2D Amorphous GaOX Gate Dielectric for ß-Ga2O3 Field-Effect Transistors.

Appropriate gate dielectrics must be identified to fabricate metal-insulator-semiconductor field-effect transistors (MISFETs); however, this has been challenging for compound semiconductors owing to the absence of high-quality native oxides. This study uses the liquid-gallium squeezing technique to fabricate 2D amorphous gallium oxide (GaOX) with a high dielectric constant, where its thickness is precisely controlled at the atomic scale (monolayer, ∼4.5 nm; bilayer, ∼8.5 nm). Beta-phase gallium oxide (ß-Ga2O3) with an ultrawide energy bandgap (4.5-4.9 eV) has emerged as a next-generation power semiconductor material and is presented here as the channel material. The 2D amorphous GaOX dielectric is combined with a ß-Ga2O3 conducting nanolayer, and the resulting ß-Ga2O3 MISFET is stable up to 250 °C. The 2D amorphous GaOX is oxygen-deficient, and a high-quality interface with excellent uniformity and scalability forms between the 2D amorphous GaOX and ß-Ga2O3. The fabricated MISFET exhibits a wide gate-voltage swing of approximately +5 V, a high current on/off ratio, moderate field-effect carrier mobility, and a decent three-terminal breakdown voltage (∼138 V). The carrier transport of the Ni/GaOX/ß-Ga2O3 metal-insulator-semiconductor (MIS) structure displays a combination of Schottky emission and Fowler-Nordheim (F-N) tunneling in the high-gate-bias region at 25 °C, whereas at elevated temperatures it shows Schottky emission and F-N tunneling in the low- and high-gate-bias regions, respectively. This study demonstrates that a 2D GaOX gate dielectric layer can be produced and incorporated into an active channel layer to form an MIS structure at room temperature (∼25 °C), which enables the facile fabrication of MISFET devices.

Enhanced electrochemical performance of MoS2/graphene nanosheet nanocomposites.

Molybdenum disulfide (MoS2) is attractive as an anode material for next-generation batteries, because of its layered structure being favorable for the insertion/deinsertion of Li+ ions, and its fairly high theoretical capacity. However, since the MoS2 anode material has exhibited disadvantages, such as low electrical conductivity and poor cycling stability, to improve the electrochemical performance of MoS2 in this study, a nanocomposite structure consisting of MoS2 and GNS (MoS2/GNS) as an anode for LIBs was prepared, by controlling the weight ratios of MoS2/GNS. The X-ray diffraction patterns and electron microscopic analysis showed that the nanocomposite electrode structure consisted of well-formed MoS2 nanoparticles and GNS. Compared to MoS2-only, the MoS2/GNS composites exhibited high retention and improved capacity at high current densities. In particular, among these nanocomposite samples, MoS2/GNS(8 : 2) with an appropriate portion of GNS exhibited the best LIB performance, due to the lowest interfacial resistance and highest Li-ion diffusivity.

Facile one-pot synthesis of Ge/TiO2 nanocomposite structures with improved electrochemical performance.

Germanium (Ge) as an alternative to graphite exhibits a fairly high theoretical energy density and improved Li+ ion diffusivity. However, the seriously deteriorated electrochemical performance of Ge during cycling and the difficulty in the preparation of Ge-based nanostructures can hinder the utilization of Ge as an anode. Thus, in this study, a nanocomposite structure with Ge and TiO2 (Ge/TiO2) was synthesized using a facile one-pot method with different ratios of a Ge source with a dominant GeO2 phase and titanium isopropoxide. From X-ray diffraction, electron microscopy, and X-ray photoelectron spectroscopy, the Ge/TiO2 nanocomposites were found to be spherical structures homogeneously consisting of the reduced Ge as an active material and amorphous TiO2 as a matrix. In particular, the Ge/TiO2 nanocomposite with an appropriate amount of TiO2 exhibited improved electrochemical properties, i.e., a coulombic efficiency of 97% and a retention of 61% for 100 cycles, compared to commercial Ge (a coulombic efficiency of 82% and a retention of 16%). This demonstrates that the amorphous TiO2 matrix could relieve a volumetric expansion of the Ge active material in the nanocomposite electrode generated during the cycling process.

Role of polyvinylpyrrolidone in the electrochemical performance of Li2MnO3 cathode for lithium-ion batteries.

While Li2MnO3 as an over-lithiated layered oxide (OLO) shows a significantly high reversible capacity of 250 mA h g-1 in lithium-ion batteries (LIBs), it has critical issues of poor cycling performance and deteriorated high rate performance. In this study, modified OLO cathode materials for improved LIB performance were obtained by heating the as-prepared OLO at different temperatures (400, 500, and 600 °C) in the presence of polyvinylpyrrolidone (PVP) under an N2 atmosphere. Compared to the as-prepared OLO, the OLO sample heated at 500 °C with PVP exhibited a high initial discharge capacity of 206 mA h g-1 and high rate capability of 111 mA h g-1 at 100 mA g-1. The superior performance of the OLO sample heated at 500 °C with PVP is attributed to an improved electronic conductivity and Li+ ionic motion, resulting from the formation of the graphitic carbon structure and increased Mn3+ ratio during the decomposition of PVP.

TiO2-coated LiCoO2 electrodes fabricated by a sputtering deposition method for lithium-ion batteries with enhanced electrochemical performance.

We fabricated lithium cobalt oxide (LiCoO2, LCO) electrodes in the absence and presence of TiO2 layers as cathodes for lithium-ion batteries (LIBs) using a sputtering deposition method under an Ar atmosphere. In particular, TiO2 coating layers on sputtered LCO electrodes were directly deposited in a layer-by-layer form with varying TiO2 sputtering times from 60 to 120 s. These sputtered electrodes were heated at 600 °C in an air atmosphere for 3 h. The thicknesses of TiO2 layers in TiO2-coated LCO electrodes were controlled from ∼2 to ∼10 nm. These TiO2-coated LCO electrodes exhibited superior electrochemical performance, i.e. high capacities (93-107 mA h g-1@0.5C), improved retention of >60% after 100 cycles, and high-rate cycling properties (64 mA h g-1@1C after 100 cycles). Such an improved performance of TiO2-coated LCO electrodes was found to be attributed to relieved volumetric expansion of LCO and protection of LCO electrodes against HF generated during cycling.

The effects of functional electrical stimulation on muscle tone and stiffness of stroke patients.

[Purpose] The purpose of this study was to determine the effects of functional electrical stimulation on muscle tone and stiffness in stroke patients. [Subjects and Methods] Ten patients who had suffered from stroke were recruited. The intervention was functional electrical stimulation on ankle dorsiflexor muscle (tibialis anterior). The duration of functional electrical stimulation was 30 minutes, 5 times a week for 6 weeks. The Myoton was used a measure the muscle tone and stiffness of the gastrocnemius muscle (medial and lateral part) on paretic side. [Results] In the assessment of muscle tone, medial and lateral part of gastrocnemius muscle showed differences before and after the experiment. Muscle stiffness of medial gastrocnemius muscle showed differences, and lateral gastrocnemius muscle showed differences before and after the experiment. The changes were greater in stiffness scores than muscle tone. [Conclusion] These results suggest that FES on ankle dorsiflexor muscle had a positive effect on muscle tone and stiffness of stroke patients.

Effects of trunk stability exercise using proprioceptive neuromuscular facilitation with changes in chair height on the gait of patients who had a stroke.

[Purpose] The purpose of this study was to identify the effects of trunk stability exercise using proprioceptive neuromuscular facilitation with changes in chair heights on the gait of stroke patients. [Subjects and Methods] The subjects of this study were 11 stroke patients. The intervention method was trunk stability exercise using proprioceptive neuromuscular facilitation with different chair heights (50, 60, and 70 cm). These exercises were performed 5 times per week for 6 weeks. Gait velocity, cadence, stride length, gait cycle, and stance phase duration were used to measure gait function. [Results] Significant changes in gait velocity, cadence, and stride length were observed on the affected side. However, no significant changes in gait cycle and stance phase were observed on the affected side. [Conclusion] These results indicate that trunk stability exercise using proprioceptive neuromuscular facilitation with change in chair heights were effective in improving gait velocity, cadence, and stride length on the affected side. However, in this study, no significant changes were observed in gait cycle and stance phase on the affected side. Therefore, various interventions for stroke patients should be investigated in further studies.

Effects of oculo-motor exercise, functional electrical stimulation and proprioceptive neuromuscular stimulation on visual perception of spatial neglect patients.

[Purpose] The purpose of this study was to identify the effects of oculo-motor exercise, functional electrical stimulation (FES), and proprioceptive neuromuscular facilitation (PNF) on the visual perception of spatial neglect patients. [Subjects and Methods] The subjects were randomly allocated to 3 groups: an oculo-motor exercise (OME) group, a FES with oculo-motor exercise (FOME) group, and a PNF with oculo-motor exercise (POME) group. The line bisection test (LBT), motor free visual test (MVPT), and Catherine Bergego Scale (CBS) were used to measure visual perception. These were performed 5 times per week for 6 weeks. [Results] The OME group and POME group showed significant improvements according to the LBT and MVPT results, but the FOME group showed no significant improvement. According to the CBS, all 3 groups showed significant improvements. The OME and POME groups showed improvement over the FOME group in the LBT and MVPT. However, there was no significant difference among the three groups according to the CBS. [Conclusion] These results indicate that oculo-motor exercise and PNF with oculo-motor exercise had more positive effects than FES with oculo-motor exercise on the visual perception of spatial neglect patients.

The immediate effect of PNF pattern on muscle tone and muscle stiffness in chronic stroke patient.

[Purpose] The purpose of this study was to investigate the immediate effect of proprioceptive neuromuscular facilitation on muscle tone and muscle stiffness in stroke patients. [ Subjects and Methods] The subjects consisted of 15 patients with chronic stroke (stroke group) and 15 healthy persons (healthy group). We measured the effects of proprioceptive neuromuscular facilitation intervention on the lower extremity using a muscle tone measurement device; this detected changes in muscle tone and stiffness in the lower extremity muscles. [Results] Measurements taken before the intervention showed that, on average, the lower extremity muscles of the stroke group showed abnormally increased muscle tone and stiffness compared to the lower extremity muscles of the healthy group. After the intervention, the average muscle tone and stiffness in the lower extremity muscles of the stroke group decreased, but this change was insignificant, and the differences between the two groups were also insignificant. [Conclusion] Based on the findings of this study, we recommend proprioceptive neuromuscular facilitation treatment of both affected and non-affected sides to decrease the abnormally increased muscle tone and stiffness in the lower extremity muscles of chronic stroke patients.

Effect of whole-body vibration exercise in a sitting position prior to therapy on muscle tone and upper extremity function in stroke patients.

[Purpose] The purpose of this study was to determine the effect of whole-body vibration exercise in a sitting position prior to therapy in stroke patients. [Subjects and Methods] Fourteen chronic stroke patients were included in this study. Prior to occupational therapy, whole-body exercise was performed for 10 minutes, 5 times per week, for a total of 8 weeks. Muscle tone and upper extremity function were measured. The Modified Ashworth Scale (MAS) was used to measure muscle tone, and the Manual Function Test (MFT) and Fugl-Meyer Assessment scale (FugM) were used to measure upper extremity function. [Results] MAS score was significantly decreased, and MFT and FugM were significantly increased. [Conclusion] These results indicate that whole-body vibration exercise in a sitting position prior to therapy had a positive effect on muscle tone, and upper extremity function in stroke patients.

Effects of ankle plantar flexors stretching with closed kinetic chain on pelvic movements and gait speed in hemiplegia patients: a case study.

[Purpose] The purpose of this study was to identify the effects of ankle plantar flexors stretching with closed kinetic chain (CKC) in hemiplegia patients. [Methods] This study used a reversal design (A-B-A') for a stroke with hemiplagia. The intervention program consisted of 30 min sessions, once a day, for 15 days. The subjects were trained for 15 sessions in total. Pelvic movements (anterior ·posterior tilting, elevation, depression, forward·backward rotation) during walking and gait speed were measured in hemiplegia patients. [Results] Overall, the angle of pelvic movements was increased in Treatment and, Baseline II compared with Baseline I. The gait speed was maximally increased in Baseline II, followed by Treatment and Baseline I. [Conclusion] These results suggest that ankle plantar flexors stretching with closed kinetic chain had a positive effect on pelvic movements and gait speed in hemiplegia patients. Also, after treatment, its effect on gait of hemiplegia patients was maintained.

The effect of implant shape and bone preparation on primary stability.

PURPOSE: The purpose of this study was to evaluate the effects of implant shape and bone preparation on the primary stability of the implants using resonance frequency analysis. METHODS: Sixty bovine rib blocks were used for soft and hard bone models. Each rib block received two types of dental implant fixtures; a straight-screw type and tapered-screw type. Final drilling was done at three different depths for each implant type; 1 mm under-preparation, standard preparation, and 1 mm over-preparation. Immediately after fixture insertion, the implant stability quotient (ISQ) was measured for each implant. RESULTS: Regardless of the bone type, the ISQ values of the straight-screw type and tapered-screw type implants were not significantly different (P > 0.05). Depth of bone preparation had no significant effect on the ISQ value of straight-screw type implants (P > 0.05). For the tapered-screw type implants, under-preparation significantly increased the ISQ value (P < 0.05), whereas overpreparation significantly decreased the ISQ value (P < 0.05). CONCLUSIONS: Within the limitations of this study, it is concluded that bone density seemed to have a prevailing effect over implant shape on primary stability. The primary stability of the tapered-screw type implants might be enhanced by delicate surgical techniques.