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Surface contamination of an adherend has an influence on its adhesive bonding properties. To investigate this phenomenon, various contaminants, including silicone oil, mineral oil, a fluorine relea...

Laser processing of polymeric materials by means of 100-mW class QCL lasers with emission wavelength of 7.728 and 4.329 μm were examined. Polymeric materials show absorption bands based on transitions between vibronic levels in mid-infrared (MIR) wavelength. Since such absorption bands are very sharp, resonant conditions with laser wavelength are critical. Quantum cascade laser (QCL) is a promising laser source for mid-infrared laser processing; emission wavelength can be customized by changing the heterostructure. In this work, we have employed 100-mW class QCLs and applied for focused irradiation at several polymeric materials, polypropylene (PP), polycarbonate (PC), polyacetal (POM).

To inspect surface contamination of pre-bond surface for adhesive bonding, laser-induced breakdown spectroscopy (LIBS) was examined. LIBS could detect silicone oil adhered at the surface of alumini...

The mid-infrared range is an important spectrum range where materials exhibit a characteristic response corresponding to their molecular structure. A free-electron laser (FEL) is a promising candidate for a high-power light source with wavelength tunability to investigate the nonlinear response of materials. Although the self-amplification spontaneous emission (SASE) scheme is not usually adopted in the mid-infrared wavelength range, it may have advantages such as layout simplicity, the possibility of producing a single pulse, and scalability to a short-wavelength facility. To demonstrate the operation of a mid-infrared SASE FEL system in an energy recovery linac (ERL) layout, we constructed an SASE FEL setup in cERL, a test facility of the superconducting linac with the ERL configuration. Despite the adverse circumstance of space charge effects due to the given boundary condition of the facility, we successfully established the beam condition at the undulators and observed FEL emission at a wavelength of 20 μm. The results show that the layout of cERL has the potential for serving as a mid-infrared light source.

Laser lift-off is one of potential candidates for new additive manufacturing technologies since it would realize additive patterning in micron/submicron resolution under atmospheric and room-temperature conditions. We have developed a variety of laser lift-off processes towards electronics, bio-sensing and medical treatments. In this paper, two kinds of laser lift-off methods were introduced: $\underline{L}$aser-$\underline{I}$nduced $\underline{D}$ot $\underline{T}$ransfer (LIDT) for micro/nanodots printing and $\underline{L}$aser-$\underline{I}$nduced $\underline{F}$orward $\underline{T}$ransfer with $\underline{o}$ptical stamp (LIFTop) for micropatterning of various functional films.

For high quality film printing, we have newly developed a laser-induced forward transfer with optical stamp (shortly, LIFTop), that consists of a two-step transfer process. In the first step, functional films were transferred onto a transparent polymer having high adhesiveness and elasticity like PDMS, which we call “optical stamp”. This stamp helps to avoid the transferred film from pattern spread and fracture. Then, the transferred micro-pattern on the optical stamp was further transferred onto a final target. In this talk, metal and transparent conductive oxide film transfer was demonstrated using our new LIFT process.

Laser-induced dot transfer (LIDT) is one of promising additive manufacturing techniques because it can realize flexible patterning of micron and submicron-sized dots even at atmospheric room-temperature conditions. In the LIDT process, a laser pulse is tightly focused onto a source film, leading to a transient melting of the film followed by sub-spot transfer using one-to-one microdot deposition with laser-illuminated area. Recently, we have developed a novel double-pulse LIDT process using the first pulse for preheating the source film and the second pulse for dot transfer. To investigate the double-pulse effect on microdot transfer of oxides, temporal high-temperature distributions of a thick indium tin oxide source film during double-pulse irradiation have been simulated using a Finite Element Method (FEM) approach. As a result, preheating by the first pulse decreased a difference in film temperature along both the film thickness and in-plane directions. This is effective to avoid film fracture, leading to high-quality patterning of a wide variety of microdots.

A simple fabrication method for patterned carbon nanotube (CNT) films is presented, using the concept of light-induced dispersibility switching with a photoresponsive dispersant. A comparison with other dispersants highlights the important role played by an azobenzene-derived cationic molecule as a photoisomerizable dispersant in the successful manufacture of patterned CNT films. Upon UV irradiation for a short time (∼0.5 min), a dispersion composed of CNTs and photoresponsive dispersant exhibited a dispersibility change due to the photoisomerization of the photoresponsive dispersant, and then the dispersant detached-CNT deposited onto the substrate. Our method enables patterned CNT films to be obtained directly from CNT dispersions onto various substrates such as glass, polyethylene terephthalate, and silicone rubber, expanding the possible applications of CNT films. Furthermore, the process minimizes the amount of the residual dispersant in the fabricated CNT film, reducing the amount of impurities, and improving the quality of the patterned CNT film.

For higher cell-to-module efficiency in Cu(In,Ga)Se2 (CIGS) thin-film solar cells, it is important to reduce the loss of active area due to integrated connection. The integrated connection contains three scribing processes: P1 (back contact insulation), P2 (electrical connection) and P3 (transparent conductive oxide, shortly TCO front contact insulation). In this work, we focused on ultrashort-pulse laser scribing (λ=1034 nm, Δτ=300 fs) of TCO via lift-off process as damage-less P3 scribing of CIGS thin-film solar cells. The lift-off of TCO was caused by laser ablation of only an upper part of CIGS light-absorbing layer. The dependence of lift-off behavior on the laser pulse energy and TCO film thickness has been investigated. It was observed that the lift-off of TCO formed a heat-affected zone (HAZ) with a thickness up to 250 nm beneath the trench bottom, where the CIGS experienced to melt. Further, thinner TCO film required lower laser energy threshold for the TCO lift-off, which is favorable to higher solar cell efficiency due to smaller HAZ. Using the TCO liftoff as P3, a submodule with an active area of approximately 3.5 cm2 made by all laser scribing exhibited the conversion efficiency of 11.6 %. After post-annealing at 85 °C for 15 h in vacuum for recovering laser-induced damages, the efficiency was successfully improved to 15.0 %, which is comparable to mechanically-scribed one.

We have newly developed a double-pulse laser-induced dot transfer technique to realize ondemand deposition of functional oxide microdots under room-temperature atmospheric conditions. In our double-pulse system, the first pulse was irradiated to preheat an oxide source film, and then the second pulse was more tightly focused on the same position to deposit an oxide microdot onto a receiver substrate. As a model case, indium tin oxide microdots with much smaller lateral dimensions than the laser focal area were reproducibly arrayed on a silica glass substrate by the doublepulse process, while there were microdot vacancies at a rate of approximately 30 % in the case of a single-pulse process without preheating. In order to explore the effect of double-pulse, laser-induced temperature distribution was also investigated from a finite elemental approach.

Neutral fragments from a nanosecond KrF excimer laser-ablated carbon fiber reinforced plastic (CFRP, carbon fiber/epoxy resin composite) were investigated by laser-ionization time-of-flight (TOF) mass spectrometry in order to explore the laser ablation dynamics of CFRP. The neutrals were detected after the post-ionization by an ArF excimer laser pulse at variable delay times, td, relative to the ablation KrF excimer laser pulse. Depending on the ablation fluence, TOF mass spectra and laser-etched surface morphology drastically changed. At the laser fluence of 0.3 J·cm -2 , the resins were preferentially ablated. The TOF mass spectra contained a main peak at 36 amu assigned to C3 + in early delay times, and then the main peak changed to 39 amu assigned to C3H3 + . At 1.0 and 1.5 J·cm -2 , both of carbon fibers and resins were ablated. The most prominent peak was C3 + independent of the delay time. The delay-time distribution of C3 + exhibited a single peak at 0.3 J·cm -2 and then changed to two peaks at 1.5 J·cm -2 . The fits with shifted Maxwell-Boltzmann distribution gave good agreement, suggesting transient maximum CFRP temperature of 4700, 6400, and 7100 K at 0.3, 1.0 and 1.5 J·cm -2 , respectively.

To inspect surface contamination of the surfaces for adhesive bonding, laser-induced breakdown spectroscopy (LIBS) was examined. A LIBS setup which gave an improved limit of detection (LOD) of 5.29 mg mm−2 was used for evaluation of Si contamination on steel and CFRP substrates. The LOD values obtained were 1.35 and 11.4 mg mm−2 for steel and CFRP, respectively. These LOD values were affected by several factors such as efficiency of energy transfer to Si and interference with trace substances included in the surface layer of substrates. Silicone included in the resin layers of CFRP was investigated by multiple pulse LIBS measurements.

Laser-induced breakdown spectroscopy (LIBS) was examined to detect a trace substance adhered onto Al alloys for the surface inspection of materials to be adhesively bonded. As an example of Si contamination, silicone oil was employed and sprayed onto substrates with a controlled surface concentration. LIBS measurements employing nanosecond UV pulses (λ = 266 nm) and an off-axis emission collection system with different detecting heights were performed. Because surface contaminants are involved in the plasma formed by laser ablation of the substrates, the relative contribution of the surface contaminants and the substrates to the plasma emission could be changed depending on the conditions for plasma formation. The limit of detection (LOD) was evaluated under several detecting conditions for investigating the factors that affected the LOD. A significant factor was the standard deviation values of signal intensities obtained for the clean substrates. This value varied depending on the measurement conditions. For the Al alloy (A6061), the smallest LOD obtained was 0.529 μg cm−2. Furthermore, an improved LOD (0.299 μg cm−2) was obtained for the Al alloy with a lower Si content.

were fabricated with a fluence of 1.3 J/cm 2 , a pulse repetition of 80 Hz, and various pulse numbers. Special care was directed to maintaining in-focus conditions for etching. In the fabrication of 5-µmwide microtrenches, etch rates of 5.3 nm/pulse evaluated for trenches with depths of less than 4 µm increased by a factor of 2.55 to 13.5 nm/pulse when the trenches became deeper than 16 µm. Such variation in the etch rate reduced with width and became negligibly small for 20-µm-wide microtrenches. Based on a similar dependence on width, the variation in etch rate with depth can be related to the size effect observed in LIBWE. As a factor causing the size effect as well as the variation in etch rate with depth, the interaction between the laser-heated surface and the solution in an early time region of the laser-induced phenomena is proposed.

Flexible and rapid preparation of FeSi2 microdots and indium tin oxide (ITO) microstructure patterns was performed using laser-induced forward transfer with a nanosecond high-frequency diode-pumped solid-state laser/galvanometer-based point-scanning system. Different types of source materials, i.e., FeSi2 and ITO, were used to explore the materials dependence of transfer. FeSi2 spheres with a lateral diameter of 5.5 μm were successfully arrayed on a micrometer scale. Sub-spot transfer was achieved, and we refer to this as laser-induced dot transfer (LIDT). In the case of ITO, although the transferred shape is flower-like rather than spherical, site-controlled transfer was achieved. The LIDT technique is useful for integrating functional micro-patterns with sub-spot resolution under room-temperature atmospheric conditions.

An indirect laser processing, laser-induced backside wet etching (LIBWE) is one of effective techniques for flexible laser-direct-write (LDW) type micromachining of transparent materials. Micromachining by LIBWE employing a diode-pumped solid state (DPSS) green laser and a galvanometer-based point scanning system was examined with employing organic dye solution and liquid metal as laser-absorbing media. LIBWE using liquid metal absorber showed smaller threshold pulse energies for etching (9.1 μJ/pulse) than that using organic dye solution (33 μJ/pulse). Different morphologies of etched surfaces were observed for different laser-absorbing media, indicating different mechanisms involved in the etching processes. The laser-induced dynamic phenomena were investigated by means of transient reflection measurements. The different contribution of direct and indirect actions of laser pulses was indicated for LIBWE employing different laser-absorbing media.

Slanted microstructures were fabricated on silica glass by laser-induced backside wet etching (LIBWE) with gradual shift of the area irradiated by normal incidence. Slanted microtrenches with tilting angles up to about 30 degrees could be fabricated by lateral shift of the irradiated area with the speed of ~5.0 nm·pulse under the conditions showing the vertical etching with rate of 7.0 11 nm·pulse. Tilting angle could be controlled by the speed of lateral shift the irradiated area during the etching. Such structures were formed as a result of both lateral and vertical etching at the etch front. The trench structure fabricated by drastic shift of the irradiated area indicated that the etching of the sidewalls occurred at the area with height of around 400 nm.

The well-controlled fabrication of microtrenches including inclined features using normal incidence with gradual shifting of the irradiated area was demonstrated. Based on the variation of trench width depending on the laser fluence, the existence of gaps between the edge of the irradiated area and sidewall of the trench was shown. Because of these gaps, the shifted laser pulse can stay at the bottom of the trenches in the fabrication of the inclined features. In laser-induced backside wet etching (LIBWE), the photo-activated region generated within organic solution would act on the glass surface and results in etching. It was indicated that the photo-activated region generated at the bottom of the trenches acted not only on the bottom of the trench but also on the sidewalls. Based on such etching of the sidewall, fabrication of inclined features becomes possible. In this method, the tilting angle can be changed within one deep trench. Flexible structure formation deep inside the silica glass can be achieved.

The effect of laser-induced heat on Cu(In,Ga)Se2 solar cells was evaluated by scanning spreading resistance microscopy (SSRM) to improve the laser scribing (LS) quality. Two types of LS were examined for electrical isolation; that using transparent conductive oxide (TCO) lift-off resulted in a higher conversion efficiency of 17.4% and shunt resistance of 5 × 103 Ωcm2. SSRM images confirmed the absence of shunt paths between the laser-induced low-resistance layer at the trench bottom and the top TCO layer, which resulted in the high shunt resistance. Ultrashort-pulse LS would be a promising tool for reducing the dead area and increasing the throughput by high-speed scribing.

Fabrication of FeSi2 nano- and microdot array was performed by utilizing droplet ejection through laser-induced forward transfer, which we named laser-induced dot transfer (LIDT). An amorphous FeSi2 alloy source film on a transparent support was illuminated from the support by a nanosecond excimer laser pulse patterned into migcrogrid form, resulting in size- and site-controlled dot deposition. Micro-Raman spectroscopy confirmed β-FeSi2 semiconducting crystalline phase even on unheated substrates. Moreover, the microdots exhibited near-infrared photoluminescence at the peak wavelength of 1.57 μm, which comes from the β-FeSi2 crystalline phase precipitated during the LIDT process. The dot size was successfully reduced to approximately 500 and 300 nm in diameter and height, respectively. This technique is useful for integrating functional nano- and microdots under atmospheric room-temperature conditions.

We have investigated a one-step method to fabricate a microstructure on a silica glass plate by using laser-induced backside wet etching (LIBWE) that consists of excimer laser mask projection system and diode-pumped solid state (DPSS) laser beam scanning system. Well-defined deep microtrenches without crack formations on a fused silica glass plate were fabricated by LIBWE method with the UV lasers. We have demonstrated the micro- fabrication of pits-array and patterned grating on the surface of silica glass plates by LIBWE method at 248 nm and 266 nm with dye solutions. The two new systems allow us to use rapid prototyping of high precision surface microfabrication of silica glass as laser direct-write processing.

Deep microtrenches having a high aspect ratio on the surfaces of silica glass were fabricated by laser-induced backside wet etching (LIBWE). The focused laser beam of a diode-pumped solid state (DPSS) UV laser at λ = 266 nm on the repetition rate of 30–40 kHz was directed to the sample cell of the glass by a galvanometer-based point scanning system. Vertical and inclined trench structures were successfully fabricated on the glass by changing the incident angle of the laser beam. The depth of filed (DOF) in LIBWE was analyzed by inclined laser irradiation. Flexible rapid prototyping by the mask-less exposure system was demonstrated.

By using laser-induced backside wet etching (LIBWE), we have fabricated very deep micro-trenches in silica glass of 9-μm width and 300-μm depth (aspect ratio ≈ 33). In this paper, we present the details of fabricating the micro-trenches, and discuss why such a deep micro-trench is available by the LIBWE method.

For high-resolution printing, we have developed a novel way of functional microdots deposition based on laser-induced forward transfer, which is referred to laser-induced dot transfer (LIDT). LIDT is one of promising additive manufacturing techniques because it can realize flexible patterning of micron and submicron-sized dots at atmospheric room-temperature conditions. Recently we have achieved printing of functional oxide microdots by a double-pulse LIDT with the first pulse for preheat and the second pulse for transfer, resulting in more precise control of laser-induced hightemperature and thermal-stress in a source film. In this paper, temporal temperature distributions during the transfer process have been investigated using a finite element method approach. High-resolution printing of functional microdots is promising for future optoelectronic integrations.

We have developed a novel design for a microfluidic device incorporating a two-dimensional microbead array by using silica glass plates structured by the laser-micromachining method, Laser-Induced Backside Wet Etching (LIBWE). Surface functionalized borosilicate glass and polymer microbeads 10 µm in diameter, which act as detectors, were fixed in etched microstructures and sealed with a polydimethylsiloxane plate to form a microfluidic system. The beads are regularly arranged in a two-dimensional manner without being in contact with any other. Analytes are supplied as a solution flowing in microchannels. The pressure-driven flow in the microchannels was investigated. The successful capture of fluorescein isothiocyanate by amino groups as well as that of biotin by avidin on the beads' surface was confirmed by fluorescence microscopy.

We have constructed a system for surface-microstructuring transparent materials, such as silica glass, using laser-induced backside wet etching (LIBWE), which includes an excimer laser and a mask projection system. In this report, we describe the advantages of the LIBWE method and present various results showing deep microtrenches fabricated using this method. We examine the applicability of this method to rapid prototyping, and propose a mechanism for the formation of deep microtrenches.

Microstructures with well-defined micropatterns were fabricated on the surfaces of silica glass using a laser-induced backside wet etching (LIBWE) method by diode-pumped solid state (DPSS) UV laser at the repetition rate of 10 kHz. For a demonstration of flexible rapid prototyping as mask-less exposure system, the focused laser beam was directed to the sample by galvanometer-based point scanning system. Additionally, a diagnostics study of plume propagation in the ablated products of toluene solid film was carried out with an intensified CCD (ICCD) camera.

The adsorption process and valence band structure of Ag on ZnO(1010) have been investigated by angle-resolved photoelectron spectroscopy utilizing synchrotron radiation. The coverage-dependent measurements of the Ag 4d band structure reveal that the Ag bands with a dispersing feature are formed even at low coverages and that the basic structure of the bands is essentially the same throughout the submonolayer region. These results indicate that the Ag atoms aggregate to form islands with an atomically ordered structure from the low coverages. Upon annealing the Ag-covered surface at 900 K, the Ag 4d band undergoes only a minor change, suggesting that the ordered structure within the Ag islands is persistent against mild annealing. From the dispersive feature of the Ag 4d states, we propose that the atomic structure has locally rectangular symmetry with a good lattice matching with the ZnO(1010) surface.

To generate dibenzotetrakisdehydro[12]- and dibenzopentakisdehydro[14]annulenes ([12]- and [14]DBAs) having a highly deformed triyne moiety, [4.3.2]propellatriene-anneleted dehydro[12]- and dehydro[14]annulenes were prepared as their precursors. UV irradiation of the precursors resulted in the photochemical [2 + 2] cycloreversion to generate the strained [12]- and [14]DBAs, respectively. The [12]DBA was not detected by 1H NMR spectroscopy, but it was intercepted as Diels-Alder adducts in solution, suggesting its intermediacy. Its spectroscopic characterization was successfully carried out by UV-vis spectroscopy in a 2-methyltetrahydrofuran (MTHF) glass matrix at 77 K and by FT-IR spectroscopy in an argon matrix at 20 K. On the other hand, the [14]DBA was stable enough for observation by 1H and 13C NMR spectra in solution, though it was not isolated because of the low efficiency of the cycloreversion. The [14]DBA was also characterized by interception as Diels-Alder adducts in solution and by UV-vis spectroscopy in a MTHF glass matrix at 77 K. The kinetic stabilities of the DBAs are compared with the related dehydrobenzoannulenes with respect to the topology of the pi-systems. In addition, the tropicity of the [14]DBA is discussed based on its experimental and theoretical 1H NMR chemical shifts.

Transient processes of laser ablation of a highly laser-absorbing liquid, toluene, were investigated by directly measuring (by using a fast-response pressure gauge) the transient pressure caused by toluene ablation under KrF laser irradiation . The results were compared with time-resolved images . The peak pressure P due to a shock wave decreased slowly with increasing distance d for d=100–1000 μm:P∝d-0.33. By extrapolating P to d=8.9 μm, the optical penetration depth of toluene at λ=248 nm, the estimated initial pressure due to toluene ablation was 65 MPa at 1.0 J cm-2 pulse-1. The estimated initial pressure increased linearly with the fluence. These results help clarify the mechanism of laser-induced backside wet etching.

Novel conjugated organic dyes that have N,N-dimethylaniline (DMA) moieties as the electron donor and a cyanoacetic acid (CAA) moiety as the electron acceptor were developed for use in dye-sensitized nanocrystalline-TiO2 solar cells (DSSCs). We attained a maximum solar-energy-to-electricity conversion efficiency (η) of 6.8 % under AM 1.5 irradiation (100 mW cm–2) with a DSSC based on 2-cyano-7,7-bis(4-dimethylamino-phenyl)hepta-2,4,6-trienoic acid (NKX-2569): short-circuit photocurrent density (Jsc) = 12.9 mA cm–2, open-circuit voltage (Voc) = 0.71 V, and fill factor (ff) = 0.74. The high performance of the solar cells indicated that highly efficient electron injection from the excited dyes to the conduction band of TiO2 occurred. The experimental and calculated Fourier-transform infrared (FT-IR) absorption spectra clearly showed that these dyes were adsorbed on the TiO2 surface with the carboxylate coordination form. A molecular-orbital calculation indicated that the electron distribution moved from the DMA moiety to the CAA moiety by photoexcitation of the dye.

Surface structuring of optically transparent materials toward nanometer-scale resolution for the fabrication of optics and micro-chemical devices has been performed by UV and Vacuum UV laser Ablation. Recently, we have investigated a one-step method to fabricate a microstructure on the transparent materials such as silica glass, sapphire, and fluoride crystals by using a conventional UV laser under the atmospheric pressure. Laser-Induced Backside Wet Etching (LIBWE) fabricates microstructures with well-defined micro-patterns on the surfaces. Our idea of LIBWE is based on an indirect excitation onto the surface of materials by using ablation of organic solutions such as dye solution or toluene. Upon UV laser irradiation of the solution, shock wave and vapor bubble were formed and propagated. These transient phenomena are possible for the surface microstructuring of the materials.

Diimine ruthenium(II) complexes with β-diketonate ligands were synthesized. Photophysical and electrochemical properties of these complexes were investigated. The electron-donating strength of β-diketonate can be tuned by choosing alkyl substitutents of the diketones. The complexes examined showed excellent photosensitization ability toward TiO 2 . The photoelectrochemical cell sensitized with [Ru(dcbpy) 2 (dpmo)]Cl (dpmo=dipivaloylmethanato) showed a solar light-to-electricity conversion efficiency of 6.9%. Electronic absorption spectra of the complexes were assigned by a computational calculation of molecular orbital. Transition from HOMO−2 to the LUMO and LUMO+2, which come from diketonate ligand, play an important role for absorption spectra in the longer wavelength response.

Microstructures with well-defined 1 μm-scale grating and grid patterns were fabricated on the surfaces of silica glass using a laser-induced backside wet etching (LIBWE) method by nanosecond-pulsed KrF excimer laser irradiation through a mask projection system. In the former case, gratings as narrow as 0.75 μm-sized were successfully etched on the glass surface via fine adjustments to the projection system. To investigate the etching mechanisms, formation and propagation of the shockwave and micro-bubbles after laser irradiation, at the interface of the silica glass and the toluene solution, were monitored using time-resolved shadowgraph microscopy, from the front- and side-view directions.

The IR spectra of 3,4-benzotropone (2) and naphtho[2,3-c]tropone (3) isolated in nitrogen matrices at 13 K were directly observed. These tropones were generated in the matrices by the photoisomerization of 6,7-benzobicyclo[3.2.0]hepta-3,6-dien-2-one (4) and naphtha[2,3-f]bicyclo[3.2.0]hepta-3,6-dien-2-one (5), respectively. The observed IR bands of the photoproducts were in good agreement with the theoretically predicted bands. The intense C=O/C=C bands of 2 were observed at 1607 and 1615 cm - 1 , and the corresponding band of 3 was observed at 1605 cm - 1 with shoulder peaks. The fact that the C=O/C=C band of 3 was observed at a slightly lower wavenumber than the corresponding bands of 2 indicates that benzo-annelation enhanced the contribution of the polarized resonance form to 3. The observed IR spectra of 2 in the nitrogen matrix differed significantly from the spectra observed previously in a CFCl 3 -CF 2 BrCF 2 Br-CHCl 3 matrix. Self-consistent reaction field calculations on 2 using the Onsager dipolar-sphere model revealed that the observed differences in the spectra reflect structural changes induced in the tropones by the surrounding media.

Laser-induced backside wet etching (LIBWE) of silica glass plates was performed by the excitation of a pure toluene solution with an ns-pulsed KrF excimer laser at 248 nm. Well-defined grid micro-pattern was fabricated without debris and micro-crack around the etched area. The etch rate, which increased linearly with laser fluence, was 30% higher than that in the case of acetone solution of pyrene dye at a concentration of 0.4 mol dm −3 . To understand the etching mechanism, the formation and propagation of shock wave and bubble were monitored by time-resolved optical microscopy at the interface between the silica glass and the toluene solution during etching process. Transient high pressure as well as high temperature generated by UV laser irradiation plays a key role in the etching process.

KrF excimer laser ablation of iron disilicide in the α phase (α-FeSi 2 ) has been investigated using time-of-flight (TOF) mass spectroscopy to characterize the dependence of ejected neutrals and native positive ions on laser fluence. The TOF mass spectra showed that the ejection behavior was classified into three parts at low, moderate and high fluence ranges. At laser fluences below 0.7 J/cm 2 , the presence of only Si, Fe and Si 2 neutrals was confirmed; the arrival profile of Si atoms is well described by a Maxwell–Boltzmann (MB) distribution with a translational velocity of 1.6×10 3 m/s, corresponding to a kinetic energy of 0.35 eV, and a target surface temperature of 4.0×10 3 K, indicating a thermal emission of these neutral species. With increasing the fluence, nascent positive ions, such as singly- or doubly-charged Si and Fe ions appeared; the arrival profiles of these ions are observed to fit a shifted MB distribution. Their kinetic energies range from several eV at moderate fluences to over 100 eV at high fluences up to 2.5 J/cm 2 . These high kinetic energies cannot be explained in terms of the FeSi 2 target surface reaching a temperature that would produce such energetic ions upon ablation, suggesting the ion acceleration in a dense plasma plume.

We have investigated time evolution of the plume produced during laser ablation of ZnO under ArF-excimer-laser irradiation in He atmosphere. The plume luminescence is mainly due to excited Zn atoms. The plume propagates straightforwardly within 1 μs after ablation, and then it expands and forms an anchor-like shape due to the plasma confinement by the surrounding He gas. After the disappearance of the plume luminescence at high He pressure, a second excitation with a XeCl-excimer-laser causes a luminescence that can be explained in terms of condensation and formation of oxygen molecules and ZnO nanoparticles in the plume.

Nitrogen solid film deposited on a copper plate at 10 K was irradiated with a picosecond UV laser at 263 nm in vacuum. Photo-dissociation of nitrogen molecule in the solid film was confirmed by the optical emissions, which were ascribed to atomic nitrogen, during the laser irradiation at the fluence of 5 J cm −2 pulse −1 . This photolysis was discussed by the comparison with laser-induced breakdown of nitrogen gas. At the fluence over ca. 10 J cm −2 pulse −1 , the ablation of the frozen nitrogen film was observed. Employing the ablation plume including a reactive species such as nitrogen atoms, the surface reaction of a graphite (highly oriented pyrolytic graphite (HOPG)) plate and silicon wafer was studied. XPS analysis indicated that nitrides were formed on the surfaces by the treatment. The ps-laser ablation of nitrogen solid film provides a novel technique for surface modification of materials.

The DC electric-field effect on the crystallinity of II–VI semiconductor in composite systems has been investigated for CdS–ITO films fabricated via alternative pulsed laser deposition (PLD) of CdS and indium tin oxide (ITO) on electric-field-applied substrates. The alternative laser ablation was performed under irradiation of ArF excimer laser in mixture gas of helium and oxygen. The application of electric-field facilitated the preferential crystal-growth of CdS in nanometer scale at low pressure, whereas all the films grown without the field were amorphous. There is a large difference in the crystallization between the films grown on field-applied and heated substrates; the latter showed the crystal-growth with random orientations. This difference indicates that the existence of electric-field has an influence on the transformation from amorphous to crystalline phase of CdS. The driving force for the field-induced crystallization is also discussed in the light of the Joule heat.

Toward direct observation of benzdiynes, we investigated the wavelength-selective photolyses of five kinds of benzenetetracarboxylic dianhydride derivatives in nitrogen matrixes at 13 K. In the first step of the photolyses, all dianhydrides were converted into benzynedicarboxylic anhydrides with loss of CO and CO2 upon irradiation at 308 nm. In the second step, the benzyne intermediates were photolyzed at 266 nm. In these photolyses, the generation of two kinds of benzdiynes, 3,6-difluoro-1,4-benzdiyne and 3,6-bis(trifluoromethyl)-1,4-benzdiyne, was confirmed by good correspondence between observed and calculated IR spectra. These benzdiynes were converted into the corresponding hexatriynes upon further irradiation at 266 nm. Benzdiynes were not observed in the photolyses of the other three dianhydrides: only hexatriynes were observed as major photoproducts. These results suggested that benzdiynes were generated first and then converted into hexatriynes and that the efficiency of the decomposition of benzdiynes depended on the substituents. The dynamics of the generation and decomposition of benzdiynes in the matrixes was analyzed by using a successive reaction scheme.