| Summary: | 碩士 === 輔仁大學 === 物理學系 === 87 === The synthesis of this hypothetical ultrahard material is of both fundamental and technological significance and presents a great challenge to condensed matter physicists, material scientists and chemists. In order to synthesize crystalline C3N4 , various methods have been adopted, and only some of them have shown successful synthesis of polycrystalline C3N4 solid with a size typically between nanometer and submicron.In contrast to the synthesis of C3N4, the growth of large (several tens of microns), well faceted Si-containing crystalline C-N solid (c-CN) has been achieved by microwave plasma-enhanced chemical vapor deposition (MW-PECVD).
In order to make a further survey of the growth process window of this novel material, different kinds of synthesis techniques, such as deposition on substrates with various pretreatments, were considered to serve this purpose. Various methods of substrate pretreatments, including the enhancement of nucleation density and oriented crystallization by deposition on transition metal films and on the Si substrate scratched by Si3N4 powder in micron size, were adopted in the c-SiCN synthesis process. Furthermore, nanocrystalline silicon carbon nitride with rod-like shape has been synthesized with the assisted ECR-CVD buffer layer by two-step growth process.
In the characterization of SiCN compounds, auger electron spectroscopy (AES), electron microscopy (both SEM and TEM), and X-ray photoelectron spectroscopy (XPS), have been employed to determine the composition, the morphology, the crystal structure, and the chemical binding structures of the films. Further investigation of the electronic band structure of this material was carried out with piezoreflectance (PzR) spectroscopy, photoluminescence (PL) measurement and photothermal deflection spectroscopy (PDS). It is found that the SiCN compounds have a direct band gap centered around 3.8 eV and a near band edge centered around 3.26eV at room temperature. The results of optical measurements show the potential of this wide band gap semiconductor for further optoelectronic applications.
|
|---|
