Investigations on multimagnetron sputtered Zn1-xMgxO thin films through metal-ferroelectric-semiconductor configuration

The effect of Mg doping in ZnO is investigated through structural, electrical, and optical properties. Zn1−xMgxO (0<×<0.3) thin films were deposited on Si (100) and corning glass substrates using multimagnetron sputtering. Investigations on the structural properties of the films revealed that the increase in Mg concentration resulted in phase evolution from hexagonal to cubic phase. The temperature dependent study of dielectric constant at different frequencies exhibited a dielectric anomaly at 110 °C. The Zn0.7Mg0.3O thin films exhibited a well-defined polarization hysteresis loop with a remnant polarization of 0.2 μC/cm2 and coercive field of 8 kV/cm at room temperature. An increase in the band gap with an increase in Mg content was observed in the range of 3.3–3.8 eV for x = 0–0.3. The average transmittance of the films was higher than 90% in the wavelength region λ = 400–900 nm.

Enhancement of photoluminescence intensity by photoinduced interdiffusion in nanolayered a-Se/As2S3 films

Optical parameters of chalcogenide glass multilayers with 12–15 nm modulation lengths prepared by thermal evaporation can be changed by laser irradiation. Photoluminescence (PL) studies were carried out on such nonirradiated and irradiated multilayered samples of a-Se/As2S3 (sublayer thickness of a-Se is 4–5 nm for one set of samples and 1–2 nm for the other set. However As2S3 sublayer thickness is 11–12 nm for both sets of samples.) PL intensity can be increased by several orders of magnitude by reducing the Se well layer (lower band gap) thickness and can be further increased by irradiating the samples with appropriate wavelengths in the range of the absorption edge. The broadening of luminescence bands takes place either with a decrease in Se layer thickness or with irradiation. The former is due to the change in interface roughness and defects because of the enhanced structural disorder while the latter is due to photoinduced interdiffusion. The photoinduced interdiffusion creates defects at the interface between Se and As2S3 by forming an As–Se–S solid solution. From the deconvoluted PL spectrum, it is shown that the peak PL intensity, full width half maximum, and the PL quantum efficiency of particular defects giving rise to PL, can be tuned by changing the sublayer thickness or by interdiffusion.

Structural, electrical, and optical properties of as-grown and heat treated ultra-thin SnS films

The composition, structural, electrical, and optical properties of as-grown and heat treated tin-mono-sulfide (SnS) ultra-thin films have been studied. The ultra-thin SnS films were prepared on glass substrates by thermal resistive evaporation technique. All the SnS films contained nanocrystallites and exhibited p-type conductivity with a low Hall-mobility, <50 cm(2)/Vs. All these films are highly tin rich in nature and exhibited orthorhombic crystal structure. As compared to other films, the SnS films annealed at 300 degrees C showed a low electrical resistivity of similar to 36 Omega cm with an optical band gap of similar to 1.98 eV. The observed electrical and optical properties of all the films are discussed based on their composition and structural parameters. These nanocrystalline ultra-thin SnS films could be expected as a buffer layer for the development of tandem solar cell devices due to their low-resistivity and high absorbability with an optimum band gap. (C) 2011 Elsevier B.V. All rights reserved.

Influence of Si-C bond density on the properties of a-Si(1-x)C(x) thin films

Amorphous silicon carbide (a-Si(1-x)C(x)) films were deposited on silicon (100) and quartz substrates by pulsed DC reactive magnetron sputtering of silicon in methane (CH(4))-Argon (Ar) atmosphere. The influence of substrate temperature and target power on the composition, carbon bonding configuration, band gap, refractive index and hardness of a-SiC films has been investigated. Increase in substrate temperature results in slightly decreasing the carbon concentration in the films but favors silicon-carbon (Si-C) bonding. Also lower target powers were favorable towards Si-C bonding. X-ray photoelectron spectroscopy (XPS) results agree with the Fourier Transform Infrared (FTIR), UV-vis spectroscopy results. Increase in substrate temperature resulted in increased hardness of the thin films from 13 to 17 GPa and the corresponding bandgap varied from 2.1 to 1.8 eV. (C) 2011 Elsevier B.V. All rights reserved.

Structure and Photocatalytic Activity of Ti 1- x M x O 2±δ (M = W, V, Ce, Zr, Fe, and Cu) Synthesized by Solution Combustion Method

The W, V, Ce, Zr, Fe, and Cu metal ion substituted nanocrystalline anatase TiO2 was prepared by solution combustion method and characterized by XRD, Raman, BET, EPR, XPS, IR TGA, UV absorption, and photoluminescence measurements. The structural studies indicate that the solid solution formation was limited to a narrow range of concentrations of the dopant ions. The photocatalytic degradation of 4-nitrophenol under UV and solar exposure was investigated with Ti1-xMxO2±δ. The degradation rates of 4-nitrophenol with these catalysts were lesser than the degradation rates of 4-nitrophenol with undoped TiO2 both with UV exposure and solar radiation. However, the photocatalytic activities of most metal ion doped TiO2 are higher than the activity of the commercial TiO2, Degussa P25. The decrease in photocatalytic activity is correlated with decrease in photoluminescence due to electron states of metal ions within the band gap of TiO2.

Dithienylcyclopentadienone derivative-co-benzothiadiazole: An alternating copolymer for organic photovoltaics

Alternating copolymer of 7,9-di(thiophen-2-yl)-8H-cyclopenta[a]acenaphthylen-8-one-co-benzothia diazole was synthesized by palladium(0) catalyzed Stille coupling reaction. This solution processable copolymer shows an excellent thermal stability and has a broad absorption range from 300 to 800 nm with a band gap of about 1.51 eV. High LUMO energy level and low band gap of the synthesized copolymers suggest that, this copolymer will be a suitable donor material for use in an organic photovoltaic device. Photovoltaic devices were fabricated from the blend of copolymer and phenyl-C61-butyric acid methyl ester as the active material. (C) 2011 Elsevier By. All rights reserved.

Optical, electrical and structural characterization of ZnO:Al thin films prepared by a low cost sol-gel method

ZnO:Al thin films were prepared on glass and silicon substrates by the sol-gel spin coating method. The x-ray diffraction (XRD) results showed that a polycrystalline phase with a hexagonal structure appeared after annealing at 400 degrees C for 1 h. The transmittance increased from 91 to about 93% from pure ZnO films to ZnO film doped with 1 wt% Al and then decreased for 2 wt% Al. The optical band gap energy increased as the doping concentration was increased from 0.5 wt% to 1 wt% Al. The metal oxide semiconductor (MOS) capacitors were fabricated using ZnO films deposited on silicon (100) substrates and electrical properties such as current versus voltage (I-V) and capacitance versus voltage (C-V) characteristics were studied. The electrical resistivity decreased and the leakage current increased with an increase of annealing temperature. The dielectric constant was found to be 3.12 measured at 1 MHz. The dissipation value for the film annealed at 300 degrees C was found to be 3.1 at 5 V. (C) 2011 Elsevier Ltd. All rights reserved.

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

Thin films of Sb40Se20S40 with thickness 1000 nm 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 450-900 nm. 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. (C) 2012 Elsevier B.V. All rights reserved.

Growth of rutile TiO2 nanorods on TiO2 seed layer deposited by electron beam evaporation

Dense rutile TiO2 nanorods were grown on anatase TiO2 seed layer coated glass substrate by solution technique. The crystalline nature of nanorods has confirmed by transmission electron microscopy. The band gap of the TiO2 seed layer and nanorods were calculated using the UV-vis absorption spectrum and the band gap value of the anatase seed layer and rutile nanorods were 3.39 eV and 3.09 eV respectively. Water contact angle measurements were also made and showed that the contact angle of rutile nanorods was (134 degrees) larger than the seed layer contact angle (93 degrees). The RMS surface roughness of the TiO2 seed layer (0.384 nm) and nanorods film (18.5 nm) were measured by an atomic force microscope and correlated with their contact angle values. (C) 2011 Elsevier B.V. All rights reserved.

Electrical switching and optical studies on amorphous GexSe35-xTe65 thin films

The electrical switching behavior of amorphous GexSe35-xTe65 thin film samples has been studied in sandwich geometry of electrodes. It is found that these samples exhibit memory switching behavior, which is similar to that of bulk Ge-Se-Te glasses. As expected, the switching voltages of GexSe35-xTe65 thin film samples are lower compared to those of bulk samples. In both thin film amorphous and bulk glassy samples, the switching voltages are found to increase with the increase in Ge concentration, which is consistent with the increase in network connectivity with the addition of higher coordinated Ge atoms. A sharp increase is seen in the composition dependence of the switching fields of amorphous GexSe35-xTe65 films above x = 21, which can be associated with the stiffness transition. Further, the optical band gap of a-GexSe35-x Te-65 thin film samples, calculated from the absorption spectra, is found to show an increasing trend with the increase in Ge concentration, which is consistent with the variation of switching fields with composition. The increase in structural cross-linking with progressive addition of 4-fold coordinated Ge atoms is one of the main reasons for the observed increase in switching fields as well as band gaps of GexSe35-xTe65 samples. (C) 2011 Elsevier B.V. All rights reserved.

Thermoluminescence response in gamma and UV irradiated Dy2O3 nanophosphor

Low temperature solution combustion method was employed to synthesize Dy2O3 nanophosphors using two different fuels (sugar and oxalyl dihydrazine (ODH)). Powder X-ray diffraction confirm pure cubic phase and the estimated particle size from Scherrer's method in sugar and ODH fuel was found to be 26 and 78 nm, respectively, and are in close agreement with those obtained using TEM and W-H plot analysis. SEM micrographs reveal porous, irregular shaped particles with large agglomeration in both the fuels. An optical band gap of 5.24 eV and 5.46 eV was observed for Dy2O3 for sugar and ODH fuels, respectively. The blueshift observed in sugar fuel is attributed to the particles size effect. Thermoluminescence (TL) response of cubic Dy2O3 nanophosphors prepared by both fuels was examined using gamma and UV radiations. The thermoluminescence of sugar used samples shows a single glow peak at 377 degrees C for 1-4 kGy gamma irradiations. When dose is increased to 5 kGy, two more shouldered peaks were observed at 245 and 310 degrees C. However, in TL of ODH used samples, a single glow peak at 376 degrees C was observed. It is observed that TL intensity is found to be more in sugar used samples. In UV irradiated samples a single glow peak at 365 degrees C was recorded in both the fuels with a little variation in TL intensity. The trapping parameters were estimated by different methods and the results are discussed. (C) 2012 Elsevier B.V. All rights reserved.

Structural, EPR, photo and thermoluminescence properties of ZnO:Fe nanoparticles

Zn(1-x)Fe(x)O(1+0.5x) (x = 0.5-5 mol%) nanoparticles were synthesized by a low temperature solution combustion route. The structural characterization of these nanoparticles by PXRD, SEM and TEM confirmed the phase purity of the samples and indicated a reduction in the particle size with increase in Fe content. A small increase in micro strain in the Fe doped nanocrystals is observed from W-H plots. EPR spectrum exhibits an intense resonance signal with effective g values at g approximate to 2.0 with a sextet hyperfine structure (hfs) besides a weak signal at g approximate to 4.13. The signal at g approximate to 2.0 with a sextet hyperfine structure might be due to manganese impurity where as the resonance signal at g approximate to 4.13 is due to iron. The optical band gap E-g was found to decrease with increase of Fe content. Raman spectra exhibit two non-polar optical phonon (E-2) modes at low and high frequencies at 100 and 435 cm(-1) in Fe doped samples. These modes broaden and disappear with increase of Fe do pant concentration. TL measurements of gamma-irradiated (1-5 kGy) samples show a main glow peak at 368 degrees C at a warming rate of 6.7 degrees Cs-1. The thermal activation parameters were estimated from Glow peak shape method. The average activation energy was found to be in the range 0.34-2.81 eV. (C) 2012 Elsevier B.V. All rights reserved.

Compositional dependence optical properties study of As40Se60-xSbx thin films

Thin films were thermally evaporated from the bulk glasses of As40Se60-xSbx (with x = 0, 5, 10, 15 at.%) under high vacuum. We have characterized the deposited films by Fourier Transform Infrared spectroscopy. The relationship between the structural and optical properties and the compositional variation has been investigated. Increasing Sb content was found to affect the thermal and optical properties of these films. Non-direct electronic transition was found to be responsible for the photon absorption inside the investigated films. It was found that, the optical band gap E-o decreases while the width of localized states (Urbach energy) E-e increases. (C) 2011 Elsevier B.V. All rights reserved.

Unusual photoresponse of indium doped ZnO/organic thin film heterojunction

Photoresponse of n-type indium-doped ZnO and a p-type polymer (PEDOT:PSS) heterojunction devices are studied, juxtaposed with the photoluminescence of the In-ZnO samples. In addition to the expected photoresponse in the ultraviolet, the heterojunctions exhibit significant photoresponse to the visible (532 nm). However, neither the doped ZnO nor PEDOT: PSS individually show any photoresponse to visible light. The sub-bandgap photoresponse of the heterojunction originates from visible photon mediated e-h generation between the In-ZnO valence band and localized states lying within the band gap. Though increased doping of In-ZnO has limited effect on the photoluminescence, it significantly diminishes the photoresponse. The study indicates that optimally doped devices are promising for the detection of wavelengths in selected windows in the visible. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4704655]

Cyclopentac]thiophene oligomers based solution processable D-A copolymers and their application as FET materials

Two new solution processable, low band gap donor-acceptor (D-A) copolymers (P1 and P2) comprising a cyclopentac] thiophene (CPT) based oligomers as donors and benzoc]1,2,5] selenadiazole (BDS) and 2-dodecyl1,2,3]-benzotriazole (BTAz) as acceptors were synthesized and characterized and their field effect transistor properties were studied. The internal charge transfer interaction between the electron-donating CPT based oligothiophene and the electron-accepting BDS or BTAz unit effectively reduces the band gap in polymers to 1.3 and 1.66 eV with low lying highest occupied molecular orbital (HOMO). The absorption spectrum of P1 was found to be more red shifted than that of P2 because of incorporation of the more electron-withdrawing BDS unit. The color of neutral P1 was found to be green in both solution and film states with two major bands in the absorption spectra; however, neutral P2 revealed one dominant absorption exhibiting red color in both solution and film state which could be attributed to the less electron-withdrawing effect of the BTAz unit. The polymers were further characterized by GPC, TGA, DSC and cyclic voltammetry. P1 and P2 exhibited charge carrier mobilities as high as 9 x 10(-3) cm(2) V-1 s(-1) and 2.56 x 10(-3) cm 2 V-1 s(-1), respectively with the current on/off ratio (I-on/I-off) in the order of 10(2).