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Ultrahighly Enhanced Performance of Single Cadmium Selenide Nanobelt by Plasmonic Gold Particles
摘要： Noble metal nanoparticles have been demonstrated by a huge application prospect for photodetector (PD) due to their unique and tunable optical properties. Herein, a simple strategy is presented by a combination of gold nanoparticles (Au NPs) and broadband photoresponse cadmium selenide nanobelts (CdSe NBs) to get ultrasensitive, broadband photoresponse (300–720 nm) and tunable photoresponse PD. Concretely, the Au NPs are fabricated on CdSe NBs via ion sputtering and annealing, and the morphology of Au NPs is systematically adjusted by simply tuning the sputter time from 60 to 140 s. Compared with the pure CdSe NB PD, the Au NPs hybrid CdSe NB PD exhibits a high responsivity, especially in the range of 525–575 nm with low light intensity (enhancement of (cid:3)2). The response time of the hybrid PD is (cid:1)2894% at 550 nm with 79.6 μW cm decreased substantially from 0.8 to 0.2 ms. More importantly, the hybrid PD possesses a tunable absorption in the range of 538–580 nm, which is bene?ted from tunable plasmon resonance of Au NPs. These results are con?rmed by the theoretical simulation. It is believed that this strategy offers new opportunities to design ultrasensitive, broadband spectra, and tunable wavelength PD.
关键词： cadmium selenide nanobelts,photodetectors,the discrete dipole approximation,surface plasmon resonances
更新于2025-09-11 14:15:04
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Theoretical calculation of optical absorption property of Cu@Ag core–shell composite nanoparticle
摘要： Because of their unique surface plasmon resonance (SPR) absorption in the visible region of the electromagnetic (EM) wavelength, plasmonic nanoparticles (NPs) such as gold (Au), silver (Ag) and copper (Cu) are utilized to combine with another material in devices. In this work, the optical absorption property exhibited by core–shell NPs composed of Cu cores with Ag shells (Cu@Ag) was investigated by the Discrete Dipole Approximation (DDA) method. In the theoretical calculation, at ?rst, the Ag shell thickness was ?xed at 5 nm and the Cu core diameters were varied between 10 and 30 nm. Second, the Cu core size was ?xed at 20 nm and the Ag shell thickness was varied from 2 nm to 10 nm. It was observed that as the size of the Cu core increased with a ?xed Ag shell thickness, the absorption peak gradually shifted to that of the pure Cu peaks (at ～358 nm and ～510 nm). On the other hand, the increasing Ag shell thickness showed the shifting of the absorption peak to the absorption peak of pure Ag NP (～432 nm). The results revealed that varying either the Cu core size or the Ag shell thickness could result in obtaining tuneable light absorption. Such typical nanomaterials are expected to ?nd application in future medical, solar cell and novel functional devices.
关键词： discrete dipole approximation,Cu@Ag core-shell,localized surface plasmon resonance
更新于2025-09-11 14:15:04
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Gauge invariance and origin independence of electronic charge density and current density induced by optical fields
摘要： Expressions for the first-order polarization charge density ρ(1) and current density J(1) induced in a molecule by a monochromatic plane wave, obtained by time-dependent quantum mechanical perturbation theory, have been investigated to assess their gauge invariance and independence of the coordinate system in passive and active translations. The conditions arrived at show that, within the (long wavelengths) dipole approximation, only the electric contributions to these densities are needed to rationalize the phenomenology. To the next higher quadrupole approximation, assuming that the magnetic field and the electric field gradient are uniform over the molecular dimensions, corresponding contributions to ρ(1) and J(1) are considered. It has been found that total densities are independent of the origin, whereas the contributions from electric and magnetic fields are not separately invariant. A magnetic contribution to J(1), which is by itself origin independent, can be defined by means of an approach based on continuous translation of the origin of the coordinate system.
关键词： time-dependent perturbation theory,origin independence,quadrupole approximation,current density,optical fields,gauge invariance,dipole approximation,electronic charge density
更新于2025-09-09 09:28:46
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High-order above-threshold ionization beyond the electric dipole approximation: Dependence on the atomic and molecular structure
摘要： We provide an in-depth analysis of high-order above-threshold ionization of atoms and molecules by strong laser pulses, using three different theoretical approaches beyond the electric dipole approximation: (i) the numerical solution of the time-dependent Schr?dinger equation, (ii) the classical three-step model, and (iii) the quantum-orbit model. In the classical and quantum-orbit models, we include an accurate description of the rescattering step by target-specific differential scattering cross sections. The considerable forward shift of the photoelectron momentum distributions along the laser propagation direction can be understood in terms of the nondipole electron motion after rescattering. An explanation of the additionally observed forward-backward asymmetry of the signal strength requires the accurate modeling of the rescattering step and the electron dynamics before the rescattering event. For the H2+ molecular ion, we compare the cases of parallel and perpendicular alignment of the molecular axis and we show that the interference pattern and its modification due to the nondipole effects are orientation dependent. Compared to atoms, the nondipole effects in molecular high-order above-threshold ionization appear more pronounced and amenable to experimental observation.
关键词： high-order above-threshold ionization,nondipole effects,photoelectron momentum distributions,quantum-orbit model,classical three-step model,H2+ molecular ion,electric dipole approximation,time-dependent Schr?dinger equation
更新于2025-09-04 15:30:14
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Resonance Energy Transfer in Arbitrary Media: Beyond the Point Dipole Approximation
摘要： In this work, we present a comprehensive theoretical and computational study of donor/acceptor resonance energy transfer (RET) beyond the dipole approximation, in arbitrary inhomogeneous and dispersive media. The theoretical method extends Fo?rster theory for RET between particles (molecules or nanoparticles) to the case where higher multipole transitions in the donor and/or acceptor play a significant role in the energy transfer process. In our new formulation, the energy transfer matrix element is determined by a fully quantum electrodynamic expression, but its evaluation requires only classical electrodynamics calculations. By means of a time domain electrodynamical approach (TED), the matrix element evaluation involves the electric and magnetic fields generated by the donor and evaluated at the position of the acceptor, including fields associated with transition electric dipoles, electric quadrupoles, and magnetic dipoles in the donor, and the acceptor response to the electric and magnetic fields and to the electric field gradient. As an illustration of the benefits of the new formalism, we tested our method with a 512 atom lead sulfide (PbS) quantum dot as the donor/acceptor in vacuum, and with spherical nanoparticles (toy model) possessing designed transition multipoles. This includes an analysis of the effects of interferences between multipoles in the energy transfer rate. The results show important deviations from the conventional Fo?rster dipole theory that are important even in vacuum but that can be amplified by interaction with a plasmonic nanoparticle.
关键词： multipole transitions,resonance energy transfer,plasmonic nanoparticle,quantum electrodynamics,dipole approximation,RET
更新于2025-09-04 15:30:14