A comparative investigation of gas sensing properties of SnO2 doped with WO3 based on thin film and bulk forms was achieved. Thin films were deposited by thermal evaporation technique on glass substrates. Bulk sensors in the shape of pellets were prepared by pressing SnO2:WO3 powder. The polycrystalline nature of the obtained films with tetragonal structure was confirmed by X-ray diffraction. The calculated crystalline size was 52.43 nm. Thickness of the prepared films was found 134 nm. The optical characteristics of the thin films were studied by using UV-VIS Spectrophotometer in the wavelength range 200 nm to 1100 nm, the energy band gap, extinction coefficient and refractive index of the thin film were 2.5 eV , 0.024 and 2.51, respectively. Hall measurements confirmed that the films are n-type. The NO2 sensing characteristics of the SnO2:WO3 sensors were studied with various temperatures and NO2 gas concentrations. Both thin film and bulk sensors showed maximum sensitivity at temperature of 250 oC. Thin film sensors showed enhanced response in comparison to that of pellets.
SUMMARY. – Nanocrystalline thin fi lms of CdS are deposited on glass substrate by chemical bath deposited technique using polyvinyl alcohol (PVA) matrix solution. Crystallite size of the nanocrystalline films are determining from broading of X-ray diffraction lines and are found to vary from 0.33-0.52 nm, an increase of molarity the grain size decreases which turns increases the band gap. The band gap of nanocrystalline material is determined from the UV spectrograph. The absorption edge and absorption coefficient increases when the molarity increases and shifted towards the lower wavelength.
In this paper the effect of thermal annealing on the structural and optical properties of Antimony Selenide (Sb2Se3) is investigated. Sb2Se3 powder is evaporated on clean amorphous glass substrates at room temperature under high vacuum pressure (4.5×10-6 mbar) to form thin films. The structural investigation was done with the aid of X-ray diffraction (XRD) and atomic force microscopy (AFM). The amorphous to polycrystalline transformation of these thin films was shown by X-ray diffraction analysis after thermal annealing. These films' morphology is explained. (UV-Vis ) spectra in ranges from 300 to 1100 nm was used to examine the optical properties of the films .The absorption coefficient and optical energy gap of the investigated films are
... Show MoreIn this research we studied the structural and optical properties of (CdTe) thin films which have been prepared by thermal evaporation deposition method on the glass substrate at R.T with thickness (450  25) nm., as a function of doping ratio with copper element in (1,3,5) % rate .The structure measurement by X-ray diffraction (XRD) analyses shows that the single phase of (CdTe) with polycrystalline structure with a preferred orientation [111]. The optical measurement shows that the (CdTe) films have a direct energy gap, and they decrease with the increase of doping ratio reaching to 5% . The optical constants are investigated and calculated, such as absorpti
... Show MoreNanostructural cupric oxide (CuO) films were prepared on Si and glass substrate by pulsed laser deposition technique (PLD) using laser Nd:YAG, using different laser pulses energies from 200 to 600 mJ. The X-ray diffraction pattern (XRD) of the films showed a polycrystalline structure with a monoclinic symmetry and preferred orientation toward (111) plane with nano structure. The crystallite size was increasing with increasing of laser pulse energy. Optical properties was characterized by using UV–vis spectrometer in the wave lengthrange (200-1100) nm at room temperature. The results showed that the transmission spectrum decreases with the laser pulses energy increase. Sensitivity of NO2 gas at different operating temperatures, (50°C,
... Show MoreSilver sulfide and the thin films Ag2Se0.8Te0.2 and Ag2Se0.8S0.2 created by the thermal evaporation process on glass with a thickness of 350 nm were examined for their structural and optical properties. These films were made at a temperature of 300 K. According to the X-ray diffraction investigation, the films are polycrystalline and have an initial orthorhombic phase. Using X-ray diffraction research, the crystallization orientations of Ag2Se and Ag2Se0.8Te0.2 & Ag2Se0.8S0.2 (23.304, 49.91) were discovered (XRD). As (Ag2Se and Ag2Se0.8Te0.2 & Ag2Se0.8S0.2) absorption coefficient fell from (470-774) nm, the optical band gap increased (2.15 & 2 & 2.25eV). For instance, the characteristics of thin films made of Ag2Se0.8Te0.2 and Ag2Se0.8S0.2
... Show MoreEffect of the thermal annealing at 400oC for 2 hours and Argon laser radiation for half hour on the optical properties of AgAlS2 thin films, prepared on glass slides by chemical spray pyrolysis at 360oC with (0.18±0.05) μm thickness .The optical characteristics of the prepared thin films have been investigated by UV/Vis spectrophotometer in the wavelength range (300 – 1100)nm .The films have a direct allow electronic transition with optical energy (Eg) values decreased from (2.25) eV for untreated thin films to (2.10) eV for the annealed films and to (2.00) eV for the radiated films. The maximum value of the refractive index (n) for all thin films are given about (2.6). Also the extinction coefficient (K) and the real and imaginary d
... Show MoreThin films of tin disulphide SnS2 with different thicknesses (2500,4000,5000)A0 have been prepared by chemical spray pyrolises technique on substrate of glass with temperature (603)K . The effect of thickness on the optical properties of SnS2 has been studied.the optical study that includes the absorptance and transmittance spectra in the wavelength range (300900)nm demonstrated that the value of absorption coefficient (α) ) was greater than (104 cm-1) the electronic transitions at the fundamental absorption edge were of the indirect kind whether allowed and forbidden . Absorption edge shift slightly towards higher wave length.The value of energy gaps (Eg) for all the films prepared are decreased with inc
... Show MoreThin films of CdS:Cu were deposited onto glass substrate temperature 400 °c. The optieal properties have been studied for Cds doped with (1,3, 8) wt% of Cu before and after Gamma irradiation. It was found that the irradiation caused an ( Frenkel defects) where the atom is displaced from its original site leaving vacancy and forming on interstitial atom. It was found the irradiation caused an absorption edge shifting towards long wavelength as a result of the increasing of Cu concentration.
The energy density state are the powerful factor for evaluate the validity of a material in any application. This research focused on examining the electrical properties of the Se6Te4- xSbx glass semiconductor with x=1, 2 and 3, using the thermal evaporation technique. D.C electrical conductivity was used by determine the current, voltage and temperatures, where the electrical conductivity was studied as a function of temperature and the mechanical electrical conduction were determined in the different conduction regions (the extended and localized area and at the Fermi level). In addition, the density of the energy states in these regions is calculated using the mathematical equations. The constants of energy density states are det
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