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Effect of confinement potential shape on the electronic, thermodynamic, magnetic and transport properties of a GaAs quantum dot at finite temperature
摘要： The effect of the shape of the confinement potential on the electronic, thermodynamic, magnetic and transport properties of a GaAs quantum dot is studied using the power-exponential potential model with steepness parameter p. The average energy, heat capacity, magnetic susceptibility and persistent current are calculated using the canonical ensemble approach at low temperature. It is shown that for soft confinement, the average energy depends strongly on p while it is almost independent of p for hard confinement. The heat capacity is found to be independent of the shape and depth of the confinement potential at low temperatures and for the magnetic field considered. It is shown that the system undergoes a paramagnetic-diamagnetic transition at a critical value of the magnetic field. It is furthermore shown that for low values of the potential depth, the system is always diamagnetic irrespective of the shape of the potential if the magnetic field exceeds a certain value. For a range of the magnetic field, there exists a window of p values in which a re-entrant behavior into the diamagnetic phase can occur. Finally, it is shown that the persistent current in the present quantum dot is diamagnetic in nature and its magnitude increases with the depth of the dot potential but is independent of p for the parameters considered.
关键词： transport properties,thermodynamic properties,canonical ensemble approach,electronic properties,quantum dot,GaAs,paramagnetic-diamagnetic transition,persistent current,magnetic properties,power-exponential potential model,confinement potential
更新于2025-09-11 14:15:04
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Small coupling length with a low confinement loss dual-core liquid infiltrated photonic crystal fiber coupler
摘要： In this paper, a dual-core liquid ?lled photonic crystal ?ber coupler (PCFC) with rectangular (RPCFC) and hexagonal (HPCFC) geometry is presented from the 1200 to 1800 nm wavelength range. In the proposed design, super ?int (SF10) glass is used as the background material and water, chloroform, and benzene are in?ltrated in the dual-core, independently. The properties of the guided modes are studied by the ?nite di?erence time domain (FDTD) method with a perfectly matched layer (PML) boundary condition. Results reveal very small con?nement loss with a low coupling length and birefringence for the wide wavelength range. At the 1.55 μm wavelength, RPCFC shows 0.000318, 0.000358, and 0.000379 m coupling lengths for the water, chloroform, and benzene ?lled dual-core, respectively. Additionally, the con?nement loss of 1.57×10?7, 1.22×10?7, and 1.05×10?7 db/km is achieved through RPCFC. Moreover, both the PCFCs present a small polarization variation. Therefore, the proposed PCFC models can be used in optical communication systems, and polarization-independent and high temperature-sensitive applications areas.
关键词： coupling length,liquid filled,birefringence,dual-core,photonic crystal fiber coupler,confinement loss
更新于2025-09-10 09:29:36
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A study of 8 MeV e-beam on localized defect states in ZnO nanostructures and its role on Photoluminescence and third harmonic generation
摘要： In this article we have explored an effect of electron beam irradiation (EBI) on physical and nonlinear optical properties ZnO thin nano films. Nanostructured ZnO thin films were grown by low cost spray pyrolysis technique. The irradiation dosage has been fixed at 5kGy, 10kGY, 15kGy and 20kGy. The structural investigation by Glancing angle X-Ray Diffractometer (GAXRD) confirms a polycrystalline phase of ZnO with wurtzite structure. The variation in the surface morphology upon EBI has been demonstrated using 2D and 3D Atomic force microscopy (AFM) images. Nanoscope software analysis quantifies the variation in surface roughness and average particle height upon EBI. The defect states created in the films upon irradiation experiments were investigated using UV- visible spectrophotometer, Room temperature Photoluminescence (RTPL), Raman and X-ray photoelectron spectroscopy (XPS). The increase in urbach tail validates the creation of localized defect states in the films The Gaussian fitting on RTPL spectra shows the quenching in the luminescent centers upon irradiation arised as result of recombination of vacancy defects. Phonon confinement model fitting on Raman spectra endorses that shift in the phonon modes observed on irradiation is due to spatial confinement of phonons. The elemental composition and impurity states of the EBI ZnO thin films were studied using XPS spectra. The shift in the binding energy of Zn and O elements infers the electron beam induced changes in the films. The electron beam irradiation has resulted in the increment of third order optical susceptibility χ(3) from 3.5×10-4esu to 8.13×10-3esu due to the enhancement of electronic transition to different defect levels formed in the films and through local heating effects arising due to continuous wave (CW) laser illumination. The enhanced THG signal investigated using Nd:YAG laser at 1064nm and 8 ns pulse width shows the promising features of EBI ZnO films for frequency tripling applications.
关键词： Electron beam irradiation,Phonon confinement model,third harmonic generation,ZnO nanostructures,Localized defect states
更新于2025-09-10 09:29:36
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Extremely reduced dielectric confinement in two-dimensional hybrid perovskites with large polar organics
摘要： Two dimensional inorganic–organic hybrid perovskites (2D perovskites) suffer from not only quantum confinement, but also dielectric confinement, hindering their application perspective in devices involving the conversion of an optical input into current. In this report, we theoretically predict that an extremely low exciton binding energy can be achieved in 2D perovskites by using high dielectric-constant organic components. We demonstrate that in (HOCH2CH2NH3)2PbI4, whose organic material has a high dielectric constant of 37, the dielectric confinement is largely reduced, and the exciton binding energy is 20-times smaller than that in conventional 2D perovskites. As a result, the photo-induced excitons can be thermally dissociated efficiently at room temperature, as clearly indicated from femtosecond transient absorption measurements. In addition, the mobility is largely improved due to the strong screening effect on charge impurities. Such low dielectric-confined 2D perovskites show excellent carrier extraction efficiency, and outstanding humidity resistance compared to conventional 2D perovskites.
关键词： dielectric confinement,humidity resistance,carrier mobility,exciton binding energy,2D perovskites
更新于2025-09-10 09:29:36
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Photocatalytic response of Fe, Co, Ni doped ZnO based diluted magnetic semiconductors for spintronics applications
摘要： Novel attempts were made to prepare diluted magnetic semiconductors separately with 10 at.% each of Fe, Co and Ni doped ZnO by sol-gel method. The XRD analysis of the films detect wurtzite ZnO as the pure phase present in the synthesized films. The average particle size of 10 at.% Fe, Co, Ni doped and pristine ZnO derived films are found as 10.01 nm, 12.03 nm, 15.36 nm and 16.16 nm respectively. The absorbance spectra of the oxides reveal intrinsic band gap of ZnO, Fe2O3, CoO and NiO are 3.29 eV, 2.53 eV, 2.42 eV and 3.64 eV respectively. The near band edge absorbance of pure ZnO was recorded as about 377 nm (～3.29 eV) which shifts to lower wavelength with reduction in particle size in Ni, Co and Fe doped ZnO sample as the effect of quantum confinement. The PL spectra of the developed films reveal multiple peaks between 450 nm and 500 nm, on excitation wavelength at 370 nm, as the evidence of photochemical properties of the samples. Vibrating sample magnetometer analysis reveals 10 at.% Fe doped ZnO posses minimum value of squareness 0.118 and coersivity 177.738 Oe which prove it to be the best magnetic material among all four samples prepared. Raman spectra show evidence of phonon confinement for 10 at.% Fe doped ZnO sample by broadening of Eg, T2g and A1g peaks, which is not so prominent for other samples. In addition, the photochemical degradation reaction is maximum for 10 at.% Fe doped ZnO sample which proves to be most suitable material for optoelectronic devices.
关键词： Solar spin,Zinc oxide,Photocatalytic response,Diluted magnetic semiconductors,Phonon confinement
更新于2025-09-10 09:29:36
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Non-monotonous wetting of graphene-mica and MoS2-mica interfaces with a molecular layer of water
摘要： Hydration of interfaces with a layer of water is a ubiquitous phenomenon, which has important implications for numerous natural and technologically important processes. Nevertheless, at the nanoscale the understanding of the wetting process is still limited, since it is experimentally difficult to follow. Here, graphene and monolayers of MoS2 deposited on dry mica are used to investigate wetting of the 2D material-mica interfaces with a molecularly thin layer of water employing scanning force microscopy in different modes. Wetting occurs non-monotonously in time and space for both types of interfaces. It starts at relative humidities (RH) of 10-17 % for graphenes and 8-9 % for MoS2, and it concludes with a homogeneous layer at 25-30 % and 15-20 %, respectively. Investigation of the process at the graphene-mica interface indicates that up to about 25 % RH, initially a highly compliant and unstable layer of water spreads, which subsequently stabilizes by developing labyrinthine nanostructures. Moreover, these nanostructures exhibit distinct mechanical deformability and dissipation, which is ascribed to different densities of the confined water layer. The laterally structured morphology is explained by the interplay of counteracting long-range dipole-dipole repulsion and short-range line tension, with the latter caused at least in part by the mechanical deformation of the 2D material. The proposed origins of the interactions are common for thin layers of polar molecules at interfaces, implying that the lateral structuring of thin wetting layers at sub-monolayer concentrations may also be a quite general phenomenon.
关键词： confinement,energy dissipation,hydration,slit pore,nanostructures,mechanical compliance,2D material
更新于2025-09-10 09:29:36
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Hydrostatic and uniaxial effects in InGaN/GaN quantum wells
摘要： We calculate strains, polarizations, and electric fields in InGaN/GaN quantum wells (lattice matched to GaN) under the influence of hydrostatic and uniaxial (along the c-axis) pressure. We calculate the confinement energies for electrons and holes, and we derive simple expressions for the transition energies and their pressure derivatives. We include the changes of the dielectric constant with pressure. The results seem compatible with the experimental data.
关键词： confinement energies,transition energies,uniaxial pressure,electric fields,strain,InGaN/GaN quantum wells,polarization,hydrostatic pressure
更新于2025-09-10 09:29:36
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Applied Nanophotonics || Quantum confinement effects in semiconductors
摘要： Absorption and emission of light by atoms, molecules, and solids arise from electron transitions. Electron confinement phenomena in solids with restricted geometry like nanoparticles, nanorods, or nanoplatelets gives rise to the modification of optical absorption and emission spectra and transition probabilities in semiconductor nanostructures. These phenomena are direct consequences of the wave properties of electrons. In this chapter we describe size-dependent optical properties of semiconductor nanostructures related to quantum confinement.
关键词： optical absorption,semiconductors,nanostructures,emission spectra,Quantum confinement
更新于2025-09-09 09:28:46
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Quantum Hall stripes in high-density GaAs/AlGaAs quantum wells
摘要： We report on quantum Hall stripes (QHSs) formed in higher Landau levels of GaAs/AlGaAs quantum wells with high carrier density (ne > 4 × 1011 cm?2) which is expected to favor QHS orientation along the unconventional (cid:2)1ˉ10(cid:3) crystal axis and along the in-plane magnetic ?eld B(cid:4). Surprisingly, we ?nd that at B(cid:4) = 0 QHSs in our samples are aligned along the (cid:2)110(cid:3) direction and can be reoriented only perpendicular to B(cid:4). These ?ndings suggest that high density alone is not a decisive factor for either abnormal native QHS orientation or alignment with respect to B(cid:4), while quantum con?nement of the 2DEG likely plays an important role.
关键词： quantum confinement,high carrier density,in-plane magnetic field,quantum Hall stripes,GaAs/AlGaAs quantum wells
更新于2025-09-09 09:28:46
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A Scanning Tunneling Microscopy Study of Monolayer and Bilayer Transition-Metal Dichalcogenides Grown by Molecular-Beam Epitaxy
摘要： This review presents an account of some recent scanning tunneling microscopy and spectroscopy (STM/S) studies of monolayer and bilayer transition-metal dichalcogenide (TMD) films grown by molecular-beam epitaxy (MBE). In addition to some intrinsic properties revealed by STM/S, defects such as inversion domain boundaries and point defects, their properties and induced effects, are presented. More specifically, the quantum confinement and moiré potential effects, charge state transition, quasi-particle interference and structural phase transition as revealed by STM/S are described.
关键词： transition-metal dichalcogenides,quantum confinement,structural phase transition,molecular-beam epitaxy,moiré potential,quasi-particle interference,scanning tunneling microscopy,charge state transition
更新于2025-09-09 09:28:46