Nanocrystalline films mixture

B. Fausett, M. C. Granger, M.L. Hupert, J. Wang, G. M. Swain, D. M. Gruen, The electrochemical properties of nanocrystalline diamond thin-films deposited from C60/Argon and Methane/Nitrogen gas mixtures, Electroanal., vol. 12, pp. 7-15, 2000. 

The electrodeposition of chromium in a mixture of choline chloride and chromium(III) chloride hexahydrate has been reported recently [39]. A dark green, viscous liquid is obtained by mixing choline chloride with chromium(III) chloride hexahydrate and the physical properties of this deep eutectic solvent are characteristic of an ionic liquid. The eutectic composition is found to be 1 2 choline chloride/chromium chloride. From this ionic liquid chromium can be electrode-posited efficiently to yield a crack-free deposit [39]. Addition of LiCl to the choline chloride-CrCl3-6H20 liquid was found to allow the deposition of nanocrystalline black chromium films [40], The use of this ionic liquid might offer an environmentally friendly process for electrodeposition of chromium instead of the current chromic acid-based baths. However, some efforts are still necessary to get shining... 

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). 

Gruen and co-workers[90] and Fausett et al. [81] also discussed about manufacturing smoother diamond films by modifying the growth conditions, but these films usually contain nondiamond intergranular phases. They found that nanocrystalline diamond films produced from CgolAr gas mixtures demonstrated basic electrochemical properties that were similar to... 

Diamond films have also been deposited from hydrogen-free gas mixtures such as Cgo/Ar using microwave apparatus. The deposition rates are, however, significantly lower. Additionally, use of hydrogen-poor plasmas results in nanocrystalline (3-1 Onm) diamond films in contrast to micrometer sized crystals from the hydrogen-rich plasmas [56]. 

Figure 6 shows Hall measurement data for a series of boron-doped nanocrystalline diamond films deposited with different levels of B2H6 added to the source gas mixture. Measurements of the carrier concentration and mobility were made at different temperatures up to about 500°C. At room temperature, the carrier concentration increases and the hole mobility decreases as B2H6 added to the source gas mixture with values in the range of 10 -10 cm and 10-100 cm /V-s, respectively. The carrier concentration and the doping level increase proportionally with B2H6 added. 

FIG. 6. Carrier concentrations and mobilities (holes) in boron-doped nanocrystalline diamond thin-film electrodes as a function of the B2H6 concentration added to the source gas mixture. The measurements were made in a van der Pauw geometry with Ti contacts by Dr. Toshihiro Ando at NIMS. The limit of the temperature measurements was approximately 500 K. 

Boron-doped nanocrystalline diamond films have recently been produced and evaluated as electrodes [115]. The films consist of clusters of diamond grains, 100 nm in diameter, and possess an rms surface roughness of 34 nm over a 5 x 5 pm area. The individual diamond grains are approximately 10 15 nm in diameter, as determined by TEM. Films with a thickness ranging from 0.5 to 4 pm are deposited by microwave-assisted eVD using a CH4/H2/Ar gas mixture (1/4/95%). B2H6, diluted... 

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