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AIMP2 interacts with the DIX domain of DVL and modulate Wnt/β-catenin signaling in an Aimp2 gene dosage dependent manner

Wnt/β-catenin (CTNNB1) signaling is crucial for the proliferation and maintenance of intestinal stem cells (ISC), but excessive activation leads to ISC expansion and eventually colorectal cancer. Thus, negative regulators are required to maintain optimal levels of Wnt/β-catenin signaling. Aminoacyl-tRNA synthetase–interacting multifunctional proteins (AIMP) function in protein synthesis, but have also been implicated in signaling cascades affecting angiogenesis, immunity, and apoptosis. In this study, we investigated the relationship between AIMP2 and Wnt/β-catenin signaling in a murine model of intestinal homeostasis and tumorigenesis. Hemizygous deletion of Aimp2 resulted in enhanced Wnt/β-catenin signaling, increased proliferation of cryptic epithelial cells, and expansion of ISC compartments. In an ApcMin/+ background, Aimp2 hemizygosity increased adenoma formation. Mechanistically, AIMP2 disrupted the interaction between AXIN and Dishevelled-1 (DVL1) to inhibit Wnt/β-catenin signaling by competing with AXIN. Furthermore, AIMP2 inhibited intestinal organoid formation and growth by suppressing Wnt/β-catenin signaling in an Aimp2 gene dosage-dependent manner. Collectively, our results showed that AIMP2 acts as a haploinsufficient tumor suppressor that fine-tunes Wnt/β-catenin signaling in the intestine, illuminating the regulation of ISC abundance and activity. Cancer Res; 76(15); 4559–68. ©2016 AACR.

The role of AIMP2 in intestinal Wnt signaling is dependent on β-catenin destruction complex.

Analysis of polyposis and tumor initiation in Aimp2+/-:ApcMin/+ intestine

Supplemental Materials and Methods and Supplemental figure legends

Aimp2 gene dosage negatively correlates with organoid growth

Aimp2+/- mice exhibit increased villi length, crypt depth, and colonic epithelial cell proliferation

Cell–material interactions are regulated by mimicking bone extracellular matrix on the surface of biomaterials. In this regard, reproducing the extracellular conditions that promote integrin and growth factor (GF) signaling is a major goal to trigger bone regeneration. Thus, the use of synthetic osteogenic domains derived from bone morphogenetic protein 2 (BMP-2) is gaining increasing attention, as this strategy is devoid of the clinical risks associated with this molecule. In this work, the wrist and knuckle epitopes of BMP-2 are screened to identify peptides with potential osteogenic properties. The most active sequences (the DWIVA motif and its cyclic version) are combined with the cell adhesive RGD peptide (linear and cyclic variants), to produce tailor-made biomimetic peptides presenting the bioactive cues in a chemically and geometrically defined manner. Such multifunctional peptides are next used to functionalize titanium surfaces. Biological characterization with mesenchymal stem cells demonstrates the ability of the biointerfaces to synergistically enhance cell adhesion and osteogenic differentiation. Furthermore, in vivo studies in rat calvarial defects prove the capacity of the biomimetic coatings to improve new bone formation and reduce fibrous tissue thickness. These results highlight the potential of mimicking integrin-GF signaling with synthetic peptides, without the need for exogenous GFs.

Background With organismal aging, the hypothalamic–pituitary–gonadal (HPG) activity gradually decreases, resulting in the systemic functional declines of the target tissues including skeletal muscles. Although the HPG axis plays an important role in health span, how the HPG axis systemically prevents functional aging is largely unknown. Methods We generated muscle stem cell (MuSC)‐specific androgen receptor (Ar) and oestrogen receptor 2 (Esr2) double knockout (dKO) mice and pharmacologically inhibited (Antide) the HPG axis to mimic decreased serum levels of sex steroid hormones in aged mice. After short‐term and long‐term sex hormone signalling ablation, the MuSCs were functionally analysed, and their aging phenotypes were compared with those of geriatric mice (30‐month‐old). To investigate pathways associated with sex hormone signalling disruption, RNA sequencing and bioinformatic analyses were performed. Results Disrupting the HPG axis results in impaired muscle regeneration [wild‐type (WT) vs. dKO, P

Myogenic progenitors (MPs) generate myocytes that fuse to form myofibers during skeletal muscle development while maintaining the progenitor pool, which is crucial for generating sufficient muscle. Notch signaling has been known to reserve a population of embryonic MPs during primary myogenesis by promoting cell cycle exit and suppressing premature differentiation. However, the roles of individual Notch receptors (Notch1-4) during embryonic/fetal myogenesis are still elusive. In this study, we found that Notch1 and Notch2, which exhibit the highest structural similarity among Notch receptors, maintain the MP population by distinct mechanisms: Notch1 induces cell cycle exit and Notch2 suppresses premature differentiation. Moreover, genetic and cell culture studies showed that Notch1 and Notch2 signaling in MPs are distinctively activated by interacting with Notch ligand-expressing myofibers and MP-lineage cells, respectively. These results suggest that through different activation modes, Notch1 and Notch2 distinctively and cooperatively maintain MP population during fetal myogenesis for proper muscle development.

Age-associated muscle atrophy is a debilitating condition associated with loss of muscle mass and function with age that contributes to limitation of mobility and locomotion. However, the underlying mechanisms of how intrinsic muscle changes with age are largely unknown. Here we report that, with age, Mind bomb-1 (Mib1) plays important role in skeletal muscle maintenance via proteasomal degradation-dependent regulation of α-actinin 3 (Actn3). The disruption of Mib1 in myofibers (Mib1ΔMF) results in alteration of type 2 glycolytic myofibers, muscle atrophy, impaired muscle function, and Actn3 accumulation. After chronic exercise, Mib1ΔMF mice show muscle atrophy even at young age. However, when Actn3 level is downregulated, chronic exercise-induced muscle atrophy is ameliorated. Importantly, the Mib1 and Actn3 levels show clinical relevance in human skeletal muscles accompanied by decrease in skeletal muscle function with age. Together, these findings reveal the significance of the Mib1-Actn3 axis in skeletal muscle maintenance with age and suggest the therapeutic potential for the treatment or amelioration of age-related muscle atrophy., Muscle atrophy is associated with ageing, but the underlying molecular mechanisms are not well understood. Here, they authors show that ablation of the E3 ubiquitin ligase Mib1 is important for myofibre maintenance via a mechanism that involves targeting and degradation of Actn3, and that Mib1 ablation in mice induces muscle atrophy which can be rescued by knockown of Actn3 expression.

GaN gate-all-around (GAA) vertical nanowire MOSFET (VNWMOSFET) with channel length of 300 nm and diameter of 120 nm, the narrowest GaN-based vertical nanowire transistor ever achieved from the top-down approach, was fabricated by utilizing anisotropic side-wall wet etching in TMAH solution and photoresist etch-back process. The VNWMOSFET exhibited output characteristics with very low saturation drain voltage of less than 0.5 V, which is hardly observed from the wide bandgap-based devices. Simulation results indicated that the narrow diameter of the VNWMOSFET with relatively short channel length is responsible for the low voltage operation. The VNWMOSFET also demonstrated normally-off mode with threshold voltage (VTH) of 0.7 V, extremely low leakage current of ∼10−14 A, low drain-induced barrier lowering (DIBL) of 125 mV/V, and subthreshold swing (SS) of 66–122 mV/decade. The GaN GAA VNWMOSFET with narrow channel diameter investigated in this work would be promising for new low voltage logic application.

Wnt/β-catenin (CTNNB1) signaling is crucial for the proliferation and maintenance of intestinal stem cells (ISC), but excessive activation leads to ISC expansion and eventually colorectal cancer. Thus, negative regulators are required to maintain optimal levels of Wnt/β-catenin signaling. Aminoacyl-tRNA synthetase–interacting multifunctional proteins (AIMP) function in protein synthesis, but have also been implicated in signaling cascades affecting angiogenesis, immunity, and apoptosis. In this study, we investigated the relationship between AIMP2 and Wnt/β-catenin signaling in a murine model of intestinal homeostasis and tumorigenesis. Hemizygous deletion of Aimp2 resulted in enhanced Wnt/β-catenin signaling, increased proliferation of cryptic epithelial cells, and expansion of ISC compartments. In an ApcMin/+ background, Aimp2 hemizygosity increased adenoma formation. Mechanistically, AIMP2 disrupted the interaction between AXIN and Dishevelled-1 (DVL1) to inhibit Wnt/β-catenin signaling by competing with AXIN. Furthermore, AIMP2 inhibited intestinal organoid formation and growth by suppressing Wnt/β-catenin signaling in an Aimp2 gene dosage-dependent manner. Collectively, our results showed that AIMP2 acts as a haploinsufficient tumor suppressor that fine-tunes Wnt/β-catenin signaling in the intestine, illuminating the regulation of ISC abundance and activity. Cancer Res; 76(15); 4559–68. ©2016 AACR.

Superior device characteristics have been demonstrated with a novel Al(In)N/GaN-based steep fin-type high electron mobility transistor (HEMT) with a fin width ( $W_{\mathrm{ fin}}$ ) of 120 nm, a fin height ( $H_{\mathrm{ fin}})$ of 250 nm, and a gate length ( $L_{G}$ ) of 200 nm. The proposed device achieved very low drain leakage ( $I_{\mathrm{ off}}) A/mm at 7 V and $ A/mm at 100 V, which is four orders of improvement over $I_{\mathrm{\scriptscriptstyle OFF}}$ of conventional Al(In)N/GaN HEMTs. In addition, the device exhibits a high ON-state current ( $I_{\mathrm{\scriptscriptstyle ON}})$ of 1.12 A/mm, a steep sub-threshold swing ( $S$ ) of 63 mV/decade, a low drain-induced barrier lowering of 18.5 mV/V, and a high power-gain cutoff frequency ( $f_{T}$ ) of 21 GHz.

The initially dry-etched GaN layer with trapezoidal cross-section was laterally etched along the 〈11 2 ¯ 0〉 direction in the tetramethyl ammonium hydroxide (TMAH) solution to form a sidewall normal to the direction, which is corresponding to the (11 2 ¯ 0) plane. On the other hand, the etched sidewall still maintains the trapezoidal shape with angle of 58.4° when etched along the 〈1 1 ¯ 00〉 direction, which is corresponding to the (1 1 ¯ 01) plane. The GaN lateral nanowires with two different types of cross-sections, Ω-shape which is connected to underlying thick buffer layer through very narrow neck region and rectangle shape which is completely separated from underlying buffer layer, were realized with second lateral TMAH wet etching along the 〈11 2 ¯ 0〉 direction and by using the atomic layer deposited (ALD) HfO 2 layer as a sidewall spacer. The shape is dependent on both the height of the second dry-etched GaN sidewall below the HfO 2 spacer and the second wet etching time in TMAH solution. It was found that the dangling bond density at the surface of the crystal plane is responsible for the strong lateral anisotropic etching property of the GaN layer in TMAH solution.

International audience; Normally-off AlGaN/GaN-based MOS-HEMT has been fabricated by utilizing damage-free self-terminating tetramethyl ammonium hydroxide (TMAH) recess etching. The device exhibited a threshold voltage of +2.0 V with good uniformity, extremely small hysteresis of ∼20 mV, and maximum drain current of 210 mA/mm. The device also exhibited excellent off-state performances, such as breakdown voltage of ∼800 V with off-state leakage current as low as ∼10−12 A and high on/off current ratio (Ion/Ioff) of 1010. These excellent device performances are believed to be due to the high quality recessed surface, provided by the simple self-terminating TMAH etching. Previous article in issue

We have grown AlN/GaN heterostructure which is a promising candidate for mm-wave applications. For the growth of the high quality very thin AlN barrier, indium was introduced as a surfactant at the growth temperature varied from 750 to 1070 ℃, which results in improving electrical properties of two-dimensional electron gas (2DEG). The heterostructure with barrier thickness of 7 ㎚ grown at of 800 ℃ exhibited best Hall measurement results; such as sheet resistance of 215 Ω/□, electron mobility of 1430 ㎠/V·s, and two-dimensional electron gas (2DEG) density of 2.04 ｘ 10 13 /㎠. The high electron mobility transistor (HEMT) was fabricated on the grown heterostructure. The device with gate length of 0.2 ㎛ exhibited excellent DC and RF performances; such as maximum drain current of 937 ㎃/㎜, maximum transconductance of 269 mS/㎜, current gain cut-off frequency of 40 ㎓, and maximum oscillation frequency of 80 ㎓.

In this paper, we have characterized the electrical properties related to gate leakage current in AlGaN/GaN MISHFETs with varying the thickness (0 to 10 nm) of Al₂O₃ gate insulator which also serves as a surface protection layer during high-temperature RTP. The sheet resistance of the unprotected TLM pattern after RTP was rapidly increased to 1323 Ω/□ from the value of 400 Ω/□ of the as-grown sample due to thermal damage during high temperature RTP. On the other hand, the sheet resistances of the TLM pattern protected with thin Al₂O₃ layer (when its thickness is larger than 5 nm) were slightly decreased after high-temperature RTP since the deposited Al₂O₃ layer effectively neutralizes the acceptor-like states on the surface of AlGaN layer which in turn increases the 2DEG density. AlGaN/GaN MISHFET with 8 nmthick Al₂O₃ gate insulator exhibited extremely low gate leakage current of 10 -9 A/mm, which led to superior device performances such as a very low subthreshold swing (SS) of 80 mV/dec and high Ion/Ioff ratio of ~ 1010. The PF emission and FN tunneling models were used to characterize the gate leakage currents of the devices. The device with 5 nm-thick Al₂O₃ layer exhibited both PF emission and FN tunneling at relatively lower gate voltages compared to that with 8 nm-thick Al₂O₃ layer due to thinner Al₂O₃ layer, as expected. The device with 10 nm-thick Al₂O₃ layer, however, showed very high gate leakage current of 5.5 ×10 -4 A/mm due to poly-crystallization of the Al₂O₃ layer during the high-temperature RTP, which led to very poor performances.

In this work, we have investigated a role of a thin Al 2 O 3 layer in AlGaN/GaN MISHFET by characterizing the variation of the sheet resistance of the 2DEG channel layer. The Al 2 O 3 layer, varying the thickness from 0 to 10 nm, was utilized as the gate insulator of the device as well as the surface protection layer during RTP for ohmic contact formation. After RTP, the 2DEG channel layer without the Al 2 O 3 layer was rapidly degraded by increasing the sheet resistance of the layer to 1360 Ω/□ from the sheet resistance of 400 Ω/□ of the as-grown sample. The degradation was still observed even when 1.5 nm-thick Al 2 O 3 layer was used. However, the sheet resistances of the devices remained constant with slightly decreased value from that of the as-grown sample when the thickness is larger than 3 nm, which indicates that the 3 nm-thick Al 2 O 3 layer well protects the AlGaN surface above the 2DEG channel during RTP. The slight decrease in sheet resistance is probably because some acceptor-like states existing at AlGaN surface become neutralized and hence the 2DEG density increases. The Al 2 O 3 layer was not removed for proceeding the fabrication of AlGaN/GaN MISHFET, but rather used as a gate dielectric, which simplifies the device fabrication eliminating the additional deposition steps for the gate dielectric. The threshold voltage of the device, investigated in this work, was increased to the negative direction with increasing the thickness of Al 2 O 3 layers while the transconductance was decreased. The best performances were obtained from the device with 8 nm-thick Al 2 O 3 layer, exhibiting very low gate leakage current of 10 −9 A/mm with subthreshold swing (SS) of 80 mV/dec and very high I on / I off ratio (>9 orders).

AlGaN/GaN-based fin-shaped field-effect transistors with very steep side-wall have been fabricated by utilizing electron-beam lithography and subsequent anisotropic side-wall wet etch in tetramethyl ammonium hydroxide solution. The investigate device demonstrated extremely broad transconductance ( $g_{m})$ ranging from $\sim 0$ to $\sim 8$ V at $V_{D} = 10$ V, which is essential for high linearity device performance. Pulse measurement showed that the device exhibits negligible gate lag, but still suffers from drain lag. The device with $L_{\mathrm {GD}}$ of $17~\mu \text{m}$ exhibited excellent OFF-state characteristic with subthreshold swing of $\sim 58$ mV/decade, low OFF-state leakage current of $\sim 10^{-12}$ A, and breakdown voltage of $\sim 400$ V at $V_{G}=- 9$ V.

Normally off Al 2 O 3 /GaN MOSFETs are fabricated with a tetramethylammonium hydroxide (TMAH) treatment as a postgate recess etch. The effects of the surface treatment on the etched GaN surface are investigated using low-frequency (1/f ) noise and capacitance-voltage (C-V) measurements. For a quantitative comparison with conventional devices, the oxide trap density (N ot ) is extracted using the unified 1/f noise model, whereas the interface trap density (D it ) is extracted using the high-low-frequency C-V method. After the TMAH treatment, N ot is found to have decreased from 5.40 × 10 19 to 2.50 × 10 19 eV -1 cm -3 , whereas D it is decreased from 2.8 × 10 12 to 1.1 × 10 11 eV -1 cm -2 , as compared with conventional devices. The surface treatment is thus shown to lower trap density in the Al 2 O 3 /GaN MOSFETs by smoothing the surface and suppressing plasma damage in the recessed GaN surfaces.

International audience; The AlGaN/GaN nanowire omega-shaped-gate FinFET have been successfully fabricated demonstrating much improved performance compared to conventional AlGaN/GaN MISHFET. The AlGaN/GaN omega-shaped-gate FinFET exhibited the remarkable on-state performances, such as maximum drain current of 1.1 A/mm, low on-resistance, and low current collapse compared to that of the conventional device structure. In addition, the excellent off-state performances were measured: low off-state leakage current as low as ∼10−10 mA, the theoretical SS value of ∼62 mV/dec, and high I ON /I OFF ratio (∼109). Improved dc performances were obtained for omega-shaped-gate structure due to the fully depletion of the active fin body and perfectly separation of the depleted fin from the underlying thick GaN buffer layer. Furthermore, the additional reason for the enhanced device performance of the proposed device is the improved gate controllability compared to the conventional MISHFET. The proposed nano-structure device is very promising candidate for the steep switching device applications.

Grain boundaries in graphene are formed by the joining of islands during the initial growth stage, and these boundaries govern transport properties and related device performance. Although information on the atomic rearrangement at graphene grain boundaries can be obtained using transmission electron microscopy and scanning tunnelling microscopy, large-scale information regarding the distribution of graphene grain boundaries is not easily accessible. Here we use optical microscopy to observe the grain boundaries of large-area graphene (grown on copper foil) directly, without transfer of the graphene. This imaging technique was realized by selectively oxidizing the underlying copper foil through graphene grain boundaries functionalized with O and OH radicals generated by ultraviolet irradiation under moisture-rich ambient conditions: selective diffusion of oxygen radicals through OH-functionalized defect sites was demonstrated by density functional calculations. The sheet resistance of large-area graphene decreased as the graphene grain sizes increased, but no strong correlation with the grain size of the copper was revealed, in contrast to a previous report. Furthermore, the influence of graphene grain boundaries on crack propagation (initialized by bending) and termination was clearly visualized using our technique. Our approach can be used as a simple protocol for evaluating the grain boundaries of other two-dimensional layered structures, such as boron nitride and exfoliated clays.

In spite of recent successful demonstrations of flexible and transparent graphene heaters, the underlying heat-transfer mechanism is not understood due to the complexity of the heating system. Here, graphene/glass defoggers are fabricated and the dynamic response of the temperature as a function of input electrical power is measured. The graphene/glass defoggers reveal shorter response times than Cr/glass defoggers. Furthermore, the saturated temperature of the graphene/glass defoggers is higher than for Cr/glass defoggers at a given input electrical power. The observed dynamic response to temperature is well-fitted to the power-balance model. The response time of graphene/glass defogger is shorter by 44% than that of the Cr/glass defogger. The convective heat-transfer coefficient of graphene is 12.4 × 10−4 W cm−2 °C−1, similar to that of glass (11.1 × 10−4 W cm−2 °C−1) but smaller than that of chromium (17.1 × 10−4 W cm−2 °C−1). The graphene-based system reveals the lowest convective heat-transfer coefficient due to its ideal flat surface compared to its counterparts of carbon nanotubes (CNTs) and reduced graphene oxide (RGO)-based systems.

A physical route is proposed to obtain highly crystalline graphene sheets with minimal oxygen content similar to the precursor graphite. The functional graphene sheets obtained from graphite oxide by low temperature thermal exfoliation are annealed at high temperature (1900 degrees C) in a vacuum (10(-6) torr). The D band intensity in Raman spectroscopy is reduced significantly, while the G band intensity is recovered, similar to the level of precursor graphite. No appreciable oxygen content is observed from X-ray photoelectron spectroscopy and an electrical conductivity of similar to 56 500 S m(-1) is obtained, comparable to 100 900 S m(-1) of the precursor graphite.

Use of random network carbon nanotube (CNT) transistors and their applications to complementary logic gates have been limited by several factors such as control of CNT density, existence of metallic CNTs producing a poor yield of devices, absence of stable n-dopant and control of precise position of the dopant, and absence of a scalable and cost-effective fabrication process. Here, we report a scalable and cost-effective fabrication of complementary logic gates by precisely positioning an air-stable n-type dopant, viologen, by inkjet printing on a separated semiconducting CNTs network. The obtained CNT transistors showed a high yield of nearly 100% with an on/off ratio of greater than 10(3) in an optimized channel length (∼9 μm). The n-doped semiconducting carbon nanotube transistors showed a nearly symmetric behavior in the on/off current and threshold voltage with p-type transistors. CMOS inverter, NAND, and NOR logic gates were integrated on a HfO2/Si substrate using the n/p transistor arrays. The gain of inverter is extraordinarily high, which is around 45, and NAND and NOR logic gates revealed excellent output on and off voltages. These series of whole processes were conducted under ambient conditions, which can be used for large-area and flexible thin film technology.

A vertical-type mesa-gate GaN metal–oxide semiconductor field-effect transistor (MOSFET) has been fabricated. The mesa-gate structure can be easily achieved by a single deep etch to the n+-GaN which is the drain of the device, whereas the trench-gate structure, the commonly used structure for the vertical-type MOSFETs, requires an additional etching process to define the gate region. The mesa-gate GaN MOSFET exhibited a normally-off operation with the threshold voltage of 3 V, a normalised drain current of ∼ 55 mA/mm and a high on/off current ratio of 108.

Display Omitted Subthreshold slope of wide fin is lower than 60mV/dec.Subthreshold slope of narrow fin is higher than 200mV/dec.Wide fin exhibit severe hysteresis of threshold voltage.Narrow fin exhibit negligible hysteresis of threshold voltage.Trapping effect from sidewall is correlated to the fin width. AlGaN/GaN FinFETs with various fin widths (Wfin), which have both a 2DEG channel and two sidewall MOS channels, have been fabricated by using electron-beam lithography and subsequent sidewall wet etch in tetramethyl ammonium hydroxide (TMAH) solution. The devices with wide Wfin of 150nm showed normally-on operation with threshold voltage (Vth) of -2.5 and -5.0V, respectively. The devices also exhibited broad transconductance (gm), and excellent off-state performance with very low subthreshold swing (SS). On the other hand, narrow device with Wfin of 50nm exhibited normally-off operation with Vth of 3.0V, but degraded SS due to trapping effect at the sidewall of fin.

International audience; An AlGaN/GaN-based Ω-shaped nanowire fin-shaped FET (FinFET) with a fin width of 50 nm was fabricated using tetramethylammonium hydroxide (TMAH)-based lateral wet etching. An atomic layer deposited (ALD) HfO2 side-wall layer served as the etching mask. ALD Al2O3 and TiN layers were used as the gate dielectric and gate metal, respectively. The Ω-shaped gate structure fully depletes the active fin body and almost completely separates the depleted fin from the underlying thick GaN buffer layer, resulting in superior device performance. The top-down processing proposed in this work provides a viable pathway towards gate-all-around devices for III–nitride semiconductors.

GaN-based field effect transistors (FETs) are widely used in power switching and amplifier application due to its superior material properties such as wide band-gap energy, high breakdown field, and high electron saturation velocity, which results in high output current and high breakdown voltage [1]. On the other hand, nanowire transistors are extensively investigated to improve device performance such as fin-shaped FETs (FinFETs), lateral and vertical type nanowire FETs [2 – 4]. Especially, vertical nanowire FETs (VNFETs) are currently being evaluated as a promising device technology due to its negligible trapping and leakage from the buffer layer, wrap-gated structure and possibility of very short gate length (below 20 nm). VNFETs using Si, InAs and InGaAs materials were already introduced. However, GaN-based VNFETs have been never fabricated due to difficulty in obtaining vertical nanowire structure with high aspect ratio and their complex fabrication process. In this work, we fabricated the GaN-based VNFET, for the first time, by combining conventional e-beam lithography and dry etching technique with strong anisotropic TMAH wet etching.

Vertical-channel gallium nitride (GaN) junctionless nanowire transistor (JNT) has been designed and characterized by technology computer-aided design (TCAD) simulations. Various characteristics such as wide bandgap, strong polariztion field, and high electron velocity make GaN one of the attractive materials in advanced electronics in recent times. Nanowire-structured GaN can be applicable to various transistors for enhanced electrical performances by its geometrical feature. In this paper, we analyze the direct-current (DC) characteristics depending on various channel doping concentrations (N(ch)) and nanowire radii (R(NW)). Furthermore, the radio-frequency (RF) characteristics under optimized conditions are extracted by small-signal equivalent circuit modeling. For the optimally designed vertical GaN JNT demonstrated on-state current (I(on)) of 345 μA/μm and off-state current (I(off)) of 3.7 x 10(-18) A/μm with a threshold voltage (V(t)) of 0.22 V, and subthreshold swing (S) of 68 mV/dec. Besides, f(T) and f(max) under different operating conditions (gate voltage, V(GS)) have been obtained.

Heavily doped GaN nanochannel fin-shaped field-effect transistors (FinFETs) without heterojunction have been fabricated and characterized for the first time. Simplified pragmatical technology for GaN epitaxial growth and FinFET process was used to achieve nanodevices with a channel width from 40 to 100 nm and a gate length of 1 μm. They exhibit excellent on-state performance, such as maximum drain current of 670 mA/mm and maximum transconductance of 168 mS/mm. Record off-state performance was measured: extremely low leakage current of ~ 10-11 mA and source-drain breakdown voltage of ~280 V. The subthreshold slope of 68 mV/decade is close to the theoretical limit (60 mV/decade, so far achieved only in SOI MOSFETs) and leads to very high Ion/Ioff ratio of 108 - 109. The proposed heterojunction-free nanochannel GaN FinFET is a very promising candidate not only for high-performance and high-speed integrated circuits but also for high-power applications.

Two types of fin-shaped field-effect transistors (FinFETs), one with AlGaN/GaN heterojunction and the other with heavily doped heterojunction-free GaN layer operating in junctionless mode, have been fabricated and characterized. The threshold voltages of both devices shift toward positive direction from large negative value as the fin width decreases. Both devices exhibit high ON-state performance. The heterojunction-free GaN FinFETs show superior OFF-state performance because the current flows through the volume of the GaN channel layer, which can be fully depleted. The proposed GaN nanochannel FinFETs are very promising candidates not only for high performance, but also for high power applications.

Heavily doped GaN nanochannel FinFET has been proposed and fabricated, for the first time, which does not have any p-n junction or heterojunction. In spite of its easy and simple epitaxial growth and fabrication process, the fabricated device with nanochannel width of 80 nm and gate length of 1 μm exhibited excellent off-state performances such as extremely low off-state leakage current of ~ 10-11 mA with BV of ~ 300 V and subthreshold slope of 68 mV/decade, very close to the theoretically limited value, which leads to high Ion/Ioff ratio of 107 ~ 109. The device also exhibited high on-state performances such as maximum drain current of 562 mA/mm and maximum transconductance of 138 mS/mm. The proposed nanochannel GaN FinFET can be very promising candidate not only for high performance, but also high power applications.

We have investigated the channel mobility in the gated region of a set of high-quality AlGaN/GaN high-electron-mobility transistors (HEMTs). The resistances in the contact, access, and gated regions were extracted from straightforward I D(V G) measurements on sets of HEMTs with four different gate-to-drain distances. By correcting for the effects of the contact and access resistances, much more accurate effective mobility curves in the gated region, compared to those reported in the past, have been obtained. The maximum effective mobility in that region has been found to be 1100 cm2 V−1 s−1 at carrier density n s = 7 × 1012 cm−2 at room temperature. We have extracted the mobility curves in a wide range of temperatures (80 to 520 K) and carrier concentrations (up to 1.3 × 1013 cm−2). Our systematic measurements have revealed various dominant scattering mechanisms as the temperature and carrier concentration change.

The current-voltage (I–V) characteristics of Au/polyvinyl alcohol (PVA)/n-InP Schottky diode have been measured at temperature range 175–425 K. It is found that the series resistance (R S ) values of Au/PVA/n-InP Schottky diode estimated from Cheung's and Norde's methods, are strongly temperature dependent. The values of barrier height and R S have very different especially towards to the lower temperatures. This is attributed to non-ideal I–V characteristics of the MIS structure and non-pure thermionic emission (TE) mechanism due to the low temperature effects.

The doping/dedoping mechanism of carbon nanotubes (CNTs) with AuCl(3) has been investigated with regard to the roles of cations and anions. Contrary to the general belief that CNTs are p-doped through the reduction of cationic Au(3+) to Au(0), we observed that chlorine anions play a more important role than Au cations in doping. To estimate the effects of Cl and Au on CNTs, the CNT film was dedoped as a function of the annealing temperature (100-700 °C) under an Ar ambient and was confirmed by the sheet resistance change and the presence of a G-band in the Raman spectra. The X-ray photoelectron spectroscopy (XPS) analysis revealed that the doping level of the CNT film was strongly related to the amount of adsorbed chlorine atoms. Annealing at temperatures up to 200 °C did not change the amount of adsorbed Cl atoms on the CNTs, and the CNT film was stable under ambient conditions. Alternatively, Cl atoms started to dissociate from CNTs at 300 °C, and the stability of the film was degraded. Furthermore, the change in the amount of Cl atoms in CNTs was inversely proportional to the change in the sheet resistance. Our observations of the Cl adsorption, either directly or mediated by an Au precursor on the CNT surface, are congruent with the previous theoretical prediction.

We propose bis(trifluoromethanesulfonyl)imide [(CF(3)SO(2))(2)N](-) (TFSI) as a transparent strong electron-withdrawing p-type dopant in carbon nanotubes (CNTs). The conventional p-dopant, AuCl(3), has several drawbacks, such as hygroscopic effect, formation of Au clusters, decrease in transmittance, and high cost in spite of the significant increase in conductivity. TFSI is converted from bis(trifluoromethanesulfonyl)amine (TFSA) by accepting electrons from CNTs, subsequently losing a proton as a characteristic of a Brønsted acid, and has an inductive effect from atoms with high electronegativity, such as halogen, oxygen, and nitrogen. TFSI produced a similar improvement in conductivity to AuCl(3), while maintaining high thermal stability, and no appreciable change in transmittance with no cluster formation. The effectiveness of TFSI was compared with that of other derivatives.

A flexible transparent electrically conductive film (FTCF) was formed on a poly(ethylene terephthalate) film by spraying single-walled carbon nanotubes dispersed with sodium dodecyl benzene sulfonate in water and, to improve the electrical conductivity of FTCF, the effect on plasma treatment followed by nitric acid treatment was investigated. The Ar plasma treatment was effective in dissociating the surfactant and removing impurities attached to the surface of the carbon nanotubes (CNTs). Therefore, through a cyclic treatment composed of an Ar plasma treatment and nitric acid treatment, more effective removal of surfactant and impurities attached to the spray-coated CNTs could be obtained than a cyclic treatment without the plasma treatment. With the optimized cyclic treatment, the sheet resistance (Ωs) of the spray-coated CNTs could be decreased up to 45% by removing most of the surfactant and impurities. Using the repeated cyclic treatment, the FTCF having the Ωs of 160 Ω/□ at 81.5% optical transmittance at the wavelength of 550 nm could be obtained.