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

Recovery of the Pristine Surface of Black Phosphorus by Water Rinsing and Its Device Application

Black phosphorus (BP) has attracted significant attention due to its excellent optical and electrical properties. However, the rapid degradation of BP under ambient air limits further research on its properties and implementation in various fields. This degrading behavior lowers the performance of BP-based devices and can even result in a complete failure when exposed to air for an extended period of time. In our research, the degraded surface with “bubbles” was recovered to its pristine state by rinsing with deionized water and following with post-treatments. The formation of bubbles and their optical, morphological, and electrical effects were systematically investigated by fabricating BP field-effect transistors (FETs) in conjunction with micro-Raman spectroscopy and atomic force microscopy. Water rinsing of the degraded BP flakes also allowed us to thin BP flakes down because phosphorus atoms are consumed while forming bubbles. Therefore, recovery of the pristine surface not only results in a smoother and thinner morphology but also improves device performances. After the rinsing process, field-effect mobility of the BP FET was maintained, whereas a significant enhancement in the switching behaviors was achieved in conclusion. The capability of reversing the inevitable degradation that occurs once exposed to ambient conditions can open up new opportunities for further applications of BP that was limited due to its instability

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

Highly Efficient Copper–Indium–Selenide Quantum Dot Solar Cells: Suppression of Carrier Recombination by Controlled ZnS Overlayers

Copper–indium–selenide (CISe) quantum dots (QDs) are a promising alternative to the toxic cadmium- and lead-chalcogenide QDs generally used in photovoltaics due to their low toxicity, narrow band gap, and high absorption coefficient. Here, we demonstrate that the photovoltaic performance of CISe QD-sensitized solar cells (QDSCs) can be greatly enhanced simply by optimizing the thickness of ZnS overlayers on the QD-sensitized TiO₂ electrodes. By roughly doubling the thickness of the overlayers compared to the conventional one, conversion efficiency is enhanced by about 40%. Impedance studies reveal that the thick ZnS overlayers do not affect the energetic characteristics of the photoanode, yet enhance the kinetic characteristics, leading to more efficient photovoltaic performance. In particular, both interfacial electron recombination with the electrolyte and nonradiative recombination associated with QDs are significantly reduced. As a result, our best cell yields a conversion efficiency of 8.10% under standard solar illumination, a record high for heavy metal-free QD solar cells to date

Patterning Superatom Dopants on Transition Metal Dichalcogenides

This study describes a new and simple approach to dope two-dimensional transition metal dichalcogenides (TMDCs) using the superatom Co₆Se₈(PEt₃)₆ as the electron dopant. Semiconducting TMDCs are wired into field-effect transistor devices and then immersed into a solution of these superatoms. The degree of doping is determined by the concentration of the superatoms in solution and by the length of time the films are immersed in the dopant solution. Using this chemical approach, we are able to turn mono- and few-layer MoS₂ samples from moderately to heavily electron-doped states. The same approach applied on WSe₂ films changes their characteristics from hole transporting to electron transporting. Moreover, we show that the superatom doping can be patterned on specific areas of TMDC films. To illustrate the power of this technique, we demonstrate the fabrication of a lateral p–n junction by selectively doping only a portion of the channel in a WSe₂ device. Finally, encapsulation of the doped films with crystalline hydrocarbon layers stabilizes their properties in an ambient environment

Associations between the haplotypes of two non-synonymous SNPs of <i>PON1</i> and the risk of lung cancer, according to smoking status

<p>^aAdjusted for age, sex, smoking status, and occupational history.</p><p>^bAdjusted for age, sex, and occupational history.</p><p>Associations between the haplotypes of two non-synonymous SNPs of <i>PON1</i> and the risk of lung cancer, according to smoking status</p

Interactions between <i>Paraoxonase 1</i> Genetic Polymorphisms and Smoking and Their Effects on Oxidative Stress and Lung Cancer Risk in a Korean Population

<div><p>Background</p><p>Few studies in epidemiology have evaluated the effects of gene-environment interaction on oxidative stress, even though this interaction is an important etiologic factor in lung carcinogenesis. We investigated the effects of the genetic polymorphisms of paraoxonase 1 (PON1), smoking, and the interaction between the two on lung cancer risk and oxidative stress.</p><p>Methods</p><p>This study’s subjects consisted of 416 newly diagnosed lung cancer patients and an equal number of matched controls. The GoldenGate assay was used for genotypic analyses of the <i>PON1</i> gene. Urinary 8-hydroxydeoxyguanosine (8-OHdG) and thiobarbituric acid reactive substances levels were measured as indicators of oxidative stress.</p><p>Results</p><p>The <i>PON1</i> rs662 AA genotype showed a significantly lower risk of lung cancer than the GG genotype (OR = 0.60, 95% CI: 0.36–0.99). The protective effect of the <i>PON1</i> rs662 AA genotype on lung cancer risk was limited to non-smokers. Lung cancer patients who had the rs662 A allele showed a dose-dependent association between smoking status and oxidative stress markers. Among non-smoking lung cancer patients, urinary 8-OHdG levels were significantly lower in individuals with the rs662 GA and AA genotypes than in those with the GG genotype. Furthermore, we found a significant interaction effect between <i>PON1</i> rs662 and smoking status on urinary 8-OHdG levels in lung cancer patients.</p><p>Conclusions</p><p>Our results suggest that the protective effect of <i>PON1</i> rs662 SNP against lung carcinogenesis and the induction of oxidative stress might be modulated by the interaction between <i>PON1</i> genetic polymorphisms and tobacco smoking.</p></div

General characteristics of lung cancer cases and controls.

<p>TBARS: thiobarbituric acid reactive substances; 8-OHdG: 8-hydroxydeoxyguanosine; GM: geometric mean; CI: confidence intervals.</p><p>^aAdjusted for age and sex.</p><p>^bAdjusted for age, sex and smoking status.</p><p>^cIndividuals who have work experience in occupations related lung cancer risk, such as petrochemicals, construction, mining, asbestos or rockwool production, welding, electrical manufacture, plastic or rubber manufacture, smelting, and asphalt.</p><p>^dReference category is all other occupations.</p><p>General characteristics of lung cancer cases and controls.</p

Geometric means and 95% confidence intervals for urinary oxidative stress markers (A: 8-hydroxydeoxyguanosine, B: thiobarbituric acid reactive substances) according to smoking status and <i>PON1</i> rs662 SNP in lung cancer patients and controls.

<p>*Significant difference between the genotypes in non-smokers (P = 0.017), ** Significant interaction (SNP×smoking)(P = 0.025).</p