TEM Analysis of the Observed Phases During the Growth of Oriented Diamond on Nickel Substrates
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Mat. Res. Soc. Symp. Proc. Vol. 423 0 1996 Materials Research Society
dissolved into the Ni lattice. The temperature was then lowered to about 900'C to allow diamond precipitation. Finally, the nuclei are grown using standard diamond CVD conditions of 0.5% CH 4 . A full description of the process can be found elsewhere[I]. Plan-view and cross-section TEM samples were prepared from oriented diamond on (100) single crystal Ni, that has been grown for 4 hours. The plan-view sample was prepared by standard methods [9]. For the cross-section samples difficulties arose due to extreme differences in hardness between diamond and nickel. The following technique was developed to overcome some of the difficulties. Two samples were glued together with diamond sides face to face, and mounted into a molybdenum tube with G-1 epoxy. The tube was cut into slices 400 ltm thick that were flattened, dimpled, and then polished on one side to a depth of 60 Rm. Then the sample was turned over and further ground and polished to a thickness of less than 10 gim. Finally, the sample was ion milled using "sector rotation speed control", which rotates the specimen slowly while the ion beam is perpendicular to the specimen's interfaces, and rapidly through the remaining sectors. In addition, low incident angle and low voltages were used to thin the interfacial region. Although time-consuming, this procedure resulted in good samples from which TEM images could be obtained. The microstructural studies were performed with a TOPCON EM-002B operated at 200 kV. X-ray diffraction analysis was undertaken [10] using the wide-film Debye-Scherrer XRD technique developed by Read[ 1 ]. In a typical experiment, the angle between the incident X-ray beam and diamond film surface was 15%. An excitation potential of 26 kV and tube current of 40 mA gave an adequate single-to-noise ratio after 2 hours of exposure. RESULTS AND DISCUSSION Figure 1 shows an SEM image of a highly oriented diamond nuclei grown on (100) Ni. The micro-Raman spectrum in Figure 2 shows a strong diamond peak and absence of any graphitic phase. These two results present a strong evidence that the developed multi-step deposition process yielded high quality diamond deposits on nickel substrates. 400
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Figure 1. SEM micrographs of oriented diamond nuclei formed on the Ni substrate,
Figure 2. A typical Raman spectrum from the diamond nuclei.
In order to obtain information on structural relationships and intermediate phases, extensive TEM and XRD studies were performed. Figure 3 shows a TEM micrograph of two oriented diamond particles which was attained after the sample preparation discussed above. Three distinct regions could be observed: (i) the diamond particles, (ii) an irregular approximately 0.5 gim thick interfaces, and (iii) the Ni substrate. The selected area diffraction (SAD) pattern analysis (shown in Figure 3) clearly identifies each phase. Nickel and diamond exhibited single crystalline diffraction patterns while the
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