奈米金粒鑲埋於鑽石(111)面之同質磊晶成長

Abstract

This thesis focuses on the study of growth of homoepitaxial diamond film with embedded gold nanoparticles (AuNPs) by microwave plasma chemical vapor deposition (MPCVD). The first part of this thesis deals with the preparation of gold nanoparticles on diamond (111) single crystal substrate. The effect of various plasma conditions on the distribution of gold nanoparticles on diamond (111) was explored by varying power and methane concentration in plasma. In the second part, the well fabricated AuNPs/ diamond (111) was used as the substrate for further growth of oriented diamonds by MPCVD. Finally, the results of multi-step growth of epitaxial diamond film with embedded AuNPs are presented. The gold film was deposited on ~ 2 mm sized diamond (111) single crystal substrate by electron beam evaporation. The as-deposited Au on diamond was then annealed in vacuum. The higher temperature results in more uniform distribution of AuNPs on diamond substrate. The distribution of AuNPs on diamond is also affected with the thickness of the deposited gold layer and the MPCVD conditions for homoepitaxial diamond film including hydrogen/methane concentration, microwave . The morphology and roughness after the plasma treatment were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results show that the as-deposited diamond on 20nm thickness of gold layer has more uniform distribution in 0.5% methane plasma at microwave power of 800 W. In the diamond growth process, oriented diamond films were deposited on diamond substrate covered with gold by the same process parameters including mixed ratio of CH4 and H2, pressure, power, etc. Comparing with the diamond film in the various time, we can set up the growth model of diamond characterized by AFM and X-ray diffraction (XRD). At the beginning, the growth of diamond islands appears between AuNPs, followed by lateral overgrowth with coalenscence when diamond islands covers the AuNPs. From cross-sectional transmission electron microscopy (TEM) observation, a graphite layer exists at the AuNPs/diamond interface. Secondly, diamond films obtained by step direct growth on diamond seed and by multi-layer growth of gold were characterized by optical microscopy (OM) and Raman spectroscopy. The results show that cracks appear after diamond film deposition for eight hours, while the film processed with multi- layer growth of gold shows no cracks. Raman spectra show the peak in the range of 1326-1332 cm-1, suggesting that diamond films are in tensile stress. XRD and reciprocal space mapping (RSM) were used to evaluate the effect of embedded AuNPs on cracking by determination of the d-spacings of diamond and embedded gold. The results show the out-of-plane and in-plane d-spacings of diamond become larger than the bulk values, whereas gold’s d-spacings become smaller. TEM reveals the distribution of embedded AuNPs and the microstructure of epitaxial lateral growth of diamond with formation of stacking faults and threading dislocations after the coalescence of islands in the step growth. After 4 step growth, the dislocation density can be reduced to 1.41x108 cm-2. It implies the embedded gold particles may restrain the formation of the cracks on diamond.