A New, Nearly Single-Domain Surface Structure of Homoepitaxial Diamond (001) Films
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were annealed with pure hydrogen plasma for 5 minutes for etching treatment while the temperature was kept at growth temperature. The samples were then transferred to an UHV chamber equipped with a STM and LEED system from CVD chamber through air. The base pressure of the UHV chamber was maintained at 1.0xl0"1° Torr while STM and LEED observations were made. STM observations were performed at room temperature in both constant height and constant current modes. After STM observations, the samples were transferred from the sample holder of the STM to that of LEED apparatus for LEED observations. RESULTS In order to analyze the morphology of the diamond (001) surface, we acquired STM images of the same film in the different regions in a 1.5 x 1.5 mm2 area. Figure 1 shows a typical 29.4 x 29.4 nm2 STM image of the diamond (001) film. It shows a dimer-type 2x1 reconstruction structure with clearly resolved dimer rows. The adjacent dimer rows are spaced 0.50 nm apart. The surface consists of A-type (2xl) terraces and B-type (lx2) terraces separated by single-layer steps, marked A and B. The dimer rows on the alternating terraces change their orientation by 900. The single-layer steps can be seen, marked SA and SB, where dimer rows on the upper terraces are parallel to or normal to the step edges, respectively. The step-down direction is from the lower right to the upper left in the [110] direction. As shown in figure 1, the dimerized surface structures comprise A-type (2xl) terraces with long dimer rows in the [110] direction and B-type (lx2) terraces with short dimer rows in the S[110] direction. The distribution of the terraces is not uniform. A-type (2xl) terraces dominate the surface, with Saverage width 3.15 rm in the [110] Sdirection, while the average width of Btype (lx2) terraces in the same [110] direction is 1.14 nm. By measurement of the average terrace width, the calculated misorientation of this surface is 2.380 toward [110] direction in agreement of the misorientation of the substrate measured by x-ray diffraction. Most of the STM images we obtained from this surface have the same 7j features as above. However, as shown in figure 2, in some regions, we observed an even distribution of A-type 5.0 nm (2xl) and B-type (lx2) terraces. The diamond (001) surface exhibits
IFig. 1 A typical STM image of the diamond (001) film
remarkably irregular domains locally in
i prown on the 2.30 off (001) diamond substrate, with 2.30 hn the [110] and 0.20 in the [110] directions showing Learly single-A-domain structure (sample bias: 860 mV; tlunneling current: 0.6 hA).
contrast to the regular atomically flat domains on the Si(001) surface. Since diamond (001) substrates are much rougher than Si(001) surfaces, it is not
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surprising to observe different features locally on the same surface of the diamond (001) films. Figure 3 shows a LEED 2x1 pattern of this surface. From the observation of surface
5.0 nm
Fig. 2 STM image of the diamond (001) film showing local even distribution of A-type (2xl) and B-type (lx2) terra
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