Diffuse reflectance and transmittance spectra of an interference layer. 2. Evaluation of tin oxide-coated glass

A model for the calculation of diffuse reflectance and transmittance of a single interference layer on a transparent substrate is applied to pyrolytically deposited tin oxide films on glass. Total as well as diffuse reflectance and transmittance spectra were measured in an integrating sphere, and scattering levels between 0.002 and 0.1 were recorded. The optical constants and the thickness of the films were determined from the total reflectance and transmittance spectra. The wavelength-dependent effective root-mean-square roughness of aluminum-coated tin oxide front surfaces was determined by the application of the scalar scattering theory. Surface roughness values between 5 and 25 nm were obtained. The obtained effective rms roughness values of the air-film interface were used together with the other film parameters to calculate the diffuse reflectance and transmittance spectra of the tin oxide-coated glass substrates. A comparison between calculated and experimental spectra showed good agreement for diffuse reflectance, diffuse transmittance, and total integrated scattering spectra.     

Gas sensing properties of graphene synthesized by chemical vapor deposition

The gas sensing properties of graphene synthesized by a chemical vapor deposition (CVD) method are investigated. Synthesis of graphene is carried out on a copper substrate using a methane and hydrogen gas mixture by a CVD process at the atmospheric pressure. The graphene films are transferred to different substrates after wet etching of the copper substrates. The Raman spectra reveal that the graphene films made on SiO₂/Si substrates are of high quality. The reflectance spectra of graphene were measured in UV/Visible region of the spectrum. Theoretically calculated reflectance spectra based on Fresnel's approach indicates that the CVD graphene has a single layer. The gas sensing properties of graphene were tested for different reducing gasses as a function of measurement temperature and gas concentration. It is found that the gas sensing characteristics such as response time, recovery time, and sensitivity depend on the target gas, gas concentration, test temperature, and the ambient gas composition. The cross sensitivity of few combinations of reducing gasses such as, NH₃, CH_4, and H₂ was also investigated.     

Reactive DC magnetron deposition of copper nitride films for write-once optical recording

Copper nitride (Cu_xN) films were prepared on glass slides by reactive direct current (DC) magnetron sputtering under different nitrogen flow rates and substrate temperature, respectively. X-ray diffraction and reflectance spectra were employed to characterize the films. The Cu_xN films can completely decompose through heat treatment at temperature as low as 160 °C. The reflectance spectra of the as-deposited films are quite different from that of the decomposed films in a wide wavelength range from UV to infrared. Its relatively low decomposition temperature and large reflectance change before and after decomposition makes it a potential write-once optical recording medium.     

Closed equation for the normal incidence reflectance of thin films on absorbing substrates

The optical constants of thin films can be obtained from inversion of spectrophotometric measurements by using minimization gradient methods. The computational approach of these minimization methods requires closed compact formulas for reflectance and/or transmittance. For normal incidence closed compact formulations for the direct transmittance, both for thin films on transparent or absorbing substrates, and for the reflectance of thin films on transparent substrates, are available in the literature. We report here a closed compact formula to evaluate reflectance spectra of thin films on absorbing substrates, and it is shown that for vanishing substrate absorption this new, to the best of our knowledge, approach gives the same results obtained from the formulation corresponding to thin films supported by transparent substrates.     

Simple Method for Determining Slowly Varying Refractive-Index Profiles from in situ Spectrophotometric Measurements

Reliable control of the deposition process of optical films and coatings frequently requires monitoring the refractive-index profile throughout the layer. In the present research a simple in situ approach is proposed that uses a WKBJ matrix representation of the optical transfer function of a single thin film on a substrate. Mathematical expressions are developed that represent the minima and the maxima envelopes of the curves transmittance versus time and reflectance versus time. The refractive index and the extinction coefficient depth profiles of different films are calculated from simulated spectra as well as from experimental data obtained during the PECVD (plasma-enhanced chemical vapor deposition) of silicon-compound films. Variation in the deposition rate with time is also evaluated from the position of the spectra extrema as a function of time. The physical and mathematical limitations of the method are discussed.     

Effect of cadmium oxide incorporation on the microstructural and optical properties of pulsed laser deposited nanostructured zinc oxide thin films

CdO doped (doping concentration 0, 1, 3 and 16 wt%) ZnO nanostructured thin films are grown on quartz substrate by pulsed laser deposition and the films are annealed at temperature 500 °C. The structural, morphological and optical properties of the annealed films are systematically studied using grazing incidence X-ray diffraction (GIXRD), energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), atomic force microscopy (AFM), Micro-Raman spectra, UV–vis spectroscopy, photoluminescence spectra and open aperture z-scan. 1 wt% CdO doped ZnO films are annealed at different temperatures viz., 300, 400, 500, 600, 700 and 800 °C and the structural and optical properties of these films are also investigated. The XRD patterns suggest a hexagonal wurtzite structure for the films. The crystallite size, lattice constants, stress and lattice strain in the films are calculated. The presence of high-frequency E₂ mode and the longitudinal optical A₁ (LO) modes in the Raman spectra confirms the hexagonal wurtzite structure for the films. The presence of CdO in the doped films is confirmed from the EDX spectrum. SEM and AFM micrographs show that the films are uniform and the crystallites are in the nano-dimension. AFM picture suggests a porous network structure for 3% CdO doped film. The porosity and refractive indices of the films are calculated from the transmittance and reflectance spectra. Optical band gap energy is found to decrease in the CdO doped films as the CdO doping concentration increases. The PL spectra show emissions corresponding to the near band edge (NBE) ultra violet emission and deep level emission in the visible region. The 16CdZnO film shows an intense deep green PL emission. Non-linear optical measurements using the z-scan technique indicate that the saturable absorption (SA) behavior exhibited by undoped ZnO under green light excitation (532 nm) can be changed to reverse saturable absorption (RSA) with CdO doping. From numerical simulations the saturation intensity (I_s) and the effective two-photon absorption coefficient (β) are calculated for the undoped and CdO doped ZnO films.     

Ag-Al_2O_3金属陶瓷复合薄膜的光学特性

采用磁控溅射技术在硼硅玻璃基片上沉积具有不同填充因子的Ag--Al2O3金属陶瓷复合薄膜,柔相济用紫外--可见--近红外分光光度计和透射电镜(TEM)分别表征复合薄膜的光谱特性及微观结构, 使用透射光谱及反 射光谱数据计算其光学常数, 研究了Ag--Al2O3复合薄膜的表面等离子体共振(SPR)吸收峰随填充因子的变化特征。结果表明, 在一定范围内, 随着填充因子的增大, SPR吸收峰增强、半峰全宽增大且峰位红移。     

Optical properties of erbium oxide thin films deposited by electron beam evaporation

Erbium oxide thin films were deposited by electron beam evaporation on substrates heated to 300 °C. The effect of the introduction of oxygen on the structural, chemical and optical properties of the films was investigated. The films were characterized using X-ray diffraction, X-ray photoelectron spectroscopy and normal-incidence transmittance and reflectance. The films had microcrystallites embedded in an amorphous matrix, and their stoichiometry was dependent on the oxygen partial pressure. The transmittance spectra of the films revealed that they were optically inhomogeneous. A model based on an inhomogeneous layer was applied to extract the refractive index and extinction coefficient from the transmittance and reflectance spectra.     

Effect of substrate temperatures on the optical properties of evaporated Sc2O3 thin films

Scandium oxide (Sc₂O₃) films were deposited by electron beam evaporation with substrate temperatures varying from 50 to 350 °C. X-ray diffraction, scanning electron microscopy, spectrometer, and optical profilograph were employed to investigate the structural and optical properties of the films. The refractive index and extinction coefficient were calculated from the transmittance and reflectance spectra, and then the energy band gaps were deduced and discussed. Laser induced damage threshold of the films were also characterized. Optical and structural properties of Sc₂O₃ films were found to be sensitive to substrate temperature.     

Simulation of the spectra and determination of the optical constants of online low-emission glass from visible to mid-infrared region

Online low emissivity glass (Low-E glass) is a promising glass product. Simulation of the spectra and determination of the optical constants of online Low-E glass are of practical interest for many applications such as product design, adjustment of coating process and comparison of samples produced using different methods. The online Low-E glass investigated here has two layers of films on 6 mm thick float glass substrate, which include the functional layer (the upper layer) and the transition layer (the lower layer). In this paper, the relation between transmittance and the parameters used in the model in the visible and near-infrared region was derived, so was the relation between reflectance and the parameters used in the model in the infrared region. The parameters used in the model were obtained by fitting the measured and simulated spectra. From the obtained parameters, the optical constants of the functional layer of online Low-E glass in the visible region and the infrared region were obtained, respectively. The sheet resistance and the infrared reflectance of Low-E glass were also calculated from the obtained fitting parameters. The simulated results are well consistent with the experimental ones.     

Spectrally selective absorber coating from transition metal complex for efficient photothermal conversion

Copper–manganese oxide (CuMnO _x ) thin films are proposed as efficient and thermally stable selective solar absorbers. The coatings were deposited on aluminum, stainless steel, and glass substrates by dip-coating method from the alcoholic solution of the Cu and Mn nitrate. An organic filmogen was introduced in order to get better adherence with the substrate hence to get uniform films even for larger substrates. The coated films were dried and subsequently heat-treated at 500 °C. X-ray diffraction spectra of the annealed film showed the formation of pure Cu–Mn oxide spinel structure (Cu_1.5Mn_1.5O₄) in the film. FTIR spectra show complete removal of the organic species after thermal treatment at 500 °C. The solar absorptance and thermal emittance were calculated from the hemispherical reflectance spectra in the UV/Vis/NIR and IR range, respectively. The maximum visible absorptance with minimizing the infrared thermal emittance was optimized by controlling the thickness of the films, choosing substrates, and introducing a SiO₂ overlayer.     

Laser-enhanced plating: A review of its mechanisms and applications

Model calculations are compared with published optical reflectance spectra for thermally oxidized samples of black chrome solar absorbing film on nickel substrates (T ≈ 600 °C). Good agreement between the model calculations and the published reflectance spectra indicates that the diffusion and oxidation of the nickel substrate is the primary cause of reflectance changes in this temperature regime (T ? 500 °C). Auger electron spectroscopy utilizing depth profiling similarly heated black chrome films on nickel substantiates this observation.     

Influence of Al concentration on structural and optical properties of Al-doped ZnO thin films

Undoped ZnO and Al-doped zinc oxide (ZnO:Al) thin films with different Al concentrations were prepared onto Si (100) substrate by pulsed filtered cathodic vacuum arc deposition system at room temperature. The influence of doping on the structural and optical properties of thin films was investigated. The preferential (002) orientation was weakened by high aluminum doping in films. Raman measurement was performed for the doping effects in the ZnO. Atomic force microscopy images revealed that the surface of undoped ZnO film grown at RT was smoother than that of the Al-doped ZnO (ZnO:Al) films. The reflectance of all films was studied as a function of wavelength using UV–Vis–NIR spectrophotometer. Average total reflectance values of about 35 % in the wavelength range of 400–800 nm were obtained. Optical band gap of the films was determined using the reflectance spectra by means of Kubelka–Munk formula. From optical properties, the band gap energy was estimated for all films.     

Determining the internal quantum efficiency of PbSe nanocrystal solar cells with the aid of an optical model

We determine the internal quantum efficiency (IQE) of the active layer of PbSe nanocrystal (NC) back-contact Schottky solar cells by combining external quantum efficiency (EQE) and total reflectance measurements with an optical model of the device stack. The model is parametrized with the complex index of refraction of each layer in the stack as calculated from ellipsometry data. Good agreement between the experimental and modeled reflectance spectra permits a quantitative estimate of the fraction of incident light absorbed by the NC films at each wavelength, thereby yielding well-constrained QE spectra for photons absorbed only by the NCs. Using a series of devices fabricated from 5.1+/-0.4 nm diameter PbSe NCs, we show that thin NC cells achieve an EQE and an active layer IQE as high as 60+/-5% and 80+/-7%, respectively, while the QE of devices with NC layers thicker than about 150 nm falls, particularly in the blue, because of progressively greater light absorption in the field-free region of the films and enhanced recombination overall. Our results demonstrate that interference effects must be taken into account in order to calculate accurate optical generation profiles and IQE spectra for these thin film solar cells. The mixed modeling/experimental approach described here is a rigorous and powerful way to determine if multiple exciton generation (MEG) photocurrent is collected by devices with EQE<100%. On the basis of the magnitudes and shapes of the IQE spectra, we conclude that the 1,2-ethanedithiol treated NC devices studied here do not produce appreciable MEG photocurrent.     

Influence of dopant concentration on the optical properties of ZnO: In films by sol-gel method

Undoped and In doped ZnO films have been deposited by sol-gel spin coating method. The effect of indium incorporation on structural and optical properties of ZnO films has been investigated. X-ray diffraction patterns of the films showed the hexagonal wurtzite type polycrystalline structure and that indium incorporation leads to substantial changes in the structural characteristics of ZnO films. The SEM and AFM measurements showed that the surface morphology of the films was affected from the indium incorporation. Optical reflectance and transmittance were recorded with a double beam spectrophotometer with an integrating sphere. The optical band gap of these films was determined. The absorption edge shifted to the lower energy depending on the dopant materials. The optical constants of these films were determined using transmittance and reflectance spectra.     

Extraction of optical properties of flat and surface-textured transparent conductive oxide films in a broad wavelength range

An accurate characterization method is developed to determine the refractive index of smooth and surface-textured transparent conductive oxide (TCOs) films. The properties are obtained from simultaneous fitting of simulated specular reflectance/transmittance spectra to spectroscopic measurements for different polarizations and angles of light incidence. The simulations are based on a combination of physical models describing dielectric function of TCO films. Besides the refractive index also other material properties of TCO films are obtained, such as the band gap and free carrier absorption. A light scattering model is implemented into the simulations to take into account the diffused part of the light scattered at randomly-textured surfaces of TCO films.     

Optical properties of plasma-assisted molecular beam epitaxy grown InN/sapphire

The optical properties of as-grown InN/sapphire films prepared by plasma assisted molecular beam epitaxy (PA-MBE) are characterized by photoluminescence (PL), Raman scattering (RS) and infrared (IR) reflectance techniques. The PL measurements have consistently exhibited lower values of InN band gaps providing clear indications of electron concentration dependent peak energy shifts and widths. The phonon modes identified by RS are found to be in good agreement with the grazing inelastic X-ray scattering measurements and ab initio lattice dynamical calculations. An effective medium theory used to analyze IR reflectance spectra of InN/sapphire films has provided reasonable estimates of free charge carrier concentrations.     

Imaging reflectometry in situ

An innovative method of in situ real-time optical monitoring of thin film deposition and etching is presented. In this technique, intensity maps of a thin film corresponding to a series of wavelengths selected by a monochromator (300-800 nm) are recorded by a CCD camera. From the maps the reflectance spectra at individual points of the sample surface can be extracted. By fitting the reflectance spectra to the theoretical ones, the maps of a thin film morphology (including optical parameters) and their temporal development during technological processes can be obtained. The method was tested by in situ observation of the growth of silicon nitride and silicon oxide thin films prepared by ion beam sputtering and by the monitoring of etching of thermally grown SiO(2) thin films.     

Optical properties of SiOC film by PL spectrometer and reflectance

SiOC films made by the inductive coupled plasma chemical vapor deposition were analyzed by the photo luminance spectra and reflectance. Chemical shift obtained by PL spectra was observed and the reflectance was decreased at sample with low refractive index. The refractive index was in inverse proportion to the thickness of SiOC film. Lowering the reflectance caused to decrease the energy band gap and polarization, so increased an absorbance of the light. Low polarization of SiOC film was induced from the recombination and dissociation of alkyl sites by neighboring high electro negative oxygen. The electron affinity related to the energy band gap at surfaces increased at sample with low polarization, and finally, the reflectance decreased according to the reduction of polarity.     

Color modeling of stratified pictorial layers using the radiative transfer equation solved by the auxiliary function method

The diffuse reflectance spectra and the trichromatic coordinates of diffusing stratified paints are modeled. Each layer contains its own pigments, and their optical properties are first determined from experiments. The radiative transfer equation is then solved by the auxiliary function method for modeling the total light scattered by the stratified systems. The results are in good agreement with experimental spectra and validate the modeling. The calculations are then applied on the same stratified systems to study the influence of the observation angle in a bidirectional configuration and to study the influence of the thickness of the layers in a given configuration. In both cases, the reflectance spectra and the trichromatic coordinates are calculated and compared.