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Infrared plasmonics: STEM-EELS characterization of Fabry-P??rot resonance damping in gold nanowires
摘要： Materials possessing strong midinfrared responses are of current interest because of their potential application to long-wavelength metamaterials, photonic devices, molecular detection, and catalysis. Here, we utilize high-energy resolution (80 cm?1, 10 meV) electron-energy-loss spectroscopy (EELS) in a monochromated and aberration-corrected scanning transmission electron microscope (STEM) to resolve multipolar surface plasmon resonances (SPRs), sometimes called Fabry-Pérot (FP) resonances, in gold nanowires with mode energies spanning from ～1000 to 8000 cm?1. STEM-EELS provides access to these mid- to near-IR responses in a single acquisition, avoiding the difficulties inherent in obtaining the same data using near-field optical techniques. The experimentally measured FP resonance energies and linewidths, together with analytical modeling and full-wave numerical electrodynamics simulations, provide a comprehensive picture of the radiative and intrinsic contributions to the total damping rates. We find some FP modes with dephasing times >60 fs, which is almost twice the longest previously reported plasmon dephasing time for individual Au nanoparticles in the infrared. The long dephasing times and the broad tunability of the FP resonance energies throughout the infrared region suggest additional opportunities for harnessing infrared plasmonic energy before dephasing occurs.
关键词： gold nanowires,plasmon dephasing times,Fabry-Pérot resonance,infrared plasmonics,STEM-EELS
更新于2025-09-23 15:19:57
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Temperature-Controlled Fragmentation and Ripening: Synthesis of ZnSe Nanorods with Variable Dimensions and Crystal Structure Starting from Ultrathin ZnSe Nanowires
摘要： Heavy-metal-free semiconductor nanomaterials have attracted attention because of their importance in both fundamental research and commercial applications. In particular, polarized ?uorescence emission in one-dimensional (1D) semiconductors makes them highly attractive as display materials. Herein, we developed a novel colloidal synthesis approach toward 1D ZnSe nanostructures with controlled size and crystal structure, which we call “temperature-controlled fragmentation and ripening”. First, ultrathin ZnSe nanowires (NWs) with a length of 50?200 nm and diameter of ～1.1 nm were synthesized. ZnSe nanorods (NRs) have been obtained through the fragmentation of these NWs in a controlled step while keeping the same diameter, and the length of the ?nal ZnSe NRs has been tuned in the range of 10?20 nm by moderating the heating procedure. Using a higher temperature for fragmentation allowed us to break down the ZnSe NWs to shorter ZnSe NRs, whereas controlling the ?nal growth temperature of the ZnSe NRs in a subsequent ripening stage allowed us to obtain them in either cubic zinc blende (ZB; at 220 °C) or hexagonal wurtzite (WZ; at 240 °C) crystal structures. This set of growth processes ?ipping from bottom-up to top-down to form ZnSe NRs with controlled length and selection of the ?nal crystal structure (either hexagonal WZ or cubic ZB) provides a novel growth mechanism to synthesize 1D semiconductor nanostructures.
关键词： nanorods,ripening,nanowires,temperature-controlled fragmentation,ZnSe,crystal structure
更新于2025-09-23 15:19:57
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One-step fabrication of 1D p-NiO nanowire/n-Si heterojunction: development of self-powered ultraviolet photodetector
摘要： Even though there are reports on NiO-p/Si-n based photodetector, work along 1D NiO/Si self-powered photodetector remains unexplored. 1D materials offer better electron mobility and can provide ballistic transport channel, which helps in achieving high responsivity. In this work, direct single-step deposition of p-type NiO nanowires on n-type Si as a self-powered photodetector was successfully fabricated by engaging simple electrospinning technique. The structural properties as observed from XRD indicate highly crystalline NiO nanowires and FESEM images revealed 60 ~75 nm diameter with uniform distribution. Growth of nanowires by using stimuli polymer and its completely removal at high temperature was confirmed using TGA and XPS analysis. The responsivity of the fabricated photodetector was calculated to be 9.1 mA W-1 at zero bias, which can be attributed to the p-type NiO interface with the n-type Silicon, which creates an internal electrical field thereby assisting in the effective separation of the photogenerated carriers. Further, under illumination, at zero bias, the photogenerated current still exists suggesting a generation of internal voltage, which makes the fabricated device as self-powered. This fabrication method will enhance the photodetection properties, and it can be implemented in the fields of optoelectronic devices, sensors, and flexible electronics.
关键词： Electrospinning,NiO nanowires,1D material,Self-powered photodetector
更新于2025-09-23 15:19:57
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Atomistic theory of electronic and optical properties of InAsP/InP nanowire quantum dots
摘要： We present here an atomistic theory of the electronic and optical properties of hexagonal InAsP quantum dots in InP nanowires in the wurtzite phase. These self-assembled quantum dots are unique in that their heights, shapes, and diameters are well known. Using a combined valence-force-field, tight-binding, and configuration-interaction approach we perform atomistic calculations of single-particle states and excitonic, biexcitonic, and trion complexes as well as emission spectra as a function of the quantum dot height, diameter, and As versus P concentration. The atomistic tight-binding parameters for InAs and InP in the wurtzite crystal phase were obtained by ab initio methods corrected by empirical band gaps. The low energy electron and hole states form electronic shells similar to parabolic or cylindrical quantum confinement, only weakly affected by hexagonal symmetry and As fluctuations. The relative alignment of the emission lines from excitons, trions, and biexcitons agrees with that for InAs/InP dots in the zincblende phase in that biexcitons and positive trions are only weakly bound. The random distribution of As atoms leads to dot-to-dot fluctuations of a few meV for the single-particle states and the spectral lines. Due to the high symmetry of hexagonal InAsP nanowire quantum dots the exciton fine structure splitting is found to be small, of the order a few μeV with significant random fluctuations in accordance with experiments.
关键词： fine structure splitting,electronic properties,optical properties,emission spectra,tight-binding,single-particle states,excitonic complexes,InAsP quantum dots,InP nanowires,wurtzite phase,configuration-interaction,valence-force-field,atomistic theory
更新于2025-09-23 15:19:57
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[IEEE 2019 URSI Asia-Pacific Radio Science Conference (AP-RASC) - New Delhi, India (2019.3.9-2019.3.15)] 2019 URSI Asia-Pacific Radio Science Conference (AP-RASC) - Generation of Pulsed Fiber Laser: ns to fs domain
摘要： Thermionic energy converter (TEC) is a heat engine that generates electricity directly using heat as its source of energy and electron as its working fluid. Despite having a huge potential as an efficient direct energy conversion device, the progress in vacuum-based thermionic energy converter development has always been hindered by the space charge problem and the unavailability of materials with low work function. It is only recently that researchers have started to look back into this technology as recent advances in manufacturing technology techniques have made it possible to solve these problems, making TECs a viable option in replacing current energy production systems. The focus of this paper is to review the challenges of producing efficient and practical TECs, along with recent findings and developments in mitigating these challenges. Furthermore, this paper looked into potential applications of TECs, based on recent works and technologies, and found that, with certain improvements, it can be applied in many sectors.
关键词： nanowires,work function,thermionic energy conversion (TEC),space charge,Energy conversion efficiency
更新于2025-09-23 15:19:57
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Rice–Bernasconi Gorkov–Eliashberg Effect of Giant Dielectric Permittivity in Silica-Based Films Containing Interrupted Silver Nanowires
摘要： Silver nanowires of diameter * 5 nm were grown within thick ?lms (0.6 lm thickness) of sol–gel-derived xAg2O(1 - x)SiO2; x having values of 30 and 40, respectively, by an electrodeposition method. By applying suitable voltage pulses to the composites, interrupted silver nanowires were produced with lengths having values in the range 4000–5000 nm. The samples exhibited dielectric constant with values of the order of 105 and a low dielectric loss (* 0.01). The dielectric constant values calculated by using Rice–Bernasconi model which originated from Gorkov–Eliashberg theory of metallic nanoparticles were in satisfactory agreement with the experimental results. The present work not only provides strong evidence for the basis of Rice–Bernasconi model but also opens up a simple method to synthesize high dielectric constant materials which will be useful in fabricating devices for very large-scale integration applications, among others.
关键词： Interrupted silver nanowires,Electrodeposition,Nanocomposite,Rice–Bernasconi model
更新于2025-09-23 15:19:57
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Effect of thermal condensation temperature on electrochemical capacitive properties of g-C3N4 supported on reduced TiO2 nanowires/nanotubes array
摘要： In this work, effect of processing temperature in electrochemical capacitors was investigated for g-C3N4. The g-C3N4 materials (CN) were synthesized by thermal condensation of melamine precursor at different temperature (450, 550 and 650 °C). Then, the g-C3N4 materials were deposited on electrochemically reduced TiO2 nanowires/nanotubes arrays (rTWTA)/Ti substrate. The g-C3N4/rTWTA/Ti electrodes were used as supercapacitor electrodes. Morphology, crystal structure and chemical composition of the g-C3N4/rTWTA/Ti electrodes were studied by FESEM, XRD, FTIR and elemental analysis. Based on galvanostatic charge/discharge measurements, the CN(450)/rTWTA/Ti electrode exhibited the highest specific capacitance up to 22 mF/cm2 at 0.3 mA/cm2 with long cyclic durability at 96.8% capacitance retention after 500 cycle. This effect was attributed to the existence of higher nitrogen content, more active sites, the improved hydrophilicity and three-dimensional morphology of the CN(450)/rTWTA/Ti electrode as compared to the other electrodes. This research introduces the optimum thermal condensation temperature of the melamine for synthesis of the g-C3N4 with great potentials in supercapacitors.
关键词： Supercapacitor,TiO2 nanowires/nanotubes array,Processing temperature,g-C3N4,Specific capacitance
更新于2025-09-19 17:15:36
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First-principles study of electron dynamics with explicit treatment of momentum dispersion on Si nanowires along different directions
摘要： In this research, ground-state electronic structure and optical properties along with photoinduced electron dynamics of Si nanowires oriented in various directions are reviewed. These nanowires are significant functional units of future nano-electronic devices. All observables are computed for a distribution of wave vectors at ambient temperature. Optical properties are computed under the approximation of momentum conservation. The total absorption is composed of partial contributions from fixed values of momentum. The on-the-fly non-adiabatic couplings obtained along the ab initio molecular dynamics nuclear trajectories are used as parameters for Redfield density matrix equation of motion. The main outcomes of this study are transition energies, light absorption spectra, electron and hole relaxation rates, and electron transport properties. The results of these calculations would contribute to the understanding of the mechanism of electron transfer process on the Si nanowires for optoelectronic applications.
关键词： nanowires,excited state dynamics,nonadiabatic,Momentum dispersion,silicon
更新于2025-09-19 17:15:36
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Calculations of defect states in various sizes of InN nanowires
摘要： InN has received considerable attentions due to its small band-gap and unique properties in the III-nitride family. Understanding the effects of defects on optoelectronic properties of InN nanowire is essential for exploring its applications in future nanodevices. In this work, we have systematically calculated defect states in InN nanowires based on density-functional theory. Hydrogen passivation and several potential intrinsic point defects are considered in various sizes of nanowires, as well as charged defect states. For small-sized hexagonal nanowires, VN at N-poor condition or NIn at N-rich condition is the most stable defect. Whereas for larger-sized nanowires, VN and InN defects are competing when the N chemical potential changes, showing obvious size effect of the defect stability on the nanowire surface. Those defect states change the electronic structure of the nanowires drastically by introducing empty bands or deep level and provide possibility to tailor the optical properties in terms of forming different stable defects.
关键词： InN,nanowires,size effect,first-principals calculations,electronic structure,defects
更新于2025-09-19 17:15:36
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Nonlinear Optical Properties of CdS Semiconductor nanowires
摘要： In this work, we report on the nonlinear optical properties in single Cadmium sulfide nanowires (CdS NWs). The high qulity growth of CdS semiconductor nanowires were synthesized by chemical vapor deposition (CVD) method. The as-obtained products were characterized by X-ray diffraction (XRD) , Scanning electron microscopy (SEM), and the energy dispersive X-ray spectrom (EDS) was used to determine the specific elemental distribution and show purity of the CdS semiconductor nanowires . The excitation of femtosecond laser(800 nm, 50 fs, 80 MHz) was used to study the nonlinear optical properties of CdS nanowires, such as the Second Harmonic Generation(SHG) and optical waveguide effect. CdS NW has a second harmonic generation with a blue emission bands at a wavelength of 400 nm . Finally, based on the dark field image of the CCD taken and combined with the spectrum, it is proved that CdS NW has an optical waveguide effect.
关键词： Cadmium sulfide (CdS),Waveguide,nanowires (NWs),Second- Harmonic Generation (SHG),Chemical Vapor Deposition (CVD)
更新于2025-09-19 17:15:36