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Binding energy of an exciton in a GaN/AlN nanodot: Role of size and external electric field
摘要： We report the impact of an external electric field on the energy spectrum of an exciton inside a spherical shaped GaN/AlN core/shell nanodot. The modulation of the confined exciton lowest state energy by the nanodot size is also treated. Our theoretical approach, based on a variational calculation, predicts a remarkable decrease in the exciton's energy when the electric field is switched on. Furthermore, our investigation shows that for a fixed nanodot size, the energy redshift is a unique function of the external electric field strength. On the other hand, it was observed that as the nanodot size increases the lowest exciton energy decreases and vice versa.
关键词： electric field,core/shell materials,nanostructures,quantum dots,exciton
更新于2025-09-19 17:15:36
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Theoretical Study on Nanostructural Modifications of the Si (111) Surface
摘要： Modified Si(111) surface with designed nanostructural modifications including grown pits, nanobars and nanoislands as well as deposited hill-, diamond- and cage-like nanoclusters were studied using density-functional theory (DFT) calculations. The thermal stabilities, electronic structures and optical properties of these various nanostructural modifications of the Si(111) surface were calculated and discussed. The results indicate that the optical absorption of the modified Si(111) surface can be enhanced by these surface modifications especially when depositing diamond-like nanoclusters on the surface.
关键词： electronic structures,Si(111) surface modifications,Si nanostructures,optical properties
更新于2025-09-19 17:15:36
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Green Synthesis of Bismuth Sulfide Nanostructures with Tunable Morphologies and Robust Photoelectrochemical Performance
摘要： Manipulating the morphology of chalcogenide semiconductor crystals to tailor their shape- and size-dependent properties is much desired but remains a grand challenge. Herein, we for the first time develop a green, facile and surfactant-free hydrothermal approach for the synthesis of bismuth sulfide (Bi2S3) with highly tunable morphologies in H2WO4 aqueous solution. The H2WO4 is prone to balance the concentration of Bi3+ to S2- in aqueous solution, thus modulating the nucleation and epitaxial growth of Bi2S3. Specifically, in the presence of lower H2WO4 concentration, low number of Bi2S3 nuclei facilitates the preferred growth of nanorod structures along [001] direction, while the Bi-deficient, S-rich conditions in higher H2WO4 concentration give rise to Bi2S3 nanotubes, presumably due to the stronger interlayer interaction and preferred growth in [hk0] direction. The resulting Bi2S3 nanostructures exhibit broad absorption overlapping UV-Visible-NIR regions and red-shifted absorption edges owing to the increased S/Bi molar ratio in Bi2S3 lattices. The Bi2S3 nanorods with higher aspect ratio demonstrate an enhanced photocurrent response by virtue of the improved charge carrier mobility along [001] direction. Different from previous synthetic methodologies, this work details a facile, effective, and environmentally-benign protocol for the synthesis of Bi2S3 nanomaterials in the aqueous medium without any organic reagents. Noteworthy, the excellent and tailorable photoelectrochemical (PEC) performance endows these Bi2S3 nanostructures with vast potential in solar cell and photodetector applications.
关键词： Photoelectrochemical performance,Morphology control,Nanostructures,Green synthesis,Bismuth sulfide
更新于2025-09-19 17:15:36
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Elastic Properties of Suspended Conducting GaAs/AlGaAs Nanostructures by Means of Atomic Force Microscopy
摘要： This paper demonstrates the applicability of nanoindentation technique using atomic-force microscope cantilever for studying the elastic properties of suspended semiconductor structures on the basis of relatively thick GaAs/AlGaAs membranes in the case when their stiffness significantly exceeds that of the cantilever of atomic-force microscope, which is confirmed by the agreement between the experimentally determined values of both relative and absolute stiffness measured at different points of the investigated structure with theoretical predictions.
关键词： nanoelectromechanical systems,GaAs/AlGaAs,atomic-force microscopy,suspended nanostructures
更新于2025-09-19 17:15:36
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Methodical engineering of defects in MnXZn1-X O(x?=?0.03, and 0.05) nanostructures by electron beam for nonlinear optical applications: A new insight
摘要： A series of MnxZn1-xO (x = 0.03, 0.05) nanostructures have been grown via the solution based chemical spray pyrolysis technique. Electron beam induced modifications on structural, linear and nonlinear optical and surface morphological properties have been studied and elaborated. GXRD (glancing angle X-ray diffraction) patterns show sharp diffraction peaks matching with the hexagonal wurtzite structure of ZnO thin films. The upsurge in e-beam dosage resulted in the shifting of XRD peaks (101) and (002) towards lower angle side, and increase in FWHM value. Gaussian deconvolution on PL spectra reveals the quenching of defect centers, implying the role of electron beam irradiation regulating luminescence and defect centers in the nanostructures. Irradiation induced spatial confinement and phonon localization effects have been observed in the films via micro Raman studies. The later are evident from spectral peak shifts and broadening. Detailed investigations on the effect of electron beam irradiation on third order nonlinear optical properties under continuous and pulsed mode of laser operation regimes are deliberated. Third order absorptive nonlinearity of the nanostructures evaluated using the open aperture Z-scan technique in both continuous and pulsed laser regimes shows strong nonlinear absorption coefficient β eff of the order 10-4 cm/W confirming their suitability for passive optical limiting applications under intense radiation environments. Laser induced third harmonic generation (LITHG) experiment results supports the significant variation in nonlinearities upon electron beam irradiation, and the effect can be utilized for frequency conversion mechanisms in high power laser sources and UV light emitters.
关键词： Mn:ZnO nanostructures,8MeV e-beam,Spatial confinement effects,Defects quenching,Third harmonic generation
更新于2025-09-19 17:15:36
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Selective formation of ternary Cu–Ge–S nanostructures in solution
摘要： Selective formation of ternary Cu–Ge–S nanostructures in solution. In this paper, special attention is given to ternary copper germanium sulfides (Cu–Ge–S), which belong to an important class of mixed-metal chalcogenide materials called the copper-based multinary sulfides (CMSs). Like most members of the CMS family, the Cu–Ge–S compounds display enormous potential in energy-related applications especially in their nanostructured forms, but there exists very little research on the preparation of Cu–Ge–S materials in the nanometer size range. Herein, we report a simple noninjection protocol for the selective synthesis of Cu–Ge–S nanomaterials. We show that variations in the solvent environment can lead to different types of Cu–Ge–S nanostructures (i.e., from large, faceted Cu8GeS6 to smaller, irregularly-shaped Cu2GeS3). Our investigation of the growth process revealed interesting formation pathways, which could help advance our understanding of the selective formation of compositionally and structurally diverse multinary materials in solution.
关键词： selective synthesis,solvent environment,formation mechanism,Cu–Ge–S nanostructures,noninjection protocol
更新于2025-09-19 17:15:36
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Wave functions and spectra of charge carriers in a toroidal nanostructure: The transition from ring to bulk states
摘要： A basis set expansion is employed to calculate spectra and eigenstates of charge carriers within a toroidal volume characterized by major radius R and minor radius a immersed in an azimuthally symmetric magnetic field. The angular variables appearing in the Schr?dinger equation are eliminated by contour methods, yielding effective potentials that reduce computational time by a large factor. An approximation formula for the single particle spectrum is presented that allows efficient construction of the partition function necessary for rapid calculation of thermodynamic quantities. The heat capacity is calculated as a function of torus aspect ratio and temperature, showing the transition from ring-type to bulk-type behavior.
关键词： Toroidal quantum dot,Toroidal nanostructures
更新于2025-09-19 17:15:36
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The mechanochemical synthesis of PbTe nanostructures: following the Ostwald ripening effect during milling
摘要： A fundamental understanding of the Ostwald ripening effect (ORE) during the mechanochemical synthesis of PbTe nanostructures is presented. The ripening process involves the coarsening of larger particles from those of smaller size; this phenomenon was systematically evaluated at different stages of milling by microscopy analyses (AFM, TEM, STEM and HRTEM). At the early stage of milling, smaller particles and quantum dots are eventually dissolved to lower the total energy associated with their surfaces. The ripening process – during milling – involves short-range mass transfer among particles. HRTEM analyses allowed us to identify that coarsening occurs by thermo-mechanically activated cooperative mechanisms. The detachment of the atoms from smaller particles to form bigger ones plays a major role in the particle coarsening. It was found that the coarsening process was not limited to crystalline nanostructures; so grain boundaries, edge dislocations and boundaries among crystalline and amorphous phases also play an important role to determine how species migration contributes to generate coarse particles. Those serve as sites for inducing coarsening in an equivalent way as surfaces do. Secondary ion mass spectrometry and elemental chemical mapping (EDX-STEM) revealed that both the purity and the chemical homogeneity of the PbTe nanostructures are prominent features of this material. Additionally, a direct band gap enhancement (780 nm) compared to bulk PbTe (3859 nm) was detected. It occurred due to the quantum confinement effect, lattice imperfections and even surface properties of the nanostructures. It is important to point out that the whole optical behaviour of the PbTe nanostructures was dependent upon the embedded nanoparticles and quantum dots in the clusters and coarse particles ranging from 15 nm to 35 nm.
关键词： PbTe nanostructures,microscopy analyses,quantum confinement effect,mechanochemical synthesis,Ostwald ripening effect,high-energy milling
更新于2025-09-19 17:15:36
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High‐Performance Solution‐Processable Flexible SnSe Nanosheet Films for Lower Grade Waste Heat Recovery
摘要： Lower grade waste heat recovery near room temperature is limited due to multiple technology challenges including low efficiency, high cost, and scalability. Here, a low-cost and scalable solution process is reported to fabricate a nanostructured SnSe thin film, and a high thermoelectric performance near room temperature is demonstrated. This transport study reveals strong phonon scattering near the interfaces between SnSe nanosheets that introduces a large thermal boundary resistance and an ultralow thermal conductivity of 0.09 W m?1 K?1. Moreover, it is demonstrated that the SnSe thin film can be readily implemented on flexible plastic substrates and preserve the high thermoelectric performance over 1000 bending cycles. Together, this study demonstrates a low-cost and scalable approach to achieve high-performance flexible thin film energy harvesting devices to power electronics and sensors near room temperature.
关键词： energy efficiency,2D van der Waals materials,solution-processing,thermoelectrics,thermal energy harvesting,phonons,nanostructures,flexible electronics
更新于2025-09-19 17:15:36
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High Resolution Characterization of Plasmonic Hybridization in Silver Nanostructures
摘要： Surface plasmon resonances (SPR) in metallic nanostructures arise from the collective oscillation of conduction electrons, which create strong confined electric fields around the nanostructures. This confinement of electromagnetic (EM) energy at nanoscale dimensions holds potential towards the miniaturization of photonic devices [1]. Tremendous effort has been devoted towards optimization and design of nanostructures for several applications [2,3,4]. Most of these applications involve arrays of closely-spaced nanostructures: the plasmonic properties of the array differ from those of its isolated parts due to the interaction of evanescent fields. The study of SPR in these arrays, in particular the coupling of resonant modes, requires a characterization technique with both high spatial and energy resolution. Electron energy loss spectroscopy (EELS) meets these requirements, but has previously been limited to energies in the range of visible light or higher, mainly because of the relative intensities of the zero loss peak (ZLP) and low energy loss signal.
关键词： electron energy loss spectroscopy,metallic nanostructures,Surface plasmon resonances,hybridization,silver nanostructures
更新于2025-09-19 17:13:59