Akiyoshi Chayahara

Gold nanoparticles ion implanted in glass with enhanced nonlinear optical properties

Silica glass with dispersed colloid Au particles was synthesized by ion implantation. Colloid Au particles were found to grow through an Ostwald ripening mechanism controlled by diffusion in the silica glass. The third‐order nonlinear optical susceptibility χ(3) of this glass was found to be proportional to the fourth power of the radius of the colloid particles or the fourth power of the absorption coefficient at the peak of a plasmon band when the total volume of the colloid particles was constant. Furthermore, χ(3) of the glass was inversely proportional to the third power of the total volume of colloid particles when the absorption coefficient of the plasmon band was constant.

Au + -Ion-Implanted Silica Glass with Non-Linear Optical Property

Au+ ions have been implanted in silica glass at an acceleration energy of 1.5 MeV and a fluence level of 1017 ions/cm2. The Au ions form colloid particles with the radius of 2.9 nm after heat treatment. The glass with Au colloid particles shows the large third order non-linear susceptibility; χ(3)=1.2×10-7 esu. The large χ(3) value of the glass is attributed to the high concentration of Au colloid particles in the narrow region.

Metastable GaAsBi Alloy Grown by Molecular Beam Epitaxy

GaAs1-xBix has been grown at a substrate temperature (Tsub) between 350 and 410°C by molecular beam epitaxy. The relationship between GaBi molar fraction (x) evaluated by Rutherford backscattering spectroscopy and the lattice constant showed good linearity. To achieve Bi incorporation into the epilayer, As flux was adjusted in a limited range on the brink of As shortage on the growing surface. The Bi incorporation was saturated at a large Bi flux, probably due to a low miscibility of Bi with GaAs. The value of x increased up to 4.5% with decreasing Tsub to 350°C.

Widening of optical bandgap of polycrystalline InN with a few percent incorporation of oxygen

The absolute concentration of oxygen in polycrystalline InN was measured using a combination of Rutherford backscattering and x-ray photoemission spectroscopy. Polycrystalline InN was grown on quartz and glassy carbon at 500 °C by molecular-beam epitaxy using In metal and activated nitrogen species generated in rf plasma. The optical bandgap of polycrystalline InN increased from 1.55 to 2.27 eV with increasing oxygen concentration from 1% to 6%. Polycrystalline InN with an optical bandgap of 1.9 eV, which has often been reported, contains oxygen of a molar fraction of 3%.

Function of Substrate Bias Potential for Formation of Cubic Boron Nitride Films in Plasma CVD Technique

Cubic BN thin films are formed in RF discharge in B2H6 and N2 at low pressures under a magnetic field to confine the plasma, for negatively self-biased substrate electrodes. Ion bombardment on the growing surface is suggested to play an important role in the formation of cubic BN. The deposited films are characterized by infrared absorption spectroscopy and transmission electron microscopy which show that they are composed of microcrystals of cubic BN with 100-200 A grain size.

Fabrication of 1 Inch Mosaic Crystal Diamond Wafers

We fabricated so-called mosaic single-crystal-diamond (SCD) wafers that consist of SCD sub-crystals with identical characteristics. These sub-crystal clones were obtained from a SCD seed crystal by repeating the lift-off process using ion implantation. We found that the junctions between the cloned sub-crystals were smoothly covered and no abnormal crystal growth occurred along the junctions. Therefore, the lift-off process can be applied to the production of freestanding SCD wafers with the same size. Based on these findings, we have succeeded in synthesizing 1 in. mosaic diamond wafers.

High-Dose Implantation of MeV Carbon Ion into Silicon

The formation of SiC in silicon wafer by 1.5 MeV C+ implantation to doses of 1.5×1018 ions/cm2 followed by annealing is demonstrated using infrared absorption spectra and Rutherford backscattering (RBS). From the results of He+ backscattering under the channeling condition, the surface layer of Si is observed to remain crystalline even before annealing.

A new PBIID processing system supplying RF and HV pulses through a single feed-through

A new type of plasma based ion implantation and deposition system (PBIID) was developed. In this system, an RF pulse for plasma generation and a high-voltage pulse for ion implantation were supplied to a target through a single feed-through. Temporal and spatial evolutions of RF plasma around a spherical RF antenna were measured with a Langmuir probe. The plasma density had the largest value close to the RF antenna, while the electron temperature was almost constant in space. The plasma density after the RF pulse decreased almost exponentially in time and reduced more quickly in the region near the antenna. Using hydrocarbon gases in the PBIID system, the DLC film was prepared on an Si wafer substrate on each surface of the hexagonal sample holder. The thickness of each film was significantly uniform (93% in uniformity). The average thickness was 3.8±0.24 μm for a deposition time of 4 h, showing a deposition rate of 0.95 μm/h.

Nano-indentation testing for plasma-based ion-implanted surface of plastics

We have developed a technique to modify the surface of plastics to improve the hardness. Carbon ions were implanted with 20 and 10 keV energy into the plastic surface using the conventional ion-implantation and the plasma-based ion-implantation methods. The modified surface was loaded to 1 mN and unloaded using the diamond tip of the nano-indentation equipment. We found that the deformation of the modified surface was elastic deformation. According to the surface Youngs modulus FEM simulation of plastics, surface Youngs modulus was improved from 1.8 to 25 GPa using the plasma-based ion-implantation process.

Rutile‐type TiO2 formation by ion beam dynamic mixing

A compact dynamic mixing system with a bucket type electron cyclotron resonance (ECR) ion source is used for the formation of oxide films. The oxygen ion energy can be varied between 1 and 25 keV with sufficient current density for the oxide film formation. Titanium oxide films were prepared by Ti evaporation and O2+/O+ ion beam bombardment onto Si wafers and quartz plates. X‐ray diffraction (XRD) of films prepared at about 3×10−3 Pa presents polycrystal rutile structure of TiO2 alone and the crystallization is influenced by ion energy and its arrival rate. Rutherford backscattering spectroscopy of these films indicates that the film composition has stoichiometry of TiO2 with or without ion bombardment. The composition is greatly affected by the background cold O2 flow onto samples and at about 3×10−4 Pa the film shows the structure of TiO by ion bombardment.