Showing papers by "Kuei-Hsien Chen published in 1998"

Crystalline silicon carbon nitride: a wide band gap semiconductor

Abstract: Crystalline thin films of SiCN have been grown by microwave plasma-enhanced chemical vapor deposition using H2, CH4, N2, and SiH4 gases. The ternary compound (C;Si)xNy exhibits a hexagonal structure and consists of a network wherein the Si and C are substitutional elements. While the N content of the compound is about 35–40 at. %, the extent of Si substitution varies and can be as low as 10 at. %. Optical properties of the SiCN compounds have been studied by photoluminescence (PL), piezoreflectance (PzR), and photothermal deflection (PDS) spectroscopies. From the PzR measurement, we determine the direct band gap of the new crystals to be around 3.8 eV at room temperature. PDS measurement shows two absorption features with the first peak at around 3.2 eV which is related to an indirect band gap. The second PDS peak occurred around 3.8 eV and is quite consistent with the direct band gap determined by PzR. From the PL measurement, it is also found that the SiCN compounds have a near band edge emission center...

The use of a biomolecular target for crystalline carbon nitride film deposition by Ar ion-beam sputtering without any other source of nitrogen

Abstract: Carbon nitride films have been synthesized by argon ion-beam sputtering from a biomolecular compound target, 8-aza-6-aminopurine (C4N6H4). The compound has a six-membered ring structure similar to that existing in the hypothetical β-C3N4. Except for the target material, no other source of nitrogen was used during sputtering deposition. It was found that crystalline carbon nitride with high N/C atomic composition ratios of 0.43–0.56 can be formed even at room temperature. The infrared spectra of the film exhibit two peaks at 1383 and 1643 cm−1, corresponding to C–N and C=N stretching modes, respectively. No detectable peak at 2200 cm−1 (C≡N stretching mode) is observed. Both x-ray diffraction and transmission electron microscopy show a very strong broad peak at 3.2 A, comparable to the d spacing of the (110) orientation in the β-C3N4 structure. However, it is suggested that the film contains a nanocrystalline phase with a crystal structure yet to be determined.

Effects of substrate pretreatment and methane fraction on the optical transparency of nanocrystalline diamond thin films

Abstract: Optical transmittance of the nanocrystalline diamond films has been studied as a function of grain size of the diamond powder used for substrate pretreatment and the methane fraction in the source gas. It has been observed that for CH4 fractions below 13%, the films grown on substrates pretreated with finer diamond powder are more transparent, while this trend reverses for CH4 fractions above 13%. These variations in the transparency of the films correlate very well with their corresponding surface roughness. Nanocrystalline/amorphous diamond films with transmittance of greater than 80% beyond 700 nm and with average surface roughness as low as 61 A have been obtained for CH4 fractions as high as 42% in the source gas. Interestingly, these films do not show an obvious presence of any graphitic carbon, and the structural ordering of the amorphous sp3-bonded phase also seems to be insensitive to the CH4 content of the source gas.

Synthesis and characterization of an organic–inorganic hybrid compound: [WO3 (2,2′-bipy)] (2,2′-bipy=2,2′-bipyridine)

Abstract: The hydrothermal synthesis and characterization of an organic–inorganic hybrid compound [WO3(2,2′-bipy)] (2,2′-bipy=2,2′-bipyridine) is presented. This compound was characterized by various techniques including Raman and IR spectroscopy, XRD and thermogravimetric analysis. Structural analysis of the compound by Raman and IR data shows that it has a novel tungstate structure with 2,2′-bipy coordinated to tungsten. The X-ray powder diffraction data of the compound are indexed to a monoclinic cell with a=14.313(4), b=9.603(2), c=7.288(2) A,β=102.07(2)°. The structure of [WO3(2,2′-bip\y)] adopts a chain-like framework consisting of corner-shared distorted octahedra (WO4N2) with 2,2′-bipy acting as a bidentate ligand whose rings fan out from the chain. Upon heating, [WO3(2,2′-bipy)] retains its structural integrity until 300°C, followed by a gradual loss of 2,2′-bipy which leads to the formation of WO3 at ca. 475°C. The thermal decomposition is observed to proceed through a transitional intermediate, [W4O12(2,2′-bipy)], the structure of which is proposed and discussed.