Microcrystalline diamond films

Catledge, S., Baker, R, Tarvin, J., and Vohra, Y., Multilayer nanocrystalline/microcrystalline diamond films studied by laser reflectance interferometry, in Diamond and Related Mater., 9 (8), 1512-1517 (2000). 

It is well known that nitrogen can be easily incorporated in diamond, and usually, it must be very eareful of the air leak in the CVD chamber to prevent nitrogen contamination of diamond films. It is also known that addition of too much nitrogen to the source gas resulted in microcrystalline diamond films rather than well-faceted films. However, Koidl s group found [90] using a NIRIM-type reactor that an addition of small amount of N2 gas to the source gas of c=l-2%CH4/H2 resulted in pronounced (100)-textured films, while the film became microcrystalline without N2 addition. More specifically, an addition of 40-200 ppm of N2 to the... 

The soultrananocrystalline diamond (UNCD) is a special form of polycrystalline diamond films consisting of nanoscopically small individual crystallites with diameters of 3-10 nm (Figure 6.4). Owing to this fine structure, the portion of carbon atoms being part of grain boundaries is in its turn markedly increased as compared to microcrystalline diamond films, which again influences properties like the surface conductivity. 

The names for these two film types arise from their nominal crystallite size and morphology. Figure 5 shows scanning electron microscopy (SEM) images of the two types of boron-doped diamond thin film deposited on Si. High quality microcrystalline diamond films are deposited from CH4/H2 source gas mixtures with volumetric ratios of 0.3 to 1.0%,... 

FIG. 9. Background cyclic voltammetric i-E curves for (a) glassy carbon, (b) a moderately boron-doped microcrystalline diamond film electrode, and (c) a heavily boron-doped microcrystalline diamond film electrode in 0.1 M HCIO4. Electrode area = 0.2 cm. Scan rate = 0.1 V/s. 

FIG. 19. Cyclic voltammetric i-E curves for 1 mM cadaverine in 0.01 M carbonate bulfer/0.1 M NaQ04, pH 10.6, at a microcrystalline diamond film deposited from a 0.67% CH4/H2 ratio. (A) As deposited and (B) acid-washed and rehydrogenated diamond film. Scan rate = 10 mV/s. (Reprinted with permission from Anal. Chem., 71,1188 (1999). Copyright (1999) American Chemical Society.) (From Ref. 39.)... 

CCL-Diamond, http //www.ccl diamond.com/HTML/Products Electrodes.html Microcrystalline thin-film BDD electrodes Coated on Ti, W, Mb, Si... 

Ru(NH3)6, 0.1 mM IrClg, and 0.05 mM methyl viologen (MV ) at a boron-doped microcrystalline diamond thin-film electrode. Scan rate = 0.1 V/s. Electrolyte = 1 M KCl. 

Cyclic Voltammetric and Heterogeneous Electron Transfer Rate Constant Data for Four Aqueous-Based Redox Systems at Boron-Doped Microcrystalline Diamond Thin-Film Electrodes... 

One important electrochemical technology where diamond electrodes have made a significant impact is in the area of electroanalysis. CVD diamond offers advantages over other electrodes, especially sp carbon (e.g., glassy carbon), in terms of linear dynamic range, limit of detection, response time, response precision, and response stability. Some of the reported applications of diamond in electroanalysis are highlighted below. Unless stated otherwise, all the diamond electrodes mentioned below are boron-doped, microcrystalline thin films deposited on a conducting substrate (e.g.. Si). 

Figure 18 shows typical cyclic voltammetric i-E curves for 1.0 mM (A) cadaverine (CAD), (B) putrescine (PUT), (C) spermidine (SPMD), and (D) 0.8 mM spermine (SPM) in borax buffer pH 11 (BBpHll) at a microcrystalline diamond thin film deposited from a 0.5% CH4/H2 ratio and 10 ppm B2H6. Similarly shaped curves were observed for several other amines and polyamines (e.g., methylamine, ethylamine, propylamine, ethylenediamine, 1,3-diaminopropane, 1,6-hexamethylenediamine, and... 

Figure 23B presents IR transmission spectra for (5) an optically pure and mechanically polished white diamond disc, (6) an undoped and polished (both sides) Si substrate, and (7 and 8) moderately and heavily boron-doped microcrystalline diamond thin films deposited on the undoped Si. The white diamond is relatively free of structural defects and chemical impurities. There is reduced transparency between 2500 and 1500 cm due to the two-phonon absorption. Diamond films with more... 

FIG. 23. Transmission spectra for different materials in the (A) UV/Vis and (B) IR regions of the electromagnetic spectrum. The electrodes in (A) are (1) a thin film of ITO on quartz, (2) a thin film of boron-doped nanocrystalline diamond on quartz, (3) a thin film of mechanically polished and boron-doped diamond on an optically pure, white diamond substrate, and (4) a free-standing, boron-doped, and mechanically polished diamond disc. The electrodes in (B) are (5) an optically pure and mechanically polished white diamond disc, (6) an undoped and polished (both sides) Si substrate, and (7 and 8) moderately and heavily boron-doped microcrystalline diamond thin films deposited on the undoped Si. (Reprinted with permission from Interface 2003, 12, 33. Copyright (2003) The Electrochemical Society, Inc.) (From Ref. 158.)... 

Diamond OTEs are also useful for studying the electrochemical and optical properties of important biomolecules, like cytochrome c. We recently reported that boron-doped microcrystalline diamond thin film electrodes are quite responsive for horse heart cytochrome c, exhibiting a very active and stable cyclic voltammetric response without any pretreatment or surface modification [119,124]. Heterogeneous electron-transfer... 

---