Microstructure and optical properties of plasmapolymer thin films with embedded silver nanoparticles

Plasmapolymer thin films with embedded silver nanoparticles were deposited by simultaneous plasma polymerization and metal evaporation. The particle size and shape were determined by transmission electron microscopy (TEM) and analysed by optical image processing. The optical properties in the UV/ VIS/NIR spectral region were determined by the plasma resonance absorption of the silver particles. Transmittance spectra were calculated with the Bergman effective medium theory and compared with experimental spectra.     

Intrinsic optical and structural properties of SrS thin films

SrS thin films were deposited by electron beam evaporation on heated silica substrates. The optical properties of the layers – complex refractive index and optical band gap –were derived from optical transmission spectra, measured by means of UV-VIS-NIR spectrophotometry. The influence of post-deposition annealing by rapid thermal processing (RTP) was studied. X-ray powder diffraction (XRD) was used to study the film crystal structure and preferential orientation.     

Electrical and optical properties of copper-complexes thin films grown by the vacuum thermal evaporation technique

In this work, the synthesis and characterization of molecular materials formed from K₂[Cu(C₂O₄)₂], 1,8-dihydroxyanthraquinone and its potassium salt are reported. These complexes have been used to prepare thin films by vacuum thermal evaporation. The synthesized materials were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), fast atomic bombardment (FAB+) mass and ultraviolet–visible (UV–vis) spectroscopy. Electrical transport properties were studied by dc conductivity measurements. The electrical activation energies of the complexes, which were in the range of 0.36–0.65 eV, were calculated from their Arrhenius plots. Optical absorption studies in the 100–1100 nm wavelength range at room temperature showed thin films' optical band gaps in the 2.3–3.9 eV range for direct transitions. On the other hand, strong visible photoluminescence (PL) at room temperature was noticed from the thermally-evaporated thin solid films. The PL of all investigated samples were observed with the naked eye in a bright background. The PL and absorption spectra of the investigated compounds are strongly influenced by the molecular structure and nature of the organic ligand.     

Structural and optical properties of thermally evaporated 1,4,8,11,15,18,22,25-octahexylphthalocyanine thin films

Metal-free 1,4,8,11,15,18,22,25-octahexylphthalocyanine was prepared directly by the cyclotetramerization of 3,6-dihexylphthalonitrile using lithium butoxide in butanol. Thin films of the material were deposited on glass substrates by the thermal evaporation technique. The structure of the films was found to be in the form, and showed a strong peak indicating preferential orientation. The surface morphology of the thin films was investigated by atomic force microscopy and showed that the molecules of 1,4,8,11,15,18,22,25-octahexylphthalocyanine grow in stacks of parallel rows. The spectrophotometric measurements of transmittance and reflectance were carried out in the wavelength range 190–3000 nm. The refractive index, n, and absorption index, k, were found to be independent of annealing at 373 K. The B band absorption occurred at 356 nm, and the Q band showed a doublet at 667 and 739 nm. Other optical parameters, such as absorption coefficient and optical dielectric constant ε, were determined.     

Measurement of the thermal conductivity of erasable phase-change optical recording media

We describe a method to estimate the thermal conductivity of the substrate, the dielectric layer, the phase-change (PC) layer, and the reflective layer of PC optical recording media. The method relies on the amorphous-to-crystalline phase transition that occurs in the PC layer and takes advantage of the difference in the thermal diffusion behavior under different-sized focused spots. All the results obtained here are reliable with better than ?5% accuracy, which is within the margin of our experimental error.     

Amorphization induced by subnanosecond laser pulses in phase-change optical recording media

We have investigated the dynamics of amorphization induced in phase-change optical recording media by focused laser pulses of subnanosecond duration. We initiated localized amorphism by using a focused laser beam to melt the phase-change material and completed the change by rapid cooling by means of thermal diffusion. These studies were conducted by use of real-time reflectivity measurements with a pump-and-probe technique in which both pump and probe pulses had a duration of approximately 510 ps. Our transient-reflectivity measurements indicate that the process that leads to amorphism has three distinct stages, namely, rapid melting, solidification, and slow relaxation.     

Polarization dependence of thermal behavior in rewritable phase-change optical recording media

Thermal behavior in land-groove phase-change optical recording has been examined for different polarizations of the incident beam. Three-dimensional temperature distribution in the grooved medium is evaluated by the numerical solution of Maxwell's equations and the heat transfer equation with the finite-difference method. Both experiments and calculations have shown that the thermal behavior in the medium is dependent on the state of polarization and the nature of the track. The calculated mark shapes in a quadrilayer stack are in good agreement with experimental observations.     

Measurement of the thermal coefficients of rewritable phase-change optical recording media

We describe a method to estimate the heat capacity of the substrate, the dielectric layer, and the phase-change layer of phase-change optical recording media as well as the thermal conductivity of the phase-change layer in its crystalline state. Measurements were carried out on spinning disks with the beam of light focused and locked onto the groove track. The method relies on the identification of the solid-to-liquid phase transition that occurs in the phase-change layer and takes advantage of the dependence of thermal diffusion on track velocity and irradiation time.     

Measurement of the thermal coefficients of nonreversible phase-change optical recording films

We have developed a procedure to obtain the critical temperature for the amorphous-to-crystalline phase transition as well as the thermal conductivity and the specific heat of the phase-change media of optical recording. The procedure involves estimating the thermal conductivity from the data obtained by measuring the threshold cw laser power required for inducing phase transition. Then, from the data obtained in short-pulse measurements, we estimate the specific heat. In principle this method can yield the thermal parameters of any number of layers, so long as one of the layers is made of a phase-change material having a well-defined transition temperature.     

Structural, morphological and optical properties of thermal annealed TiO thin films

Structural, morphological and optical properties of TiO thin films grown by single source thermal evaporation method were studied. The films were annealed from 300 to 520 °C in air after evaporation. Qualitative film analysis was performed with X-ray diffraction, atomic force microscopy and optical transmittance and reflectance spectra. A correlation was established between the optical properties, surface roughness and growth morphology of the evaporated TiO thin films. The X-ray diffraction spectra indicated the presence of the TiO₂ phase for the annealing temperature above 400 °C.     

Structural and optical properties of CdS thin films grown by chemical bath deposition

Cubic cadmium sulphide (CdS) thin films with (111) preferential orientation were prepared by chemical bath deposition (CBD) technique, using the reaction between NH₄OH, CdSO₄ and CS(NH₂)₂. The films properties have been investigated as a function of bath temperature and deposition time. Structural properties of the obtained films were studied by X-ray diffraction analysis. The structural parameters such as crystallite size have been evaluated. The transmission spectra, recorded in the UV visible range reveal a relatively high transmission coefficient (70%) in the obtained films. The transmittance data analysis indicates that the optical band gap is closely related to the deposition conditions, a direct band gap ranging from 2.0 eV to 2.34 eV was deduced. The electrical characterization shows that CdS films' dark conductivities can be controlled either by the deposition time or the bath temperature.     

Structural and optical properties of GaGeTe thin films

Smooth and pinhole-free thin films of Ga₅Ge₁₉Te₇₆ have been obtained by vacuum evaporation. The as-deposited films are amorphous. Thermal annealing at 222°C leads to an amorphous-to-crystalline transition. A maximum contrast of 30% in reflectivity (measured at 1 µm) has been obtained on phase transition from amorphous to crystalline state. The optical constants and the bandgap are reported.     

Behavior of GeSbTeBi phase-change optical recording media under subnanosecond pulsed laser irradiation

We investigated the variations in reflectivity during the phase transition between amorphous and crystalline states of a Bi-doped GeTe-Sb2Te3 pseudobinary compound film with subnanosecond laser pulses, using a pump-and-probe technique. We also used a two-laser static tester to estimate the onset time of crystallization under 2.0-micros pulse excitation. Experimental results indicate that the formation of a melt-quenched amorphous mark is completed in approximately 1 ns, but that crystalline mark formation on an as-deposited amorphous region requires several hundred nanoseconds. Simple arguments based on heat diffusion are used to explain the time scale of amorphization and the threshold for creation of a burned-out hole in the phase-change film.     

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.     

Determination of optical constants and inhomogeneity of optical films by two-step film envelope method

A simple two-step film envelope method has been proposed to determine the optical constants and small inhomogeneity of the optical films, which uses maximum envelopes and minimum envelope of the normal incidence transmittance of the two-step film. The two-step films were prepared by stopping the deposition process in the middle of the designed sputtering time, and then, after a full cooling down to room temperature, repeating the same deposition process again to complete the whole preparation of the films. The optical constants of Nb₂O₅-TiO₂ mixed films were calculated by two-step film envelope method and traditional envelope method. The experimental results demonstrate that the average refractive index and extinction coefficient calculated by two-step film envelope method are more accurate than those calculated by the traditional envelope method.     

Annealing dependence of optical properties of Ga20S75Sb5 and Ga20S40Sb40 thin films

Amorphous Ga₂₀S₇₅Sb₅ and Ga₂₀S₄₀Sb₄₀ thin films were prepared onto glass substrates by using thermal evaporation method. The effect of annealing (under vacuum) at different temperatures on the optical parameters was investigated in the temperature range 373-593 K. The optical absorption coefficient (α) for the as-deposited and annealed films were calculated from the reflectance and transmittance measurements in the range 190-900 nm. X-Ray diffraction indicates that the as-deposited films and those annealed up to the glass transition temperature (T_g) exhibit amorphous state. On annealing above the glass transition temperature these films show a polycrystalline structure. Analysis of the optical absorption data indicates that the optical band gap E_g^opt of these films obeys Tauc's relation for the allowed non-direct transition. It was found that the optical band gap E_g^opt increases with annealing temperature up to T_g, whereas above T_g there is a remarkable decrease. The obtained results were interpreted on the basis of amorphous- crystalline transformation.     

Effect of laser repetition frequency on the structural and optical properties of ZnO thin films by PLD

ZnO thin films were grown on Si (1 1 1) substrates by pulsed laser deposition (PLD) at various laser repetition frequency in order to investigate the structural and optical properties of the films. The optical properties of the films were studied by photoluminescence spectra using a 325 nm He-Cd laser. The structural properties of the films were investigated by XRD measurement. The results suggest that films grown at 5 Hz have excellent UV emission and high-quality crystallinity. Laser repetition frequency can affect the structural and optical properties obviously. In addition, the thickness of all samples is about 200 nm and is not as expected that the film thickness was in direct proportion to laser repetition frequency. The authors think that one laser pulse is not corresponding to one growth instantaneousness. There is a growth ambience containing essential components and partial pressure in the work cavity.     

Thickness dependence of structural and optical properties of indium tin oxide nanofiber thin films prepared by electron beam evaporation onto quartz substrates

Indium tin oxide (ITO) thin films, produced by electron beam evaporation technique onto quartz substrates maintained at room temperature, are grown as nanofibers. The dependence of structural and optical properties of ITO thin films on the film thickness (99-662 nm) has been reported. The crystal structure and morphology of the films are investigated by X-ray diffraction and scanning electron microscope techniques, respectively. The particle size is found to increase with increasing film thickness without changing the preferred orientation along (2 2 2) direction. The optical properties of the films are investigated in terms of the measurements of the transmittance and reflectance determined at the normal incidence of the light in the wavelength range (250-2500 nm). The absorption coefficient and refractive index are calculated and the related optical parameters are evaluated. The optical band gap is found to decrease with the increase of the film thickness, whereas the refractive index is found to increase. The optical dielectric constant and the ratio of the free carrier concentration to its effective mass are estimated for the films.     

Correlations between optical properties, microstructure, and processing conditions of Aluminum nitride thin films fabricated by pulsed laser deposition

Aluminum nitride (AlN) films were deposited using pulsed laser deposition (PLD) onto sapphire (0001) substrates with varying processing conditions (temperature, pressure, and laser fluence). We have studied the dependence of optical properties, structural properties and their correlations for these AlN films. The optical transmission spectra of the produced films were measured, and a numerical procedure was applied to accurately determine the optical constants for films of non-uniform thickness. The microstructure and texture of the films were studied using various X-ray diffraction techniques. The real part of the refractive index was found to not vary significantly with processing parameters, but absorption was found to be strongly dependent on the deposition temperature and the nitrogen pressure in the deposition chamber. We report that low optical absorption, textured polycrystalline AlN films can be produced by PLD on sapphire substrates at both low and high laser fluence using a background nitrogen pressure of 6.0 × 10^− 2 Pa (4.5 × 10^− 4 Torr) of 99.9% purity.     

Effect of alumina doping on structural, electrical, and optical properties of sputtered ZnO thin films

A systematic study of the influence of alumina (Al₂O₃) doping on the optical, electrical, and structural characteristics of sputtered ZnO thin films is reported in this study. The ZnO thin films were prepared on 1737F Corning glass substrates by R.F. magnetron sputtering from a ZnO target mixed with Al₂O₃ of 0-4 wt.%. X-ray diffraction (XRD) analysis demonstrates that the ZnO thin films with Al₂O₃ of 0-4 wt.% have a highly (002) preferred orientation with only one intense diffraction peak with a full width at half maximum (FWHM) less than 0.5°. The electrical properties of the Al₂O₃-doped ZnO thin films appear to be strongly dependent on the Al₂O₃ concentration. The resistivity of the films decreases from 74 Ω·cm to 2.2 × 10^− 3 Ω·cm as the Al₂O₃ content increases from 0 to 4 wt.%. The optical transmittance of the Al₂O₃-doped ZnO thin films is studied as a function of wavelength in the range 200-800 nm. It exhibits high transparency in the visible-NIR wavelength region with some interference fringes and sharp ultraviolet absorption edges. The optical bandgap of the Al₂O₃-doped ZnO thin films show a short-wavelength shift with increasing of Al₂O₃ content.