L-C. Leu, M-H. Hon /Journal of Crystal Growth 236(2002)171-175 droplet with different dimensions in an intermedi shortest incubation time for Sic whisker nuclea ate stage of incubation where the smaller whiskers tion was found for droplets of 2 um in diameter have already nucleated from their respective instead of those with larger or smaller dimensions droplets, while larger ones are still under the process of nucleation 4. Conclusion The financial support from the National Science The nucleation behavior of Sic whiskers pre- Council of the Republic of China, TAIWAN ared by the thermal decomposition of MTS on under contract No. NSC89-2216-E-006-072 is Ni-coated graphite substrates was studied. The greatly appreciated effect of Ni droplet size on the incubation period of Sic whiskers was determined. According to the above experimentation, results and discussion the ollowing conclusion can be drawn. It is found that References the incubation period for whiskers to nucleate to noticeable dimension depends on the size of the Ni [s. Motojima, M. Hasegawa, T. Hattori, J. Crystal Growth 87(1988)311 particles. It takes about 3 min for the whiskers to [2]K.Hiruma, et al., J. Appl. Phys. 77 (2)(1995)447 appear and about 8 min to complete the whole nucleation stage for the case of Ni coating Mimo orales, C M. Lieber, Science 279(1998)208 hickness of 2.5 um and the Cvd parameters [R.S. Wagner, w.C. Ellis, Appl. Phys. Lett. 4(5)(1964)85 employed. The nucleation density took about [6]K. Sugiyama, et al., J. Crystal Growth 44(1978)499 8 min to achieve a value of 10% P.D. Shalek, W.J. Parkinson. Mat. Res. Soc. Symp Proc remains at about this value through the whole [82 Wokulski, J. Crystal Growth 82(1987)427 period of CVD deposition. Besides, due to the 9I.C. Leu, Y M. Lu, M.H. Hon, J. Crystal Growth 167 balance between the volume and the curvature (1996)607 effect of the liquid droplet of Ni catalyst formed [10] D.A. Porter, K.E. Eastering, Phase Transformation in Metals and Alloys, Van Nostrand Reinhold Co., New on the graphite substrate during CVD process, the York,1981,p.45droplet with different dimensions in an intermedi￾ate stage of incubation where the smaller whiskers have already nucleated from their respective droplets, while larger ones are still under the process of nucleation. 4. Conclusion The nucleation behavior of SiC whiskers pre￾paredby the thermal decomposition of MTS on Ni-coated graphite substrates was studied. The effect of Ni droplet size on the incubation period of SiC whiskers was determined. According to the above experimentation, results anddiscussion the following conclusion can be drawn. It is found that the incubation periodfor whiskers to nucleate to noticeable dimension depends on the size of the Ni particles. It takes about 3 min for the whiskers to appear andabout 8 min to complete the whole nucleation stage for the case of Ni coating thickness of 2.5 mm andthe CVD parameters employed. The nucleation density took about 8 min to achieve a value of 109 m
2 , andthen remains at about this value through the whole period of CVD deposition. Besides, due to the balance between the volume andthe curvature effect of the liquiddroplet of Ni catalyst formed on the graphite substrate during CVD process, the shortest incubation time for SiC whisker nuclea￾tion was foundfor droplets of 2 mm in diameter insteadof those with larger or smaller dimensions. Acknowledgements The financial support from the National Science Council of the Republic of China, TAIWAN under contract No. NSC89-2216-E-006-072 is greatly appreciated. References [1] S. Motojima, M. Hasegawa, T. Hattori, J. Crystal Growth 87 (1988) 311. [2] K. Hiruma, et al., J. Appl. Phys. 77 (2) (1995) 447. [3] A.M. Morales, C.M. Lieber, Science 279 (1998) 208. [4] S. Iijima, Nature 354 (1991) 56. [5] R.S. Wagner, W.C. Ellis, Appl. Phys. Lett. 4 (5) (1964) 89. [6] K. Sugiyama, et al., J. Crystal Growth 44 (1978) 499. [7] P.D. Shalek, W.J. Parkinson, Mat. Res. Soc. Symp. Proc. 168 (1990) 255. [8] Z. Wokulski, J. Crystal Growth 82 (1987) 427. [9] I.C. Leu, Y.M. Lu, M.H. Hon, J. Crystal Growth 167 (1996) 607. [10] D.A. Porter, K.E. Eastering, Phase Transformation in Metals andAlloys, Van NostrandReinholdCo., New York, 1981, p. 45. I.-C. Leu, M.-H. Hon / Journal of Crystal Growth 236 (2002) 171–175 175