Third Exam of Characterization

What does Z stand for?

Formula units
Also tells us stochiometric position in U.C.

How many imaginery lattices particles are in the body centered unit cell

2

How many imaginery lattices particles are in the face centered unit cell

4

How many imaginery lattices particles are in the primitive centered unit cell

1

How many imaginery lattices particles are in the rhombohedral centered unit cell

3

What is the location of imaginary lattices in primitive unit cell

(000)

What is/are the location of imaginary lattices in face unit cell

(000), (0 1/2 1/2), (1/2 0 1/2), or (1/2 1/2 0)    

What is/are the location of imaginary lattices in body unit cell

(000), (1/2 1/2 1/2)

What is/are the location of imaginary lattices in rhombohedral unit cell

(000), (1/3 2/3 1/3), (2/3 1/3 2/3)

XRD

x-ray diffraction

XRF

x-ray fluorescence

XPS

x-ray photoelectron spectroscopy

UPS

UV photoelectron spectroscopy

AES

Auger Electron Spectroscopy

ISS

Ion Scattering Spectroscopy

MEIS

Medium Energy Ion Scattering

RBS

Rutherford Backscattering Spectrometry

SIMS

Secondary Ion Mass Spectrometry

SEM

Scanning Electron Microscope

TEM

Transmission Electron Microscopy

SPM

Scanning Probe Microscopy

STM

Scanning Tunneling Microscopy

AFM (SFM)

Atomic Force Microscopy (Scanning Force Microscopy)

What is the principle of XPS?

Uses photoelectric effect - X-rays strike a surface and eject core electrons

What is the key equation of XPS?

Eb = hv - Ek - phi

What is the full form of XPS?

X-ray Photoelectron Spectroscopy

What are some information obtained by XPS?

Elemental Composition (all except H, He, Li), oxidation/chemical state (via binding energy shifts), surface contamination, and film thickness & uniformity (1-10 nm surface depth)

What is the setup diagram of XPS?

X-ray Source --> Sample source --> electron analyzer --> detector

Notes for XPS

Charge correction using C 1s peak = 284.4 eV, spin-orbit doublets (e.g. Cu 2p 3/2 and Cu 2p 1/2) identify specific elements, & peaks shift + 1 eV for higher oxidation state

What is the principle of AES?

After an inner-shell electron is ejected, an outer electron drops down, and the energy released ejects a third electron.

What is the full form of AES?

Auger Electron Spectroscopy

What is the energy of AES?

Independent of excitation energy --> depends only on atomic levels
Each element has unique Auger transition (e.g., KLL, LMM)

What is the surface sensitivity of AES?

~ 3 nm

What are advantages of AES?

Detect all elements except H, He
Excellent lateral resolution
Superior monolayer sensitivity
Fast

What is the principle of UPS?

Similar to XPS but uses ultraviolet photons (He I = 21.2 eV) to probe valence electrons

What is the full form of UPS?

UV Photoelectron Spectroscopy

What is the purpose of UPS?

Determines electronic states, Fermi level, and work function.
Excellent for semiconductors and organic molecules.

What is the depth sensitivity of UPS?

1 - 3 nm (surface only)

What is the source of XPS?

X-rays

What is the source of UPS?

UV light

What electrons do XPS analyze?

Core

What electrons do UPS analyze?

Valence

What information does XPS give?

Elemental & chemical

What information does UPS give?

Electronic & bonding

What is the principle of XRF?

Atoms excited by primary X-rays emit secondary characteristic X-rays.

Each emitted X-ray corresponds to a transition between inner shells (Kα, Kβ, etc.).

What is the full form of XRF?

X-Ray Fluorescence

What is the key concept of XRF?

Uses Bragg’s Law

What is the instrumentation of XRF?

Primary X-ray Source: Usually a tube (targets: Cu, Mo, Rh, etc.)

Analyzing Crystal: Selects wavelength via Bragg reflection.

Detector: Measures intensity --> proportional to concentration.

What are the two types of XRF?

EDS (Energy Dispersive Spectroscopy, also called EDXRF)
WDS (Wavelength Dispersive Spectroscopy, also called WDXRF)

Give description of WDS

Crystal separates X-rays by λ

Give description of EDS

Si(Li) or SDD detector directly measures energy

What are some advantages and disadvantages of WDS?

Advantages: High resolution, low background, works for both multi elements and single elements
Disadvantages: Slow, high cost & complexity, and large instrument size

What are some advantages and disadvantages of EDS?

Advantages: Fast, compact, and multielement 
Disadvantages: Lower resolution and accuracy, poor sensitivity for light elements (<= Carbon)

What are applications of XRF?

Elemental composition of solids, liquids, and thin films
Film thickness measurement
Non-destructive quality control

What are some limitations of XRF?

Cannot detect very light elements (absorbed in air or windows)
Sample must be homogeneous

What is the setup diagram of XRF?

X-ray tube --> Sample emits fluorescence --> Analyzing crystal --> Detector

What is the full form of EXAFS?

Extended X-Ray Absorption Fine Structure

What are region breakdown in EXAFS?

XANES/NEXAFS: Near-edge; gives oxidation state and symmetry info.

EXAFS: Far-edge; gives bond length, coordination number, disorder

What is the key equation for EXAFS?

Fourier transform --> radial distribution function

Why use EXAFS?

To see the small mediation & to see energy not flocculating.

What does EXAFS require?

Synchrotron source, monochromator, and precise calibration.

What is the full form of RBS?

Rutherford Backscattering Spectroscopy 
Sometimes also called HEIS - high-energy ion scattering spectroscopy

What is the principle of RBS?

Measure energy of ions elastically backscattered from nuclei --> depends on mass and depth.

What are typical ions for RBS?

1 - 2 MeV He^+

What information does RBS give?

Elemental ID and thickness
Layer composition and interface depth
Crystal quality (via channeling)

What is the depth resolution of RBS?

~ 20 - 30 nm

What are advantages of RBS?

Non-destructive, quantitative, requires no standards.

What is the full form of ISS?

Ion Scattering Spectroscopy
Sometimes also called (LEIS) - low energy ion spectroscop

What is the principle of ISS?

Low-energy ions (0.5 - 5 keV) scatter inelastically from surface atoms --> energy spectrum identifies atomic species.

What is the sensitivity of ISS?

Topmost atomic layer (~ 1 nm)

What is the purpose of AFM?

Detects surface contamination, oxidation, and adsorbates.
Often complements AES.

What is the full form of MEIS?

Medium Energy Ion Scattering

What is the range of MEIS?

Range: 50 - 400 keV 

What is the range of RBS?

1 - 3.4 MeV

What is the range of ISS?

100 eV - 5 KeV

What is the advantage to using MEIS?

Depth profiling with A-level precision (atomic-layer resolution)

What is the principle of Geiger-Müller Counter?

Gas-filled tube at high voltage (~1500 V).
One X-ray quantum ionizes gas --> triggers full avalanche --> large identical pulse.

What is the key behavior for Geiger-Muller Counter?

Gas amplification factor A ~ 10^8 - 10^9
All pulses have same height (no energy info).
Dead time ~ 200 us (slow recovery).

What are advantages of Geiger-Muller Counter?

Simple and robust
High sensitivity

What are disadvantages of Geiger-Muller Counter

Cannot distinguish X-ray energies
Counting losses at > few hundred cps
Now obsolete for XRD

What is the diagram for Geiger-Muller Counter?

X-rays —> Gas chamber + wire anode —> Avalanche —> Pulse Output

What is the principle of Scintillation Counter?

X-rays excite a NaI (Ti) crystal --> emits visible light
Lights hits a photomultiplier tube (PMT) --> cascade of electrons --> measurable pulse

What are the key features of Scintillation Counter?

Gain ~ 10^7 (10 dynodes x 5 gain each)
Pulse size proportional to X-ray energy
Very fast (10^5 cps)
Excellent efficiency (nearly 100% for typical X-rays)

What are the advantages of Scintillation Counter?

Fast response
Proportional pulse size --> energy discrimination possible
Used in XRF and XRD

What are the disadvantages of Scintillation Counter?

Moderate resolution (broader pulse peaks than Si(Li))
Sensitive to moisture --> crystal sealed in Al housing

What is the principal of proportional counter?

Gas-filled chamber operated around ~1000 V - primary ionization electrons cause secondary ionization (gas amplification) near the wire anode.

What is the gas amplification factor (A) for proportional counter?

~ 10^3 - 10^5

Why is the name of the counter called proportional?

Pulse size is proportional to the energy of the incoming X-ray photon.

What is the voltage behavior for proportional counter?

Below 200 V —> ionization chamber region (no amplification).
~ 1000 V —> proportional region (linear amplification).
1500 V —> Geiger region (avalanche saturation)

What are the advantages for proportional counter?

Can distinguish X-rays of different energies.
Fast, reliable, and simple.

What are the disadvantages of proportional counter?

Lower sensitivity than scintillation.
Requires careful voltage control.

What is proportional counter used in?

Older diffractometers and spectrometers before scintillation became standard

What distinguishes AES from XPS in terms of emitted electron origin?

AES electrons come from non-radiative relaxation (Auger process), not photoemission.

Why is AES considered extremely surface sensitive?

Auger electrons originate from the topmost 2–3 nm of the surface.

Between XPS and UPS, which is better for analyzing chemical bonding?

UPS (because it examines valence-band structures).

What analyzing crystal might be used in WDXRF?

LiF, PET, or TAP crystals.

What is XANES and what does it reveal?

X-ray Absorption Near Edge Structure; gives oxidation state and local symmetry.

What source is essential for EXAFS measurements?

Synchrotron radiation (provides tunable monochromatic X-rays).

What physical parameter does the Debye–Waller factor in EXAFS represent?

Atomic disorder (thermal + structural).

What makes RBS quantitative without standards?

It measures backscattered ion energy directly related to atomic mass and density.