Xianju Zhou

Silicon nanowires as chemical sensors

Chemical sensitivity of silicon nanowires bundles has been studied. Upon exposure to ammonia gas and water vapor, the electrical resistance of the HF-etched relative to non-etched silicon nanowires sample is found to dramatically decrease even at room temperature. This phenomenon serves as the basis for a new kind of sensor based on silicon nanowires. The sensor, made by a bundle of etched silicon nanowires, is simple and exhibits a fast response, high sensitivity and reversibility. The interactions between gas molecules and silicon nanowires, as well as the effect of silicon oxide sheath on the sensitivity and the mechanisms of gas sensing with silicon nanowires are discussed.

β-SiC nanorods synthesized by hot filament chemical vapor deposition

A one-step procedure has been developed to grow β-SiC nanorods from a solid carbon and silicon source on a Si substrate by hot filament chemical vapor deposition. This process is catalyzed by metallic particles which come from impurities in the solid source which is a plate made by pressing a mixture graphite and silicon powders at 150 °C. Hydrogen was introduced into the reaction chamber to react with the solid plate to produce hydrocarbon and hydrosilicon radicals which presumably reacted to form SiC nanorods. The nanorods consisted of a crystalline β-SiC core with an amorphous silicon oxide shell layer and grew along the [100] direction. The nanorods were 10–30 nm in diameter and less than 1 μm in length.

Bulk-quantity GaN nanowires synthesized from hot filament chemical vapor deposition

The bulk-quantity synthesis of single-crystal GaN nanowires has been achieved through a simple method of hot filament chemical vapor deposition without using a nanometer-sized catalyst. The microstructures and optical properties of GaN . nanowires have been studied by electron microscopy and photoluminescence PL measurements at room temperature. The GaN nanowires had diameters of 5-12 nm and lengths of a few micrometers, and were highly pure. They possessed a 4 hexagonal wurtzite structure and had a growth direction perpendicular to the 1101 plane. The PL spectra showed a broad emission peak centered at 420 nm. q 2000 Published by Elsevier Science B.V.

Thin β-SiC nanorods and their field emission properties

Abstract Beta-silicon carbide (β-SiC) nanorods (diameter, ca. 5–20 nm; length, 1 μm) have been grown on porous silicon substrates by chemical vapor deposition with an iron catalyst. The turn-on field of the grown β-SiC nanorods on a porous silicon substrate is 13–17 V/μm.

Straight β-SiC nanorods synthesized by using C–Si–SiO2

Straight beta-silicon carbide nanorods have been grown on silicon wafers using hot filament chemical vapor deposition with iron particles as catalyst. A plate made of a C–Si–SiO2 powder mixture was used as carbon and silicon sources. Hydrogen, which was the only gas fed into the deposition system, acts both as a reactant and as a mass transporting medium. The diameter of the β-SiC nanorod ranged from 20 to 70 nm, while its length was approximately 1 μm. A growth mechanism of beta-silicon carbide nanorods was proposed. The field emission properties of the beta-silicon carbide nanorods grown on the silicon substrate are also reported.

Highly efficient and stable photoluminescence from silicon nanowires coated with SiC

Abstract A reaction of silicon nanowires (SiNW) with methane and hydrogen has been performed to produce a thin coating layer of cubic silicon carbide (β-SiC) using an ion beam deposition technique. High resolution transmission electron microscopy (HRTEM) showed that silicon oxide shells originally cladding the as-grown SiNW were removed and replaced by a thin layer of nano-sized crystals of β-SiC. This has led to stable photoluminescence (PL) observed from the SiC-coated SiNW with high efficiency almost tripled as compared with that before SiC coating.

Manipulation of the equilibrium between diamond growth and renucleation to form a nanodiamond/amorphous carbon composite

Composite films of ∼10 nm nanodiamond particles embedded in an amorphous carbon matrix were formed using a double bias assisted hot filament chemical vapor deposition system with a feeding gas mixture of 1% CH4:99% H2. The structure was obtained via the equilibrium of a multistage process including: (1) bias enhanced nucleation of diamond in an amorphous carbon matrix, (2) growth of both amorphous carbon and diamond, (3) suppression of the diamond growth by the surrounding amorphous carbon matrix, and (4) bias enhanced renucleation of diamond on the new amorphous carbon boundaries. The work adds insight to the diamond nucleation and growth processes.

Heteroepitaxial nucleation of diamond on Si(100) via double bias-assisted hot filament chemical vapor deposition

A new process has been developed to obtain high density epitaxial diamond nucleation via a double bias-assisted hot filament chemical vapor deposition (HFCVD). In the process, a negative bias voltage is applied to the Si substrate and a positive bias voltage is applied to a steel grid placed on top of the hot filaments. With this arrangement, a stable plasma can be generated between the grid and the hot filaments. Ions in the plasma are then drawn to the substrate by a negative substrate bias voltage. The impinging rate of these ions can be easily controlled by adjusting the grid current, and the ion energy can be independently controlled by adjusting the substrate bias voltage. Hence, the energy and dosage of ion bombardment onto the Si(100) substrate can be controlled easily and independently. With the controlled ion bombardment, high density and heteroepitaxial nucleation can be achieved routinely. After the nucleation process, highly textured diamond films were grown by either the HFCVD or the microwave plasma chemical vapor deposition process (MPCVD).

Deposition and properties of a-C:H films on polymethyl methacrylate by electron cyclotron resonance microwave plasma chemical vapor deposition method

Abstract a-C:H films were deposited on polymethyl methacrylate (PMMA) using electron cyclotron resonance (ECR) microwave plasma (MP) decomposition of CH 4 diluted in Ar gas. The effect of substrate on the deposition process, optical properties and structure of the a-C:H films was studied. A transparent polymer-like carbon film formed on PMMA, while a semi-transparent diamond-like carbon (DLC) formed on silicon under the same growth conditions. The a-C:H films grown under certain conditions were found to substantially improve the wear resistance of PMMA substrates.

A soft X-ray absorption study of nanodiamond films prepared by hot-filament chemical vapor deposition

Abstract Nanodiamond films synthesized by a hot-filament chemical-vapor-deposition method using a methane–hydrogen mixture have been investigated with near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The carbon K-edge NEXAFS of the nanodiamond film exhibits a blue-shifted exciton peak and absorption threshold relative to that of the CVD diamond film. These features are characteristic of quantum confinement behavior. This observation confirms the presence of a nanodiamond film as was revealed by transmission electron spectroscopy. The results show that the correlation of the blue shift with the grain size of the nanodiamond is in the same direction but smaller than results previously reported in the literature.