Diamond metal deposition

Silicon, diamond, and metal deposition are all examples of elemental deposition. Compounds, particularly oxides, are also deposited by chemical vapor deposition. Some of the important oxides deposited as thin films include SiC>2, BaTiC>3, LiNbC>3, YBa2Cu30,. indium-doped SnC>2, and LiCoC>2. These materials have properties such as superconductivity or lithium ionic conductivity that make their production as thin films a much-studied area of research. If the oxide is to be deposited on the bare metal (e.g., depositing SiC>2 onto Si), chemical vapor deposition is not really needed. Controlling the oxygen partial pressure and temperature of the substrate will produce the oxide film Whether the film sticks to the substrate is another question The production of SiC>2 films on Si is an advanced technology that the integrated-circuit industry has relied on for many years. Oxide films on metals have been used to produce beautiful colored coatings as a result of interference effects (Eerden et al., 2005). 

In a HFCVD process (Fig. 2a), a gas mixture containing 0.1-2 vol.% CH4 in H2 enters a reactor that is evacuated to approximately 10-100 torr, and flows past a wire or mesh made of a metal such as W, Ta, Mo, or Re, heated to about 2000-2400°C (Tables 1 and 2). Under these conditions, 2-10% of H2 is dissociated into atomic H, and CH4 undergoes pyrolysis reactions leading to the formation of radicals such as CH3 and CH2, and stable species such as C2H2, C2H4, and C2Hg. Diamond is deposited on a substrate made of Si, Mo, or silica, etc., which is mounted at a distance of 0.5 to 2 cm from the glowing filament and kept at 700 to 1000°C either by the radiation from the filament or by a separate substrate heater. 

Chemical vapor deposition on hot filament surfaces Solid surface of carbon, graphite or metal filaments o Short diamond/carbon and diamond/metal sheath/core fibers 0 Diamond microtubes, microcoils... 

Second, when multiple metals are deposited simultaneously, as is the case in a real stripping voltammetric measurement, not only is their interaction with the diamond surface important, but equally critical is their interaction with each other. There is a possibility of intermetallic compounds or alloys forming, both of which will affect the oxidation or stripping potential for each. When these heterogeneous deposits form, the oxidation of a particular metal can occur from different sites on the diamond surface or from another metal surface. Oxidation from these multiple sites leads to peak broadening due to a spread in reaction kinetics. Ideally, for this application, highly dispersed metal deposits of low volume, without any intermetallic interactions, are desired. Even with these complexities, it is supposed that diamond will become a useful electrode for the determination of trace metal ions via anodic-stripping voltammetry. 

Simm, A.O., Ji, X., Banks, C.E., Hyde, M.E. and Compton, R.G. (2006) AFM studies of metal deposition instantaneous nucleation and the growth of cobalt nanoparticles on boron-doped diamond electrodes. ChemPhysChem, 1, 704. 

The ligand-based chemistry also has several attractive features for use as an advanced metallization process where high throughput, adhesive, selective metallization on a variety of substrates is crucial (55). The versatility of the process with regard to surface attachment of UTFs to most key technological materials such as polymers, plastics, and diamond has already been demonstrated 20, 21, 34). The elimination of an acceleration step simplifies and reduces the overall cost of the EL metallization process also, the selective metal deposition is... 

However, our interest here is more related to the electrochemical characteristics. The often cited intrinsic electrochemical characteristics of diamond, including extreme stability, low background current and large potential working range, are also advantages for the fundamental study of the electrochemical characteristics of solid materials. The electroanalytical applications of electrochemical metal deposition will be treated in Chapter 16. The materials of interest in the present chapter are those with applications as battery electrodes, capacitor electrodes and electrocatalysts. There may even be cases in which diamond can play a role as a practical support material. 

An SEM image (Fig. 16.2) shows the morphology of the metallic lead that deposits on the diamond surface when the solution concentration is relatively high. Lead was deposited for 2 minutes (Fig. 16.2c) and 10 minutes (Fig. 16.2d) at 0.7 V vs. SCE. It is clear that metal islands deposit on the BDD crystal planes as well as on the grain boundaries. These metallic deposits are of the type that cannot be quantitatively stripped. 

The effectiveness of electrolytic accumulation depends substantially upon the choice of the working electrode. Normally, the surface of bare sohd electrodes is not optimal due to a poorer adherence of most of the heavy metal deposits. Of course, exceptions can be found represented by some materials with particular surface conditions, which is the case of boron-doped diamond (see, e.g., references (14, 39))... 

Another example of epitaxy is tin growdi on the (100) surfaces of InSb or CdTe a = 6.49 A) [14]. At room temperature, elemental tin is metallic and adopts a bet crystal structure ( white tin ) with a lattice constant of 5.83 A. However, upon deposition on either of the two above-mentioned surfaces, tin is transfonned into the diamond structure ( grey tin ) with a = 6.49 A and essentially no misfit at the interface. Furtliennore, since grey tin is a semiconductor, then a novel heterojunction material can be fabricated. It is evident that epitaxial growth can be exploited to synthesize materials with novel physical and chemical properties. 

Another important function of metallic coatings is to provide wear resistance. Hard chromium, electroless nickel, composites of nickel and diamond, or diffusion or vapor-phase deposits of sUicon carbide [409-21-2], SiC , SiC tungsten carbide [56780-56-4], WC and boron carbide [12069-32-8], B4C, are examples. Chemical resistance at high temperatures is provided by aUoys of aluminum and platinum [7440-06-4] or other precious metals (10—14). 

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