CHAPTER 5 ATOMIC HYDROGEN

Transcription

1 CHAPTER 5 TEMPERATURE DEPENDENT ETCHING OF THE DIAMOND (100) SURFACE BY ATOMIC HYDROGEN 5.1 Introduction Described in previous chapters of this dissertation are the results of the initial UHV STM studies of CVD diamond (100) epitaxial films. In Chapter 3, UHV STM studies were presented in contrast to STM studies of diamond by others that were done in air [1]. Careful measurement of the diamond (100) atomic surface reconstruction that resulted after CVD diamond growth was made and the reconstruction was determined to be a dimer (2x1) reconstruction. As described in Chapter 4, UHV STM studies of the growth mechanism of CVD diamond (100) were then carried out. The results of these experiments support a recent model for CVD diamond (100) growth that involves atomic hydrogen, which is the main ingredient in the CVD gas [2]. In this model, atomic hydrogen etches and/or converts nondiamond forms of carbon on the growth surface into diamond and this was supported by the data presented in Chapter 4. In this chapter, I describe the next step in my investigations, which was to examine the effects of prolonged exposure to atomic hydrogen on the diamond (100) surface. The interaction of atomic hydrogen with diamond is important not only because atomic hydrogen is involved in the CVD diamond growth process, but also because atomic hydrogen is used to etch diamond for microelectronic applications. This chapter describes experiments on the 50

2 effects of prolonged exposure to atomic hydrogen after the growth layer has been etched away and the (100)-(2x1) surface has reached a quasi steady state. In addition, the substrate temperature was varied during atomic hydrogen exposure in order to determine the temperature dependence of the etching of the diamond (100) surface. It is a common technique to end the CVD diamond growth process with a final step consisting of etching by atomic hydrogen. This serves two purposes, to remove any nondiamond forms of carbon remaining on the diamond surface, and to hydrogen terminate the diamond surface in order to make it more inert in air [3] and to increase surface electrical conductivity [4]. The hydrogen termination of the diamond (100) surface has been an area of considerable study [5]. Various techniques of hydrogen termination have been employed such as polishing the diamond surface on an iron wheel with diamond grit and a hydrocarbon, usually olive oil [6], hydrogen plasma exposure using a microwave cavity, and exposure to atomic hydrogen made by a hot tungsten filament. There have been reports of low-energy-electron diffraction (LEED) studies of atomic hydrogen etching of the diamond (100) surface [3] and a comparison between etching resulting from atomic hydrogen produced by a hot tungsten filament and a microwave plasma by Cheng et al. [7]. In Reference [7], it was concluded that atomic hydrogen produced by a hot filament made the diamond (100) surface rough and that atomic hydrogen produced by a microwave plasma made the surface smooth. This conclusion leads one to question what difference it makes how the atomic hydrogen is formed. It has been suggested that the difference is caused by the higher velocity ions in a hydrogen plasma [7]. The experiments in Reference [7] involved exposing the diamond (100) surface to atomic hydrogen at an 51

3 elevated temperature of 827 C for one hour. Then, the sample was exposed to atomic hydrogen at a much lower temperature of 527 C for 30 minutes. This last exposure was carried out to hydrogen terminate the diamond surface and it was assumed that it would not influence the surface morphology. To my knowledge, there have not been any reports of an investigation at the atomic scale that involves a temperature dependent study of the diamond (100) surface exposed to atomic hydrogen. I found that atomic hydrogen etches diamond (100) at temperatures much lower than 827 C, the growth temperature of CVD diamond. The results described here, the final chapter of this dissertation, show that the surface morphology resulting from atomic hydrogen etching is highly temperature dependent. It was found that etching by atomic hydrogen results in a rough surface at the atomic scale at T 200 C, a surface having vacancy islands and pits at T 500 C, and a smooth surface at T 1000 C. This explains the reported observations of Cheng et al. that the hot tungsten filament technique produced a rough (100) surface [7]. The final step of Cheng et al. was an atomic hydrogen etch at the low temperature of 527 C, which results in a rough surface. The STM results presented in Chapters 3 and 4 were limited to small area scans due to tunneling instabilities resulting from physisorbed hydrogen and carbon on the sample surface. Imaging such a surface with loosely bound atoms was problematic and short lived but necessary in order to study the CVD diamond growth process. Scanning tips did not last long because of contamination from the surface to the tip. During instances of tunneling current instabilities caused by this contamination, tip crashes would occur and often this 52

4 resulted in rendering the tip useless. In this case, a tip crash is when the digital feedback over corrects or under corrects as a result of the current instabilities and the tip comes into hard contact with the sample surface, usually deforming the tip. The results presented in this final chapter are without these problems because of three factors. The first important factor is that the samples are etched by atomic hydrogen after growth for at least five minutes, thereby removing the excess and loosely bound carbon from the surface. The second factor is that I found that desorbing the loosely bound hydrogen from the surface by heating the substrate to 800 C for one minute resulted in improvement of the tunneling current stability, which produced clearer STM images. Further heating to 1000 C removed the hydrogen-terminated surface and further enhanced the STM image quality. These techniques for cleaning the diamond surface can only be performed in UHV. The third and very important factor was the use of ultrasharp tungsten tips that are described in Chapter 2. These factors make possible the significant accomplishment of atomic resolution STM imaging over large areas measuring 80 x 80 nm 2. From images of large areas, both the atomic structure and large-scale morphology of the surface resulting from etching, growth, and other processes can be studied, as has been reported for Si and other semiconductors [8,9]. In addition, a better understanding of the temperature dependent etching of diamond (100) by atomic hydrogen will help in developing etching techniques for microfabrication, sample preparation and increase the reproducibility of experimental results. 5.2 Experiment The CVD diamond films were grown epitaxially on 2mm x 2mm x 0.25mm type 2b (100) diamond substrates. The films were grown for two hours in the UHV compatible hot 53

5 tungsten filament CVD reactor and were approximately 2 microns thick. The films were doped with boron during growth to increase their conductivity for STM studies. Without the incorporation of boron, the diamond surface would have become highly insulating when the hydrogen was desorbed by heating in UHV [10]. The CVD growth pressure was 30 Torr with the hydrogen, methane, and diborane gases having flow rates of 200 sccm, 0.5 sccm and 6.0 sccm, respectively. The substrates were resistively heated to 900 C using a tantalum heater foil. The tungsten filament temperature was that typically used for CVD diamond growth of 2200 C. The growth process was terminated by shutting off the methane flow and maintaining all of the other parameters for 5 minutes. This step is the post-growth etch with atomic hydrogen. The filament was then turned off followed by the sample heater and then the hydrogen flow being turned off. After the growth process was terminated, the CVD reactor was evacuated to 1x10-8 Torr and the samples were transferred to the UHV STM chamber via the linear translator without exposure to air. After verifying by STM that the diamond films were of good quality, the samples were returned to the CVD reactor, via the linear translator, for additional exposure to atomic hydrogen. The hydrogen flow rate, pressure, and filament temperature were 200 sccm, 30 Torr, and 2200 C, respectively. These parameters were the same as those for the CVD diamond growth to insure that the diamond surface was exposed to the same amount of atomic hydrogen flux as during growth. From this point on, two different groups of experiments were done. In group A, the sample temperature was a constant of 500 C and the atomic hydrogen exposure times were 2, 7, 12, and 17 minutes. After each additional 54

6 (a) UNSTRAINED BACKBOND (b) (d) [011] STRAINED BACKBOND [011] (c) (1 x 1) (2 x 1) [100] S B Step SILICON (3 x 1) [011] HYDROGEN [011] Dimer row Figure 5.1 Schematic of the Si (100) hydrogen-terminated surface reconstructions. (a) (1x1) dihydride configuration. (b) (2x1) monohydride configuration. (c) (3x1) with both the dihydride and monohydride configurations. (d) Top view of the hydrogen free (100) surface near an S B step. The sizes of the circles are in descending order from the topmost atomic layer to inner atomic layers. The open circles in (d) represent atoms with dangling bonds. exposure, the sample was translated to the UHV STM and analyzed to determine if additional etching had an effect on the surface morphology. In the group B experiments, the exposure time was held constant, 5 minutes, with the substrate temperature being the variable and having the values of 200, 500 and 1000 C. Each diamond sample was then returned to the UHV STM to determine whether the atomic surface structure had changed as a result of the atomic hydrogen etching at the different temperatures. 5.3 Results and Discussion In order to understand diamond and its possible surface reconstructions, Si would be a good example to consider. Si has the same crystal lattice composed of tetrahedral bonds as diamond. In addition, Si (100), like diamond (100), reconstructs in the hydrogen-terminated (1x1), (2x1) and (3x1) configurations and the clean (2x1) configuration. Figure 5.1 shows the Si (100) surface accommodates hydrogen in the monohydride and dihydride configurations. 55

7 (3x1) I I S B (2x1) I S A Figure 5.2 UHV STM image of diamond (100) (2x1):H surface exposed to atomic hydrogen acquired using a tip voltage of 1.5 V. Islands marked I having a (3x1) reconstruction are observed. The arrows marked indicate antiphase boundaries. The image area is 20 x 20 nm 2. Figure 5.2 shows a UHV STM image of a CVD grown boron doped epitaxial diamond (100) film after exposure to atomic hydrogen for 5 minutes at a sample temperature of 500 C. As stated in Chapter 3, the diamond (100)-(2x1) surface exposed to atomic hydrogen is known to be monohydride terminated [11], and is denoted as diamond (100)- (2x1):H. In Figure 5.2, terraces are observed consisting of atomic planes with dimer rows rotated in the x-y plane 90 relative to the dimer rows in the adjacent atomic planes, indicating a two domain (2x1) dimer reconstruction. Two different types of terrace steps are observed, marked S A and S B in Figure 5.2. Single atomic steps that consist of dimer rows parallel to the step edge are S A steps, and single atomic steps that consist of dimer rows that 56

8 (3x1) Figure 5.3 UHV STM image of diamond (100)-(2x1):H surface using a tip voltage of 1.5 V showing a (3x1) reconstruction on the step edge. The image area is 9.5 x 9.5 nm 2. are perpendicular to the step edge are S B steps. In Figure 5.2, unmarked arrows indicate regions where S A steps were etched perpendicular to the rows resulting in islands marked I. I believe the islands are due to etching and not the growth process because the islands were not observed until the 500 C etching. The islands have a (3x1) reconstruction consisting of a wide monohydride-terminated row and a narrow dihydride-terminated row, as indicated in Figure 5.2. The (3x1) reconstruction on diamond (100) has been previously observed along step edges [12]. There are many anti-phase boundaries in Figure 5.2 marked Φ, and these boundaries are necessary in order for a terrace to accommodate both (2x1) and (3x1) reconstructions. 57

9 Figure 5.4 UHV STM image of an area to the left of the area shown in Figure 5.2. An etch pit with a bright structure inside is observed. The image area is 20 x 10nm 2. Figure 5.3 shows a higher resolution UHV STM image of the same film using negative tip polarity. In Figure 5.3, the S A step of the large terrace has a (3x1) reconstruction. Adjacent to the (3x1) reconstruction, I observe, for the first time, two rows of atomic-sized structures, indicated by the arrow in Figure 5.3. I conjecture that these structures are sites where the atoms of the dihydride row have rebonded with atoms of the underlying plane. In the hydrogen-terminated Si (100)-(3x1):1.3H surface, the reconstruction occurs in large domains [13]. In diamond (100), I conjecture that the (3x1) reconstruction occurs only on islands and step edges because the small lattice constant of diamond does not provide enough space for dihydride formation within the terraces. It has been theoretically predicted that the diamond (100)-(3x1):1.3H surface is more stable than the diamond (100)-(2x1):H surface [14]. The greater stability of the (3x1) reconstruction may result in a lower etch rate for this reconstruction. A lower etch rate may explain why the islands observed in Figure 5.3 have a (3x1) reconstruction. Figure 5.4 shows a UHV STM image of an area located slightly to the left of the area shown in Figure 5.2. A square etch pit several atomic layers deep and containing a bright 58

10 Figure 5.5 UHV STM image of a different area of the film shown in Figure 5.4 showing an etch pit with a bright structure inside. The image area is 25.0 x 22.5nm 2. circular structure having a diameter of approximately 2.5 nm is observed. Other regions of the film showed similar etch pits with bright structures, as shown in Figure 5.5. I conjecture that the bright structures are etch by-products or groups of hydrogen atoms because the structures disappear after the sample is heated to 1000 C, as shown in Figures 5.6 and 5.7. It is well known that hydrogen can be stored in carbon nanotubes and nanostructured carbon materials [15]. Similar sized bright structures have been observed in etched Si and attributed to etch byproducts [13,16]. The pit in Figure 5.5 is pyramidal in shape and has {111} faces. This shows that, at 500 C, the etch rate in the {111} direction is slower than that in the {100} and {110} directions. As a result, step retreat is not fast enough to erase the etch pits. 59

11 a) b) c) α α d) e) β α β α β Figure x 80nm 2 of a diamond (100) film after sequential etching by atomic hydrogen at 500 C. (a) After 2 minutes of etch. (b) After 7 total minutes. (c) After 12 total minutes. (d) After oxygen exposure and 5 additional minutes for a total of 17 minutes of atomic hydrogen. (e) After heating in UHV to 1000 C for 1 minute. The unmarked arrows indicate material aggregated in the pits. α indicates the original etch pits and β indicates the new etch pits after oxygen exposure. 60

12 a) b) c) α β α Figure 5.7 UHV STM images 40 x 40 nm 2 of a CVD epitaxial diamond (100) film after sequential exposures to atomic hydrogen at 500 C. (a) After 2 minutes of exposure. (b) After 7 total minutes of exposure and heated in UHV to 800 C for 1 minute. (c) After exposure to Torr of oxygen for 1 minute and an additional 5 minute atomic hydrogen etch for a total of 17 minutes and heated in UHV to 1000 C for 1 minute. The unmarked arrows indicate hydrogen that has aggregated in the etch pits. α indicates the original nucleated etch pits and β indicates the new etch pits that were nucleated by the oxygen. 61

13 Group A, Constant Temperature Experiments In order to further explore pit formation and how pits evolve, the previously mentioned group A experiments were done. Figures 5.6 and 5.7 show the results of the 500 C time exposure experiments of group A. These results show that the pit nucleation density does not significantly change with added exposure to atomic hydrogen. But, with increasing exposure time, the pits increase in area and depth which is what one might expect with additional surface etching. Although the pits are becoming larger with additional atomic hydrogen exposure, the pits on each new surface are about the same size relative to each other. The small variation in pit size indicates that over time no new pits are being nucleated. The arrows marked α in figures 5.6 and 5.7 are indicating the original pits. Only until exposure to oxygen and then further etching with atomic hydrogen are new pits nucleated, as indicated in Figures 5.6(d), 5.6(e) and 5.7(c) by the arrows marked β. It is unknown what the cause of nucleation is for the first group of pits, but I hypothesize that they are the result of lattice dislocations. It is well known that etch pits on crystal surfaces are nucleated on lattice dislocations [17]. Figures 5.7(a), 5.7(b) and 5.7(c) show the dramatic improvement in the STM imaging of diamond (100) after annealing in UHV. Figure 5.7(a) is a UHV STM image of the hydrogen saturated (2x1) surface before annealing in UHV. Figure 5.7(b) shows the sample after heating to 800 C in UHV for 1 minute resulting in desorbtion of only the loosely bound hydrogen, and leaving the (2x1):H surface and the aggregated hydrogen in the pits. Figure 5.7(c) shows the sample after it was heated to 1000 C for 1 minute resulting in desorbtion of all the hydrogen in the etch pits and removal of the hydrogen that terminated 62

14 the (2x1) surface. Note the dramatic improvement in image quality shown in Figure 5.7(c) after the 1000 C anneal. Group B, Variable Temperature Experiments Figures show UHV STM images of the diamond (100)-(2x1) surface after exposure to atomic hydrogen for 5 minutes at substrate temperatures of 200, 500, and 1000 C. In these images, the diamond (100) surface was heated to 1000 C for 1 minute in UHV after the atomic hydrogen exposure in order to desorb the hydrogen physisorbed and chemisorbed on the surface. Using LEED and electron-energy-loss spectroscopy, it has been reported that desorbtion of hydrogen at 1000 C in UHV results in a non-hydrogen terminated diamond (100)-(2x1) surface [18], in agreement with Figures I found that the stability of the tunneling current increases after the hydrogen desorbtion. For example, Figures 5.9 and 5.10 show tiled STM images obtained one after the other showing excellent reproducibility. To my knowledge, STM images of the non-hydrogen terminated diamond (100)-(2x1) surface have not been reported in the open literature. I observe that, in the diamond (100)-(2x1) surface, the dimer rows are narrower than those in the diamond (100)- (2x1):H surface. Figures show that the temperature of the surface during exposure to atomic hydrogen had a significant effect on the resulting morphology. I have found that the morphologies shown in Figures are due to the atomic hydrogen exposure at the various temperatures instead of the subsequent annealing at 1000 C in UHV. 63

15 Figure 5.8 UHV STM image of the diamond (100)-(2x1) surface after atomic hydrogen etching with the sample temperature at 200 C, and annealed at 1000 C in UHV for 1 minute. The surface has a (2x1) reconstruction and is rough at the atomic scale. The image area is 40 x 40nm 2. 64

16 Figure 5.9 UHV STM tiled images of the diamond (100)-(2x1) surface after atomic hydrogen etching with the sample temperature at 500 C, and annealed at 1000 C in UHV for 1 minute. The area of each image is 40 x 40 nm 2. The arrow indicates one of many vacancy islands. 65

17 D A S A = Single step parallel to rows S B = Single step perpendicular to rows D = Double step parallel to rows S A S B Figure 5.10 UHV STM tiled images of the diamond (100)-(2x1) surface after atomic hydrogen etching with the sample temperature at 1000 C, and annealed at 1000 C in UHV for 1 minute. The area of each image is 40 x 40nm 2. The arrow marked indicates an antiphase island. The unmarked arrow is explained in the text. 66

18 Figure 5.11 UHV STM image of the diamond (100)-(2x1) surface after atomic hydrogen etching with the sample temperature at 1000 C, and annealed at 1000 C in UHV for 1 minute. The image area is 40 x 40nm 2. The arrow marked indicates an antiphase island. The unmarked arrows are explained in the text. 67

19 For example, additional annealing of the surface at 1000 C in UHV for 15 minutes did not result in any observable changes in morphology. In addition, films with any one of the three different morphologies shown in Figures could be converted to any of the two other morphologies by simply etching at that specific temperature. For example, a film with the smooth morphology of Figure 5.10 was exposed to atomic hydrogen with a sample temperature of 200 C and resulted in producing a surface morphology like that of Figure 5.8. The observed morphology was then changed back to the smooth morphology by etching at 1000 C. As shown in Figure 5.8, exposure at 200 C results in a very rough surface at the atomic scale. The rough surface shows that etching at 200 C is isotropic. No large pits are observed and the largest domain size is about 6.25nm 2. As shown in Figure 5.9, exposure at 500 C results in a surface that is smoother at the atomic scale with larger domains measuring about 100nm 2. In addition, this surface contains large single atomic layer vacancy islands, single height steps and deep pits. The pits have a pyramidal shape, as was previously discussed in the Group A experiments. The vacancy islands have an average length along the dimer rows that is 2.1 times greater than the average length perpendicular to the dimer rows. This shows that etching at 500 C is anisotropic and that it is 2.1 times more likely to occur along the dimer rows than perpendicular to them. Shown in Figures 5.10 and 5.11, exposure at 1000 C results in a smooth surface with single and double atomic steps, and the largest domains of the three experiments measuring approximately 350 nm 2. 68

20 The step morphology in Figures 5.10 and 5.11 shows that S B steps, in which the dimer rows are perpendicular to the steps, are very rough. However, S A steps, in which the dimer rows are parallel to the steps, are very smooth. In contrast, the 500 C etched sample shown in Figure 5.9 has rough S A steps. In addition, S A steps having a few dimer rows above them are not etched, as shown by the unmarked arrows in Figures 5.10 and Vacancy islands in Figures 5.10 and 5.11 consist mainly of single row vacancies and no large pits. These observations show that etching at 1000 C is highly anisotropic with the etch rate along the dimer rows much greater than that perpendicular to the rows. Si (100) has a similar anisotropic etch rate as diamond (100) in that Si etches faster parallel to the dimer rows than perpendicular to the dimer rows but, short-range step attraction and repulsion are also a determining factor of step morphology in Si (100) etching [19]. The S B steps are attracted to the lower S A steps and as a result, double B type steps (D B ) are the dominant double step in Si (100) [20]. In addition, the S B steps are repelled from the upper S A steps which inhibits double A type steps (D A ) [19, 20]. In Si (100) these short-range step interactions are enough to dominate the etch anisotropy [21]. In my results, S A and S B steps on diamond (100) do not interact enough to overcome the etch anisotropy. As a result, the dominant double step on diamond (100) formed as a result of etching is the A type, as shown in Figures 5.10 and This result is the opposite of what is found in Si (100) etching where D B steps are the dominant double step [21]. The S B to S A step attraction in Si (100) is attributed to the rebonding of the S B step to the lower terrace that has the S A step [19, 20]. In addition, etching of the Si dimers parallel to the rows is done in pairs [21]. This is because removal of one dimer would result in a 69

21 R Figure 5.12 UHV STM image 20 x 20nm 2 of a CVD boron doped diamond (100)-(2x1) film after a 5 minute atomic hydrogen etch with the sample temperature at 1000 C and a 1 minute 1000 C anneal in UHV. The arrows marked R indicate S B step rebonding and the arrow marked indicates an aniphase boundary. nonrebonded step and a dangling bond on the lower terrace. Figures 5.12 and 5.13 show that in diamond (100) the S B step does rebond to the lower terrace as indicated by the arrows marked R. In addition, it can be seen in Figures 5.12 and 5.13 that the dimers that are removed from the ends of the dimer rows are removed in pairs. Since these results parallel those of Si it would be expected that the step interaction would allow D B steps to form. In diamond (100), D A steps are formed and therefore the step-step interaction must be much weaker. 70

22 R Figure 5.13 UHV STM image 20 x 20nm 2 of a CVD boron doped diamond (100)-2x1 film after a 5 minute atomic hydrogen etch with the sample temperature at 500 C and a 1 minute 1000 C anneal in UHV. The arrows marked R indicate S B step rebonding. 5.4 Conclusion Surface preparation of CVD diamond (100) was found to be important in STM studies. After CVD diamond (100) growth, it was necessary to etch the new film with atomic hydrogen and this resulted in removing the amorphous carbon growth layer. In addition desorbtion of hydrogen in UHV at 800 C resulted in removing the loosely bound hydrogen from the surface and improved the STM tunneling stability and therefore the image quality. The STM image quality was then further improved with additional heating of the diamond (100) film in UHV to a temperature of 1000 C. This resulted in removing the hydrogen- 71

23 terminated surface and hydrogen that may be aggregated in small surface structures such as pits by desorbing all of the remaining hydrogen. The temperature dependence on atomic hydrogen etching of the diamond (100) surface was investigated, and it was found that the higher temperatures, 1000 C, resulted in an atomically smooth surface with few dimer vacancies and large (2x1) dimer domains and a combination of S A, S B, and double A type steps. In addition, the higher the temperature the more the etch became anisotropic. With lower sample temperatures, as low as 500 C, the interaction with atomic hydrogen produced a qualitatively different surface morphology. This surface consisted of smaller (2x1) domains, small dimer islands, large etch pits, single atomic layer vacancy islands, many single dimer vacancies, and S A and S B steps. The S A steps of the 500 C etch experiments were rougher in comparison to the 1000 C etch experiments. In the 200 C atomic hydrogen etch experiments the sample surface morphology that was produced was atomically rough. This surface had the smallest (2x1) domains of the three temperature dependent experiments. The S A and S B steps were equally rough indicating isotropic etching. These results show that temperature has a significant effect on the interaction of atomic hydrogen with the diamond (100)-(2x1) surface. At high temperatures, the interaction occurs predominantly at the ends of dimer rows. These results may have implications for CVD diamond growth, which is currently not well understood. It is observed that CVD growth of high quality diamond requires a large ratio of hydrogen to methane gas and surface temperatures from 800 to 1000 C [22]. The high surface temperatures may be necessary to 72

24 limit the interaction of hydrogen to only carbon atoms at the ends of dimer rows thereby resulting in growth via step flow. 73

25 REFERENCES 1. J. B. Cui, K. Amtmann, J. Ristein, and L. Ley, Noncontacted temperature measurements of diamond by Raman scattering spectroscopy, J. Appl. Phys. 83(12), 7929 (1998). 2. D. S. Olson, M.A. Kelly, S. Kapoor, and S. B. Hagstrom, A mechanism of CVD diamond film growth deduced from the sequential deposition from sputtered carbon and atomic hydrogen, J. Mater. Res. 9, 1546 (1994). 3. B. D. Thoms, M. S. Owens, J. E. Butler, and C. Spiro, Production and characterization of smooth, hydrogen-terminated diamond C(100), Appl. Phys. Lett. 65, 2957 (1994). 4. S. Albin, and L. Watkins, Electrical properties of hydrogenated diamond, Appl. Phys. Lett. 56, 1454 (1990). 5. I. L. Krainsky, G. T. Mearini, and V. M. Asnin, Auger electron spectroscopy of the hydrogen terminated chemical vapor deposited diamond surface, Appl. Phys. Lett. 68, 2017 (1996). 6. B. B. Pate, Surf. Sci. 165, 83 (1986). 7. C. L. Cheng, H. C. Chang, J. C. Lin, and K. J. Song, Direct observation of hydrogen etching anisotropy on diamond single crystal surfaces, Phys. Rev. Lett. 78, 3713 (1997). 8. A. Hoeven, J. Lenssinck, D. Dijkkamp, E. van Loenen, and J. Dieleman, Scanningtunneling microscopy study of single-domain Si(001) surfaces grown by molecular-beam epitaxy, Phy. Rev. Lett. 63, 1830 (1989). 9. M. Chandler, D. A. Goetsch, C. M. Aldao and J. H. Weaver, Determination of dynamic parameters controlling atomic scale etching of Si(100)-(2x1) by chlorine, Phys. Rev. Lett. 74, 2014 (1995). 10. M. I. Landstrass, and K. V. Ravi, Hydrogen passivation of electrically active defects in diamond, Appl. Phys. Lett. 55, 1391 (1989). 11. R. E. Thomas, R. A. Rudder and R. J. Markunas, Atomic hydrogen adsorption on the reconstructed diamond (100)-(2x1) surface, J. Chem. Vap. Depos. 1, 6 (1992). 12. Y. Kuang, Y. Wang, N. Lee, A. Badzian, T. Badzian, and T. Tsong, Surface structure of homoepitaxial diamond (001) films, a scanning tunneling microscopy study, Appl. Phys. Lett. 67, 3721 (1995) 74

26 13. J. J. Boland, Role of bond-strain in the chemistry of hydrogen on the Si(100) surface, Surf. Sci. 262, 17 (1992). 14. S. H. Yang, D. A. Drabold, and J. B. Adams, Ab initio study of diamond (100) surfaces, Phys. Rev. B 48, 5261 (1993). 15. Y. Ye, C. C. Ahn, C. Witham, and B. Fultz, Hydrogen adsorption and cohesive energy of single-walled carbon nanotubes, App. Phys. Lett. 74, 2307 (1999). 16. J. J. Boland, Scanning tunneling microscopy of the interaction of hydrogen with silicon surfaces, Adv. Phys. 42, 129 (1993). 17. C. Kittel, Introduction to Solid State Physics, seventh edition, (John Wiley & Sons, Inc., New York, 1996), pp S. T. Lee and G. Apai, Surface phonons and CH vibrational modes of diamond (100) and (111) surfaces, Phys. Rev. B. 48, 2684 (1993). 19. E. Pehlke and J. Tersoff, Phys. Rev. Lett. 67, 465 (1991). 20. J. J. de Miguel, C. E. Aumann, S. G. Jaloviar, R. Kariotis, and M. G. Lagally, Phys. Rev. B 46, (1992). 21. Y. Gong, D. W. Owens, and J. H. Weaver, Etching of double-height-stepped Si (100)- 2x1: Steps and their interactions, Phys. Rev. B. 53, 144 (1996). 22. W.A. Yarbrough and R. Messier, Current issues and problems in the chemical vapor deposition of diamond, Science 242, 688 (1990). 75