constant
Current flows out radially from the tip as hemispheres.
17
Q
spectroscopic ellipsometry Pros &Cons
A
Non-destructive technique
Film thickness measurement, can measure down to <1 nm
Can measure optical constants 𝑛 and 𝑘 for unknown materials
─ Absorption coefficient, band gap, carrier concentration, mobility, effective
mass, etc.
Can also measure film composition, porosity and roughness
Absolute measurement for thickness（senstitivity: A) : do not need any reference.
Rapid measurement: get the full spectrum (190nm up1700nm) in few seconds
Can be used for in-situ analysis
Small equipment footprint: do not require a lot of lab space
Cons:
Can only measure flat, parallel and reflecting surfaces
Some knowledge of the sample is required: number of layers, type of layers, etc.
SE is an indirect measurement: does not give directly the physical parameters
A realistic physical model of the sample is usually required to obtain useful
information
18
Q
Peak energy in PL
A
Compound identification Band gap/electronic levels Impurity or exciton binding energy Quantum well width Impurity species Alloy composition Internal strain Fermi energy
19
Q
Peak width in PL
A
Structural quality/chemical purity
Quantum well interface roughness
Carrier or doping density
20
Q
Peak intensity in PL
A
Relative quantity Polymer conformation Relative efficiency Surface damage Excited state lifetime Impurity or defect concentration
21
Q
Strengths of PL
A
─ Very little to none sample preparation ─ Non destructive technique ─ Very informative spectrum ─ Rapid data acquisition ─ Moderate cost
22
Q
Weaknesses of PL
A
─ Often requires low temperature (down to LHe).
─ Data analysis may be complex (many transition levels).
─ Laser with different wavelengths may be needed as probe.
─ Many materials have weak luminescence intensity (e.g. indirect
gap semiconductor)
23
Q
Modulation spectroscopy
A
Modulation Spectroscopy is an analog method for taking the derivative of an optical spectrum (reflectance or transmittance) of a material by modifying the measurement conditions in some manner. This procedure results in a series of sharp, derivative-like spectral features in the photon energy region corresponding to electronic transitions between the filled and empty quantum levels of the atoms that constitute the bulk or surface of the material.
possible to measure the photon energies of the
interband transitions to a high degree of accuracy and precision.
24
Q
The modulation is applied by periodical
changes of one of the system parameters:
A
Electric field: modulation of the electric field by ─ applying a periodic bias: Electroreflectance ─ applying a periodic light probe: Photoreflectance (PR) Temperature: thermoreflectance (TR) Strain: piezoreflectance
25
Photoreflectance -- photoinduced change in reflectivity when light on and off
Changes in reflectivity ∆𝑅/𝑅
can be related to the perturbation of the dielectric function of the material, 𝜀 = 𝜀1 + 𝑖𝜀2:
∆𝑅/𝑅= 𝛼 （𝜀1, 𝜀2） ∆𝜀1 + 𝛽 （𝜀1, 𝜀2） ∆𝜀2
where 𝛼 and 𝛽 are the Seraphin coefficients, ∆𝜀1 and ∆𝜀2 represent photo-induced changes of the real and imaginary parts of the dielectric function, respectively.
26
SIM sum
1. can be used to determine the composition of organic and inorganic solids at the outer 5nm of a sample;
2. Generate spatial or depth progiles of elemental or molecular concentrations (used for elemental mappling)
3.used for detection of impurities or trace elemnets, especially in semiconductors
e.g . dopant
4. secondary ion images have resolurion on the order of 0.5 -5 mium
5.detection limits for trace elemnets range between 10 12 to 10 16 atoms/cc
6. sensiticity and depth resolution cannot be optimized simultaneously: best sensiticity with high sputtering rate and large detected atra;
best depth resolution with low impact energy, reduced ion penetration into sample, low sputtering rate and small detected area.
SIMS is the most sensitice elemental and isotopic surface microanalysis (bulk concentration of impurities around 1 part per billion) but very pricey
27
Static SIMS
Range of elements H to U: all isotopes
Destructive Yes, if sputtered long enough
Chemical bonding Yes
Depth probed Outer 1 to 2 monolayers
Lateral resolution Down to below 100 nm
Imaging/mapping Yes
Quantification Possible with suitable standard
a Mass range Typically up to 1000 amu, 10000 amu (ToF)
Main application Surface chemical analysis, organics, polymers
28
Dynamic SIMS
Range of elements H to U: all isotopes
Destructive Yes, if sputtered long enough
Chemical bonding Yes
Depth probed Outer 1 to 2 monolayers
Lateral resolution Down to below 100 nm
Imaging/mapping Yes
Quantification Possible with suitable standard
Mass range Typically up to 1000 amu, 10000 amu (ToF)
Main application Surface chemical analysis, organics, polymers
29
Pros of SIMS
excellent sensitivity, esp. for light elements
high surface sensitivity
depth profiling with excellent depth resolution(NM) (dynamic)
good spatial resolution <1-25 miu m
small analyzed volume (down to 0.3 miu m3) so little sample is needed
information about the chemical surface composition( due to ion molecule static)
elements from H to U can be detected with excellent mass resolution
30
weakness of SIMS
```
destructive
element specific selectivity
standards needed for quantification
sample must be vacuum compatible
sample must have a flat surface
high cost
```
31
Selection of primary ions:
```
Inert gas (Ar, Xe, etc.)
─ Minimize chemical modification
Oxygen
─ Enhance positive ions
Cesium
─ Enhance negative ions
Liquid metal (Ga)
─ Small spot for enhanced
lateral resolution
```
32
Scanning Transmission electron microscopy
Focused narrow beam across the sample makes these microscope suitable for analysis techniques such as mapping by EDS, EELS, ADF, HAADF
33
EDS energy dispersive spectroscopy
Analytical tools used for elemental analysis, in SEM/STEM, incident electrons are used as the excitation source creasing characteristic x-ray from different ele
34
EELS electron energy loss spectroscopy
E- loss energy through inner-shell ionisations
Useful for detecting elemental components of materials:
- detailed shape of the spectral profiles gives information on electronic structure, chemical bonding and nearest neighbor distances for each atomic species
—quantitative elemental concentration for 3-35 (Z)
35
High angle annular dark-field imaging (HAADF)
Using high angle detector, atomic resolution images where the contrast is directly related to the atomic number (Z-contrast image) can be formed
36
X-ray powder diffraction
XRD is used for phase identification of crystalline material, provide information on unit cell dimensions
Detector always ready to detect the Bragg diffracted beam 2dsin0 = n rounds
37
Application of XRD
```
Phase composition of a samaple
Unit cell lattice parameters and bra is lattice summetry
Residual strain(macrostrain)
Epitaxy/texture/orientation
Crystalline size and micro strain
```
38
Atomic scattering factor —structure factor
F(0) proportional to Ronda*Z
Denser atom greater intensity in XRD
Intensity decrease as scattering angle increases
/sin(0/2)
39
XRD
Basis —> intensity
| Lattic structure —> the position of lines
40
in XRD: possible reason for differential peak shift; intensity ratio different from the calculated value
diffraction peaks broadening: not uniformed microstrain;
| for different intensity
41
Preferred orientation of crystallites
Preferred orientation of crystallises can crease variation in diffraction peak intensities & can be used
Qualitatively analysed using 1D diffraction pattern (powder pattern)
Quantitatively analysed by a pole figure which maps the intensity of a single peak as a function of tilt and rotation of the sample
42
Crystalline size in XRD
For size < 120 no. Create broadening of diffraction peaks
Peak broadening: quantify the avg crystallite size of annoparticle using Scherrer Eq
(Instrument contributions broadening know by using a standard sample e.g. single crystal)
B(2sigma) = KRoumda/LCos sigma
B : 2sigma FWHM
Rounds: x-ray wavelength
L grain size
K = 0.9
Peak position moved by uniform strain
While non uniform strain caused broadening b = d2sigma =-2dd/d tan sigma
43
4 point probe
Commonly used for resistivity of semiconductor wafer
Outer 2 probes are connected to a current source
2 inner probed are high impedance voltage sensors
Uniformed & constant sample thickness
44
Hall Effect
The behaviour of red carrier in a semiconductor when an electric and magnetic field are applied
45
for insulator, what should be scanning probe
c
46
Van deer Paul method
Technique commonly used to measure the resistivity and hall coefficient RH of a sample of any arbitrary shape
Give free carrier concentration in hall
Give free carrier mobility
47
Capacitance voltage profiling
C-V profilings : technique for characterising semiconductor materials and devices
Use metal-semiconductor junction (Schottky barrier, could be destructive)
By varying voltage applied to the junction. Depletion width varied —> profiling capability
Plot of 1/C^2 - V ‘s slope “ 2/ (££0A|e| N(x)) N(x) : net ionised dopant concentration
48
Thermopower information
See beck coefficient and conduction type
49
UV-vis- NIR Spectroscopy/. Spectrophotometry
Measure reflection/transmission property
Find absorption coefficient of thin film via beer lambert law
—> derived the electronic properties
Ploy of (alpha hv)^(1/n) = A(he-Eg). Plot Ahv )^(1/n) -hv —-> bandgap Eg; direct gap material or indirect gap material
50
Spectroscopic ellipsometry (SE)
Sample layer structure with iotucal constant (Nicki) and thickness ti
SE measure the change inpolariztion as the incident radiation interact with material of interest
Polarisation change is quantified by the amplitude ratio and phase dfiffenrece
51
Pros of spectroscopic ellipsometry (SE)
Non destructive
Film thickness measurement down to 1nm
Optical constant n&k for unknown materials
—Absorption coefficient, band gap, carrier concentration mobility effective mass
Can measure film composition, porosity and roughness
Absolute measurement: no reference
Rapid full spectrum obtained in few second
Can be used for in situ
Small footprint: do not need large lab space
52
Cons of spectroscopic ellipsometry
Only flat, reflecting, parallel surface
Knowledge of the sample required: layers type, numbers
SE indirect measurement: does not give directive physical parameter
A realistic physical model of the sample is usually required to obtain useful info
53
Modulation
Spectroscopy
Take the derivative of an optical spectrum of the material by modifying the measurement conditions in some manner
54
Modulation chages of sky’s parameters
```
Electrical field
-applying bias: electroreflectance
-periodic light probe: photo reflect ace
Temp: thermoreflectance
Strain: piezoreflectance
```
Photo reflect ace
Change in reflectivity dR/R —> perturbation of the dielectric function £=£1+£2
55
Secondary ion yield
< sputtering yield of (2nd particles). 5-15
| Secondary ion yield 10^-4 -10^-6
56
Ion yield is influenced by
Matrix effects
Surface coverage of reactive elements
Background pressure
Orientation of crystallographic axes wrt sample surface
Angle of emission of detected secondary ions
57
XPS
```
An x-ray beam incident on surface —> photoelectron emitted from the surface of the sample, with KE analysed
X-ray photoemission spectroscopy provides elemental information and information about chemical bond through the kinetic energy of detected e- (BE= hv- KE -if spec)
Surface sensitive (<10nm)
```
58
Quantatized surface roughness after ion beam bombarded
c
59
XPS core level vs Valence band spectra
Core level: elemental identification
Chemical composition
Oxidation state (valence state) —chemical shift
Composition profile: sputter depth profiling
Valence band spectrum:
Valence band position (wrt fermi level)
Surface/ interface band bending
Band offsets between thin films
60
Chemical shift
Change in binding energy of a core electron of an element due to change in the chemical bonding of that element
BE = energy of the final state - energy of the initial state
Withdrawal of VB e- —-> increasing in binding energy
61
AES Elemental identification
Concentrating on major peaks and comparing positions with AE energy chart
Referring to the standard spectra of the elements in question and making positive identification of major constituent
Labelling all peaks related to the identified major constituents
Repeat 1-3 for unlabelled peaks
62
Scanning auger microscopy
| SAM
Give SEM images, Auger spectra and Auger maps
63
AES summary
Uses a focused e-beam to excite auger electrons
Auger electron have energies characteristic of the elements
Auger electron spectra: reveal elemental composition, chemistry of the surface
Chemical bonding of atoms
Depth profiling in conjunction with ion sputtering
High spatial resolution of e- beam and surface specificity —> high resolution microanalysis and elemental mapping (SAM)
AES attributes: high lateral resolution, reasonable sensitivity, semi-quantitative analysis without empirical standards, and chemical bonding information
64
2 mode of operation of sims and informations
according to primary ion energy & current
1. Static SIMS: 0.1-10 keV ions,
current surface densityies: nA/cm2
total erosion of 1st monolayer take even 1hr;
information: Ultra surface analysis;
Elemental/molecular analysis;
analysis completed before significant fraction of molecules destroyed
Dynamic - SIMS: 10-30keV: \ ions with current surface densityies in miuA-mA/cm2
eroded continuously&acquired mass spectra enable the monitoring of constituting elements along the sample depth
information:
profiling; elemental analysis; material removal
65
3 fundamental concepts in rutherford BSE
1. kinetic factor: elastic energy transfer from a projectile to a target atom can be calculated from collision kinematic --> mass determination;
2. scattering cross-section: the probability of the elastic collision between the projectile and target atom can be calculated --> quantitative analysis of atomic composition;
energy loss: inelastic energy loss of the projectile ions through the target --> perception of depth
66
specify information from rutherford concepts
kinetic factor: element identification: Km=EM/E0
scattering cross section: composition y/x =Area Ba/AreaY.(ZY/ZBa)^2
z/x = Area(Cu)/AreaY>(Zy/ZCu)^3 film thickness =deltaE/(S0)
67
main advantages of ion beam techniques
For RBS:
Pros:
Simple inprinciple; fast n direct; quantitative without standard;
depth profilling without chemical or physical sectioning;
non-destructive; wide range of elemental coverage; no special specimen preparation required;
can be applied to crystalline or amorphous materials;
simultaneous analysis with several ion beam techniques
68
auger electron and secondary electrons purpose
a
69
technique for insulator
AFM: for surface topography & many other propeties (limited by spot srea &
70
name difference between Wavelength dispersive spectroscopy and energy dispersive spectroscopy
c
71
name difference between energy dispersive spectroscopy and EELS ( )
c
72
comparing the information obtained from hall effect and CV profiling
c
73
what is the necessary step to obtain bandgap of semiconductor in a spectrophotometer (UV-Vis-NIR) with sketching
for semiconductor bandgap:
74
information from spectroscopic ellipsometry
d
75
modulation spectroscopy
what modulated:
effect of such modulation on the reflectancce or transmission
what modulated:
| effect of such modulation on the reflectancce or transmission
76
name 3 mode of operation in AFM
contact mode: heavily influenced by frictional forces adhesive forces, can damage samples and distort images;
non-contact mode: lower resolution with cantilever oscillated with typically a few nm-mium, for soft materials;
tapping mode: eliminate frictional forces and prevent the tip from trapped by adhesive contanminants
77
information from measuring the peak position,peak wideth and peak intensity in xrd
peak position:
peak width:
peak intensity
78
resolution of images formbed by SE, BSE, x-ray photons in SEM
SE:
BSE:
x-ray photon
79
```
compare SEM and AFM
probing mechanism:
surface structure
chemical composition
working environment
```
probing mechanism:
surface structure
chemical composition
working environment:
probing mechanism:
surface structure
chemical composition
working environment:
80
for polycrystalline with mium crystal grain how to obtain its composition and crystal symmetry of precipitates
c
81
calculate the lattice constant and d220
c
82
Auger e- and XPS mechanism with sketching
c
83
why vacuum for AES n XPS
c
84
if energy of source varied in AES & XPS, will energy of auger electron varied / photonelectrons varied?
c
85
bulk Boron concentration in p-silicon
SIMS
86
whether Cr state in Mg alloy
heavy @ light matri下？
87
depth in 100 nm thick sio2 on Ti (suspect TiO2)
c
88
crystal orientation of FeSi2 films in Si
c
89
ratio of 13C and 12 C in materials
SIMS: available for isotope component analysis
90
SEM advantages
good depth of field; higher magnification &greater resolution; compositional and crystallographic information
91
escape volume vs interaction volume
escape volume:
The volume responsible for the
respective signal is called the
escape volume of that signal
Interaction volume
The combined effect of the elastic and inelastic interactions is to distribute the
beam of electrons over a three-dimensional interaction volume. The actual
dimensions and shape of the interaction volume are dependent upon a number
of parameters: accelerating voltage, atomic number and tilt
The interaction volume increases while the probability of elastic scattering
decrease with accelerating voltage
The interaction volume decreases while the probability of elastic scattering
increases with higher atomic number elements.
92
SPM Pros
resolution not limited by diffraction effects but the size of the probe-sample interaction volume (pm)
able to measure small local diferences in objec theight
tip limited laterally probe-sample interaction
interaction can modify the samples to create fine structure
can be measured inair/liquid
93
SPM cons
detailed shape of scanning tip could be difficult to determine--> resulting data esp. (specimen variation in heights)
slower in imaging
affected by time-domain effects like specimen drift, feedback loop oscillation and mechanical vibration
maximum image size is generallly small
not useful for examining buried solid-solid or L-L interfaces
94
STM modes
constanct current mode:
1. use feedback to keep tunneling current constant by adjusting height of the scanner at each measurement point;
2. voltage applied to piezoelectric scanner is adjusted bto increase /decrease the disatnce between the tip and the sample;
3. plot tip height vs. the lateral tip position;
constant height mode:
1. tunneling currents is monitored as the tip is scanned parallel to the surface(constant height);
2. periodic variation in separation distance between the tip and surface atoms;
3. plot tunneling current - tip position --> periodic variation (represents the surface structure) a direct "image" (not ture " of the surface
95
AFM vs STM
AFM
measurements:
e- DOS, not nuclear position-- not true topographic imaging;
high lateral&vertical resolution (exponential dependence of tunneling current on the distance)
probe electronic properties (including spin states)
generally applicable only to conducting & semiconductor;
writing voltage & tip-sample spacing are interfrally linked
AFM:
Real topographic imaging;
lower lateral resolution;
AFM force-distance dependence is more complex;
probe various physical properties: magnetic, electrostatic, hydrophobicity, friction, elastic modulus,etc.
aoollied to both conductors and insulators
writing voltage & tip-surface spacing can be controlled independently
96
hydrogen forward scattering (HFS/elastic recoil detection)
quantitative hydrogen and deuterium profiling
good sensitivity -0.01 at% of J
can be perform simultaneously with RBS and PIXE
profiling with any light element in solid (using heavy ion beam ERD)
97
Particle induced X-ray Emission (PIXE)
basic principle:
incident proton kick core shell e- out and a noter outer e- fill the vacancy and emit x-ray;
suitable for trace minor element composition & light impurity in heavy matrix
98
ion channeling
```
substitutional;
small dislocation;
large dislocation;
centre of channel(interstitial);
random;
substitutional+interstitial
```
99
component for OM
eyepiece: ocular lens;
revovlving nose piece: hold multiple objective lenses)
objective lenses;
focus knob (coarse & fine) (to make wide/ small range focus adjustment to the microscopic);
stage : to hold the specimen
light source: below sample
Condenser lens: focus ray of light through sample;
diaphram: regulate the amount of light into condenser
100
Bright field (BF) &Dark Field(DF)
BF: use full illumination of light source
DF: illuminate the sample with peripheral light by blocking the axial rays, producing a dark, almost black, backgroud with bright object on it (visually impressive but very sensitive to dirt @ light path; need high intensity of illumination
101
Optical Microscopy & Overall magnification
OM: a compound microscope uses a very short focal length objective lens( greatly enlarged) + a longer forcal length eyepiece(Ocular; simple magnifier)
Overall magnification M= mome = - L25/Fofe
102
resolutin of OM
Resolution dmin = 1.22入/2NA = 0.61入/NA
103
comparison between OM, SEM, TEM
probeL light or electrons beam
| specimen position
104
signals in SEM (1-50 keV)
secondary electrons, backscatterd electrons, characteristic X-rays, photons(cathodoluminescence) CL,
105
Chromatic abberation
due to unequal refraction of colors, the focal length for blue s slightly smaller than red
106
Spherical Aberration
spherical surface: rays paralleled to opic axis with different distance to it, fails to converge to the same point,
result in hazy/blur/ slightly out of focus image
107
SEM magnification
magnification range: 6 order magnitude from 10 - 500,000X
| Magnification = Ratio of Area on the monitor/on the specimen
108
spatial resolution of SEM
controlle dby 1. size of electron spot ( dependends on both wavelength of electrons and electron-optical system: quality of lens )
2. the size of interactions/escape volume
SEM resolutin 1nm-20nm
109
TEM(transmission electron microscopy)
diffraction[attern in the back focal plane with e- scattered by samples; & xmobines them to generate an image in the image plane
110
the 2nd condenser aperture use
control brightness and convergence
| limit the beam diverging & number of e- (intensity)
111
the objective aperture in TEM
control contrast(BF,DF, High resolution)
control contrast in the image
112
what determine the Diffraction pattern/ image pattern in TEM
the strength of intermediate lens determine ( on the view screen)
113
TEM Pros
offer very powerful magnificationresolution
wide range of application
provides information on element and compound structrue
high quality and detailed images
chemiical information with analytical attachments
114
TEM Cons
large and expensive
laborious sample preparation
Special Trainin gfor Operation and analysis
smaple: small size (mm_ and must be electron transparent
require special housing and maintenance
Only BW image
115
STEM(Scanning Transmission Electron Microscopy)
e- beam focuse on narrow spot--> scanned over the sample in a rastering mode
enable mapping bu : energy-dispersive x-ray(EDX) spectroscopy (EDX)]eletron energy loss spectroscopy (EELS)
annular drak-field imaging (ADF)
+ use high angle detector (High angle annular drak-field HAADF) , atomic resolution images where the contrast is directly related to the atomic number (Z-contrast imge) can be formed
116
EDX Energy dispersive x-ray spectroscopy
analytical technique for elemental analysis
117
XRD peak width
this peak broadening can be used to quantify the average crystallite size of
nanoparticles using the Scherrer equation
𝐵 (2𝜃) =
𝐾𝜆/𝐿 cos 𝜃
