Masafumi Yoneda

Observation of sp3 bonding in tetrahedral amorphous carbon using visible Raman spectroscopy

Visible Raman spectroscopy excited at 532 nm was used to characterize the carbon bonding in tetrahedral amorphous carbon (ta-C) films. The vibrational modes of the sp3 bonding in ta-C films were revealed directly. An additional Raman band occurring below 1350 cm−1 was observed. It consisted of two features centered on ∼1270 and ∼1170 cm−1, which were associated with sp3 bond stretching. The observed sp3 related Raman spectrum approached the vibrational density of states of amorphous diamond.

Structural and bonding properties of carbon nitride films synthesized by low energy nitrogen-ion-beam-assisted pulsed laser deposition with different laser fluences

Carbon nitride films were deposited by pulsed Nd:yttrium–aluminum–garnet laser ablation of graphite with assistance of low energy nitrogen-ion-beam bombardment. The nitrogen to carbon (N/C) atomic ratio, surface morphology, bonding state, and microstructure of the deposited carbon nitride films were characterized by x-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, micro-Raman spectroscopy, atomic force microscopy (AFM), and x-ray diffraction. The influence of laser fluence on the synthesis of carbon nitride films was investigated. The N/C atomic ratio of the carbon nitride films can reach the maximum at the highest laser fluence. XPS and FTIR analyses indicated that the bonding state between the carbon and nitrogen in the deposited films was significantly influenced by the laser fluence during deposition. The carbon–nitrogen bonding of C–N and C=N were observed in the films. In addition, α and β C3N4 phases were found to coexist in the carbon nitride films with relat...

Effect of temperature on carbon nitride films synthesized by ion-beam-assisted pulsed laser deposition

Carbon nitride thin films were deposited by pulsed laser deposition with nitrogen ion beam assistance at a substrate temperature varying from room temperature to 800 °C. The effect of the substrate temperature on the nitrogen content, surface morphology, structure, and electrical property of the carbon nitride films was investigated. The deposited films were characterized by atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and four-probe resistance. The nitrogen content of the deposited films reached its maximum value of 25% at a substrate temperature of 400 °C. AFM images revealed that an island structure occurred and developed on the surface of the films deposited at the high substrate temperature. FTIR and XPS spectra showed the existence of sp3C–N and sp2C=N bonds in the deposited films. The deposited carbon nitride films had an amorphous structure with two carbon nitride phases inclusions, which had a stoichiome...

Irradiation effect of low energy nitrogen-ion beam during pulsed laser deposition process on the structural and bonding properties of carbon–nitride thin films

Carbon–nitride thin films were deposited by pulsed laser ablation of graphite with assistance of low energy nitrogen-ion-beam irradiation. The nitrogen to carbon (N/C) atomic ratio, bonding state, microstructure, surface morphology, and electrical property of the deposited carbon–nitride films were characterized by x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, micro-Raman spectroscopy, x-ray diffraction (XRD), atomic force microscopy, and four-probe resistance. The irradiation effect of low energy nitrogen-ion beam on the synthesis of carbon–nitride films was investigated. The N/C atomic ratio of the carbon–nitride films reached the maximum at the ion energy of ∼200 eV. The energy of ∼200 eV was proposed to promote the desired sp3-hybridized carbon and the C3N4 phase. Electrical resistivity of the deposited films was also influenced by the low energy nitrogen-ion-beam irradiation. However, the low energy irradiation had little effect on the surface morphology of the films. XRD...

Diagnostics of KrF- and Nd:YAG-Laser Produced Carbon Plumes by Time- and Spatially-Resolved Spectroscopy

Graphite was ablated by three lasers and the resultant carbon plumes were investigated by time- and spatially-resolved spectroscopy. A KrF excimer laser (248 nm) and an Nd:YAG laser (1064 and 266 nm) were used. Near the target surface, C2 (Swan band) and ionic emissions from the plume produced by the 1064-nm laser at a fluence of 6 J/cm2 were stronger than those produced by the 248-nm and 266-nm lasers. The C emission lines (247.9 and 193.1 nm) produced by the KrF excimer laser were stronger than those produced by the other lasers. The most probable velocity of C+ was highly dependent upon the laser wavelength. The dependence of the most probable velocity on the fluence was small. The velocity of C+ ablated by the 248-nm laser was twice as fast as that ablated by the 1064-nm laser, when the fluence of the 1064-nm laser was six times as large as that of the 248-nm laser.

Effect of gas flow rate on shapes of weld bead sections. Study on high‐speed surface treatment by arc with laser (2nd report)

Introduction In our previous report, with respect to the phenomenon of the arc becoming unstable when the base metal is travelling at a high speed, an investigation was made by using the TIG arc and by varying the travelling speed of the base metal, the distance between the base metal and the tungsten electrode, and current values for the arc. The report then described that, when the arc which shows unstable behaviour is stabilised by using the laser together, the arc voltage stabilises and at the same time the shape of the weld bead improves. The main reason found for the stabilisation of the TIG arc was that the arc follows the movement of the base metal even when it moves at a high speed because (1) the anode spots of the arc can be easily formed around the molten pool produced by the laser and because (2) the tip of the arc where the stiffness of the arc weakens is drawn into the laser plume and as a result the plume tends to act as the path for the arc. In this report, in respect of the geometry of penetration by use of the TIG arc and the CO2 laser together, an investigation was made into the effect of the shielding gas flow rate and the laser beam mode to examine the behaviour of the arc.

Optical emission of plasmas in ultraviolet and infrared laser ablation of graphite by time-resolved spectroscopy

The optical emission spectra of the plasma produced by infrared and ultraviolet laser ablation of graphite in a vacuum were observed. The fundamental output of an Nd: YAG laser was used as the infrared laser. The fourth harmonic output of an Nd: YAG laser and a KrF excimer laser were used as the ultraviolet lasers. The emission intensity of the ionic carbon as well as C2 and C3 from the plasma produced by the infrared laser were stronger than that produced by the UV lasers at the same fluences. The C2 and C3 emission intensities decreased rapidly with increasing the distance from the target. The emission intensity of atomic carbon at 247.8 nm from the plasma produced by the KrF excimer laser was much stronger than that produced by the other lasers at the same laser fluence, due to the wavelenght of the KrF laser being so close to that of atomic carbons emission line as to raise its electrical state.

Influence of laser fluence on the synthesis of carbon nitride thin films by nitrogen-ion-assisted pulsed laser deposition

Carbon nitride films were deposited by pulsed Nd:YAG laser ablation of graphite with assistance of nitrogen ion beam bombardment. The nitrogen to carbon (N/C) atomic ratio, surface morphology and bonding state of the deposited carbon nitride films were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM). The influence of laser fluence on the synthesis of carbon nitride films was investigated. The N/C atomic ratio of the carbon nitride films can reach the maximum at the highest laser fluence. XPS and FTIR analyses indicated that the bonding state between the carbon and nitrogen in the deposited films was influenced by the laser fluence during deposition. The carbon-nitrogen bonding of C-N, C=N together with very few CequalsVN were found in the films. Results indicated that the laser fluence also had critical effect on the surface morphologies of the carbon nitride films.

Electrical and optical properties of ITO films deposited by excimer-laser-assisted EB method

In-situ excimer laser irradiation on growing films is expected to progress the surface reaction i.e. oxidation and surface migration of adatoms. This method therefore will be adequate for the low temperature formation of oxide semiconductor films showing a wide band energy gap. We studied the effect of in-situ excimer laser irradiation on the electron beam deposited Indium-Tin-Oxide (ITO) films and evaluated the electrical and optical properties. The ITO films deposited without laser irradiation at room temperature were opaque and had an amorphous structure, and its resistivity was higher than 0.04 (Omega) cm. On the other hand, the ITO films deposited with in-situ laser irradiation at room temperature showed good transparency and electric properties. The low resistivity, smaller than 9 X 10-4 (Omega) cm, and high transparency, more than 90 percent, were achieved simultaneously at room temperature. The films crystallized with in-situ laser irradiation had a cubic crystalline structure. The Hall mobility and carrier density of the ITO film were 12 cm2/Vs and 5.5 X 1022 cm-3, respectively. These result suggested that the in-situ excimer laser irradiation progressed the surface oxidation and eliminated the unstable adatoms on the surface of growing ITO films.