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Type-II heterostructures of <b>α</b> -V <sub/>2</sub> O <sub/>5</sub> nanowires interfaced with cadmium chalcogenide quantum dots: Programmable energetic offsets, ultrafast charge transfer, and photocatalytic hydrogen evolution
摘要： We synthesized a new class of heterostructures by depositing CdS, CdSe, or CdTe quantum dots (QDs) onto α-V2O5 nanowires (NWs) via either successive ionic layer adsorption and reaction (SILAR) or linker-assisted assembly (LAA). SILAR yielded the highest loadings of QDs per NW, whereas LAA enabled better control over the size and properties of QDs. Soft and hard x-ray photoelectron spectroscopy in conjunction with density functional theory calculations revealed that all α-V2O5/QD heterostructures exhibited Type-II band offset energetics, with a staggered gap where the conduction- and valence-band edges of α-V2O5 NWs lie at lower energies (relative to the vacuum level) than their QD counterparts. Transient absorption spectroscopy measurements revealed that the Type-II energetic offsets promoted the ultrafast (10?12–10?11 s) separation of photogenerated electrons and holes across the NW/QD interface to yield long-lived (10?6 s) charge-separated states. Charge-transfer dynamics and charge-recombination time scales varied subtly with the composition of heterostructures and the nature of the NW/QD interface, with both charge separation and recombination occurring more rapidly within SILAR-derived heterostructures. LAA-derived α-V2O5/CdSe heterostructures promoted the photocatalytic reduction of aqueous protons to H2 with a 20-fold or greater enhancement relative to isolated colloidal CdSe QDs or dispersed α-V2O5 NWs. The separation of photoexcited electrons and holes across the NW/QD interface could thus be exploited in redox photocatalysis. In light of their programmable compositions and properties and their Type-II energetics that drive ultrafast charge separation, the α-V2O5/QD heterostructures are a promising new class of photocatalyst architectures ripe for continued exploration.
关键词： α-V2O5 nanowires,cadmium chalcogenide quantum dots,photocatalytic hydrogen evolution,programmable energetic offsets,Type-II heterostructures,ultrafast charge transfer
更新于2025-09-12 10:27:22
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European Microscopy Congress 2016: Proceedings || Analytical electron microscopy characterization of light-emitting diodes based on ordered InGaN nanocolumns
摘要： Self-assembled nanocolumns (NCs) with InGaN/GaN disks constitute an alternative to conventional light emitting diodes (LED) planar devices [1]. However, their efficiency and reliability are hindered by a strong dispersion of electrical characteristics among individual nanoLED. Polychromatic emission derives from an inhomogeneous distribution of indium concentration due to the inherent tendency of InGaN alloys to develop composition fluctuations as a function of the polarity of the growth crystallographic planes [2]. The recent development of selective area growth of NCs by molecular beam epitaxy has allowed the achieving of highly homogeneous and controllable GaN/InGaN NCs with improved crystalline quality and higher control over the indium distribution [3]. In this work, we present the characterization performed on LEDs based on ordered NCs with InGaN active disks (figure 1). The detailed structural characterization of the nanostructures has been performed by scanning transmission electron microscopy (STEM) carried out on an aberration-corrected JEOL-JEMARM200 microscope. High crystal quality of the NCs is set by the analysis of atomically-resolved high angle annular dark field (HAADF) images. The indium distribution within the InGaN disks is studied by EDS elemental mapping while the polarity of the semiconductor NCs is followed by locating the nitrogen atomic columns in annular bright field (ABF) images while (figure2). Direct correlation of the optical and structural properties on a nanometer-scale was achieved using low temperature cathodoluminescence (CL) spectroscopy in an FEI STEM Tecnai F20 [4].
关键词： nanowires,EDS,annular bright field,InGaN,LEDs,atomic-resolution STEM
更新于2025-09-12 10:27:22
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Growth of multi-morphology amorphous silicon oxycarbide nanowires during the laser ablation of polymer-derived silicon carbonitride
摘要： Multi-morphology amorphous SiOC nanowires were successfully prepared within the interfacial interstices between the una?ected SiCN ceramic and the bracket during the laser ablation of polymer-derived SiCN ceramic in a low-pressure argon atmosphere. Laser irradiation experiments were performed using a continuous-wave CO2 laser, and the gas source for the growth of amorphous SiOC nanowires was provided by the laser ablation of the SiCN ceramic. X-ray photoelectron spectroscopy shows that the amorphous SiOC nanowires possess a SiO2 dominated nanostructure, and the formation of amorphous SiOC nanowires is attributed to the good di?usivity of CO in SiO2. The morphologies of the amorphous SiOC nanowires include straight nanowires, beaded nanowires, helical nanowires, and branched nanowires, and these are determined by the ?owing state of the reactant gases, the laser power, and the surface morphology of the SiCN ceramics. Each amorphous SiOC nanowire with speci?c morphology can be uniformly distributed in separate regions, which makes it possible to control the growth of amorphous SiOC nanowires in di?erent morphologies.
关键词： Laser ablation,SiOC,Polymer-derived ceramics,Amorphous nanowires,Multi-morphology
更新于2025-09-12 10:27:22
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Ultrasensitive ZnO Nanowire Photodetectors with a Polymer Electret Interlayer for Minimizing Dark Current
摘要： Zinc oxide (ZnO) nanowires have attracted extensive interests in ultraviolet photodetection fields owing to their outstanding optoelectronic properties. The detectivity of ZnO nanowire photodetectors is often limited by large dark current due to a number of defect-induced carriers. Herein, a thin layer of poly(2-vinyl naphthalene) (PVN) is introduced between the ZnO nanowire and gate dielectric to deplete defect-induced carriers with the help of the electrostatic field generated by trapped electrons in the PVN layer. The dark current is successfully reduced from 2.2 × 10?9 to 1.6 × 10?14 A. Particularly, ZnO nanowire photodetectors with a large Ilight/Idark ratio (>107), high photoresponsivity (>106 A W?1), and ultrahigh detectivity (>1018 Jones) are achieved, which are among the best performance in reported ZnO-based photodetectors. The present simple scheme offers a new strategy to suppress dark current in semiconducting nanomaterials for ultrasensitive photodetection applications.
关键词： polymer electret,detectivity,ultraviolet photodetection,ZnO nanowires
更新于2025-09-12 10:27:22
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Transparent Flexible Polymer Actuator with Enhanced Output Force Enabled by Conductive Nanowires Interlayer
摘要： In this work, an approach to enhance the output force of polymer actuators by increasing the dielectric permittivity of the electroactive polymer (EAP), poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) (P(VDF-TrFE-CTFE)), via incorporation of a nanowire interlayer into the polymer matrix is presented. The interlayer is formed by a network of highly conductive silver nanowires with high aspect ratio. Due to the enhanced dielectric properties, the output force of the resultant composite actuator is double that of a neat EAP actuator. This advantage can be utilized to improve user perception of tactile feedback produced by the modified EAP actuator. The higher output force translates to a lower excitation voltage which is 60% of what is required to excite a neat EAP actuator. The resultant-modified EAP maintains its transparency and flexibility, while enhancing the dielectric properties without severe degradation of the electrical breakdown strength. The excellent transparency and flexibility of the modified EAP allows for a wider range of possible applications such as direct and localized haptic feedback on flexible electronic displays, touch screens, etc.
关键词： silver nanowires,haptic feedback,transparent flexible actuators,electroactive polymers,space charge
更新于2025-09-12 10:27:22
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Mask-less MOVPE of arrayed n-GaN nanowires on site- and polarity-controlled AlN/Si templates
摘要： We present a novel approach to attain Ga-polar n-GaN nanowires on n-Si(111)/AlN templates, by site- and polarity-controlled metal organic vapor phase epitaxy. A three-stage process is developed to (i) form equally-sized Ga-polar GaN islands, (ii) change the growth direction towards the vertical direction and finally, to (iii) obtain continuous nanowire epitaxy. Homogeneous islands are achieved by minimizing parasitic nucleation and adjusting the adatom diffusion length to the used nanoimprint pattern. The influence of the carrier gas composition on the polarity is studied, achieving pure Ga-polarity by mostly using nitrogen carrier gas. Enhancing the Si/Ga-ratio leads to an amplification of the vertical growth, but also to a reduced number of NWs. 100% growth is attained by a height dependent V/III-ratio adjustment. The results are supported by a qualitative model, explaining how suppression of multi-pod, parasitic and inhomogeneous crystallization can be realized by trading off in situ SiNx passivation and localized GaN growth.
关键词： GaN nanowires,MOVPE,site-controlled,Si templates,polarity-controlled
更新于2025-09-12 10:27:22
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Sn-doped CdS Nanowires with Low Temperature Lasing by CW-Laser Excitation
摘要： Sn-doped CdS nanowires, with the inside coexisting Sn(II)S, Sn2(III)S3 and Sn(IV)S2 identified by in situ Raman and XPS spectra, are grown via a simple thermal evaporation deposition technique. Its room-temperature photoluminescence (PL) spectrum shows a broad ingap emission band out of different Sn dopants which is also superposed by a series of weak modes from a microcavity due to the wire size and its structure, besides the CdS bandedge emission and a sideband emission due to SnS2. The ratio of the intensity of the ingap emission versus that of the bandedge emission is only 1/4 at room temperature, but it can be remarkably increased to about 7 at 80K. This significant enhancement of the ingap emission may be attributed to the local plasma coming from more bound carriers and enhanced microcavity effect at low temperature by analyzing the temperature-dependent PL and Raman spectra in detail. For these reasons, the bandedge and ingap emission both can realize lasing excitated by a continuous laser at 80K. The results would provide a way to get temperature tunable low threshold microscale lasers and study the plasma-polariton process within microcavity.
关键词： Sn-doped nanowires,plasma,cavity modes,lasing,coupled cavity
更新于2025-09-12 10:27:22
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Cation exchange synthesis of CuIn <sub/>x</sub> Ga <sub/>1?x</sub> Se <sub/>2</sub> nanowires and their implementation in photovoltaic devices
摘要： CuInxGa1(cid:1)xSe2 (CIGS) nanowires were synthesized for the ?rst time through an in situ cation exchange reaction by using CuInSe2 (CIS) nanowires as a template material and Ga-OLA complexes as the Ga source. These CIGS nanowires maintain nearly the same morphology as CIS nanowires, and the Ga/In ratio can be controlled through adjusting the concentration of Ga-OLA complexes. The characteristics of adjustable band gap and highly e?ective light-absorbances have been achieved for these CIGS nanowires. The light-absorbing layer in photovoltaic devices (PVs) can be assembled by employing CIGS nanowires as a solar-energy material for enhancing the photovoltaic response. The highest power conversion e?ciency of solar thin ?lm semiconductors is more than 20%, achieved by the Cu(InxGa1(cid:1)x)Se2 (CIGS) thin-?lm solar cells. Therefore, these CIGS nanowires have a great potential to be utilized as light absorber materials for high e?ciency single nanowire solar cells and to generate bulk heterojunction devices.
关键词： CIGS nanowires,solar cells,photovoltaic devices,light absorber materials,cation exchange
更新于2025-09-12 10:27:22
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III–V nanowire array telecom lasers on (001) silicon-on-insulator photonic platforms
摘要： III–V nanowires have recently gained attention as a promising approach to enable monolithic integration of ultracompact lasers on silicon. However, III–V nanowires typically grow only along h111i directions, and thus, it is challenging to integrate nanowire lasers on standard silicon photonic platforms that utilize (001) silicon-on-insulator (SOI) substrates. Here, we propose III–V nanowire lasers on (001) silicon photonic platforms, which are enabled by forming one-dimensional nanowire arrays on (111) sidewalls. The one-dimensional photonic crystal laser cavity has a high Q factor >70 000 with a small footprint of (cid:2)7.2 (cid:3) 1.0 lm2, and the lasing wavelengths can be tuned to cover the entire telecom bands by adjusting the nanowire geometry. These nanowire lasers can be coupled to SOI waveguides with a coupling ef?ciency > 40% while maintaining a suf?ciently high Q factor (cid:2)18 000, which will be bene?cial for low-threshold and energy-ef?cient operations. Therefore, the proposed nanowire lasers could be a stepping stone for ultracompact lasers compatible with standard silicon photonic platforms.
关键词： monolithic integration,III–V nanowires,telecom lasers,photonic crystal laser cavity,silicon photonic platforms
更新于2025-09-12 10:27:22
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Germanium quantum dot infrared photodetectors addressed by self-aligned silicon nanowire electrodes
摘要： Germanium quantum dots (GeQDs), addressed by self-aligned and epitaxial silicon nanowires (SiNWs) as electrodes, represent the most fundamental and the smallest units that can be integrated into Si optoelectronics for 1550 nm wavelength detection. In this work, individual GeQD photodetectors have been fabricated based on a low temperature self-condensation of uniform amorphous Si (a-Si)/a-Ge bilayers at 300 oC, addressed by self-aligned silicon nanowire electrodes. The photodetectors demonstrate a responsivity of 1.5 mA/W and a photoconductive gain exceeding 102 to the communication wavelength signals, which are related to the beneficial type-II Ge/Si alignment, gradient Ge/Si epitaxial transition and a larger QD/NW diameter ratio. Importantly, this hetero GeQD/SiNW photodetectors can be deployed into predesigned locations for scalable device fabrication. These results indicate a new approach to batch-fabricate and integrate GeQDs for ultra-compact Si-compatible photodetection and imaging applications.
关键词： Ge quantum dots,self-condensation,photodetectors,Si nanowires
更新于2025-09-12 10:27:22