Volatilization sputtering

For intermediate temperatures from 400-1000°C (Fig. 11), the volatilization of carbon atoms by energetic plasma ions becomes important. As seen in the upper curve of Fig. 11, helium does not have a chemical erosion component of its sputter yield. In currently operating machines the two major contributors to chemical erosion are the ions of hydrogen and oxygen. The typical chemical species which evolve from the surface, as measured by residual gas analysis [37] and optical emission [38], are hydrocarbons, carbon monoxide, and carbon dioxide. 

Once the silicon disc is cleaned, the first step is diffuse ions into either side of the silieon disc to first form either the p-layer or the n-layer. Some manufacturers like to have the n-layer closer to the light source, as shown in the above diagram, while others prefer the opposite. At any rate, ions like and are generally used to form the active electrical layers. A number of differing processes have been developed to do this, the exact nature of which depending upon the speeific manufacturer of solar cells. Sputtering, vapor-phase and evaporation are used. The most common process uses a volatile boron or phosphorous compound to contact the surface. 

Cooled FAB probes have been designed to prolong the acquisition time for FAB measurements with more volatile matrices. [117] Research on sputtering processes from solid gases has contributed to FAB at cryogenic temperatures. [118,119]... 

Unfortunately, since ion milling is a purely physical process, selectivity is generally poor. Indeed, selectivity in such systems depends almost exclusively on differences in sputter yield between materials. Finally, since the etch products are not volatile, redeposition and trenching can be serious limitations (146). 

The vacuum system must be able to attain the required pressures reliably despite these high gas loads. In the example shown, the system is evacuated with a combination of a backing and Roots pump. A diffusion pump along with a cold surface forms the high vacuum pump system. The cold surfaces pump a large portion of the vapor and volatile substances emitted by the plastic parts while the diffusion pump basically removes the non-condensable gases as well as the noble gas required for the sputter process. 

The various methods of preparation employed to prepare nanoscale clusters include evaporation in inert-gas atmosphere, laser pyrolysis, sputtering techniques, mechanical grinding, plasma techniques and chemical methods (Hadjipanyas Siegel, 1994). In Table 3.5, we list typical materials prepared by inert-gas evaporation, sputtering and chemical methods. Nanoparticles of oxide materials can be prepared by the oxidation of fine metal particles, by spray techniques, by precipitation methods (involving the adjustment of reaction conditions, pH etc) or by the sol-gel method. Nanomaterials based on carbon nanotubes (see Chapter 1) have been prepared. For example, nanorods of metal carbides can be made by the reaction of volatile oxides or halides with the nanotubes (Dai et al., 1995). 

Synthesis of niobates and tantalates of alkaline metals at high temperatures may result in the products with unintended stoichiometry because of high volatility of alkaline metal (especially lithium) oxides. Therefore, their synthesis in the form of efficiently sintering powders presents a serious problem. Films of alkaline niobates and tantalates can find wide range of applications in acousto- and optoelectronics and are usually prepared by rf-sputtering techniques, also giving rise to stoichiometry problems. 

Several years ago, a novel sample preparation technique was developed (10) for sputtering Intact organic molecules from surfaces. The key feature of the technique Is the use of a viscous, non-volatile liquid surface from which to sputter and generate organic secondary Ions. 

These data offer basic possibilities of developing efficient electrodes made of corrosion-resistant carbonaceous material (DLC) by introducing a small admixture of an electrocatalyst metal, like Pt, into its bulk. A simultaneous magnetron sputtering of carbon and Pt targets is best suited for the purpose. When using CVD techniques, a volatile Pt compound should be added to the reaction gas mixture. 

---