Preparation Methods for Diamond Films

In the following, the HF-CVD method will be presented in some detail because of its simplicity and scientific as well as technical importance (thanks to its up-scaling potential). Several results of studies on HF-CVD processes are of fundamental importance for an understanding of diamond deposition in general. The presentation of plasma-based methods will focus on microwave-activated processes because they are probably the most often used diamond CVD growth methods for virtually impurity-free material. 

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Preparation Methods for Diamond-like Carbon Films... 

The chemical vapor deposition has developed into the leading method for the preparation of thin diamond films. It is mainly characterized by a precipitation of carbon from the gas phase onto a substrate. Applicable sources of carbon include methane, acetylene, or ethylene, which are normally admixed with a current of hydrogen. The latter, in an atomic state, turned out to be essential for an efficient production of high-quality diamond films. Actually, atomic hydrogen is generated in situ from... 

To conclude with the primary electrode characteristics, we describe briefly the DLC electrodes. The data are scarce and partly contradictory, probably due to the differences in film preparation methods. According to Howe [60], even films as thin as 50 nm are quite stable against corrosion. However, in later works [61, 62] such thin films turned permeable for electrolytes. The penetration of the electrolyte to a substrate metal resulted in its corrosion and, ultimately, in film peeling. Thicker films (0.1 to 1 pm) were less subjected to damage. The current-potential curves in supporting electrolytes resemble those for crystalline diamond electrodes (see Figs. 7, 8) the potential window is narrower, however [63], Fluorination of a-C H enhances corrosion resistance of the films significantly [64],... 

Process of chemical vapor deposition (CVD) is one of the most effective methods for preparation of flat emission cathodes. This method allows to produce different carbon structures on the cathode substrate. Depending on conditions of deposition, derivable carbon surface can be diamond-like films [1], amorphous graphite [2], various carbon constitutions, including carbon nanotubes [3], Investigation results of field emission properties produced cathodes have shown this is a promising technology for production Field Emission Display (FED). 

Since that time, synthetic diamond films have developed into an important high-tech product employed for many purposes. In comparison to other forms of diamond, the most attractive difference is the facile generation of diamond coated workpieces in almost any desired shape. The preparation of thin layers, for example, for electronic applications, became possible as well only after the development of CVD methods. 

Depending on the method of preparation, the surface of a diamond film is either functionalized aheady, for example, covered by hydrogen atoms, or it exhibits an array of so-called surface dimers (it-bonds arising from reconstruction). The latter case is mostly found for samples that have been subject to a secondary thermal treatment to remove their initial, usually inhomogeneous surface functionalization. 

Diamond films may be polycrystalline or monocrystalline layers. In polycrystalline films, the diameter of particles is either on the range of micrometers, or they measure just a few nanometers across (UNCD). The preparation is mostly achieved by deposition from the gas phase (CVD methods). A variety of gaseous hydrocarbons like methane serve as carbon source. Film formation only occurs in the presence of atomic hydrogen that must be generated in situ, for example, in a plasma, on a hot filament, or in a flame. The deposition takes place on a substrate heated at 800-1200 °C. 

Further applications of diamond films lie in a mechanically resistant coating of components and implants. Moreover, the use in electronic devices seems near at hand now, and one may well assume that diamond films will at least partially replace silicon in this field. The optical quahties of diamond render free-standing films an ideal material for windows in spectroscopic apparatus, etc. Rehable methods of preparation and a controllable doping have been estabhshed, which altogether allow for a large scale, commercial apphcation of diamond films. 

FTIR has been used extensively for identification of coatings. Important methods for the study of paint material are KBr pellets prepared from scratched off paint material, ATR measurement of coated surfaces and measurements on cross sections of a coating with FTIR microspectroscopy. FTIR is an excellent way of obtaining information quickly about the basic chemical class of a binding material. Samples are placed in a diamond anvil cell and compressed to a thin film a beam condenser focuses the IR beam to an area of 1.0 mm [99]. Qther methods for determining the binder structure of cross-linked systems comprise PyGC. 

Besides the proper diamond flhns obtained by vapor deposition, the same method also allows for the preparation of further, similar materials. These include the so-called a-C H- and a-C-phases that are alternatively termed diamond-like carbon (DLC) films. ... 

Diamond thin films can be produced from microwave-discharge-heated methane or from carbon that is sputtered by ion bombardment [63-65]. Discuss the methods of preparation and the possible reasons for the formation of metastable phases by these methods. 

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