Conductivity diamond films

Thermal conduction (diamond films, AIN) Heat sinks in electronic devices... 

So far there have been only a few reports concerning the chemical modification of diamond, either insulating or electrically conducting diamond films that would potentially be useful as electrodes. Smentkowski and Yates reported on a facile approach for modifying the hydrogen-... 

The attractive characteristics of electrodes based on conductive diamond films have led a number of research groups around the world to use these electrodes for electroanalytical applications. As a way to extend the analytical capabilities of diamond electrodes, researchers have also become interested in chemically modifying the diamond surface. One of the principal motivations is to impart selectivity for analytical purposes. Closely associated with this is the desire to impart electrocatalytic activity for specific electrochemical reactions, making use of diamond as a highly robust support. One of the more interesting recent applications of the modified diamond surface is the fabrication of DNA arrays. 

The outstanding properties of diamond make it a very attractive material for use in many potential applications. In particular, the superior electrochemical properties of highly boron-doped conductive diamond films, prepared by the CVD process, have received attention from electrochemists. This article reports the fabrication of boron-doped diamond (BDD) electrodes, creating various functional structures or functional surfaces such as microdisk array (MDA) electrodes, ion-implanted BDD electrodes, and electrodes with ultrasmooth surfaces. Studies have been made of the electrochemical properties of each system and their applications in electroanalysis arediscussed. 

CVD diamond films can be used for electrochemical applications, especially in harsh or corrosive environments. Conducting diamond electrodes, made by adding boron to CVD diamond films, are very inert compared to other electrode materials (such as platinum). Such diamond electrodes may find applications in analysis of contaminants, such as nitrates, in water supplies, and even in the removal of those contaminants. 

Recently Butler et al. [4] reported the deposition of nanocrystalline diamond films with the conventional deposition conditions for micrometer-size polycrystalline diamond films. The substrate pretreatment by the deposition of a thin H-terminated a-C film, followed by the seeding of nanodiamond powder, increased the nucleation densities to more than 10 /cm on a Si substrate. The resultant films were grown to thicknesses ranging from 100 nm to 5 fim, and the thermal conductivity ranged from 2.5 to 12 W/cm K. 

Fullerenes have potential applications in the preparation of carbon support catalyts and diamond films. They have high electrical conductivity and chemical reactivity. 

Diamond Hints, although not approaching bulk diamond, are harder than most refractory nitride and carbide thin films, which makes them attractive for tribological coatings. Transparency in the visible and infrared regions of the optical spectrum can be maintained and index-of-refraction values approaching that of bulk diamond have been measured. Electrical resistivities of diamond films have been produced within the full range of bulk diamond, and thermal conductivities equivalent to those of bulk diamond also have been achieved. As substrates for semiconductor electronic devices, diamond films can be produced by both the PACVD and IBRD techniques. 

Similar conclusions on the character of conductance in the polycrystalline diamond films were derived in [33], The resistive intercrystallite boundaries can involve nonlinear resistance in polycrystalline diamond films moderately doped with boron [34]. Later, more sophisticated analysis [35-37] of the frequency dependence of impedance of polycrystalline diamond films resulted in a conclusion that at higher temperatures, in addition to the aforementioned electric conductance caused by the motion of free holes in the valence band, a second component of conductance manifests itself. The second component is due to the hopping of charge carriers between local traps possibly associated with the intercrystallite boundaries. 

In Section 2 we showed that the properties of amorphous carbon vary over a wide range. Graphite-like thin films are similar to thoroughly studied carbonaceous materials (glassy carbon and alike) in their electrode behavior. Redox reactions proceed in a quasi-reversible mode on these films [75], On the contrary, no oxidation or reduction current peaks were observed on diamondlike carbon electrodes in Ce3+/ 41, Fe(CN)63 4. and quinone/hydroquinone redox systems the measured current did not exceed the background current (see below, Section 6.5). We conventionally took the rather wide-gap DLC as a model material of the intercrystallite boundaries in the polycrystalline diamond. Note that the intercrystallite boundaries cannot consist of the conducting graphite-like carbon because undoped polycrystalline diamond films possess excellent dielectric characteristics. 

Specific conductive silicon substrates have to be carefully prepared before use. For the diamond-deposition process, substrates have to be cleaned, seeded with diamond nanocrystalline seeds at high surface density, and then coated with a grown thick diamond film (from less than 1 pm up to several p,m) by hot filament chemical vapor deposition (HF-CVD). At Adamant, deposition processes are performed automatically in programmable controlled process units, which allow growing diamond on scale up to 0.5 m2. The process is performed under low pressure (1 < 0.1 bar) and high temperature (filament temperature 2,500°C and substrate temperature 800-1,000°C) with a gas mixture composed of CH4, H2 (CH4/H2 ratio <1%), and a boron source (typically trimethyl boron). 

Conductive diamond thin-films in electrochemistry. Diam. Relat. Mater. 12,1940-1949. Internet presentation (2005) Advanced systems for substrate sterilization. http //www.substrate-tech.com/producers.html (access 21. Feb. 2005). 

Amorphous carbons, carbon black, soot, charcoals, and so on, are forms of graphite or fullerenes. The physical properties depend on the nature and magnitude of the surface area. They show electrical conductivity, have high chemical reactivity due to oxygenated groups on the surface, and readily intercalate other molecules (see later). Graphite and amorphous carbons as supports for Pd, Pt, and other metals are widely used in catalysis and for the preparation of diamond films.18... 

Typically these electrodes are fabricated from an inert and electrically conducting material. Common examples would range from liquid mercury to solid platinum and some forms of carbon (i.e. glassy carbon or graphite). Mercury electrodes (Bond, 1980) are used in the form of dropping electrodes in which the surface is continuously renewed or a hanging mercury drop electrode. Recently diamond film electrodes have been utilized for studies that require wide potential windows (Tenne et al., 1993). Typically, the solid... 

X1 ( -s H High conductivity thin materials - thin diamond film - grease/adhesive with high k fill material (i.e.. silver, sraphite. diamond, MMC) Simple and conventional High pressure between contact surfaces. Limited capability Inefficient for a non-uniform heat flux (i.e.. hot spot)... 

Table 13.1 summarizes the experimental results of carrier concentrations and mobilities of various diamond films at room temperature. The electrical conduction of B-doped diamond films (polycrystalline diamond films, HOD films, and homo-epitaxial diamond layers) was also investigated in Ref [417] in the temperature... 

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