Question

Problem 2: Theory

a. What are the factors that contribute to gaussian lineshape broadening in spectroscopy?

b. Is it possible to do XRD of a gold sample with a carbon Mα radiation?

c. What is the probing depth of a common lab XPS?

d. Write down the basic equation for photoemission from a solid, and explain the meaning of the terms.

e. What are the main differences between SEM and TEM? Enumerate at least three.

f. What is a fractal and why we can obtain fractal structures in the flame synthesis?

Answer 1

1. There are following factors that contribute to gaussian lineshape bradening in spectroscopy

• The Zeeman effect
• Thermal Doppler broadening
• Collisional broadening
• Velocity broadening.

by measuring the broadening of line shape we can measure the temperature and density properties of a sample. spectral line broadening also depends on the the time of excited states exit. if it is large we will got narrow peaks.

2. No, Only a short wavelength of range of about 0.5 to 2.5 A is used for XRD. Crabon requires a very large energy to excite electrons and there may be chances of polychromatic radiations which is difficult to separate in xrd curve.

3. XPS is a surface analysis technique with a probing depth of less than 5 nm or equal to 5nm and therefore it is suitable for the compositional analysis of of ultrathin layers.

4. The basic equation given by Einstein for PHOTO EMISSION OF ELECTRON is as follows.

hv = hv(not) + Kinetic energy .......................... 1

hv(not) = thereshhold energy or work function of metal.

hv = energy provided by one photon

KE = kinetic enrgy in excess provided by photon that imparts velocity to coming electrons

5. 1. SEM uses reflected electrond to create image on the otherhand TEM uses transmitted electrons to create image.

5.2. SEM provides sample surface and its composition , TEM provides information about suface morphology and crystal struture.

5.3. SEM usually uses acceleration voltage up to 30ev and TEM uses in range of 30ev to 600ev .

6. A fractal iis a never ending non- regular geometric shape . it have smae degree of non-regularty in all scales .