Decrease In Optical Band Gap Research Articles

Optical properties change with the addition and diffusion of Bi to As2S3 in the Bi/As2S3 bilayer thin film

The role of Bi layer (thickness ∼7nm) on As2S3 film was extensively studied for different optical applications in which Bi (top layer) as active and diffusing layer and As2S3 as barrier (matrix) layer. Bilayer thin films of Bi/As2S3 were prepared from Bi and As2S3 by thermal evaporation technique under high vacuum. The decrease of optical band gap with the addition of Bi to As2S3 has been explained on the basis of density of states and the increase in disorder in the system. It was found that the efficient changes of optical parameters (transmission, optical band gap, refraction) could be realized due to the photo induced diffusion activated by the focused 532nm laser irradiation and formation of different bonds. The diffusion of Bi into As2S3 matrix increases the optical band gap producing photo bleaching effect. The changes were characterised by different experimental techniques.

Influence of laser-irradiation on structural and optical properties of phase change Ga25Se75−xTex thin films

Ga25Se75−xTex chalcogenide thin films of thickness 400nm were deposited by thermal vacuum evaporation technique. These films were irradiated by transversely-excited atmospheric-pressure (TEA) nitrogen laser for 15min. As-prepared and laser-irradiated thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and UV/VIS/NIR spectroscopy. The XRD results revealed the amorphous nature of as-prepared films whereas, the laser-irradiated thin films showed the polycrystalline nature. The results were discussed in terms of the structural change, i.e. amorphous to polycrystalline phase change after laser irradiation. These structural changes were associated with the interaction of the incident photon and the lone-pair electrons, which affects the band gap of the Ga25Se75−xTex thin films. It was observed that the optical band gap decreases whereas, the absorption coefficient increases with increasing Te concentration and also inducing laser-irradiation. This decrease in the optical band gap was explained on the basis of changes in the structural behavior of films, i.e. from amorphous to polycrystalline state.

Characterization of phase change Ga15Se77Ag8 chalcogenide thin films by laser-irradiation

Phase change Ga15Se77Ag8 chalcogenide thin films were prepared by thermal evaporation technique. Thin films were then irradiated by Transverse Electrical Excitation at Atmospheric Pressure (TEA) nitrogen laser for different time intervals. The X-ray structural characterization revealed the amorphous nature of as-prepared films while the laser irradiated films show the polycrystalline nature. Field Emission Scanning Electron Microscope (FESEM) has been used to study the structural changes. The results are discussed in terms of the structural aspects and amorphous to crystalline phase change in Ga15Se77Ag8 chalcogenide thin films. The observed changes are associated with the interaction of the incident photon and the lone-pairs electrons which affects the band gap of the Ga15Se77Ag8 chalcogenide thin films. The optical constants of these thin films are measured by using the absorption spectra measurements as a function of photon energy in the wavelength region 400–1100nm. It is found that the optical band gap decreases while the absorption coefficient and extinction coefficient increases with increasing the laser-irradiation time. The decrease in the optical band gap has been explained on the basis of change in nature of films, from amorphous to polycrystalline state. The dc conductivities and activation energies of these thin films are also measured in temperature range 313–393K. It has been found that the activation energy in Ga15Se77Ag8 thin films decreases whereas the dc conductivity increases at each temperature by increasing the laser-irradiation time.

Structural, optical and electrical properties of laser irradiated Pb doped Ga–Se chalcogenide thin films

Using the Transverse Electrical Excitation at Atmospheric Pressure (TEA) nitrogen laser, we had irradiated the amorphous thin films of Ga10Se81Pb9 chalcogenide glass and the results have been discussed in terms of the structural aspects of Ga10Se81Pb9 glass. The observed changes are associated with the interaction of the incident photon and the lone-pairs electrons which affects the band gap. The X-ray structural characterization revealed the amorphous nature of as prepared films and polycrystalline nature of the laser irradiated films. The optical band gap of these thin films is measured by using the absorption spectra as a function of photon energy in the wavelength region 400–1200 nm. It is found that the optical band gap decreases while the absorption coefficient increases with increasing the irradiation time. The decrease in the optical band gap has been explained on the basis of change in nature of films, from amorphous to polycrystalline state, with the increase in exposure time. The dc conductivities and activation energies of these thin films are measured in temperature range 303–403 K. It has been found that the activation energy in Ga10Se81Pb9 chalcogenide thin films decreases whereas the dc conductivity increases at each temperature by increasing the irradiation time.

Influence of thickness on optical properties of a-(Se80Te20)96Ag4 thin films

Abstract Bulk sample of (Se 80 Te 20 ) 96 Ag 4 was prepared by quenching technique. Thin films of (Se 80 Te 20 ) 96 Ag 4 glasses of different thickness (500–950 nm) were deposited on dry clean glass substrates by thermal evaporation technique. Energy dispersive X-ray spectroscopy (EDX) indicates that samples are nearly stoichiometric. X-ray diffraction patterns indicate that they are in the amorphous state. The optical constants, refractive index, absorption index, and optical band gap have been calculated from transmittance and reflectance data in spectral range of 400–2500 nm. It has been found that the optical band gap decreases, but the refractive index, extinction coefficient, optical conductivity, real and imaginary dielectric constant increase with increase in thickness of (Se 80 Te 20 ) 96 Ag 4 thin films. The results are discussed on the basis of rearrangements of defects and disorders in the chalcogenide systems.

Conversion of Ce3+ to Ce4+ ions after gamma ray irradiation on CeO2–PbO–B2O3 glasses

Abstract The structural and optical parameters of gamma ray irradiated cerium doped lead borate glasses have been analyzed using FTIR, UV–visible absorption, transmittance and density measurement techniques. It has been observed that due to gamma ray exposure, the optical band gap decreases, density increases and molar volume decreases correspondingly. FTIR spectroscopy confirms the conversion of [BO 3 ] to [BO 4 ] and also shows the presence of [CeO 4 ] groups of cerium in glass samples. The transmittance of the glass samples decreases due to formation of hole centers.

Role of substrate temperature on the structural, morphological and optical properties of CuGaSe2 thin films grown by Pulsed Electron Deposition technique

CuGaSe2 (CGS) thin films were grown on uncoated and Mo-coated soda lime glass by Pulsed Electron Deposition (PED) technique at substrate temperatures comprised between 25°C and 475°C. X-ray diffraction analysis reveals that CGS samples exhibit a noteworthy crystal quality even at low growth temperature, Tg=100°C, whereas the out-of-plane preferential orientation of CGS chalcopyrite phase switches from <220> to <112> by increasing the substrate temperature. Annealing treatments seem to enhance the crystallinity of the film and to release the residual strain energy. Visible/near-infrared absorbance spectra show a monotonic decrease of CGS optical bandgap (from 1.75 to 1.65eV) by enhancing the substrate temperature. Yet the morphology of CGS films strongly depends on Tg, which promotes the formation of larger columnar grains perpendicular to the growth plane. Grain dimensions of ~2μm are achieved when CGS films are grown at high temperature (>400°C) on Mo-coated glass. The results indicate that PED is a promising growth technique for achieving good-quality CGS that can be useful as absorber layers in thin film solar cells.

High electronic excitation induced modifications by 100 MeV O7+ and 150 MeV Ni11+ ions in Makrofol KG polycarbonate film

Makrofol-KG polycarbonate (M-KG PC) films are irradiated with 150MeV Ni11+ and 100MeV O7+ ion beams at various fluences ranging from 1×1011 to 3×1012ions/cm2. We have investigated the effect of irradiation parameters such as energy and ions fluence on optical, structural and chemical properties of the studied polymer, respectively. UV–Visible, Fourier Transform Infrared (FTIR) and X-ray diffraction (XRD) spectral studies have been employed in the present investigation. UV–Visible spectra exhibit a shift towards the higher wavelength regime after irradiation. This shift clearly reflects decrease in optical band gap after irradiation. The FTIR spectrum shows a decrease in intensity of the typical bands whereas the formation of new bands indicates the degradation of the polymer after irradiation. The XRD pattern of M-KG PC shows the decreasing intensity of peak positions with increase in ions fluence, which suggests loss of crystallinity of the films due to irradiation. Observed results indicate the formation of disordered system in the irradiated films. Magnitude of effect of irradiation is greater in case of 150MeV Ni11+ rather than 100MeV O7+ ions due to high electronic energy loss of Ni11+ ions in M-KG PC. The results can be correlated on the basis of linear energy transfer (LET) of the irradiated ions.

Preparation and physical properties of (PVA)0.7(NaBr)0.3(H3PO4)xM solid acid membrane for phosphoric acid – Fuel cells

A solid acid membranes based on poly (vinyl alcohol) (PVA), sodium bromide (NaBr) and phosphoric acid (H3PO4) were prepared by a solution casting method. The morphological, IR, electrical and optical properties of the (PVA)0.7(NaBr)0.3(H3PO4)xM solid acid membranes where x=0.00, 0.85, 1.7, 3.4, 5.1M were investigated. The variation of film morphology was examined by scanning electron microscopy (SEM) studies. FTIR spectroscopy has been used to characterize the structure of polymer and confirms the complexation of phosphoric acid with host polymeric matrix. The temperature dependent nature of ionic conductivity and the impedance of the polymer electrolytes were determined along with the associated activation energy. The ionic conductivity at room temperature was found to be strongly depends on the H3PO4 concentration which it has been achieved to be of the order 4.3×10−3S/cm at ambient temperature. Optical measurements showed a decrease in optical band gap and an increase in band tail width with the increase of phosphoric acid. The data shows that the (PVA)0.7(NaBr)0.3(H3PO4)xM solid acid membrane is promising for intermediate temperature phosphoric acid fuel cell applications.

Characterization of ZnO threads obtained using dip coating method at room temperature

In this work ZnO thin films were prepared using the sol–gel method; these films have been deposited on glass substrates using the dip coating technique. The surface characteristics of the films were analyzed with atomic force microscope and could see that the morphology of these films was in thread forms. These threads are formed at the time of deposit of the sol–gel solution with the deep coating. After the heat treatment, these threads keep their shape. The structural characteristics of the films were analyzed using an X-ray diffractometer using the X-ray beam technique, we can found the wurtzite (ZnO) phase in our films and the crystallite sizes were calculated using Scherrer equation. The optical properties were studied by a UV–Visible spectrophotometer where we find that the transmittance percentage is over 50%. The band gap of ZnO films was found in 3.02 for the film with 1 layer and conform we increased the number of layers the optical band gap decrease.

Structure and optical properties of GeGaS films deposited by thermal evaporation

Amorphous GeGaS thin films have been successfully deposited onto glass slides at room temperature by the thermal evaporation technique. The structural units of the films were studied using Raman spectroscopy. In addition to the basic structural units of GeS4 tetrahedra, there are some SS and GeGe homopolar bonds which exist in the films. The increase in Ge atoms leads to the replacement of SS bonds by GeGe bonds, and the isolated Ge(Ga)S4 tetrahedra units transform into corner-sharing or edge-sharing Ge(Ga)S4 tetrahedra units in the films. The refractive index and optical band gap were derived from transmission spectra of films. The values of optical band gap decrease while the refractive indices increase with increasing Ge content. Composition dependence of optical band gap and refractive index has also been interpreted in terms of the variation in the structure of films based on Raman spectra.

Modification of structure and optical band-gap of nc-Si:H films with ion irradiation

Hydrogenated nano-crystalline silicon (nc-Si:H) films fabricated by using hot-wire chemical vapor deposition are irradiated at room temperature with 6.0MeVXe-ions. The irradiation fluences are 1.0×1013, 5.0×1013 and 1.0×1014Xe-ions/cm2. The structure and optical band-gap of the irradiated films varying with ion fluence are investigated by means of X-ray diffraction, Raman and UV–Vis–NIR spectroscopes, as well as transmission electron microscopy. It is found that the crystallite size, the crystalline fraction and the optical band-gap decrease continuously with increasing the ion fluence. The crystalline fraction of the films irradiated to the fluences from 0 to 1.0×1014Xe-ions/cm2 decreases from about 65.7% to 2.9% and the optical band-gap decreases from about 2.1 to 1.6eV. Possible origins of the modification of the nc-Si:H films under 6.0MeVXe-ions irradiation are briefly discussed.

Physical Properties of the SiC&lt;sub&gt;x&lt;/sub&gt;N&lt;sub&gt;y&lt;/sub&gt;H&lt;sub&gt;z&lt;/sub&gt; Films

The SiCxNyHz Films Were Prepared by PECVD Method Using Organosilicon Volatile Compound Hexamethyldisilazane as a Precursor. Some Important Physical and Chemical Properties Were Studied by the Complex of Modern Physical Methods. It Was Shown that at Low Deposition Temperatures the Films Contain the Chemical Bonds of Organic Nature and Have Low Values of Young’s Modulus, Refractive Index and Density. They Possess High Elasticity which Indicates to their Polymeric-Like Structure. At Higher Deposition Temperatures the Films Are Inorganic Composite Materials Consisting of Amorphous Part and Nanocrystals of Graphite and Silicon Nitride. Decrease in Optical Band Gap and Coefficient of Thermal Expansion Is Observed with Deposition Temperature Increase.

Carbon ion beam induced modifications of optical, structural and chemical properties in PADC and PET polymers

We report a study on the carbon ion beam induced modifications on optical, structural and chemical properties of polyallyl diglycol carbonate (PADC) commercially named as CR-39 and Polyethyleneterepthalate (PET) polymer films. These films were then irradiated by 55MeV C5+ ion beam at various fluences ranging from 1×1011 to 1×1013 ions/cm2. The pristine as well as irradiated samples were subjected to UV–Visible spectral study (UV–Vis), Photoluminescence (PL), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. It has been found that ion irradiation may induce a sort of defects in the polymers due to chain scission and cross linking as observed from PL spectral study. It is revealed from UV–Vis spectra absorption edge shifted towards longer wavelength region after irradiation with increasing ion fluence. This shift clearly reflects decrease in optical band gap. The XRD study indicates the gradual decrease in intensity in case of PADC with increasing ion fluence. However, the intensity pattern increased in case of PET at fluence of 1011 ion/cm2 then decreased with further increase in fluence. Crystalline size of PADC was found to be decreasing gradually with increase of ion fluence. Whereas, the crystalline size of PET films found to increase with lower fluence and decreases with higher ion fluence. FTIR spectrum also shows the change in intensity of the typical bands after irradiation in the both the polymers. The results so obtained can be used successfully in heavy ions dosimetry using well reported techniques.

Optical spectroscopy study of damage induced in 4H-SiC by swift heavy ion irradiation

Single crystals of 4H-SiC were irradiated with swift heavy ions (332 MeV Ti, 106 MeV Pb and 2.7 GeV U) in the electronic energy loss regime. The resulting damage was investigated with UV–visible optical absorption spectroscopy and micro-Raman spectroscopy. The evolution of the Raman data with fluence shows an accumulation of isolated point defects without amorphization of the material and a partial recrystallization of the structure, but only at the lowest fluence. Furthermore, the longitudinal optical phonon–plasmon coupling mode disappears upon irradiation, suggesting a strong perturbation of the electronic structure. This evolution is consistent with the optical bandgap decrease and the Urbach edge broadening that was also previously observed for the irradiation with 4 MeV Au ions.

Optical properties change in Sb40S40Se20 thin films by light-induced effect

Thin films of Sb40Se20S40 with thickness 1000nm were prepared by thermal evaporation technique. The amorphous nature of the thin films was verified by X-ray diffractometer. The chemical composition of the deposited thin films was examined by energy dispersive X-ray analysis (EDAX). The changes in optical properties due to the influence of laser radiation on amorphous thin films of Sb40Se20S40 glassy alloy were calculated from absorbance spectra as a function of photon energy in the wavelength region 450–900nm. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It has been observed that laser-irradiation of the films leads to a decrease in optical band gap while increase in absorption coefficient. The decrease in the optical band gap is explained on the basis of change in nature of films due to disorderness. The optical changes are supported by X-ray photoelectron spectroscopy and Raman spectroscopy.

Photo-induced effects on structural and optical properties of Ga15Se81Ag4 chalcogenide thin films

Thin films with thickness of 400nm have been obtained from the Ga15Se81Ag4 ternary chalcogenide glass prepared by the melt quenching technique. The behavior of several optical constants has been studied from absorption and reflection spectra as a function of photon energy in the wavelength region 400–1200nm. The amorphous nature of the sample was examined by X-ray diffraction and non-isothermal DSC measurements. Thin films were illuminated by shining white light using 1500W tungsten lamp with different exposure time. The ambient temperature during the illumination process was controlled and kept at 348K, selected by DSC thermogram. Analysis of the optical absorption data shows that the rule of non-direct transition predominates. It is found that the optical band gap decreases by increasing the illumination time. It has also been observed that the value of absorption and extinction coefficients increases while the refractive index decreases by increasing the illumination time from 0 to 150min. The decrease in optical band gap is explained on the basis of the change in nature of the films, from amorphous to crystalline state, with increase of the illumination time.

Optical properties of petal-like aggregated nanocrystalline zinc oxide synthesized by laser ablation

The results of the investigations carried out on the third-order nonlinearity in zinc oxide (ZnO) nanocrystals (NCs) by Z-scan technique are included in this paper. ZnO NCs show negative nonlinearity and good nonlinear absorption behavior at 532nm. The third-order optical susceptibility χ(3) increases with enlargement of NCs due to the size dependent enhancement of exciton oscillator strength.The synthesis of ZnO NCs was performed by laser ablation from a high-purity metallic target of Zn in distilled water medium. For the ablation process, a high frequency pulsed Nd:YAG laser was employed operating at 532nm with 100ns pulse duration. UV–vis absorption spectroscopy illustrated the enhancement of the size of ZnO NCs upon increasing the laser pulse energy applied in ablation process. Accordingly the corresponding optical band gap (Eg) decrease by increasing the size of NCs. X-ray diffraction (XRD) associated with transmission electron microscopy (TEM) was utilized to characterize the crystalline phase and also for determining the ZnO NCs morphology.

Quantum confinement effect of CdSe induced by nanoscale solvothermal reaction

We report a novel method, nanoscale solvothermal reaction (NSR), to induce the quantum confinement effect of CdSe on nanostructured TiO(2) by solvothermal route. The time-dependent growth of CdSe is observed in solution at room temperature, which is found to be accomplished instantly by heat-treatment in the presence of solvent at 1 atm. However, no crystal growth occurs upon heat-treatment in the absence of solvent. The nanoscale solvothermal growth of CdSe quantum dot is realized on the nanocrystalline oxide surface, where Cd(NO(3))(2)·4H(2)O and Na(2)SeSO(3) solutions are sequentially spun on nanostructured TiO(2), followed by heat-treatment at temperatures ranging from 100 °C to 250 °C. Size of CdSe increases from 4.4 nm to 5.3 nm, 8.7 nm and 14.8 nm, which results in decrease in optical band gap from 2.19 eV to, 1.95 eV, 1.74 eV and 1.75 eV with increasing the NSR temperature from 100 °C to 150 °C, 200 °C and 250 °C, respectively, which is indicative of the quantum confinement effect. Thermodynamic studies reveal that increase in the size of CdSe is related to increase in enthalpy, for instance, from 3.77 J mg(-1) for 100 °C to 8.66 J mg(-1) for 200 °C. Quantum confinement effect is further confirmed from the CdSe-sensitized solar cell, where onset wavelength in external quantum efficiency spectra is progressively shifted from 600 nm to 800 nm as the NSR temperature increases, which leads to a significant improvement of power conversion efficiency by a factor of more than four. A high photocurrent density of 13.7 mA cm(-2) is obtained based on CdSe quantum dot grown by NSR at 200 °C.

Effect of Ge Incorporation on Bandgap and Photosensitivity of Amorphous SiGe Thin Films

We investigated the structural and optical properties of amorphous-SiGe thin films synthesized via a low-cost, high-growth rate deposition method. Films were formed by e-beam evaporation of mixed pellets of Si and Ge. Film composition was varied by changing the weight ratio of Si and Ge pellets mixture. Films were amorphous with a composition uniform. Ge-rich films are in tensile stress, while Si-rich films are in compressive stress. As the Ge fraction increases (from 22 at.% to 94 at.%), the optical bandgap decreases (from 1.7 eV to 0.9 eV) and the photosensitivity of the films extends into IR band of solar spectrum. By changing the weighted ratio of the evaporation source mixture, the bandgap and optical sensitivity of a-SiGe films can be easily tuned. Our studies prove that a-SiGe films are a tunable absorber. This can be used for photo-detector, photovoltaic and microelectronic applications to extend the spectral response.