Papers by Keyword: Optical Constant

Abstract: The effect of thermal treatment on optical constants of pure PMMA and with addition (15 and 35) ml of coumarin at different temperatures (100, 110 and 120) C⁰ for 1 hour were investigated. Cast method used to prepares films of pure PMMA and PMMA with (15 and 35) of coumarin. UV/VIS spectrometer technique used to measure the absorption spectra for these films. The optical constant (absorption spectra and absorption coefficient) don’t changes after applied temperatures in pure PMMA film but the optical constant (absorption spectra and absorption coefficient) in PMMA with (15 and 35) ml of coumarin increased with applied temperatures. The optical energy gap of pure PMMA and PMMA with (15 and 35) ml of coumarin slightly decreased after applied temperature up to 120⁰ C.

Abstract: CdSe quantum dots possess a tuning energy gap which can control gap values according to the size of the quantum dots, this is made the material able to absorb the wavelengths within visible light. A simple model is provided for the absorption coefficient, optical properties, and optical constants for CdSe quantum dots from the size 10nm to 1nm with the range of visible region between (300-730) nm at room temperature. It turns out that there is an absorption threshold for each wavelength, CdSe quantum dots begin to absorb the visible spectrum of 1.4 nm at room temperature for a wavelength of 300 nm. It has been noted that; when the wavelength is increased, the absorption threshold also increases. This applies to the optical properties and optical constants, where their values start to change from the threshold at 1.4 nm. The obtained results indicate that the range of the absorption coefficient can cover the ultraviolet, visible and to the infrared region when the quantum sizes are relatively large ( the size  9 nm), while the small sizes give small ranges of it, as only the ultraviolet region (the size = 1.4 nm) or part of the visible region ( the size > 1.4 nm ). What resulted from this difference in the results of the absorption coefficient, had a significant impact on the optical properties. Although the material has high transmittance ( reach more 75%), it is considered to have low absorbance ( less than 0.01%), at the same time the reflectivity had been valued between ( 14% to 22%) according to of size dot. The optical conductivity is proportional to quantum dot size, where an increase of it depends on the increasing of quantum dot size. It was also found that the real part of the dielectric constant is much greater than the imaginary part values, this is an indication that; the numbers of polarized charges towards the electric field were much greater than the polarized charges opposite to the direction of the field. It is worth noting that the behaviour of the refractive index is similar to the real part, while the extinction index resembles that of the imaginary part.

Abstract: Simple and low-cost homemade Rotating Analyzer Ellipsometer (RAE) configuration has been developed. Ellipsometer measures the changes of the reflected light polarization of the sample, yielding to the ratio of amplitude (ψ) and phase difference (Δ) between p- and s-polarization. Based on the ψ and Δ values, the dielectric constant of the sample can be extracted. However, the available manufacturer-made ellipsometer is quite expensive and is not a good choice for the student to learn the optical concept since the complexity of its structure could hide the simple optical concept during the measurement. In this work, we have built RAE that constituted of relatively simple components and low-cost as well as simple configuration. Here, we also show the principle of measurement and the ellipsometry data analysis using the optical model related to the system under study Drude-Lorentz model. The calibration of our SE has been done by measuring standard materials in the energy range of 1.5 to 3.3 eV and it was compared to the reference measurement using standard ellipsometer. The result is surprisingly accurate within the error of 5%. This research can be used for studying the several important optical concepts as well as for investigating nanostructured materials.

Abstract: Transmission spectrum and reflectance spectrum have long been used to characterize gap semiconductor. Transmission spectrum can be measured very directly, but the influence of substrate absorption is often unavoidable. However, when using the reflectance spectrum measurement, the absorption of thin film, substrate absorption, and coherent interference will make the reflectance spectrum much more complicated. In this paper, Considering the absorption of thin film, substrate absorption, and coherent interference, we use the envelope curves algorithm to achieve the calculation formula of refractive index deduced from the reflectance spectrum. Through the analysis of the reflectance spectrum of Ga₂O₃ film, we achieved thickness of the film, refractive index, extinction and absorption coefficient and dispersion constant.

Abstract: Zirconium oxide (ZrO₂) thin films were deposited on Si-wafer and glass slide substrates by reactive DC unbalanced magnetron sputtering at different deposition times. A pure metallic zirconium target (99.97%) was sputtered in a gas mixture of argon and oxygen. The crystal structure was characterized by GI-XRD (grazing-incidence X-ray diffraction) whereas surface morphologies and films thickness were evaluated by AFM (atomic force microscopy). The transmittance spectrum was measured by spectrophotometer. The optical constants of the as-deposited films were calculated by Swanepoel method. It was found that the ZrO₂ films deposited on silicon substrates showed a highly monoclinic phase (-1 1 1). The as-deposited films showed high transmittance in visible range. The thickness and roughness varied from 155 nm to 502 nm and 3.1 nm to 3.6 nm, respectively, with increasing of deposition times. The optical constants namely refractive index (n) and extinction coefficient (k), at 550 nm, was about 1.9 - 2.1 and 0.0003 - 0.0009, respectively. In addition, the energy band gap (E_g) of the as-deposited film was approximately 4.17 eV.

Abstract: Titanium dioxide (TiO₂) nanothin films were deposited on unheated substrate, the glass slide and Si-wafer, by DC reactive magnetron sputtering with different substrate-target distance (d_st), in range of 8 to 14 cm. The structural, surface morphology and transmittance spectrum of TiO₂ thin films were characterized by grazing-incidence X-ray diffraction (GI-XRD), atomic force microscopy (AFM) and spectrophotometer, respectively. XRD results show that as-deposited TiO₂ films with short substrate-target distance have only anatase crystal structure corresponding to the anatase in (101) and (200) plane, and turn to be amorphous with long substrate-target distance. The thickness and roughness varied from 50 nm to 142 nm and 1.6 nm to 3.5 nm, respectively. The as-deposited TiO₂ films exhibited high visible transmittance. The optical constants of the films, refractive index (n) and extinction coefficient (k), were calculated by Swanepoel method, at 550 nm, was about 2.43 - 2.76 and 0.082 - 0.187, respectively. The energy band gap (E_g) of the as-deposited TiO₂ films in the range of 3.20 - 3.25 was observed.

Abstract: Cubic ZnTiO₃ thin films have been prepared by radio frequency magnetron sputtering on n-type (100) Si substrate at different temperatures. The morphological and optical properties of ZnTiO₃ films in relation to substrate temperatures are investigated by spectroscopic ellipsometry (SE) and AFM as well as SEM in detail. X-ray diffraction (XRD) measurement shows that all the films have a cubic phase structure and the optimum substrate temperature to form crystalline ZnTiO₃ thin film is 250 °C. Through SEM and AFM, the particle size in thin films and film surface roughness increase with increasing the substrate temperature. Based on a parameterized TaucLorentz dispersion model, the optical constants and surface roughness of ZnTiO₃ films related to the substrate temperature are systematically extracted by SE measurement. The surface roughness of the film measured from AFM agrees well with result extracted from SE, which proved that the established SE model is reasonable. With increasing substrate temperature, the refractive index decreases and the main factor in determining the refractive index was deduced to be the surface roughness related to the film packing density. The extinction coefficient of the samples is close to zero, but increases slightly with the increase of the substrate temperature, which is due to the enhancement of scattering effect in the crystalline ZnTiO₃ film.

Abstract: Aluminum nitride (AlN) thin films have been deposited on the glass slide and Si-wafer by reactive DC magnetron sputtering technique at different sputtering power. The as-deposited films have been characterized by grazing-incidence X-ray diffraction (GIXRD), atomic force microscopy (AFM) and optical transmittance, respectively. The results show that the as-deposited films were transparent and have high transmittance in visible regions. The crystal structure from XRD results show that the as-deposited films are amorphous with low sputtering power and turn to crystal structure with high sputtering power, which showed orientation of AlN structure corresponding to the AlN(1 0 0), AlN(1 0 1) and AlN(1 1 0). The roughness values and the films thickness from AFM was varied from 0.4 nm to 3.9 nm and 199 nm to 905 nm, respectively. The optical constants namely the refractive index n and the extinction coefficient k, were determined from transmittance spectrum in the visible regions by using envelope method. For 500 nm, n and k, were in the range of 1.8 2.0 and 0.014 0.004 respectively.

Abstract: The transmittance spectrograms of quartz glass slabs are measured in spectral range 1.34-4.20μm. A new inversion method of optical constants (k is extinction coefficient and n is refractive index) of glass was proposed to calculate the optical constants. The optical constants of selenide glass attained in the references were selected as the true values, and the spectral transmittance radio of the semitransparent solid based on the direct model simulation were regarded as the experimental values, and validation of the new inversion method was investigated. Then the optical constants of quartz glass were achieved by the inverse model.

Abstract: CdS thin films were prepared by chemical bath deposition (CBD) at different ammonia concentration and different temperature using cadmium chloride hydrate, thiourea, ammonium chloride, ammonia and deionized water as precursors. The morphology structure and the optical properties of CdS thin films were characterized by scanning electron microscope (SEM), ultraviolet-visible spectra and spectroscopic ellipsometry. The results indicated that CdS thin film could be grown when ammonia concentration at the range of 0.4-1.0 mol /L and in the temperature range of 50 °C -80 °C. Within 600-980 nm wavelength，the average value of the refractive index was found to be 1.70 and the extinction coefficient was less than 0.08.