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CO and H2 activation over g-ZnO layers and w-ZnO(0001)
摘要： Graphene-like ZnO (g-ZnO) nanostructures (NSs) and thin films were prepared on Au(111) and their reactivities towards CO and H2 were compared with that of wurtzite ZnO (w-ZnO) (0001) single crystal. The interaction and reaction between CO/H2 and the different types of ZnO surfaces were studied using near-ambient-pressure scanning tunneling microscopy (NAP-STM), X-ray photoelectron spectroscopy (XPS) and Density functional theory (DFT) calculations. The reactivity of the w-ZnO(0001) surface towards CO and H2 was found to be more prominent than those on the surfaces of g-ZnO/Au(111). CO oxidation took place primarily at the edge sites of w-ZnO(0001) and the interface between g-ZnO NSs and Au(111), while g-ZnO thin films on Au(111) appeared inert at below 600 K. Similarly, the w-ZnO(0001) surface could dissociate H2 at 300 K, accompanied by a substantial surface reconstruction, while g-ZnO on Au(111) appeared inert for H2 activation at 300 K. DFT calculations showed that the reactivities of ZnO surfaces towards CO could be related to the formation energy of oxygen vacancy (EOvf), which could be related to the charge transfer to lattice oxygen atoms or surface polarity.
关键词： CO oxidation,NAP-STM,ZnO,XPS,surface polarity,oxygen vacancy
更新于2025-09-23 15:23:52
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Dislocation bending and stress evolution in Mg-doped GaN films on Si substrates
摘要： P-type doping using Mg is essential for realizing a variety of electronic and optoelectronic III-nitride devices involving hetero-epitaxial thin films that also contain a significant number of dislocations. We report on the effect of Mg incorporation on dislocation and stress evolution during the growth of GaN thin films by using in situ curvature measurements and ex situ transmission electron microscopy. A complete picture involving the interplay between three effects—dopant size effect, dislocation bending, and polarity inversion—is presented. Mg aids dislocation bending, which in turn generates tensile stresses in Mg-doped GaN films. As a result, the compressive stress expected due to the dopant size difference effect can only be discerned clearly in films with dislocation densities below 5 × 10^9 cm^?2. Polarity inversion at doping exceeding 10^19 cm^?3 is associated with a sharp drop in screw dislocation density. A kinetic stress evolution model has been developed to capture dislocation bending and size difference effects, and a match between calculated bending angle from the model and that measured from TEM images is obtained.
关键词： Mg doping,stress evolution,dislocation bending,in situ curvature measurements,transmission electron microscopy,polarity inversion,GaN
更新于2025-09-23 15:23:52
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Photoinduced triboelectric polarity reversal and enhancement of a new metal/semiconductor triboelectric nanogenerator
摘要： We reported a novel metal/semiconductor triboelectric nanogenerator (TENG) based on Au and TiO2 as the friction layers. Upon illumination, the current polarity rapidly reverses compared to the dark state. The negative and positive short-circuit current approximately increase by 12 and 2 times, respectively. Particularly, a photocurrent plateau appears due to the formation of metal-semiconductor Schottky contact in the device. By carefully analyzing the charge transfer in dark and under illumination, it is found that the accumulation of a large number of photoelectrons on the surface of TiO2 and the increase of conductivity are the reasons for the reversal current polarity and significant current increase under illumination. Our work provides a new approach for improving TENG output and a new understanding about the effect of surface states on the triboelectric performance especially the polarity of TENG.
关键词： ultrathin Au,photoelectrons,triboelectric polarity reversal,Triboelectric nanogenerator,TiO2 surface states
更新于2025-09-23 15:23:52
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GFP-Forked, a genetic reporter for studying <i>Drosophila</i> oocyte polarity
摘要： The polarized organization of the Drosophila oocyte can be visualized by examining the asymmetric localization of mRNAs, which is supported by networks of polarized microtubules (MTs). In this study, we used the gene forked, the putative Drosophila homologue of espin, to develop a unique genetic reporter for asymmetric oocyte organization. We generated a null allele of the forked gene using the CRISPR-Cas9 system and found that forked is not required for determining the axes of the Drosophila embryo. However, ectopic expression of a truncated form of GFP-Forked generated a distinct network of asymmetric Forked, which first accumulated at the oocyte posterior and was then restricted to the anterolateral region of the oocyte cortex in mid-oogenesis. This localization pattern resembled that reported for the polarized MTs network. Indeed, pharmacological and genetic manipulation of the polarized organization of the oocyte showed that the filamentous Forked network diffused throughout the entire cortical surface of the oocyte, as would be expected upon perturbation of oocyte polarization. Finally, we demonstrated that Forked associated with Short-stop and Patronin foci, which assemble non-centrosomal microtubule-organizing centers. Our results thus show that clear visualization of asymmetric GFP-Forked network localization can be used as a novel tool for studying oocyte polarity.
关键词： ncMTOC,Oocyte,Drosophila,Polarity,Forked,Microtubules,CRISPR
更新于2025-09-23 15:22:29
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Polarity Control in Growing Highly Ga-doped ZnO Nanowires with Vapor-liquid-solid Process
摘要： Surface behavior modification by forming surface transparent conductive nanowires (NWs) is an important technique for many applications, particularly when the polarities of the NWs can be controlled. The polarities of Ga-doped ZnO (GaZnO) NWs grown on templates of different polarities under different growth conditions are studied for exploring a polarity control growth technique. The NWs are formed on Ga- and N-face GaN through the vapor-liquid-solid (VLS) process using Ag nanoparticles as growth catalyst. The NWs grown on templates of different polarities under the Zn- (O-) rich condition are always Zn (O) polar. During the early stage of NW growth, because the lattice sizes among different nucleation islands formed at the triple-phase line are quite different, high-density planar defects are produced when lateral growths from multiple nucleation islands form a GaZnO double-bilayer. In this situation, frequent domain inversions occur and GaZnO polarity is unstable. Under the Zn- (O-) rich condition, because the lateral growth rate of GaZnO in the Zn- (O-) polar structure is higher due to more available dangling bonds, the growth of Zn- (O-) polar structure dominates NW formation such that the NW eventually becomes Zn (O) polar irrespective of the polarity of growth template. Therefore, the polarity of a doped-ZnO NW can be controlled simply by the relative supply rates of Zn and O during VLS growth.
关键词： catalyst,Ga-doped ZnO nanowire,vapor-liquid-solid growth,triple-phase line,polarity
更新于2025-09-23 15:21:21
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Arl13b Interacts With Vangl2 to Regulate Cilia and Photoreceptor Outer Segment Length in Zebrafish
摘要： Mutations in the gene ARL13B cause the classical form of Joubert syndrome, an autosomal recessive ciliopathy with variable degrees of retinal degeneration. As second-site modifier alleles can contribute to retinal pathology in ciliopathies, animal models provide a unique platform to test how genetic interactions modulate specific phenotypes. In this study, we analyzed the zebrafish arl13b mutant for retinal degeneration and for epistatic relationships with the planar cell polarity protein (PCP) component vangl2. Photoreceptor and cilia structure was examined by light and electron microscopy. Immunohistochemistry was performed to examine ciliary markers. Genetic interactions were tested by pairwise crosses of heterozygous animals. Genetic mosaic animals were generated by blastula transplantation and analyzed by fluorescence microscopy. At 5 days after fertilization, photoreceptor outer segments were shorter in zebrafish arl13b?/? mutants compared to wild-type larvae, no overt signs of retinal degeneration were observed by light or electron microscopy. Starting at 14 days after fertilization (dpf) and continuing through 30 dpf, cells lacking Arl13b died following transplantation into wild-type host animals. Photoreceptors of arl13b?/?;vangl2?/? mutants were more compromised than the photoreceptors of single mutants. Finally, when grown within a wild-type retina, the vangl2?/? mutant cone photoreceptors displayed normal basal body positioning. We show that arl13b?/? mutants have shortened cilia and photoreceptor outer segments and exhibit a slow, progressive photoreceptor degeneration that occurs over weeks. The data suggest that loss of Arl13b leads to slow photoreceptor degeneration, but can be exacerbated by the loss of vangl2. Importantly, the data show that Arl13b can genetically and physically interact with Vangl2 and this association is important for normal photoreceptor structure. The loss of vangl2, however, does not affect basal body positioning.
关键词： Arl13b,planar polarity,photoreceptor,cilia,zebrafish,retina,Vangl2
更新于2025-09-23 15:21:21
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Schottky Contacts on Polarity-Controlled Vertical ZnO Nanorods
摘要： Polarity-controlled growth of ZnO by chemical bath deposition provides a method for controlling the crystal orientation of vertical arrays of nanorods. The ability to define the morphology and structure of the nanorods is essential to maximising the performance of optical and electrical devices such as piezoelectric nanogenerators; however, well-defined Schottky contacts to the polar facets of the structures have yet to be explored. In this work, we demonstrate a process to fabricate metal-semiconductor-metal device structures from vertical arrays with Au contacts on the uppermost polar facets of the nanorods and show the O-polar nanorods (~0.44 eV) have a greater effective barrier height than the Zn-polar nanorods (~0.37 eV). Oxygen plasma treatment is shown by Cathodoluminescence (CL) spectroscopy to reduce mid-gap defects associated with radiative emissions that improves the Schottky contacts from weakly-rectifying to strongly-rectifying. Interestingly, the plasma treatment was shown to have a much greater effect in reducing the number of carriers in O-polar nanorods through quenching of the donor-type substitutional hydrogen on oxygen sites (HO) when compared to the zinc vacancy related hydrogen defect complexes (VZn, Hn) in Zn-polar nanorods that evolve to lower coordinated complexes. The effect on HO in the O-polar nanorods coincided with a large reduction in the visible range defects producing a lower conductivity and creating the larger effective barrier heights. This combination can allow radiative losses and charge leakage to be controlled enhancing devices such as dynamic photodetectors, strain sensors, and LEDs while showing the O-polar nanorods can outperform Zn-polar nanorods in such applications.
关键词： ZnO,Cathodoluminescence,Electrical Transport,Polarity,Schottky Contacts,Nanorods,Defects
更新于2025-09-23 15:21:01
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[IEEE 2019 Compound Semiconductor Week (CSW) - Nara, Japan (2019.5.19-2019.5.23)] 2019 Compound Semiconductor Week (CSW) - Suppressing beam deflections by introducing phosphorous in the GaAs-based terahertz MEMS bolometers
摘要： This paper presents a novel and analytical approach to identifying a lightning strike after it has struck an overhead transmission line. The identi?cation method is mainly based on the traveling waves’ time-domain parameters, such as polarity, amplitude, and half-wavelength. The main differences in these parameters across different strike types are analyzed. Subsequently, a robust identi?cation algorithm is proposed. An instrumentation system is implemented to verify the algorithm. The overall performances of the instrumentation system and the methodology are demonstrated using an on-site application with excellent results.
关键词： instrumentation system,current traveling wave,half-wave length,shielding failure,Back ?ashover,amplitude,polarity
更新于2025-09-23 15:21:01
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[IEEE 2019 Innovations in Power and Advanced Computing Technologies (i-PACT) - Vellore, India (2019.3.22-2019.3.23)] 2019 Innovations in Power and Advanced Computing Technologies (i-PACT) - High Performance Visible-Range Photodetector for Wide-Bandwidth Applications
摘要： This paper presents a novel and analytical approach to identifying a lightning strike after it has struck an overhead transmission line. The identi?cation method is mainly based on the traveling waves’ time-domain parameters, such as polarity, amplitude, and half-wavelength. The main differences in these parameters across different strike types are analyzed. Subsequently, a robust identi?cation algorithm is proposed. An instrumentation system is implemented to verify the algorithm. The overall performances of the instrumentation system and the methodology are demonstrated using an on-site application with excellent results.
关键词： instrumentation system,current traveling wave,half-wave length,shielding failure,Back ?ashover,amplitude,polarity
更新于2025-09-23 15:21:01
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Characterization of Graphite/ZnO Schottky Barriers Formed on Polar and Nonpolar ZnO Surfaces
摘要： The authors demonstrate that the electrical properties of Schottky junctions fabricated by the deposition of colloidal graphite strongly depend on the crystallographic orientation of the ZnO substrate. The current-voltage, capacitance-voltage, and impedance measurements indicate that near-ideal Schottky junctions form on c-plane, while on a- and m-plane the junctions are laterally inhomogeneous. This behavior is assigned to higher concentration of native point defects in the near-surface region of nonpolar ZnO substrates. The authors further present an extended equivalent circuit model, which corresponds to actual structure of the junctions, and sheds light on their electrical transport properties.
关键词： impedance spectroscopy,graphite,equivalent circuit,ZnO,crystal polarity,Schottky contact
更新于2025-09-23 15:21:01