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Spectrophotometric Characterization of Thin Copper and Gold Films Prepared by Electron Beam Evaporation: Thickness Dependence of the Drude Damping Parameter
摘要： Copper and gold films with thicknesses between approximately 10 and 60 nm have been prepared by electron beam evaporation and characterized by spectrophotometry from the near infrared up to the near ultraviolet spectral regions. From near normal incidence transmission and reflection spectra, dispersion of optical constants have been determined by means of spectra fits utilizing a merger of the Drude model and the beta-distributed oscillator model. All spectra could be fitted in the full spectral region with a total of seven dispersion parameters. The obtained Drude damping parameters shows a clear trend to increase with decreasing film thickness. This behavior is discussed in the context of additional non-optical characterization results and turned out to be consistent with a simple mean-free path theory.
关键词： optical constants,gold,copper,ultrathin metal films,thickness dependence
更新于2025-11-21 11:01:37
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Planar plasmonic nanocavity for efficient enhancement of photoluminescence of molecular emitters
摘要： Effects of plasmonic gap mode formation due to coupling between metal nanoparticles and thin metal film separated by thin dielectric luminescent film-spacer (gap) have been studied by means of light extinction and photoluminescence in three-layer planar Au NPs monolayer/shellac-dye film/Au film nanostructure with spacer thickness varied in the range 8–47 nm. The 3-fold enhancement of light extinction and 90 nm red shift of the plasmon mode have been observed in extinction spectra. The 37-fold enhancement of dye photoluminescence and the significant (48 nm) red shift of dye photoluminescence band have been observed for Au NPs monolayer/shellac-dye film/Au film nanostructure in comparison with bare shellac-dye film for the spacer thickness of 8 nm. The decrease of the spacer thickness causes the increase of the enhancement factor of dye photoluminescence indicating the strengthening of the gap mode field. FDTD calculations of the dependence of the intensity of the field of gap mode on the gap thickness have demonstrated good quantitative agreement with experimental data that proves the key role of gap mode in the enhancement of the electromagnetic field in planar metal NPs monolayer/dielectric film/metal film plasmonic nanocavity nanostructures. The variation of the gap thickness provides the possibility to tune controllably the spectral position and enhancement factor of the light emission from the molecular emitters located in the gap that can be used in the novel nanophotonics devices and for highly sensitive detection of the single molecules.
关键词： Near field coupling,Gap thickness dependence,Molecular emitters,Gap mode,Plasmonic nanocavity,Photoluminescence enhancement
更新于2025-11-19 16:46:39
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Thickness-dependent bandgap of transition metal dichalcogenides dominated by interlayer van der Waals interaction
摘要： Based on a bandgap thermodynamic approach, the thickness-dependent bandgap of two-dimensional transition metal dichalcogenides is modeled without any adjustable parameter. An efficient expansion in bandgap upon lowering the thickness is predicted. The thickness-dependence of bandgap is believed originated from the interlayer van der Waals (vdW) interaction, while the surface effect is characterized by the difference in atomic thermal vibration between the surface and the interior. Due to the suppression role of the interlayer vdW interaction on the thermal vibration of interior chalcogen atoms, the surface effect is variable, which changes from monotonic increase for sulfides to decrease for tellurides. The role of the interlayer vdW interaction depends on the polarity of metal-chalcogen bonds. The model predictions agree with available experiment and simulation results.
关键词： Surface effect,Thickness-dependence,Bandgap,Interlayer van der Waals interaction,Thermodynamics
更新于2025-09-23 15:23:52
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Thickness dependence of structural, morphological and optical properties of Mn-Co-Ni-O thin films grown by chemical solution deposition on SiO2/Si(100) substrate
摘要： Mn1.56Co0.96Ni0.48O4 (MCNO) thin film with different thicknesses ranging from 180 nm to 600 nm were deposited onto a SiO2/Si(100) substrate at 600 °C by using the chemical solution deposition method. The thickness dependent structural and optical properties of the MCNO films were investigated in this study. As identified by the SEM pictures and X-ray diffraction (XRD) spectra, all samples showed polycrystalline cubic spinel structure, and the stoichiometric status is improved with growing thickness according to XRD results. Spectroscopic ellipsometry spectra were measured in this study to investigate the thickness dependent optical properties of MCNO film in the range of 300-1000 nm. The samples showed three absorption structures locating at 1.6-1.9 eV, 2.6 eV, and above 3.5 eV, corresponding to the charge transfer transition involving 2p orbitals of O2- and 3d orbitals of Mn and Co ions, respectively. The absorption structure at above 3.5 eV decreases gradually as the thickness grows, while the peak around 1.6-1.9 eV weakens slightly before it enhances again with film thickness above 430 nm, which can be explained by a combined effect of crystallinity improvement and increase in Mn4+/Mn3+ ratio.
关键词： optical properties,Mn1.56Co0.96Ni0.48O4 thin film,thickness dependence,chemical solution deposition,absorption structures
更新于2025-09-23 15:22:29
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Unusual Electronic States and Superconducting Proximity Effect of Bi Films Modulated by NbSe2 Substrate
摘要： Heterostructures of two-dimensional layered materials can be functionalized with exotic phenomena that are unpresented with each constituting component. The interface effect plays a key role in determining the electronic properties of the heterostructure, whose characterization requires a correlation with the morphology with atomic-scale precision. Here, we report an investigation on the electronic properties of few-layer Bi(110) films mediated by NbSe2 substrate. By utilizing scanning tunneling microscopy and spectroscopy, we show a significant variation of the density of states at different Bi film thicknesses, resulting in an unusual superconducting proximity effect that deviates from the conventional monotonous decay behavior. Moreover, the electronic states of the Bi films are also prominently modulated by the Moiré pattern spatially. With first-principles calculations, we illuminate these findings as the results of covalent-like quasi-bonds formed at the Bi/NbSe2 interface, which profoundly alter the charge distributions in the Bi films. Our study indicates a viable way of modulating the electronic properties of ultrathin films by quasi-covalent interfacial couplings beyond conventional van der Waals interactions.
关键词： few-layers bismuth(110),two-dimensional heterostructures,thickness dependence,scanning tunneling microscopy,density functional theory calculations,covalent-like quasi-bonds,proximity effect
更新于2025-09-23 15:22:29