| Summary: | 碩士 === 淡江大學 === 物理學系碩士班 === 99 === Due to the mismatch in the lattice parameters of diamond and silicon, prenucleation process is necessary to grow diamond on the Si-substrate. The conventional way of nucleating the Si-substrates, the ultrasonication in diamond and Ti-powder solution, requires long processing time (i.e., 45 min) and imposed significant damage on the Si-substrates. Once prenucleated, the diamond films are readily grown on the Si-substrates by using the Microwave Plasma Chemical Vapor Deposition (MWPCVD) process in CH4/Ar or CH4/H2 plasma. In this study, we developed an bias-enhanced nucleation and bias-enhanced growth (BEN-BEG) process for synthesizing the nanocrystalline (NCD) diamond films.
In the beginning, we systematically adjust the processing parameters, including bias voltage, microwave power, total pressure and methane concentration, so as to optimized the electron field emission properties of the diamond films (BEN for 10 min and BEG for 60 min in CH4(5-7%)/H2 plasma). Then we investigated the effect of bias voltage on the characteristics, microstructure and EFE properties, of the diamond films. In the third part of research, we examined the evolution of microstructure and EEE properties during the BEN-BEG process. In the final part of research, we compared the characteristics of the NCD films prepared by BEN-BEG process with those of the two-step processed UNCD films. The two-step process includes the formation of UNCD layer to serve as nucleation layer, followed by the growth in CH4/Ar/H2 plasma. We used the optical emission spectroscopy (OES) and the bias current to monitor the BEN-BEG process and used Raman spectroscopy, SEM/TEM and EFE to characterize the diamond films.
We observed that the processing parameters imposed significant change on the morphology and EFE properties of the diamond films. The NCD films prepared by BEN-BEG process exhibit superior EFE properties to the UNCD films prepared by the CH4/Ar plasma (or the two-step MCD/UNCD process). Transmission Electron Microscopy (TEM) examination revealed that the diamond films prepared by BEN-BEG process have grains about 50 nm in size, which is markedly smaller than those prepared by conventional MPECVD (CH4/H2) process (~500 nm), but is not as small as those synthesized in CH4/Ar-MPECVD process (~5 nm). Moreover, the diamond nucleated on Si-substrates without the formation of amorphous carbon (a-C) phase and there formed a graphitic filament inside the NCD films, which can account for the lower EFE turn-on field with higher EFE current density for the BEN-BEG derived NCD films, as compared with the two-step processed UNCD films.
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