Physical vapor deposition evaporation

Metallization layers are generally deposited either by CVD or by physical vapor deposition methods such as evaporation (qv) or sputtering. In recent years sputter deposition has become the predominant technique for aluminum metallization. Energetic ions are used to bombard a target such as soHd aluminum to release atoms that subsequentiy condense on the desired substrate surface. The quaUty of the deposited layers depends on the cleanliness and efficiency of the vacuum systems used in the process. The mass deposited per unit area can be calculated using the cosine law of deposition ... 

Physical Vapor Deposition Processes. The three physical vapor deposition (PVD) processes are evaporation, ion plating, and sputtering... 

Chemical vapor deposition may be defined as the deposition of a solid on a heated surface from a chemical reaction in the vapor phase. It belongs to the class of vapor-transfer processes which is atomistic in nature, that is the deposition species are atoms or molecules or a combination ofthese. Beside CVD, they include various physical-vapor-deposition processes (PVD) such as evaporation, sputtering, molecular-beam epitaxy, and ion plating. 

Chemical vapor deposition competes directly with other coating processes which, in many cases, are more suitable for the application under consideration. These competing processes comprise the physical vapor deposition (PVD) processes of evaporation, sputtering, and ion plating, as well as the molten-material process of thermal spray and the liquid-phase process of solgel. A short description of each process follows. For greater detail, the listed references should be consulted. 

This is why companies like Berstorff use PVD-coated screws for this purpose as they exhibit better wear protection than screws with nitrided or stellited surfaces. PVD stands for physical vapor deposition and refers to the evaporation of chrome and its accelerated application onto the surface. In combination with nitrogenous gases, the metal ions form hard nitrides that multiply the wear resistance of the screws. 

Physical vapor deposition Electron-beam evaporation Electroplating Reactive ion etching Wet etching Molecular beam epitajty Chemical-mechanical polishing Rapid thermal processing Vacuum sealing... 

Increased control of film composition, structure and size can be achieved by limiting the rate of reaction. This is possible using gas phase deposition where the amount of reactant is relatively low. Gas phase deposition loosely covers any hybridization strategy where at least one of the hybrid components is in the gas phase. This includes chemical vapor deposition (CVD), physical vapor deposition (PVD) and atomic layer deposition (ALD) as well as various plasma, sputtering and evaporation processes. 

In physical vapor-deposited as well as sputter-deposited films, incorporated gases can also increase stress and raise annealing temperatures. Similar effects are present in electron beam-evaporated films. 

It becomes clear from the above discussion that metal catalyst films suitable for ATR spectroscopy must be very thin. Such films are generally not homogeneous. In many cases physical vapor deposition leads to films composed of metal islands. The morphology depends on the substrate (IRE), the metal, and preparation conditions such as evaporation rate, substrate temperature, and background gas. 

Reproducibility of film preparation and stability of the resulting films are important issues for practical applications. Cleanliness of the IRE before metal deposition can play a decisive role in determining reproducibility. Depending on the conditions, metal films may not be stable and may peel off (36,37). The stability and reproducibility of metal films can be enhanced by evaporating a metal oxide support material (such as AI2O3) prior to evaporation of the desired metal. Contaminants on the IRE are covered or displaced by evaporation of the metal oxide. It was reported that a 50-100-nm-thick AI2O3 layer deposited on a Ge IRE by electron beam physical vapor deposition hardly affected the reflectivity in an ATR experiment. Thin platinum films directly deposited onto it were found to be rather stable under catalytic reaction conditions (26,38). 

Figure 4.34. Schematic of physical vapor deposition apparati. Shown are (a) an evaporation system and (b) a sputtering system.

Such an approach is usually followed for physical vapor deposition (PVD) (i.e. sputter deposition or e-beam evaporation). In figure 2.7 we have given the situation for a two dimensional case. Inside the contact the deposition rate can be described by ... 

Coating and thin films can be applied by a number of methods. In thermal or plasma spraying, a ceramic feedstock, either a powder or a rod, is fed to a gun from which it is sprayed onto a substrate. For the process of physical vapor deposition (PVD), which is conducted inside an enclosed chamber, a condensed phase is introduced into the gas phase by either evaporation or by sputtering. It then deposits by condensation or reaction onto a substrate. A plasma environment is sometimes used in conjunction with PVD to accelerate the deposition process or to improve the properties of the film. For coatings or films made by chemical vapor deposition (CVD), gas phase chemicals in an appropriate ratio inside a chamber are exposed to a solid surface at high temperature when the gaseous species strike the hot surface, they react to form the desired ceramic material. CVD-type reactions are also used to infiltrate porous substrates [chemical vapor infiltration (CVI)]. For some applications, the CVD reactions take place in a plasma environment to improve the deposition rate or the film properties. 

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