Table of contents

We describe for the first time delamination of a single crystalline silicon film from a substrate caused by the formation of a hydrogen layer under the surface due to dc plasma hydrogenation of a trap layer. The process involves first forming a buried trap layer by implanting ions of gases in doses of 1×10¹⁵ cm^-2 to 4×10¹⁶ cm^-2, and then hydrogenating with a dc plasma. Following thermal annealing, delamination occurs with a depth corresponding to the maximum of vacancy-enriched defects (about R_p/2) for the lowest implantation doses and up to R_p for the high implantation doses. This process may be used as a step in the process of fabricating thin silicon-on-insulator (SOI) wafers. The authors suggest that vacancy clusters at R_p/2 serve as nuclei of hydrogen platelets that continue to grow under hydrogenation and act as infinite-capacity traps for hydrogen.

A novel thinning process was proposed for the preparation of bonded and etched silicon-on-insulator (BE-SOI) wafers with high quality and good thickness uniformity by adopting a spin etching and subsequent selective etching as a thinning process. A solution comprising HNO₃, HF, H₃PO₄ and H₂SO₄ was used for the spin etching process. The spin etching process removed the damaged layer originating from a back-grinding process, which simultaneously yielded SOI wafers with better thickness uniformity than usual back-ground ones. Selective etching adopting a layer with high boron concentration as an etch stop layer was subsequently carried out to achieve better thickness uniformity than that obtained after the spin etching process. The solution for the selective etching process was prepared by diluting NH₄OH and H₂O₂ with de-ionized water. BESOI wafer with excellent surface roughness equivalent to that of a polished Si wafer could be prepared by removing the surface layer of high boron concentration during a chemical mechanical polishing (CMP) process.

In order to enhance the strength of thick Al wire bonds while eliminating damage, we have developed a new high-temperature thick Al wire bonding technology. The 300-µm-diameter Al wires were bonded to Al pads on an insulated gate bipolar transistor (IGBT) chip at varying substrate temperatures and ultrasonic powers. Al wire bonds joined at 423 K with 2.0 W ultrasonic power exhibited high bonding strength compared to those joined at room temperature with 5.0 W power. The main reason for the high bonding strength exhibited by the high-temperature bonding process with low ultrasonic power may be the ease of deformation of Al wires and Al electrode films which results in the enhancement of the true bonded area between Al wires and Al electrode films. We also confirmed that Si damage did not occur during this high temperature bonding process using low ultrasonic power. High-temperature thick Al wire bonding technology is considered to be a promising candidate for the production of reliable IGBT modules.

We have measured photothermal signals of a bulk GaN crystal by the photothermal divergence (PTD) method in the temperature range from 110 K to 370 K. The thermal conductivity and the scattering time of phonons contributing to the thermal conductivity have been evaluated from the photothermal signals. A phonon-defect interaction has been expected to play a crucial role in determining the thermal properties of the sample employed here in the above temperature range.

GaN films were grown on (La_0.29,Sr_0.71)(Al_0.65,Ta_0.35)O₃ (LSAT) (111) substrates, the lattice constant of which matched the 3×3 structure of GaN (0001) and the thermal expansion coefficient of which was close to that of GaN, by atmospheric metalorganic chemical vapor deposition. It was found that the surface of LSAT having a perovskite crystal structure was damaged in ambient of NH₃ and TMG gas. However, the epitaxial growth of GaN film on the LSAT substrate was achieved by using an AlN blocking layer to prevent the damage by these gases. The crystallographic orientation was evaluated from a phi-scan of 4-cycle X-ray diffraction to be GaN[1100]∥LSAT[110] rotating in plane by 30° against the expected orientation (GaN[2110]∥LSAT[110]). The 30° rotation would be caused by the bond configuration of the surface of the LSAT substrate. The interface structure at the substrate and the threading dislocation in the films were also investigated using a cross-sectional transmission electron microscope.

The degradation characteristics under various bias stress conditions are systematically investigated in hydrogenated n- and p-channel polysilicon thin film transistors (poly-Si TFTs) with a sidewall spacer. The device characteristics after a relatively long stress in the p-channel TFTs exhibit more serious degradation than those in the n-channel TFTs. Moreover, the stress time dependence of the threshold voltage shift in the former devices shows more complicated behavior than that in the latter. These serious and complicated time-dependent degradation characteristics (induced only in p-channel devices) can be explained by the generation of two defect states in which hydrogen plays an important role: one is positively charged traps that correspond to Si⁺ atoms generated by the injection of H⁺ ions into the gate oxide near the source and appear after a certain stress time. The other is deep traps that correspond to dangling bonds generated by the dissociation of Si–H bonds at/near the interface near the source and appear after a long stress time.

The bias-stress-induced degradation characteristics of p-channel polysilicon (poly-Si) thin film transistors (TFTs) hydrogenated by plasma, H₂ and H₂/plasma processes are investigated. It is found that the stress time dependence of the transfer characteristics and the threshold voltage shift is affected by the hydrogenation processes and the quantity of hydrogen in the active channel layer of TFTs. These behaviors are mainly caused by the difference in the generation of defect states, that is, band tail states, deep traps corresponding to dangling bonds at/near the poly-Si/SiO₂ interface, and positively charged traps corresponding to Si⁺ atoms created by H⁺ ions in the oxide. We propose a model to explain these behaviors.

We investigated the tensile stress in poly-Si thin films crystallized by excimer-laser annealing (ELA). The stress was analyzed with the frequency shift of the optical-phonon line, Δω, detected by Raman scattering spectroscopy. The value of Δω is affected not only by stress but also by the presence of microcrystals. In the case of the full-width at half-maximum (FWHM) of the spectrum being smaller than 8 cm^-1, the stress can be estimated from Δω without the influence of microcrystals. The primary origin of the stress was attributed to the thermal stress generated by selective heating of films by ELA. The presence of thermal stress in poly-Si was confirmed by comparing the stress in solid-phase crystallized films on fused quartz and on Si substrates. The stress in ELA poly-Si varied widely with conditions, such as irradiated-shot number, substrate temperature and postannealing temperature. It was deduced that the thermal stress being the dominant stress factor is relaxed by annealing performed after laser irradiation.

A stable cuprous oxide Cu₂O film is prepared by low-temperature oxidation of a sputtered copper (Cu) thin film at 300°C. Although the carrier concentration in Cu₂O is determined by the excessive oxygen (O) concentration, the concentration of such O atoms is controlled by the exposure to atomic hydrogen (H) generated by the catalytic reaction between the heated tungsten catalyst and H₂ gas. By this method, the carrier concentration in a 100-nm-thick Cu₂O film is decreased from 1 ×10¹⁶ cm^-3 to 2 ×10¹⁵ cm^-3 and the Hall effect mobility is increased from 5.6 cm²/Vs to 28.9 cm²/Vs. Atomic H exposure is a useful tool for improving the properties of Cu₂O.

We have investigated self-narrowing and photoetching effects on the size distribution of CdS quantum dots (QDs). The QDs with a narrow size distribution are prepared by a reverse-micelle method and their mean radii are controlled by changing the water content in the reverse micelle. The mean radius and size-distribution width estimated from the line-shape analysis of absorption spectra agree well with those obtained from transmission electron microscope images, which indicates that the analysis is a convenient and reasonable method of estimating the size-distribution width. For the QDs whose initial size distribution is larger than ∼10%, the size-distribution reduction due to a "self-narrowing process" is observed: The size-distribution width is spontaneously reduced with the time elapsed after the QD preparation. The further reduction of the size-distribution width is achieved by performing a photoetching treatment. The above results clearly show the possibility of preparing CdS QDs with the narrow size distribution by using the self-narrowing and photoetching effects.

Effects of dry processing on photoluminescence (PL) properties of high-quality ZnTe homoepitaxial layer exposed to CH₄/H₂ plasma have been investigated. The etched ZnTe layer exhibits a strong deep level luminescence band around 2.25 eV together with a weak free excition emission at low temperature. By analyzing the dependence of the PL spectra on temperature and excitation power intensity, we find that the band around 2.25 eV is characteristic of a donor-acceptor pair recombination emission related to V_Zn complexes. The amount of surface damage decreases with increasing CH₄ concentration in the gas mixtures due to the effect of chemical etching.

We report the interband photoluminescence from high Γ-electron subbands and mid-infrared electroluminescence originating from an intersubband transition in a simple GaAs (15.3 nm)/AlAs (4.5 nm) superlattice embedded in a p–i–n structure. Interband photoluminescence properties under applied bias voltages provide conclusive evidence that electrons populate the fourth Γ (Γ4) electron subband in the GaAs layer. This electron population results from the carrier injection into the Γ4 subband from the adjacent X1 subband in the AlAs layer, which is initiated by the X1–Γ4 resonance. We calculate the overlap integral of the envelope functions for Γ-electron and heavy-hole subbands in order to discuss the carrier population in high Γ subbands based on the photoluminescence intensities. The results of analysis suggest that a population inversion can be obtained between the Γ4 and Γ3 subbands under the X1–Γ4 resonant condition. The energy of the intersubband electroluminescence, 100 meV, agrees with the energy spacing between the Γ4 and Γ3 subbands. This demonstrates that the carrier injection into the higher Γ subband using X–Γ scattering will be useful for designing of intersubband-emission devices.

Spacer bottom oxide in the nitride spacer lightly doped drain (LDD) device, which is used to prevent huge interfacial states between the nitride and silicon interface, plays an important role in the hot carrier test. Because of the stress due to atomic size mismatch between the nitride spacer and silicon, trap-assisted hot electron tunneling is more significant in a nitride spacer LDD device than in the oxide spacer counterpart. A thicker bottom oxide can eliminate this effect. However, the optimal thickness of the nitride spacer bottom oxide should be varied for different poly-silicon gate structures. The hot carrier stress in a nitride spacer LDD device causes multi-stage degradation under I_sub,max stress. It is dominated by electron trapping at the early stage, interfacial state (N_it) creation at the second stage, and self-limiting hot carrier degradation at the final stage. The degradation for I_g,max stress in nitride spacer LDD devices is mostly caused by electrons trapped in the nitride/oxide interface.

We report on a study of current crowding in AlInGaN multiple quantum well based deep ultra-violet light emitting diodes. For lateral geometry devices on sapphire substrates, our study concludes that the thickness and doping level of the high Al-content buffer and the cladding n-AlGaN layers is a key contributor to the lateral resistance and hence current crowding at the mesa edges. The inhomogeneous pumping of large area devices results in increased differential resistance causing a pronounced localized overheating. This degrades the device performance under high dc current operation. We also show stripe geometry to be a better choice for high power deep ultra-violet light emitting diodes on sapphire.

We have developed wide field-of-view cavity radiometers which can be used under the solar simulator radiation and are traceable to the World Radiometer Reference (WRR) scale. Simultaneous measurements of direct solar radiation were performed with these new instruments and the official standard radiometer PMO-6 which was used to maintain the WRR scale in Japan. The results show good agreement within the range of accuracy of the instruments and clarify the relationship of the new instruments to the WRR scale. In addition, the solar simulator irradiance measured by the new instruments was compared with the integrated irradiance measured by the spectroradiometer calibrated against the Electrotechnical Laboratory (ETL) spectral irradiance scale which was employed for the reference cell calibration in Japan. Consequently, we found that the irradiance based on the WRR scale was about 2% lower than the integrated irradiance based on the ETL spectral irradiance scale.

The gate tunneling current in n⁺-polysilicon gate n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) in accumulation regime has been simulated quantum-mechanically. The two current components, due to hole tunneling from the accumulation layer on the p-silicon surface and due to electron tunneling from the accumulation layer on the n⁺-polysilicon gate, have been investigated for bulk and silicon-on-insulator (SOI) MOSFETs with various SOI layer thicknesses. For bulk MOSFETs, the electron current from the gate becomes much larger than the hole current from the silicon surface. On the other hand, as the SOI layer thickness (t_SOI) decreases, the hole current increases, but the electron current decreases, and thus the hole current exceeds the electron current at a certain t_SOI. The total gate current increases with decreasing t_SOI (>2 nm). For extremely thin t_SOI, the contribution of the electron current almost disappears. Moreover, the quantum-mechanical effects on the tunneling current in accumulated SOI MOSFETs have been discussed in detail.

In trench isolation technology, the surface layers of poly-Si buried in the trench are contaminated with silica particles and chemical impurities by the conventional chemical-mechanical polishing (CMP) method. These contaminations produce some unexpected patterns and crystal defects in the wafer surface layer after oxidation. Furthermore, it is difficult to remove them by the conventional wet cleaning techniques. In this work, we have established a new post-CMP cleaning method, using electrolytic ionized water containing a small quantity of HCl. The anode water is shown to have a cleaning effect on the metallic and organic contamination, whereas the cathode water is shown to have a removing effect on the particles and an etching effect on the poly-Si surface. We present the optimization results of the post-CMP cleaning condition by investigating the surface-related properties by means of a particle counter, ellipsometry, secondly electron microscopy (SEM), atomic force microscopy (AFM), inductively coupled plasma/mass spectroscopy (ICP/MS), and secondary ion mass spectroscopy (SIMS). Our newly established cleaning method is currently applicable to the actual CMP planarization process for VLSI.

Complete filling of 0.13-µm vias and deposition of Cu with a low resistivity of about 2.3 µΩ·cm were obtained using an electrolyte with 2-aminobenzothiazole (2ABT) as the filling promoter. Due to the moderate charge transfer polarization characteristic realized by the addition of 2ABT, the film resistivity and the activation energy for thermal grain growth were similar to those for electrolytes without it. After rapid thermal annealing (RTA) at 400°C for 30 s, the resistivity was further reduced to ∼1.9 µΩ·cm.

Corrosion of W plugs in LSI interconnects during chemical solvent stripping was investigated by scanning Maxwell-stress microscopy (SMM). The surface potential of TiN, Al and W, of which the interconnects are composed, was measured by SMM, and the changes in electrostatic charging and work functions through the processes were estimated. After immersion in aqueous amine stripper, which actually caused the W plug corrosion, the work functions of the Al and W films were comparable. Due to the similarity of the work function to the electrochemical reduction potential, we consider that the corrosion protection of the Al/W contact becomes inactive in the aqueous amine stripper. This is also supported by the electrode potential measurement in the aqueous amine stripper, for which the Al potential exhibited a higher value than that of W only for the films after O₂ ashing. We consider that the W plug corrosion is caused by the electrochemical interaction between the aqueous amine stripper and the material deposited on the Al by O₂ ashing.

To achieve the high level in photolithographic technology that is needed for current microelectronic devices, it is strongly required to consider emerging key parameters that were not critical drawbacks in previous photolithographic techniques. Flare existing in optical elements is one example of such emerging key parameters. In this paper, undesirable linewidth variation due to flare and a measurement method of flare are described. Various phenomena related to linewidth variation due to flare are experimentally observed and theoretically analyzed. Finally, the photomask linewidth correction is introduced to compensate this undesirable linewidth variation due to flare.

One integrated tungsten (W) chemical mechanical polishing (CMP) process characterization with wide production margin is developed for W plug application in sub-quarter micron technology. In this study, it is identified that donut-type function failure and reliability degradation on a designed application specific integrated circuit (ASIC) product vehicle result from an extra oxide layer atop the W plugs. W recess in via holes makes the plugs more vulnerable to oxide layer formation. CMP polish rate uniformity, layout dependence of via holes and queue-time (Q-time) control between WCMP and post-cleaning treatment are key parameters for preventing failure from interfacial oxide layer. Integrated optimization of WCMP process combined with W extrusion by a slight oxide polish immediately after WCMP is proposed to achieve a robust W plug process. Significant yield improvement from 45% to 82% in wafer edge region and 0% failure in three qualification lots in a product reliability test are demonstrated.

A large gate leakage current in AlGaN/GaN high electron mobility transistors (HEMTs) was observed. Temperature dependence of I_g-V_g characteristics revealed that tunneling current is dominant in the leakage current. By introducing ECR plasma treatment before the gate metal deposition, the gate leakage current was reduced by two to three orders of magnitude.

Tunneling current induced luminescence (TCIL) spectra of capped InGaAs quantum dots (QD) are presented. In contrast to the inhomogeneously broadened photoluminescence, the TCIL shows sharp excitonic lines of typical widths of 1.5–2 meV. Due to the high spatial resolution afforded by using a scanning tunneling microscope tip, TCIL spectra have been measured at various spatial locations on a capped QD sample. It is proposed that the measured luminescence spectra are of a single QD, a pair of coupled QDs and an ensemble of QDs.

The electrical characteristics of ZrO₂ were investigated relative to its use in SiGe metal-oxide-semiconductor (MOS) gate dielectric applications. Compared to ZrO₂ directly deposited on SiGe, ZrO₂, when deposited on a silicon capping layer shows a significant improvement in electrical characteristics such as low leakage current, negligible hysteresis, less fixed charge density and a lower interface state density (D_it) after low-temperature wet vapor annealing. The improvement in the electrical characteristics of ZrO₂, with a silicon capping layer can be attributed to the negligible Ge segregation and surface roughness at the interface. Based on an Auger electron spectroscopy (AES) depth profile of Ge, we were able to confirm that Ge is segregated at the interface.

Magnetic field dependence of Fiske steps has been investigated using Nb/Al–AlO_x/Nb tunnel junctions formed with a normal-distribution function with a dispersion parameter of σ= 0.45. Fiske steps are due to the different resonance mode appearing in the current–voltage characteristics when an external magnetic field is applied to the junctions at 4.2 K. Both positions in the voltage scale and current amplitude of Fiske steps were systematically measured. We found that the amplitudes of the Fiske steps increased gradually, and then decreased monotonically with an increase in magnetic field. All Fiske steps almost completely disappeared at a magnetic field of less than 1 mT, at which the dc Josephson critical current also decreased to less than 10^-3 of the maximum. The position of Fiske steps in the voltage scale was analyzed using a diamond-shaped junction which corresponds to a 45-degree-rotated square junction.

We report on the structural and electrical properties of a-axis oriented PrBa₂Cu₃O_7-δ film deposited on (001) YBa₂Cu₃O_7-δ single crystal. a-Axis oriented PrBa₂Cu₃O_7-δ film, expected to be a barrier layer, was prepared using a dc-95 MHz hybrid plasma sputtered on YBa₂Cu₃O_7-δ single crystals that are superconducting ground planes. The atomic force microscopy image showed that the surface of PrBa₂Cu₃O_7-δ film on (001) YBa₂Cu₃O_7-δ single crystal was smooth with a mean roughness of 2.9 nm. The resistivity of a-axis PrBa₂Cu₃O_7-δ film on (001) YBa₂Cu₃O_7-δ single crystal measured after patterning into the mesa structure was small in comparison with that of a-axis PrBa₂Cu₃O_7-δ film on (100)SrTiO₃ substrate and decreased with decreasing temperature.

The effect of glass addition on the magnetic properties of 3Ba_0.5Sr_0.5O·2CoO·12Fe₂O₃ (Co₂Z) ferrites was investigated. The densification of Co₂Z ferrites was enhanced by the addition of glass at low sintering temperature (<900°C) due to the liquid-phase sintering. The initial permeability and Q value of Co₂Z ferrite sintered at low temperature were improved by the addition of glass. Multilayer chip inductors made of Co₂Z ferrite containing glass exhibit excellent magnetic properties. The device offered low impedance at 100 MHz and high impedance at frequencies between 500 MHz and 1000 MHz. Therefore, it could be used as an electromagnetic interference countermeasure component effective in suppressing GHz band noise.

DC resistivity of Mn_xNi_0.5-xZn_0.5Fe₂O₄ with compositions x=0.05 to 0.4 prepared by the citrate precursor method has been investigated. It has been observed that resistivity decreases with increase in Mn concentration. The observed temperature variation curves show two linear regions. Activation energy corresponding to both regions has been calculated. Possible conduction mechanisms contributing to the processes have been discussed. Variation of resistivity with sintering temperature establishes a correlation between microstructure and conductivity.

The sputtering pressure effects on magnetization reversal and magnetic switching volumes of CoSm/Cr films have been investigated. It is found that the magnetization reversal changed from wall pinning for samples prepared at low pressure to single particle rotation for samples prepared at high pressure. The magnetic switching volumes increased with increasing the Ar pressure to values in the range of 5.2-9.0 ×10^-18 cm³. These switching volumes satisfy Sharrock's requirement for the thermal stability of high-density magnetic recording.

Electron beam (e-beam) and X-ray lithographic techniques have been used to fabricate permalloy (Ni₈₀Fe₂₀) and nickel rectangular and triangular dots and antidots on an area of (1×1) mm². Dot dimensions and spacings range from 500 nm to 1 µm and from 250 nm to 50 nm, respectively. The changes of the magnetic properties induced by patterning have been studied by means of magneto-optic Kerr effect (MOKE) magnetometry and the Brillouin light scattering (BLS) technique.

We constructed spinel-type superlattices consisting of antiferromagnetic ZnFe₂O₄/diamagnetic ZnGa₂O₄ along the <111> direction. The stacking periodicity was controlled from 27 to 2 unit cells in order to reduce the dimensionality. X-ray diffraction patterns confirmed that ZnFe₂O₄/ZnGa₂O₄ superlattice was formed up to the stacking periodicity of 2 units. Spin-freezing temperatures decreased from 54 K to 36 K and maximum magnetizations shifted from 0.24_µB/2Fe to 0.13_µB/2Fe with decreasing periodicity from 27 units to 2 units.

We theoretically analyze the spatial anisotropy and polarization dependences of enhanced backscattering of light using a double-scattering approximation. The polarization of light is calculated in terms of the Jones vector and the scattering amplitude matrix. We discuss the cases where the individual scattering event is isotropic and governed by Rayleigh scattering for the media in which scatterers are homogeneously dispersed and aggregated. The spatial properties of the far-field intensity distribution can be demonstrated by asymptotic expansions in the region of the large backscattering angle. As a result, we theoretically reveal the polarization anisotropy of the decreasing variation in the far-field intensity distribution dependent on the fractal dimension, the azimuth in the backscattering angle, and the polarization state.

We present a detailed experimental characterization of a confocal microscope readout system in a photochromic polymer under two-photon excitation. In particular, the effect of writing power, exposure time and recording depth on the contrast of the readout signal is explored. The reflected intensity of the recorded data bits is shown to be strongly dependent on the intensity of the writing laser and exposure time. The relative intensity initially shows an I² dependence on power, followed by saturation. The saturation effect is also evident as exposure time is varied. These saturation features allow for reading of the stored bits with objectives whose numerical aperture is less than that used for writing (1.4 N.A.). Furthermore, a decrease in contrast is observed with an increase in layer depth.

In high-power applications of multimode optical fibers, such as high-power beam delivery and optical phase conjugation, the estimation of the critical power of stimulated Brillouin scattering is important. Nevertheless, no estimations to date have taken account of the mode dispersion effect. Based on our experimental results, we show that the critical power in a multimode fiber depends on the numerical aperture (NA) of the fiber, i.e., mode dispersion. The critical power increases as the fiber NA increases.

We performed the experiment of self-induced transparency in samarium atomic vapor under the condition of high temperature and high density. The sudden onset of the transmission, the maximum pulse delay and the pulse broadening were observed with π pulse. With this result we estimate the dipole moment of the transition line for ¹⁵²Sm. The peak amplification, the pulse narrowing and the pulse breakup were observed when the pulse area was above 3π. These observations are strong evidences of self-induced transparency. Our result is the observation of self-induced transparency under the highest-temperature, highest-density condition and the first observation of this phenomenon in samarium vapor to our knowledge.

Single-crystal Si single quantum well (SQW) structures sandwiched between two SiO₂ layers were fabricated using oxygen implantation followed by thermal oxidation. After annealing in hydrogen, the SQW structures emitted two-peak (blue and yellow) photoluminescence (PL) at room temperature. The blue PL (∼2.9 eV) has an invariable peak position regardless of the Si layer thickness or the temperature. The yellow PL changes from 2.0 eV to 2.6 eV with thinning of the Si layer from 5.5 to 1.0 nm. We found that yellow PL disappears at temperatures below 160 K. It is concluded that the blue PL is related to defects in SiO₂, and we inferred that the yellow PL is caused by a recombination of the localized electrons at the Si/SiO₂ interface and quantum confined holes.

The thermal characteristics of thin-film vertical-cavity surface-emitting lasers (VCSELs) have been studied by means of finite element analysis. The thin-film VCSELs transferred onto a selected substrate, which we have already demonstrated, are very attractive for integrated optoelectronic devices. However, structural design based on thermal analysis is required to improve the performance especially for small aperture VCSELs. We confirmed that an AlN submount used as the transferred substrate was satisfactory from the viewpoint of thermal conductivity. We also numerically showed that an Au plating layer on the top surface and an oxide-defined layer would improve the thermal characteristics. Although the thermal resistance R_th of 5 µm air-post thin-film VCSEL is very high, the 5 µm oxide-defined aperture with 35 µm mesa and an Au plating layer of 3 µm thickness can reduce R_th by about 27%.

A high-power copper vapor laser (CVL) scaled up to a 100 mm bore has been developed. In a large-bore CVL, there is a problem that the radial beam profile becomes nonuniform, which is caused by the high temperature of the buffer gas. Two methods have been applied to gas cooling: hydrogen addition to the buffer gas and insertion of gas cooling plates. Modeling of the increased thermal conductivity by hydrogen addition and of the radiation effect by plate insertion predicted that the buffer gas temperature would drop from 4160 K to 2650 K under typical operating conditions. Experimental results showed that the beam profile was improved especially at high repetition frequencies and high input powers. The CVL with a plasma tube length of 2.3 m was able to generate an output power of 329 W as an oscillator.

The singlet oxygen generator (SOG) generates singlet oxygen for a chemical oxygen iodine laser (COIL), using the gas-liquid reaction between basic hydrogen peroxide (BHP) and Cl₂ gas. The Jet-SOG has been widely used, wherein jet BHP from small orifices reacts with Cl₂ gas, and the BHP utilization is less than 1% in a single pass through the reaction zone. To improve BHP utilization, the reaction surface with Cl₂ gas should be increased, and the droplet diameter of BHP should be decreased. In this study, two types of mist generators were tested for the SOG, with which 65-µm- and 15-µm-diameter droplets were generated. In the 65 µm mist generator, BHP utilization was 22.5% at the Cl₂ flow rate of 8.3 mmol/s, and in the 15 µm mist generator, BHP utilization was 41.5% at the Cl₂ flow rate of 9.0 mmol/s, that is, BHP utilization of the new SOG, Mist-SOG, markedly exceeded that of the conventional Jet-SOG.

Temporal waveform transformation of terahertz electromagnetic pulses near the focus was studied by experiments and simulations. The terahertz pulses were generated by a large-aperture photoconductive emitter, and focused by an off-axis parabolic mirror. Changes of the temporal waveforms due to the propagation near the focus were measured using the electro-optic sampling method. Experimentally observed waveforms were compared with those of simulations based on the Gaussian beam model, and good agreement between them was obtained. A simple analytical expression describing the amplitude and the temporal shape of the focused THz waveform was also derived.

Using a double-tubed coaxial-line-type microwave plasma chemical vapor deposition (MPCVD) system, hydrogenated amorphous silicon (a-Si:H) nanoball films, which include Si nanocrystals, can be fabricated. Photoluminescence (PL) is observed at room temperature after the a-Si:H nanoball film is oxidized by heating in air or pure oxygen gas. We fabricate a-Si:H nanoball films with various the DC bias voltages applied to the substrate of this system and discuss the influence of the ion bombardment energy on the film properties and the PL characteristics. From the calculations it is clear that the number of Si nanocrystals existing per unit area of the a-Si:H nanoball film is almost proportional to the PL intensity. We propose the creation mechanism of Si nanocrystals and calculate the number of Si nanocrystals. From the calculation result it is clear that one a-Si:H nanoball contains 4 to 12 Si nanocrystals.

Low-reflection microstructures were formed by the use of a two-beam interference patterning on a photosensitive ZrO₂ gel film. Gel films coated on SiO₂ glass were exposed to an interference fringe of 325 nm He–Cd laser beams. The substrate was rotated by 90° between the first and second irradiation steps. Island and lattice type periodic two-dimensional structures with a pitch of 1 µm were formed after the irradiation followed by leaching with ethanol. Reflectance of 0.1% for an optically polished SiO₂ surface was attained at around a 1750 nm wavelength by the formation of an island-type microstructure. The transmission spectrum was successfully simulated by the rigorous coupled wave analysis. The heat treatment of the microstructure up to a temperature of 200°C was possible in an ambient atmosphere without a conspicuous increase in reflectance.

In this paper, performance of the complex phase code (CPC) which is recently proposed as a practical phase encoding method for volume hologram multiplexing is analyzed in detail. This new CPC has been known to have not only random and orthogonal properties but also the potential to generate a relatively large number of address beams in a holographic memory. For performance analysis of the CPC in a holographic memory system, four types of phase code, the new CPC, as well as the conventional pure random code (PR), random code with equality (RCE), WHM (Walsh Hadamard Matrix), are generated and used as the address beam. In computer simulations, the size of the address beam is fixed at 32×32 pixels and 0%–25% phase-error ratio in a pixel are intentionally added to the ideal phase values to consider the nonlinear phase-modulation characteristics of the practical spatial light modulator. From comparative analysis of crosstalks and signal-to-noise ratios for these phase codes by calculating auto-correlation and cross-correlation, it is found that the new CPC have the lowest cross-correlation mean value of 0.021, the lowest standard deviation of 0.0113 and the highest SNR of 26.9 among the four types of phase code. In addition, from the calculation of the number of all possible address beams for these four types of phase code as the size of the address beam is fixed to 32×32 pixels, the CPC is found to have 6.334×10⁴⁹ address beams, which are relatively higher number than that of the conventional phase codes.

Near-field optical recording of photochromic materials is carried out using a scanning near-field optical microscope (SNOM). We constructed a simplified yet fully functional SNOM by installing bent cantilever fiber probes in an atomic force microscope. Photochromic diarylethene films are used as re-writable near-field recording media, and we successfully record erasable recording marks having a minimum of 600 nm width in a writing time as short as 30 ms.

Laser short-pulse heating of metallic substrates results in nonequilibrium heating in the surface region of the substrate material. In this case, electron temperature rises at faster rate than lattice site temperature. Moreover, when modelling the heating process, thermomechanical coupling should be accommodated in the energy transport equation to account for the thermomechanical response of the substrate material. In the present study, laser short-pulse heating of gold, copper, and gold–copper assembly is considered. The energy transport inside the substrate material is modelled using an electron kinetic theory approach. Thermomechanical coupling is included in the analysis when modeling the nonequilibrium heating process. Since stress levels exceed the plastic limit of the substrate material, elasto-plastic analysis is employed in the analysis. It is found that 0.5 µm gold layer does not result in temperature gradient change across the gold–copper interface. The plastic region is formed in the surface region of the substrate material, which extends up to almost ∼ 2×10^-8 m below the surface.

We report patterning studies of corona-poled aromatic rigid polymers bearing a nonlinear optical (NLO) chromophore as a side group. Patterned NLO domains were prepared on micropatterned electrodes by corona poling above T_g of the polymer. According to the results, the mode and extent of chromophore attachment play a significant role in the patterning of these domain-forming polymers, and the patterns can be controlled in principle by appropriately designing the materials and electrodes. The patterned domains exhibited a grating effect due to differential separations of domains of nearly uniform lateral size. This approach to control NLO the domain structures on patterned electrodes may be of importance for photonics applications.

In this investigation, α-Ga₂O₃ powder is synthesized by the heat treatment of gallium oxyhydroxide (GaOOH) under O₂ and NH₃ gas flow conditions, and the temperature dependence of its photoluminescence characteristics is systematically examined, for the first time. A new UV emission band with high intensity and narrow bandwidth is observed at 3.469 eV for the α-Ga₂O₃ powders synthesized in NH₃. This new luminescence band thermally relaxes and decays when the temperature is higher than 130 K, which is ascribed to the radiative recombination of the shallow donor-bound excitons. These phenomena are thought to be due to the nitrogen atoms incorporated into the α-Ga₂O₃ crystal lattice from NH₃ gases during the heat treatment of GaOOH.

In a microcavity that consists of an emissive layer, a filler layer and resonator mirrors, we observed the emission enhancement with a higher photoluminescence (PL) intensity and a narrower linewidth than those of the noncavity type. The modification of the PL characteristics by the microcavity structure is described using the model that treats the microcavity as a Fabry–Perot resonator and regards the emissive material as an assembly of emitting dipoles. Also, we obtained the reflectivity and the phase shift of the distributed feedback (DFB) mirror using an optical transfer matrix formalism. The optical constants of the photoluminescent polymer, OxdEH-PPV, are obtained by measuring the interferometric fringe for the reference wavelength (633 nm) and then by applying the subtractive Kramers–Kronig transformation to the absorption spectrum and the reference refractive index. In order to attain the optical feedback as well as the PL excitation, we fabricated the aluminum and DFB mirrors. The DFB mirror was prepared by evaporating an alternating stack of quarter-wave TiO₂ (n_H) and SiO₂ (n_L) layers onto the glass plate.

This paper is concerned with the noncentrosymmetric alignment of betaine molecules dispersed in a polymeric matrix by an all-optical poling process. Two types of betaine molecules were used: one is betaine-azo with an azobenzene moiety in the molecule and the other is betaine-C8 without an azobenzene moiety in the molecule. The effect of the azobenzene moiety in the molecule on the optical poling efficiency, the formation of χ⁽²⁾ structure, and its thermal stability was studied. Optical anisotropy of the χ⁽²⁾ tensor components formed in the matrix in the writing process with linearly polarized beams was evaluated by rotating a sample film or rotating the polarization direction of the fundamental reading beam.

The refractive indices of eleven kinds of polyimide (PI) films formed on silicon substrates have been measured at three wavelengths (0.633, 1.320, and 1.523 µm) in the transverse electric (TE) and transverse magnetic (TM) polarization modes using the prism-coupling method. The wavelength dependence of average refractive indices was fitted using the simplified Cauchy's formula, and the estimated refractive indices at infinite wavelength (n_inf) and the coefficients of wavelength dispersion (D) were determined. The PIs having higher n_inf exhibit larger D, and the values of D are linearly proportional to n_inf for aromatic PIs, while those of wholly alicyclic PIs are very small and deviate from the linearity. In a similar manner, the in-plane/out-of-plane birefringence (Δn) values of the aromatic PIs having higher refractive indices are large and show significant wavelength dependence, while the values of Δn of alicyclic PIs are negligible. Approximate equations are presented for aromatic PIs to estimate n_inf and refractive indices at 1.320 and 1.523 µm from a refractive index at 0.633 µm.

We have investigated the effect of ZnO films used as buffer layers on the triboluminescence (TrL) intensity of ZnS:Mn thin films on quartz substrates using the RF magnetron sputtering method and annealing technique. Highly oriented ZnO film was first deposited on quartz glass substrate and then the ZnS:Mn film was successfully deposited on the highly oriented ZnO film. By annealing at 5% H₂ in Ar ambient, the crystallinity of both ZnO and ZnS:Mn films was improved. It was found that the addition of the ZnO buffer layer greatly improves the TrL intensity of the ZnS:Mn films.

Thermoluminescence has been observed in light and X-ray irradiated CdS-doped glasses and light irradiated CdSSe-doped glasses. The intensity of thermoluminescence was measured as a function of irradiation intensity and irradiation time. Applicability of CdS-doped glasses as a material for a radiation dosimeter was discussed.

We present an interesting transient electro-optical phenomenon including double optical bounce during the rising period of a quasi-homeotropic liquid crystal (QHLC) cell with an asymmetrical polar-alignment boundary condition. The unique optical behavior of the QHLC cell is produced by the flow effect together with the complicated alignment condition of the substrates, which is a combination of the deviation of azimuthal alignment and the asymmetrical polar alignment. We have found that the symmetrical characteristic of polar alignment plays a critical role in the dynamical behavior of the QHLC cell. Furthermore, our simulation results show that the double optical-bounce phenomenon appears even when the difference between the top and bottom tilt angles is only 0.1°. The experimental results and numerical calculation are described in this paper.

The role of the grain boundary on the room temperature resistivity of Pb(Fe_1/2Nb_1/2)O₃ (PFN) was investigated using parameters such as temperature dependence of resistivity, complex impedance spectroscopy and X-ray photoelectron spectroscopy. The low resistivity of PFN has been reported to be due to the electron hopping between Fe²⁺ and Fe³⁺ driven by the reduction of PFN. However a reconsideration of the reduction equilibrium constant (K_Re) revealed that this theory could not fully explain the effect of the sintering temperature on the room temperature resistivity. The role of the grain boundary on the total resistivity was introduced in order to account for this behavior, which was confirmed by complex impedence spectroscopy. Furthermore, the annealing data and X-ray photoelectron spectroscopy (XPS) results showed that the grain boundary properties were irreversibly changed at 1423 K, which appeared to be due to Pb volatilization.

Complex impedance spectroscopy study was done on 0.91Pb(Zn_1/3Nb_2/3)O₃–0.09PbTiO₃ (PZN–PT) single crystals in the wide range of temperatures (25–525°C) and frequencies (1 kHz–1 MHz). The ac conductivity was computed from the impedance data and the activation energy for conduction at different frequencies was determined. Frequency explicit plots of imaginary components of impedance exhibit Debye-like peak shapes. Cole–Cole diagrams were observed in the high temperature regime. Temperature dependent conductivity measurement and Cole–Cole plots fairly establish the existence of quenched random defects in the PZN–PT system.

Ba(Co_1/3Nb_2/3)O₃ (BCN) ceramics has a 1:2 ordered hexagonal structure and the degree of the 1:2 ordering slightly decreased when the sintering temperature exceeded 1400°C. A large amount of the liquid phase was found in the BCN ceramics sintered above 1400°C the formation of which is related to the evaporation of CoO. The liquid phase contains high concentrations of Ba and Nb ions. The grain size increased for the specimens sintered above 1400°C due to the presence of the liquid phase during the sintering. The Q-value of BCN increased with increasing sintering temperature and the specimen sintered at 1400°C had the maximum Q-value. When the sintering temperature exceeded 1400°C, however, the Q-value significantly decreased. The presence of a large amount of liquid phase could be responsible for the decrease of the Q-value. BCN ceramics were also sintered for various times at 1400°C and 1450°C and the variations of the microwave dielectric properties were explained in terms of the grain size and the relative density.

Polarization retention characteristics of ferroelectric Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films, fabricated on Pt/TiO₂/SiO₂/Si substrates by pulsed laser deposition, have been investigated. The retained polarization showed a power-law-like decay within one second of writing and the normalized retained polarization was well scaled with respect to the initial polarization regardless of the write/read pulse fields. Thermally accelerated retention failure tests, performed at 120°C for 3.6 ×10⁵ s, showed that the BLT films had quite good retention characteristics, retaining 85% of the value measured at t=1 s. It was also found that there was an accompanying imprint phenomenon during the retention test. However, the retention loss cannot be explained solely by imprint but polarization charge compensation by redistribution of defect charges should also be considered.

Polycrystalline HfO₂ thin film capacitors were prepared by anodizing sputter-deposited Hf films, and their capacitor and leakage current properties were studied. Electrical measurements were performed for the parallel-plate Hf anodized capacitors with an Al–HfO₂–Hf (metal–insulator–metal) structure, and high capacitance density (0.6 µF/cm²) and low dielectric loss (0.0095) were obtained for a very thin-oxide capacitor anodized at 10 V. In addition, the leakage current density of this capacitor was about 5 ×10^-9 A/cm² at an applied voltage of 5 V. The leakage current density (J) of HfO₂ capacitors as a function of applied electric field (E) was investigated for several capacitors with different oxide thicknesses, by plotting ln (J) vs E^1/2 curves. As a result, it was revealed that the conduction mechanism is due to Schottky emission, irrespective of the oxide thickness.

A new technique for the direct evaluation of the influences of the substrate/liquid crystal (LC) and air/LC boundary conditions on molecular alignment and dynamics using a transferred ferroelectric liquid crystal film has been proposed. The in-plane polarization reversal current in the transferred film has been measured as a function of film thickness and temperature using an interdigitated electrode on the substrate. It is found that spontaneous polarization in a thin film is influenced by the boundary conditions. The polarization reversal current has been observed even above the Curie temperature in a thin film, which is enhanced with decreasing film thickness. This anomaly is discussed in terms of the surface clinic effect of the molecules at the air/LC interface, and the flexoelectric effect.

Molecular orientational ordering in an antiferroelectric liquid crystal was studied by observing polarized Raman scattering in a homogeneously aligned thin sample exposed to static electric field. The apparent orientational order parameters gradually increased with the applied electric field strength even in the pretransitional regime from antiferro- to ferroelectric phase although the averaged molecular orientation was hardly changed. This change in the order parameters indicates the deformation of the c-director and is represented by the similar equation describing the nematic director deformation induced by an external electric field, in which the electric coherence length was inversely proportional to the applied electric field strength.

In the in-plane optical geometry, the achromatic and viewing properties of reflective liquid crystal displays (LCDs) are studied within the framework of the 2 ×2 Jones matrix formalism. For obtaining high brightness, high contrast and good achromaticity, LCD cell parameters such as the molecular rotation angle of LC and the effective phase retardation through the LC layer are optimized in the geometry such that the average optic axis of the LC layer lies on the plane parallel to the substrates. The resultant viewing properties are consistent with previous experimental results for a reflective antiferroelectric LCD.

We proposed a new flexible ferroelectric liquid crystal (FLC) device containing polymer walls and networks between plastic film substrates. The solution of FLC and monomer sandwiched between the substrates was irradiated with ultraviolet (UV) light through a photomask to form the polymer walls. Polymer walls without optical anisotropy were formed from an isotropic-phase solution to prevent light leakage through the polymer walls under crossed polarizers. Subsequently, uniform UV light was irradiated without a photomask on the solution containing the remaining monomer, and then polymer networks were formed on all except the polymer wall areas. The fabricated FLC device enabled grayscale display operation in the areas with the polymer networks. Even when the device was bent or cut, the device maintained spatial uniformity of light modulation because the polymer structures formed by the above two-step UV irradiation method maintained a constant composite film thickness.

A new method for the measurement of the pretilt angle of liquid crystal (LC) using an LC lens cell with hybrid alignment is proposed. We show that the distance of the disclination line from the center of the lens cell is approximately proportional to the pretilt angle of LC at the surface of the plane substrate. The pretilt angle can therefore be derived from the position of the disclination line. The measurement of pretilt angles of LCs in several regions of one substrate is presented. The results are in agreement with those obtained by the crystal rotation method.

In mechanical alloying (MA) of Fe–C and Fe–N materials with additive elements A such as Nb, Ti, Cr, and Co in an Ar atmosphere using a ball mill, the amorphization of MA powders is most crucially dependent on the interaction parameter W_AX (X=C or N) among the several properties of additives A, including their melting points and atomic sizes, and the milling energy supplied to MA materials. The parameter W_AX represents the difference between the bonding energies of the atomic A–X pair (U_AX) and the Fe–X pair (U_FeX) in the Fe–A–X solution, i.e., W_AX=U_AX-U_FeX. Additives such as Cr and Nb with negative W_AX values markedly promote the amorphization of MA materials, in contrast to Co or Ni which have positive W_AX values. When V–VI group elements with negative and moderate W_AX values, such as Nb, Ta, and Cr, are employed as the ternary additives, the amorphization of Fe–C and Fe–N materials is readily attained.

Microstructure and characteristics of Ba(Ti,Zr)O₃ ceramics are significantly influenced by the addition of 4PbO.B₂O₃. The melting temperature of 4PbO.B₂O₃ was approximately 500°C, and thus it provides a liquid phase during sintering. At low sintering temperatures, the grain growth of Ba(Ti,Zr)O₃ ceramics is enhanced by capillary rearrangement and solution-reprecipitation from the liquid phase. At high sintering temperatures, exaggerated grain growth of Ba(Ti,Zr)O₃ ceramics is restrained by the presence of a liquid phase. The spreading liquid can penetrate the solid-solid interfaces. Penetration leads to disintegration of the solid and the subsequent rearrangement of fragments. With increasing amounts of 4PbO.B₂O₃, the tetragonal c/a ratio and Curie point temperature increase, but the dielectric loss tangent is depressed. With a suitable amount of glass frit and temperature for sintering, the density is enhanced and the values of the planar coupling factor and the poled dielectric constant are improved.

Commercial thick-film resistor pastes were printed on and embedded in cordierite+borosilicate glass low-temperature co-firable ceramic (LTCC) substrates. The electrical properties of the resistors were found to depend on the final microstructure. Anorthite crystals were produced by the interaction between the substrates and glass composition of the resistor films at boundaries. The anorthite crystals grown into the substrate and the resistor layer increased the overall resistance. Sedimentation of the conductive particles and glass migrating to the substrates decreased the resistor thickness during sintering. Conductive particles in the resistor films flocculated after firing at 850° and 900°C. Formation of anorthite crystals, conductive particle sedimentation, glass migration, and inter-diffusion were determined to be three major factors determining film resistivity.

The measurement of the intensity of sonoluminescence, subharmonic generation and sound emission with different pulse parameters is reported using a new method of stimulating the acoustic cavitation effect at high frequency (700 kHz) with a low-frequency (20 kHz) ultrasonic field. It is found that stimulation enhances the intensity of sonoluminescence and subharmonic generation at reduced threshold transducer voltage and inverse pulse duty ratio, while sound emission is oppositely affected. The bi-frequency effect arises due to space–time interaction. This work contributes to the understanding of the mechanism of light emission and nonlinear behavior of bubble dynamics.

The liquid crystal (LC) lens is prepared using planoconvex-shaped metal substrates as electrically controlled quasi-optical millimeter-wave devices. The millimeter-wave focusing properties of the LC lens are calculated by the finite-difference time-domain (FDTD) method and measured at 94 GHz. The focusing effects of the LC lens and changes in the focusing properties induced by the applied voltage have been obtained. The measured focusing properties of the LC lens agree with those calculated by the FDTD method.

The refractive index and dielectric constant of garnet single crystals grown by the Czochralski method were measured. New results were obtained which revealed that both the refractive index and dielectric constant increased with the increase of their lattice parameters depending on their ionic radius of rare-earth ions.

The amorphous Si–Ge–Au thin films were consecutively annealed to determine annealing effects on the amorphous structures. Electrical resistivities were measured to investigate the amorphous structural changes. The electrical resistivies of the specimen annealed up to 1000 K were changed with hysteresis at high temperatures, but returned to same values of electrical resistivity at room temperature. Increasing of the upper limit of thermal annealing temperature from 1000 K to 1100 K made the electrical resistivity change irreversibly over the entire temperature range. Therefore, the expected transition temperature of the amorphous phase is considered to be between 1000 K and 1100 K.

Multilayer Mo/Al films for soft X-ray optics have been fabricated by a DC magnetron sputtering method. The characteristics of multilayer films have been investigated using a transmission electron microscope for observing the cross-sectional microstructure, electron diffraction for determining the crystalline properties, and a small-angle X-ray diffractometer and synchrotron radiation reflectometer for obtaining refractivity. The roughness of the multilayer films was controlled by increasing the number of layers and applying a negative bias to the substrate. While the reflectivity of the reference multilayer film was 23.3% at a normal incidence angle of 5°, it increased to 29.2% as a result of the increase in the number of layers. The surface roughness of the multilayer film decreased and became similar to that of the aluminum monolayer, when the number of layers increased. This was the main reason for the increase in reflectivity. Bias sputtering reduced the roughness of the film and as a result, reflectivity increased to 33.5%, however, at higher bias voltages, probably due to the diffusion of Al or Mo through the interface, reflectivity did not increase any further.

A simulation model for estimating in-plane distortion (IPD) of extreme ultraviolet lithography (EUVL) mask in a flat state was developed on the basis of a two-dimensional plane stress theory. An EUVL mask made of quartz glass was assumed in the simulation. IPD of three types of EUVL masks was investigated. The model predicts not only IPD but also the strain in the direction perpendicular to the surface. One of the IPD sources is stress gradient of the multilayer and absorber films. Discontinuity stress gradient in the pattern edge is one source of fluctuation-like displacement amplitude. A peak placement error on the mask of ±6 nm was predicted in the range of ±500 MPa absorber stress and -100 MPa multilayer stress. The fluctuation in surface height of 0.4 nm was 1/100 and below compared with the absorber thickness of 100 nm.

A new dry cleaning technology for removal of silicon (Si) native oxides from contact holes employing a hot ammonium (NH₃)/nitrogen trifluoride (NF₃) mixture has been studied. The NH₃/NF₃ mixture heated at a high temperature in a quartz tube enabled etching of the silicon dioxide (SiO₂) film placed in the downstream region. The mechanism of the etching reaction which was investigated using in-situ infrared spectroscopy and X-ray photoelectron spectroscopy analysis was revealed as follows: NF₃ alone in the NH₃/NF₃ mixture was decomposed above 600°C, probably producing NF_x (x=1, 2) and fluorine atoms. These active species reacted with NH₃, thereby generating ammonium hydrogen fluoride (NH₄F ·HF) and/or ammonium fluoride (NH₄F) in the gas phase which are considered to be SiO₂ etchants. The reaction of these molecules with SiO₂ generated an ammonium hexafluorosilicate ((NH₄)₂SiF₆) product on the Si surface which was liberated at a temperature above 70°C, leaving the hydrogen terminated surface. The application of this method to actual contact holes demonstrated successful removal of the Si native oxide grown on the Si surface at the hole bottom.

Glassy carbon is one of several types of amorphous carbon and has a complicated network structure made up of multilayers consisting of sp² hybridized carbon. We briefly reported the phenomenon of the hardening of glassy carbon induced by KrF excimer laser (λ=248 nm) irradiation. In this study, ArF, KrF, XeCl, fundamental generation and 2nd harmonic generation waves of Nd:YAG lasers were applied on the glassy carbon target directly under the atmospheric pressure of argon to confirm the appropriate conditions for the hardening of glassy carbon. Surface hardening was observed with variations of the surface morphology and the structure of the modified layer.

Tantalum nitride films were prepared by RF magnetron sputtering. The thermal diffusivity of these films was measured using a traveling thermal wave method. The measured values of thermal diffusivity are within the range 0.10–0.15 cm²/s with a deviation ±0.01 cm²/s and proportional to the nitrogen contents. The incorporation of oxygen impurity in the TaN films was found not available as examined by transmission electron microscopy (TEM) and X-ray photoelectron spetroscopy (XPS) quantitative analyses. TEM examination shows that the microstructure in TaN film, deposited with an N₂/Ar flow ratio 1:19, is composed of metallic particles dispersed in an amorphous matrix. High resolution TEM photograph reveals that the amorphous structure further contains a nano-crystalline phase embedded in a continuous amorphous phase. The nano-crystalline particles are characterized as hexagonal Ta₂N phase with a lattice spacing d₁₁₀=3.05 Å. By XPS Ta(4f) spectra, some Ta–N and Ta–O signals were evidenced to co-exist in a broadened peak. Furthermore, by FTIR analysis, a new vibration not reported before in the literature was found at 1118 cm^-1 that has been assigned to the Ta–N–O linkage in the films.

We report the structural and gas sensing properties of tungsten trioxide (WO₃) thin films prepared by the KrF excimer pulsed laser deposition technique. The WO₃ thin films having amorphous, crystallized tetragonal and triclinic structures were fabricated at the oxygen pressure of 10–300 mTorr and the substrate temperature of 150–800°C. We revealed the effect of the oxygen pressure and substrate temperature during the deposition on the crystal phases of the WO₃ thin films. The atomic force microscopy measurement shows that the average grain size and the average number of grains are approximately 200 nm and 8/µm², respectively. The triclinic WO₃ thin film with a thickness of 1 µm showed high sensitivity of 254 in NO (60 ppm) gas at a low operating temperature of 150°C.

SrRuO₃ thin films were epitaxially grown on (001)SrTiO₃ and (001) [(LaAlO₃)_0.3–(SrAl_0.5Ta_0.5O₃)_0.7] (LSAT) substrates by rf magnetron sputter deposition and metalorganic chemical vapor deposition (MOCVD), and their crystal structure, electric property and thermal stability were investigated. SrRuO₃ films prepared by MOCVD (MOCVD-SrRuO₃ films) had almost the same volume of unit cell as that of the single crystal, while those prepared by rf magnetron sputter deposition (sputter-SrRuO₃ films) had a larger volume. This large volume of the unit cell of sputter-SrRuO₃ films decreased by the post annealing up to 830°C but did not reach that of the single crystal one. Temperature dependence of the resistivity of MOCVD-SrRuO₃ films was in good agreement with that of the single crystal, which corresponds to metallic behavior, while that of sputter-SrRuO₃ films showed semiconductor-like behavior below 120 K.

Coulomb-blockade-based displacement current staircases are observed in the displacement current–voltage characteristics of double barrier tunneling junctions with a vibrating probe. Displacement current flows periodically in accordance with the mechanical oscillation of the reservoir and is separated from the tunneling current using a two-phase lock-in amplifier. The theoretical displacement current staircase is successfully fitted to the measurement. This displacement current staircase demonstrates the mechanical single-electron turnstiles in which the quantized number of electrons on the gold dots alternates periodically with the mechanical oscillation.

The initial stage of Cs adsorption on a Si(111)7×7 surface is studied by means of scanning tunneling microscope (STM) and local tunneling barrier height (LBH) imaging which provides the microscopic work function distribution. Utilizing the combination of STM and LBH imaging, the Cs adsorption features can be classified into three types; clustering, adsorption on an adatom site, and adsorption on a rest atom site. For all these adsorption types, LBH is reduced locally just at the Cs adsorption sites. On the other hand, the increase in the local density of states at the adatom next to the adsorbed Cs is observed. This is considered as a long-ranged effect of Cs adsorption, which has been pointed out in theoretical works.

A new deposition system for preparing a highly sensitive flammable gas sensor has been developed. In this method, tin oxide (SnO₂) thin films were deposited on Si(100) and Al₂O₃ substrates using the pulsed Nd:YAG (532 nm) laser deposition (PLD) method and palladium (Pd) thin films were deposited on the same substrate using d.c. sputtering simultaneously. Experimental results suggest that Pd-doped SnO₂ thin films can be prepared using this new method. The sensitivity of the Pd-doped SnO₂ film sensor prepared using this new deposition system is about 3.2 times higher than that of a pure SnO₂ film sensor prepared by the conventional PLD method.

In connection with X-ray lasers, theoretical line intensity ratios of neon (Ne)-like argon (ArIX) and krypton (KrXXVII) ions in high energy density plasmas have been investigated considering 27 levels of the 2s²2p⁶, 2s²2p⁵3s, 2s²2p⁵3p, and 2s²2p⁵3d configurations. It was found that some line intensity ratios are sensitive to the electron density, the electron temperature, and also opacity in the interest regime of ArIX and KrXXVII X-ray lasers. Our attention is devoted to studying the opacity effects of the important radiative transitions for the lasing condition, namely; those of the 3d ¹P₁–2p⁶¹S₀, 3d ³D₁–2p⁶¹S₀, 3d ³P₁–2p⁶¹S₀, 3s ³P₁–2p⁶¹S₀, and 3s ¹P₁–2p⁶¹S₀ transitions on the line intensity ratios in both static and cylindrically imploding plasmas under the Sobolev approximation that includes the effect of the large velocity gradient.

A nonthermal plasma produced by the streamer corona discharge at an atmospheric pressure was investigated for the treatment of fluorocarbon. The effective treatment of fluorocarbons was performed by controlling the discharge parameters of the plasma. The decomposition rate of fluorocarbon was investigated by varying (a) discharge modes, (b) dilution gases and (c) discharge characteristics, that is, applied voltage V_A-K of the main discharge gap and its steepness dV_A-K/dt. The maximum decomposition rate of 92% was achieved by the streamer corona discharge.

The characteristics of an axis-encircling electron beam using an annular Pierce-type electron gun are calculated analytically. The analytical calculation is carried out by considering the initial canonical angular momentum spreads at the cathode and the crossing of the electron beam with the magnetic flux line before the magnetic cusp. The analytically calculated characteristics of an axis-encircling electron beam such as the axial velocity spread, the velocity ratio, the Larmor radius, and the guiding center radius are in good agreement with the simulated result obtained using an electron trajectory program. In this comparison, a 30 kV, 1.0 A electron beam is used with a peak magnetic flux density of 4.38 kG using the magnetic field with a single cusp. The result obtained by this analysis also shows that the electron beam with a fairly low axial velocity spread of less than 1% can be realized by employing a suitable distance between the cathode and magnetic cusp.

We have deposited hydrogenated amorphous carbon (a-C:H) films called diamond-like carbon (DLC) on an electrically floating disk using a compact electron-beam-excited plasma (EBEP) employing toluene and ethylene as feed gases. Since the EBEP source enables us to control the ion sheath bias on the floating substrate by changing the electron-beam energy, the substrate ion bombardment energy needed to form the DLC film can be determined without applying an additional bias power supply such as RF. The relationship among the DLC film properties, the deposition rate and the electron-beam acceleration voltage for both feed gases has been investigated. In order to achieve uniform deposition on a disk of 80 mm diameter, the optimization of the compact EBEP source has been examined as well. A high-quality DLC film with good film uniformity on the disk was synthesized at high acceleration voltage employing toluene gas.

The construction and characteristics of a new low-energy Penning ionization gauge (PIG)-type ion source assisted by RF magnetron discharge are described. A two-stage scheme of the ion source is realized by using RF magnetron plasma as the cathodes for the PIG discharge. This scheme permits the independent control of both the ion beam energy and the parameters of discharge plasma in which the ions are produced. A divergent magnetic field configuration provides high current efficiency, reaching 50% under certain conditions. The source produces synthesized ion–electron flow with an ion beam current density of 1.5 mA/cm² and an ion energy of up to 100 eV under a low working pressure of p=(1-8)×10^-4 Torr using inert and reactive gases as the working gas.

The attenuated phase-shifting mask (Att. PSM) is one of the most useful technologies for deep sub-micron lithography. However, several critical mask parameters including critical dimension (CD), sidewall slope and morphology affect the phase-shift layer (MoSiON). In this work, the effects of added Cl₂ gas and dc bias voltage in inductively coupled CF₄-based plasma were studied. As results of our experiment, the most vertical profile and smoothest surface were obtained at 10 sccm Cl₂ and -200 V dc bias. By increasing the dc bias voltage, the undercut of the MoSiON layer decreased. As Cl₂ gas increased in the CF₄/O₂/He plasma, surface roughness decreased but the edge of the Cr slope was damaged at 15 sccm Cl₂. It is suggested that the pattern profile and surface roughness of the MoSiON layer can be controlled by both the quantity of Cl₂ gas and the dc self-bias voltage.

A new driving system of an insulated probe is proposed and compared in Ar RF plasma with the conventional insulated probe system using an operational amplifier for probe current detection. In this system, the probe is driven by a low-output-impedance driver through a transmission line as long as a half-wavelength of the fundamental component of the RF, and the probe current is detected at the midpoint of this transmission line as a voltage signal. It was shown that measurement almost equivalent to that using an operational amplifier is possible with the use of a transmission line. The advantage of this system is that the flexibility of geometric design of the probe system is greatly improved without the parasitic effect due to the increase of stray capacitance.

We discuss the effects of electron energy distribution function (EEDF) on the number densities of excited states of Ar I in a microwave discharge argon plasma in the pressure range of 0.1 to 10 Torr. We experimentally generate the microwave discharge argon plasma and find the electron temperature and density to be 5–12 eV and (1 -4)×10¹¹ cm^-3, respectively. Single probe analysis also shows that its EEDF is approximately Druyvesteynian, but with a large uncertainty. We measure the number densities of excited states of Ar I by spectroscopic examination. For numerical analysis, we obtain the number densities of the excited states by using a collisional radiative model, substituting experimentally observed electron temperature and density. The number densities of excited states calculated by the collisional radiative model agree well with the experimental ones when we adopt the Druyvesteynian distribution as EEDF, whilst the Maxwellian distribution gives poor results.

We successfully produced the multi-charged Ga ions using metal ions from volatile compounds (MIVOC) method from liquid-He-free super conducting electron cyclotron resonance ion source at RIKEN (RAMSES). The beam intensities of Ga¹⁵⁺ and Ga¹⁶⁺ ions were 5 and 4 eµA at the injected microwave power of 200 W, respectively.

Langmuir films of 1:x (x≤1) mixtures of an amphiphilic merocyanine dye (DSe) and a fatty acid prepared at an air–pure water interface were characterized by in-situ observation of their visible absorption spectra. A distinct J-band was observed at low surface pressures even with x≪1. The time and x dependence of the absorption spectra indicate that the fatty acid assists the nucleation of the J-aggregates and that one J-aggregate can contain 10² DSe molecules. In addition, a surface pressure-induced phase transition was detected, suggesting that, in these Langmuir films, J-aggregated DSe requires a larger area than non-J-aggregated DSe.

The dissociative ionization process of BrCN was studied using the threshold ionization mass spectrometry. The threshold of the production of C⁺ was determined as 23.3±1.0 eV. From the discussion based on this result, the low (≤0.2) concentration of the N atoms in the amorphous carbon nitride films formed from the dissociative excitation reaction of BrCN with the electron cyclotron resonance plasma of Ar was considered to originate in the effective production of C and C⁺ by the impact of high-energy electrons.

In this paper, we present an analysis of the velocity dispersion and wave attenuation of a layered piezoelectric medium loaded with a viscous liquid. The eight-dimensional formalism of the surface wave and the recursive formula were adopted to obtain the impedance tensor of a piezoelectric layered half-space and that of viscous liquids. The dispersion equation of the surface waves in such a layered system was formulated under the continuity conditions at the solid-liquid interface. Numerical examples of half-space (lithium niobate), single-layered (lithium niobate/sapphire) and double-layered half-space (ST-cut quartz/lithium niobate/sapphire, lithium niobate/ST-cut quartz/sapphire) loaded with a viscous liquid are presented and discussed as well.

We demonstrate gas sensing using a fiber ring laser composed of an erbium-doped fiber as the laser medium and a compact gas cell module. Acetylene absorption at 1.5 µm is enhanced by an intracavity configuration, in which multiple band-pass filters are used to control the wavelength of laser oscillation. A maximum enhancement factor of about 80 is achieved with an 18.3 mm cell under a pressure range below 100 Pa. Experimental results can reasonably be explained by a ring laser theory that describes the influence of acetylene pressure on the threshold and slope efficiency of the laser output characteristics.

Using a scanning Hall-sensor microscope with an active area of 50 µm×50 µm, we succeeded in visualizing the breakdown of the paramagnetic austenite phase in 304 stainless steel induced by plastic strain at room temperature, resulting from a transformation to the ferromagnetic martensite phase. Magnetic images of spontaneous magnetization on the surface of the strained sample show the degree and location (and/or the extent) of phase breakdown. Furthermore, the images nearly agree with the calculated results for the principal shear stress rather than the principal stress under plastic deformation, which is indicative of the driving force of this breakdown. The study should pave the way for nondestructive evaluation of 304 stainless steel to prevent deterioration of both heat and corrosion resistances, as well as the occurrence of cracks under the materialization process.

Uniaxially aligned vacuum deposited films of copper phthalocyanine (CuPc) have been studied by means of angle-dispersive grazing-incidence X-ray diffraction. The lateral structure of the top surface of a 100-nm-thick film was successfully probed. It was revealed that the microcrystals near the surface have a finite in-plane distribution with a full-width at half maximum of 17.5°. In-plane diffraction profiles were transformed into a reciprocal space map that reproduced the electron diffraction pattern of a CuPc thin film reported previously.

A significant increase in the yield of electroformed nickel nozzle plates of piezo ink-jet printer heads was realized by (1) plasma-enhanced sputter deposition of a nickel–3 wt% vanadium alloy cathode electrode onto a Si (100) substrate wafer maintained at 650°C (2) electroforming nickel nozzle plates on one side of a pre-patterned cathode electrode in a nickel sulfamate bath containing appropriate additives. The electroformed nozzle plates were easily peeled off from the cathode electrode while the cathode electrode adhered quite strongly to the Si (100) wafer substrate. The successful fabrication of the nozzle plates was attributed to (1) compressive stress induced by argon plasmas impinging upon the cathode, (2) improved adhesion of the cathode onto the Si (100) wafer substrate by probable formation at 650°C of a nonmetallic compound, e.g., nickel silicide at the cathode/substrate wafer interface, and (3) proper selection and control of the most suitable electroforming condition which enabled linear correlation of current densities and compressive stress levels in the electroformed substrate wafers, thereby enabling a wider range of current densities for mass-production of nozzle plates.

We have been investigating the determination of three-dimensional electric field distributions using the reconstruction technique modified by the computed tomography technique and the Kerr electrooptic method. For the reconstruction using this technique, the light intensity must be measured from many directions around the measured distribution. Therefore, we studied the effect of the number of measurement directions on the reconstructed electric field distributions.

Optics for a planar display device demand solutions of a system of differential equations for numerous different wavelengths and angles of incidence. Berreman's midpoint piece-wise stratification method is generally used to compute display optics because it converges rapidly to the true solution of the differential system. Two algebraic variants of Berreman's approach, the eigenvector method and the Cayley–Hamilton method, are widely known and implemented. A new variant is introduced here that computes the same approximate solutions as the other techniques, but is faster because it requires less arithmetic.

The development of a submillimeter wave catheter for irradiating on living bodies using a gyrotron as the radiation power source is described. The gyrotron FU-IV is optimized for development. The gyrotron is operated in the CW mode at a frequency of 302 GHz under a magnetic field of approximately 11 T. Irradiation tests using various antennas were performed on cow livers, living rats and malignant tumors implanted in living mice. Irradiation results were considered based on the microwave theory and ray optics.

A clear image of a wooden chopstick penetrating the soft palate of a pig-head was obtained using highly coherent synchrotron X-ray. The image was recorded on a mammography film with an intensifying screen at an X-ray energy of 35 keV. The tubular tissues as sieve tubes or ducts in the chopsticks appeared as white-black line images by means of X-ray refraction contrast. This method may enable development of an accurate diagnostic method in the field of penetrating trauma by wood.