Barrier Height, Ideality Factor and Role of Inhomogeneities at the AlGaN/GaN Interface in GaN Nanowire Wrap-Gate Transistor.

It is essential to understand the barrier height, ideality factor, and role of inhomogeneities at the metal/semiconductor interfaces in nanowires for the development of next generation nanoscale devices. Here, we investigate the drain current (Ids)-gate voltage (Vgs) characteristics of GaN nanowire wrap-gate transistors (WGTs) for various gate potentials in the wide temperature range of 130-310 K. An anomalous reduction in the experimental barrier height and rise in the ideality factor with reducing the temperature have been perceived. It is noteworthy that the variations in barrier height and ideality factor are attributed to the spatial barrier inhomogeneities at the AlGaN/GaN interface in the GaN nanowire WGTs by assuming a double Gaussian distribution of barrier heights at 310-190 K (distribution 1) and 190-130 K (distribution 2). The standard deviation for distribution 2 is lower than that of distribution 1, which suggests that distribution 2 reflects more homogeneity at the AlGaN/GaN interface in the transistor's source/drain regions than distribution 1.

Carrier Trap and Their Effects on the Surface and Core of AlGaN/GaN Nanowire Wrap-Gate Transistor.

We used capacitance-voltage (C-V), conductance-voltage (G-V), and noise measurements to examine the carrier trap mechanisms at the surface/core of an AlGaN/GaN nanowire wrap-gate transistor (WGT). When the frequency is increased, the predicted surface trap density promptly drops, with values ranging from 9.1 × 1013 eV-1∙cm-2 at 1 kHz to 1.2 × 1011 eV-1∙cm-2 at 1 MHz. The power spectral density exhibits 1/f-noise behavior in the barrier accumulation area and rises with gate bias, according to the 1/f-noise features. At lower frequencies, the device exhibits 1/f-noise behavior, while beyond 1 kHz, it exhibits 1/f2-noise behavior. Additionally, when the fabricated device governs in the deep-subthreshold regime, the cutoff frequency for the 1/f2-noise features moves to the subordinated frequency (~102 Hz) side.

Temperature-Dependent Carrier Transport in GaN Nanowire Wrap-Gate Transistor.

For the creation of next-generation nanoscale devices, it is crucial to comprehend the carrier transport mechanisms in nanowires. Here, we examine how temperature affects the properties of GaN nanowire wrap-gate transistors (WGTs), which are made via a top-down technique. The predicted conductance in this transistor remains essentially unaltered up to a temperature of 240 K and then increases after that as the temperature rises. This is true for increasing temperature at gate voltages less than threshold voltage (Vgs < Vth). Sharp fluctuations happen when the temperature rises with a gate voltage of Vth < Vgs < VFB. The conductance steadily decreases with increasing temperature after increasing the gate bias to Vgs > VFB. These phenomena are possibly attributed to phonon and impurity scattering processes occurring on the surface or core of GaN nanowires.

Viscosity-Controllable Graphene Oxide Colloids Using Electrophoretically Deposited Graphene Oxide Sheets.

Graphene oxide (GO) is one of the interesting ink materials owing to its fascinating properties, such as high dissolubility in water and high controllable electric properties. For versatile printing application, the viscosity of GO colloids should be controlled in order to meet the specific process requirements. Here, we report on the relatively rapid fabrication of viscosity-increased GO (VIGO) colloids mixed with electrophoretically deposited GO sheets (EPD-GO). As the GO colloid concentration, applied voltage, and deposition time increase, the viscosity of the GO colloids becomes high. The reason for the improved viscosity of GO colloids is because EPD-GO has parallel stacked GO sheets. The GO and VIGO colloids are compared and characterized using various chemical and structural analyzers. Consequently, our simple and fast method for the fabrication of GO colloids with enhanced viscosity can be used for producing inks for flexible and printed electronics.

Impact of the gate geometry on adiabatic charge pumping in InAs double quantum dots.

We compare the adiabatic quantized charge pumping performed in two types of InAs nanowire double quantum dots (DQDs), either with tunnel barriers defined by closely spaced narrow bottom gates, or by well-separated side gates. In the device with an array of bottom gates of 100 nm pitch and 10 µm lengths, the pump current is quantized only up to frequencies of a few MHz due to the strong capacitive coupling between the bottom gates. In contrast, in devices with well-separated side gates with reduced mutual gate capacitances, we find well-defined pump currents up to 30 MHz. Our experiments demonstrate that high frequency quantized charge pumping requires careful optimization of the device geometry, including the typically neglected gate feed lines.

High Device Performances and Noise Characteristics of AlGaN/GaN HEMTs Using In Situ SiCN and SiN Cap Layer.

We fabricated and characterized AlGaN/GaN high-electron mobility transistors (HEMTs) with a nano-sized in situ cap layer (one is a silicon carbon nitride (SiCN) layer, and the other is a silicon nitride (SiN) layer) comparing to the conventional device without an in situ cap layer. The pulse characteristics and noise behaviors for two devices with in situ cap layers are much superior to those of the reference device without a cap layer, which means that the in situ cap layer effectively passivates the AlGaN surface. On the other hand, the device with an in situ SiCN cap layer showed the excellent device characteristics and noise performances compared to the other devices because of the reduced positive ionic charges and enhanced surface morphology caused by carbon (C) surfactant atoms during the growth of the SiCN cap layer. These results indicate that the AlGaN/GaN HEMT with the in situ SiCN cap layer is very promising for the next high-power device by replacing the conventional HEMT.

Replantation of Multilevel Amputation of the Hand of an Elderly Patient: A Case Report.

Replantation of multilevel amputation of the hand requires considerable hospital resources, and the surgical outcomes in older adults have not been described in detail. Thus, replantation for this injury was mostly confined to young patients. Here, we describe the case of a 63-year-old patient with multilevel amputation of the hand in whom replantation surgery was successful with grasp and pinch functions by the last follow-up. We report the clinical, functional, and patient-reported outcomes and discuss the indications. As the patient transfer system and communication technology develops, more patients will arrive at hospitals in a critical time for replantation. Accordingly, hand surgeons should consider offering replantation option for multilevel amputation after evaluating the indications.

Nano-Thermal Analysis of Defect-Induced Surface Pre-Melting in 2D Tellurium.

Thermal properties, such as thermal conductivity, heat capacity, and melting temperature, influence the efficiency and stability of two-dimensional (2D) material applications. However, existing studies on thermal characteristics-except for thermal conductivity-are insufficient for 2D materials. Here, we investigated the melting temperature of 2D Tellurium (2D Te) using the nano-thermal analysis technique and found anomalous behavior that occurs before the melting temperature is reached. The theoretical calculations present surface pre-melting in 2D Te and Raman scattering measurements suggest that defects in 2D Te accelerate surface pre-melting. Understanding the pre-melting surface characteristics of 2D Te will provide valuable information for practical applications.

Phase Controlled Growth of Cd3As2 Nanowires and Their Negative Photoconductivity.

The bottom-up synthesis process often allows the growth of metastable phase nanowires instead of the thermodynamically stable phase. Herein, we synthesized Cd3As2 nanowires with a controlled three-dimensional Dirac semimetal phase using a chemical vapor transport method. Three different phases such as the body centered tetragonal (bct), and two metastable primitive tetragonal (P42/nbc and P42/nmc) phases were identified. The conversion between three phases (bct → P42/nbc → P42/nmc) was achieved by increasing the growth temperature. The growth direction is [110] for bct and P42/nbc and [100] for P42/nmc, corresponding to the same crystallographic axis. Field effect transistors and photodetector devices showed the nearly same electrical and photoelectrical properties for three phases. Differential conductance measurement confirms excellent electron mobility (2 × 104 cm2/(V s) at 10 K). Negative photoconductance was first observed, and the photoresponsivity reached 3 × 104 A/W, which is ascribed to the surface defects acting as trap sites for the photogenerated electrons.

Controllable p-n junctions in three-dimensional Dirac semimetal Cd3As2 nanowires.

We demonstrate a controllable p-n junction in a three-dimensional Dirac semimetal (DSM) Cd3As2 nanowire with two recessed bottom gates. The device exhibits four different conductance regimes with gate voltages, the unipolar (n-n and p-p) and bipolar (n-p and n-p) regimes, where p-n junctions are formed. The conductance in the p-n junction regimes decreases drastically when a magnetic field is applied perpendicular to the nanowire. In these regimes, the device shows quantum dot behavior, whereas the device exhibits conductance plateaus in the n-n regime at high magnetic fields. Our experiment shows that the ambipolar tunability of DSM nanowires can enable the realization of quantum devices based on quantum dots and electron optics.

Characteristics of GaN-Based Nanowire Gate-All-Around (GAA) Transistors.

We investigate the DC, C-V, and pulse performances in GaN-based nanowire gate-all-around (GAA) transistors with two kinds of geometry: one is AlGaN/GaN heterostructure with two dimensional electron gas (2DEG) channel and the other is only GaN layer without 2DEG channel. From I-V and C-V curves, the fabricated GaN nanowire GAA transistor with AlGaN layer clearly exhibits normally-on operation with negative threshold voltage (Vth) due to the existence of 2DEG channel on the trapezoidal shaped GaN nanowire. On the other hand, the GaN nanowire GAA transistor without AlGaN layer presents a positive Vth (normally-off operation) due to the absent of 2DEG channel on the triangle shaped GaN nanowire. However, both devices show the similar temperaturedependent I-V characteristics due to the combination of bulk channel and surface channel in GaN nanowire GAA channel are mostly contributed, rather than the 2DEG channel. GaN-based nanowire GAA transistors demonstrate to almost negligible current collapse phenomenon due to the perfect GAA gate structure in GaN nanowire. The proposed GaN-based nanowire GAA transistors are very promising candidate for both high power device and nano-electronics application.

Investigation of Chemical Origin of White-Light Emission in Two-Dimensional (C4H9NH3)2PbBr4 via Infrared Nanoscopy.

The broadband light emission in low-dimensional organic lead halide perovskites (OHPs) is a fascinating property for white light-emitting diodes (LEDs). However, unique emission has been observed in highly distorted low-dimensional OHPs such as (110) and (111) perovskites. Herein, we report the first observation of white-light emission under ambient (21 °C) conditions in a rectangular microsheet of (C4H9NH3)2PbBr4, a (100) perovskite. The origin of white-light emission in (C4H9NH3)2PbBr4 was revealed as defect-assisted radiative recombination via excitation power-dependent photoluminescence measurement. Additionally, the origin of the defect was confirmed to be organic cation vacancies formed by intercalated water molecules via infrared nanoscopy. This result can help to improve the performance of white LEDs using low-dimensional OHPs.

Reliable low-temperature die attach process using Ag/Sn/Ag sandwich structure for high-temperature semiconductor devices.

A low-cost and eco-friendly die attach process for high temperatures should be developed owing to the expansion of the field of high-temperature applications, such as high-power and high-frequency semiconductors. Pb-based and Au-based systems have been used as conventional die attach materials for high-temperature devices. However, these materials exhibit environmental problems and are expensive. Here, we show that the die attach process using the backside metal of the Ag/Sn/Ag sandwich structure is successfully developed for the mass production of Si devices. It has a low-temperature bonding process (235 °C), a high remelting temperature (above 400 °C), and rapid bonding time (20 ms). In addition, it exhibits better properties than Au-12Ge and Pb-10Sn backside metals, which are conventional materials for the high-temperature die attach process. After the die bonding process, various reliability tests of Si devices with the Ag/Sn/Ag backside metal structure were performed.

Exfoliation of Transition Metal Dichalcogenides by a High-Power Femtosecond Laser.

Thin layer two-dimensional (2-D) transition metal dichalcogenide (TMD) materials have distinctive optoelectronic properties. Therefore, several methods including mechanical exfoliation, chemical vapor deposition, and liquid-phase exfoliation have been attempted to obtain uniform TMDs. However, such methods do not easily produce high-quality few-layer TMDs with high speed. Here, we report the successful fabrication of few-layer TMD materials by femtosecond laser irradiation. It shows that TMD samples can be exfoliated from bulk to ~3 layers. This method is much faster and simpler than other exfoliation methods. The size and number of the layers were confirmed by atomic force microscopy, scanning electron microscopy, Raman spectroscopy, and photoluminescence experiments. It is expected to be used for the mass production of thin 2-D TMD materials.

Highly Efficient Thin-Film Transistor via Cross-Linking of 1T Edge Functional 2H Molybdenum Disulfides.

Thin-film transistors (TFTs) have received great attention for their use in lightweight, large area, and wearable devices. However, low crystalline materials and inhomogeneous film formation limit the realization of high-quality electrical properties for channels in commercial TFTs, especially for flexible electronics. Here, we report a field-effect TFT fabricated via cross-linking of edge-1T basal-2H MoS2 sheets that are prepared by edge functional exfoliation of bulk MoS2 with soft organic exfoliation reagents. For edge functional exfoliation, the electrophilic 4-carboxy-benzenediazonium used as the soft organic reagent attacks the nucleophilic thiolates exposed at the edge of the bulk MoS2 with the help of an amine catalyst, resulting in 1T edge-functional HOOC-benzene-2H basal MoS2 nanosheets (e-MoS2). The cross-linking via hydrogen bonding of the negatively charged HOOC of the e-MoS2 sheets with the help of a cationic polymer, polydiallyldimethylammonium chloride, results in a good film formation for a channel of the solution processing TFT. The TFT exhibits an extremely high mobility of 170 cm2/(V s) at 1 V (on/off ratio of 106) on SiO2/Si substrate and also a high mobility of 36.34 cm2/(V s) (on/off ratio of 103) on PDMS/PET substrate.

Validation of the Korean version of the Spinal Appearance Questionnaire.

OBJECTIVE: To evaluate the reliability and validity of an adapted Korean version of the Spinal Appearance Questionnaire (SAQ). METHODS: Translation/retranslation of the English version of the SAQ was conducted, and all steps of the cross-cultural adaptation process were performed. The Korean version of the SAQ (K-SAQ) and the previously validated appearance domain of the Korean version of the Scoliosis Research Society-22 Outcomes questionnaire (K-SRS-22) were mailed to 160 patients with adolescent idiopathic scoliosis (AIS). Reliability assessments were conducted using kappa statistics to assess item agreements, and intraclass correlation coefficients (ICC) and Cronbach's α values were calculated. Convergent validity was evaluated by comparing K-SAQ and K-SRS-22 appearance domain scores and discriminant validity by analyzing relationships between K-SAQ scores and patient characteristics. RESULTS: All items of the K-SAQ had kappa values of agreement of > 0.6. The K-SAQ showed excellent test/re-test reliability with an intraclass correlation coefficient of 0.922. Internal consistency of the K-SAQ was found to be very good (α= 0.883). Convergent validity testing demonstrated a moderate correlation between the K-SAQ and K-SRS-22 (r=-451). The correlation between the K-SAQ and major curve magnitude was significant (r= 0.812). Discriminant validity was confirmed by significant differences in K-SAQ scores and individual K-SAQ domain scores among patients requiring observation, bracing, or surgery. CONCLUSIONS: The adapted Korean version of the SAQ showed satisfactory reliability and validity, and thus, is considered suitable for the evaluation of spinal deformity appearance in Korean speaking patients with adolescent idiopathic scoliosis.

Reconstruction of Postburn Contracture of the Forefoot Using the Anterolateral Thigh Flap.

BACKGROUND: Severe forefoot deformities, particularly those involving the dorsum of the foot, cause inconvenience in daily activities of living including moderate pain on the dorsal aspect of the contracted foot while walking and difficulty in wearing nonsupportive shoes due to toe contractures. This paper presents clinical results of reconstruction of severe forefoot deformity using the anterolateral thigh (ALT) free flap. METHODS: Severe forefoot deformities were reconstructed using ALT flaps in 7 patients (8 cases) between March 2012 and December 2015. The mean contracture duration was 28.6 years. RESULTS: All the flaps survived completely. The size of the flaps ranged from 8 cm × 5 cm to 19 cm × 8 cm. The mean follow-up period was 10 months (range, 7 to 15 months). There was no specific complication at both the recipient and donor sites. There was one case where the toe contracture could not be completely treated after surgery. All of the patients were able to wear shoes and walk without pain. Also, the patients were highly satisfied with cosmetic results. CONCLUSIONS: The ALT flap may be considered ideal for the treatment of severe forefoot deformity.

Metal-Insulator-Semiconductor Diode Consisting of Two-Dimensional Nanomaterials.

We present a novel metal-insulator-semiconductor (MIS) diode consisting of graphene, hexagonal BN, and monolayer MoS2 for application in ultrathin nanoelectronics. The MIS heterojunction structure was fabricated by vertically stacking layered materials using a simple wet chemical transfer method. The stacking of each layer was confirmed by confocal scanning Raman spectroscopy and device performance was evaluated using current versus voltage (I-V) and photocurrent measurements. We clearly observed better current rectification and much higher current flow in the MIS diode than in the p-n junction and the metal-semiconductor diodes made of layered materials. The I-V characteristic curve of the MIS diode indicates that current flows mainly across interfaces as a result of carrier tunneling. Moreover, we observed considerably high photocurrent from the MIS diode under visible light illumination.

Semiconductor-Insulator-Semiconductor Diode Consisting of Monolayer MoS2, h-BN, and GaN Heterostructure.

We propose a semiconductor-insulator-semiconductor (SIS) heterojunction diode consisting of monolayer (1-L) MoS2, hexagonal boron nitride (h-BN), and epitaxial p-GaN that can be applied to high-performance nanoscale optoelectronics. The layered materials of 1-L MoS2 and h-BN, grown by chemical vapor deposition, were vertically stacked by a wet-transfer method on a p-GaN layer. The final structure was verified by confocal photoluminescence and Raman spectroscopy. Current-voltage (I-V) measurements were conducted to compare the device performance with that of a more classical p-n structure. In both structures (the p-n and SIS heterojunction diode), clear current-rectifying characteristics were observed. In particular, a current and threshold voltage were obtained for the SIS structure that was higher compared to that of the p-n structure. This indicated that tunneling is the predominant carrier transport mechanism. In addition, the photoresponse of the SIS structure induced by the illumination of visible light was observed by photocurrent measurements.

A Van Der Waals Homojunction: Ideal p-n Diode Behavior in MoSe2.

A MoSe2 p-n diode with a van der Waals homojunction is demonstrated by stacking undoped (n-type) and Nb-doped (p-type) semiconducting MoSe2 synthesized by chemical vapor transport for Nb substitutional doping. The p-n diode reveals an ideality factor of ≈1.0 and a high external quantum efficiency (≈52%), which increases in response to light intensity due to the negligible recombination rate at the clean homojunction interface.