UNIVERSITY OF OSLO. Faculty of Mathematics and Natural Sciences

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UNIVERSITY OF OSLO Faculty of Mathematics and Natural Sciences Exam in MENA3100 Characterization of materials Day of exam: 8 th June 2017 Exam hours: 14:30 18:30 This examination paper consists of 7

Permitted materials: Electronic calculator of accepted type, ruler, pair of compasses, eraser Make sure that your copy of this examination paper is complete before answering.

1 UNIVERSITY OF OSLO Faculty of Mathematics and Natural Sciences Exam in MENA3100 Characterization of materials Day of exam: 8 th June 2017 Exam hours: 14:30 18:30 This examination paper consists of 7 pages including the periodic table. Permitted materials: Electronic calculator of accepted type, ruler, pair of compasses, eraser Make sure that your copy of this examination paper is complete before answering. Upon censoring all sub exercises will be weighted equally. We reserve the right to do some adjustments. Exercise 1 a) Deduce Braggs law geometrically taking a primitive cubic lattice and (001) planes as a starting point. b) The cubic close packed (ccp) structure can be described with a cubic face centered (fcc) lattice. With the above deduction as a starting point, show why reflections from (001) are extinct for such an lattice. Figure 1a) below shows the unit cell of NaCl. Cl - is located at the lattice points and Na + fills the octahedral holes. In figure 1b) you see several unit cells projected along the [110] direction. The (111) plane, oriented perpendicular to the paper plane, has also been drawn. Figure 1a): The unit cell of sodium chloride. The larger spheres represent Cl -, and the smaller Na +. Figure 1b): Several unit cells seen along the [110] zone axis. The position of the (111) plains are indicated. The origin is in the center of the figure. 1

2 c) For an element that crystalizes with cubic close packing, the reflection arising from diffraction from the (111) plane is the strongest. Based on figure 1b), what can you state about the relative intensity of the 111 reflection of NaCl. Will it be different from that of a crystal that only has atoms at the lattice points? Figure 2 shows a diffractogram of sodium chloride, NaCl, recorded using monochromated CuKα 1 -radiation. The peak positions and the corresponding d-values are given in table 1. Figure 2: Diffractogram of sodium chloride recorded with CuK 1 -radiation. Table 1: 2θ peak positions from figure 2 with the corresponding d-values. 2θ/ o d/å d) Index (give the hkl-values) for the first five reflexes (those with the largest 2θ values) and find the unit cell dimension, a, of NaCl. Seltin is an alternative to ordinary table salt (NaCl) containing less sodium since 2

$some NaCl is replaced with KCl. KCl also have the NaCl type structure. The diffractogram of Seltin is shown in Figure 3 below.$ Exercise 2 Seltin, which is a mixture of sodium chloride and potassium chloride, is depicted in Figure 4. The images are recorded in a scanning electron microscope using secondary electrons.

Exercise 2 Seltin, which is a mixture of sodium chloride and potassium chloride, is depicted in Figure 4. The images are recorded in a scanning electron microscope using secondary electrons.

3 some NaCl is replaced with KCl. KCl also have the NaCl type structure. The diffractogram of Seltin is shown in Figure 3 below. Figure 3: X-ray diffractogram of the product Seltin with main ingredients NaCl and KCl. e) Has KCl got a larger or a smaller unit cell than NaCl? Give arguments for your answer. Exercise 2 Seltin, which is a mixture of sodium chloride and potassium chloride, is depicted in Figure 4. The images are recorded in a scanning electron microscope using secondary electrons. Image a) has been recorded in a high vacuum mode while image b) is recorded in a low vacuum mode where water vapour is present in the specimen chamber. (Pressure being 60 Pa.) Figure 4: Seltin depicted with secondary electrons (SE). a) Image recorded in a high vacuum mode. b) Image recorded in a low vacuum mode. 3

a) Discuss the reasons why the images look so different. b) The image in Figure 5 has been recorded using back scattered electrons (BSE) (in compositional mode, Compo).

4 a) Discuss the reasons why the images look so different. b) The image in Figure 5 has been recorded using back scattered electrons (BSE) (in compositional mode, Compo). Is the crystal marked A NaCl or KCl? Give arguments for your answer. Figure 5: Seltin (NaCl and KCl) depicted using back scattered electrons. x indicates the position of the electron beam during an EDS analysis. See the text for A. c) We record an X-ray spectrum (EDS-analysis) while the electron beam is located in the positon marked as x in Figure 5. In addition to chlorine, the spectrum shows both sodium and potassium. One of the two is dominating. Does this imply that the crystal we have analyzed actually contain ions of the other alkali metal? Argue for your answer. d) Describe the process behind the creation of characteristic X-rays. Exercise 3 a) Make a drawing of a SAD pattern, free of choice, from NaCl. Index three reflections, not located along the same row of reflections, and state which zone axis you have drawn. b) Where are the SAD apertures and the objective apertures located along the optical pathway in a TEM. c) How does one obtain TEM bright field (BF) and a dark field (DF) images. What kind of contrast do they show? 4

Exercise 4 Figure 6 and 7 are examples of electron energy loss spectra (EELS) of NaCl and KCl, respectively, and show some of the characteristic signals one can observe.

5 Exercise 4 Figure 6 and 7 are examples of electron energy loss spectra (EELS) of NaCl and KCl, respectively, and show some of the characteristic signals one can observe. a) What do the peaks A and B in Figure 6 represent and which effect does the specimen thickness have on the signals? b) What does the edges named Cl-L 2,3 and K-L 2,3 in Figure 7 represent? Figure 6: Low loss EELS-spectrum of NaCl. Figure 7: EELS-spectrum of KCl from ev. The intensity in the spectrum is generally dropping towards the right. In order to see details in the spectrum the Y-axis is rescaled after ~150 ev. The K-L 2,3 edge is located at 293,6 ev and the Cl-L 2,3 edge at 200,0 ev. 5

6 Figure 8 shows the result of an analysis of KCl with the use of XPS where both photo- and Auger electrons have been recorded. Figure 8: XPS spectrum from the analysis of KCl with a monochomated Al Kα radiation. c) What is the physical mechanism behind the creation of photo- and Auger-electrons? Which of the peaks in Figure 8 are associated with the Auger-electrons? d) What is the origin of the background in the XPS spectra? Why does the background increase towards higher binding (lower kinetic) energies? 6

7 Appendix 1 7

UNIVERSITY OF OSLO. Faculty of Mathematics and Natural Sciences

UNIVERSITY OF OSLO. Faculty of Mathematics and Natural Sciences Page 1 UNIVERSITY OF OSLO Faculty of Mathematics and Natural Sciences Exam in MENA3100 Characterization of materials Day of exam: 12th. June 2015 Exam hours: 14:30 This examination paper consists of 5