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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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Core-Shell Modeling of Light Scattering by Vesicles: Effect of Size, Contents, and Lamellarity
摘要： Having a fast, reliable method for characterizing vesicles is vital for their use as model cell membranes in biophysics, synthetic biology, and origins of life studies. Instead of the traditionally used Rayleigh-Gans-Debye approximation, we use an exact extended Lorenz-Mie solution for how core-shell particles scatter light to model vesicle turbidity. This approach enables accurate interpretations of simple turbidimetric measurements and is able to accurately model highly scattering vesicles, such as larger vesicles, those with multiple layers, and those with encapsulated material. We uncover several surprising features, including that vesicle lamellarity has a larger effect on sample turbidity than vesicle size and that the technique can be used to measure the membrane thickness of vesicles. We also examine potential misinterpretations of turbidimetry and discuss when measurements are limited by forward and multiple scattering and by the geometry of the instrument.
关键词： Lorenz-Mie theory,turbidimetry,membrane thickness,vesicles,lamellarity,light scattering
更新于2025-11-19 16:56:35
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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 of sublimation grown SiC layers measured by scanning Raman spectroscopy
摘要： We have grown homoepitaxial high resistivity SiC layers on conducting SiC substrates. We develop a method to determine the thickness of grown layers by scanning confocal Raman spectroscopy (SCRS). We also grow epitaxial graphene on SiC layers to label the top sample surface, and, we correlate the top surface position with Rayleigh scattering (RS). The interface between the high resistivity SiC layer and conductive SiC substrate is probed by the transition from LO phonon to the coupled LO phonon-plasmon Raman mode. The layer thickness measurements are veri?ed by ellipsometry and Secondary Ion Mass Spectroscopy (SIMS). We show that the SCRS method provides superior lateral and vertical resolution, it is robust against errorneous conclusions based on ad-hoc models, and it is easy to implement.
关键词： SiC layer thickness,Graphene,Raman spectroscopy
更新于2025-11-14 15:19:41
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An experimental and theoretical study of the structural ordering of the PTB7 polymer at a mesoscopic scale
摘要： Our extensive study based on optoelectronic and electric measurements (which consisted of: UV-Vis absorption, photoluminescence, surface photovoltage measurement, charge extraction by linearly increasing voltage, and energy-resolved electrochemical impedance spectroscopy) revealed the fundamental role of the thickness of the formation of intra- and interchain interaction in poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) films. We have shown that the final optoelectronic and electronic properties of PTB7 films are governed by the structural ordering development of the transition from nano- to submicroscale. The ordering of polymer chains and competition between the formation of J- and H-aggregates results in a non-trivial dependence of luminescence, exciton diffusion length, transport band gap, and defect concentration. According to a theoretical analysis, the driving forces responsible for the observed phenomena are associated with the thickness threshold dependence of the thin film drying mode which can proceed with or without the polymer skin formation on the surface of forming film.
关键词： low band-gap,thickness dependences,Conjugated polymers
更新于2025-10-22 19:40:53
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Retinal vascular density evaluated by optical coherence tomography angiography in macular telangiectasia type 2
摘要： Purpose To evaluate the retinal and choroidal vascular changes through optical coherence tomography angiography (OCTA) in patients with macular telangiectasia type 2 (MacTel 2). Methods Our study included 20 patients (40 eyes) with MacTel 2, and age-matched and sex-matched 18 subjects (36 eyes) in the control group. Fundus color photographs, fundus autofluorescence, fundus fluorescein angiography, spectral-domain optical coherence tomography and OCTA were performed. Foveal vascular density and parafoveal vascular density (PFVD), and foveal retinal thickness and parafoveal retinal thickness, choroidal thickness (CT) and retinal ganglion cell–inner plexiform layer (GCIPL) were compared between MacTel 2 patients and normal age-matched controls. Results The retinal whole vascular density and PFVD of the deep plexus were significantly lower in patients with MacTel 2 than that of the control group (56.93% vs. 58.54%, p = 0.003; and 60.38% vs. 61.66%, p = 0.045). The foveal avascular zone (FAZ) of the deep plexus was significantly enlarged in patients with MacTel 2 than that of the control group (0.44 vs. 0.36, p = 0.009). There was a positive and statistically significant correlation between the FAZ of the superficial and deep plexus and CT in patients with MacTel 2. There was a positive and statistically significant correlation between retinal whole, parafoveal temporal quadrant vascular density of the superficial and deep plexus and GCIPL thickness in patients with MacTel 2. Conclusions Our study demonstrated that important retinal vascular density and FAZ changes in MacTel 2 occur in the deep capillary plexus of the retina.
关键词： Macular telangiectasia type 2,Vascular density,Choroidal thickness,Retinal ganglion cell–inner plexiform layer,Optical coherence tomography angiography
更新于2025-09-23 15:23:52
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Simulated and observed horizontal inhomogeneities of optical thickness of Arctic stratus
摘要： Two-dimensional (2D) horizontal fields of cloud optical thickness derived from airborne measurements of solar spectral radiance during the Vertical Distribution of Ice in Arctic Clouds (VERDI) campaign (carried out in Inuvik, Canada in April/May 2012) are compared with semi-idealized Large Eddy Simulations (LES) of Arctic stratus performed with the COnsortium for Small-Scale MOdeling (COSMO) atmospheric model. The input for the LES is obtained from collocated airborne dropsonde observations. Four consecutive days of a persistent Arctic stratus observed above the sea-ice free Beaufort Sea are selected for the comparison. Macrophysical cloud properties such as cloud top altitude and vertical extent are well captured by COSMO. Cloud horizontal inhomogeneity quantified by the standard deviation and one-dimensional (1D) inhomogeneity parameters show that COSMO produces only half of the measured horizontal cloud inhomogeneities, while the directional structure of the cloud inhomogeneity is well represented by the model. Differences between the individual cases are mainly associated with the wind shear near cloud top and the vertical structure of the atmospheric boundary layer. A sensitivity study changing the wind velocity in COSMO by a vertically constant scaling factor shows that the directional cloud inhomogeneity structures strongly depend on the mean wind speed. A threshold wind velocity is identified, which determines when the cloud inhomogeneity stops increasing with increasing wind velocity.
关键词： airborne measurements,COSMO model,horizontal inhomogeneity,wind speed sensitivity,Large Eddy Simulation,Arctic stratus,cloud optical thickness
更新于2025-09-23 15:23:52
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Choroidal thickness in healthy eyes using enhanced depth imaging optical coherence tomography and comparison with cases of retinitis pigmentosa
摘要： Introduction. — The goal of this study was to measure by spectral domain optical coherence tomography (SD-OCT) with EDI the choroidal thickness in healthy subjects and to compare these parameters with those of patients with retinitis pigmentosa (RP). Methods. — Data were obtained from 60 healthy patients without history or family history of retinal or choroidal disease or glaucoma. A case-control study was also conducted on 40 eyes of 20 patients with RP and 40 eyes of 20 healthy refraction- and age-matched controls, selected from among the 60 healthy patients. OCT was used with the EDI protocol. The primary outcome measure was choroidal thickness. Results. — Among healthy patients, the overall choroidal thickness was 287.7 μm. Mean choroidal thickness was lower on the nasal side (236.6 μm from the fovea) compared with the temporal side (262.3 μm, P = 0.002). It also varied according to age, being highest among 20—29-year-old patients and decreasing thereafter with increasing age. Choroidal thickness was significantly higher in healthy patients than in RP patients, regardless of the location (P < 0.001). Conclusion. — This observational study confirms that choroidal thickness varies with age and location. It decreases in subjects with RP and is related to worsening of retinal damage, independently of age-related thinning. Further studies are needed to understand whether choroidal vascular alteration is a cause or a consequence of the degenerative pathology.
关键词： Photoreceptor degeneration,Choroidal thickness,Case-control study,Retinitis pigmentosa,Enhanced depth imaging optical coherence tomography
更新于2025-09-23 15:23:52
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Optical thickness identification of few-layer MoS <sub/>2</sub> deposited by chemical vapor deposition
摘要： The physical and optoelectronic properties of MoS2 are closely related to their thickness. Few-layer molybdenum disulfide (MoS2) has been intensively studied for its potential applications. In this work, monolayer and few-layer MoS2 nanosheets with large size and high crystallization quality were successfully prepared by chemical vapor deposition (CVD). Then, the layer number of CVD-grown MoS2 nanosheets were identified for the first time by extracting the R channel contrast of the optical image of the sample with ImageJ software. Compared with Raman spectra and PL spectra, this method can identify the layer number of CVD-grown MoS2 nanosheets efficiently and accurately, which provides a simple and feasible method for the study of the layer number of CVD-grown MoS2 nanosheets and can help us exploiting their applications in the future.
关键词： Thickness identification,chemical vapor deposition,MoS2,optical microscopy,Raman spectroscopy
更新于2025-09-23 15:23:52
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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