SEM Electron beam sample

Question 1

Electron Sample Interactions

Answer 1

When the electron beam strikes the sample, both photon and electron signals are emitted

(look at all pictures)

Question 2

Key Applications of Energy Dispersive X-Ray Spectroscopy (EDS)

Answer 2

• Near surface and bulk elemental information

• Films >few hundred Å thick can be detected
• Sampling depth to several microns can be achieved
• Quantitative for some classes of samples

• Particles and small area analysis

• Used primarily on particles > few thousand Å
• Parallel detection makes elemental imaging fast
• Quick ‘first look’ technique for failure analysis

Question 3

Strengths and Weaknesses

Answer 3

Strengths
- Quick, ‘first look’ analysis
- Versatile & inexpensive
- Quantitative for some samples (flat, polished, homogeneous)
Weaknesses
- Quantification
o samples must be flat, polished & homogeneous
- Size restrictions on samples
- Samples must be vacuum compatible
- Analysis (and coating) may spoil subsequent surface analysis

Question 4

Wavelength Dispersive X-Ray Spectrometry (WDS)

Answer 4

• WDS identifies the elemental composition of materials imaged in the SEM with an order of magnitude better spectral resolution, sensitivity and ability to determine concentrations of light elements than is achievable with EDS. Most elements are detected below 0.1% and some as low as a few ppm.
• The characteristic X-ray photons excited by the electron beam are sorted using a diffracting crystal, whose angular placement relative to the sample and photodetector is a unique measure of their wavelengths.

Question 5

X-Ray diffraction eq

Answer 5

nlamda=2dsin (theta)

lamda= wavelength of interest
d= interplanar spacing of the diffractor
(theta) angle of x-ray incidence
n= an integer

Question 6

The wavelength of X-ray is measured which is related to the energy according to the Planck’s law:

Answer 6

E= h*c/ lamda

E= energy of xray photon

h=plancks constant 6.6262*10^34 Js

lamda= wavelength of xray photon

c= speed of light= 3.0*10^8

Question 7

applications of xray diffraction

Answer 7

• Applications include

• Identification of spectrally overlapped elements, such as
• Detection of low concentration species (down to 100 or even 10 ppm)
• Analysis of low atomic number elements

Question 8

WDS vs EDS

Answer 8

• X-ray microanalysis in the scanning electron microscope is accomplished using EDS and/or WDS.
• EDS is more commonly applied due to its simplicity and speed.
• WDS offers an important and often critical refinement of EDS data by providing:
o Analysis for light elements with at least an order of magnitude higher sensitivity than available (ultra thin X-ray window) EDS instruments
o Resolution of severely overlapped spectrum peaks for improved element specificity
o Lowered detection limits over the entire periodic table
o More accurate quantitative analyses.

(look at all pictures)