Narumi Inoue

Electrical properties of evaporated polycrystalline Ge thin-films

Abstract Electrical properties of Ge thin films evaporated on Si3N4 CVD-coated Si substrate were improved by introducing a heat treatment after the deposition of Ge films. Evaporation conditions were optimized by changing the substrate temperature and deposition rate, and then, heat treatment was performed. At substrate temperatures during the evaporation lower than 300 °C and higher than 400 °C, deposited films were amorphous and polycrystalline, respectively. At substrate temperatures lower than 400 °C, Ge films were evaporated without degrading the surface roughness. The Hall mobility of films evaporated at room temperature increased with increasing the substrate and heating temperature and showed about 400 cm2 V−1 s−1 for the hole concentration of 4 × 1017 cm−3 at the heating temperature of 900 °C. This value was almost comparable to that of p-type Ge single crystal.

Photochemical modification of silicone films using F2 laser for selective chemical etching

Silicone ([SiO(CH3)2]n) films were photochemically modified into SiO2 by irradiation with a 157 nm F2 laser. The dissociation of Si–CH3 bonds of silicone simply depended on the photon number of the F2 laser. The quantum yield of the modification was estimated to be approximately 1×10-2. Mechanisms of oxidation and O–H production in the modified films were clarified. The depth of the modification was not limited by the absorption coefficient of silicone because SiO2 of the modified films is transparent for the F2 laser. A fine pattern of the 1.5-µm-thick silicone films could be fabricated by immersing the modified samples in 0.2 wt% hydrogen fluoride solution.

Fabrication of SiO2-Humps on Silicone Rubber Using F2 Laser

The surface of silicone rubber swelled and was modified to a SiO2 glass layer when irradiated by a 157-nm F2 laser. Ten minutes of irradiation of the laser with fluence of 14 mJ/cm2 operating at 20 Hz produced 3-µm-thick SiO2 humps, but the surface was not modified when a 193-nm ArF laser was used. High photon energy of the F2 laser may cause the two phenomena. This is a useful new technique which enables both processing and modification to be carried out at the same time.

Annealing effect of vacuum evaporated InSb thin films

Abstract A method of single-source vacuum evaporation for preparing InSb thin films, having high electron mobilities onto glass substrates is studied. Electron mobilities of 6500 cm 2 /Vs in the 1.7μm thick InSb film is obtained by single-source vacuum evaporation followed by capped annealing. The effects of the source temperature, the substrate temperature and the post annealing conditions on electrical and crystal properties of the deposited films are discussed.

A new pulsed laser deposition method using an aperture plate

A new off-axis pulsed laser deposition method using an aperture plate is proposed for the purpose of depositing high surface-quality Ta2O5 thin films without large fragments and/or droplets. The angular distribution of droplets and growth species emitted from the target is examined. Then, the oxygen pressure and laser energy dependencies of the number of droplets and the film thickness are also examined. The results indicate that the aperture plate plays an important role of limiting the path of the traveling droplets and of capturing the droplets traveling toward the off-axis substrate. On the other hand, the film deposition rate is not slow even when using the plate because the species pass through the aperture hole and reach the substrate by scattering. Using a 5 mm aperture plate, a good surface quality Ta2O5 film is obtained under the optimum condition of 200–300 mTorr oxygen pressure.

Microlenses Fabricated on Silicone Rubber Using F2 Laser

Microlenses are fabricated on silicone rubber surfaces employing phenomena in which silicone rubber swells and is modified to SiO2 by F2 laser irradiation at a laser fluence lower than the ablation threshold. In this method, silicone rubber is irradiated using a F2 laser beam through a mask which has circular apertures 10, 20, and 25 µm in diameter. Since silicone rubber swells by laser irradiation, it is necessary to separate the mask from the silicone rubber surface. The swelling is spherical and its surface becomes smooth when the distance between the mask and the silicone rubber surface is very small. The focal lengths of the microlenses are 10–170 µm, which are controlled by adjusting the number of irradiated pulses. Additionally, a 790 nm femtosecond laser beam is focused by the fabricated microlenses, and enables the microdrilling of fluorinated rubber.

SiO2 Humps Formed on Silicone Rubber by F2 Laser Irradiation

An unexpected finding of SiO2 humps on silicone rubber fabricated by a 157 nm F2 laser at a laser fluence less than the ablation threshold was made. The fabrication of the humps which progressed by increasing the number of laser pulses was examined by measuring the height and surface roughness of the humps and by Fourier transform infrared spectroscopy (FT-IR). The FT-IR spectra showed that the position of the Si–O peak of the fabricated hump agreed with that of a synthetic fused silica. The chemical composition of the entire hump was also confirmed to be SiO2 by X-ray photoelectron spectroscopy (XPS). The SiO2 hump could be removed completely by 1 wt% hydrofluoric acid. This finding resulted from swelling of the silicone surface and the subsequent photodissociation of Si–CH3 from the swelled silicone. We could not fabricate the SiO2 humps by a 193 nm ArF laser.

Femtosecond laser-driven shock synthesis of hexagonal diamond from highly oriented pyrolytic graphite

We synthesized hexagonal diamond directly from highly oriented pyrolytic graphite (HOPG) using a femtosecond laser pulse without catalyst. A femtosecond laser pulse with wavelength of 800 nm, pulse width of 130 fs, the intensity of 2×1015 W/cm2 was irradiated onto the HOPG surface in air. Crystalline structures of the fs laser-affected region in the HOPG were analyzed using grazing-incidence XRD method. We found that the hexagonal diamond which is the metastable high-pressure phase of carbon appeared in the HOPG which was irradiated by the femtosecond laser normal to the basal plane. We suggest that the femtosecond laser-driven shock wave induces the graphite – hexagonal diamond transformation and that the hexagonal diamond is synthesized due to the rapidly cooling in the shock heated region.

Femtosecond-pulsed laser deposition of diamond-like carbon films onto silicone rubber

Low frictional, textured diamond-like carbon (DLC) films were deposited onto silicone [SiO(CH3)2]n] rubber by femtosecond laser ablation of frozen pentanel (C5H11OH). Deposition rate of the films for silicone rubber was higher than that for Si wafer. A broad Raman peak centred at 1530 cm−1 was measured from the films deposited on silicone, showing a DLC film. The Raman spectra of the DLC films on silicone and Si wafer, a textured DLC films were also formed on silicone rubber. A coarse texture of the films was obtained by increasing the deposition time. The textured DLC films could improve frictional property of a sticky silicone rubber.

White-Light Emission from Silicone Rubber Modified by 193 nm ArF Excimer Laser

The photochemical surface modification of silicone ([SiO(CH3)2]n) rubber has been successfully demonstrated using a 193 nm ArF excimer laser, and white light of strong intensity was emitted upon exposure to a 325 nm He–Cd laser. The photoluminescence spectra of the modified silicone showed broad peaks centered at 410, 550, and 750 nm wavelengths. The modified surface was carbon-free silicon oxide, and the chemical composition ratio of O/Si was approximately 2. However, the surface was not silica glass (SiO2), as clarified by IR spectroscopy. Instead, nanometer-size particles of silicon oxide were formed on the surface of the modified silicone rubber.