Epitaxial GaN Microdisk Lasers Grown on Graphene Microdots

Direct epitaxial growth of inorganic compound semiconductors on lattice-matched single-crystal substrates has provided an important way to fabricate light sources for various applications including lighting, displays and optical communications. Nevertheless, unconventional substrates such as silicon, amorphous glass, plastics, and metals must be used for emerging optoelectronic applications, such as high-speed photonic circuitry and flexible displays. However, high-quality film growth requires good matching of lattice constants and thermal expansion coefficients between the film and the supporting substrate. This restricts monolithic fabrication of optoelectronic devices on unconventional substrates. Here, we describe methods to grow high-quality gallium nitride (GaN) microdisks on amorphous silicon oxide layers formed on silicon using micropatterned graphene films as a nucleation layer. Highly crystalline GaN microdisks having hexagonal facets were grown on graphene dots with intermediate ZnO nanowalls via epitaxial lateral overgrowth. Furthermore, whispering-gallery-mode lasing from the GaN microdisk with a <i>Q</i>-factor of 1200 was observed at room temperature

Thermoelectric Properties of As-Based Zintl Compounds Ba_1–<i>x</i>K_<i>x</i>Zn₂As₂

As-based Zintl compounds Ba_1–<i>x</i>K_<i>x</i>Zn₂As₂ were prepared by solid-state reaction followed by hot pressing. Ba_1–<i>x</i>K_<i>x</i>Zn₂As₂ (<i>x</i> ≤ 0.02) crystallizes in the α-BaCu₂S₂-type structure (space group <i>Pnma</i>) upon cooling from 900 °C, whereas it crystallizes in the ThCr₂Si₂-type structure (space group <i>I</i>4<i>/mmm</i>) for <i>x</i> ≥ 0.04. The lattice thermal conductivities are almost equivalent for both crystal structures with relatively low values of 0.8–1.1 W/mK at 773 K. The values are comparable to those of Sb-based Zintl compounds, though Ba_1–<i>x</i>K_<i>x</i>Zn₂As₂ consists of As atoms, which are lighter than Sb atoms. The electrical resistivity and Seebeck coefficient decreases with increasing <i>x</i>, indicating successful hole doping by K substitution. The dimensionless figure-of-merit ZT is 0.67 at 900 K for <i>x</i> = 0.02, opening a new class of thermoelectric materials with the As-based 122 Zintl compounds

Normally Off WSe₂ Nanosheet-Based Field-Effect Transistors with Self-Aligned Contact Doping

Despite the advantages of ambipolar semiconductors, high off-currents and narrow off-state bias window limit their application in enhancement-mode field-effect transistors (FETs). We demonstrate the normally off operation of a low-dimensional ambipolar WSe2 semiconductor FET by forming the lateral p–n homojunction. The self-aligned n-doping of the ambipolar WSe2 was obtained by intentionally forming Se vacancy via mild Ar-ion treatment. The UV-ozone-assisted growth of the WOX layer increased the hole concentrations of the WSe2 channel, where its high work function makes the underlying WSe2 electron-deficient. A high on/off ratio of ∼108 and a wide off-range gate bias with the normally off operation were obtained in the n–p–n nanostructured WSe2 FETs, which was also characterized by photocurrent mapping analysis. The electrical characteristics of the devices exhibited their thermal stability up to an operating temperature of 140 °C, which was enabled by the formation of the p–n homojunction barrier. High on/off ratios, wide off-range bias, and decent field-effect carrier mobility of the normally off nanosheet-based WSe2 FET were well maintained at elevated temperatures, which indicates that the low-dimensional ambipolar semiconductor with a junction barrier can play a pivotal role in the next-generation device architecture

Rb(Zn,Cu)₄As₃ as a New High-Efficiency Thermoelectric Material

The thermoelectric performance of RbZn4–xCuxAs3 crystallized in the KCu4S3-type structure was investigated. Samples were synthesized via solid-state reactions, followed by hot pressing. Hole carriers were doped by substituting Zn with Cu until x = 0.02, resulting in an increase of the power factor from 0.049 to 0.52 mW/mK2 at T = 797 K. The lattice thermal conductivity was substantially low, with a value of 1.61 W/mK at T = 312 K, independent of doping. This can be attributed to the large vibration of the Rb atoms, as demonstrated by the neutron diffraction analysis. The maximum dimensionless figure of merit, ZT, was 0.53 at T = 797 K, representing the highest value for the 143-Zintl compounds. The result indicated that the 143-Zintl compounds could be a new class of high-performance thermoelectric materials

Additional file 6 of CrebH protects against liver injury associated with colonic inflammation via modulation of exosomal miRNA

Additional file 6: Figure S4 CrebH protein expression was determined by western blotting using antibody against CrebH. HepG2 cells were transiently transfected with plasmid expressing pcDNA3, CrebH-full form, and CrebH-active form (N-terminal region) and selected by incubation with G418

Band Anisotropy Generates Axis-Dependent Conduction Polarity of Mg₃Sb₂ and Mg₃Bi₂

Materials that exhibit axis-dependent conduction polarity, meaning simultaneous p- and n-type conduction along different crystallographic directions, could be used to develop novel electronic and energy harvesting technologies, such as transverse thermoelectric devices. The present work demonstrates that layered Zintl-phase Mg3Sb2 and Mg3Bi2 possess this property. Single crystals of electron-doped Mg3Sb2 were found to show axis-dependent conduction polarity at low charge carrier concentrations (less than 1 × 1018 cm–3) based on the contribution of holes to conduction in the cross-plane direction. Mg3Bi2 also exhibited this same characteristic but over a wider range of doping with carrier concentrations greater than 1 × 1019 cm–3. This difference was attributed to the semimetallic band structure of Mg3Bi2. First-principles calculations established that axis-dependent conduction polarity appeared in these compounds as a consequence of band anisotropy that arises from the isotropic conduction band minimum and the anisotropic valence band maximum. Specifically, electron bands were primarily responsible for carrier conduction in the in-plane direction, whereas hole bands were dominant in the cross-plane direction. It is evident from these results that 122-type Zintl phases represent a new platform for the exploration of axis-dependent polarity based on band anisotropy engineering

Correlational Effects of the Molecular-Tilt Configuration and the Intermolecular van der Waals Interaction on the Charge Transport in the Molecular Junction

Molecular conformation, intermolecular interaction, and electrode–molecule contacts greatly affect charge transport in molecular junctions and interfacial properties of organic devices by controlling the molecular orbital alignment. Here, we statistically investigated the charge transport in molecular junctions containing self-assembled oligophenylene molecules sandwiched between an Au probe tip and graphene according to various tip-loading forces (<i>F</i>_L) that can control the molecular-tilt configuration and the van der Waals (vdW) interactions. In particular, the molecular junctions exhibited two distinct transport regimes according to the <i>F</i>_L dependence (i.e., <i>F</i>_L-dependent and <i>F</i>_L-independent tunneling regimes). In addition, the charge-injection tunneling barriers at the junction interfaces are differently changed when the <i>F</i>_L ≤ 20 nN. These features are associated to the correlation effects between the asymmetry-coupling factor (η), the molecular-tilt angle (θ), and the repulsive intermolecular vdW force (<i>F</i>_vdW) on the molecular-tunneling barriers. A more-comprehensive understanding of these charge transport properties was thoroughly developed based on the density functional theory calculations in consideration of the molecular-tilt configuration and the repulsive vdW force between molecules

Optoelectronics of Multijunction Heterostructures of Transition Metal Dichalcogenides

Among p–n junction devices with multilayered heterostructures with WSe2 and MoSe2, a device with the MoSe2–WSe2–MoSe2 (NPN) structure showed a remarkably high photoresponse, which was 1000 times higher than the MoSe2–WSe2 (NP) structure. The ideality factor of the NPN structure was estimated to be ∼1, lower than that of the NP structure. It is claimed that the NPN structure formed a thinner depletion region than that of the NP structure because of the difference of carrier concentrations of MoSe2 and WSe2. Hence, the built-in electric field was weaker, and the motion of the photocarriers was facilitated. These behaviors were confirmed experimentally from a photocurrent mapping analysis and Kelvin probe force microscopy. The work function depended on the wavelength of the illuminator, and quasi-Fermi level was estimated. The surface photovoltage on the MoSe2 region was higher than that on WSe2 because the lower bandgap of MoSe2 induces more electron–hole pair generation

Additional file 7 of CrebH protects against liver injury associated with colonic inflammation via modulation of exosomal miRNA

Additional file 7: Table S3 Differently regulated miRNA lists (WC-exo vs. WD-exo)