ELSEVIER Surface and Coatings Technology 154(2002)276-28 Fabrication of silicon carbide whiskers and whisker-containing composite coatings without using a metallic catalyst Hyung Suk Ahn, Doo Jin Choi* Department of Ceramic Engineering, Yonsei University, 134 Shinchon-dong, Sudaemun-ku, Seoul 120-749 South Korea Received 2 October 2001; accepted 2 January 2002 Abstract Silicon carbide has been focused on by many researchers because of its outstanding mechanical and chemical properties. Silicon carbide whiskers are important for the reinforcement of ceramic matrix composites. However, metallic catalysts, which are ry for the growth of whiskers, can cause degradation of their properties. Thus, we have made silicon carbide whiskers without using the metallic catalyst. Whiskers were obtained with an input gas ratio of above 20, and their diameter decreased as he input gas ratio increased. As the input gas ratio [H2 (+N2)/MTS] increases, a transition from whisker growth to film growth occurred at a higher pressure. We also deposited whisker-containing coatings based on the above conditions by alternating the whisker growth and the matrix filling process. The coatings showed pebble-like structures, and their morphologies differed according to the growth condition of the whiskers in the coating layer. c 2002 Elsevier Science B V. All rights reserved Keywords: Silicon carbide, Whisker; CVD; Coating 1. Introduction fabricated by the former process did not show homo- geneous properties. Moreover, in order to synthesize Silicon carbide is an important material for potential whiskers by chemical vapor deposition, an additional applications in photoelectronics, high temperature sem process of forming the metallic catalyst is necessary. In conducting devices. hard wear resistant coatings and addition, the metallic catalyst that exists at the tip of protective barriers for corrosion or thermal oxidation. the whisker acts as an impurity. This can cause degra- All these applications are due to its unique properties dation in the mechanical properties of the composites such as wide band gap, high electron mobility, high To prevent this, another additional process is required to thermal conductivity and a high melting point. Thus, remove these catalysts. Considering all of these prob- many researchers have studied this material for various lems, we have made silicon carbide whiskers without using the metallic catalyst. We could then make Silicon carbide whiskers have been the subject of whisker-containing composite coating as well esearch for various applications because they are effec- tive materials for the reinforcement of various composite 2. Experimental materials due to their superb mechanical and chemical properties [1, 2]. Whiskers have been produced by sev eral processes, such as carbothermal reduction of silica Fig. I shows a schematic diagram of a LPCVD [3-5 reaction between silicon halides and CCL [6] system, which was used in these experiments. Silicon carbide whiskers and the whisker-containing coatings and chemical vapor deposition using a metallic catalyst were grown in a hot-wall type horizontal CVD reactor, such as Ni or Fe [7, 8]. Among these, the carbothermal which had a double-tube structure to prevent turbulent reduction and the chemical vapor deposition methods flow Methyltrichlorosilane(CH3 SiCl3, mrS)was used have been widely used. However, whiskers that were as a precursor. Since it has silicon and carbon in the Corresponding author. Fax: +82-2-365-5882 same mole ratio. it is easier to obtain stoichiometric E-mail address: drchoidj yonsei ac kr(D.. Choi) silicon carbide than other precursors [19-11]. Hydrogen 0257-8972/02/S- see front matter c 2002 Elsevier Science B V. All rights reserved PI:S0257-8972(02)000099
Surface and Coatings Technology 154 (2002) 276–281 0257-8972/02/$- see front matter 2002 Elsevier Science B.V. All rights reserved. PII: S0257-8972Ž 0 2. 00009-9 Fabrication of silicon carbide whiskers and whisker-containing composite coatings without using a metallic catalyst Hyung Suk Ahn, Doo Jin Choi* Department of Ceramic Engineering, Yonsei University, 134 Shinchon-dong, Sudaemun-ku, Seoul 120-749 South Korea Received 2 October 2001; accepted 2 January 2002 Abstract Silicon carbide has been focused on by many researchers because of its outstanding mechanical and chemical properties. Silicon carbide whiskers are important for the reinforcement of ceramic matrix composites. However, metallic catalysts, which are necessary for the growth of whiskers, can cause degradation of their properties. Thus, we have made silicon carbide whiskers without using the metallic catalyst. Whiskers were obtained with an input gas ratio of above 20, and their diameter decreased as the input gas ratio increased. As the input gas ratio wH2 2 (qN )yMTSx increases, a transition from whisker growth to film growth occurred at a higher pressure. We also deposited whisker-containing coatings based on the above conditions by alternating the whisker growth and the matrix filling process. The coatings showed pebble-like structures, and their morphologies differed according to the growth condition of the whiskers in the coating layer. 2002 Elsevier Science B.V. All rights reserved. Keywords: Silicon carbide; Whisker; CVD; Coating 1. Introduction Silicon carbide is an important material for potential applications in photoelectronics, high temperature semiconducting devices, hard wear resistant coatings and protective barriers for corrosion or thermal oxidation. All these applications are due to its unique properties such as wide band gap, high electron mobility, high thermal conductivity and a high melting point. Thus, many researchers have studied this material for various applications. Silicon carbide whiskers have been the subject of research for various applications because they are effective materials for the reinforcement of various composite materials due to their superb mechanical and chemical properties w1,2x. Whiskers have been produced by several processes, such as carbothermal reduction of silica w3–5x, reaction between silicon halides and CCl w6x, 4 and chemical vapor deposition using a metallic catalyst such as Ni or Fe w7,8x. Among these, the carbothermal reduction and the chemical vapor deposition methods have been widely used. However, whiskers that were *Corresponding author. Fax: q82-2-365-5882. E-mail address: drchoidj@yonsei.ac.kr (D.J. Choi). fabricated by the former process did not show homogeneous properties. Moreover, in order to synthesize whiskers by chemical vapor deposition, an additional process of forming the metallic catalyst is necessary. In addition, the metallic catalyst that exists at the tip of the whisker acts as an impurity. This can cause degradation in the mechanical properties of the composites. To prevent this, another additional process is required to remove these catalysts. Considering all of these problems, we have made silicon carbide whiskers without using the metallic catalyst. We could then make a whisker-containing composite coating as well. 2. Experimental Fig. 1 shows a schematic diagram of a LPCVD system, which was used in these experiments. Silicon carbide whiskers and the whisker-containing coatings were grown in a hot-wall type horizontal CVD reactor, which had a double-tube structure to prevent turbulent flow. Methyltrichlorosilane (CH SiCl , MTS 3 3 ) was used as a precursor. Since it has silicon and carbon in the same mole ratio, it is easier to obtain stoichiometric silicon carbide than other precursors w9–11x. Hydrogen
H.S. Ahn, D.J. Choi / Surface and Coatings Technology 154(2002)276-28 277 MFC 1 MFC 3 Fig 1. A schematic diagram of CVD-SiC system Table I The details of the deposition conditions for whisker growth and the composite coating Experim put gas Dilute Temperature MrS Dilute Deposition write [H2 (+N2)/MTSI Whisker growth 10 20 30 1100 1000 20/20 H2/N2 25/50 500/1050 30/20 25/50 750/1050 filling) was used as a carrier gas and as a diluting gas. Nitrogen was also used as a diluting gas to deposit the matrix in the whisker-containing coatings. The carrier gas and dilute gas flow rates were controlled by the mass flow controller(MFC). The source gas flow rate was con- trolled by adjusting the bubbler pressure and equilibrium vapor pressure of the MTs. all the processes, whisker- ing and coating were performed on isotropic graphite E substrates(Tokai Carbon Co., G347, Japan). All depo- sitions were performed at 1100 C. Details of the deposition conditions are in Table 1 g0012 Deposition rates were measured by comparing the weight changes before and after the depositions. The crystalline phase was confirmed with X-ray diffract try(Xrd)at a waveleng 15418A CuKa radiation). The microstructures of the deposit were examined with ing electron microscopy (SEM, Hitachi S-2700/FESEM, Hitachi S-4200) 3. Results Input Gas Ratio(H, /MTS) Fig. 2 shows the variation of the deposition rate as a Fig. 2. The variation of the deposition rate as a function of imput gas function of the input gas ratio at 1100C. As the input ratio (T-=1100C, deposition time=2 h)
H.S. Ahn, D.J. Choi / Surface and Coatings Technology 154 (2002) 276–281 277 Fig. 1. A schematic diagram of CVD–SiC system. Table 1 The details of the deposition conditions for whisker growth and the composite coating Experimental Input gas Dilute Temperature MTS Dilute gas Deposition ratio gas (8C) flow rate qcarrier gas time wH (qN )yMTSx 2 2 (sccm) flow rate (h) (sccm) Whisker growth 10 H2 25 250 2 20 500 30 750 40 1100 1000 Composite coating 20y20 H2 2 yN 25y50 500y1050 1y4 (whisker growthy 30y20 25y50 750y1050 matrix filling) Fig. 2. The variation of the deposition rate as a function of imput gas ratio. (Ts1100 8C, deposition times2 h.) was used as a carrier gas and as a diluting gas. Nitrogen was also used as a diluting gas to deposit the matrix in the whisker-containing coatings. The carrier gas and dilute gas flow rates were controlled by the mass flow controller (MFC). The source gas flow rate was controlled by adjusting the bubbler pressure and equilibrium vapor pressure of the MTS. All the processes, whiskering and coating were performed on isotropic graphite substrates (Tokai Carbon Co., G347, Japan). All depositions were performed at 1100 8C. Details of the deposition conditions are in Table 1. Deposition rates were measured by comparing the weight changes before and after the depositions. The crystalline phase was confirmed with X-ray diffractometry (XRD) at a wavelength of 1.5418 A˚ (using CuKa radiation). The microstructures of the deposits were examined with scanning electron microscopy (SEM, Hitachi S-2700yFESEM, Hitachi S-4200). 3. Results Fig. 2 shows the variation of the deposition rate as a function of the input gas ratio at 1100 8C. As the input
78 H.S. Ahn, D.J. Choi/Surface and Coatings Technology 154(2002)276-287 um 6um Fig 3 SEM images of the deposits which were produced at different input gas ratios: (a)a=10;(b)a=20; (c)a=30; and(d)a=40 gas ratio increased from 10 to 40, the deposition rates Frank, the axial growth occurs where screw dislocations decreased. In addition, the growth rate was exceedingly exist at the tip of the whisker, because those dislocations reduced between the input gas ratios of 10 and 20. The act as accommodation sites for the atoms to attach decreasing tendency became rather smoother and linear Thus, they can make growth proceed without two- over the input gas ratio of 20. The change in the growth rate relates to a difference in the deposition mechanism of CVD [12]. This difference seems to be caused by differences in deposition mechanisms Fig 3 are SEM images of the deposits. Their mor- phologies look quite different compared to that of an input gas ratio of 10. When the input gas ratio was 10, a film with a pebble-like structure was deposited. How- g ever, when the input gas ratio was over 20, whisker- shaped deposits were obtained. This tendency consistent with the deposition rate. Also, there are some differences between Fig. 3b and Fig. 3c, d. In Fig. 3b, thick and short whiskers were shown. In other words. a radial growth of the whisker occurred as well as an 5 axial growth. However, thin and long whiskers were s observed in Fig. 3c, d. Within these conditions, the axial growth seems to be the predominant growth mechanism Usually, the whisker growth can be separated into two Input Gas Ratio(H/MTS) mechanisms: axial growth and the radial growth, when it is done by vapor-solid mechanism. As reported by Fig. 4. The effect in input gas ratio on the mean whisker diameter
278 H.S. Ahn, D.J. Choi / Surface and Coatings Technology 154 (2002) 276–281 Fig. 3. SEM images of the deposits which were produced at different input gas ratios: (a) as10; (b) as20; (c) as30; and (d) as40. Fig. 4. The effect in input gas ratio on the mean whisker diameter. gas ratio increased from 10 to 40, the deposition rates decreased. In addition, the growth rate was exceedingly reduced between the input gas ratios of 10 and 20. The decreasing tendency became rather smoother and linear over the input gas ratio of 20. The change in the growth rate relates to a difference in the deposition mechanism of CVD w12x. This difference seems to be caused by differences in deposition mechanisms. Fig. 3 are SEM images of the deposits. Their morphologies look quite different compared to that of an input gas ratio of 10. When the input gas ratio was 10, a film with a pebble-like structure was deposited. However, when the input gas ratio was over 20, whiskershaped deposits were obtained. This tendency is consistent with the deposition rate. Also, there are some differences between Fig. 3b and Fig. 3c,d. In Fig. 3b, thick and short whiskers were shown. In other words, a radial growth of the whisker occurred as well as an axial growth. However, thin and long whiskers were observed in Fig. 3c,d. Within these conditions, the axial growth seems to be the predominant growth mechanism. Usually, the whisker growth can be separated into two mechanisms: axial growth and the radial growth, when it is done by vapor-solid mechanism. As reported by Frank, the axial growth occurs where screw dislocations exist at the tip of the whisker, because those dislocations act as accommodation sites for the atoms to attach. Thus, they can make growth proceed without two-
H.S. Ahn, D.J. Choi / Surface and Coatings Technology 154(2002)276-28 279 (b (c)Eesy1,o×3 m (e)a (f) 1032a(b4 es of deposits which were obtained at different deposition pressures: (a)3.93 torr;(c)5 torr; and(e)7 torr at T 34 torr;(d)6 torr; and(f7 torr at T=1100C, a=40) dimensional nucleation, which is necessary for the crys- all the things mentioned above, we could infer that an al growth [13] input gas ratio of 20 is a transition point of whisker The radial growth might be induced by microfacets growth, and is also an intermediate area between film which formed by microtwins due to the random deposition and whisker growth width of stacking faults [14]. Several closed-packed structures which include faceted planes on their side plane, could also be energetically feasible because of low stacking-fault energy 1.9x10-3 Jm-2)[15]. Those microfacets on the side plane can also act as preferred sites of the crystal x Film Growth growth, as reported by Leu et al. 14] The variation in the main growth mechanism from 3 film growth to whisker growth with the increase of the input gas ratio could be explained by the change of the orientation of the vapor deposits at different atomic concentrations of the source. From studies of McMahon A0 et al. and wang et al. silicon carbide whiskers were developed to a direction of(111).[15, 16] In the case of silicon carbide film growth, the texture coefficient of 111)increased as the input gas ratio increased [17].In addition, Lee reported that a development of orientation Pressure(Torr) of vapor deposits is affected by the atomic concentration Fig. 6. Pressure dependency on the whisker growth at different input of source adjacent to the deposit [18]. As we consider gas ratios (T=1100C, P-14-10 torr, a=1-40)
H.S. Ahn, D.J. Choi / Surface and Coatings Technology 154 (2002) 276–281 279 Fig. 5. Surface morphologies of deposits which were obtained at different deposition pressures: (a) 3.93 torr; (c) 5 torr; and (e) 7 torr at Ts 1100 8C, as20 and (b) 5.84 torr; (d) 6 torr; and (f) 7 torr at Ts1100 8C, as40). Fig. 6. Pressure dependency on the whisker growth at different input gas ratios. (Ts1100 8C, Ps1.4–10 torr, as1–40.) dimensional nucleation, which is necessary for the crystal growth w13x. The radial growth might be induced by microfacets which were formed by microtwins due to the random width of stacking faults w14x. Several closed-packed structures which include faceted planes on their side plane, could also be energetically feasible because of low stacking-fault energy of SiC (1.9 ergcm or y2 1.9=10 Jm ) w15x. Those microfacets on the side y3 y2 plane can also act as preferred sites of the crystal growth, as reported by Leu et al. w14x. The variation in the main growth mechanism from film growth to whisker growth with the increase of the input gas ratio could be explained by the change of the orientation of the vapor deposits at different atomic concentrations of the source. From studies of McMahon et al. and Wang et al., silicon carbide whiskers were developed to a direction of N111M. w15,16x In the case of silicon carbide film growth, the texture coefficient of N111M increased as the input gas ratio increased w17x. In addition, Lee reported that a development of orientation of vapor deposits is affected by the atomic concentration of source adjacent to the deposit w18x. As we consider all the things mentioned above, we could infer that an input gas ratio of 20 is a transition point of whisker growth, and is also an intermediate area between film deposition and whisker growth
80 H.S. Ahn, D.J. Choi Surface and Coatings Technology 154 (2002)276-287 The whisker diameter was also influenced by the ratIo shown in fig. 4. a mean whisker diameter decreased as the input gas ratio increased Measured diameters were 0.94, 0.44 and 0.39 um when nput gas ratios were 20, 30 and 40, respectively Pressure also took an effect on the growth behavi ig. 5 show microstructural changes of deposits, which were obtained at two different input gas ratio, 20 and 40 at 1100C, as pressure increased. In both input gas ratio, morphologies changed from whisker shape to film shape as deposition pressure increases. In addition,a whisker diameter and a grain size of pebble-like struc 20(degree ture increased as pressure increased as shown in Fig 5c, e and Fig. 5b, d, respectively. These phenomena may be induced by an increase of vapor residual time that increases as pressure increases [17]. However, there was a slight difference between the two input gas ratios When the input gas ratio was 40, the transition point from whisker growth to film growth shifted to a higher pressure in comparison with that of the input gas ratio As examined above, the pressure and input gas ratio played important roles in the whisker growth, so we clarified the data in Fig. 6, with pressure and input gas ratio as x and y axes, respectively. At a rather lower pressure and a higher input gas ratio, whisker growth deposited at 1100.C: (a)whisker was grown at a-20 with H2 dilute occurred. As the pressure increases or the input gas ratio gas and(b)whisker was grown at a=20 with N2 dilute gas and vth mechanism char whisker was grown at a=30 with H2 dilute gas, filled and coated at a=20 with N, dilute gas Whiskers that were grown by this process differ from those that were grown by the other processes [3-8 Both coatings have a pebble-like surface. However, The later usually have metal impurities on their tips. In the coating that was deposited after growing whiskers the case of the vapor-solid mechanism, the whisker at an input gas ratio of 20 has larger grains than were diameter changed periodically [19], but the whisker type formed at an input gas ratio of 30. Usually, deposited grown in this study was not similar to any of those films are affected by substrate characteristics, such as reported by other researchers [3-8, 19 morphologies, lattice constants and thermal expansion As reported by Lee et al. and Oh et al., de coefficients, etc. Thus, the difference in grain size seems which were grown using hydrogen and nitrogen as the to be caused by the difference in the diameters of the dilute gas, showed different morphologies [20, 21].In whiskers grown before depositing a silicon carbide particular, from the results of Oh et al., a whisker-shaped coating deposit was obtained at the input gas ratio of 20; and 4. Conclusions when hydrogen was used as the dilute gas; howeve film-shaped deposit was grown at the same input gas We have successfully grown silicon carbide whisk ratio when nitrogen was used as the dilute gas at 1 100 nd the whisker-containing coatings without using a oC [21]. Therefore, by using hydrogen and nitrogen as metallic catalyst. Whiskers started to appear when the the dilute gases, whisker-containing coatings were made input gas ratio was over 20. Whisker diameters were at input gas ratios of 20 and 30 and a temperature of 0.94, 0.44, and 0.39 um, respectively, and decreased as It was confirmed that both coatings are the input gas ratio increased. The deposits showed composed of silicon carbide in Fig. 7. Fig. 8 shows whisker shaped morphologies at low pressure and peb- surface and cross-sectional views of whisker-containing ble-like film structures at rather high pressure. As input coatings. Both in Fig. 8b, d, there are two layers: the gas ratio increases, transition from whisker growth to lower are the whisker-containing coating and the upper film growth shifted to a higher pressure. Matrices of are normal silicon carbide coatings. Hence, we can see whisker-containing coatings were deposited by using that whisker-containing composite coatings were suc- nitrogen as the dilute gas. They showed pebble-like structures and different grain sizes according to the
280 H.S. Ahn, D.J. Choi / Surface and Coatings Technology 154 (2002) 276–281 Fig. 7. XRD patterns of whisker-containing coatings which were deposited at 1100 8C: (a) whisker was grown at as20 with H dilute 2 gas and (b) whisker was grown at as20 with N dilute gas and 2 (b) whisker was grown at as30 with H dilute gas, filled and coated at 2 as20 with N dilute gas. 2 The whisker diameter was also influenced by the input gas ratio. As shown in Fig. 4, a mean whisker diameter decreased as the input gas ratio increased. Measured diameters were 0.94, 0.44 and 0.39 mm when input gas ratios were 20, 30 and 40, respectively. Pressure also took an effect on the growth behavior. Fig. 5 show microstructural changes of deposits, which were obtained at two different input gas ratio, 20 and 40 at 1100 8C, as pressure increased. In both input gas ratio, morphologies changed from whisker shape to film shape as deposition pressure increases. In addition, a whisker diameter and a grain size of pebble-like structure increased as pressure increased as shown in Fig. 5c,e and Fig. 5b,d, respectively. These phenomena may be induced by an increase of vapor residual time that increases as pressure increases w17x. However, there was a slight difference between the two input gas ratios. When the input gas ratio was 40, the transition point from whisker growth to film growth shifted to a higher pressure in comparison with that of the input gas ratio of 20. As examined above, the pressure and input gas ratio played important roles in the whisker growth, so we clarified the data in Fig. 6, with pressure and input gas ratio as x and y axes, respectively. At a rather lower pressure and a higher input gas ratio, whisker growth occurred. As the pressure increases or the input gas ratio decreases, the growth mechanism changed to film growth. Whiskers that were grown by this process differ from those that were grown by the other processes w3–8x. The later usually have metal impurities on their tips. In the case of the vapor–solid mechanism, the whisker diameter changed periodically w19x, but the whisker type grown in this study was not similar to any of those reported by other researchers w3–8,19x. As reported by Lee et al. and Oh et al., deposits which were grown using hydrogen and nitrogen as the dilute gas, showed different morphologies w20,21x. In particular, from the results of Oh et al., a whisker-shaped deposit was obtained at the input gas ratio of 20; and when hydrogen was used as the dilute gas; however, a film-shaped deposit was grown at the same input gas ratio when nitrogen was used as the dilute gas at 1100 8C w21x. Therefore, by using hydrogen and nitrogen as the dilute gases, whisker-containing coatings were made at input gas ratios of 20 and 30 and a temperature of 1100 8C. It was confirmed that both coatings are composed of silicon carbide in Fig. 7. Fig. 8 shows surface and cross-sectional views of whisker-containing coatings. Both in Fig. 8b,d, there are two layers: the lower are the whisker-containing coating and the upper are normal silicon carbide coatings. Hence, we can see that whisker-containing composite coatings were successfully deposited. Both coatings have a pebble-like surface. However, the coating that was deposited after growing whiskers at an input gas ratio of 20 has larger grains than were formed at an input gas ratio of 30. Usually, deposited films are affected by substrate characteristics, such as morphologies, lattice constants and thermal expansion coefficients, etc. Thus, the difference in grain size seems to be caused by the difference in the diameters of the whiskers grown before depositing a silicon carbide coating. 4. Conclusions We have successfully grown silicon carbide whiskers and the whisker-containing coatings without using a metallic catalyst. Whiskers started to appear when the input gas ratio was over 20. Whisker diameters were 0.94, 0.44, and 0.39 mm, respectively, and decreased as the input gas ratio increased. The deposits showed whisker shaped morphologies at low pressure and pebble-like film structures at rather high pressure. As input gas ratio increases, transition from whisker growth to film growth shifted to a higher pressure. Matrices of whisker-containing coatings were deposited by using nitrogen as the dilute gas. They showed pebble-like structures and different grain sizes according to the
H.S. Ahn, D.J. Choi/Surface and Coatings Technology 154(2002)276-28 [2] T. Fukasawa, Y Goto, M. Kato, J Mater. Sci. Lett. 16(1997) 1423-1425 B]R V. Krishinarao, M.M. Godkhindi, P G. Iyengar Mukunda, M. Chalraborty, J. Am. Ceram Soc. 74(1991)2869-2875 [4] N.K. Sharma, W.S. Williams, J. Am. Ceram Soc. 67(1984) 715-720. [5] J.G. Lee, L.B. Cutler, Am. Ceram. Soc. Bull. 54(1975) 16 kV *2.8 95-198 [6] N. Sedaka, K. Ajiri, J. Am. Ceram. Soc. 55(1972)540 [7 J V. Milewski, F D. Gac, J.J. Petrovic, S.R. Skaggs, J.Mater. Sci.20(1985)1160-1166 [8] K.M. Merz, in: R.J. O'Conner, J. Smiltens(Eds Carbide, A High Temperature Semiconductor, Pergamon, Oxford, 1960, p. 73 [9] J. Chin, P.K. Gantzel, R.G. Hudson, Thin Solid Films 40 (1977)57-72 [10] T D. Gulden, J. Am. Ceram Soc. 51(8)(1968)424-427 [11 A W.C. Van Kemenade, C.E. Stemfoort, J Cryst. Growth 12 Fig. 8. Surface and cross-section SEM images of whisker-containing (1972)13-16 coatings:(a) and(b)whisker was grown at a=20 with H2 dilute [12] J D. Plummer, M.D. Deal, P.B. Griffin, in: C. Sodini(Ed) gas, filled and coated at a= 30 with N2 dilute gas and(c)and(d) Silicon VLSI Technology, Fundamentals, Practice and Model whisker was grown at a=30 with H] dilute gas, filled and coated at ing, Prentice Hall, 2000, p. 517 [13] E.C. Frank, Discuss Farad. Soc. 5(1949)48-54 [l4 whiskers that were contained in the lower section of the [15] G. MeMahon, G.J. C. Carpenter, T F. Malis, J Mater. Sci. 26 (1991)5655-5663 [16] L. Wang, H. Wada, L.E. Allard, J. Mater. Res. 7(1992) Acknowledgments 48-16 This work was supported by KOSEF (Korea Science [18] D.N. Lee, J Mater. Sci. 24(1989)4375-42>1999 [17] YJ. Lee, Thesis, Yonsei University, South Kore and Engineering Foundation) and CPRC (Ceramic Proc [19] L. Wang, H. Wada, L F. Allard, J. Mater. Res. 7(1992) 48-163 References [20] Y.J. Lee, D.J. Choi, J Y, Park, K W. Hong, J. Mater. Sci. 3 (2000)45194526 [I] HH Moeller, W.G. Long, A.J. Caputo, RA.Lowden, Ceram 21 B.J. Oh, Y.J. Lee, D.J. Choi, G W. Hong, J.Y. Park, WJ.Kim Eng.Sci.Proc.8(1987)977-984 JAm. Ceram.Soc.84(2001)245-247
H.S. Ahn, D.J. Choi / Surface and Coatings Technology 154 (2002) 276–281 281 Fig. 8. Surface and cross-section SEM images of whisker-containing coatings: (a) and (b) whisker was grown at as20 with H dilute 2 gas, filled and coated at as30 with N dilute gas; and 2 (c) and (d) whisker was grown at as30 with H dilute gas, filled and coated at 2 as30 with N dilute gas. 2 whiskers that were contained in the lower section of the coatings. Acknowledgments This work was supported by KOSEF (Korea Science and Engineering Foundation) and CPRC (Ceramic Process Research Center). References w1x H.H. Moeller, W.G. Long, A.J. Caputo, R.A. Lowden, Ceram. Eng. Sci. Proc. 8 (1987) 977–984. w2x T. Fukasawa, Y. Goto, M. Kato, J. Mater. Sci. Lett. 16 (1997) 1423–1425. w3x R.V. Krishinarao, M.M. Godkhindi, P.G. Iyengar Mukunda, M. Chalraborty, J. Am. Ceram. Soc. 74 (1991) 2869–2875. w4x N.K. Sharma, W.S. Williams, J. Am. Ceram. Soc. 67 (1984) 715–720. w5x J.G. Lee, I.B. Cutler, Am. Ceram. Soc. Bull. 54 (1975) 195–198. w6x N. Sedaka, K. Ajiri, J. Am. Ceram. Soc. 55 (1972) 540. w7x J.V. Milewski, F.D. Gac, J.J. Petrovic, S.R. Skaggs, J. Mater. Sci. 20 (1985) 1160–1166. w8x K.M. Merz, in: R.J. O’Conner, J. Smiltens (Eds.), Silicon Carbide, A High Temperature Semiconductor, Pergamon, Oxford, 1960, p. 73. w9x J. Chin, P.K. Gantzel, R.G. Hudson, Thin Solid Films 40 (1977) 57–72. w10x T.D. Gulden, J. Am. Ceram. Soc. 51 (8) (1968) 424–427. w11x A.W.C. Van Kemenade, C.F. Stemfoort, J. Cryst. Growth 12 (1972) 13–16. w12x J.D. Plummer, M.D. Deal, P.B. Griffin, in: C. Sodini (Ed.), Silicon VLSI Technology, Fundamentals, Practice and Modeling, Prentice Hall, 2000, p. 517. w13x F.C. Frank, Discuss. Farad. Soc. 5 (1949) 48–54. w14x I. Leu, Y. Ku, M. Hon, Mater. Chem. Phys. 56 (1998) 256–261. w15x G. McMahon, G.J.C. Carpenter, T.F. Malis, J. Mater. Sci. 26 (1991) 5655–5663. w16x L. Wang, H. Wada, L.F. Allard, J. Mater. Res. 7 (1992) 148–163. w17x Y.J. Lee, Thesis, Yonsei University, South Korea, 1999. w18x D.N. Lee, J. Mater. Sci. 24 (1989) 4375–4378. w19x L. Wang, H. Wada, L.F. Allard, J. Mater. Res. 7 (1992) 148–163. w20x Y.J. Lee, D.J. Choi, J.Y. Park, K.W. Hong, J. Mater. Sci. 35 (2000) 4519–4526. w21x B.J. Oh, Y.J. Lee, D.J. Choi, G.W. Hong, J.Y. Park, W.J. Kim, J. Am. Ceram. Soc. 84 (2001) 245–247
