Vacuum-based techniques

Vacuum based techniques are capable of producing new materials or new forms of existing materials either in bulk form or as surface layers. There is a wide range of different techniques and applications, only some of which have been covered here. It is clear from the literature that much needs to be done in both the fundamental and applied aspects of such work. For example, relatively little is known about the effects caused by the arrival of clusters or charged particles at a growing film. 

The primary methodologies for forming thin-film materials with atomic level control are molecular beam epitaxy (MBE) [4-9], vapor phase epitaxy (VPE) [10-12], and a number of derivative vacuum based techniques [13]. These methods depend on controlling the flux of reactants and the temperature of the substrate and reactants. 

Film Deposition by Sputtering and Vacuum-Based Techniques... 

Photoelectron spectroscopy is an ultrahigh-vacuum-based technique for two reasons. The measurement of the energy spectrum of the emitted electrons by means of suitable electrostatic energy analyzers involves electron trajectories with typical lengths of the order of a meter, where collisions with other particles must be avoided. More importantly, because of its surface sensitivity, surface contamination rates by residual gas molecules must be reduced to low-enough values (see Chapter 3.1.2.3) in order to allow for the typical measurement times, which are of the order of minutes to hours. The method is widely used hence standard equipment is commercially available. 

This section considers only those techniques employed via the emersion approach as being the closest to in situ observation. However, as has been discussed briefly in other sections, the use of the emersion approach is still controversial and a source of much debate. Thus, in order to employ UHV-based techniques via emersion the electrode has to be transferred from the electrochemical cell to the vacuum chamber. Ideally, there should be no... 

Eberspacher, C. Fredric, K. Pauls, K. Serra, J. 2001. Thin-film CIS alloy PV materials fabricated using non-vacuum, particles-based techniques. Thin Solid Films 387 18-22. 

The first step in sample preparation is the deposition of a thin metal film on an insulating substrate (e.g. a glass microscope slide). This base electrode is deposited by conventional vacuum deposition techniques with the electrode geometry defined by a shadow mask. Next, this electrode is oxidized either by exposing the film to room air or oxygen, or by establishing an oxygen plasma within the vacuum chamber. In the case of Al-electrodes, a remarkably uniform oxide layer is formed, typically 1-2 nm thick. The oxide film may then be dosed with the compound of interest this is achieved in one of three ways. 

Conventional pressure or vacuum filtration techniques are widespread in industry for separating cells and other biological materials from a liquid phase which can be solvent based or aqueous. A pressure differential between the dirty and clean sides of the filter, created with over pressure or vacuum, provides a driving force for the liquid to be forced through the filter material which retains solids above a particular size. This type of filter is often used in conjunction with a precoat material on the filter to improve the separation characteristics. 

Cryogenic [-273 to -101°C (-459 to -150°F)] High Vacuum This technique is based on the Dewar flask, which is a double-walled vessel with reflective surfaces on the evacuated side to reduce radiation losses. Figure 11-66 shows a typical laboratory-size Dewar. Figure 11-67 shows a semiportable type. Radiation losses can be further reduced by filling the cavity with powders such as perlite or silica prior to pulling the vacuum. 

The dry nature of CVD process enables copolymerization more easily than solution based techniques. This approach has been utilized to tailor the thermal and electrical properties of parylene thin films for ULSI applications. One of the first reports of vacuum copolymerization of xylylene was done with maleic anhydride as the comonomer. Subsequently, 9-vinylanthracene, 4-vinylbiphenyl and perfluoro-octyl methacrylate were successfully copolymerized with parylenes, and reported in... 

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