Monitoring Faceting on Ceramic Surfaces
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Monitoring Faceting on Ceramic Surfaces Shelley R. Gilliss, Arzu Altay, Jessica Reisterer, N. Ravishankar and C. Barry Carter Dept. of Chemical Engineering and Materials Science, University of Minnesota 421 Washington Ave. S.E., Minneapolis MN 55455 USA
Paper # S0208
To be submitted to the 2002 MRS Fall Meeting
Preferred Symposia: Y
Please address all correspondence to: Prof. C. Barry Carter Ph: 612-625-8805 Fax: 612-626-7246 email: [email protected]
Y8.38.1
Y8.38.2
MONITORING FACETING ON CERAMIC SURFACES Shelley R. Gilliss, Arzu Altay, Jessica Riesterer, N. Ravishankar§ and C. Barry Carter Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455-01432 §
Now at Materials Research Center, Indian Institute of Science, Bangalore 560 012, India Abstract Faceting is the transformation of a planar surface into two or more surfaces of lower energy. Metal, semiconductor and ceramic surfaces can all undergo faceting. The evolution of facets formed on the m-plane (101 0) of alumina has been monitored using atomic-force microscopy (AFM). When heat-treated, the (101 0) surface reconstructs into a hill-and-valley morphology. The present study investigates the manner in which facets originally form and grow to cover a surface. A gravity-loaded indenter (load of 25 grams) was used to mark a 25 µm x 25 µm square area on as-received, polished alumina specimens. An initial heat-treatment of 1400˚C for 10 minutes is carried out to initiate faceting. With the indents as guides the same area can be identified and imaged after each subsequent heat-treatment. The morphology of the facets can be described as being comprised of a “simple” and “complex” surface. The simple surface corresponds to the (1 1 02) plane which is stable over the course of heat treatments, whereas the complex surface gradually transforms to a lower energy surface after several heat treatments and acts as a nucleation site for new facet growth. †
1. Introduction Surfaces of ceramics, semiconductors and metals can each undergo the phenomenon of faceting. Herring explained the faceting process in terms of a material minimizing its total surface energy [1]. In the case of the m-plane (101 0) of alumina it has been shown to facet into a hill-and-valley morphology [2]. The mechanism in which a material transforms from a flat surface to the final low-energy state is not well understood. TEM investigations of the dewetting behavior of CaAl2Si2O8 glass on m-plane alumina indicate that when diffusion is enhanced (in the presence of the glass); the hilland-valley morphology is comprised of the (1 1 02) simple surface and the (10 1 1 ) complex surface [3]. The complex surface, along with the simple surface, is present when reconstruction occurs beneath a glass droplet (and where diffusion is a maximum). Faceting, which occurs outside of the glass droplet, consists of different surfaces due to † † slower kinetics [4]. Mullins described the evolution into a final hill-and-valley morphology in terms of the reduction in su
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