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Muons are part of natural cosmic radiation but can also be generated at spallation sources for material science and particle physics applications. Recently, pulsed muons have been used to characterize the density of free charge carriers in semiconductors and their recombination lifetime. Muon beam irradiation can also result in the formation of dilute levels of crystal defects in silicon. These crystal defects are only detected in high carrier lifetime silicon samples that are highly sensitive to defects due to their long recombination lifetimes. This work investigates the characteristics of these defects in terms of their formation, recombination activity, and deactivation. Charge carrier lifetime assessments and photoluminescence imaging have great sensitivity to measure the generated defects in high-quality silicon samples exposed to ∼4 MeV (anti)muons and their recombination activity despite the extremely low concentration. The defects reduce the effective charge carrier lifetime of both p- and n-type silicon and appear to be more detrimental to n-type silicon. Defects are created by transmission of muons through the wafer, and there are indications that slowed or implanted muons may create additional defects. In a post-exposure isochronal annealing study, we observe that annealing at temperatures of up to 450 °C does not by itself fully deactivate the defects. A recovery of charge carrier lifetime was observed when the annealing was combined with Al2O3 surface passivation, probably due to passivation of bulk defects from hydrogen from the dielectric film. [ABSTRACT FROM AUTHOR]

We conducted spin Hall magnetoresistance (SMR) measurements to investigate the Ru-doping effect on the Morin transition of α-Fe2O3(0001) films, which is the transition from the low-temperature antiferromagnetic state with c-axis magnetic moments to the high-temperature weak ferromagnetic state with c-plane magnetic moments, under a thickness of 6–100 nm. We clarified that the Morin temperature of the 2.6 at. % Ru-doped α-Fe2O3 film was greater than 400 K when the thickness was 100 nm and decreased with a decrease in thickness. Our results demonstrated that SMR measurements are a valid verification method for the Morin transition of very thin α-Fe2O3 films down to several nm. [ABSTRACT FROM AUTHOR]

We discovered large electric-field-induced strain in pyro-vanadate-phosphate Cu2−xZnxV1.8P0.2O7. Distinct from conventionally used piezoelectric materials including lead-zirconate-titanate, this material expands almost isotropically at room temperature when an electric field is applied. This volume change, exceeding 1000 ppm under the field of E = 3900 V/cm, is of the largest class induced by an electric field. The strain is phenomenologically interpreted as electrostriction because it is symmetric about E = 0 and because it obeys a higher term than E-linear such as E squared. The present x-ray diffraction experiments suggest that the applied electric field distorts the crystal lattice, although there is no structural phase transition. This material performs a volume-change-driven actuator function that is distinct from the strain-driven counterpart of piezoelectric materials. The discovery of actuator functionality in a material system with a non-perovskite structure, unlike the actuator materials developed to date, is a major breakthrough for future actuator engineering. [ABSTRACT FROM AUTHOR]

High Aspect Ratio Contact (HARC) hole etch is one of the most challenging processes that require many efforts to optimize etch condition. As the aspect ratio increases, novel issues, such as "distortion" and "twisting," have been highlighted. Since they cause nonaxisymmetric features along the hole axis, it is difficult to understand the etch mechanism correctly, and therefore, taking a 3D profile image is essential to evaluate the exact etch profile. In this study, we created the models for HARC etch with a cell-based Particle Monte Carlo topography simulator by fitting both vertical and horizontal cross-sectional profiles carefully to the experimental results. Moreover, we attempted to apply a model optimization algorithm. By collaboration of human and the algorithm, modeling engineers can minimize a try-and-error approach, and a precise 3D simulation model can be created much faster than before. As a result, the distortion and twisting profiles were reproduced very well on the simulator, and thus, it is expected that the simulator can be utilized as a practical tool for an assistance of process optimization. [ABSTRACT FROM AUTHOR]

The control of laser emission angles in laser devices is essential for many optoelectronic and photonic applications such as optical sensing and displays. In this context, we studied the light diffraction pattern of laser beams in a one-dimensional sampled distributed feedback resonator having organic gain media. The gratings consist of the repetition of supercells having a mixed-order sampled grating in which 1st-order gratings surround a 2nd-order grating. The experimental results showed that the diffraction angles of the laser beams are quite diverse depending on the supercell structures. We demonstrate that the interval of the diffraction angle (θ) of the laser beams is inversely proportional to the length of the supercell experimentally and theoretically. By tuning the length of supercells as well as the length of 1st-order and 2nd-order regions, the interval θ was tuned from 0.1° to 43° with the different arc emission patterns. With the reduction of θ, i.e., the longer 1st-order region, a significant decrease in the laser threshold was obtained, resulting in the lowest lasing threshold of 2.5 ± 0.1 μJ/cm2 with ∼3.5 ns of a long pulse width excitation source. [ABSTRACT FROM AUTHOR]

Polymers are extensively employed in diverse industries, including electrical equipment and electronic devices. Recent technological advancements have intensified the demand for dielectric polymers with both high insulation resistance and high thermal conductivity. We employed molecular dynamics simulations to clarify the intricate relationship between molecular structures, thermal conductivity, and ionic mobility from an atomistic point of view. Examined polymers include polyethylene, polyvinyl alcohol, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene, polyoxymethylene, and polyethylene oxide. Based on the elucidated correlations among force field parameters, we found that the parameters can be clustered into four groups: group 1 (atomic and bond parameters and force constant of the bond angle), group 2 (equilibrium angle and force constant of dihedral angle), and group 3 (side chain atom charges). Thermal conductivity showed relationships with parameters in group 1, with correlation coefficients mostly exceeding 0.7 in the absolute value. Considering the correlations between the parameters, we systematically altered the parameters within each group and computed thermal conductivity and ionic mobility. When altering the force field parameters of groups 1 and group 2, a trade-off relationship between thermal conductivity and ionic mobility becomes evident. Conversely, altering the force field parameters in group 3 increased thermal conductivity while decreasing ionic mobility, breaking the trade-off relationship. The proposed clustered-parameter variation method can predict the changes in the electrical and thermal conductivity of polymers through molecular structure modifications. The method, being a general and first-principles approach, is likely to have significant advantages in the molecular design across a diverse range of polymers. [ABSTRACT FROM AUTHOR]

A recent experiment [Nakajima, et al., Nature 613, 479 (2023)] has reported a pair of oppositely polarized spins under an alternating electric current in a superconductor with a chiral structure. However, these behaviors cannot be explained by the conventional Edelstein effect and require a new mechanism. In this Letter, we propose a mechanism of spin current generation under an external electric field due to chiral phonons in a chiral-structure superconductor based on the Bogoliubov de Gennes and the Boltzmann equations. In our mechanism, chiral phonons are induced by electric field due to inversion symmetry breaking and electron–phonon interaction. They work as an effective Zeeman field and hence spin-polarize Bogoliubov quasiparticles in the superconductor. As a result, the spin current carried by the quasiparticles flows along the screw axis and shows a quadratic dependence on the electric field at the low-field range, leading to a nonreciprocal spin transport. The spin current also shows a nonmonotonic temperature dependence, reaching its maximum at around the superconducting transition temperature. [ABSTRACT FROM AUTHOR]

A needle-free injector using a highly focused microjet has the potential to minimize the invasiveness of drug delivery. In this study, the jet penetration depth in a soft material—which is a critical parameter for practical needle-free injections—was investigated. We conducted jet penetration experiments by varying the inner diameter of the injection tube and the standoff distance between the meniscus surface and the soft material. Interestingly, the results showed that the penetration depths peaked at certain distances from the meniscus, and the positions shifted further away as the inner diameter was increased. By analyzing the velocity distribution of the microjet, the peak positions of the penetration depth and the maximum velocities were inconsistent due to the effects of the jet shape. To account for this, we introduce the concept of the "jet pressure impulse," a physical quantity that unifies the velocity and jet shape. However, direct estimation of this parameter from experimental data is challenging due to limitations in spatiotemporal resolution. Therefore, we used numerical simulations to replicate the experimental conditions and calculate the jet pressure impulse. Remarkably, the results show that the jet pressure impulse has peak values, which is consistent with the penetration depth. In addition, there is a correlation between the magnitude of the jet pressure impulse and the penetration depth, highlighting its importance as a key parameter. This study underlines the importance of the jet pressure impulse in controlling the penetration depth of a focused microjet, providing valuable insights for the practical use of needle-free injection techniques. [ABSTRACT FROM AUTHOR]

We present a numerical analysis of the rheology of a suspension of red blood cells (RBCs) for different volume fractions in a wall-bounded, effectively inertialess, small amplitude oscillatory shear (SAOS) flow for a wide range of applied frequencies. The RBCs are modeled as biconcave capsules, whose membrane is an isotropic and hyperelastic material following the Skalak constitutive law. The frequency-dependent viscoelasticity in the bulk suspension is quantified by the complex viscosity, defined by the amplitude of the particle shear stress and the phase difference between the stress and shear. SAOS flow basically impedes the deformation of individual RBCs as well as the magnitude of fluid-membrane interactions, resulting in a lower specific viscosity and first and second normal stress differences than in steady shear flow. Although it is known that the RBC deformation alone is sufficient to give rise to shear-thinning, our results show that the complex viscosity weakly depends on the frequency-modulated deformations or orientations of individual RBCs but rather depends on combinations of the frequency-dependent amplitude and phase difference. The effect of the viscosity ratio between the cytoplasm and plasma and of the capillary number is also assessed. [ABSTRACT FROM AUTHOR]

Expanding pipes with orifice plates are often utilized as silencers for fluid machinery. However, intense tonal sounds can be generated from a flow through such expanding pipes. To clarify the mechanism of tonal sound from a flow through a circular expanding pipe with two orifice plates and the conditions for intense acoustic radiation, the flow and acoustic fields are directly solved based on the compressible Navier–Stokes equations. Phase-averaged flow fields indicate the occurrence of periodic vortex shedding in the free shear layers of the expanding pipe, resulting in acoustic radiation. The effects of the orifice radius and freestream Mach number on the acoustic radiation are focused on. The computational results demonstrate that vortex rings or spiral vortices are generated in the cavities formed by the orifice plates, where the primary vortical shape changes, depending on the freestream Mach number and orifice radius. The collision of the vortex ring and spiral vortex with the orifice plate or downstream edge of the expanding pipe leads to the occurrence of circumferentially in-phase and one-wavelength-mode pressure fluctuations, respectively. The orifice radius also affects the convective velocity of vortices and the position of the acoustic source, varying the frequency of the acoustic radiation. The findings of this research provide the first clarifications of fluid–acoustic interactions in an expanding pipe with orifice plates. [ABSTRACT FROM AUTHOR]

Photoexcited muon spin spectroscopy (photo-μSR) is used to study excess charge carrier lifetimes in silicon. Experiments are performed on silicon wafers with very high bulk lifetimes with the surface passivation conditions intentionally modified to control the effective lifetime. When the effective lifetime is low (<500 μs), implanting the muons to different depths enables the reliable measurement of carrier lifetime as a function of distance from a surface. It is also demonstrated that the photo-μSR technique can measure effective carrier lifetimes in completed commercial gallium doped silicon passivated emitter and rear cell devices, with results validated with harmonically modulated photoluminescence imaging. It is discovered, however, that prolonged muon irradiation of samples with very long effective lifetimes (>10 ms) results in detectable degradation of the measured lifetime. Re-passivation of degraded samples with a temporary room temperature superacid-based passivation scheme demonstrates that degradation occurs in the silicon bulk. Deep-level transient spectroscopy measurements reveal the existence of several defect-related traps near the muon-exposed surface in concentrations of order 1010 cm−3 that are not present near the surface not exposed to muons. In contrast to the common perception of the μSR technique, our results demonstrate that muons are not inert probes and that beam-induced recombination activity modifies the bulk lifetime significantly in samples with high effective carrier lifetimes. [ABSTRACT FROM AUTHOR]

We investigated the synthesis of amorphous aluminum titanium oxide Al1−xTixOy thin films from a Al(acac)3 and Ti(acac)4 mixture using CH3OH/H2O as a solvent through mist chemical vapor deposition (mist-CVD) for application as a high dielectric material. The Ti composition ratio x in the Al1−xTixOy thin films depends on the Al(acac)3 and Ti(acac)4 mixing ratios and CH3OH/H2O volume ratio. A bandgap energy of Al1−xTixOy films was decreased from 6.38 to 4.25 eV and the surface roughness also decreased when the Ti composition ratio was increased from 0 to 0.54. The capacitance–voltage plot revealed that the dielectric constant of Al1−xTixOy thin films increased from 6.23 to 25.12. Consequently, Al1−xTixOy thin films with a bandgap energy of 5.12 eV and a dielectric constant of 13.8 were obtained by adjusting the ratio x of 0.26. This Al0.74Ti0.26Oy layer was applied as a gate dielectric layer for metal-oxide-semiconductor field-effect transistors (MOSFETs) using a mechanically exfoliated two-dimensional (2D) transition metal dichalcogenide (TMDC), MoSe2, and As-doped WSe2 flakes as a channel layer. The MoSe2-based MOSFETs with source/drain gold electrodes exhibit n-channel behavior with a field-effect mobility of 85 cm2/(V s), a threshold voltage of 0.92 V. On the other hand, an on/off ratio of ∼106. As-doped WSe2-based MOSFETs with source/drain platinum electrodes also showed an ambipolar behavior, which was applied for use in logic applications. These findings suggest that Al0.74Ti0.26Oy by mist-CVD is promising as a high-k material for TMDC-based MOSFETs. [ABSTRACT FROM AUTHOR]

The control of the velocity of a high-speed laser-induced microjet is crucial in applications such as needle-free injection. Previous studies have indicated that the jet velocity is heavily influenced by the volumes of secondary cavitation bubbles generated through laser absorption. However, there has been a lack of investigation of the relationship between the positions of secondary cavitation bubbles and the jet velocity. In this study, we investigate the effects of secondary cavitation on the jet velocity of laser-induced microjets extracted using explainable artificial intelligence (XAI). An XAI is used to classify the jet velocity from images of secondary cavitation and to extract features from the images through visualization of the classification process. For this purpose, we run 1000 experiments and collect the corresponding images. The XAI model, which is a feedforward neural network (FNN), is trained to classify the jet velocity from the images of secondary cavitation bubbles. After achieving a high classification accuracy, we analyze the classification process of the FNN. The predictions of the FNN, when considering the secondary cavitation positions, show a higher correlation with the jet velocity than the results considering only secondary cavitation volumes. Further investigation suggested that secondary cavitation that occurs closer to the laser focus position has a higher acceleration effect. These results suggest that the velocity of a high-speed microjet is also affected by the secondary cavitation position. [ABSTRACT FROM AUTHOR]

This report describes the actuator functionality of a ceramic composite that uses the volume change caused by the insulator–metal (I–M) transition of VO2. When an electrical field was applied at 295 K, 50 vol. %-VO2/Al2O3 ceramic composite underwent the I–M transition because the VO2 powder dispersed in the composite became metallic. Simultaneous measurement of I–V characteristics and linear strain demonstrated that this I–M transition was accompanied by a positive strain. This strain increased with increase in the limit current value, which limits excessive current flow after transition. The strain exceeded 1300 ppm at maximum. Its magnitude corresponded to the volume change obtained from thermal expansion measurements on the composite. This composite performs a volume-change-driven actuator function that is distinct from the strain-driven counterpart of piezoelectric materials. [ABSTRACT FROM AUTHOR]

InGaSb-on-insulator (InGaSb-OI) and InAs/InGaAs/InAs-on-insulator (InAs/InGaAs-OI) structures have been realized on Si by a direct wafer bonding (DWB) technology using atomic-layer-deposition Al2O3. While strain introduced in InGaSb channel layers grown on InAs can enhance the hole mobility of the Sb-based channel layers, a difficult issue of fabricating InGaSb-OI wafers is to obtain a smooth InGaSb surface, which is mandatory for wafer bonding. In this study, the surface of a 20-nm-thick In0.185Ga0.815Sb channel grown on an InAs (100) substrate and an InAs (2.5 nm)/In0.185Ga0.815Sb (20 nm)/InAs (2.5 nm) channel with a 20-nm-thick GaSb buffer layer grown on an InAs (100) substrate by metal-organic chemical vapor deposition have a root mean square of the surface roughness as low as 0.16 and 0.22 nm, respectively, over a scan area of 10 × 10 μm2, which are smooth enough to employ the wafer bonding. As a result, the fabrication of the InGaSb-OI wafers by the DWB and the operation of InGaSb-OI p-channel metal-oxide-semiconductor field-effect transistors (p-MOSFETs) by using the DWB wafers are demonstrated. Also, the performance of InGaSb-OI p-MOSFETs is found to be improved by inserting ultrathin InAs layers between InGaSb and insulating buried oxide layers. An InGaSb-OI and an InAs/InGaAs-OI p-MOSFET under the accumulation-mode operation exhibit a peak mobility of ∼161 and ∼273 cm2/V s, respectively. The channel hole mobility of the InGaSb-OI p-MOSFET is higher than that of the GaSb-on-insulator (GaSb-OI) p-MOSFET and can exceed that of Si p-MOSFETs. [ABSTRACT FROM AUTHOR]

The effects of a gel network structure on purple membrane (PM) spontaneous stacking are discussed, with particular emphasis on the relationship between the PM periodic pre-structures before gelation. Such peculiar intermembrane pre-structures with a periodic distance of ∼20 nm have recently been found to provide an important key to PM stacking, which is critical for the engineering applications of PM. Here, we investigated how the PM stacking differs depending on the gel network of a poly(vinyl alcohol) gel. On the basis of the results, we propose a plausible interplay between the PM periodic pre-structures and the type of gel network for PM stacking. The results indicate that a porous gel network, in addition to the PM periodic pre-structure in solutions, is necessary for PM stacking in immobilized gel samples. [ABSTRACT FROM AUTHOR]

The requirements of the epitaxially grown InGaAs channel layers for tunnel field-effect transistors (TFETs) have been studied by a comparison between the experimental results and technology computer-aided design (TCAD) simulations. It is observed that the threshold voltage (Vth) of InGaAs TFETs with high In contents is shifted more toward the negative bias direction and the off-characteristics are degraded more than that expected in simulation results. These results are attributable to the increase in n-type effective carrier concentration (Nch) in the InGaAs and InAs channels, which can be caused by lattice relaxation because of the large lattice mismatch between the epitaxial layer and the substrate. The use of a thin channel layer with high In content InGaAs and/or InAs can be a solution for achieving high on-current and low off-current simultaneously. It is found that p-type doping in the InGaAs and InAs channels can mitigate the degradation of the cut-off properties. Moreover, it is observed that increased Nch by unintentional Si impurity atoms at the epitaxial layer and the substrate interface can affect the performance of TFETs with thin InGaAs channels, which can be suppressed by introducing an insertional undoped buffer layer. The impact of Nch is also studied for the short channel devices by TCAD simulations. The p-type doping in InGaAs channels can also mitigate short channel effects in comparison to the n-type doping. The carefully controlled epitaxial growth of InGaAs and InAs channel layers with Nch <1 × 1017 cm−3 is required to realize superior performance InGaAs TFETs. [ABSTRACT FROM AUTHOR]

Positive muons can be implanted into silicon carbide (SiC), where they model the isolated hydrogen defect in the negative, neutral, or positive charge states and act as either an acceptor or a donor with midgap energy levels [Lichti et al., Phys. Rev. B 70, 165204 (2004); Lichti et al., Phys. Rev. Lett. 101, 136403 (2008)]. The charge states evolve after implantation depending on the temperature and material doping. We have measured optically induced effects on muons implanted in 6H-SiC using a pulsed, tunable laser [Yokoyama et al., Rev. Sci. Instrum. 87, 125111 (2016)]. In n-type 6H-SiC at 85 K and 40 K, with a laser pulse of energy below the bandgap, we observe photoionization of the doubly occupied level ( Mu −) to the neutral defect Mu 0 and also ionization of Mu 0 to Mu +. Varying the timing of the laser pulse relative to muon arrival confirms that the laser interacts directly with the muons in a stable or metastable state. There is no evidence of any interaction when the laser pulse is timed to arrive before the muons, so either few free carriers are generated by absorption at other dopant sites or the excess carriers have a very short lifetime (≪ 100 ns). Wavelength scans show absorption edges corresponding to the possible interstitial sites within the structure. Combining these data and the existing muon results shows that at low temperature, we have co-existence of Mu 0 and Mu − charge states, with the muon or hydrogen acting as a deep compensating impurity. The technique can be applied to many other semiconductors where the muon has been observed to be electrically active, modeling hydrogen. [ABSTRACT FROM AUTHOR]

The effects of wet chemical treatments before treatment using (NH4)2S solutions in atomic layer deposition Al2O3/InGaAs metal-oxide-semiconductor (MOS) interfaces are experimentally examined. It is found that no chemical treatment before sulfur passivation leads to high interface state density (Dit) in spite of the (NH4)2S treatment. Furthermore, the value of Dit is dependent among the pretreatments using NH4OH, HCl, and BHF solutions before the sulfur treatment. HCl + (NH4)2S and BHF + (NH4)2S combinations show the lowest values of Dit. In addition, all of the Al2O3/InGaAs MOS interfaces with the sulfur treatment show a small amount of arsenic oxide. Thus, much higher Dit of the interfaces with the sulfur treatment indicates that the amount of arsenic oxide is not a deterministic factor for Dit. On the other hand, the amount of arsenic oxide before the sulfur treatment is found to correlate with Dit after sulfur treatment. Also, the interfaces with higher Dit after the sulfur treatment show a larger number of sulfur atoms remaining at the interfaces. These experimental results mean that there is a strong correlation among Dit, the amount of arsenic oxide, and the number of sulfur atoms remaining at the Al2O3/InGaAs interfaces. As a result, we can interpret for the present experimental results that the sulfur treatment can have two opposite impacts on Dit at the Al2O3/InGaAs interfaces: the decrease in Dit due to etching of native oxides and suppression of oxidation by sulfur passivation and the increase in Dit due to defect generation through some interaction between sulfur and arsenic oxide. [ABSTRACT FROM AUTHOR]

Integrated lithium niobate (LN) electro-optic (EO) modulators are emerging for applications in next-generation optical fiber communication networks. To date, LN crystal waveguides have led the technology for high-speed modulators. On the other hand, on-chip LN modulators are expected to realize scalable signaling devices with mature complementary metal–oxide–semiconductor technology. In this study, a silicon-loaded LN modulator on the insulator substrate featuring a small footprint, a low driving voltage, and high-speed EO modulation is designed and fabricated. No etching or patterning of the LN is required. The measured halfwave-voltage length product is 1.9 V cm with a static modulation extinction ratio of 17.9 dB. The fabricated LN modulator has a modulation bandwidth of 60 GHz and supports high-speed signaling at a data rate up to 200 Gbit/s. [ABSTRACT FROM AUTHOR]

Understanding the electrical contact properties of carbon nanotube (CNT) ends is important to use the high conductance of CNTs in the CNT on-axis direction in applications such as through-silicon via structures. In this study, we experimentally evaluated the contact resistivity between single-/multi-walled CNT ends and a metal nanoprobe using conductive atomic force microscopy (C-AFM). To validate the measured end contact resistivity, we compared our experimentally determined value with that obtained from numerical calculations and reported values for side contact resistivity. The contact resistivity normalized by the length of the CNT ends was 0.6–2.4 × 106 Ω nm for single-walled CNTs. This range is 1–2 orders of magnitude higher than that determined theoretically. The contact resistivity of a single-walled CNT end with metal normalized by the contact area was 2–3 orders of magnitude lower than that reported for the resistivity of a CNT sidewall/metal contact. For multi-walled CNTs, the measured contact resistivity was one order of magnitude higher than that of a CNT forest grown by remote plasma-enhanced chemical vapor deposition, whereas the contact resistivity of a top metal electrode was similar to that obtained for a single-walled CNT forest. [ABSTRACT FROM AUTHOR]

Electrical-field-induced insulator-to-metal (I-to-M) transition of samarium monosulfides was investigated systematically. Experiment results demonstrate that Sm0.9Ca0.1S undergoes the I-to-M transition when in a small electric field of 250 V/cm at liquid-nitrogen temperatures. However, simultaneous measurement of I–V characteristics and strain did not detect the electrical-field-induced strain expected from the large volume contraction originating from the valence transition of Sm. Mid-infrared to visible region reflectivity spectroscopy in the field-induced transition revealed no spectral change other than the temperature change attributable to Joule heat. This lack of change contrasts to the large-scale spectrum changes, such as a sharp rise in reflectivity, which appear in the metallic phase induced by pressure or element substitution. The detailed analysis of the field-induced strain suggests that filamentary metallic paths are formed during the breakdown process, just as they are for strongly correlated insulators. [ABSTRACT FROM AUTHOR]

Microfluidic tools are well suited for studying bacteria as they enable the analysis of small colonies or single cells. However, current techniques for studying bacterial response to antibiotics are largely limited to static dosing. Here, we describe a microfluidic device and a method for entrapping and cultivating bacteria in hydrogel plugs. Ring-shaped isolation valves are used to define the shape of the plugs and also to control exposure of the plugs to the surrounding medium. We demonstrate bacterial cultivation, determination of the minimum inhibitory concentration of an antibiotic, and transient dosing of an antibiotic at sub-1-h doses. The transient dosing experiments reveal that at dose durations on the order of minutes, ampicillin's bactericidal effect has both a time and concentration dependency. [ABSTRACT FROM AUTHOR]

We study the metal-GaSb alloy formation, the structural properties and the electrical characteristics of the metal-alloy/GaSb diodes by employing metal materials such as Ni, Pd, Co, Ti, Al, and Ta, in order to clarify metals suitable for GaSb p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) as metal-GaSb alloy source/drain (S/D). It is found that Ni, Pd, Co, and Ti can form alloy with GaSb by rapid thermal annealing at 250, 250, 350, and 450 °C, respectively. The Ni-GaSb and Pd-GaSb alloy formation temperature of 250 ° C is lower than the conventional dopant activation annealing for ion implantation, which enable us to lower the process temperature. The alloy layers show lower sheet resistance (RSheet) than that of p+-GaSb layer formed by ion implantation and activation annealing. We also study the electrical characteristics of the metal-alloy/GaSb junctions. The alloy/n-GaSb contact has large Schottky barrier height (øB) for electrons, ~0.6 eV, and low øB for holes, ~0.2 eV, which enable us to realize high on/off ratio in pMOSFETs. We have found that the Ni-GaSb/GaSb Schottky junction shows the best electrical characteristics with ideal factor (n) of 1.1 and on-current/off-current ratio (Ion/Ioff) of ~104 among the metal-GaSb alloy/GaSb junctions evaluated in the present study. These electrical properties are also superior to those of a p>+-n diode fabricated by Be ion implantation with activation annealing at 350 °C. As a result, the Ni-GaSb alloy can be regarded as one of the best materials to realize metal S/D in GaSb pMOSFETs. [ABSTRACT FROM AUTHOR]

Photonic crystal waveguide slow-light grating emits a free-space optical beam and steers it widely by changing the optical wavelength or waveguide refractive index. In the reverse process, returned light is coupled into the device again. We have proposed to use this optical transmission and reception antenna as a beam scanner for light detection and ranging (LiDAR). Ideally, a large-aperture antenna can narrow the transmission beam and enhance the reception efficiency. Actually, however, the transmission and reception performance is not scalable owing to waveguide loss even though the waveguide is simply lengthened. A serial array configuration in which the waveguide is divided into multiple antennas is effective for mitigating this problem. In this study, we fabricated such a device using Si photonics technology and obtained a small beam divergence of 0.02° at a telecom wavelength. Then, we observed the ranging operation by adding an optical setup of frequency-modulated continuous-wave (FMCW) LiDAR and confirmed that the divided antenna device improved the reception intensity by 12 dB. Moreover, we fabricated a FMCW LiDAR chip in which the serial array antennas were integrated in parallel with switch trees and Ge photodiodes and obtained point cloud images by two-dimensional beam scanning. [ABSTRACT FROM AUTHOR]

Quantum optimal control calculations have been carried out for isotope-selective vibrational excitations of the cesium iodide (CsI) molecule on the ground-state potential energy curve. Considering a gaseous isotopic mixture of 133CsI and 135CsI, the initial state is set to the condition that both 133CsI and 135CsI are in the vibrational ground level (v=0) and the target state is that 133CsI is in the v=0 level while 135CsI in the first-excited level (v=1). We find that, using the density-matrix formalism, perfect isotope-selective excitations for multilevel systems including more than ten lowest vibrational states can be completed in much shorter time scales than those for two-level systems. It is likely that this multilevel effect comes from the large isotope shifts in the vibrational levels of v>1. To check the reliability of the calculation we also carry out optimal control calculations based on the conventional wave-packet formalism, where the wave-function amplitude is temporally propagated on the grid points in real space, and obtain almost the same results as those with the density-matrix formalism. [ABSTRACT FROM AUTHOR]

Potential energy curves (PECs) for the ground and low-lying excited states of the cesium iodide (CsI) molecule have been calculated using the internally contracted multireference configuration interaction calculation with single and double excitation method with the relativistic pseudopotentials. PECs for seven Λ-S states, X 1Σ+, 2 1Σ+, 3Σ+, 1Π, and 3Π are first calculated and then those for 13 Ω states are obtained by diagonalizing the matrix of the electronic Hamiltonian H⁁el plus the effective one-electron spin-orbit (SO) Hamiltonian H⁁SO. Spectroscopic constants for the calculated ground X 0+-state PEC with the Davidson correction are found to agree well with the experiment. Transition dipole moments (TDMs) between X 0+ and the other Ω states are also obtained and the TDM between X 0+ and A 0+ is predicted to be the largest and that between X 0+ and B 0+ is the second largest around the equilibrium internuclear distance. The TDMs between X 0+ and the Ω=1 states are estimated to be nonzero, but they are notably small as compared with those between the 0+ states. Finally, vibrational levels of the X 0+ PEC for the two isotopic analogs, 133CsI and 135CsI, are numerically obtained to investigate the isotope effect on the vibrational-level shift. It has been found that the maximized available isotope shift is ∼30 cm-1 around v=136. [ABSTRACT FROM AUTHOR]

Exclusively selective OD bond dissociation of HOD has been demonstrated by the ultraviolet photodissociation at 243.1 nm through the fourth overtone state of the OD stretching mode (5νOD). Branching ratio between the OH and OD bond dissociation channels has been determined by detecting H and D atoms, utilizing a (2+1) resonance-enhanced multiphoton ionization (REMPI) process. The OD bond dissociation has been solely observed with the branching ratio [uppercase_phi_synonym](D+OH)/[uppercase_phi_synonym](H+OD)>12, which has been determined by the detection limit for the H atom. Time-dependent wave-packet calculations reveal two important features for the highly selective OD bond dissociation: (1) strong local-mode character of the 5νOD state and (2) limitation of the total excitation energy lower than the saddle point between the OH and OD dissociation channels in the à state. Additionally, the recoil velocity and angular distribution of the nascent D atom are roughly evaluated by analyzing the Doppler-resolved REMPI spectrum. Based on these results, the dynamics of the selective OD dissociation has been discussed in detail. [ABSTRACT FROM AUTHOR]

The selective assembly of carboxyphenyl substituted porphyrins on the Au (111) surface has been studied using scanning tunneling microscopy. We find that conformational isomers of the porphyrins are induced upon adsorption and are selectively assembled into hydrogen-bonded supramolecular clusters or wires on the surface. The conformation selective assembly is attributed to the coplanar intermolecular interactions between hydrogen-bonded carboxyphenyl groups.© 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Optimal laser control for ultrafast selection of closely lying excited states whose energy separation is smaller than the laser bandwidth is reported on the two-photon transition of atomic cesium; Cs (6S→7Dj, J=5/2 and 3/2). Selective excitation was carried out by pulse shaping of ultrashort laser pulses which were adaptively modulated in a closed-loop learning system handling eight parameters representing the electric field. Two-color fluorescence from the respective excited states was monitored to measure the selectivity. The fitness used in the learning algorithm was evaluated from the ratio of the fluorescence yields. After fifty generations, a pair of nearly transform-limited pulses were obtained as an optimal pulse shape, proving the effectiveness of the "Ramsey fringes" mechanism. The contrast of the selection ratio was improved by ∼30% from the simple "Ramsey fringes" experiment. [ABSTRACT FROM AUTHOR]

Ultraviolet photodissociation of NHD[sub 2] excited to the fourth overtone state of the NH stretching mode (5ν[sub NH]) and NH[sub 2]D excited to that of the ND stretching mode (5ν[sub ND]) has been investigated by using a crossed laser and molecular beams method. Branching ratio between the NH and ND bond dissociations has been determined by utilizing a (2+1) resonance enhanced multiphoton ionization scheme of H and D atoms. For the photolysis of NHD[sub 2] in the 5ν[sub NH] state, the NH dissociation cross section is 5.1±1.4 times as large as the ND dissociation cross section per bond. On the other hand, for the photolysis of NH[sub 2]D in the 5ν[sub ND] state, the ratio of the NH dissociation cross section per bond to the ND dissociation cross section decreases to 0.68±0.16. In comparison with the branching ratios for the photolysis of vibrationally unexcited NH[sub 2]D and NHD[sub 2] [Koda and Back, Can. J. Chem. 55, 1380 (1977)], the present results indicate that the excitation of the NH stretching mode enhances the NH dissociation with ca. two times larger NH/ND branching ratio, whereas the excitation of the ND stretching mode results in the preferential ND dissociation with ca. 3–4 times larger ND/NH branching ratio than that for the vibrational ground states. The mechanism of the bond-selective enhancement has been discussed in terms of the energetics and dynamics of wave packet. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ultraviolet photolysis of highly vibrationally excited NH[sub 3](&Xtilde;[sup 1]A[sup ', sub 1]) in the 5 ν[sub N-H] band has been studied using a crossed laser and molecular beams method. Relative cross sections of N-H bond dissociation via the à ← &Xtilde; transition have been determined by the measurement of the action spectrum, utilizing a (2 + 1) resonance enhanced multiphoton ionization scheme of product H atoms. The obtained cross section for the photolysis of the 4 ν[sub 1] + ν[sub 3] state (4 quanta in the symmetric stretching and 1 quantum in the antisymmetric stretching) was 1.23±0.06 times as large as that of the 5 ν[sub 1] state. To interpret the ratio of the obtained cross sections, we have evaluated the FranckCondon factors for these vibrational states, by utilizing time-dependent wave-packet calculations on the potential energy surfaces constructed by an ab initio molecular orbital procedure. [ABSTRACT FROM AUTHOR]

Self-assembly of tetracene on an anisotropic surface of Ag(110) has been investigated using scanning tunneling microscopy and low-energy electron diffraction. We observe multistage structural transformations of the self-assembled tetracene on Ag(110) as a function of molecular coverages, which are accompanied by the changes in molecular orientations. They are analyzed by a balance between multiple molecule-molecule and anisotropic substrate-molecule interactions. [ABSTRACT FROM AUTHOR]

By tuning the structural phase transition in Zn2–xMgxP2O7, large negative thermal expansion (NTE) was achieved at room temperature. An earlier report described that Zn2P2O7 undergoes a structural phase transition at 405 K, accompanied by volume contraction of 1.8% on heating. Results showed that as Mg doping proceeds, the transition temperature decreases. Also, the volume change becomes gradual with respect to temperature. Particularly, Zn1.6Mg0.4P2O7 has a large negative coefficient of linear thermal expansion αL of −60 ppm/K at 280–350 K. Structural analysis using synchrotron radiation revealed that this dilatometric NTE is almost identical to that of crystallographic unit cells, indicating less dominant structural effects on NTE. We also verified thermal expansion compensation capabilities of powdered Zn1.6Mg0.4P2O7 by evaluating the thermal expansion of the epoxy resin matrix composites. The present phosphates are promising for use as practical thermal expansion compensators because they are free of toxic or expensive elements and can be fabricated in air using the simple solid-state reaction method. [ABSTRACT FROM AUTHOR]

Discovery of giant negative thermal expansion (NTE) of Ti2O3 is reported herein. Ti2O3 undergoes a phase transition from a low-temperature (low-T) insulating state to a high-T metallic state gradually at temperatures of 400–600 K, accompanied by highly anisotropic thermal deformation of the crystallographic unit cell. This anisotropic deformation induces large bulk NTE in the sintered body, although the unit-cell volume estimated from diffraction experiments shows positive thermal expansion in this T range. Results of this study also demonstrate that partial replacement of Ti with Nb increases the total volume change related to bulk NTE and show that it lowers the operating-T range of NTE to include room temperature. The development of NTE materials particularly addressing such microstructural effects is effective and promising. [ABSTRACT FROM AUTHOR]

This study is aimed at predicting the characteristics of vibration and sound radiation of violins and understanding the relationships among the properties of its wood, vibration, and sound radiation. Numerical simulations of the vibration mode of a violin body are performed, and the sound radiated by it are analyzed using the finite element method. The geometry of a real violin is scanned using a micro-computed tomography scanner, and the orthotropic properties of spruce and maple, such as Young's modulus, rigidity modulus, and Poisson's ratio, are set as the parameters of the numerical simulation. The main vibration modes, such as A0 and center bout rotation, and the acoustic pressure level around the violin body are calculated. This paper describes the influence of the density and longitudinal stiffness on the eigenfrequencies and sound radiation. [ABSTRACT FROM AUTHOR]

The elastic properties of glasses from different metallic systems were studied in the light of the atomic packing density and bonding character. We found that the electronegativity mismatch (Δe-) between the host- and the major solute-elements provides a plausible explanation to the large variation observed for Poisson's ratio (ν) among metallic glasses (MGs) (from 0.28 for Fe-based to 0.43 for Pd-based MGs), notwithstanding a similar atomic packing efficiency (Cg). Besides, it is found that ductile MGs correspond to Δe- smaller than 0.5 and to a relatively steep atomic potential well. Ductility is, thus, favored in MGs exhibiting a weak bond directionality on average and opposing a strong resistance to volume change. [ABSTRACT FROM AUTHOR]

The sensor system utilizing a surface plasmon resonance (SPR) with nanoparticles and nanostructures measures a peak wavelength shift. In order to enhance the measurement accuracy, it is important to acquire the higher and sharper peak wavelength so as to identify accurately the position of the peak wavelength. We developed an enhanced SPR sensor substrate by investigating the configuration of a periodic nanohole array. We simulated the effects of the configuration parameters. The simulation results revealed that the proposed sensor substrate achieved the higher and sharper peak wavelength by strengthening the SPR intensity as the number of holes per unit structure was increased from one to three, and with allocation of the unit structure in a triangular lattice so as to have one rotational symmetry. We also verified our simulation results experimentally by fabricating nanohole array sensor substrates. [ABSTRACT FROM AUTHOR]

Vitreous silica (v-SiO2) shows anomalous temperature dependence of velocity, including positive temperature coefficient of velocity (TCV) and velocity minimum around 70 K. The former characteristic allows its application in acoustic-resonator devices as a temperature compensating material. In this paper, we study the temperature dependence of velocity of fluorine-doped v-SiO2 (v-SiO2-xFx) thin films using picosecond ultrasonic spectroscopy. To correct the temperature increase caused by irradiation with light pulses, we calculated the steady temperature increase in the measuring volume with a finite volume method, considering the temperature dependence of thermal conductivity, and find that temperature in the measurement region remains high even when the back surface is cryogenically cooled. Using the corrected temperature, we determine TCV of v-SiO2-xFx thin films for 0 < x < 0:264, which increases as x increases and is smaller than reported bulk values by a factor of 0:5 - 0:7. The velocity minimum is absent for the film with x = 0, but it is clearly observed at 70 K for the film with the highest fluorine concentration of x = 0.264. These temperature behaviors are attributed to the change in the Si-O-Si bond angle caused by the fluorine doping. [ABSTRACT FROM AUTHOR]

The adsorption and self-assembled structures of a-sexithiophene (α-6T) have been investigated on a Si(111)-Ag surface using scanning tunneling microscopy (STM), low-energy electron diffraction, and density functional theory calculations. The adsorbed α-6T molecules are arranged into unidirectional molecular rows with a side-by-side orientation. The molecular rows reveal three kinds of appearances in the filled-state STM images, which reflect the distinct adsorption sites. From tunneling spectroscopy, we find that the filled-state STM images of &3945;-6T should be influenced by the surface states of Si(111)-Ag. At one monolayer coverage, sequentially ordering of the triple molecular rows results in the close-packed arrangement of the α-6T overlayer. [ABSTRACT FROM AUTHOR]

Muons, as a bulk probe of materials, have been used to study the depth profile of charge carrier kinetics in Si wafers by scanning the muon implantation depth. The photoexcited muon spin spectroscopy technique can optically generate excess carriers in semiconductor wafers, while muons can measure the excess carrier density. As a result, carrier recombination lifetime spectra can be obtained. The depth-dependent lifetime spectra enable us to accurately measure the bulk carrier lifetime and surface recombination velocity by fitting the spectra to a simple one-dimensional diffusion model. Unlike other traditional lifetime spectroscopy techniques, the bulk and surface recombination properties can be readily de-convoluted in this method. Here, we have applied the technique to study silicon wafers both with and without passivation treatment and have demonstrated that the model can correctly describe the carrier kinetics in these two cases. [ABSTRACT FROM AUTHOR]