Influence on characteristics of 'micro-crystalline diamond/ultra nano-crystalline diamond' in addition of argon gas
| Autor: | Horng-Yi Chiang, 江泓逸 |
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| Rok vydání: | 2011 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 99 Diamond films possess excellent physical, chemical, and mechanical properties, such that the syntheses of diamond films have been the focus of research. Moreover, the diamond films own marvelous field emission properties and have great patential for the application on the electron field emission devices. The chemical vapor deposition (CVD) has been the most widely utilized process for growing the diamond films. In this study, we used microwave plasma enhanced chemical vapor deposition (MPECVD) technique to synthesize microcrystalline diamond/ultrananocrystalline diamond (MCD/UNCD) composite films, for the purpose of investigating the growth mechanism and the related microstructural characteristics of the MCD/UNCD composite films. We first grow ultrananocrystalline diamond (UNCD) thin films as nucleation layers, followed by a secondary MPECVD process for growing microcrystalline diamond (MCD) thin films. We used Raman spectroscopy, field emission scanning electron microscopy (FESEM), optical emission spectroscopy (OES), and transmission electron microscopy (TEM) to characterize the MCD/UNCD thin films. The growth mechanism was discussed based on these investigations. In the first part of research, different proportion of argon (0-90 %) was added into CH4/H2 plasma for the deposition of the secondary MCD layer. Among them, the 50% Ar plasma results in the best electron field emission properties, that is, the turn-on field of 6.50 V/μm for (MCD50)1h/UNCD1h and of 5.0 V/μm for (MCD50)1h/UNCD3h films. TEM examinations indicated that the two step MPECVD process markedly modified the gannular structure of UNCD films, resulting in large-grain/small-grain duplex microstructure. In the second part of research, we changed the deposition time for growing the MCD layer (with 50% Ar plasma). We observe that 1 h deposition of MCD layer leads to the best electron field emission properties. The best electron field emission properties obtainable are：turn-on field of 5.0 V/μm with EFE current density of 0.70 mA/cm2 at an applied field of 27.5 V/μm. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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