Other Physical Vapor Deposition Techniques

Hollow planar waveguides have been fabricated by several techniques, including physical vapor deposition and CVD of silver and dielectric layers on metallic substrates. Nevertheless, better results can be obtained by taking advantage of silicon micromachining techniques. Perhaps the most important advantage of silicon hollow waveguides over other hollow structures is the... 

For the formation of a metallic film in addition to thick film silk-screen technique, thin film metallization is another means for the film deposition. Deposition of thin film can be accomplished by either physical or chemical means, and thin film technology has been extensively used in the microelectronics industry. Physical means is basically a vapor deposition, and there are various methods to carry out physical vapor deposition. In general, the process involves the following 1) the planned deposited metal is physically converted into vapor phase and 2) the metallic vapor is transported at reduced pressure and condensed onto the surface of the substrate. Physical vapor deposition includes thermal evaporation, electronic beam assisted evaporation, ion-beam and plasma sputtering method, and others. The physical depositions follow the steps described above. In essence, the metal is converted into molecules in the vapor phase and then condensed onto the substrate. Consequently, the deposition is based on molecules and is uniform and very smooth. 

Hot Wall Epitaxy (HWE). HWE is a high vacuum variant of physical vapor deposition with a base pressure of 10 6 mbar [9], In contrast to many other growth techniques it utilizes the near field of the molecular beam by moving the sample close or even into the hot wall tube that holds the film material. The walls of the tube can be heated separately and are held on a higher temperature than the sample and the source. This prevents deposition on the tube wall and helps to create a uniform flux of molecules. The main advantages of HWE are that the films are grown close to the thermodynamic equilibrium. The main drawback is that the position of the sample close to the evaporator makes an in situ characterization of the film growth impossible. 

There are various nanoparticle production methods reported. Most common approaches include solid-state methods (grinding and milling), vapor methods (physical vapor deposition and chemical vapor deposition), chemical synthesis/ solution methods (sol-gel approach and colloidal chemistry), and gas-phase synthesis methods [1]. Chemical approaches are the most popular methods for the production of nanoparticles. Other novel production methods include microwave techniques, a supercritical fluid precipitation process, and biological techniques. 

Although they have not yet been applied to the production and screening of photoelectrolysis materials, we will briefly mention some other approaches to produce metal oxide libraries using well-established thin film deposition techniques (meant here to include physical vapor deposition, sputtering, pulsed laser deposition, and molecular beam epitaxy). These techniques have been used for the production of combinatorial metal oxide libraries in the search for more effective luminescent materials [90,91], transparent conducting oxides [92,93], and dielectrics [94,95]. It would presumably be straightforward to apply the same techniques to the production of material libraries to be screened for photoelectrolysis activity. 

---