Control of Growth and Morphology of a Crystal Surface by Induced Spatio-Temporal Oscillations of Surface Temperature
- PDF / 3,699,420 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 104 Downloads / 153 Views
0960-N03-03
Control of Growth and Morphology of a Crystal Surface by Induced SpatioTemporal Oscillations of Surface Temperature Mikhail Khenner Mathematics, State University of New York at Buffalo, College of Arts and Sciences, 244 Mathematics Bldg., Buffalo, NY, 14260 ABSTRACT This paper presents the model for pattern formation in the course of thermodynamically stable and unstable crystal growth from vapor phase, which is in uenced by rapid spatiotemporal variations of substrate and lm temperature. In the model, such variations result from the interference heating of a substrate by weak pulsed laser beams. In the thermodynamically stable case the surface relaxational dynamics is in uenced by surface di usion mass transport from hot to cold regions of a substrate; this leads to accumulation of mass in cold regions and depletion in hot regions. In the thermodynamically unstable case the underlying faceting (spinodal) instability coupled to di usion mass uxes from hot to cold regions leads to formation of pyramidal surface structures. The scale of stationary coarsened structure increases as the separation distance of the adjacent interference fringes decreases (relative to the intrinsic faceting wave length, which is determined by the balance between the corner regularization energies and the surface energy anisotropy). On the other hand, the coarsening rates decrease with decreasing the separation distance, at least at particular typical deposition strength. The deposition strength and the separation distance of the interference fringes determine the transient and stationary pattern shape. By e ectively redistributing adatoms on a substrate through the enhanced, spatially inhomogeneous di usion, the interference heating mechanism delays, for large separation distances, the onset of spatiotemporal chaos as the growth rate increases. INTRODUCTION Recent experimental work done in the group of Ramki Kalyanaraman at Washington University [1]-[3] demonstrates that temperature eld could be used to engineer morphologies. These researchers observed spatial organization of structures on growing surfaces of thin solid lms irradiated by weak, pulsed laser beams that are made to interfere on a substrate. It was suggested that the non-isothermal surface di usion resulting from the rapid spatio-temporal variations of the surface temperature is the cause of pattern formation. It is well-known that on thermodynamically unstable crystal surfaces structures are formed by the combined action of the deposition, faceting instability and coarsening of faceted domains [4]-[6]. Thus the proposed model for morphology evolution in the presence of weak spatial non-uniformity of the surface heating is formulated in terms of regularized, unstable evolutionary partial di erential equation (PDE). The interference heating is factored in through Arrhenius dependence of the adatom di usivity on temperature, and manifests in space-dependent coe cients (temperature dependence of the surface energy anisotropy can be included in a similar fashion). The
Data Loading...
