I\~H I ~ CRYSTAL GROWTH ELSEVIER Journal of Crystal Growth 142 (1994) 209—214 The influence of vibration on microstructural uniformity during floating-zone crystal growth R.N. Grugel ‘i’, X.F. Shen, A.V. Anilkumar, T.G. Wang Center for Microgra city Research and Applications, Vanderbilt University, P. O.Box 6079, Station B, Nashville, Tennesee 37235, USA Received 4 February 1994; manuscript received in final form 7 April 1994 Abstract Previously, we have shown that temperature gradients can be smoothed, and thermocapillary convection suppressed, in a model half-zone of silicone oil and also in a float-zone of sodium nitrate, by inducing an opposing surface streaming flow through vibration of one of the supporting end-walls. In this work we demonstrate the effect of vibration in promoting uniform microstructures during the float-zoning of NaNO 3—Ba(N03)7 eutectic “alloys.” 1. Introduction the return flow in the bulk towards the vibrating wall. When this controlled surface streaming was Crystals grown by the floating-zone method employed to balance an opposing steady thermo- eliminate interactions from crucible walls, thereby capillary flow, initiated in the silicone oil half- minimizing contamination and/or defects [1,21. zone, the radial temperature gradients smoothed Unfortunately, temperature gradients in the liq- considerably. uid [3,41 give rise to internal flow from surface This technique was then applied during float- tension (thermocapillary) and buoyancy effects zone processing of sodium nitrate (NaNO3) [13]. [5—71 which can promote non-uniform mi- Advantages of using NaNO3 include (1) the abil- crostructures [8]. To minimize these detrimental ity to form a stable floating-zone, (2) the propen- effects a number of techniques, which met with sity for strong thermocapillary convection, and (3) limited success, have suggested or tried [9—111 allowing for direct observation of flow patterns during float-zone processing. and, importantly, solid/liquid interfaces. Fur- We have shown [12] that thermocapillary flow thermore, it has a convenient melting tempera- can be weakened and even reversed in a model ture, is chemically stable, and is insensitive to half-zone of silicone oil by vibrating one of the normal contamination of the free surface. In the supporting end walls. Briefly, vibration drives a experiments, 6 mm diameter rods of NaNO5 were surface flow in the zone away from the wall with cast with fine quartz particles which served as tracers for flow pattern visualization. Here, owing _______ to the combined convective and radiative heating, * Corresponding author, the establised steady thermocapillary flow had a 0022-0248/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDJ 0022-0248((94)00179-P