Argon-ion bombardment

Samples may either be those in which the surface of interest has been exposed to the environment before analysis, or the surface to be examined is created in the UHV chamber of the instrument. The latter method is generally preferable, and also argon-ion bombardment is commonly used to clean sample surfaces in situ in the spectrometer. In metallurgical studies, the fracture sample is particularly important the sample is machined to fit the sample holder, and a notch is cut at the desired point for fracture. The fracture stage is isolated from the analytical chamber and is pumped down to UHV. Liquid nitrogen cooling is often provided, as this encourages... 

Figure 2.5. XPS spectra produced from a sample of iron which has been cleaned by argon ion bombardment, using (a) Aluminium Ka radiation, and (b) Magnesium Ka radiation. (Reproduced by...

Spectra for a series of Cu-Ni alloys have been obtained (91) and these are reproduced in Fig. 11. Because of overlapping of peaks from the component metals, separate indications of each element are only obtained from the 925 eV Cu peak and the 718 eV Ni peak. The results have only qualitative significance because the quoted nickel concentrations are bulk values. Nevertheless, they do suggest that for these particular samples of Cu-Ni alloys, the surface composition varies smoothly from pure copper to pure nickel. Auger spectroscopy has subsequently shown that the surface composition of the (110) face of a 55% Cu-Ni crystal was identical with the bulk composition (95a). Ono et al. (95b) have used the technique to study cleaning procedures argon ion bombardment caused nickel enrichment of... 

The same type of voltammogram has been obtained with a Pt (111) electrode after its ordered surface was subjected to argon ion bombardment, introducing structural defects like randomly distributed steps (14). The similar effects of oxygen electrosorption and ion bombardment show clearly that the former perturbs the surface order,... 

FIG. 70. Voltammograms on an argon ion-bombarded, annealed CdTe( 100) surface in 50 mM K2SO4 pH = 5.6 (A) reduction from the open circuit potential to —2.0 V (B) oxidation from the open circuit potential to -1-0.30 V and reversing to —0.55 V, under illuminated conditions (C) reduction following (B) from open circuit potential to —1.8 V and reversing to —0.50 V. 

For pure WO3 the fine structure of the W(4f) peak shows considerable changes after reduction of the crystal. With the nonreduced stoichiometric crystal only two levels 4f7yj and 4f5/2 are observed, but after reduction the superposition of two doublets induces broadened features. Shifts due to the transformation of W to are revealed by a curve fitting procedure however, more drastic reduction can only be effected by hydrogen and argon ion-bombardment when W " " and W° states appear (Fig. 19). 

Fig. 19. W(4f) spectra fronts WO, sample A, as prepared B, after argon ion bombardment at 300 K for 30 min C, same as for B, but taken with a reduced take-off angle D, after further extensive bombardment (150 min).

The cleaning of the various catalyst samples has to be scrutinized for each material studied. For iron for example, the major impurity is sulfur, and its removal must be carried out outside the vacuum system in a furnace in a constant hydrogen flow for a long period of time (days). Trace metallic impurities or nonmetallic impurities may be removed either by argon ion bombardment in the vacuum chamber or by chemical treatment using gas-surface interactions of different types. 

Final cleaning involved repeated argon ion bombardment (5 x 10 6 torr, 0.3 pA, 450 V) of the crystal held at 750 K, followed by an anneal for 10 to 20 min at 1100 K, until sharp (lxl) LEED patterns were obtained, and thermal desorption results for CO agreed with those reported by Benziger and Madix (16). 

Cleaning the crystal surface by a combination of heating at 800° to 900° C., argon ion bombardment, and subsequent annealing results in a close approximation to an atomically clean surface with the exposed surface composed predominantly of (100) planes (2). By varying the amount of annealing subsequent to ion bom-... 

Figure 3. Peak current vs. log10 (pressure X time) for five diffraction beams shown in Figure 2, after argon ion bombardment of crystal surface followed by...

Figure 8 shows scanning electron photomicrographs of ion-etched surfaces of the three pure polymers. Presumably, argon-ion bombard-... 

E. Vietzke, K. Flaskamp, V. Philipps Hydrogen formation in the reaction of atomic hydrogen with pyrolytic graphite and the synergistic effect of argon ion bombardment. J. Nucl. Mater. 111-112, 763 (1982)... 

METHODS OF OBTAINING atomically-clean surfaces of solids are listed with comments on their advantages and limitations. The method of argon-ion bombardment is reviewed with a discussion of the operating conditions and precautions necessary for successful results. The low-energy electron-diffraction method is used to determine the condition of the surface. Experimental results indicate that the relative positions of the atoms in the clean (100) surface planes of germanium and silicon are not the same as those of similar planes in the bulk crystals. 

Total time of heating the crystal was 400 hr at 600-650°C. Total argon-ion bombardments were 25 for 5 min each at 500 v, 100-150p A. Each bombardment was followed by annealing at 600-650°C for 10 min. Total time of heating tungsten flash filament was 1000 hr at 2000°K. 

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