Nucleation and Growth of Oriented Diamond Films on Nickel Substrates
- PDF / 1,053,894 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 1 Downloads / 243 Views
high pressure and high temperature(HPHT) conditions [5]. Thus, it is interesting to consider if this same characteristic can be made useful in a low pressure CVD process. Sato et al. reported that both (11) and (100) oriented diamond nuclei could be grown on Ni substrates, but the overall percentage of oriented nuclei was rather low [6]. We have observed that under special conditions oriented diamond nuclei precipitate from supersaturated Ni-C-H solution [7]. A similar phenomenon has been observed for the heteroepitaxial growth of diamond on (111) Pt by Kobashi and Tachibana [8]. Roy also reported on precipitation of diamond particles from different mixtures of diamond and metal powders [9]. In this paper, we report on a multi-step CVD process that results in nucleation of oriented diamond on Ni substrates without a graphite interlayer. The following sections describe in detail experimental conditions, results of analytical characterization, and suggest an explanation of the observed phenomena. EXPERIMENT The experiments were carried out in a hot-filament CVD (HFCVD) system. A schematic diagram of the system is shown in Fig. 1. The HFCVD chamber was a water-cooled, modified sixway cross. The substrate holder was made of molybdenum or stainless steel. The substrates were heated by radiation from the tungsten filament which was kept at a constant temperature between 2300TC to 2400'C. The substrate temperature was controlled by adjusting the distance between the filament and the substrate, and by water cooling the substrate holder. All cited temperatures were calibrated against the melting points of Ge and Ni-Cu alloys, and measured with thermocouples 281 Mat. Res. Soc. Symp. Proc. Vol. 423 01996 Materials Research Society
*
He-Ne Laser prism _,Gas Inputs
Photo diode
,. Chopper
•Laser RaRm
.
----
Water cooling Thermocouple Li ear Transfer
Filament ample
for Filament Substrate cooling To Pump,, Water Inlets
Sample Manipulator
Fig. 1 Schematic diagram of the hot HFCVD and Laser reflection systems. contacting the subsurface of the substrates. A laser reflection system was set up to monitor sample surface reflectivity during the nucleation and growth process. Both (100) and (11l) single crystal Ni were used as substrates. The substrates were polished using standard metal polishing techniques [10] and subsequently cleaned with acetone and DI water. A suspension of 0-2 Jtm diamond powder in acetone was used for seeding. Samples were simply immersed into suspension and allowed to dry. As an alternative, non-diamond carbon seeds were also used. They included graphite and fullerene (C60) powders, and graphite layers obtained by decomposition of hydrocarbons. All these seeds were effective in producing oriented diamond nuclei. The nucleation and growth procedure consisted of a three -step process: (1) deoxidization, (2) high temperature annealing, and (3) diamond deposition. Step I involved annealing of the seeded substrates at a temperature of 900TC in a hydrogen atmosphere for 10-30 minutes to remove oxides. In ste
Data Loading...
