Diffuse reflectance and transmittance spectra of an interference layer: 1. Model formulation and properties

A model for the calculation of the diffuse reflectance and transmittance of a single interference layer with rough interfaces on a transparent substrate is presented. The model is based on electric field calculations and scalar scattering theory, and it assumes that the interfaces of the layer are totally uncorrelated. Examples are given of calculated spectra in which the parameters of the model are varied systematically to show the influence from different interface roughness and refractive index combinations as well as absorption in the film. A wavelength-dependent effective root-mean-square roughness is introduced. This depends on the nature of the roughness, and the bandwidth limits are given by the experimental conditions. Finally, total integrated scattering spectra are calculated and the importance of taking multiple reflections in the substrate into account is shown.     

Interfacial analysis and properties of regioregular poly(3-hexyl thiophene) spin-coated on an indium tin oxide-coated glass substrate

Interfacial analysis of the rrP3HT samples spin-coated on a glass substrate was studied in detail using transmission electron microscopy (TEM) and SEM measurements. Very homogeneous and smooth polymer (P3HT and PEDOT:PSS) layers are observed on the glass substrate. The ITO surface shows a surface roughness, with a layer of about 15 nm. Structural characteristics of the polymer blends were studied using Raman spectroscopy and photoluminescence (PL). The complete reduction of PL of P3HT after mixing with C₆₀ in a 1:1 wt.% indicates an effective charge transfer from P3HT to C₆₀. Thermo-gravimetric analysis showed that the commercially bought materials are of high purity.     

Preparation and optical characterization of lanthanum modified lead zirconate titanate thin films on indium-doped tin oxide-coated glass substrate

Lanthanum modified lead zirconate titanate (PLZT) thin films were fabricated on indium-doped tin oxide (ITO)-coated glass substrate by sol-gel method. The structure of the films was characterized with X-ray diffraction and scanning electron microscopy. The optical properties were investigated in the wavelength range of 220-2400 nm. The sample was modelled as a three layer structure on finite substrate, and optical constants of this system were calculated from the transmission and reflection spectra. The calculated dielectric function was fitted with the Drude model in the case of ITO and a sum of Lorentzian oscillators in the case of PLZT films. For PLZT film the anomalous behaviour of imaginary part of dielectric function was observed below the absorption edge. The possible reasons of that behaviour were discussed.     

Synthesis and conductive performance of antimony-doped tin oxide-coated TiO2 by the co-precipitation method

The synthesis of Sb–SnO₂/TiO₂ (SST) composites by assembling antimony-doped tin oxide (Sb–SnO₂) nanoparticles on the surface of titanium dioxide (TiO₂) is systematically investigated. X-ray diffraction data show that the SST composite materials with good crystallinity can be indexed as anatase TiO₂ phase and cassiterite SnO₂ phase. The scanning electron microscopy and transmission electron microscopy indicate that Sb–SnO₂ particles with average diameter of 25 nm have been successfully coated on the surface of TiO₂. In addition, the Ti–O–Sn band can be detected on the surface of TiO₂ through Fourier translation infrared spectroscopy. The influences of pH, Sn/Ti mole ratio, hydrolysis temperature and calcination temperature on the electrical resistivity of the SST powders are studied. Under the optimum experimental conditions, the electrical resistivity of the composite conductive powders is 2.546 × 10³ Ω cm. Therefore, the SST composite conductive powders are useful as conductive fillers for the application in antistatic materials.     

Thin-film optical function acquisition from experimental measurements of the reflectance and transmittance spectra: a case study

Journal of Materials Science: Materials in Electronics - The determination of the spectral dependence of thin-film optical functions from experimental measurements of the optical response,...     

Scattering and absorption cross sections of light diffusing materials retrieved from reflectance and transmittance spectra of collimated radiation

Four-flux radiative transfer models have been extensively used to describe reflectance and transmittance (R&T) spectra of light scattering and absorbing (S&A) media. Solutions to the differential equations corresponding to the collimated fluxes are obtained by subsequent application of boundary conditions. Explicit expressions for the collimated R&T of light are reported, when considering a light S&A medium contained between two glass slides, an experimental arrangement which is appropriate for liquid suspensions and viscous matrices containing solid particles. A spectral simulated annealing method is applied to retrieve, from measured R&T spectra of collimated light under normal incident radiation, the scattering and absorption coefficients of the composite medium. First, the accuracy of the method is established by applying it to synthetic collimated R&T data. Secondly, we apply the method to experimental data and use it to determine the S&A coefficients of a layer of TiO₂ particles dispersed in a PVP/water matrix.     

Metal/dielectric transmission interference filters with low reflectance. 2. Experimental results

The successful fabrication of metal/dielectric multilayer filters requires not only accurate control of the individual layer thicknesses, but also a good knowledge of the optical constants of the materials used in the filters. In the case of metal films, it is also essential to know whether any transition layers are formed at the interfaces and, if so, how their thicknesses and optical constants depend on the deposition conditions. An automatic, real-time process control, magnetron sputtering deposition system was modified to permit the manufacture of metal/dielectric filters using optical monitoring techniques. To illustrate the performance of this system, two bandpass filters, a short-wavelength pass filter, and a neutral density filter were produced, all having a low reflectance for light incident on one side. The metal layers used in these filters consisted of either Ni or Ag. TheAg films could be protected from the O(2) plasma using thin Ni or Si films. Good agreement was obtained between the calculated and measured spectral transmittance and reflectance curves.     

Synthesis of tin oxide-coated gold nanostars and evaluation of their surface-enhanced Raman scattering activities

Tin oxide-coated gold nanostar hybrid nanostructures are prepared by first synthesizing gold nanostars (ca. 400 nm), then introducing Na₂SnO₃ precursor followed by its hydrolysis and formation of a tin oxide layer on nanoparticle surface. The synthesized hybrid structures have been characterized by combination of UV–Vis spectroscopy, transmission electron microscope (TEM), energy-dispersive X-ray studies, scanning electron microscope (SEM), X-Ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The TEM and SEM analyses showed that gold nanostars have a coating with an approximate thickness of 15 nm. The tin (IV) oxide coating on the gold nanostars was identified by XRD and XPS analyses and confirmed by FTIR spectroscopy. Surface-enhanced Raman scattering (SERS) spectroscopy was performed on tin oxide-coated and uncoated gold nanostars with crystal violet as a probe molecule. The SERS studies revealed field enhancement properties of Au nanostars, thus their strong SERS activity remained after tin oxide coating.     

Evaluation and unification of some methods for estimating reflectance spectra from RGB images

The problem of estimating spectral reflectances from the responses of a digital camera has received considerable attention recently. This problem can be cast as a regularized regression problem or as a statistical inversion problem. We discuss some previously suggested estimation methods based on critically undersampled RGB measurements and describe some relations between them. We concentrate mainly on those models that are using a priori information in the form of high-resolution measurements. We use the "kernel machine" framework in our evaluations and concentrate on the use of multiple illuminations and on the investigation of the performance of global and locally adapted estimation methods. We also introduce a nonlinear transformation of reflectance values to ensure that the estimated reflection spectra fulfill physically motivated boundary conditions. The reported experimental results are derived from measured and simulated camera responses from the Munsell Matte, NCS, and Pantone data sets.     

Evaluation of the telegrapher's equation and multiple-flux theories for calculating the transmittance and reflectance of a diffuse absorbing slab

We study the propagation of light through a medium containing isotropic scattering and absorption centers. With a Monte Carlo simulation serving as the benchmark solution to the radiative transfer problem of light propagating through a turbid slab, we compare the transmission and reflection density computed from the telegrapher's equation, the diffusion equation, and multiple-flux theories such as the Kubelka-Munk and four-flux theories. Results are presented for both normally incident light and diffusely incident light. We find that we can always obtain very good results from the telegrapher's equation provided that two parameters that appear in the solution are set appropriately. We also find an interesting connection between certain solutions of the telegrapher's equation and solutions of the Kubelka-Munk and four-flux theories with a small modification to how the phenomenological parameters in those theories are traditionally related to the optical scattering and absorption coefficients of the slab. Finally, we briefly explore how well the theories can be extended to the case of anisotropic scattering by multiplying the scattering coefficient by a simple correction factor.     

Diameter measurement of glass fiber by an interference method

Measurement Techniques -     

Polychromatic reflectance and transmittance of a slab with a randomly rough boundary

We investigated four different approximation models for describing the polychromatic reflectance and transmittance of a slab with a randomly rough boundary while taking into account the coherent and the incoherent scattering of the rough boundary. Comparisons with experiments (an etched-silicon wafer) show that approximation models that apply a two-scale roughness to the randomly rough boundary and that take into account the coherent and the incoherent scattering yield better agreement and extend the range of validity of the approximation to shorter wavelengths.     

Infrared reflectance and transmission spectra of semiconducting non-stoichiometric CdGe x As2

The infrared reflectance and transmission spectra of amorphous CdGe _x As₂ were investigated to study the amorphous structure with varying Ge content. The mid-infrared optical absorption edges of amorphous CdGe _x As₂ with 0<x<1.2, were observed in the range 1.6–1.7 m, indicating a structural similarity in short-range order throughout. Comparing the reflectance and transmission spectra of amorphous and devitrified crystalline phases established that the structures of amorphous CdGe _x As₂ transformed from the CdAs₂ basic structure to the chalcopyrite (CdGeAs₂) structure, as one progressed fromx=0 tox=1.2. The infrared spectra were interpreted interactively with radial distribution function, magnetic susceptibility, density measurements, and crystallization studies. The crystallization behaviour of amorphous CdGe _x As₂ that was heat treated at different temperatures was investigated using far-infrared transmission spectra.     

Sample holder and methodology for measuring the reflectance and transmittance of narrow-leaf samples

Measuring the reflectance and transmittance of narrow samples can be difficult, as the width of the illuminating beam may be greater than the width of the sample. The small sample area can also compound the already time-consuming process of reconfiguring the instrument between reflectance and transmittance measurements by introducing additional alignment problems. A method of measuring the reflectance and transmittance properties of narrow-leaf samples using reflectance configurations only is developed and tested. The method uses a mask and mask correction and relationships between reflectance measurements against contrasting backgrounds to determine sample reflectance and transmittance. The design of the accompanying sample-holding apparatus is also described. In testing, the mean error was less than 1% reflectance/transmittance, and standard deviation of the error was approximately 1% reflectance and 2% transmittance as compared to samples measured using conventional measurement configurations.