Activated CVD

Figure 15 shows the variation of diamond deposition rates by various activated CVD techniques as well as the HP—HT technique (165). It can be seen that the highest growth rate of activated CVD diamond synthesis is stiU an order of magnitude lower than the HP—HT technique. However, CVD has the potential to become an alternative for diamond growth ia view of the significantly lower cost of activated CVD equipmeat and lower miming and maintenance costs. 

Fig. 15. Variation of diamond deposition rates by various activated CVD techniques as well as the HP—HT technique (165).

The activated CVD diamond techniques can be mote attractive in cases where the huge capital investment (several hundred million dollars) requited for the HP—HT technology is not available or where the high level of technical knowledge requited for HP—HT synthesis is not available. In addition, most wear-resistant apphcations requite diamond coatings only of the order of a few micrometers thick. Such coatings can be deposited ditecdy on the finished product without the need for further finishing if CVD techniques are employed. 

Glaze coatings (58) are appHed to dry or bisque-fired clay ceramics to form a strong, impermeable surface that is aesthetically pleasing. Protective ceramic coatings can also be deposited by CVD (68,90). Plasma activated CVD has been used extensively to produce diamond and diamondlike films. Diamond films can also be used to make optical coatings with a tailored refractive index. 

Several other silicides of potential interest are the obj ect of active CVD development. 

Up to now three chemical vapor deposition (CVD) techniques have proved suitable for the preparation of high quality optical fibers the outside vapour phase oxidation (OVPO) process8, the modified CVD (MCVD) process9 and the plasma-activated CVD (PCVD) process10. The last mentioned process will be the main subject of this article. To give a better appreciation of the principles the alternative processes will be described briefly. 

CVD can also be classified using its activation methods. Thermal activated CVD processes are initiated only with the thermal energy of resistance heating, RF heating or by infrared radiation. They are widely used to manufacture the materials for high-temperature and hard-to-wear applications. In some cases enhanced CVD methods are employed, which includes plasma-enhanced CVD (PECVD), laser-induced CVD (LCVD), photo CVD (PCVD), catalysis-assisted CVD and so on. In a plasma-enhanced CVD process the plasma is used to activate the precursor gas, which significantly decreases the deposition temperature. 

Coatings are made by CVD, MT (medium temperature)-CVD, PVD, and plasma-activated CVD. The latter technique was recently successful in producing adherent diamond layers. The keenest edges are now produced by PVD coating. 

Ways have been investigated to reduce or avoid leaching of plasticizers. Barreto et al. (2012) deposited a barrier coating onto PVC, resulting in a reduction of more than 80% of leaching of the plasticizer. The barrier was established by means of plasma-activated CVD used to polymerize octamethylcyclotetrasiloxane (OMCTS) and hexamethyldisiloxane (HMDSO). Covalent bonding of the plasticizer to PVC... 

The conventional CVD method uses thermal energy to activate chemical reactimis, which is commonly known as thermally activated CVD (TACVD). CVD reactions can be initiated by using different energy sources. Plasma and light energy are currently being used to activate the chemical reactions. Other types of CVD include atomic layer epitaxy, metal-organic CVD, flame-assisted CVD, and electrochemical vapor deposition. They are briefly discussed herewith [1,5]. 

Reactors for conventional thermally activated CVD are of two types cold-wall and hot-wall reactors, respectively internally and externally heated. The disadvantage of a hot-wall reactor is deposition on the wall and partial depletion of reactants leading to nonuniform coatings. A correct reactor geometry and gas inlet manifold can compensate for gas depletion in hot-wall reactors. There is no limit to the form of the objects to be coated, but sizes are restricted. In a cold-wall reactor the substrates to be coated are heated by a graphite susceptor that is inductively heated by an rf generator. Only the hot parts are coated and not the reactor walls, which remain relatively cold. 

Kimura et al. [327] used a thermally activated CVD process to form AlN-P-SiC powder mixtures. Here, by the reaction of AICI3 with a N2-NH3 mixture, AlN is deposited on submicron SiC particles in a fluidized powder bed. 

CCVD combustion chemical vapor deposition MOCVD mettil-organic-assisted CVD PECVD plasma-enhanced CVD FACVD flame-assisted CVD AACVD aerosol-assisted CVD ESAVD electrostatic-atomization CVD LPCVD low-pressure CVD APCVD atmospheric-pressure CVD PACVD photo-assisted CVD TACVD thermtil-activated CVD EVD electrochemical vapor deposition RTCVD rapid thermal CVD UHVCVD ultrahigh-vacuum CVD ALE atomic-layer epitaxy PICVD pulsed-injection CVD... 

The IR spectra of diamond-like carbon (DLC) films from dielectric barrier discharge plasma showed the presence (vCH) of CH3, CH2 and CH units in the approximate ratios 10 21 69. IR and Raman spectra were used to characterise DLC films on stainless steel or silicon substrates. Transmission IR spectra included bands due to v, and VasCH2 of sp CH2 units at 2870 and 2960 cm respectively. The FTIR spectrum of a diamond-like nanocomposite (DLN) film formed by thermally-activated CVD on a silicon substrate showed the presence of a diamond-like a-C a-Si 0 network. Several other papers described vibrational spectroscopic studies on diamond-like materials. ... 

---