Table of contents

In this paper, an investigation of a vinylidene fluoride–trifluoroethylene (VDF/TrFE) copolymer film for use in a nonpolarized energy harvester is presented. The Fourier transform infrared spectroscopy and X-ray diffraction analysis of a nonpolarized VDF/TrFE copolymer film indicate that polymer crystallinity depends on film thickness. Furthermore, the growth of the polar structure (β phase) is observed upon the reduction in the thickness. However, power generation does not exhibit a linear behavior because the generation capacity increases with the thickness. These results indicate that the film thickness for a nonpolarized harvester must be optimized to obtain the maximum output.

We investigated perpendicular exchange bias switching by a magnetoelectric field cooling process in a Pt-spacer-inserted Cr₂O₃/Co exchange-coupled system exhibiting small Cr₂O₃ magnetization. Although higher magnetoelectric switching energies with decreasing Cr₂O₃ thickness due to the exchange bias were reported in Cr₂O₃/Co all-thin-film systems, in this study, we demonstrated low-energy switching in a magnetoelectric field cool process regardless of the exchange-bias magnitude; we balanced the exchange-bias energy with the Zeeman energy associated with finite magnetization in Cr₂O₃. We proposed a guideline for realizing low-energy switching in thin Cr₂O₃ samples.

Coaxial random-access reading in multilayered optical data storage using a pair of counter-propagating pulse-shaped spatial solitons was experimentally investigated. Counter-propagating second-harmonic spatial solitons, which are formed by focusing titanium sapphire pulsed lasers, induced nonlinear collision and determined the depth readout address in a strontium barium niobate crystal. The nonlinear interaction between the collision and the locally-reversed crystal domains, which represents single-bit data, changed the spectrum and intensity of the transmitted second-harmonic beam. Coaxial random-access reading associated with the spatial soliton of the multilayered bit datum was demonstrated by scanning collision points along the direction of the depth.

We performed a thermodynamic analysis of GaN metalorganic vapor phase epitaxy considering the (0001) and $(000\bar{1})$ surface states. Surface reconstruction, which depends on growth conditions such as temperature and partial pressure, affects growth processes. To discuss the effects of surface states on growth processes, we investigated the driving force of precursor deposition to form the surface phase defined stoichiometrically. In both N₂ and H₂ carrier gas cases, we showed surface phase diagrams, calculated driving forces, and discussed the difference in growth orientation.

We attempted the quantification of carbon concentration in Czochralski-grown Si crystals for solar cells by luminescence activation in the concentration range lower than the detection limit of IR absorption spectroscopy. A positive correlation was found between the relative intensity of the C-line and the substitutional carbon (C_s) concentration determined by IR absorption in the low 10¹⁵ cm⁻³ range. The detection limit was estimated to be approximately 5 × 10¹² cm⁻³. We measured and compared the C_s concentrations in the wafers sliced from ingots grown under different conditions. The variations in C_s concentrations in the respective ingots were consistent with the segregation effect.

Phosphorus or aluminum ions were directly implanted into semi-insulating 4H-SiC substrates with no epitaxial layers to form n- or p-type layers, respectively, with doping densities in the range from 10¹⁷ to 10¹⁹ cm⁻³. The electrical properties of these implanted layers annealed at 1650 °C were characterized by Hall effect measurements in the temperature range of 160–900 K. The electrical activation ratios of implanted dopants were 88–98%. The density of compensating defects was higher in Al⁺-implanted layers than in P⁺-implanted ones. The mobilities of the implanted layers were mostly comparable to those of epitaxial layers in the doping range investigated.

Recently, Kosugi et al. have reported that the inclination growth of epilayers on a mesa top occurs when the mesa direction misaligns from the off-direction of a 4H-SiC wafer, i.e., the $[11\bar{2}0]$ direction [Jpn. J. Appl. Phys. 56, 04CR05 (2017)]. The cause of the inclination growth has been theoretically investigated. It was found that the inclination is attributable to the step-flow growth, and a formula was derived from the geometrical relationship between the progress direction of steps and the mesa direction. The calculated curve agreed well with the experimental results. The formula suggests that the inclination angle increases steeply with decreasing off-angle.

To analyze the early stage of oxygen precipitation in n-type multicrytalline Si, the spectral change of photoluminescence (PL) induced by thermal treatment at 450–650 °C was investigated in relation to the changes in excess donor and interstitial oxygen concentrations. We observed the characteristic PL bands in the near-band-edge region and sharp lines in the deep-level region in correspondence with the generation of thermal donors and new donors. The observed PL spectral variation is essentially the same as that in Czochralski-grown Si annealed at 450–650 °C.

The thermoelectric effects of an amorphous Ga–Sn–O (a-GTO) thin film have been evaluated as a physical parameter of a novel oxide semiconductor. Currently, a-GTO thin films are greatly desired not only because they do not contain rare metals and are therefore free from problems on the exhaustion of resources and the increase in cost but also because their initial characteristics and performance stabilities are excellent when they are used in thin-film transistors. In this study, an a-GTO thin film was deposited on a quartz substrate by RF magnetron sputtering and postannealing was performed in air at 350 °C for 1 h using an annealing furnace. The Seebeck coefficient and electrical conductivity of the a-GTO thin film were −137 µV/K and 31.8 S/cm at room temperature, and −183 µV/K and 43.8 S/cm at 397 K, respectively, and as a result, the power factor was 1.47 µW/(cm·K²) at 397 K; these values were roughly as high as those of amorphous In–Ga–Zn–O (a-IGZO) thin films. Therefore, a-GTO thin films will be a candidate material for thermoelectric devices fabricated in a large area at a low cost by controlling the carrier mobility, carrier density, device structures, and so forth.

Thin-film negative-temperature-coefficient (NTC) silicon (Si) thermistors using laser-sintering of solution-processed Si-nanoparticles (SiNP) thin film are proposed. The SiNP films are spin-coated on glass and plastic substrates and sintered by laser irradiation to form a continuous Si layer. A temperature increase of 150 °C is found to result in a decrease in the resistance of the laser-sintered Si layer by approximately three orders of magnitude. The flexibility and high-speed temperature change response of thermistors on plastic substrates is demonstrated successfully.

(Bi_1−xSb_x)₂Se₃ thin films were prepared by molecular beam epitaxy (MBE). The existence of strong and robust topological surface states was demonstrated in the (Bi_1−xSb_x)₂Se₃ ternary system by angle-resolved photoemission spectroscopy (ARPES). The sheet carrier density n_2D was found to be decreased by 75% by doping Sb into Bi₂Se₃, compared with that in the case of undoped Bi₂Se₃. The enhancement of the surface state transport due to Sb doping was also revealed via the high-field Hall effect and weak antilocalization measurement. Our results reveal the potential of this system for the study of tunable topological-insulator based device physics.

We fabricated self-organized FePd multilayer films with specific nanostructures by using Au/Fe bilayer films as a template. Au/Fe bilayer films were prepared as a template layer by forming a self-organized nanostructure through the agglomeration phenomenon. Using this Au/Fe bilayer as a template, FePd multilayers were deposited. The surface morphologies of FePd multilayer closely resembled the self-organized Au/Fe bilayer. As a result, we successfully manufactured self-organized FePd nanodots, with a shape closely resembling that of the agglomerated Au/Fe bilayer. In addition, it is confirmed that the agglomerated FePd nanodots were formed in the L1₀ phase by annealing at 350 °C.

In this study, the latest published first-principles Chachiyo correlation functional has been implemented to obtain the phonon dispersion relation of silicon. The calculations are based on local-density approximation (LDA) within the plane-wave pseudopotential method. We obtain good agreement and sufficient accuracy results compared with the experimental data and phonon dispersion curves from the typical Perdew–Zunger functional. As such, the Chachiyo formula used in phonon dispersion calculation has proven to be valid and therefore extends the use of LDA from relying on fitting to the first-principles correlation functional that provides a higher predictive power.

Polarization dynamics in a 1550 nm vertical-cavity surface-emitting laser (1550 nm VCSEL) under parallel optical injection (POI) is investigated experimentally, and we experimentally observe the state bistability (SB) between pure- and mixed-mode states by scanning the injection power along different routes. Such a SB occurs only when the frequency of injection light is lower than that of the excited mode of a free-running 1550 nm VCSEL. Moreover, the effect of frequency detuning on the hysteresis loop width is analyzed.

The valence band offset at both SiO₂/β-Ga₂O₃ and HfSiO₄/β-Ga₂O₃ heterointerfaces was measured using X-ray photoelectron spectroscopy. Both dielectrics were deposited by atomic layer deposition (ALD) onto single-crystal β-Ga₂O₃. The bandgaps of the materials were determined by reflection electron energy loss spectroscopy as 4.6 eV for Ga₂O₃, 8.7 eV for Al₂O₃ and 7.0 eV for HfSiO₄. The valence band offset was determined to be 1.23 ± 0.20 eV (straddling gap, type I alignment) for ALD SiO₂ on β-Ga₂O₃ and 0.02 ± 0.003 eV (also type I alignment) for HfSiO₄. The respective conduction band offsets were 2.87 ± 0.70 eV for ALD SiO₂ and 2.38 ± 0.50 eV for HfSiO₄, respectively.

This paper reports on the development of a novel buffer layer structure, (100)SrRuO₃/(100)LaNiO₃/(111)Pt/(111)CeO₂, for the epitaxial growth of a (100)/(001)-oriented Pb(Zr,Ti)O₃ (PZT)-based thin film on a (111)Si wafer. (111)Pt and (111)CeO₂ were epitaxially grown on (111)Si straightforwardly. Then, the crystal orientation was forcibly changed from (111) to (100) at the LaNiO₃ layer owing to its strong (100)-self-orientation property, which enabled the cube-on-cube epitaxial growth of the subsequent (100)SrRuO₃ layer and preferentially (100)/(001)-oriented PZT-based thin film. The PZT-based epitaxial thin films were comprehensively characterized in terms of the crystallinity, in-plane epitaxial relationships, piezoelectricity, and so forth. This buffer layer structure for the epitaxial growth of PZT can be applied to piezoelectric micro-electro-mechanical systems (MEMS) vibrating ring gyroscopes.

We demonstrate the homogeneous photoalignment of low-molecular-weight liquid crystals (LC) using nematic LCs (NLCs) doped with photoalignable low-molecular-weight LC materials, achieved in the absence of substrate surface treatment; in-plane switching (IPS) is also shown using an IPS-mode LC cell. The exposure of the LC cells to linearly polarized (LP) light in the isotropic temperature range of the NLC composites generates homogenous NLC orientation, but exposure at room temperature results in the random orientation of the NLCs. Small amounts of photoalignable LC materials on the substrates, which have undergone axis-selective photoreaction, are found to control the NLC alignment.

A cavity-resonator-integrated guided-mode resonance filter (CRIGF) consisting of waveguide gratings on a transparent substrate can provide not only a narrowband reflection spectrum but also a steep reflection-phase spectrum. Reflection-phase spectra of CRIGFs were discussed in detail theoretically with an analytical expression. It was found that CRIGFs can be categorized into two types showing a phase variation of 2π rad, namely, reflection-phase rotation, or no rotation. On the other hand, the same structure on a high-reflection mirror, instead of the transparent substrate, normally shows the rotation. The two types of CRIGFs were designed and fabricated with different core thicknesses so that theoretically predicted reflection-phase characteristics with and without rotation could be demonstrated experimentally.

Periodic microswelling structures were photochemically induced on a silicone rubber surface using a 193 nm ArF excimer laser. Microspheres made of silica glass (SiO₂) of 2.5 µm diameter were aligned on the silicone rubber surface during laser irradiation; the laser beam was focused on the silicone surface underneath each microsphere. The height and diameter of the formed microswelling structures were found to be controllable by changing the Ar gas flow rate, single-pulse laser fluence, and laser irradiation time. The chemical bonding of the laser-irradiated sample did not change and thus remained to be a silicone, as analyzed by X-ray photoelectron spectroscopy. As a result, microswelling structures of approximately 1.3 µm height and 1.3 µm diameter were successfully obtained. The contact angles of water on the microstructured silicone were measured to be 150° and larger, clearly indicating superhydrophobicity. The mechanism by which the microswellings form their shape was discussed on the basis of the changes in the focal point and spot size during laser irradiation through the SiO₂ microsphere.

Terahertz absorption spectra and X-ray diffraction patterns were measured for amorphous poly(ethylene naphthalate) (PEN) while the sample temperature was elevated from 25 to 230 °C then lowered back to 25 °C. Before the elevation of the temperature, PEN exhibited broad absorption with a maximum at around 2.6 THz. This absorption seems to originate from amorphous regions. As the sample temperature increases, PEN becomes crystallized in the form of α crystal. With this change in crystallinity, the 2.6 THz absorption becomes smaller, while another absorption peak at 2.05 THz, originating from crystalline regions, becomes larger. Furthermore, in the cooling process to 25 °C, the 2.05 THz absorption shifts to 2.15 THz and the lattice constants associated with this absorption become smaller. Therefore, intermolecular vibrations closely related to the crystal growth in PEN at high temperatures seem to be responsible for the THz absorption.

Single-end-access real-time fiber-optic distributed strain sensing has recently been demonstrated using an ultrahigh-speed configuration of Brillouin optical correlation-domain reflectometry (BOCDR). Its extremely high sampling rate was, however, achieved at the cost of a limited strain dynamic range (<0.2%). Here, by employing a noise-floor compensation technique, we develop a new cost-effective higher-speed configuration of BOCDR with a wide strain dynamic range (up to 2.0%; evaluated by static strain measurement). This value is larger than that of any other BOCDR configuration. Using this configuration, we demonstrate some fundamental distributed strain measurements and breakage detection.

We demonstrate 43% slope efficiency for generation of ∼3200 nm light, a wavelength considered to be ideal for laser induced ultrasound generation in carbon fiber reinforced plastic. High slope efficiency was obtained by optimizing crystal lengths, cavity length and mirror reflectivity using a two crystal optical parametric oscillator+difference frequency mixing (OPO+DFM) nonlinear wavelength conversion scheme. Mid-IR output >12 mJ was obtained from a 1064 nm Nd:YAG pump laser with 12 ns pulse width (FWHM) and containing pulse energy of 43 mJ. A compact, single temperature crystal oven is described along with some suggestions for improving the slope efficiency.

Eddy current testing plays a significant role in detecting surface defects in a nondestructive testing field. The magnetoresistive sensors based on magnetic tunnel junction devices attracted considerable attention for their use in eddy current testing owing to their high sensitivity and capability of being miniaturized. We investigated the detection of surface cracks in eddy current testing using a single magnetic tunnel junction. A perpendicular component with a secondary magnetic field from an eddy current was measured by using an optimized rectangular magnetic tunnel junction device with an aspect ratio of 4 (20 × 80 µm²). Furthermore, according to the extracted ΔX and ΔV from the sensor output signal, surface cracks with various widths (0.1, 0.3, and 0.5 mm) and depths (0.5, 1.0, 1.5, and 3.0 mm) in aluminum specimens were successfully estimated using the magnetic tunnel junction device in eddy current testing when an excitation frequency of 1000 Hz was used.

We prepared SmBa₂Cu₃O_y (SmBCO) films including Ba₂SmNbO₆ (BSNO) by Nd:YAG pulsed laser deposition (PLD) on LaAlO₃ single-crystalline substrates. The BSNO formed many nanorods with a large diameter of 35 nm, which is the largest nanorod diameter in REBa₂Cu₃O_y films, and their in-plane distribution was random. The matching field estimated from the number density of 202 µm⁻² was 0.42 T. We measured J_c–B curves at various measurement temperatures and these J_c–B curves had a J_c peak at approximately 0.37 T. Interestingly, the irreversibility line showed a "reverse S" shape and an anomalous curve was observed at approximately 0.37 T near T_c. To the best of our knowledge, this is the first time that these distinctive features were found in this sample. We concluded that these peculiar behaviors originated from the large-diameter, straight, and threading BSNO nanorods.

Keeping two-dimensional lattice structures formed by nanoparticles covered with DNA in mind, we carry out Brownian dynamics simulations to study the effect of interaction strength on a two-dimensional lattice structure formed in a binary system. In our previous study [H. Katsuno, Y. Maegawa, and M. Sato, J. Phys. Soc. Jpn. 85, 074605 (2016)], we carried out simulations using the Lennard-Jones potential, in which the difference in interaction length was taken into account. When the interaction length between different species, σ', is smaller than that between the same species, σ, various lattice structures were formed with changing the ratio σ'/σ. In this paper, taking the difference in the interaction strength into account, we study the effect of the difference in interaction strength on the two-dimensional lattice structure.

Using the density functional theory combined with an effective screening medium method, we studied the electronic structure of N-doped graphene under an external electric field. The electronic states near the Fermi level depend on the carrier concentration reflecting their wave function distribution. The electronic states associated with the dangling bond shift upward with increasing electron concentration, following the upward shift of the Fermi level. The electronic states associated with nonbonding π states almost retain their energy upon hole/electron doping by the external electric field.

A method of graphene synthesis at a desired position on polymer substrates by laser irradiation has been studied. Polyethylene naphthalate films were used as substrates, on which a thin Ni film was deposited as a catalyst layer. The irradiation of a focused laser made a hole in the Ni film and the graphene was synthesized in the hole by the surface decomposition of the polymer. The laser power dependence of the hole radius was successfully explained by a dynamical model of thermodiffusion. The quality of the laser-synthesized graphene was studied by micro-Raman scattering. Typical ambipolar characteristics of the synthesized graphene were observed in field-effect transistors. We studied the application of the laser-synthesized graphene to strain sensors using the sensitivity of the electric conductance to the strain induced by the bending deformation of substrates.

In this study, we fabricated a bicontinuous carbon structure (BCS) with high porosity and a loosely connected framework structure. The role of the BCS is to support a concrete supercapacitor active electrode structure. Poly(acrylonitrile) was used as a precursor for the BCS material, which was a porous polymer monolith carbonized by heat treatment (at 1100 °C). The BCS was prepared by mixing with an active material, graphene or an activated carbon. The mixed materials were used as an electrode material in a supercapacitor. The BCS13 + AC sample (∼107.5 F/g) showed a higher specific capacitance than the commercial activated carbon cell (∼76 F/g). The BCS13 + graphene sample (∼75 F/g) also exhibited a higher specific capacitance than the graphene cell (∼49 F/g). This BCS monolith had many macro- and micropores in its structure, enabling fast electrolyte ion movement and excellent electrochemical performance with a low equivalent series resistance (ESR).

We theoretically study the energetics of the Rashba spin–orbit interaction (SOI) in the two-dimensional (2D) system by comparing the numerical calculation of the exact diagonalization with the analytical calculation based on the perturbation approach and also with the unitary transformed effective Hamiltonian method. The Rashba SOI consists of ls-like and Zeeman-like components, and the out-of-plane application of the external electric field generates the ls-like component, whereas the in-plane application generates the Zeeman-like part. Accordingly, we can separate them by tuning the direction of the applied external electric field. Interestingly, these features do not change provided the confinement is isotropic. The unitary transformation of the total Hamiltonian and the Liouvillian operator expansion technique demonstrate that the Rashba SOI energetics is represented fully in terms of the six orders, in the Rashba coupling. Consequently, the second-order perturbation approach satisfactorily describes the inherent features. When anisotropy is introduced in the confinement, the angular momentum is no longer a good quantum number. The resulting energetics of the Rashba SOI is then unified into the isotropic ground-state type (l = 0).

We investigated the effects of grain boundary (GB) misorientation and the change in GB energy on the generation of dislocations during the directional growth of a crystalline silicon ingot. For this purpose, two ingots were grown using artificially designed seeds to introduce plural GBs with and without misorientation from an ideal coincident site lattice boundary. We revealed that dislocations are frequently generated from Σ3 GB with misorientation. On the other hand, dislocations are hardly observed around naturally formed perfect Σ3 GBs. In addition, we found that Σ5 and Σ25 GBs with higher GB energies are not sensitive to misorientation, and few dislocations are found around Σ25 GBs.

The growth mechanism of multicrystalline silicon ingots in directional solidification using single-layer silicon beads (SLSB) coated with Si₃N₄ was investigated. The grains in the SLSB-seeded ingot were smaller than those in a nonseeded ingot, but still larger than those in a polycrystalline Si (poly-Si)-seeded ingot. The dislocation density in the SLSB-seeded ingot was lower than that in the nonseeded ingot, but higher than that in the poly-Si-seeded ingot. The minority carrier lifetime mapping showed that a higher production yield was obtained in the SLSB-seeded ingot than in the poly-Si-seeded ingot. Grain refinement by the SLSB-seeding method was associated with the increase in nucleation rate. The increase in the surface area of the bottom of the crucible cannot quantitatively explain the grain refinement. Therefore, it is considered that SLSB may supply many nucleation sites because of their uneven structure.

We report on a method for composition and doping control for metalorganic chemical vapor deposition of a double heterojunction bipolar transistor (DHBT) with a hybrid base structure consisting of a compositionally graded InGaAsSb for boosting an average electron velocity and a heavily doped thin GaAsSb for lowering the base contact resistivity. The GaAsSb contact layer can be formed by simply turning off the supply of In precursor tetramethylindium (TMIn) after the growth of the composition and doping graded InGaAsSb base. Consequently, the solid composition and hole concentration of hybrid base can be properly controlled by just modulating the supply of only TMIn and carbon tetrabromide. Secondary ion mass spectroscopy for the DHBT wafer reveals that the contents of In, Ga, and C inside the base are actually modulated from the collector side to the emitter side as expected. Transmission-line-model measurements were performed for the compositionally graded-InGaAsSb/GaAsSb hybrid base. The contact resistivity is estimated to be 5.3 Ω µm², which is lower than half the value of a compositionally graded InGaAsSb base without the GaAsSb contact layer. The results indicate that the compositionally-graded-InGaAsSb/GaAsSb-contact hybrid base structure grown by this simple method is very advantageous for obtaining DHBTs with a very high maximum oscillation frequency.

We have investigated the electronic structure and properties of Na_0.28PtSi, which is a Pt-based intermetallic compound with no reported physical properties. Na_0.28PtSi powder with an average grain size of 15 µm was demonstrated to be stable in a strongly acidic aqueous solution. The ab initio calculations revealed that there is a band crossing the Fermi level and that the density of states (DOS) under the Fermi level mainly consists of d orbitals of Pt atoms. Here, we used the model of Na_0.25PtSi with an approximately ordered structure (space group I4, full Na site occupation), which was set instead of the reported statistically disordered structure of Na_0.28PtSi (I4/mcm, Na site occupancy: 0.258). The calculated electronic structure corresponded to the measured metallic properties of the Na_0.28PtSi sintered body: i.e., the electrical resistivity of Na_0.28PtSi was increased from 1.77 × 10⁻⁸ Ω m at 30 K to 2.67 × 10⁻⁷ Ω m at 300 K and the Seebeck coefficient was 0.11 µV K⁻¹ at 300 K.

Surface morphology is one of the main factor affecting the secondary electron (SE) emission from a rough metal surface. To overcome the limitation of only using the roughness to reveal the SE emission properties of a rough surface morphology, the fluctuation correlation length, which represents the spatial frequency of surface fluctuation, is thus introduced. In addition, the effects of the rough surface morphology on SE emission properties from the metal surface, which considers both the surface roughness and the fluctuation correlation length, are examined in this work. On the basis of the mechanism of electron interaction with morphology including the shading, multigeneration, and oblique effects, the SE emission properties versus the rough surface morphology, primary electron energy, and incident angle can be reasonably explained. The results further reveal the effect of surface morphology on SE emission, which gives a comprehensive insight into the control of SE emission properties using surface morphology.

For the synthesis of magnetic nanoparticles (NPs), we used plasma-assisted electrolysis in which atmospheric-pressure DC glow discharge using a liquid electrode is combined with electrolysis. The solution surface is exposed to positive ions or electrons in plasma. To synthesize magnetic NPs, aqueous solutions of FeCl₂ or an iron electrode immersed in liquid was used to supply iron ions in the liquid. Magnetic NPs were synthesized at the plasma–liquid interface upon the electron irradiation of the liquid surface. In the case of using aqueous solutions of FeCl₂, the condition of magnetic NP synthesis depended on the gas species of plasma and the chemical agent in the liquid for controlling oxidization. The amount of magnetic NPs synthesized using plasma is not very large. On the other hand, in the case of using an iron electrode immersed in NaCl solution, magnetic NPs were synthesized without using FeCl₂ solutions. When plasma-assisted electrolysis was operated, the iron electrode eluted Fe cations, resulting in the formation of magnetic NPs at the plasma–liquid interface. Magnetic NP synthesis depended on the concentration of NaCl solution and discharge current. The magnetic NPs were identified to be magnetite. By using this method, more magnetite NPs were synthesized than in the case of plasma-assisted electrolysis with FeCl₂ aqueous solutions. The pH of the liquid used in plasma-assisted electrolysis was important for the synthesis of magnetite NPs.

For the etching of organic films in H₂/N₂ plasma, etched profiles are significantly determined by substrate temperature. Here, we control the substrate temperature variation within 3 °C during processing by modulating the plasma-discharge time. The evolution of the cross-sectional profile of line-and-space patterns was observed every 10 s. At 60 and 100 °C, sidewall etching was observed during overetching, but not at 20 °C. During the main etching, the sidewalls were protected by the adsorption of by-products at various temperatures. Moreover, we investigated the temperature dependence of protection layer formation by analyzing the surface components of the organic film. The CN layer formed by N radicals has a protective effect that depends on the components of the CN layer. It was found that the ratio of C–N sp³ to C–N sp² in the sidewall was highest at 100 °C. By evaluating the radical contribution to CN layer formation, C–N sp³ bonds were observed to be formed by ions and radiation-assisted reaction.

Line edge roughness (LER) is a significant concern for electron beam (EB) lithography used for the production of photomasks and nanoimprint molds owing to the trade-off relationships between resolution, LER, and sensitivity. In this study, the relationship between exposure pattern width and chemical gradient (an indicator of LER) was investigated, assuming the use of a chemically amplified resist consisting of a partially protected polymer, an acid generator, and a photodecomposable quencher. The formation of line-and-space patterns with 16 nm half-pitch was calculated on the basis of the sensitization and reaction mechanisms of chemically amplified EB resists. The effects of exposure pattern width on the chemical gradient were clarified in terms of sensitivity, the concentration of sensitizers, and the diffusion constant of photodecomposable quenchers. The exposure pattern width should be set by taking into account these factors to maximize the chemical gradient for the suppression of LER.

LiNbO₃ crystals are important for applications such as optical devices and surface acoustic wave filters. However, defects in such crystals can negatively affect device characteristics. Consequently, control of defects is important during device manufacturing. In this study, a new defect detection method using a cross Nicol optical system with a heating function and defect image enhancement is proposed. Experiments confirmed that defects detected by this method correspond to those imaged by X-ray topography. It was found that additional defects are formed by charge induced during heating.

To date, we have developed a temperature sensor based on multimodal interference in a polymer optical fiber (POF) with an extremely high sensitivity. Here, we experimentally evaluate the influence of annealing (heat treatment) of the POF on the temperature sensitivity at room temperature. We show that the temperature sensitivity is enhanced with increasing annealing temperature, and that, by annealing the POF at 90 °C, we can achieve a temperature sensitivity of +2.17 nm/°C, which is 2.9 times larger than that without annealing (+0.75 nm/°C).

The composition pulling effect in metalorganic vapor-phase InGaN epitaxy was theoretically investigated by thermodynamic analysis. The excess energies of biaxial-strained In_xGa_1−xN were numerically calculated using empirical interatomic potentials considering different situations: (i) coherent growth on GaN(0001), (ii) coherent growth on In_0.2Ga_0.8N(0001), and (iii) bulk growth. Using the excess energies, the excess chemical potentials of InN and GaN alloys were computed. Our results show that compressive strain suppresses In incorporation, whereas tensile strain promotes it. Moreover, assuming chemical equilibrium, the relationship between the solid composition and the growth conditions was predicted. The results successfully reproduced the typical composition pulling effect.

Epitaxial ε-Ga₂O₃ thin films with smooth surfaces were successfully grown on c-plane AlN templates by mist chemical vapor deposition. Using X-ray diffraction 2θ–ω and φ scans, the out-of-plane and in-plane epitaxial relationship was determined to be (0001) ε-Ga₂O₃$[10\bar{1}0]$ ∥ (0001)AlN$[10\bar{1}0]$. The gallium/oxygen ratio was controlled by varying the gallium precursor concentration in the solution. While scanning electron microscopy showed the presence of large grains on the surfaces of the films formed for low concentrations of oxygen species, no large grains were observed under stoichiometric conditions. Cathodoluminescence measurements showed a deep-level emission ranging from 1.55–3.7 eV; however, no band-edge emission was observed.