Yukihiko Yamagata

Optical emission study of ablation plasma plume in the preparation of diamond-like carbon films by KrF excimer laser

Optical emission study of the laser ablation plasma plume during the preparation of diamond-like carbon (DLC) films using KrF excimer (248 nm) pulsed laser deposition (PLD) has been carried out by means of a monochromator equipped with an intensified optical multichannel analyzer. In high vacuum (1×10−7 Torr), the emission lines from carbon ions of C+, C2+, and C3+ are observed in addition to atomic carbon emission lines, while no emission from the diatomic carbon molecule (C2) is observed. With increasing background nitrogen pressure up to 500 mTorr, the emission intensities of the C2 Swan band and the carbon nitride (CN) violet band increase. The diamond-like character of deposited DLC film degrades with background nitrogen pressure. The vibrational temperature of C2 and CN molecules decreases with the increasing of nitrogen pressure. The CN vibrational temperature for the first 2 μs after the laser pulse is very high and in agreement with the kinetic energy of monatomic carbon ions. The C2 vibrational ...

Comparative study of pulsed laser ablated plasma plumes from single crystal graphite and amorphous carbon targets. Part I. Optical emission spectroscopy

A comparative study of ablation plasma plumes originated from single crystal graphite (SCG) and amorphous carbon (a-C) targets during the preparation of diamond-like carbon (DLC) films by KrF excimer pulsed laser deposition (PLD) has been carried out by means of a monochromator equipped with an intensified optical multichannel analyzer. In high vacuum, the emission lines of carbon neutral C and ions of C+, C2+, and C3+ can be observed from both the SCG and a-C plasma plumes. The emission intensity from C atoms increases with laser energy density (EL) increase for both cases. The C2 emission intensity from the SCG plasma plume changes drastically with EL, while that from the a-C plasma plume is almost constant. The C2/C emission intensity ratio for the a-C case decreases with EL increase. As for the SCG case, the C2/C ratio decreases with EL increase up to 3.0 J/cm2, and increases slightly with further EL increase. Nanohardness of the deposited films decreases with the increase of the C2/C emission intensi...

Electrostatic measurement of plasma plume characteristics in pulsed laser evaporated carbon

A triple Langmuir probe measurement has been implemented to investigate plasma plume character in low fluence (∼3.0 J/cm2) pulsed laser evaporation (PLE) discharges and has been found to be an extremely valuable tool. Absolute plasma plume density estimates are found to reside in the range 1.0×1013–2.0×1014 cm−3 for vacuum pulses. A simple heavy particle streaming model for vacuum pulses allows estimates of the plume ionization fraction of ∼10%. This is consistent with typical deposition inventory suggesting that high kinetic energy ions may play an important role in diamond-like carbon (DLC) film deposition. Electron temperature inferred from the electrostatic probe is found to consistently reside in the range 0.5–3.0 eV, and appears to be uninfluenced by operating conditions and large variations in Ar and N2 fill gas pressure. Consistent with strong plume ion and neutral particle coupling to the background fill, constancy of Te suggests expulsion of background gas by the energetic plume. The leading edg...

Structure and polarization in epitaxial ferroelectric PbZr0.52Ti0.48O3/YBa2Cu3O7−x/Nd:YAlO3 thin films

We fabricate epitaxial PbZr0.52Ti0.48O3/YBa2Cu3O7−x submicron film ferroelectric/superconductor heterostructures on the single-crystal YAlO3+1%Nd2O3 substrate by the pulsed laser deposition technique. Frequency independent low loss tan δ=0.04 and dielectric constant of 950, high electric resistivity ρ (150 kV/cm)=6×1011Ω cm, remnant polarization of 32 μC/cm2, no visible fatigue after 107 short bipolar pulses switching indicate excellent electrical performance of the new capacitor structure. The slight crystallite polar axis misalignment and depolarizing effect were found to be responsible for the shape of the apparent polarization loop. The only fitting parameter depolarizing coefficient N=2.37×10−4 gives the best fit between theory and experimental data and corresponds to prolate ellipsoidal shaped crystallites with the length-to-diameter ratio of 140.

Optical emission study of the laser plasma plume produced during diamondlike carbon thin film preparation

Abstract We have studied the application of the diamondlike carbon (DLC) film as a protective coating layer for high temperature superconducting thin films. Recently, the DLC film was proposed as an attractive material for field electron emitter device. We report on spectroscopic properties of the KrF laser plasma plume produced during the DLC thin film deposition. Optical emission measurements showed appearance of such neutral and ionic species as H, C, C + , CH, CH + , C 2 H + . Strong emission from neutral and ionic molecules CH, C 2 , C 2 H + produced by the reaction in the gaseous phase has been observed with the ambient hydrogen gas pressure increase. The calculated velocities of CH and C 2 H + molecules at the distances of 10–20 mm from the target are found to be 5.0×10 3 m/s and 9.1×10 3 m/s, correspondingly. The properties of the DLC thin films are strongly affected by the laser plasma plume dynamics. The DLC film deposited on MgO (100) at room temperature and 200 mTorr hydrogen pressure was almost transparent in the visible light range and had an optical band energy gap of 2.0 eV, which is about half of that of a diamond.

Performance tests of newly developed adsorption/plasma combined system for decomposition of volatile organic compounds under continuous flow condition

The adsorption/plasma decomposition with the combination of adsorption honeycomb-sheets and a plasma element is a new technology for small-sized apparatuses to decompose volatile organic compounds (VOCs) at concentrations lower than about 100 ppm. The feasibility of the prototype adsorption/plasma decomposition apparatus was evaluated with the simulated exhausts containing one VOC component and with real exhausts from a painting booth and an adhesion factory. The apparatus decomposed VOCs effectively at the painting booth exhaust but not always satisfactorily at the adhesion factory exhaust. The performance test results with real exhausts were discussed with respect to the concentration and discharge pattern of the exhausts and the basic properties of the system such as cooperation of adsorption and plasma reaction and the concentration dependence of the performance.

Application of the dielectric barrier discharge to detect defects in a teflon coated metal surface

In the semiconductor industry, flexible stainless steel tubes, the inside of which are coated with thick Teflon films, by the splay coating method, have been used to prevent their degradation and erosion by organic solvents. We have developed an inspection system to detect pinholes and cracks in the deposited Teflon films, and the dielectric barrier discharge (DBD) was employed to reduce residual substances and damages to the coated film in the tube. Conducting water contained in the cylinder-like glass pipe was used as a liquid electrode to apply a high voltage at any portion of the tube tested. A defective part with a pinhole was modelled by a point electrode in this experiment, because the uncoated defective part has a lower electric breakdown voltage. High frequency voltage (10 kHz) was applied between the point electrode and the liquid electrode. The level of the liquid electrode was varied to detect the occurrence of a microdischarge. It is found that the number of current pulses due to the microdischarge can be used to estimate the size and location of the defective uncoated point of the sample tube.

Investigation of the thermalization of sputtered atoms in a magnetron discharge using laser‐induced fluorescence

The thermalization of sputtered atoms in a magnetron discharge was investigated using laser‐induced fluorescence. The results clearly indicated for the first time that the velocity distribution agrees well with the Thompson formula [M. W. Thompson, Philos. Mag. 18, 377 (1968)] for d/λ≪1, while a thermalized component becomes appreciable for d/λ≳1, where d is the distance from the cathode surface and λ is the mean free path of sputtered atoms for collisions with filling gas atoms.

Laser-ablated plasma for deposition of ZnO thin films on various substrates

Abstract We report optical and structural properties of ZnO films deposited by pulsed laser deposition technique on 1100) n-typesilicon and quartz substrates at various pressures of back ground gas. ZnO plasma was created using KrF laser 1248 nm) atvarious pressures of the ambient gas, oxygen. Laser induced plasma at varying fluence on the target was investigated using optical emission spectroscopy and 2-D images of the expanding plumes. X-ray diffraction, atomic force microscopy, and spectro-photometry were used to characterize as grown films.

Spatial distribution of carbon species in laser ablation of graphite target

We report on the temporal evolution and spatial distribution of C2 and C3 molecules produced by KrF laser ablation of a graphite target using laser induced fluorescence imaging and optical emission spectroscopy. Spatial density profiles of C2 were measured using two-dimensional fluorescence in various pressures of different ambient (vacuum, nitrogen, oxygen, hydrogen, helium, and argon) gases at various ablation laser fluences and ablation area. A large yield of C2 is observed in the central part of the plume and near the target surface and its density and distribution was affected by the laser fluence and ambient gas. Fluorescent C3 was studied in Ar gas and the yield of C3 is enhanced at higher gas pressure and longer delay times after ablation.