High Thermal Conductivity in Wafer Scale Cubic Silicon Carbide Crystals

High thermal conductivity electronic materials are critical components for high-performance electronic and photonic devices as either active functional materials or thermal management materials. We report an isotropic high thermal conductivity over 500 W m-1K-1 at room temperature in high-quality wafer-scale cubic silicon carbide (3C-SiC) crystals, which is the second highest among large crystals (only surpassed by diamond). Furthermore, the corresponding 3C-SiC thin films are found to have record-high in-plane and cross-plane thermal conductivity, even higher than diamond thin films with equivalent thicknesses. Our results resolve a long-lasting puzzle that the literature values of thermal conductivity for 3C-SiC are perplexingly lower than the structurally more complex 6H-SiC. Further analysis reveals that the observed high thermal conductivity in this work arises from the high purity and high crystal quality of 3C-SiC crystals which excludes the exceptionally strong defect-phonon scatterings in 3C-SiC. Moreover, by integrating 3C-SiC with other semiconductors by epitaxial growth, we show that the measured 3C-SiC-Si TBC is among the highest for semiconductor interfaces. These findings not only provide insights for fundamental phonon transport mechanisms, also suggest that 3C-SiC may constitute an excellent wide-bandgap semiconductor for applications of power electronics as either active components or substrates

複雑な系における非断熱動力学への量子化学的アプローチ: 励起分子の無輻射緩和及びハライドペロブスカイト中のキャリア挙動

早大学位記番号:新8772早稲田大

Charge Carrier Trapping at Surface Defects of Perovskite Solar Cell Absorbers: A First-Principles Study

The trapping of charge carriers at defects on surfaces or grain boundaries is detrimental for the performance of perovskite solar cells (PSCs). For example, it is the main limiting factor for carrier lifetime. Moreover, it causes hysteresis in the current–voltage curves, which is considered to be a serious issue for PSCs’ operation. In this work, types of surface defects responsible for carrier trapping are clarified by a comprehensive first-principles investigation into surface defects of tetragonal CH₃NH₃PbI₃ (MAPbI₃). Considering defect formation energetics, it is proposed that a Pb-rich condition is preferred to an I-rich one; however, a moderate condition might possibly be the best choice. Our result paves the way for improving the performance of PSCs through a rational strategy of suppressing carrier trapping at surface defects

Inorganic Lattice Fluctuation Induces Charge Separation in Lead Iodide Perovskites: Theoretical Insights

The high performance of recently emerged lead halide perovskite based photovoltaic devices has been attributed to remarkable carrier properties in this kind of material: long carrier diffusion length, long carrier lifetime, and low electron–hole recombination rate. However, the charge separation mechanism underlying such carrier properties is still debated in this research field. In this work, using first-principles molecular dynamics simulations, we have demonstrated that the charge separation is induced by the structural fluctuation of the inorganic lattice, assuming that the charge carriers occupy the band edge. It is shown that the charge separation is attributed to the electrostatic potential fluctuation coupled to the inorganic lattice dynamics, on the basis of both simple tight-binding-model-based analyses and first-principles calculations. These results suggest that the organic cations, which are often used as components of lead halide perovskites, are unlikely to be essential for the above-mentioned carrier properties. Hence, it is expected that all-inorganic lead halide perovskite based photovoltaics might be able to rival organic–inorganic lead halide perovskite based ones in performance

Detailed analysis of charge transport in amorphous organic thin layer by multiscale simulation without any adjustable parameters

Hopping-type charge transport in an amorphous thin layer composed of organic molecules is simulated by the combined use of molecular dynamics, quantum chemical, and Monte Carlo calculations. By explicitly considering the molecular structure and the disordered intermolecular packing, we reasonably reproduce the experimental hole and electron mobilities and their applied electric field dependence (Poole-Frenkel behaviour) without using any adjustable parameters. We find that the distribution of the density-of-states originating from the amorphous nature has a significant impact on both the mobilities and Poole-Frenkel behaviour. Detailed analysis is also provided to reveal the molecular-level origin of the charge transport, including the origin of Poole-Frenkel behaviour

Necrotizing Fasciitis Secondary to a Primary Suture for Anoperineal Trauma by Motorcycle Accident in a Healthy Adult

A 41-year-old man experienced a swollen scrotum three days after a motorcycle accident and presented to our hospital. He had had a primary suture repair for anoperineal trauma in an outside hospital at the time of the injury. He presented to us with general fatigue, low grade fevers, and perineal pain. Abdominal computed tomography showed subcutaneous emphysema from the scrotum to the left chest. The sutured wound had foul-smelling discharge and white exudate. We made the diagnosis of necrotizing fasciitis and immediately opened the sutured wound and performed initial debridement and lavage with copious irrigation. We continued antibiotics and lavage of the wound until the infection was controlled. Fortunately, the necrotizing fasciitis did not worsen and he was discharged after 15 days. Our experience indicates that anoperineal injuries should not be closed without careful and intensive follow-up due to the potential of developing necrotizing fasciitis

The Validation of Automated Social Skills Training in Members of the General Population Over 4 Weeks: Comparative Study

BackgroundSocial skills training by human trainers is a well-established method of teaching appropriate social and communication skills and strengthening social self-efficacy. Specifically, human social skills training is a fundamental approach to teaching and learning the rules of social interaction. However, it is cost-ineffective and offers low accessibility, since the number of professional trainers is limited. A conversational agent is a system that can communicate with a human being in a natural language. We proposed to overcome the limitations of current social skills training with conversational agents. Our system is capable of speech recognition, response selection, and speech synthesis and can also generate nonverbal behaviors. We developed a system that incorporated automated social skills training that completely adheres to the training model of Bellack et al through a conversational agent. ObjectiveThis study aimed to validate the training effect of a conversational agent–based social skills training system in members of the general population during a 4-week training session. We compare 2 groups (with and without training) and hypothesize that the trained group’s social skills will improve. Furthermore, this study sought to clarify the effect size for future larger-scale evaluations, including a much larger group of different social pathological phenomena. MethodsFor the experiment, 26 healthy Japanese participants were separated into 2 groups, where we hypothesized that group 1 (system trained) will make greater improvement than group 2 (nontrained). System training was done as a 4-week intervention where the participants visit the examination room every week. Each training session included social skills training with a conversational agent for 3 basic skills. We evaluated the training effect using questionnaires in pre- and posttraining evaluations. In addition to the questionnaires, we conducted a performance test that required the social cognition and expression of participants in new role-play scenarios. Blind ratings by third-party trainers were made by watching recorded role-play videos. A nonparametric Wilcoxson Rank Sum test was performed for each variable. Improvement between pre- and posttraining evaluations was used to compare the 2 groups. Moreover, we compared the statistical significance from the questionnaires and ratings between the 2 groups. ResultsOf the 26 recruited participants, 18 completed this experiment: 9 in group 1 and 9 in group 2. Those in group 1 achieved significant improvement in generalized self-efficacy (P=.02; effect size r=0.53). We also found a significant decrease in state anxiety presence (P=.04; r=0.49), measured by the State-Trait Anxiety Inventory (STAI). For ratings by third-party trainers, speech clarity was significantly strengthened in group 1 (P=.03; r=0.30). ConclusionsOur findings reveal the usefulness of the automated social skills training after a 4-week training period. This study confirms a large effect size between groups on generalized self-efficacy, state anxiety presence, and speech clarity