The Formation of Smooth, Defect-free, Stoichiometric Silicon Carbide Films from a Polymeric Precursor
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0911-B05-01
The Formation of Smooth, Defect-free, Stoichiometric Silicon Carbide Films from a Polymeric Precursor Michael Pitcher1, and Patricia Bianconi2 1 Department of Chemistry, METU, Ankara, 06531, Turkey 2 Department of Chemistry, University of Massachusetts at Amherst, Amherst, MA, 01003 ABSTRACT Silicon carbide (SiC) materials, which are used in a variety of applications, are often produced using powder processing, sintering or bulk crystal growing techniques. The formation of silicon carbide films or shaped products, via these methods, is often extremely difficult and/or requires high temperatures. Here we report the synthesis and characterization of a polymeric precursor, Polymethylsilyne (PMSy), and it subsequent conversion to β-SiC. The polymer is simple to synthesize and is easily manipulated in air. The ceramic produced from PMSy is extremely pure, stoichiometric SiC and is produced in high yields (up to 85%). The ceramic films that can be produced from PMSy on a variety of substrates, from ceramics to metals, are again stoichiometric SiC and are smooth, continuous and defect free; possibly enabling the use of these films in electronic applications. INTRODUCTION Polysilynes, a relatively new class of polymers were first synthesized by Bianconi and Weidman in 1988 [1]. The synthesis involves the reduction of alkyl or arylsilicon trihalides with liquid sodium-potassium alloy (NaK). High intensity ultrasound is used to ensure rapid and a more homogeneous reaction environment. These silicon-silicon bonded network polymers adopt a unique structure, in which each silicon bears one pendant group and is joined by three single bonds to three other silicon atoms, forming a continuous random network backbone. These silicon network polymers have a distinctive yellow color, very broad Nuclear Magnetic Resonance (NMR) resonances and a broad and intense Ultraviolet (UV) absorption band edge tailing into the visible. More recently Huang and Vermeulen have synthesized these network polymers electrochemically [2]. Silicon polymers of all types have attracted considerable attention due to their unique properties [3], not least of which, is their use as ceramic precursors to silicon carbide. As an advanced ceramic material, silicon carbide (SiC) has been used in applications requiring a hard, lightweight, temperature-and-wear-resistant material. Its good fracture strength, hardness, low theoretical density (ρ = 3.21g/cc) and thus relatively high strength/weight ratio, make it an attractive material for numerous applications. Conventionally produced SiC materials are manufactured using SiC powder processing and sintering. In this process, forming shaped products is difficult and requires temperatures in excess of 2100O C [4-6]. Since the early 1970’s when Yajima [7] first obtained non-oxide ceramics from the thermal decomposition of polymer precursors, there has been much interest in the polymer precursor route to SiC. The polymeric nature of the ceramic precursors makes the production of fibers, coatings, binders, etc fe
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