Grain-Boundary and Free-Surface Induced Thermodynamic Melting: A Molecular Dynamics Study in Silicon
It is well known that melting of a solid generally proceeds from the surface. For example, it was observed in measurements on silica1 and phosphorous pentoxide2 that melting was not a homogeneous process; invariably it occurred at free surfaces and grain boundaries. A variety of experimental data now exists which points to the controlling role of an extrinsic surface.3 Small atomic clusters, with a significant fraction of the particles on or close to the surface, have been observed to exhibit quite different melting behavior from that of the bulk substance; for example, melting-point depression of up to 30% has been measured in metal clusters of diameter 20–30Å4, as has substantial superheating of argon bubbles of similar size formed in an aluminum lattice,5 and of hydrogen bubbles in amorphous silicon.6 Superheating has also been observed recently in small single crystals of silver coated with gold, the latter with a higher melting point.7 The implication of these results is that while melting is a thermodynamic transition, in general it is initiated at either an external surface or an internal interface, such as a grain boundary or a dislocation.
KeywordsFree Surface Grain Boundary Poly Silicon Molecular Dynamics Study Ideal Crystal
Unable to display preview. Download preview PDF.
- 4.Ph. Buffat and J.-P. Borel, Size Effect of the Melting Temperature of Gold, Phys. Rev. A13:2287 (1976).Google Scholar
- 7.J. Daeges, H. Gleiter, and J.H. Perepezko, Superheating of Metal Crystals, Phys. Lett. A119:79 (1986).Google Scholar
- 8.S.R. Phillpot, J.F. Lutsko, D. Wolf and S. Yip, Molecular Dynamics Study of Lattice-Defect Nucleated Melting in Silicon, submitted to Phys. Rev. B.Google Scholar
- 9.S.R. Phillpot, J.F. Lutsko and D. Wolf, Nucleation and Kinetics of Thermodynamic Melting: A Molecular Dynamics Study of Grain-Boundary Induced Melting in Silicon, to be published.Google Scholar
- 10.D.A. Smith and T.Y. Tan, Effects of Doping and Oxidation on Grain Growth in Polysilicon in: “Grain Boundaries in Semiconductors”, H.J. Leamy, G.E. Pike, and C.H. Seager, ed. (North Holland, 1982).Google Scholar
- 11.F.H. Stillinger and T.A. Weber,, Computer Simulation of Local Order in Condensed Phases of Silicon, Phys. Rev. B31:5262 (1985).Google Scholar
- 12.J.Q. Broughton and X.P. Li, Phase Diagram of Silicon by Molecular Dynamics, Phys. Rev. B35:9120 (1987).Google Scholar
- 14.U. Landman, W.D. Luedtke, M.W. Ribarsky, R.N. Barnett, and C.L. Cleveland, Molecular-Dynamics Simulations of Epitaxial Growth from the Melt. I—Si (100), Phys. Rev. B37:4637 (1988); W.D. Luedtke, U. Landman, M.W. Ribarsky, R.N. Barnett, and C.L. Cleveland, Molecular-Dynamics Simulations of Epitaxial Growth from the Melt. II—Si (111), Phys. Rev. B37:4647 (1988).Google Scholar
- 15.S.R. Phillpot and D. Wolf, Atomistic Simulation of Silicon Grain Boundaries, Proc. MRS Symp. on “Interfacial Structure, Properties, and Design in Solids”, Reno, NV 1988; S.R. Phillpot and D. Wolf, Structure-Energy Correlation for Grain Boundaries in Silicon, submitted to Phil. Mag. A.Google Scholar