Bias nucleation process

A bias nucleation process has been developed to overcome the problem of the low diamond nucleation density on untreated nondiamond substrates wherein a negative bias is apphed to the substrate during deposition. ... 

The nucleation process was monitored by LRI (see Section 11.10), and the application of bias voltage was terminated if diamond nucleation was detected by LRI. No appreciable diamond nucleation was observed in the AC-BEN treatment, if the voltage was less than 125 Vrms ( 175 V peak to peak). The optimum biasing time for the AC-BEN treatment was 45 min, much longer than the DC-BEN treatment that needed only 12 min. In terms of the number of oriented nuclei, it was more than 50% for the AC-BEN treatment, while it was only less than 10% for the DC-BEN treatment. It was hence inferred that concurrent processes of forming an epitaxial SiC layer and the diamond nucleation, induced by the AC-BEN treatment, were responsible for the increase in the number of oriented diamond nuclei. 

The core of the nucleation model proposed in Refs. [362, 363] is an assumption based on the experimental data that epitaxially oriented nucleation sites are formed in the SiC layer of about 10-nm thickness during the bias treatment. These sites are exposed at the SiC surface, while plasma etching of SiC is occurring during both the BEN treatment and the successive diamond growth process. The model of nucleation process is schematically depicted in Figure 11.57 ... 

The essential feature of PC materials is the ultrafast phase transition between amorphous and crystalline structures that occurs on a nanosecond time scale. In the previous sections, we have discussed extensively the amorphous and crystalline structures of GST and their properties. These correspond to the starting and end points for the actual phase transition, which are crucial to understand the function of PC materials. We now present results for the nucleation-driven crystallization process of GST using DF calculations combined with MD [31], A sample of fl-GST with 460 atoms was studied at 500, 600, and 700 K, and a second sample of 648 atoms was simulated at 600 K. In all cases we used a fixed crystalline seed (58 atoms, 6 vacancies) in order to speed up the crystallization process. More recent experience has shown that the time scale for the crystallization is of the order of several nanoseconds for these system sizes in the absence of a fixed seed, while those here are of the order of 0.3-0.6ns. This means that we cannot discuss the onset of nucleation, but this is also true in the case of smaller systems (<200 atoms) discussed by other groups. In very small systems, periodic boundary conditions bias the process severely. Our larger samples reduce finite-size effects, and we show the effect of choosing different annealing temperatures. Simulations of this scale (up to 648 atoms over 1 ns) are near the limit of present day DF/MD calculations. 

The joint action of pinning and Lorentz forces on vortex chain depends on the geometrical symmetry of the nanostructure. For the SMN of N-type the vortex chain is located in the center of N layer and the pinning force obstructs the vortex penetration inside the S layer. As bias current flows through the superconducting parts of the sample, dissipative processes are absent and the resistive transition is sharp (Fig. 1). For S-type nanostructures, vortex chain nucleates inside the central superconducting layer. Electromagnetic interaction between vortices and bias current leads to dissipation, it follows that in the central layer the sample resistance is not suppressed completely and the resistive transition becomes wider. 

Gerber J, Robertson J, Sattel S, Ehrhardt H. Role of surface diffusion processes during bias-enhanced nucleation of diamond on Si. Diamond Relat Mater 1996 5 261-5. 

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