'n ISS studie van die (110), (111) en (100)-enkel-kristalvlakke van NiAI

English: In this study the [110]-, the [111]- and the [1OO]-single crystal surfaces of Ni Al were investigated. The aim was to firstly harmonize the existing knowledge of these surfaces and secondly to create a clear and coherent overview of their properties. The essence of a problem of this kind is the determination of the structure and composition of the surface of a material. In this study, low energy ion scattering (LEISS) was used as primary investigative technique. Other techniques such as ICISS ("Impact Collision" ISS", Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) were used in conjunction with LEISS. Several intensive investigations of the NiAI(IIO)-surface were launched in recent times. The results of these investigations were largely similar and are widely accepted. In this study the results of several previous investigations are discussed. It is shown that the surface is largely a simple truncation of the bulk in the (110)-direction, but that the surface exhibits a ripple effect due to the particular way in which the Al and Ni atoms in the surface and second layer relaxes. In contradiction with the NiAI(ll O)-surface, there is still a measure of uncertainty regarding the properties of the NiAI(ll I)-surface. As part of this study, the NiAI(111)-surface was investigated using LEISS. The results of this investigation are given and is compared with the results of previous studies of the surface from the literature. It is shown that the surface consists of small Al-areas on top of a Ni-layer. One of the studies showed that the Al-areas could be removed by heating the surface to 1300 K. From other studies however, including this one, it seems that the removal of the Al-atoms from the surface may be inhibited or prevented by the presence of oxygen. As in the case of the NiAI(110)- and NiAI(l1 l j-surfaces, a large number of investigations were done on the NiAI( 1OO)-surface. Contradictory results were however a commonplace occurrence. In this study, the NiAI(lOO)-surface was subjected to a comprehensive LEED, LEISS, ICISS and AES investigation with the aim of clarifying the structure and composition of the surface. An overview of results of previous, as well as this investigation is given. It is shown that the NiAI(100)-surface is very sensitive to changes in temperature and that the surface composition and sometimes also the surface structure undergo several changes during heating. At low temperatures (approximately 500 K), a largely AItermination can be found, but with heating from 500 K to 873 K the surface composition changes to 65 at. % Al and 35 at. % Ni and voids. At this temperature the surface undergoes a reconstruction process so that it exhibits a c (Ji x 3.J2)R45°- LEED pattern. Further heating leads to another change in composition to 75 at. % Al and 25 at. % Ni and voids at 1073 K. At this temperature the surface exhibits a p(1 x 1)-LEED pattern. At temperatures above 1073 K the Al concentration in the surface starts to decline until the Al atoms are complete removed at approximately 1300 K. After this point the surface consists of only Ni atoms.