Tamiko Ohshima

Synthesis of p-type ZnO thin films using co-doping techniques based on KrF excimer laser deposition

Preparation of N-doped ZnO thin films was attempted using various co-doping methods. A ZnO:Ga (Ga 2 O 3 of 5 wt.%) target was ablated in NO gas by pulsed laser deposition (PLD). In addition, a nitrogen ion gun and an ECR nitrogen plasma source were used as post-N-doping treatment of undoped ZnO films. Optical emission from elemental Zn I, Ga I and O I, as well as from N 2 molecules, was identified in the plasma plume. The structural, optical and electrical properties of these synthesized films were investigated. All films show n-type conduction, with resistivity in the range 10 -3 -10 -2 Ω cm and carrier density from 10 17 to 10 20 cm -3 .

Preparation of boron carbide thin film by pulsed KrF excimer laser deposition process

Pulsed laser deposition (PLD) technique has been widely used in thin film preparation because of its wonderful and excellent properties. Boron carbide (B 4 C) thin films are recognized to have potential for applications like hard coating and electron field emission devices. B 4 C is the third hardest material after diamond and cBN, with a highest hardness of HV ∼5000. Furthermore, B 4 C is interesting from the point of view of wear resistance and stability at high temperature. We have deposited B 4 C thin films by KrF excimer laser (λ = 248 nm) ablation of a stoichiometric B 4 C target in high vacuum. In this paper, we have prepared the B 4 C thin films on Si(100) substrates under various conditions, such as substrate negative DC bias voltage from between 0 to -800 V, substrate temperatures from room temperature up to 550 °C, and laser fluence between 2 and 8 J/cm 2 on the target. The typical absorption of B-C stretching bonds was detected from the infrared absorption measurement by FTIR of the deposited B 4 C thin films. We concluded that the hardness of the B 4 C thin films increases as the boron/carbon (B/C) ratio increases. The B/C ratio depends on the laser fluence. We obtained the maximum B/C ratio of 3.42 at 5 J/cm 2 . The hardness of that sample reached 5.84 times of that of the Si(100) substrate.

Preparation of crystalline TiC thin films grown by pulsed Nd:YAG laser deposition using Ti target in methane gas

Abstract Titanium carbide (TiC) thin films that are smooth and pinhole-free have been synthesized on Si(100) substrates by a pulsed neodymium:yttrium–aluminum–garnet (Nd:YAG) laser deposition method using titanium and TiC targets in methane gas. Glancing angle X-ray diffraction (GXRD) showed that polycrystalline films with components of TiC and Ti can be prepared using a Ti target. Single-phase TiC films can be synthesized using a TiC target. It was found that the methane gas pressure can control the crystallinity and composition. The root-mean-square (RMS) roughness of the film, as measured by an atomic force microscope (AFM), was lower than 2 nm in all the deposition areas. The film thickness, measured by α-step, was about 92 nm and the growth rate was approximately 3.1 nm/min. Measurements of optical emission spectra were performed to estimate the processing plasma state.

TiO2/TiN/TiO2 heat mirrors by laser ablation of single TiN target

Titanium oxide (TiO2 ) and titanium nitride (TiN) multilayered films grown by pulsed laser deposition (PLD) technique have been tested as a heat mirror, which have a high transmittance in the visible region and a high reflectance in the infrared. Three layer TiO2 /TiN/TiO2 heat mirrors were grown on Corning glass substrates ablating single TiN target. Switching of TiO2 -to-TiN layers composition was achieved by changing gas atmosphere (oxygen-to-nitrogen). Grown TiO2 /TiN/TiO2 heat mirrors are highly transparent in visible (above 60% at 525nm), opaque in infrared (10% at 2600nm) and in the range from 400 nm to 2600 nm they possess almost the same properties as films prepared using two targets: TiO2 and TiN. XPS confirms similarity of chemical composition of multilayered TiO2 /TiN films prepared by single TiN and two TiO2 and TiN targets techniques. Furthermore, multifunctional self cleaning properties of TiO2 /TiN heat mirrors are expected through the precise control of the composition of the top TiO2 layer operating as a photocatalyst.

Characterization of Tantalum Nitride Thin Films Fabricated by Pulsed Nd:YAG Laser Deposition Method

Growth mechanisms of crystalline tantalum nitride (TaN) films have been studied on silicon substrates using a pulsed Nd:YAG laser deposition method. Experimental results show that the properties of the TaN films strongly depend on the substrate temperatures and nitrogen gas pressures. This suggests that both the phase reaction in the plasma plume and the surface reaction on the substrate are important for preparing crystalline TaN films.

Effect of Oxygen Gas Pressure on Electrical, Optical, and Structural Properties of Al-Doped ZnO Thin Films Fabricated by Pulsed Laser Deposition for Use as Transparent Electrodes in All-Solid-State Electrochromic Devices

Low-resistivity and high-transmittance Al-doped ZnO (AZO) thin films were obtained by pulsed laser deposition with the substrate at room temperature. The electrical, optical, and structural properties of the AZO thin films deposited at various oxygen gas pressures (PO2) were investigated. X-ray diffraction shows that the AZO thin films have (002) preferred orientation and the diffraction angle of the (002) plane shifts to a higher value with increasing oxygen gas pressure. All AZO thin films deposited under ambient oxygen gas pressure conditions have an optical transmittance of over 80% in the visible region. AZO thin films deposited at lower PO2 of ≤1 Pa have resistivities of 1 Pa. The AZO film deposited at PO2 = 1 Pa had the lowest resistivity (5.8 ×10-4 Ω cm) with a high carrier concentration of 1.1 ×1021 cm-3.

Influence of ambient gas on diamond-like carbon films prepared by KrF pulsed laser deposition

Abstract We have studied the diamond-like carbon (DLC) and carbon nitride (CN) thin films deposited by KrF excimer laser (248 nm) ablation under various ambient gas conditions. DLC thin films were deposited on quartz and Si(100) substrates in pure hydrogen and helium gas at laser fluence of 2–10 J/cm 2 . Optical absorption measurements show that the DLC films prepared in a H 2 atmosphere of 800 mTorr with 8 J/cm 2 have an optical band gap of 2.0 eV. The tetrahedral amorphous carbon (ta-C) films deposited in helium gas have an optical band gap of approximately 1.0 eV. Incorporation of nitrogen atoms in the DLC films showed marked change in the optical properties when the N 2 mixture ratio in hydrogen exceeded 50%. The composite layered structures consisting of DLC and CN were formed to investigate the optical property in stacked CN films. Laser-induced fluorescent technique was used to study the dynamics of C 2 molecules produced by pulsed laser deposition at various ambient gas conditions.

Gas flow dependence on dynamic behavior of serpentine plasma in gliding arc discharge system

Gliding arc discharge systems have been used in various applications. However, the power of conventional gliding arc plasmas is relatively high and the system requires an additional discharge for its ignition and a resistor for current protection, which causes further total energy consumption. We have proposed ultraviolet (UV)-assisted gliding arc discharge systems supported by time-resolved understanding for electrical characteristics and dynamic behavior of serpentine plasmas. In this paper, we report on gas flow dependence on dynamic behavior of serpentine plasmas in a gliding arc discharge system with the irradiation of a low-pressure mercury lamp. Time-resolved evaluation was carried out using the results of synchronized measurement for serpentine plasmas with a high-speed camera, a high-voltage probe, and a current sensor. Waveforms and mean values of the applied voltage, current, power, impedance, and energy for serpentine plasmas in the UV-assisted gliding arc discharge system were studied. The power and impedance per unit plasma length were also evaluated.

Preparation of the hard CNX thin films using NO ambient gas by pulsed laser deposition

Abstract Pulsed laser deposition (PLD) technique has been widely used in thin film preparation because of its wonderful and excellent properties and amorphous carbon nitride (CNx) thin films are recognized to have potential for applications like hard coating and electron field emission device. We have deposited CNx thin films by KrF excimer laser – (λ= 248 nm) ablation of pure graphite target in pure NO gas ambient condition. In this paper, we have prepared the CNx thin films at various ambient NO gas pressure of 1.3–26 Pa and laser fluence of 2– 5J cm−2 on Si (100) substrate. We consider that the hardness of CNx thin films improves due to the increase the nitrogen/carbon (N/C) ratio. The N/C ratio depended on the ambient NO gas pressure and laser fluence. We obtainedthe maximum N/C ratio of 1.0 at NO 3.3 Pa. The typical absorption of CN bonds such as sp2 C–N, sp3 C–N, G band and D band were detected from the infrared absorption measurement by FTIR in the deposited CNx thin films.

Effects of Surface Coating on Cylinder Rods Prepared Using Sputtering Deposition Method with Modulated Magnetic Field

Tungsten (W), carbon (C), and titanium (Ti) thin films were prepared on carbide steel cylinder rods using a new magnetron sputtering deposition method to prevent their corrosion or increase their friction resistance. In this method, plasma was generated between the cylinder rod anode substrate and the cylinder pipe targets, and it moved toward the axial direction with the generation of a modulated magnetic field by a low-frequency alternating coil current. Experimental results showed that the surface morphology of the film became smooth, and the surface roughness of the film decreased. Deposition rate and film uniformity increased with the use of a modulated magnetic field, and friction coefficient increased as a result of the film preparation used.