清华大学2007年电子显微分析期末考试试题

清华大学2007年电子显微分析期末考试试题

考试科目：电子显微分析

考试时间： 2007年

试卷类型：本科期末

Examination of Electron Microscopy and Analysis (Jan. 2007)

Question sheet A

Department: Name (in Chinese): Student ID No.:

Section I Section II Section III

Total

Score

Section I. (20 marks. The answers should be written in English on this question sheet)

1. There are two diffraction spots G1 and G2 in an electron diffraction pattern. The excitation error (s)

of G1 is m and the excitation error

of G2 is 2m (m>0). Which diffraction spot looks brighter, G1 or G2?

( ) (2 marks)

2. The thickness of a TEM specimen is usually thinner than 100nm. Write out two TEM specimen preparation methods that can make TEM specimen of ceramic samples with the required thickness. ( ) (2 marks)

3. You want to take an atomic resolution image of a specimen, but you do not want the image contrast to alter with a change in defocusing. Which technique should you use? (HRTEM, HAADF, EF-TEM) (2 marks)

4. O Ka line is at 520eV and Cr La is at 590eV. If you want to separate them using an X-ray analysis technique in SEM, which technique should you use? ( ). If you want to distinguish diamond from graphite using microanalysis technique in TEM, which technique should you use ? ( ) If you want to determine if a materials is polycrystalline or amorphous using TEM, which technique should you

use?( ) (3 marks)

5. The side length of the CRT of a SEM is 100mm and the scanning distance of the electron beam on an object in a specimen is 0.02mm. What is the real length of this object if the image of the object displayed on the CRT has a length

of 5mm? ( ) (3

marks)

6. The Kikuchi lines can be used for measuring a small tilting angle. If you tilt

a sample holder by a small angle and the corresponding movement of the Kikuchi lines is 7mm, how many degree have you tilted (assume the camera length L

is 800mm) ? ( ) (4 marks)

7. The TEM of a Philips CM-120 has an accelerating voltage of 120kV. What is the wavelength of the electron beam (Relativistic effects should be taken into account )? (

) Assume n=1 and sina=0.95, what is the theoretical resolution of this TEM. ( ) (4 marks)

Section II. (30 marks. The answers should be written in English or Chinese on the answer book)

1. Explain briefly what is a bright field (BF) image and what is a centered dark field (CDF) image. (The optical ray diagram of BF and CDF images should be drawn).

(10 mar ks)

2. What is the principle of observing defects in crystalline material using diffraction contrast imaging? Are the shape and size of the real defect the same as those of its diffraction contrast image? (Give an example to support your answer) (10 marks)

3. The size of the selected area in selected area diffraction (SAD) of TEM depends on the size of the SAD aperture. Is it possible to obtain a SAD from an area of 0.05 mm in diameter if the size of the SAD aperture is 0.05mm? (The reason should be given). Are there any other methods that can be used to obtain a electron diffraction pattern from an area of 0.05 mm in size? (If yes, give the names of the

techniques.) (10 marks)

Section III. (50 marks. The answers should be written in English on the answer book) 1． (1) Find the corresponding twin reflection of the matrix reflection (420) in an fcc material if [HKL]=111, and determine if the diffraction spots of the twin reflection superimpose with the diffraction spots of the matrix reflection?

(2) Find the corresponding twin reflections of the matrix reflection (110) in

a bcc material if [HKL]= 11, and determine if the diffraction spots of the twin

reflection superimpose with the diffraction spots of the matrix

reflection? (10 marks)

2. The electron diffraction pattern of an fcc material is shown in the figure, where

R1＝R2=10mm, R3=16.3mm, the angle between R1 and R2 is q1＝70°, and the angle between R2 and R3 is q2＝35°. The camera constant Ll is 2.05mm · nm. Index the diffraction pattern and determine the crystal direction

[uvw]. (20 marks)