Growth of Crystalline Tungsten Carbides Using 1,1,3,3-Tetramethyl-1,3-disilacyclobutane on a Heated Tungsten Filament

Abstract

A method of forming crystalline tungsten carbides was reported by exposing the heated tungsten filament to 1,1,3,3-tetramethyl-1,3-disilacyclobutane (TMDSCB) in a hot-wire chemical vapor deposition process. Methyl radicals produced from the decomposition of TMDSCB on the filament serve as the carbon source. The formation of tungsten carbides was investigated by X-ray diffraction, cross-sectional scanning electron microscopy, and in-situ filament resistance measurements. A pure W2C phase was formed at a high temperature of 2400 °C after 1–2 h exposure time with a growth rate of 4.4 μm min–1. The growth of the W2C layer is found to be a diffusion-controlled process. Our study at longer deposition time of 3–4 h shows that once the metal filament is fully carburized to form W2C, the carbon-rich WC phase starts to form on the outside layer upon further exposure to TMDSCB. A WC layer with no contamination from the W2C phase was found to be formed at 2400 °C and 4 h deposition time.

Structural Changes in Tungsten and Tantalum Wires in Catalytic Chemical Vapor Deposition Using 1,3-Disilacyclobutane

“…Although the formation of cubic 3C-SiC was not observed in our previous studies using SCB 8 Further LeBail refinement supported this observation and determined the cell parameters as a = 4.785(6) Å, b = 6.074(7) Å, c = 5.245(7) Å, and V = 152.4(6) Å 3 . The observation of crystalline W 2 C is similar to our recent study using TMDSCB 12,20 and other studies. [10][11][12]19 For the W filaments exposed to DSCB for longer time of 3 hr and beyond, weak XRD peaks due to W 5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 the parabolic law where the thickness is linearly proportional to the square root of time.…”

“…It is known that the formation of WC/W 2 C is due to decomposition of the gaseous precursors on the heated filament surface, followed by diffusion of carbon into the bulk tungsten. 12,20,27 The silene and silylene species (I -V) are very reactive and rich in both carbon and silicon. Therefore, they are good precursors to form SiC as well as W 2 C. The transformation from W 2 C to SiC observed at 1200 ºC in our experiments is due to the fact that W 2 C is unstable below 1250 °C.…”

“…As can be noticed, the peaks associated with W 2 C (39.6°, 52.3°, 61.9°, and 69.8°) have dominated over the peaks corresponding to 3C-SiC, WC, and W for all 4 hrs. In our previous work on the alloying of W filament using TMDSCB, 20 we concluded that a carbon-rich WC phase formed on the wire surface was converted to form the carbon-deficient W 2 C, and a pure W 2 C layer was formed at 2400 ºC. With longer times of deposition of 3 -4 h, carbon diffusion into the outer W 2 C layer caused the re-formation of WC, and a pure WC phase was observed after 4 h of deposition at 2400 ºC.…”

“…The increase in filament resistance is a common observation in filament aging studies. 10,20,27 Typically, electrical resistivity increases as temperature rises for pure metals. The conductor's resistance changes with temperature according to the following equation:…”

“…12,20 In addition, a pure crystalline WC layer with no contamination from W 2 C and W was formed by treating the W wire with TMDSCB at 2400 ºC for 4 hours of deposition time. 20 Tungsten monocarbide (WC) has found many industrial applications as heterogeneous catalysts 21,22 and promising anode materials for direct methanol fuel cell (DMFC). 23 Similarly, metal silicides have attracted applications in microelectronics and electrochemical nanodevices.…”