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In order to achieve a high-quality SiC crystal in solution growth, one of the most difficult issues is to grow a thick layer on Si face avoiding polytype transformation. In this case, two-dimensional nucleation, which leads to the polytype transformation, is frequently induced because a density of threading screw dislocations acting as a source of spiral step decreases and wide terraces form by step bunching as growth proceeds. Therefore, it is very difficult to stabilize the polytype of crystals grown with extremely low density of threading screw dislocations. In this study, we tried to overcome these problems by using specially designed seed crystal and optimizing growth temperature and temperature distribution. We successfully grew thick low-threading-dislocation density SiC crystal without polytype transformation under the condition of high growth temperature and homogeneous temperature distribution.

The relationship between surface morphology and spatial distribution of basal plane dislocations in 4H-SiC crystal grown by top-seeded solution growth on the C face was investigated by the differential interference microscopy as well as X-ray topography. Basal plane dislocations were generated at the boundaries of the domains with the different macrosteps advance directions. On the other hand, at the position where macrosteps advance to the same direction, BPDs were hardly observed. This results suggest that BPD density can be decreased by the suppression of the collision of macrosteps during the solution growth on the C face controlling the surface morphology.

Dendritic growth at the Li anode during charging is caused by a morphological inhomogeneity of Li electrodeposition. In this study, we investigate the dependence of the morphology of Li electrodeposited on a polycrystalline Cu current collector on the Cu grain orientation both experimentally and by numerical analysis. The experimental results show that the Li precipitates that form on Cu grains that have close to (111) orientations are the smallest and the most uniform in size. Such a morphology is expected to be effective for the suppression of dendrite growth. Numerical analysis indicates that the initial stage of electrodeposition plays an important role in determining morphological variation, and this is due to the crystal orientation dependence of the adatom concentration at equilibrium.

For solution growth of 4H-SiC with Si 0.6−x−y Cr 0.4 Al x Sn y solvents, the changes in surface morphology and polytype induced by the addition of Sn and Al to the Si 0.6 Cr 0.4 solvent were investigated. Growth with Si 0.6 Cr 0.4 solvents resulted in a rough surface covered with large macrosteps that were several micrometers high, and the polytype of the grown layer transformed to 6H and 15R-SiC. The surface roughening and polytype instability were suppressed when more than 2 at% Al was added to the SiCr 0.4 solvent. We also found that the combined addition of both 2–4 at% Sn and 0.5–1 at% Al resulted in smooth surface morphology. We discussed the modification of the surface morphology of 4H-SiC caused by the additives in terms of the wetting properties of the solvents. Based on the results of experiments and thermodynamic calculations, the addition of both Sn and Al increased the liquid/solid interfacial energy. Because the two-dimensional nucleation energy increases with the interfacial energy, we conclude that smooth step flow growth of 4H-SiC was achieved by lowering the frequency of two-dimensional nucleation on the growth surface.

The contrast features of synchrotron X-ray topographic images of screw-type basal plane dislocations (BPDs) in on-axis 4H-SiC wafers have been studied. Screw BPD images are categorized into two types: one exhibiting a white line bordered by black lines and the other a pure black line contrast. Similar images for off-axis specimens and the corresponding ray-tracing simulations demonstrate that these contrasts can be attributed to the depth of the screw BPDs below the crystal surface. The correlation of the contrast features between simulations and the screw BPD topography images can be used to estimate the depth.

Birefringence imaging is one of the powerful methods for non-destructive characterization of defects in the semiconductor crystals. However, due to the complicated and unclear contrasts of dislocations in the birefringence image, it was considered to be difficult to automatically detect the position of the dislocation contrasts by the conventional image processing. In the present study, we designed the automatic detection algorithm for the dislocation contrasts taking into account the characteristic feature of the dislocation contrasts, which were always pair of black and white contrasts. To detect the large change in the contrast level near the dislocation contrast, the automatic detection algorithm was constructed by using a variance filter. Finally, we succeeded in detecting the position of the dislocation contrasts with relatively high precision and sensitivity.

The conversion of threading screw dislocations (TSDs) to defects on the basal plane during SiC solution growth caused by macrostep advance is a key factor to improve crystal quality. We realized the TSD conversion in 4H-SiC C face solution growth by modification of the surface morphology including macrosteps by addition of 5 atom % Ti into pure Si solvent. Synchrotron X-ray topography revealed that the possibility of TSD conversion increased to about 10% with the addition of 5 atom % Ti. In addition, the TSD conversion ratio depends on the shape of the macrostep edge. The gentle slope hardly made TSD conversion. The elastic energy of dislocations in anisotropy crystals was postulated as an explanation for the influence of step shape on TSD conversion behavior.

Defects generated during 4H-SiC (0001) solution growth have been investigated by synchrotron X-ray topography and transmission electron microscopy (TEM). The defects unidentified before are recognized as V-shaped contrast features in the X-ray topographic images. The detailed analysis combining TEM results revealed that the newly generated defects are identified as a pair of dislocations on a basal plane with opposite Burgers vectors parallel to the [1120] direction. It is found that no defects in the substrate are directly associated with the formation of the V-shaped defects. Geometric analysis of the size and shape of the V-shaped defects indicates that they nucleate in pairs intermittently during the growth process. On the basis of the observed morphology of these defect configurations, a mechanism of two-dimensional nucleation during solution growth is postulated for the generation of the V-shaped defects.

We investigated the spatial distribution of carrier concentration in n-type 4H-SiC grown by the solution method from the peak frequency of the longitudinal optical phonon-plasmon coupled (LOPC) mode of the Raman spectra on the surface. The carrier concentration at the position of the smooth terrace was higher than the carrier concentration at the position where the macrosteps were formed. This indicates the nitrogen incorporation efficiently occurs on the smooth surface where the density of macrosteps is relatively low. The different incorporation of nitrogen depending on the surface morphology can be understood from the view point of the adsorption time of impurity on the terrace. The present result implies that the uniform surface morphology is necessary to achieve uniform doping concentration in SiC crystal.

We achieved a high growth rate in solution growth of AlN single crystal by suppressing unintentional precipitations near the surface of solvent and by increasing the equilibrium nitrogen concentration in the solvent. In order to suppress unintentional precipitations, we made the solvent supersaturated just above the surface of the substrate by optimizing the composition of the solvent and the temperature distribution based on thermodynamic numerical analysis. In particular, we focused on interactions between nitrogen or aluminum and solvent elements, leading to the increase of the equilibrium nitrogen concentration. We selected chromium and cobalt due to their high affinity with nitrogen or aluminum. Consequently, we successfuly achieved growth rate as high as 200 μm/h in maximum.

We demonstrate that a statistically-significant chiral bias in NaClO3 chiral crystallization can be provoked by inducing nucleation via the optical trapping of Ag nano-aggregates using a continuous wave visible circularly polarized laser (λ = 532 nm). The laser was focused at the interface between air and an unsaturated NaClO3 aqueous solution containing Ag nanoparticles. The “dominant” enantiomorph was switchable by changing the handedness of the incident circularly polarized laser, indicating that the chiral bias is enantioselective. Moreover, it has been found that the resulting crystal enantiomeric excess (CEE) reached approximately 25%. The CEE is much higher than the typical enantiomeric excess (EE) in the asymmetric photosynthesis of organic compounds ranging from 0.5 to 2%. The efficient induction of the nucleation and the large chiral bias imply the contribution of localized surface plasmon resonance of the Ag nanoaggregates to chiral nucleation. Our method has potential to offer the benefit for studies on the spatiotemporal nucleation control, optical resolution of chiral compounds and biohomochirality.

The strain field of the tilted threading dislocation (TD) in a hydride vapor-phase epitaxy-grown c-plane (0001) GaN single crystal is demonstrated using Raman spectroscopy. In the two-dimensional mapping image of the E2 H peak shift around TDs, high-contrast areas corresponding to pairs of high and low wavenumber regions of the peak shift are observed, and the edge component of the Burgers vector can be specified. Deformed contrast areas extending in the specified direction are also observed. This deformed contrast region indicates tilted dislocations since 2D mapping also detects strain deep below the surface due to the transmission of the laser beam. Simulation of the E2 H peak shift mapping around the TD, tilted at 0° and 60° in the 11 2 ¯ 0 direction and having a Burgers vector b = 1 / 3 11 2 ¯ 0 , is also performed. The simulation of the 60° tilted dislocation shows that the contrast extends in one direction. The line profiles of the E2 H peak shift by simulation are in agreement with the experimental results. We propose that the dislocation line tilt can be analyzed from the 2D Raman mapping images.

We developed an angle-resolved photoemission spectroscopy system for the analysis of conduction-band electrons. By forming a negative electron affinity surface on a semiconductor surface, electrons in conduction bands are emitted into a vacuum and measured by using an analyzer. This method enables us to determine the energy and momentum of the conduction electrons. Furthermore, it can be used to determine unoccupied conduction band structures. The main challenges of this method are that the energies of the emitted electrons are extremely low and the trajectories of the electrons change due to various influences. We overcame these problems by placing the shielding mesh close to the sample and parallel to the sample surface. The entire chambers, including the shielding mesh, were grounded, and a negative bias voltage was applied only to the sample. This configuration realizes the acceleration of electrons while preserving the momentum component parallel to the sample surface. Another problem is the establishment of a method for converting a detected angle into the corresponding wavevector. We focused on the emission angle of electrons emitted from a sample and their minimum energy and then established an analytical method for converting detected angles into corresponding wavevectors on the basis of the minimum energy.

Transition of zinc morphology and crystallographic orientations with increasing charge capacity is examined to identify the origin of non-uniform electrodeposition. Galvanostatic charge experiments for zinc are carried out for both polycrystalline and oriented zinc substrates to investigate the effects of electrodeposited zinc on electrodepositing zinc. The results show that the crystallographic orientations of the zinc substrates strongly affect the morphology of the electrodeposited zinc. Non-uniformity appears in the (0001)-oriented case prior to the polycrystalline, 10 1 ¯ 0 - and 2 1 ¯ 1 ¯ 0 -oriented cases. The (0001) plane initiates non-uniform zinc electrodeposition even in the polycrystalline case. It is attributed to the high density and low diffusivity of the ad-atom on the wide terrace structure. It is also indicated that porous structure appears from aggregated hexagonal hillocks with random orientations which initially are oriented hexagonal hillocks.

For the solution growth of 4H–SiC with Si 1− x Cr x solvents, the change in surface step structure by 4 at% Al addition to the solvent was investigated. Without Al addition, step bunching resulted in the formation of giant macrosteps with height greater than several micrometers, and trench-like surface defects formed with solvent inclusion. The edge of the giant macrosteps composing trench-like defects was faceted into low-index facet planes, ( 1 1 ¯ 0 m ) ( m =1–4). The formation of the trench-like surface defects is considered to originate from the self-pinning of macrosteps owing to the step-faceting phenomenon, which facilitates further development of macrosteps. On the other hand, the addition of Al to the solvents significantly improved the surface roughening, and suppressed the formation of the trench-like surface defects. In this case, smaller bunched steps with heights from several nanometers to about 10 nm formed on the terraces of the macrosteps, while regularly arranged trains of unit-cell-size steps formed on the terrace of macrosteps in growth without Al addition. The decrease in step stiffness might be a possible cause for the formation of the smaller bunched steps on the terrace in growth with Al addition.

We realized the growth of 3C-SiC crystal on sapphire by solution growth method. The carbon deposition on a sapphire substrate before growth is the key point for this technology. This carbon layer plays a role to protect the dissolution of sapphire by Si solvent. Single crystal of 3C-SiC was grown on the whole surface of the sapphire substrate. Surprisingly, the 3C-SiC layer did not directly grown on the sapphire substrate. The single crystal 3C-SiC layer formed by the reaction between the deposited carbon and the Si wafer that is a solvent material below the melting point of silicon during heating process before the growth. The 3C-SiC grew on the 3C-SiC layer. In this process, the deposited carbon play another important role.

The solution growth of SiC on an off-axis seed is effective on the reduction of threading dislocations. We proposed a novel method to grow a SiC crystal on an off-axis seed by top-seeded solution growth (TSSG). In our previous study, a unidirectional solution flow above a seed crystal is effective to suppress surface roughness in the growth on the off-axis seed. However, it is difficult to apply the unidirectional flow in an axisymmetric TSSG set-up. In this study, the unidirectional flow could be achieved by shifting the rotational axis away from the center of the seed crystal. As a result, the smooth surface was obtained in the wider area where the solution flow direction was opposite to the step-flow direction.

Surface morphology of the SiC crystal grown on the C face of the 4H-SiC seed crystal by TSSG method using pure Si, Si-1at%Ti-C, Si-5at%Ti-C and Si-20at%Ti-C solvents was investigated. The surface morphology of the crystal grown from pure Si solvent was smooth. By the addition of Ti to the solvent, the surface morphology became rougher. The RMS value is not proportional to the concentration of Ti. The formation of macrosteps with several micrometers was observed when the addition of Ti increased to 5at% indicating the possibility of the threading screw dislocation conversion on the C face of the 4H-SiC crystal.

Solution growth of SiC has attracted significant attention due to its potential for the production of high-quality SiC wafers. We have recently investigated the dislocation propagation behavior during SiC solution growth with the aim of reducing the dislocation density. Threading dislocations were found to be converted to defects on the basal planes during solution growth. Utilizing this dislocation conversion phenomenon, we have proposed a dislocation reduction process during solution growth and achieved high-quality 4H-SiC crystal growth. Here we confirm the potential of SiC solution growth for the production of high-quality SiC wafers.

We achieved the convex growth interface shape in top-seeded solution growth of SiC applying non-axisymmetric solution convection induced by non-axisymmetric temperature distribution. The detailed solution flow, temperature distribution and carbon concentration distribution were calculated by 3-dimensional numerical analysis. In the present case, the solution flow below the crystal was unidirectional and the supersaturation was increased along the solution flow direction. By the rotation of the crystal in the unidirectional flow and the temperature distribution, we successfully obtained the crystal with the convex growth interface shape.

Chiral symmetry breaking during the chiral crystallization from a sodium chlorate (NaClO3) aqueous solution is an intriguing phenomenon because it provides insights into the prebiotic process of biohomochirality. However, a mechanism of the emergence and amplification of chirality remains controversial, especially for crystallization from highly supersaturated solution, and one of the hypotheses proposed before is a transition toward the homochiral state during the early stages of crystallization. In this contribution, we directly examined the early stage of crystallization by in situ polarized-light microscopy. The observation revealed that achiral crystals, which appear prior to the formation of chiral crystals, transform to the chiral crystal through two kinds of polymorphic transformations: (1) martensitic transformation (MT) and (2) solution-mediated phase transition (SMPT). The SMPT is remarkably facilitated by contact with a chiral crystal. Notably, the resulting enantiomorph through contact-facili...

The solubility of the metastable achiral monoclinic phase in NaClO 3 crystallization from an aqueous solution, which appears prior to the nucleation of chiral crystals, was successfully measured in the range from 10 °C to 23 °C. Antisolvent crystallization method was used to obtain metastable crystals for the measurement. The solubility was determined to be about 1.6 times higher than that of the chiral stable cubic phase by observing growth or dissolution of the crystal in aqueous solution at the temperature and concentration of which is predetermined.

The nitrogen doping behavior of 4H–SiC was investigated by the top-seeded solution growth technique using Si–Ti solvent. Growth experiments were performed under a mixed gas of helium and nitrogen at atmospheric pressure at 1940 °C, in which nitrogen content ranged between 0.17 and 0.5 vol%. The electrical property and structural quality of nitrogen-doped crystals were examined. The nitrogen doping level increased with the increase of nitrogen content in the growth furnace. The most heavily nitrogen-doped SiC with a concentration of 1.1×10 20 cm −3 was obtained; however, stacking faults (SFs) were abruptly generated above a nitrogen concentration of 3.0×10 19 cm −3 . The lowest resistivity of approximately 0.010 Ω cm was obtained with SFs-free. Based on the both undoped and nitrogen-doped growth experimental results, the nitrogen incorporation behavior by employing our solution growth technique was discussed.

Surface morphology and threading dislocation conversion behavior during solution growth of 4H-SiC using pure Si and Al-Si solvents was investigated. The growth surfaces on the C face were smoother than the Si face. By the addition of Al to the solvent, the growth surface became smooth on the C face and rough on the Si face. Threading screw dislocation conversion took place only in the grown crystals on the Si face and threading edge dislocation conversion occurs both on the Si face and the C face using the pure Si solvent. On the other hand, in the grown crystal on the C face using the Al-Si solvent, the threading dislocation conversion was hardly observed. These results indicate that the threading dislocation conversion behavior is influenced by the surface morphology.

Threading dislocations (TDs) in a HVPE-grown c-plane (0001) GaN single crystal were analyzed by micro Raman spectroscopy mapping. The mapping image exhibited the pairs of higher and lower wavenumber regions of peak shift of GaN, which corresponded to the compressive and tensile strains due to TDs. By comparing X-ray topography and etch pit images, the contrasts are considered as the edge component of TDs. By analyzing the existing 290 TDs in 80 × 80 μm2, the directions of the contrast were mainly dominant toward A few brighter contrasts toward were also observed. These TDs are affiliated with Burgers vectors and respectively. Judging from experimental and simulated result, it is confirmed that the contrast in the Raman mapping image of the has a larger magnitude than the

Chiral symmetry breaking in NaClO3 crystallization from an aqueous solution with perturbations has been of great interest. To understand the mechanism, several models focusing on the early stage of the crystallization have been proposed. However, they are ambiguous because the early stage has been barely explored directly. Here, we investigate the early stages of the crystallization process driven by droplet evaporation using a combination of direct in situ microscopic observations and cryogenic single-crystal XRD experiments. We demonstrate that an achiral crystal having P21/a symmetry, which is newly discovered for a solution growth, first appears in the droplet and then transforms into the chiral crystals. Additionally, determination of the lattice constants by XRD experiments (a = 8.42 A, b = 5.26 A, c = 6.70 A, β = 109.71°) revealed that the achiral phase should be identical to Phase III (a = 8.78 A, b = 5.17 A, c = 6.83 A, β = 110°), which is a high-temperature phase from a melt growth of NaClO3. We...

The control of step bunching by solution flow in 4H-SiC solution growth is proposed. We achieved the solution flow control with the specially designed top-seeded solution growth method as follows: by deviating a seed crystal from the center of a crucible and rotating the crucible in one direction, the solution flow direction was controlled to be parallel or antiparallel to the step-flow direction. After the growth, the widely spaced, accumulated macrosteps were observed and the surface of the grown crystal became rough under the parallel flow. On the other hand, the development of the macrosteps was suppressed under the antiparallel flow. As the growth proceeds, the surface roughness of the growth surface increases under the parallel flow, while the surface roughness decreases under the antiparallel flow. This fact suggests the solution flow control can be an effective method to suppress the step bunching during the solution growth of SiC single crystals.

Reduction of threading screw dislocation without polytype transformation from 4H-SiC was performed by the combination of step-flow growth and spiral growth. On a vicinal 4H-SiC seed crystal, threading screw dislocations are converted to Frank-type stacking faults by step-flow during solution growth. As the growth proceeds, the defects are excluded to the crystal. Thus utilizing the conversion, high quality SiC crystal growth without threading screw dislocations is expected to achieve. However, at the same time, polytype transformation is caused by the occurrence of 2D nucleation. By using the special shape of seed crystal, we successfully grew high quality 4H-SiC crystal without threading screw dislocation and polytype transformation.

In this paper, we review our researches on the high-quality 3C-SiC bulk crystal growth. The polytype control and the suppression of defects are essential in the growth 3C-SiC on hexagonal SiC seed crystals. The growth polytype of SiC is usually controlled by the inheritance of the seed crystal. In contrast, we established kinetic polytype control in which the preferential growth of 3C-SiC can be achieved by the difference in the growth rates depending on supersaturation for the polytypes. In the growth of 3C-SiC, double positioning boundaries (DPBs) are often formed by the existence of twinned domain. The elimination of DPBs can be achieved utilizing the anisotropy of the step advance velocity.

We investigated the dislocation behaviors during the solution growth on Si-face and C-face off-axis 4H-SiC seed crystals by using synchrotron X-ray topography. On Si-face, almost all threading screw dislocations (TSDs) and threading edge dislocations (TEDs) are converted into Frank-type defects and basal plane dislocations (BPDs), respectively. On the other hand, on C-face, TSDs were hardly converted. Some of TEDs were converted to BPDs and BPD-TED reconversion was often occurred. Therefore, to reduce density of threading dislocations in the grown crystal, it is better to use Si-face off-axis seed crystal.

We realized the polytype-selective growth of 3C–SiC and 6H–SiC on a 6H–SiC (0 0 0 1) seed crystal by controlling the supersaturation. Both 6H–SiC and 3C–SiC grew on the 6H–SiC seed crystal at low supersaturation, but 3C–SiC increased with increasing supersaturation. At high supersaturation, 3C–SiC grew so rapidly that it completely covered the 6H–SiC seed crystal. The growth rates of 3C–SiC and 6H–SiC have different dependences on supersaturation. In the present case, the growth rate of 3C–SiC in 2D nucleation mode is compared with that of 6H–SiC in spiral growth mode. The present kinetic polytype-control technique is based on polytypes having different growth rates and it differs considerably from the conventional technique that is based on “inheritance” of stacking sequence, which is well known as “step-controlled epitaxy”.

Polytype transformations on the 4H-SiC(0001) Si face during top-seeded solution growth have been investigated by transmission electron microscopy and micro-Raman spectroscopy. 4H-, 15R-, and 6H-SiC...

We introduce a method to grow 4H-SiC single polytype stably by controlling the surface morphology. The polytype transition on on-axis 4H-SiC C-face was investigated from a viewpoint of surface morphology of grown layers. At the area where several hillock-like structures grew adjacently, the polytype transition from 4H-SiC to 6H-SiC or 15R-SiC often occurred. Therefore, we tried a modified seeded method to suppress the formation of hillock-like structures. As a result, the hillock-like structure on the grown layer was dramatically reduced. Moreover, the ratio of 4H-SiC polytype to the whole grown surface was increased to be almost 100%.

Solution growth is considered to be a powerful method for high quality SiC crystals. This work reports that the conversion process from a threading screw dislocation into a few Frank partial dislocations in basal planes was investigated by synchrotron X-ray topography. This process was effectively assisted by step-flow growth on off-oriented (0001) seed crystals. The Frank partials were not extended into the crystal grown toward the [0001] direction perpendicular to the basal plane. Thus, the conclusion of this study suggests the use of off-oriented seed crystal is important to improve crystal quality.

The crystal structure and microstructure of ReSi1.75 were investigated by synchrotron X-ray diffraction combined with scanning transmission electron microscopy. ReSi1.75 contains an ordered arrangement of vacancies in Si sites in the underlying tetragonal C11b lattice of the MoSi2-type and the crystal structure is monoclinic with the space group Cm. Atomic positions of Si atoms near vacancies are considerably displaced from the corresponding positions in the parent C11b structure, and they exhibit anomalously large local thermal vibration accompanied by large values of atomic displacement parameter. There are four differently-oriented domains with two of them being related to each other by the 90° rotation about the c-axis of the underlying C11b lattice and the other two being their respective twins. The habit planes for domain boundaries observed experimentally are consistent with those predicted with ferroelastic theory.

The threading edge dislocations in a GaN crystal are analyzed via micro-Raman spectroscopy mapping. A clear contrast image of the peak shift from a higher wavenumber to a lower wavenumber is simulated. The direction from the higher-wavenumber region to the lower-wavenumber region is found to be in the 90? rotation from the Burgers vector. The Burgers vector is experimentally determined to be using transmission electron microscopy. The magnitude of the Burgers vector agrees well between the simulated and experimental results. Thus, the density, direction, and magnitude of the edge component of the threading dislocations are identified using Raman spectroscopy mapping.

Because the expansion of single Shockley stacking faults (1SSFs) is an important problem for the viability of SiC bipolar devices, there is a need to suppress it during device operation. The expansion mechanism, however, is still unclear. Therefore, the method to suppress the expansion has never been established. An important factor for the expansion could be carrier recombination in 1SSFs because the expansion has only been observed during bipolar operation or light illumination. In this study, we characterized carrier recombination by observing the photoluminescence from 1SSFs and partial dislocations (PDs). The luminescence from 1SSFs and PDs showed a fast decay component compared with that from the band edge. This result indicates that the carrier recombination in 1SSFs and at PDs was faster than that in regions without 1SSFs in 4H-SiC. In addition, because of the slower recombination at Si-core PDs compared with that in 1SSFs and at C-core PDs, the velocity of 1SSF expansion would be limited by the carrier recombination at Si-core PDs. The temperature dependence of the decay time implies that the recombination at the Si-core PD was enhanced on increasing the temperature.

Li metal anode is an attractive material for secondary batteries due to its high capacity of 3860 mAh/g. However, Li metal is well known for its hazardous behavior with air and moisture. Therefore, reducing the amount of Li metal in anodes is effective not only increasing energy density but also guarantee the safety of the batteries. For these reason, anode-free lithium batteries(AFLBs), in which Li electrodeposits onto Cu current collector, has been proposed by in-situ formation of Li metal1. Despite the potential increase in energy density of AFLBs comparing to conventional Li-ion batteries2, low coulombic efficiency due to non-uniform deposition nature of Li metal prevents AFLBs for practical applications. To address this issue, many methods such as high concentrated electrolyte, formation of protective layer, and electrolyte additives are developed, but AFLBs are still not realized. On the other hand, our previous work3 revealed that shape of Li precipitates is influenced by crystal orientation of Cu current collectors. This fact suggests that cycling stability of Li metal anode is also affected by the orientation of the Cu collector. Thus, in the present work, we performed cyclic voltammetry to investigate the transition of the characteristics. The experiments of Li electrodeposition and stripping on single crystal Cu current collectors were conducted in a three-pole cell. The orientation of Cu are (111), (101), and (001). Counter and reference electrodes are both Li metal. Prior to experiments, the crystal orientation of collectors was analyzed by electron backscatter diffraction (EBSD). An electrolyte is consisted of 1 M LiPF6 in EC:EMC=5:5. Li was deposited at a current density of 0.5 mA/cm2 with charge capacity of 0.1 mA/cm2. Subsequently, the Li was stripped at same current density with 0.05 mA/cm2. Cyclic voltammetry was performed at a scan rate of 5.0 mV/s. SEM analysis was also conducted to examine Li morphology. Figure 1 shows cyclic voltammograms of Li deposition and stripping on various Cu collectors. Negative and positive peaks represent Li deposition and stripping respectively. Each peak current decreases substantially as cycle proceeds, probably because of the development of the resistive SEI layer. The smallest overpotential for the first Li deposition was observed in Cu(111), followed by Cu(101) and Cu(001). Uniform formation of the resistive layer expectedly causes this since the SEM analysis revealed that Li morphology on Cu(111) is the most homogeneous. Moreover, Cu(111) delivered the lowest and the most stable overpotential over 10 cycle, while those in the other cases are larger and increase as the cycle progress. Therefore, it can we concluded that crystal orientation of collectors is an important factor for Li metal batteries and Cu(111) is effective for high cycle stability. References [1] B. J. Neudecker, et. al., J. Electrochem. Soc. 2000, 147(2), 517-523. [2] J. Qian, et. al., Adv. Funct. Mater. 2016, 26, 7094-7102. [3] K.Ishikawa, et. al., Cryst. Growth Des. 2017, 5, 2379-2385. Figure 1

We are developing “thermal switching materials”, whose thermal conductivity varies over a wide range. It has a wide range of applications such as temperature controls, thermal energy storages and so on. WO3 is expected as a thermal switching material because the electrical conductivity of WO3 can widely change owing to the metal-insulator transition (MIT) caused by hydrogen interactions. Moreover, hydrogens can be intercalated into and deintercalated from WO3 film reversibly and quickly by an electrochemical reaction. Therefore, the thermal conductivity is expected to change reversibly. Here, we report the thermal conductivity changes in WO3 film associated with hydrogen intercalations. WO3 film was prepared on ITO coated glass at room temperature by RF magnetron sputtering method in an Ar-O2 atmosphere. The total pressure and the oxygen content of the atmosphere were 4.0 Pa and 13%, respectively. The thickness of WO3 film was 0.7-1.4 μm. Hydrogen intercalations into WO3 film on ITO coated glass were performed in an 0.5 M H2SO4 electrolyte with a Pt counter electrode and a calomel reference electrode. The structure of the films was determined by x-ray diffraction analysis. The thermal diffusivity of the films was measured by an ac calorimetric method and the thermal conductivity was calculated by the differential method using measured thermal diffusivity. The electrical conductivity was measured by a four-point probe method. X-ray diffraction measurements showed that the WO3 films were amorphous. The value of thermal conductivity decreased with increasing hydrogen content x in H x WO3, from x = 0 to x = 0.33, and the value of thermal conductivity increased markedly with increasing x above x = 0.33. The hydrogen content of x = 0.33 is close to that of MIT. On the other hand, the electrical conductivity after MIT was 1×105 times higher than that before MIT. However, a variation of the electron thermal conductivity given from the electrical conductivity by the Wiedemann-Franz law is much smaller than a variation of the thermal conductivity. Therefore, the lattice thermal conductivity is expected to contribute to a change in the thermal conductivity. Present results indicate that the thermal conductivity of WO3 film can be controlled by hydrogen intercalations and potentialize the hydrogen-induced active control of thermal switches.

An in-situ X-ray topography system using monochromatic synchrotron radiation for the observation of the stacking faults in 4H-SiC during a high-temperature annealing process was developed. We demonstrated that the stacking faults in nitrogen-doped 4H-SiC not only expand but also shrink at high temperatures. Furthermore, it was confirmed that the types of the core structure of partial dislocations enclosing the stacking fault can be determined at high temperatures.An in-situ X-ray topography system using monochromatic synchrotron radiation for the observation of the stacking faults in 4H-SiC during a high-temperature annealing process was developed. We demonstrated that the stacking faults in nitrogen-doped 4H-SiC not only expand but also shrink at high temperatures. Furthermore, it was confirmed that the types of the core structure of partial dislocations enclosing the stacking fault can be determined at high temperatures.

We succeeded in measuring the density and direction of the edge component of threading dislocations (TDs) in c-plane (0001) GaN by micro-Raman spectroscopy mapping. In the micro-Raman spectroscopy mapping of the E2 H peak shift between 567.85 and 567.75 cm−1, six different contrast images are observed toward directions of . By comparing X-ray topography and etch pit images, the E2 H peak shift is observed where the edge component of TDs exists. In contrast, the E2 H peak is not observed where the screw component of TDs exists.

The changes in microstructure and defect structure of two different semiconducting transition-metal silicides, ReSi1.75 and Ru2Si3 with ternary alloying of substitutional elements with a valence electron number different from that of the constituent metal have been investigated in order to see if the crystal and defect structures of these silicides and thereby their physical properties can be controlled through defect engineering according to the valence electron counting rule. The Si vacancy concentration and its arrangement can be successfully controlled in ReSi1.75 while the relative magnitude of the metal and silicon subcell dimensions in the chimney-ladder structures can be successfully controlled in Ru2Si3.

Visible-light photoemission spectroscopy (VPS) is a novel angle-resolved photoemission spectroscopy developed by us for measuring conduction electrons emitted from a surface with negative electron affinity state. In this study, InGaAs/GaAsP quantum well superlattice was analyzed by the VPS method with changing the excitation photon energy. By comparing with comparison of the energy distribution curves obtained by different excitation energy, the first and second conduction mini-band structures were directly clarified.