Open Access
Add to BibSonomyAbstract
Combination of the oxidation of reaction-sintered silicon carbide (RS-SiC) and the polishing of the oxide is an effective way of machining RS-SiC. In this study, anodic oxidation, thermal oxidation, and plasma oxidation were respectively conducted to obtain oxides on RS-SiC surfaces. By performing scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDX) analysis and scanning white light interferometry (SWLI) measurement, the oxidation behavior of these oxidation methods was compared. Through ceria slurry polishing, the polishing properties of the oxides were evaluated. Analysis of the oxygen element on polished surfaces by SEM-EDX was conducted to evaluate the remaining oxide. By analyzing the three oxidation methods with corresponding polishing process on the basis of schematic diagrams, suitable application conditions for these methods were clarified. Anodic oxidation with simultaneous polishing is suitable for the rapid figuring of RS-SiC with a high material removal rate; polishing of a thermally oxidized surface is suitable for machining RS-SiC mirrors with complex shapes; combination of plasma oxidation and polishing is suitable for the fine finishing of RS-SiC with excellent surface roughness. These oxidation methods are expected to improve the machining of RS-SiC substrates and promote the application of RS-SiC products in the fields of optics, molds, and ceramics.
© 2013 Optical Society of America
1. Introduction
Reaction-sintered silicon carbide (RS-SiC) is a promising material for optical mirror devices in space telescope systems [1], mold components in aspheric lens formation apparatus [2], substrates for composites in nuclear fusion equipment [3], and ceramic corrosion-resistant parts in chemical plants [4], as it has excellent mechanical and chemical properties such as a low thermal expansion coefficient, high thermal conductivity, high radiation resistance, high specific stiffness, good size stability, high bending strength, and a low manufacturing cost [5, 6]. Therefore, the fabrication and machining of RS-SiC are a focus of research in the fields of optics, molds, and ceramics [7, 8].
However, RS-SiC is a difficult-to-machine material because of its high hardness and chemical inertness [9, 10]. Moreover, the composition and structure of RS-SiC are not uniform [11, 12]. The fabrication process of RS-SiC generates SiC and Si domains as the major components in the substrate [13, 14]. Therefore, both the rough figuring and fine finishing of RS-SiC are difficult to realize and the application of RS-SiC products is limited.
Up to now, many techniques have been developed for processing RS-SiC [15, 16], but few of them can achieve a high material removal rate in rough figuring and yield an ultrasmooth surface in fine finishing. In the case of the widely used techniques of diamond lapping [17] and plasma chemical vaporization machining (PCVM) [18], scratches and bumpy structures can be observed on the processed surfaces by scanning electron microscopy (SEM) and scanning white light interferometry (SWLI), as shown in Figs. 1(a) to 1(d) because the hardnesses and chemical reactivities of Si and SiC in RS-SiC differ.
Fig. 1 SEM and SWLI images of the processed RS-SiC surfaces. (a) Mechanical material removal by diamond lapping observed by SEM. (b) Chemical material removal by PCVM observed by SEM. (c) Mechanical material removal by diamond lapping observed by SWLI. (d) Chemical material removal by PCVM observed by SWLI.
Fortunately, the oxidation product of both Si and SiC is silica (SiO2) [19, 20], which makes it feasible to transform the complex hard RS-SiC surface to a uniform soft oxide layer. In addition, a high material removal rate in the rough figuring and an excellent surface roughness in the fine finishing of SiO2 can be obtained by many existing techniques [21, 22]. Therefore, an effective way of obtaining a high material removal rate or yielding an ultrasmooth surface in the machining of RS-SiC substrates is to combine the surface oxidation of RS-SiC and the polishing of the oxide.
To evaluate the combined process, we generated oxide layers on RS-SiC surfaces by anodic oxidation, thermal oxidation, and plasma oxidation. To clarify the characteristics of these three oxidation methods, we compared the surface morphology before and after oxidation by SEM. To further clarify the oxidation behaviors of these three oxidation methods, the oxygen element distributions of the three oxidized RS-SiC surfaces were determined by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDX). To assess the polishing properties of the oxide layers on these three oxidized surfaces, ceria slurry polishing was conducted and surface roughnesses were measured by SWLI, and the rms and Ra values of the surface roughness were presented as a function of the polishing time. To further elaborate the oxidation and polishing processes, schematic diagrams of the three oxidation methods with corresponding polishing parameters were constructed, and suitable application conditions for these three oxidation methods were proposed.
2. Oxidation apparatus
The initial RS-SiC specimens were prepared by diamond lapping, and the surface morphology of a specimen is shown in Figs. 1(a) and 1(c). The anodic oxidation of RS-SiC was conducted using a three-phase potentiostat (VersaSTAT 4: Princeton Applied Research Corporation). The electrolyte used in the oxidation system was a mixture of hydrogen peroxide (H2O2), hydrochloric acid (HCl), and ultrapure water (H2O). A schematic diagram of the anodic oxidation system is shown in Fig. 2(a). The thermal oxidation was conducted utilizing a lamp annealer (MILA-5000: ULVAC-RIKO Inc.). Atmospheric-pressure water vapor plasma was generated applying RF (f = 13.56 MHz) electric power, and helium-based water vapor (He + H2O) with a flow rate of 1.52 SLM was supplied as a process gas. A schematic diagram of the plasma oxidation system is shown in Fig. 2(b). The experimental parameters in the anodic oxidation, thermal oxidation, and plasma oxidation of RS-SiC are summarized in Table 1.
Table 1. Experimental parameters in oxidation of RS-SiC
3. Oxidation behavior and analysis
The surfaces before and after 10 min anodic oxidation, 30 min thermal oxidation, and 90 min plasma oxidation are shown in Figs. 3(a) and 3(d), Figs. 3(b) and 3(e), and Figs. 3(c) and 3(f), respectively. To elucidate the oxidation behaviors of the three methods, the anodic-oxidized surface, thermally oxidized surface, and plasma-oxidized surface were observed by SEM under high magnification, as shown in Figs. 4(a) to 4(c), respectively. To evaluate the oxide distributions of the three oxidized RS-SiC surfaces, the oxygen element distributions were analyzed by SEM-EDX, as shown in Figs. 5(a) to 5(c), respectively.
Fig. 3 Comparisons of surface morphologies before and after oxidation by SEM. (a) Before anodic oxidation. (b) Before thermal oxidation. (c) Before plasma oxidation. (d) After 10 min anodic oxidation. (e) After 30 min thermal oxidation. (f) After 90 min plasma oxidation.
Fig. 4 Particulars of the oxidized RS-SiC surfaces observed by SEM under high magnification. (a) Anodic-oxidized surface. (b) Thermally oxidized surface. (c) Plasma-oxidized surface.
Fig. 5 Surface morphologies and oxygen element distributions of (a) anodic-oxidized surface, (b) thermally oxidized surface, and (c) plasma-oxidized surface.
As shown in Figs. 3(d) to 3(f), there are few scratches on the three oxidized surfaces, although the initial surfaces, which were prepared by diamond lapping, had many scratches, as shown in Figs. 3(a) to 3(c). We hypothesize that there are two reasons for the disappearance of scratches from the oxidized RS-SiC surfaces [5]. First, the area with scratches has a larger surface area than the other areas, and the oxidation of RS-SiC increases its volume; thus, the scratches are closed by the expansion of the oxide. Second, the area surrounding the scratches has a higher oxidation rate because of lattice strain; thus, the rapidly expanding oxide fills the scratches. Through the closing and filling of scratches by oxidation, scratches are eliminated from the oxidized RS-SiC surfaces. This is the main similarity among the three oxidation methods. However, as the oxidation mechanisms differ among the three methods, there are many differences in the oxidation behaviors, which will be presented in turn.
3.1 Characteristics after anodic oxidation
From the anodic-oxidized surfaces in Figs. 3(d), 4(a), and 5(a), it was found that the SiC domains have a higher oxidation rate than the Si domains, which can be clearly concluded from the oxygen element distribution. We had also investigated the anodic oxidation of single-crystal Si and 4H-SiC in our system. Under the same experimental conditions, it was observed that the oxidation rate of 4H-SiC was slightly higher whereas that of Si was much lower than that of RS-SiC. Moreover, for most anodic-oxidized grains, the boundary areas had a higher oxidation rate than the central areas. Furthermore, there were many cracks and projections on the anodic-oxidized surface. We hypothesize that is because the oxidation of Si/SiC to SiO2 is a volume expansion process, and the swelling pressure is generated in both the thickness direction and the plane direction. The distribution of this pressure generated by an oxidized grain is determined by the oxidation rate distribution of the grain. Therefore, in the thickness direction, the pressure ejects the oxide, resulting in the formation of projections; in the plane direction, the pressure presses the neighboring grains, causing the introduction of cracks in the weak areas.
3.2 Characteristics after thermal oxidation
From the thermally oxidized surfaces in Figs. 3(e), 4(b), and 5(b), it is interesting to note that the thermal oxidation rate of Si grains is higher than that of SiC grains in RS-SiC as the oxide layer of the Si grains is thicker than that of the SiC grains. This is considerably different from the behavior of anodic-oxidized RS-SiC. This can also be proved by the experimentally verified fact that single-crystal Si has a higher thermal oxidation rate than single-crystal SiC [19, 20]. Moreover, it was found that the oxidized surface of each crystal grain of Si or SiC is very smooth, which indicates that the oxidation rate in each crystal grain is uniform. Taking one crystal grain in RS-SiC into consideration, regardless of whether it is Si or SiC, the thermal oxidation behavior exhibits no difference from that of a single Si or SiC crystal; thus, the oxide surface of each crystal grain in RS-SiC is flat. However, the oxidation rate is different among different Si and SiC crystal grains, as shown in Figs. 4(b) and 5(b), because the orientation of each crystal grain is different. Therefore, the thermal oxidation rate is not uniform over the entire RS-SiC surface and there are bumpy structures on the thermally oxidized surface. However, there are no cracks or projections on the thermally oxidized surface, which is in strong contrast to the anodic-oxidized surface. Although there was also swelling pressure generated by the volume expansion of the oxide in the thermal oxidation of RS-SiC, the oxidation rate in each Si and SiC grain is uniform; thus, this pressure is limited to within the thickness direction, and the pressure distribution is uniform. Therefore, the limited and uniform pressure leads to a smooth oxide surface in each grain without any cracks or projections.
3.3 Characteristics after plasma oxidation
From the plasma-oxidized surfaces in Figs. 3(f) and 4(c), it is difficult to judge whether the oxidation rate of Si grains in RS-SiC is higher or lower than that of SiC grains. Moreover, the uniform oxygen element distribution on the entire plasma-oxidized surface in Fig. 5(c) indicates that the oxidation rate is almost uniform in Si and SiC domains in the plasma oxidation of RS-SiC, which is considerably different from the cases of anodic oxidation and thermal oxidation. As the plasma oxidation rate is uniform on the entire surface, there are no projections or cracks in contrast to the anodic-oxidized surface. Furthermore, as the oxidation rates of different Si and SiC grains are uniform, there are no bumpy structures on the plasma-oxidized surface, which is also in contrast to the thermally oxidized surface.
4. Polishing of oxide by ceria slurry
As the aim of the oxidation is to machine RS-SiC, the polishing properties of the oxide layers on the three oxidized surfaces are the critical criteria for evaluating the three oxidation methods. Therefore, we conducted the ceria slurry polishing of the anodic-oxidized surfaces, thermally oxidized surfaces, and plasma-oxidized surfaces, and discuss the evolution of surface roughness with the polishing time.
4.1 Ceria slurry polishing system
The surfaces were evaluated after 10 min anodic oxidation, 30 min thermal oxidation, or 90 min plasma oxidation, as shown in Figs. 6(a) to 6(c), and the rms and Ra values of their surface roughness were 159.968 nm and 98.434 nm, 7.171 nm and 5.569 nm, and 1.090 nm and 0.864 nm, respectively. The surface roughnesses increased after anodic oxidation and after thermal oxidation relative to those of the original surface in Fig. 1(c), because there were projections and cracks on the anodic-oxidized surface and bumpy structures on the thermally oxidized surface. After oxidation, the three oxidized surfaces were polished with ceria slurry. A schematic diagram of the ceria slurry polishing system is shown in Fig. 7. The specimen and polishing pad were both immersed into the slurry, and the specimen surface was abraded by the polishing pad. The polishing parameters are listed in Table 2.
Fig. 6 Surface roughnesses measured by SWLI. (a) After 10 min anodic oxidation. (b) After 30 min thermal oxidation. (c) After 90 min plasma oxidation.
Table 2. Ceria slurry polishing parameters
4.2 Polishing results and discussion
After a certain polishing time, we measured the surface roughness by SWLI then continued the polishing process, with the aim of obtaining the evaluation of surface roughness evolutions with the polishing time. The appropriate polished results obtained for an anodic-oxidized surface, thermally oxidized surface, and plasma-oxidized surface are shown in Figs. 8(a) to 8(c); the rms and Ra of their surface roughness were 4.556 nm and 3.477 nm, 0.920 nm and 0.726 nm, and 0.626 nm and 0.480 nm, and the corresponding polishing times were 220 min, 60 min, and 40 min, respectively. The power spatial density (PSD) is compared among the three oxidized surfaces in Fig. 6 and the three appropriate polished surfaces in Fig. 8, as shown in Fig. 9(a). The evolution of the rms and Ra values of the three polished surfaces is summarized in Fig. 9(b). SEM-EDX analyses of the three appropriate polished surfaces in Fig. 8 were conducted to evaluate the newly exposed surfaces, as shown in Fig. 10(a) to 10(c).
Fig. 8 Appropriate polished results of (a) anodic-oxidized surface (polishing time: 220 min), (b) thermally oxidized surface (polishing time: 60 min), and (c) plasma-oxidized surface (polishing time: 40 min).
Fig. 9 Comparative analysis of polishing results. (a) PSD comparisons among the three oxidized surfaces and the three appropriate polished surfaces. (b) The evolution of the rms and Ra values of the three polished surfaces with the polishing time.
Fig. 10 Surface morphologies and oxygen distributions of appropriate polished (a) anodic-oxidized surface, (b) thermally oxidized surface, and (c) plasma-oxidized surface.
From the SWLI measurement results in Fig. 8 and the PSD comparisons in Fig. 9(a), we found that the surface roughnesses were significantly reduced after polishing for an appropriate time. As shown in Fig. 9(b), with increasing polishing time, the surface roughnesses of the anodic-oxidized surface rapidly decreased in the first 100 min of polishing, whereas further polishing had little effect. The rms and Ra values for the thermally oxidized surface reached their optimal values of 0.920 nm and 0.726 nm after 60 min polishing, respectively, and deteriorated after further polishing. For the plasma-oxidized surface, rms and Ra attained optimal values of 0.626 nm and 0.480 nm after 40 min polishing, respectively, and deteriorated after further polishing. The different polishing properties of the three oxidized surfaces depended on differences in the oxidation rate and oxide morphology. For the anodic-oxidized surface, the oxidation rate of SiC grains was higher than that of Si grains in RS-SiC and projections and cracks were generated; thus, the surface roughnesses could be reduced by removing the uneven oxide and it was difficult to obtain an ultrasmooth rms surface roughness of less than 1 nm. For the thermally oxidized surface, the oxidation rate of SiC grains was lower than that of Si grains and bumpy structures were introduced; thus, after a suitable polishing time an optimized rms surface roughness of 0.920 nm was obtained, which increased with further polishing. For the plasma-oxidized surface, the oxidation rate of SiC grains was similar to that of Si grains and there were uniform oxide layers; thus, an optimal rms surface roughness of 0.626 nm was obtained after an appropriate polishing time, which increased with further polishing, similar to the polishing properties of the thermally oxidized surface.
From the surface morphologies and oxygen element distributions of the three appropriate polished surfaces in Fig. 10, we found that after polishing for an appropriate time, there was little, a large amount, and hardly any oxide remaining on the anodic-oxidized surface, thermally oxidized surface, and plasma-oxidized surface, respectively. The different amounts of the oxides on these three surfaces were in accord with the analysis of surface roughness evolution in Fig. 9(b). As the thickness of the oxide layer is on the order of magnitude of 1 nm or 10 nm, it has almost no effect on the excellent properties of the RS-SiC body. In some fields, the remaining oxide will not affect the application of the polished RS-SiC substrate, such as RS-SiC mirrors for space telescope systems, because a thin metal film will be uniformly deposited to obtain high reflectivity. However, in other applications, such as mold components or ceramic corrosion-resistant parts, the remaining oxide will affect the chemical, thermal, electrical, and mechanical properties of the newly exposed RS-SiC surface. Therefore, in these applications there should be no oxide remaining on the polished surface, which can be achieved by a combination of plasma oxidation and polishing.
5. Schematic analysis and application prospects
Schematic diagrams of anodic oxidation, thermal oxidation, and plasma oxidation combined with polishing processes are shown in Figs. 11(a) to 11(c), respectively. The oxidation behavior and polishing properties of the oxide layers determine the suitable application conditions for these three oxidation methods. Through a schematic analysis of the three oxidation methods followed by polishing the optimal combination of a suitable oxidation method of RS-SiC and an appropriate polishing of the oxide separately or simultaneously can be determined; thus, the rapid figuring of RS-SiC with a high material removal rate and the fine finishing of RS-SiC with an excellent surface roughness can be easily obtained.
Fig. 11 Schematic diagrams of the three oxidation methods combined with polishing process. (a) Anodic oxidation and polishing. (b) Thermal oxidation and polishing. (c) Plasma oxidation and polishing.
Since the anodic oxidation rate of SiC grains in RS-SiC is higher than that of Si grains, the material compositions from the surface to the interior along the cross-sectional direction are pure oxide, oxide + Si, oxide + Si + SiC, then Si + SiC. The Vickers hardnesses (GPa) of SiC, ceria, SiO2, and Si are 24-28 [23], 5-7.5 [24], 7.6 [25], and 7-9 [26], respectively. On the anodic-oxidized surface, the projections can be easily and gently removed, as the hardness of ceria is slightly lower than that of SiO2 or Si. However, the cracks are difficult to remove, particularly the cracks that penetrate deeply into the SiC grains, as the hardness of ceria is much lower than that of SiC. Therefore, it is difficult to obtain an ultrasmooth surface by anodic oxidation. However, anodic oxidation can transform the hard SiC grains in RS-SiC to soft oxide, and the hardness of SiO2 is similar to that of Si and much lower than that of SiC; thus, anodic oxidation can be used for the rapid figuring of RS-SiC.
To verify the feasibility of anodic oxidation for the rapid figuring of RS-SiC, according to the anodic oxidation parameters in Table 1, we calculated the average oxidation depth in the anodic oxidation of RS-SiC by SWLI measurements before and after hydrofluoric acid (HF) etching. The surface profiles after 5 s, 60 s, and 1800 s anodic oxidation are shown in Figs. 12(a) to 12(c); the corresponding average oxidation depths are 25 nm, 70 nm, and 163 nm, respectively, and the average oxidation depth as a function of the oxidation time is shown in Fig. 12(d). The oxidation area in our anodic oxidation system is 1 cm2 and the average oxidation depth after 5 s anodic oxidation is 25 nm. Therefore, if we conduct the anodic oxidation of RS-SiC and the polishing of the oxide simultaneously, the material removal rate can exceed 30 × 10−3 mm3/min, which is ten times larger than that of PCVM [18], and the surface roughness after anodic oxidation and polishing is lower than that after PCVM. Furthermore, the anodic oxidation rate can be easily improved by applying a power with higher potential and an electrolyte with higher concentration, and the oxidation area can also be enlarged by increasing the contact area. Therefore, although the surface roughness after polishing an anodic-oxidized surface is unsatisfactory, combination of simultaneous anodic oxidation and polishing is efficient for the rapid figuring of large-scale RS-SiC substrates.
Fig. 12 Profiles of anodic oxidize surfaces and average oxidation depth as a function of the oxidation time. (a) After 5 s oxidation. (b) After 60 s oxidation. (c) After 1800 s oxidation. (d) The average oxidation depth as a function of the oxidation time.
Since the thermal oxidation rate of SiC grains in RS-SiC is lower than that of Si grains, the material compositions from the surface to the interior along the cross-sectional direction are pure oxide, oxide + SiC, oxide + Si + SiC, then Si + SiC [5]. Therefore, to obtain an ultrasmooth surface by polishing a thermally oxidized surface, the polishing depth should be kept to within the uniform oxide layer. As there is some remaining oxide, which will affect the properties of the newly exposed surface, polishing of the thermally oxidized surface can be used when the application is unaffected by the presence of surface components, such as RS-SiC mirrors used in space telescope systems, as mentioned previously. Moreover, thermal oxidation is not limited by the shape of the substrate; thus, it can be used for machining RS-SiC mirrors with complex shapes by polishing the thermally oxidized surface.
Since the plasma oxidation rate of SiC grains in RS-SiC is almost identical to that of Si grains, the material compositions from the surface to the interior along the cross-sectional direction are only pure oxide followed by Si + SiC. Therefore, it is easy to obtain an ultrasmooth surface by polishing the plasma-oxidized surface for an appropriate time, and there is no oxide remaining on the newly exposed RS-SiC surface, meaning that the excellent properties of RS-SiC are fully maintained. Therefore, the combination of plasma oxidation and polishing is considered to be an ideal technique for the fine finishing of RS-SiC substrates.
6. Conclusions
In this study, we conducted a comparative analysis on the oxidation behavior and polishing properties of oxide layers on RS-SiC, which were generated by anodic oxidation, thermal oxidation, and plasma oxidation. The following conclusions were obtained.
- (1) The combination of the oxidation of RS-SiC and the polishing of the oxide is an effective means of machining RS-SiC. As there are three kinds of oxidation methods have been introduced, most RS-SiC substrates can be processed by applying the most suitable of the three oxidation methods and appropriate polishing parameters.
- (2) Anodic oxidation is suitable for the rapid figuring of RS-SiC. Although the rms surface roughness increases after anodic oxidation, it can be reduced to 4.556 nm by polishing for an appropriate time. As the oxidation depth after 5 s anodic oxidation is 25 nm, if we simultaneously conduct the anodic oxidation of RS-SiC and the polishing of the oxide, a high material removal rate of 30 × 10−3 mm3/min can be easily obtained. Furthermore, the anodic oxidation rate can be improved by applying a power with higher potential and an electrolyte with higher concentration, and the oxidation area can also be enlarged by increasing the contact area.
- (3) Thermal oxidation can be used to obtain an ultrasmooth RS-SiC surface with an rms surface roughness of 0.920 nm after polishing for an appropriate time because a uniform oxide layer exists on the thermally oxidized surface. Although the oxidation area is limited by the equipment and there is oxide remaining on the appropriate polished surface, thermal oxidation is a suitable process for fabricating RS-SiC mirrors with complex shape for space telescope systems.
- (4) Plasma oxidation has a uniform oxidation rate on the entire RS-SiC surface, making it suitable for the fine finishing of RS-SiC, since it is easy to obtain an ultrasmooth surface with an rms roughness of 0.626 nm after slurry polishing. After polishing for an appropriate time, the excellent properties of RS-SiC are preserved on the newly exposed surface without any remaining oxide. Therefore, the combination of plasma oxidation and polishing is considered to be an ideal technique for the fine finishing of RS-SiC substrates.
Therefore, the combination of the three oxidation methods with appropriate polishing parameters will improve the machining of RS-SiC substrates and promote the application of RS-SiC products in the fields of optics, molds, and ceramics.
Acknowledgments
This work was supported by the staffs and students of the Research Center for Ultra-precision Science and Technology of Osaka University. The authors also express their gratitude to Prof. Y. Sano of Osaka University for providing the thermal oxidation equipment.
References and links
1. S. Suyama, T. Kameda, and Y. Itoh, “Development of high-strength reaction-sintered silicon carbide,” Diamond Related Materials 12(3–7), 1201–1204 (2003). [CrossRef]
2. S. W. Pang, T. Tamamura, M. Nakao, A. Ozawa, and H. Masuda, “Direct nano-printing on Al substrate using a SiC mold,” J. Vac. Sci. Technol. B 16(3), 1145–1149 (1998). [CrossRef]
3. A. Sayano, C. Sutoh, S. Suyama, Y. Itoh, and S. Nakagawa, “Development of a reaction-sintered silicon carbide matrix composite,” J. Nucl. Mater. 271–272, 467–471 (1999). [CrossRef]
4. D. A. Ersoy, M. J. McNallan, and Y. Gogotsi, “Carbon coatings produced by high temperature chlorination of silicon carbide ceramics,” Mater. Res. Innovations 5(2), 55–62 (2001). [CrossRef]
5. X. M. Shen, Y. F. Dai, H. Deng, C. L. Guan, and K. Yamamura, “Ultrasmooth reaction-sintered silicon carbide surface resulting from combination of thermal oxidation and ceria slurry polishing,” Opt. Express 21(12), 14780–14788 (2013). [CrossRef] [PubMed]
6. S. P. Lee, Y. S. Shin, D. S. Bae, B. H. Min, J. S. Park, and A. Kohyama, “Fabrication of liquid phase sintered SiC materials and their characterization,” Fusion Eng. Des. 81(8–14), 963–967 (2006). [CrossRef]
7. S. Suyama, Y. Itoh, K. Tsuno, and K. Ohno, “Φ650 mm optical space mirror substrate of high-strength reaction-sintered silicon carbide,” Proc. SPIE 5868, 58680E, 58680E-10 (2005). [CrossRef]
8. H. Y. Tam, H. B. Cheng, and Y. W. Wang, “Removal rate and surface roughness in the lapping and polishing of RB-SiC optical components,” J. Mater. Process. Technol. 192–193, 276–280 (2007). [CrossRef]
9. H. Kitahara, Y. Noda, F. Yoshida, H. Nakashima, N. Shinohara, and H. Abe, “Mechanical behavior of single-crystalline and polycrystalline silicon carbides evaluated by Vickers indentation,” J. Ceram. Soc. Jpn. 109(1271), 602–606 (2001). [CrossRef]
10. Z. Y. Zhang, J. W. Yan, and T. Kuriyagawa, “Study on tool wear characteristics in diamond turning of reaction-bonded silicon carbide,” Int. J. Adv. Manuf. Technol. 57(1–4), 117–125 (2011). [CrossRef]
11. Y. W. Kim, M. Mitomo, H. Emoto, and J. G. Lee, “Effect of Initial α‐Phase Content on Microstructure and Mechanical Properties of Sintered Silicon Carbide,” J. Am. Ceram. Soc. 81(12), 3136–3140 (1998). [CrossRef]
12. O. P. Chakrabarti, P. K. Das, and J. Mukerji, “Growth of SiC particles in reaction sintered SiC,” Mater. Chem. Phys. 67(1–3), 199–202 (2001). [CrossRef]
13. T. Grande, H. Sommerset, E. Hagen, K. Wiik, and M. A. Einarsrud, “Effect of Weight Loss on Liquid-Phase-Sintered Silicon Carbide,” J. Am. Ceram. Soc. 80(4), 1047–1052 (1997). [CrossRef]
14. S. S. Shinozaki, J. E. Noakes, and H. Sato, “Recrystallization and Phase Transformation in Reaction-Sintered SiC,” J. Am. Ceram. Soc. 61(5–6), 237–242 (1978). [CrossRef]
15. J. Yan, Z. Zhang, and T. Kuriyagawa, “Mechanism for material removal in diamond turning of reaction-bonded silicon carbide,” Int. J. Mach. Tools Manuf. 49(5), 366–374 (2009). [CrossRef]
16. H. Cheng, Z. Feng, Y. Wang, and S. Lei, “Magnetorheological finishing of SiC aspheric mirrors,” Mater. Manuf. Process. 20(6), 917–931 (2005). [CrossRef]
17. H. Deng and K. Yamamura, “Smoothing of reaction sintered silicon carbide using plasma assisted polishing,” Curr. Appl. Phys. 12(3), S24–S28 (2012). [CrossRef]
18. K. Yamamura, Y. Yamamoto, and H. Deng, “Preliminary Study on Chemical Figuring and Finishing of Sintered SiC Substrate Using Atmospheric Pressure Plasma,” in 45th CIRP Conference on Manufacturing Systems 2012 3, 335–339 (2012).
19. Y. Song, S. Dhar, L. C. Feldman, G. Chung, and J. R. Williams, “Modified Deal Grove model for the thermal oxidation of silicon carbide,” J. Appl. Phys. 95(9), 4953–4957 (2004). [CrossRef]
20. B. E. Deal and A. S. Grove, “General Relationship for the Thermal Oxidation of Silicon,” J. Appl. Phys. 36(12), 3770–3778 (1965). [CrossRef]
21. K. Yamauchi, H. Mimura, K. Inagaki, and Y. Mori, “Figuring with subnanometer-level accuracy by numerically controlled elastic emission machining,” Rev. Sci. Instrum. 73(11), 4028–4033 (2002). [CrossRef]
22. F. H. Zhang, X. Z. Song, Y. Zhang, and D. R. Luan, “Figuring of an ultra-smooth surface in nanoparticle colloid jet machining,” J. Micromech. Microeng. 19(5), 054009 (2009). [CrossRef]
23. J. Qian, G. Voronin, T. W. Zerda, D. He, and Y. Zhao, “High pressure, high temperature sintering of diamond-SiC composites by ball milled diamond-Si mixtures,” J. Mater. Res. 17(08), 2153–2160 (2002). [CrossRef]
24. A. B. Shorey, K. M. Kwong, K. M. Johnson, and S. D. Jacobs, “Nanoindentation hardness of particles used in magnetorheological finishing (MRF),” Appl. Opt. 39(28), 5194–5204 (2000). [CrossRef] [PubMed]
25. E. Pippel, J. Woltersdorf, H. Ö. Ólafsson, and E. Ö. Sveinbjörnsson, “Interfaces between 4H-SiC and SiO2: microstructure, nanochemistry and near-interface traps,” J. Appl. Phys. 97(3), 034302 (2005). [CrossRef]
26. J. S. Williams, B. Haberl, and J. E. Bradby, “Nanoindentation of ion implanted and deposited amorphous silicon,” MRS Online Proceedings Library 843, T6.3.1/R10.3.1- T6.3.5/R10.3.5 (2005),DOI: http://dx.doi.org/10.1557/PROC-843-T6.3/R10.3.
