Munehide Katsumura

An ion source using laser ablation

This article describes the measurement of the fractional ionization in an ablated plume produced by excimer laser, and the application of the plume as an ion source. Laser ablation of iron, aluminum, and tantalum with a KrF excimer laser was performed in a vacuum chamber. The ablated plume was caught by a cup type electrode used to measure the amount of charged particles as current wave forms. Applying electrostatic potential larger than 40 V, the current wave forms were separated into electropositive and electronegative peaks. Each peak indicates ions and electrons, respectively. The amount of ions, 6×1013 ions/pulse, was estimated by integrating the electropositive peak. The ionization degree of 1.7% was also estimated by a series of analyses. For an aluminum target, the ion current reached 2 A at the peak and 1 mA on average at 60 kJ/m2, 500 mJ, and 50 Hz.

Chemical structure change of thin films prepared from nonpolymeric organic compounds by pulsed laser deposition

Thin films from six kinds of nonlinear optical nonpolymeric organic compounds were prepared by pulsed laser deposition (PLD) using a KrF excimer laser (248 nm) at various fluences up to 50 mJ/cm2. Changes in the chemical structure of the films with changes in fluence were studied. The experimental results show that for every compound at least minor decomposition has already started at the threshold fluence for deposition. More serious degradation occurs with increasing fluences, and little of the original chemical structure remains in films prepared by PLD at a fluence of 50 mJ/cm2.

New bonding method of metals and ceramics using laser ablation

A new application of excimer laser, surface modification of ceramics for bonding a metals to ceramics is demonstrated in this paper.Excimer laser irradiation of Si3N4and AIN gave an Si and AI rich layer on the surface of Si3N4 and AIN, respectively. These layers were the by-products of the decomposition of ceramics. Although they often cause deterioration of qualities in processing such as cutting and ablation, we found them effective as the binder for bonding ceramics to metals such as Cu and AI. The strength of the bonding interface between the laser irradiated Si3N4 and the ion sputtered surface of the Cu, for example, exceeds the strength obtained by conventional bonding methods. The tensile strength of 100-200MPa were obtained even at low bonding temperature, 560K.A new application of excimer laser, surface modification of ceramics for bonding a metals to ceramics is demonstrated in this paper.Excimer laser irradiation of Si3N4and AIN gave an Si and AI rich layer on the surface of Si3N4 and AIN, respectively. These layers were the by-products of the decomposition of ceramics. Although they often cause deterioration of qualities in processing such as cutting and ablation, we found them effective as the binder for bonding ceramics to metals such as Cu and AI. The strength of the bonding interface between the laser irradiated Si3N4 and the ion sputtered surface of the Cu, for example, exceeds the strength obtained by conventional bonding methods. The tensile strength of 100-200MPa were obtained even at low bonding temperature, 560K.

In-situ laser crystallization of EB-deposited ITO films

We formed tin- doped Indium oxide (ITO) films at room temperature (R.T.) by using the excimer laser assisted electron- beam(EB) deposition method. The effect of laser irradiation on crystallization of EB-deposited ITO films was investigated. We made crystallographic analysis for ITO films deposited on glass and single crystal plates.By using the excimer laser assisted EB- deposition method ITO film is hetero-epitaxially grown on an YSZ single crystal substrate at R.T.. The value of misfit strain between substrates and films is suggested to intensely influence the growth orientation of films.The best resistivity and transparency were obtained for ITO films deposited at R.T. at the laser fluence of 22mJ/cm2, resistivity, ρ, mobility, μ, and free-carrier density, n, being ρ = 9×10−4 Ω cm, μ = 12cm2/ Vs and n= 5.5×1020cm−3, respectively. The film formed without laser assist is black and opaque, whereas the film formed with laser assist is transparent in the visible region of the spectrum, 400 ∼ 800nm, where t...

A particle filtering method for pulsed laser deposition

This paper describes both the velocity distribution of laser-ablated tantalum atoms in a plume and the plume temperature in order to discuss the behavior of particles inpulsed laser deposition (PLD). Optical time-of-flight (TOF) was used for the analysis. The velocity distributions of tantalum atoms ablated at the laser fluence in a range of 4-20J/cm2 agreed well with the Maxwell-Boltzmann distribution with center-of-mass velocity. This agreement enabled us to estimate the atom density distribution in the plume.Based on the analysis of atom density distribution in the plume, a simple particle filter for PLD using a pair of thin plates with parallel slits was designed to reduce the number of large particles, such as splashed liquid, which often deposit on the film surface causing to deterioration in film properties; i.e., in transparency, uniformity and corrosion resistance.With the particle filter, tantalum films with a smooth and particle-free surface were obtained in a vacuum over a range of 10−3-10Pa.This paper describes both the velocity distribution of laser-ablated tantalum atoms in a plume and the plume temperature in order to discuss the behavior of particles inpulsed laser deposition (PLD). Optical time-of-flight (TOF) was used for the analysis. The velocity distributions of tantalum atoms ablated at the laser fluence in a range of 4-20J/cm2 agreed well with the Maxwell-Boltzmann distribution with center-of-mass velocity. This agreement enabled us to estimate the atom density distribution in the plume.Based on the analysis of atom density distribution in the plume, a simple particle filter for PLD using a pair of thin plates with parallel slits was designed to reduce the number of large particles, such as splashed liquid, which often deposit on the film surface causing to deterioration in film properties; i.e., in transparency, uniformity and corrosion resistance.With the particle filter, tantalum films with a smooth and particle-free surface were obtained in a vacuum over a range of 10−3-10Pa.

Deposition of tantalum-oxide films using laser ablation

The L-PVD of tantalum-oxide using tantalum target and KrF excimer laser was investigated experimentally in the formation of a high performance corrosion-resisting film.This report describes the effects of oxygen pressure during ablation on chemical composition, surface morphology and crystal structure of formed films. An EMPA was used to determine the chemical composition of the deposited films.Both the deposition rate of films and the oxygen content of deposited films increased gradually with increasing oxygen pressure up to 10Pa. The SEM images showed a smooth film surface in this pressure region. At 5Pa the oxygen/tantalum ratio of films measured was 2.5, which is equal to the ratio of Ta2O5. According to the XRD results, the films were amorphous. A crystallized Ta2O5 film, however, was obtained after annealing at 973K in vacuum.Both the deposition rate of films and the oxygen ratio in deposited films indicated obvious saturation around 100Pa. At oxygen pressures higher than 50Pa, the surface of deposited films abruptly became porous.The L-PVD of tantalum-oxide using tantalum target and KrF excimer laser was investigated experimentally in the formation of a high performance corrosion-resisting film.This report describes the effects of oxygen pressure during ablation on chemical composition, surface morphology and crystal structure of formed films. An EMPA was used to determine the chemical composition of the deposited films.Both the deposition rate of films and the oxygen content of deposited films increased gradually with increasing oxygen pressure up to 10Pa. The SEM images showed a smooth film surface in this pressure region. At 5Pa the oxygen/tantalum ratio of films measured was 2.5, which is equal to the ratio of Ta2O5. According to the XRD results, the films were amorphous. A crystallized Ta2O5 film, however, was obtained after annealing at 973K in vacuum.Both the deposition rate of films and the oxygen ratio in deposited films indicated obvious saturation around 100Pa. At oxygen pressures higher than 50Pa, the surface of deposi...

Deposition of amorphous alloy films by excimer laser ablation

Pulsed laser deposition method (PLD) is known to have high deposition rate per pulse which gives high cooling rate during film formation. PLD is therefore suitable for forming amorphous alloy films. In this research we examined the formation of Ta-Ni amorphous alloy films by PLD from Ta-Ni sintered targets. Ta-Ni amorphous alloys have the extremely high corrosion-resistance in both acid and alkaline solution and promising characteristics as catalyst carrier.Amorphous films in a wide composition range of Ta-40-80mass% Ni were obtained by PLD. At a laser energy density of 20J/cm2, Ni having a lower boiling point than Ta, was ablated preferentially. On the other hand, at the laser energy density of 28J/cm2, we got the films having the same composition as the targets. The grain size of the films was smaller than that of Ta-Ni amorphous flakes prepared by a splash-quenching method. It was suggested that PLD gave larger cooling rate than a splash-quenching method.Pulsed laser deposition method (PLD) is known to have high deposition rate per pulse which gives high cooling rate during film formation. PLD is therefore suitable for forming amorphous alloy films. In this research we examined the formation of Ta-Ni amorphous alloy films by PLD from Ta-Ni sintered targets. Ta-Ni amorphous alloys have the extremely high corrosion-resistance in both acid and alkaline solution and promising characteristics as catalyst carrier.Amorphous films in a wide composition range of Ta-40-80mass% Ni were obtained by PLD. At a laser energy density of 20J/cm2, Ni having a lower boiling point than Ta, was ablated preferentially. On the other hand, at the laser energy density of 28J/cm2, we got the films having the same composition as the targets. The grain size of the films was smaller than that of Ta-Ni amorphous flakes prepared by a splash-quenching method. It was suggested that PLD gave larger cooling rate than a splash-quenching method.

Deposition of Mo films by ion beam assisted excimer laser PVD method

The effect of ion beam irradiation on the adhesion strength of Mo films was examined using an ion beam assisted excimer laser PVD apparatus. We also examined the effect of energy density, target-substrate distances, and target rotation on the surface morphology. Spectroscopic diagnosis for a Mo plume was performed. The adhesion of the Mo film was improved by ion beam irradiation which removes a thin surface layer of the substrate. Smooth surface Mo films without droplets were successfully formed under laser fluence conditions of less than 0.25MJ/m2, a target-substrate distance greater than 40mm, and with target rotation. Mo films with a b.c.c. structure show the (110) preferred orientation of . The Mo plume generated by laser ablation is in an excited state containing Mo+.The effect of ion beam irradiation on the adhesion strength of Mo films was examined using an ion beam assisted excimer laser PVD apparatus. We also examined the effect of energy density, target-substrate distances, and target rotation on the surface morphology. Spectroscopic diagnosis for a Mo plume was performed. The adhesion of the Mo film was improved by ion beam irradiation which removes a thin surface layer of the substrate. Smooth surface Mo films without droplets were successfully formed under laser fluence conditions of less than 0.25MJ/m2, a target-substrate distance greater than 40mm, and with target rotation. Mo films with a b.c.c. structure show the (110) preferred orientation of . The Mo plume generated by laser ablation is in an excited state containing Mo+.