Surface Of Quartz Substrate Research Articles

Ultrafast absorptive and refractive nonlinearities in multiwalled carbon nanotube films

By using femtosecond laser pulses at a wavelength range from 720 to 780nm, we have observed absorptive and refractive nonlinearities in a film of multiwalled carbon nanotubes grown mainly along the direction perpendicular to the surface of quartz substrate. The z-scans show that both absorptive and refractive nonlinearities are of negative and cubic nature in the laser irradiance range from a few to 300GW∕cm2. The magnitude of the third-order nonlinear susceptibility, χ(3), is of an order of 10−11esu. The degenerate pump–probe measurement reveals a relaxation time of ∼2ps.

Peculiar sponge-like structure of yttrium–iron–garnet nanocrystals on quartz substrate surface

Nanoscale amorphous yttrium–iron–garnet (YIG) particles were prepared by the alkoxide method. They were dispersed in a kerosene solvent, coated on a quartz plate substrate, and calcined at a temperature of 1273 K for 2 h. Surface morphology and cross-sectional microstructure of the thin coated films were examined by atomic force microscopy and transmission electron microscopy, respectively. During the calcination, amorphous YIG particles were transformed to YIG nanocrystals of ≈25 nm in mean diameter, and no extended grain growth or fusion of the multigrains was observed. Each particle was individually crystallized, but interconnected to each other, forming a sponge-like structure of 600 nm in thickness. Electron diffraction and energy dispersion x-ray analysis verified that the sponge-like layer consisted of YIG nanocrystalline particles. A rather dense intermediate layer of ≈100 nm in thickness was formed as a result of interfacial reactions between YIG and SiO2 decomposing to α-Fe2O3 and Y2Si2O7. The change in the Si concentration across the interlayer depth was modeled by thermal diffusion. This peculiar sponge-like structure of YIG nanoparticles supports our previous interpretation of the shift of the light absorption spectral peak, i.e., due to this peculiar structure, electrons are localized in each YIG particle, which act as a quantum dot, attributing to the quantum size effect observed in the spectral shift.

Preparation of Carbon Thin Films by CVD Method of Organic Compounds with Low Molecular Weight and Their Electrical Propertie

Carbon thin films on the surface of quartz substrates were prepared by the thermal decomposition of organiccompounds with low molecular weight, such as benzene, cyclohexane, tetrahydrofuran and pyridine. The structure andelectrical properties of the films obtained were studied. From SEM observations, it was found that the thickness of thecarbon films increased with the increase of the deposition time. The homogeneous films without any cracks and withoutany peeling off from the substrates were obtained with a thickness less than 1 μm. By the XRD measurements of the filmson the substrate, it was clarified that the graphitization degree of these films had very low. In order to examine thechemical bonding state in the carbon films, X-ray photoelectron spectroscopy was carried out in all films obtained. Inthe case of the film prepared from pridine, the nitrogen existed as a tertiary bonding state, replacing carbon atoms inhexagonal layers. The electrical conductivity of the film obtained from cyclohexane showed the high value of 2.5 × 105S/m, but that of the film prepared from benzene gave a small value of 0.3 × 105 S/m. Hall coefficient was found to showextremely small values at room temperature in all films obtained, ranging from 2.3 × 10-9 to-2.4 × 10-9 m3/C.

Effect of hydrogen pressure on the deposition of amorphous silicon films by tetrode RF sputtering

Hydrogenated amorphous silicon (a-Si:H) films were deposited on the surface of quartz substrates using the tetrode RF sputtering technique. The conditions for film deposition were controlled by changing the pressure ratio of hydrogen to argon gas, ξ, in the atmospheric gas. We studied the dependence of the optical and electrical properties of deposited films on ξ, and discuss the complex changes of optical absorption coefficient, α, and electrical conductivity, σ, at ξ ≧ 20% in terms of the silicon-hydrogen configuration from the results of infra-red absorption and SEM measurements.