Argon bombardment with

Fig. 8. Calculated sputtering yield of several materials bombarded with argon ions at various energy levels. The materials Hsted parenthetically also have...

The Duoplasmatron (Eig. 3.18). In the Duoplasmatron, gas-discharge ion sources are used for bombardment with oxygen or argon. In dynamic SIMS, especially, the use of O2 ions is common because of the chemical enhancement effect. With a duoplasmatron ion beam currents of several microamps can be generated. The diameter of the beam can be focused down to 0.5 pm. 

Figure 6.6. The surface of a liii crystal following bombardment with 5 kcV argon ions, imaged in a. scanning electron microscope (Stewart and Thompson 1969).

UHV is necessary but not sufficient to ensure an uncontaminated surface. Certainly, the surface will not be contaminated by atoms arriving from the vacuum space, but such contamination as it had before the vacuum was formed has to be removed by bombardment with argon ions. This damages the surface structurally, and that has to be healed by in situ heat treatment. That, however, allows dissolved impurities to diffuse to the surface and cause contamination from below. This problem has to be dealt with by many cycles of bombardment and annealing, until the internal contaminants are exhausted. This is a convincing example of Murphy s Law in action one of the many corollaries of the Law is that new systems generate new problems . 

Considerable effort has been expended on Ag atoms and small, silver clusters. Bates and Gruen (10) studied the spectra of sputtered silver atoms (a metal target was bombarded with a beam of 2-keV, argon ions produced with a sputter ion-gun) isolated in D, Ne, and N2. They found that an inverse relationship between Zett of the metal atom and the polarizability of rare-gas matrices (as determined from examination of... 

Fig. 9 EPR spectra of color center in MgCl2 films for two different preparation conditions a film grown at lower temperature b initially well-ordered film after bombardment with electrons and argon ions...

Fast atom bombardment with xenon or argon... 

Ion-Assisted Processes An alternative use of ion beams generated from low cost sources is to assist particular chemical reactions, or vapour deposition. An example here is in etching processes (Figure 16). The simultaneous use of an argon beam with XeFp gas compared with the use of either separately, to etch silicon produces an etch rate of a factor of at least fourteen. The use of ion beams can also increase the directionality (23) of the process (Figure 17). Examples are given in Table IV of how ion bombardment during film formation modifies the final film. 

Sputtering is a reasonably well understood phenomenon [6]. Sputter yields depend on the properties of the sample as well as on those of the incident ions. Sputter yields of the elements vary roughly between I and 10 (see Fig. 4.3), with a few exceptions on the low side, such as bismuth with a sputter yield around 0.1 under SIMS conditions, and on the high side, such as zinc, which has a sputter yield of around 15 under 5 keV argon bombardment. 

The sample surface is bombarded with a beam of around 1 keV ions of some gas such as argon and neon. The action of the beam sputters atoms from the surface in the form of secondary ions, which are detected and analyzed to produce a characterization of the elemental nature of the surface. The depth of the analysis is usually less than a nanometer, making this process the most suitable for analyzing extremely thin films. 

Chemical reactions between adsorbed species and substrate material, which are induced by ion bombardment (e.g., Ar ), will be discussed in this section. Consider, for example, the XeFj—Si—Ar" system. The reaction probability for XeFj(gas) with silicon at room temperature is significant . However, simultaneous bombardment with argon ions greatly enhances the probability that the incident fluorine from the XeFj will react to form SiF4(gas). Reactions involving this type of synergistic effect are the topic of this section. 

Neon, argon, and krypton, often used in electrified gas tube signs, are colorless noble gases. The nobility do not mix with other classes, so elements that do not combine with other elements (i.e., are nonreactive) are called noble. They like to remain uncombined and alone. When these noble gas atoms are bombarded with electricity, electrons, the atoms become excited. Some of the atomic electrons... 

Fig. 3.29 Auger sputter depth profile of a layered Zr02/SiC>2/Si model catalyst. While the sample is continuously bombarded with argon ions which remove the outer layers of the sample, the Auger signals of Zr, O, Si and C are measured as a function of time. The depth profile is a plot of Auger peak intensities against sputter time. The profile indicates that the outer layer of the model...

The sample is to be bombarded with argon ions at a minimum beam current of 1 pA with the preparation chamber at 1 O 8 mbar. The gun is operating at a current density of 1 mA cm 2 and an electron current of 10 mA. The constant for the gun in 5 mbar 1. 

Fast atom bombardment the sample in solution in a non-volatile solvent such as glycerol is ionized under vacuum by bombardment with accelerated neutrals such as argon. 

E. Vietzke, K. Flaskamp, V. Philipps Differences in the CH3 and CH4 formation from graphite under bombardment with hydrogen ions and hydrogen atoms/argon ions. J. Nucl. Mater. 128-129, 545 (1984)... 

On the basis of these predictions, the chemical separation scheme shown in Fig. 24 has been utilized on thick uranium targets bombarded with argon and krypton ions. With a few exceptions (bromine, iodine, arsenic), no carrier material... 

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