A Systematic Study of the Formation of Nano-Tips on Silicon Thin Films by Excimer Laser Irradiation
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J13.6.1
A Systematic Study of the Formation of Nano-Tips on Silicon Thin Films by Excimer Laser Irradiation D.G. Georgiev, R.J. Baird, I. Avrutsky, G. Auner, G. Newaz1, N. Tokranova2 Department of Electrical and Computer Engineering, Wayne State University, Detroit, MI 48202 1 Department of Mechanical Engineering, Wayne State University, Detroit, MI 48202 2 Institute for Materials, SUNY at Albany, Albany, NY 12203 ABSTRACT Recently, we reported conditions for controllable, direct laser fabrication of sharp conical tips with heights of about one micrometer and apical radii of curvature of several tens of nanometers. An individual cone is formed when a single-crystal silicon film on an insulator substrate is irradiated in air environment with a single pulse from a KrF excimer laser, homogenized and shaped to a circular spot several microns in diameter. In this work, we present a study of the formation of such tips as a function of the laser fluence, the film thickness, and the diameter of the irradiated spot. Atomic force microscopy and scanning electron microscopy were used to study the topography of the structures. A simple mechanism of formation based on movement of melted material is proposed. We have also studied structures (nano-ridges) that resulted from irradiation with narrow lines (width of several microns) instead of circular spots. INTRODUCTION High-intensity pulsed laser radiation can be used to modify surfaces of materials and fabricate technologically desirable structures on a micrometer and sub-micrometer level. Besides their technological importance, such surface modifications can be of substantial scientific interest. The processes involved in such radiation/matter interactions are complex and usually non-equilibrium due to high heating and cooling rates, large temperature gradients and a variety of chemical and photochemical transformations. These processes and their interplay are often poorly understood, and therefore systematic studies of laser irradiation of materials as a function of a certain set of parameters are essential. Recently [1], we reported conditions for controllable, direct laser fabrication of sharp conical nano-tips on silicon thin films and in this work we present additional results on this new technique. Reliable, simple and low-cost techniques for fabrication of micro- and nano-tips of silicon and other semiconductor and metal materials, as well as large, high-density arrays of such tips, are desirable in a number of technological applications. These include probes for scanning probe microscopy techniques, emitters for field-emission-based devices such as high-definition displays [2,3] and other vacuum microelectronics applications [4]. There is also a considerable amount of ongoing research on surface patterning of materials for biomedical applications [5-7], which could also benefit from new developments in the area of materials surface micro- and nano-structuring. Laser fabrication techniques that utilize high-energy UV excimer lasers with large-area homogenized beam cross-
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