Pressure-temperature conditions, diamond films

Let us illustrate this with the diamond synthesis as an example. It is common knowledge that the graphite to diamond phase transformation is only possible at ultrahigh pressures and temperatures. However, it has become habitual in recent years to synthesize diamond whiskers and fine diamond films under far from extreme conditions. 

Unlike other thin film deposition processes, conditions for diamond CVD have three unique features (i) high substrate temperature typically at 700-1200 °C, (ii) high gas pressure P at 20-150Torr (lTorr= 133.3 Pa), and (iii) low methane (CH4) concentration of usually 1-5% with respect to the dilution gas, hydrogen (H2). A standard temperature for diamond growth, monitored by an optical pyrometer without emissivity correction, is 800 °C. It is, however, considered that the surface temperature of the specimen exposed to the plasma is actually higher. Under these conditions, at least more than 95% of the deposited film can be crystalline diamond,... 

Figure 2 Temperature dependence of nucleation density measured with an ellipsometric monitor. Closed circles and solid line show values for 1000 W microwave power, open, circles and broken line show values for 1400 W microwave power. Other deposition conditions 5 vol.% CO/Hj, flow rate of 100 seem, and pressure of 50 torr. Using CO as reactive gas led to diamond films containing hardly any non-diamond phases.1 1 (Reproduced with permission.)...

Advanced diamond films are synthesized using the gas-phase decomposition of volatile carbon sources such as methane (CH4), acetone (H3C-CO-CH3), carbon monoxide (CO), acetylene (HC=CH), or adamantane (CioHi ) and is conducted under temperature and pressure conditions where graphite is the stable polymorph (Fig. 5). The most important methods for producing CVD-diamond under metastable conditions are ... 

In addition to thin-film electrodes, compact diamond single crystals grown at high temperature and high pressure have become the object of electrochemical study in recent years. These so-called HTHP crystals can be obtained by crystallization from a carbon solution in a metal melt (e.g., based on the Ni-Fe-Mn system) at /arranges that correspond to the conditions of thermodynamic stability of diamond. These crystals can be also doped with boron in the course of growth. 

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