Showing papers in "Journal of Optoelectronics and Advanced Materials in 2009"

Pulsed magnetron sputtering - process overview and applications

Abstract: voltage reversals suppress arc formation at the target (a major problem during the deposition of dielectrics) and provide long-term process stability. Thus, high quality, defect-free coatings of these materials can now be deposited at competitive rates. However, pulsing the magnetron discharge in this frequency range also strongly modifies the deposition plasma; raising the time averaged electron temperature and the energy flux delivered to the substrate, in comparison with continuous DC processing. These advantageous deposition conditions have been exploited in the deposition of materials such as titanium nitride, where arcing is not considered a problem. In this case, coatings deposited by pulsed processing demonstrated enhanced structures and tribological properties in comparison with conventional coatings. This paper gives an overview of the pulsed magnetron sputtering process (pulsed DC and mid-frequency AC), describes the underlying plasma physics, gives examples of successful applications of this technology and briefly considers recent developments in this field, such as high power impulse pulsed magnetron sputtering (HIPIMS).

Current transport mechanisms of n-ZnO/p-CuO heterojunctions

Abstract: In this study, n-ZnO/p-CuO heterojunction have been fabricated by sol-gel dip-coating technique which is simple and inexpensive. The structure of the p-CuO/n-ZnO was analyzed by X-ray diffraction spectroscopy and UV-VIS spectroscopy. The electrical junction properties were characterised by temperature dependent current-voltage (I-V) characteristics and at high frequency capacitance-voltage (C-V) characteristic at room temperature. The structure showed non-ideal behaviour of I-V characteristics with an ideality factor of 3.5 at room temperature. Temperature dependent forward current-voltage measurements suggest that trap-assisted multi-step tunnelling is the dominant current mechanism in this structure.

Morphology, crystalline structure, and chemical properties of 100 MeV Ag- ion beam irradiated polyvinylidene fluoride (PVDF) thin film

Abstract: Thin films (12 μm) of polyvinylidene fluoride (PVDF) were irradiated with 100 MeV Ag- ion beam at fluence 1.875X10 11 ion/cm 2 . The changes in physical, chemical, and surface morphological properties of irradiated films have been investigated using X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy(FTIR), Field emission scanning electron microscopy (FESEM) and Energy Dispersive Analysis by X-ray (EDAX) techniques by taking unirradiated (pristine) film as reference. The diffraction pattern of PVDF films shows this polymer is in semi-crystalline form and posses crystalline α-, β-, and y- phases. A decrease in the crystallinity and increase in crystallite size has been observed due to 100 MeV Ag -ion irradiation. Using XRD data, the degree of crystallinity, crystallite size and other structural parameters such as micro strain and dislocation density of pristine and irradiated films have been estimated. In the FTIR spectra, no appreciable change in characteristic bands has been observed after irradiation, indicating that PVDF is chemically stable. EDAX result shows that the relative chemical composition of PVDF is invariant under energetic heavy ion irradiation. FESEM analysis show granular microstructure with increase in grain size and porosity upon ion irradiation.

Ring-, branchy-, and cage-like AsnSm nanoclusters in the structure of amorphous semiconductors: Ab initio and Raman study

Abstract: Ab initio calculations were performed on ring-, branchy-, and cage-like As n S m nanoclusters being the building blocks of cluster model are generally found in As x S 100-x glasses and of different crystals known in the As-S system. The optimal geometry, total energy, formation energy and Raman spectra of the As n S m nanoclusters were calculated using density functional theory (DFT). The formation probability of different types of As n S m nanoclusters in the glassy matrix were analyzed by calculating their energy components and the relative stabilities were revealed. The contribution of such structures to the experimental Raman spectra of As-S glasses, implications and some possible induced effects are also discussed.

Adherent functional graded hydroxylapatite coatings produced by sputtering deposition techniques

Abstract: The aim of this paper was to study the influence of crystallization heat treatments up to 750°C, upon the integrity and structure of hydroxylapatite thin films. Two different types of hydroxylapatite coatings were investigated: abrupt structures prepared by magnetron sputtering and respectively functional graded structures deposited by a co-sputtering technique. A clear dependence was noticed between adherence values and annealing temperature and was correlated with the SEM, XRD and FTIR results. X-ray diffraction and FTIR measurements showed that the hydroxylapatite coatings annealed at 400°C were less crystalline, similar to biological apatites. Over 550°C, the apatite coatings obtained were well crystallized and preferentially oriented on (002) HA crystal plane. The adherence of HA coating increased with annealing the temperature up to 550°C due to diffusion phenomena. At 550°C the adhesion test results indicated better adhesion values in case of functional graded structures (> 85 MPa) in comparison with abrupt ones (- 70 MPa). At 750°C an adherence decreasing occurred for both types of structures. This is mainly due to the effect of a significant thermal stress owed to the mismatch of the thermal expansion coefficients between the crystallized HA and Ti substrate. The presence of rutile lines in XRD spectrum suggests an increasing of the diffusion phenomena and a strong substrate oxidation at the HA/Ti interface with annealing temperature.

Characterization of molybdenum oxide films prepared by bias magnetron sputtering

Abstract: Thin films of molybdenum oxide were deposited on unheated glass substrates using dc magnetron sputtering method by sputtering of molybdenum target in the presence of oxygen and argon gas mixture under various substrate bias voltages in the range 0 to - 150 V. The effect of substrate bias voltage on the structure, electrical and optical properties was studied. From X - ray photoelectron spectroscopy studies revealed that the films formed on the unbiased substrates were substoichiometric with the presence of mixed oxidation states of Mo 6+ and Mo 5+ . As substrate bias voltage increased to -120 V, the films were stoichiometric with oxidation state of Mo 6+ . X-ray diffraction studies indicated that the films deposited on the unbiased substrates were amorphous in nature. The films formed at - 120 V were orthorhombic a - phase of MoO 3 . The films deposited under unbiased condition showed high electrical conductivity of 3.6x10 4 Ω -1 cm -1 due to the amorphous nature, while those films deposited at the substrate bias voltage of -120 V showed the decrease in the electrical conductivity to 4.5x10 -5 Ω -1 cm -1 due to the partial filling of oxygen vacancies. The unbiased films showed an optical band gap of 3.03 eV with the refractive index of 2.03. As the substrate bias voltage increased to -120 V the optical band gap of the films increased to 3.22 eV and refractive index increased to 2.13 due to the improvement in the crystallinity and packing density of the grown films.

Synthesis and structural characterization of MoO 3 phases obtained from molybdic acid by addition of HNO 3 and H 2 O 2

Abstract: Orthorhombic (α) MoO3 and monoclinic (β) MoO3 were successfully synthesized by cation-exchange of sodium molybdate solution applying three different routes: i) pure precursor molybdic acid solution (H2MoO4), ii) addition of HNO3 to a precursor and iii) addition of 35% H2O2 to a precursor. By route i) pure orthorhombic (α) MoO3 was synthesized. Pure monoclinic (β) MoO3 was obtained in the presence of HNO3. A polyphase product containing 72% monoclinic (β) MoO3 and 28% orthorhombic (α) MoO3 was obtained in the presence of 35% H2O2. The products obtained were characterized by XRD, IR and SEM analysis. The morphology of MoO3 strongly depended on the synthesis method applied. Smaller crystals with uniform shape were obtained in the presence of HNO3 and 35% H2O2.

Aloe vera solution synthesis and magnetic properties of Ni-Cu-Zn ferrite nanopowders

Abstract: Ni x Cu 0.25 Zn 0.75-x Fe 2 O 4 (x = 0.25, 0.35, 0.5) nanopowders were prepared by a simple solution method using metal nitrates and aloe vera plant extracted solution. The prepared samples were characterized by XRD, FT-IR, SEM, TEM and VSM. All the prepared samples are polycrystalline and have spinel structure with the particle sizes of ∼15-40 nm. The samples exhibit ferromagnetic behavior, having saturation magnetization and coercivity values in the range of 32.52-66.58 emu/g at 10 kOe and 58.46-140.47 Oe, respectively.

Structural characterization and optical properties of Co3O4 and CoO films

Abstract: Thin-film coatings based on cobalt oxides are obtained. For depositing cubic spinel Co 3 O 4 and CoO films the sol-gel dip-coating technique was used. The as-deposited films were subjected to different thermal treatments in air and in reducing atmosphere (H 2 /N 2 ), respectively. Optical absorption spectroscopy, X-ray diffraction and atomic force microscopy (AFM) were used to characterize the samples. The Swanepoel method was employed for the study of the films optical constants as a function of wavelength. By XRD studies it was established that the annealed films become polycrystalline. The films exposed in air consist in Co 3 O 4 phase, while the films annealed in reducing atmosphere (H 2 /N 2 ) exhibit the CoO phase. AFM studies showed uniform films with smooth surface. By exposing the film to H 2 /N 2 , the average rugosity increases ten times. After treatment, the cobalt oxide films transmittance values decrease. The decrease is more meaningful when the films are exposed in reducing atmosphere. The UV-VIS spectra of the films exposed in air present an absorption peak at λ= 730 nm, which corresponds to a charge transfer ligand-metal: O 2- →Co 3+ The peak which corresponds to λ= 690 nm is due to Co 2+ . These transitions confirm the existence of Co 3 O 4 . Concerning the films annealed in reducing atmosphere (H 2 /N 2 ), the band at 594 nm which appears in the spectra is typical for Co 2+ in octahedral coordination and ascribed to the 4 A 2 → 4 T 1 (P) transition. The refraction index presents a normal dispersion, the films exposed in forming gas having higher values than the films exposed in air. The films annealed in a reducing atmosphere feature only direct transitions, representing an internal oxido-reduction process Co 3+ →Co 2+ . The films exposed in air present both direct and indirect transitions. Co 3 O 4 films present an allowed direct interband transition of 1.4-1.5 eV and 2.18-2.23 eV, respectively, while CoO films have an optical band gap energy of 2.2-2.8 eV.

Advanced materials for metal implant coatings

Abstract: Metal materials have been used as implants, due to their excellent mechanical properties and corrosion resistance. However, in order to better bind to living bone they need an interfacial inorganic layer. Biological apatite is a bioactive and biocompatible inorganic material, and the main structural component of human bones. However, it has weak mechanical properties and adhesion to metal implant surfaces. Combination of the good mechanical properties of metals with the bioactive properties of apatite has fostered the application of apatite coatings on metal implants. On the other hand, carbon-based materials (diamond-like carbon, detonational nanodiamond, carbon nanotubes, amorphous carbon, etc.) significantly improve the mechanical properties of AP, increase its adhesion, and prevent metal ion release from metal implants. Our goal was to create a new advanced composite material that is to serve as a coating of metal implants. Stainless steel was used for the electrodeposition of the apatite-nanodiamond coatings in simulated body fluid. The results revealed the formation of dense and homogeneous apatite-nanodiamond composite coatings, with better ductility, hardness, cohesion and adhesion to stainless steel, in comparison to pure apatite coatings. We consider that the nanodiamond-reinforced apatite coatings can be considered as advanced materials for the surface modification of metal implants.

Influence of central metal atom in MPc (M = Cu, Zn, Mg, Co) on Raman, FT-IR, absorbance, reflectance, and photoluminescence spectra

Abstract: In this paper we present the comparative study of photoluminescence (PL), absorption (A), FT-IR, Raman scattering (RS) and reflection (R) spectra of metallophthalocyanines (MPc; M = Zn, Co, Mg, Cu) thin layers. Investigated thin films were deposited by the quasi molecular beam evaporation method on the quartz and silicon substrates. The measurements were carried out in the 350-1150 nm spectral region at wide temperature range from 13K to 320K (PL) and 70K to 550K (FT-IR, RS). The thin films of ZnPc and MgPc show PL emission from the violet to near-IR region whereas CoPc and CuPc layers do not show measurable emission. The temperature dependence of MPc photoluminescence spectra measured in such a wide spectral range are presented for the first time. The obtained emission spectra exhibit several transitions but some of them are visible only at certain temperature range. The changes of both, bands intensities and band positions versus temperature have been studied. Similar investigations have been performed for the FT-IR and Raman scattering spectra. Integral intensities and band position of Raman and FT-IR modes in MPc thin layers indicate sharp kinks at 180 K and 380 K. The obtained transmission and reflection spectra of all investigated thin layers have been also compared with mentioned above results.

Direct surface relief formation in As0.2Se0.8 layers

Abstract: The process of light-stimulated periodic surface relief formation in As 0.2 Se 0.8 layers was investigated by in situ AFM depth profiling and compared with data on diffraction efficiency η of similar holographic gratings, measured in a reflection mode. It was discovered, that the time (exposure) dependence of the surface deformation Δd has at least two components, which correspond to the stable sinusoidal relief formation up to the giant, Δd/d >10% changes in this best composition from As-Se system. It is assumed that the surface relief formation is connected with induced volume expansion (up to 1%) as well as with a lateral mass transport. A small dynamical component of η appears when the light is switched on. Most probably it depends on the charge carrier generation and corresponding changes of the refraction index.

Intercalation of salicylic acid into ZnAl layered double hydroxides by ion-exchange and coprecipitation method

Abstract: Salicylic acid was intercalated into an inorganic host consisting of ZnAl-layered double hydroxides lamella by ionic exchange and coprecipitation technique. The precursors and the intercalation compounds were examined by X-ray diffraction (XRD), FTIR spectroscopy, differential thermal and thermo gravimetric analysis and scanning electron microscopy (SEM). Powder X-ray diffractograms show that the basal spacing of the ZnAl layered double hydroxide bearing salicylate as the intergallery anion expanded from 8.7 A in the precursor to 15.4 A in ZnAl-layered double hydroxide obtained by ionic exchange and to 14.9 A in ZnAl-layered double hydroxide prepared by coprecipitation direct method, respectively. The NO - 3 peak located at 1385 cm -1 in FTIR spectra of the sample prepared by ion exchange was replaced with peaks characteristic to the intercalated salicylate anion. The thermal stability of the intercalated salicylic acid is significantly enhanced compared with the pure form before intercalation. Using the XRD results combined with a molecular simulation model, a possible representation of the salicylate anion positioning between the lamellar layers has been proposed.

Sn2Sb2S5 films for photovoltaic applications

Abstract: In this paper we propose that Sn 2 Sb 2 S 5 is one of the main candidates of thin film absorbers materials. Sulfosalt Sn 2 Sb 2 S 5 thin films have been deposited on glass substrates by vacuum evaporation method. The pressure during evaporation was maintained at 10 -5 Torr. The films were annealed in air atmosphere in the temperatures range 100-250°C. Two optical direct transitions were found. Absorption coefficients higher than 10 4 cm -1 were found. The X-ray diffraction analysis indicates that before and after annealing only the Sn 2 Sb 2 S 5 phase is present. Sn 2 Sb 2 S 5 thin films exhibit N-type conductivity after annealing. We present a model that helps to explain the evolution of photovoltaic effect.

Correlation between porosity of porous silicon and optoelectronic properties

Abstract: We calculate the optical constants and absorption coefficient of n-dopped porous silicon (PS), by using Effective media approximation (EMA) analysis. Refractive index,n, decreases with increasing porosity in visible region. However, absorption coefficient, α, increases with increasing porosity in this region. Also energy band gap of PS has been determined using absorption spectra. Our results show that band gap of PS is quasidirect.

Influence of temperature, thickness and intensity of illumination on the capacitance-voltage and current-voltage characteristics of coplanar ZnTe thin films

Abstract: This paper examines the influence of temperature, thickness and illumination of different intensities on the capacitance-voltage (C-V) and current-voltage (I-V) characteristics of coplanar ZnTe thin films of thickness range (300-700 nm). Capacitance-voltage (C-V) measurements of ZnTe thin films were performed by a sweep of voltages from -10 to +10 V at different elevated temperatures in the range 298-398 K. The temperature dependence of the measured capacitance for the different applied voltage was studied. The dependence of capacitance on the reciprocal of film thickness, yields a permittivity value of ZnTe, assuming that the capacitance follows a simple parallel plate relationship. The current-voltage (/-V) characteristics of ZnTe films at room temperature (RT) for different thicknesses showed the Ohmic conduction mechanism at low voltages, while at higher voltages, the trap-charge-limited conduction (TCLC) was dominant. The temperature dependence of current allows the determination of some essential parameters of ZnTe. Discussion of the obtained results and their comparison with the previously published data are also given.

Physical properties of V2O5 sprayed films

Abstract: Thin films of V 2 O 5 have been deposited by spray pyrolysis technique on glasses substrate with different solution concentrations (molarities) at temperature equal 300 °C. The structural, electrical and optical characteristics of the V 2 O 5 films were examined by X-ray diffraction (XRD), Van der Pauw technique and double-beam spectrophotometry. X-ray diffraction reveals that the films, which have been deposited at T S = 300 °C with different solution molarities are polycrystalline in nature having orthorhombic type crystal structure and a preferential orientation along direction. The electrical resistivity at room temperature is decreased as the solution molarity increased. Transmission measurements showed that the transmission decreased as the molarity increased. The dependence of the refractive index, n, and extinction coefficient, k, on the wavelength for a sprayed film is also reported. Optical bandgap, Eg, has been reported for the V 2 O 5 films and is equal to 2.50 eV.

Optical characterization of hydrothermally grown SnO 2 nanocrystals

Abstract: A simple hydrothermal process is proposed for the synthesis of SnO 2 nanoparticles in which ammonium hydroxide is used as the mineralizer. The crystal structure and size of the SnO 2 nanoparticles were determined by X-ray diffraction. Optical properties of so formed nanoparticles were explored by UV-Vis absorption, Photoluminescence, and Raman studies. Experimental results indicate that the as-prepared SnO 2 may have large amount of defects and local lattice disorders at the interface and surface. The visible emission from nanocrystalline SnO 2 is interpreted in terms of the size of the crystals and the presence of the defects in the material. The appearance of new Raman peak marks an additional characteristic of space symmetry due to the agglomeration of grains in nanocrystalline tin oxide.

Growth and spectroscopic, thermal, dielectric and SHG studies of L- threonine doped KDP crystals

Abstract: Potassium Dihydrogen Phosphate (KDP) crystals are one of the most popular crystals used for Non-linear Optical (NLO) applications. Most of amino acids also exhibit NLO property; therefore, the effect of doping of one of the amino acids, L ― Threonine, in KDP crystals has been investigated. Pure and L - Threonine doped KDP crystals were grown by slow solvent evaporation solution growth technique. For obtaining doped crystal, 0.3 and 0.4 weight percent solutions of L - Threonine was added to aqueous solution of KDP. Good quality transparent crystals were obtained within 8 to 10 days. Doping of amino acid in grown crystals was confirmed by paper chromatography, C H N analysis and FT - IR spectroscopy studies. The powder XRD suggested the single phase nature and the unit cell parameters were not altered due to doping. Thermal stability of the grown crystals was studied by employing TGA. It was observed that on increasing the amount of doping the decomposition of sample occurred slightly at lower temperature than that of the pure KDP crystals. The dielectric constant and the dielectric loss of L-Threonine doped KDP crystals were lower than the pure KDP crystals. Increment in the values of the second harmonic generation (SGH) efficiency was noticed in doped crystals with comparison to the pure KDP crystals. The percentage optical transmission increased with increasing the doping of L- threonine in KDP. It was found that the doping of L -Threonine does not alter the physical properties of KDP by large extent, alike in the case of other amino acids. The results are discussed.

Nylon 6/copper composites by in situ polymerization

Abstract: Composite materials based on nylon 6 (PA6) and unmodified copper particles, were prepared by in situ anionic polymerization of є–caprolactam (CL) in the presence of the metallic fillers using rotational moulding technique. The above materials were characterized by some experimental techniques, including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), wide angle X–ray diffraction (WAXD). The electrical conductivity and mechanical properties of the composites under study were also evaluated. Both molecular weight and crystallinity of the nylon 6 matrix were found to be strongly influenced by the presence of the copper powders. WAXD analysis has evidenced a close relationship between metallic filler used and nylon 6 crystal structure. The presence of copper particles into nylon 6 favours the formation of γ–phase crystal and reduces the fraction of the α–form crystal. For the copper particles incorporated in the nylon 6 matrix only one main peak at 2θ =43.4° was observed. Analysis of the results obtained on nylon 6/copper composite materials with DSC show that the incorporation of copper particles lowers the melting temperatures but rises the crystallization temperatures of the matrix of the composites while its crystallinity degree decreases. The addition of metal particles to nylon 6 played the role of nucleating agent and enhanced the crystallization rate. An improved thermal stability of the nylon 6/copper composite materials with respect to the neat nylon 6 can be noticed. The investigations on the nylon 6/copper composite materials show also that their mechanical properties are superior to those of neat nylon 6 in terms of the flexural strength and flexural modulus, but with sacrificing their impact strength.

Improving the structural description of high-temperature liquid GeSe2 from ab initio molecular dynamics simulations

Abstract: First-principles molecular dynamics simulations are performed on high temperature liquid GeSe 2 with two different gardient-corrected density functionals: the Perdue-Wang (PW) and the Becke, Lee, Yang and Parr (BLYP) functional. Structural and dynamical properties are analyzed and show a high influence depending on which is used. The BLYP functional not only increases the tetrahedral character of the system with a larger fraction of homopolor Ge-Ge bonding types, but also greatly affects the structure factor S(k) and the self-diffusion constants of the liquid. On the overall, this new functional brings the structural description closer to experimental findings determined from neutron diffraction.

Wavefront aberration correction in single mode fibre systems

Abstract: A simple control loop system was built for the purpose of optimized compensation of wavefront aberrations correction using a micromachined deformable mirror controlled by PCI cards and sound card through simulated annealing algorithm implemented by using the integration of Visual C++ and MATLAB in MATLAB environment.

Template free preparation and characterization of CuS nanoparticles in aqueous solutions of (EMIM)(EtSO 4 ) as a low cost ionic liquid using ultrasonic irradiation

Abstract: This paper presents a facile, room temperature and environmentally benign green route for the production of nanocrystalline CuS at 7 min by ultrasonic irradiating in aqueous solution of room temperature ionic liquid (RTIL), 1-ethyl-3methylimidazolium ethylsulfate, ([EMIM][EtSO4]). The X-ray diffraction (XRD) studies display that the products are well crystallized in the form of hexagonal structure. Energy dispersive X-ray spectroscopy (EDX) investigations reveal that the products are extremely pure. The morphology of as-prepared nanoparticles was characterized by scanning electron microscopy (SEM). A possible formation mechanism for the production of nanoparticles in the aqueous solution of the RTIL with the aid of ultrasonic irradiation is proposed.

Optical properties of Sol-Gel prepared nano ZnO. The effects of aging period and synthesis temperature

Abstract: In present work zinc Oxide (ZnO) nanoparticles were synthesized via Sol-Gel method in different temperatures and aging periods. The structures and morphologies of obtained nanoparticles were investigated via X-ray Diffractometer (XRD) and Transition Electron Microscope (TEM), respectively. The optical band gaps were estimated from Uv-Vis analyses. The results show high dependence of optical band gap to the synthesis conditions. The effects of these parameters on the band gap were investigated based on produced internal microstrains in the obtained zinc oxide structure. The band gap increase drastically with increase in synthesis duration. By decrease in sol-gel temperature the band gap shows a slight decrease.

Structural and optical characterization of ZnO thin films deposited by sol-gel method

Abstract: Zinc oxide is a promising semiconductor material with a variety of applications. Transparent, highly crystalline and crack-free film was deposited on corning glass. A transparent sol of 0.33 mol/l was prepared by dissolving Zinc acetate dihydrate in 2-methoxyethanol using mono-ethanolamine as sol stabilizer. Addition of few drops of water turns the sol immediately into milky gel form. The film was annealed in oxygen environment at 500°C for one hour and characterized by X-ray diffraction, Atomic force microscopy, UV-VIS spectroscopy and Raman spectroscopy. Thickness and roughness was measured by Surface profiler.

Origin of anomalous peak and negative capacitance in the forward bias C-V characteristics of Au/n-InP Schottky Barier Diodes (SBDs)

Abstract: The temperature dependence of forward and reverse bias capacitance-voltage (C-V) and conductance-voltage (G/w-V) characteristics of Au/n-lnP SBDs have been investigated in the temperature range of 80-400 K at 1 MHz. Experimental results show that the values of capacitance (C) and conductance (G/w) were found a strongly function of temperature and bias voltage. The forward bias C-V plots exhibit anomalous peaks due to the existence of a series resistance (R s ) and the magnitude of these peaks decrease with increasing temperature. In addition, a negative capacitance has been observed in the forward bias C-V plots. Physical principle of the negative capacitance has been ascribed to the interface states, the contact injection and minority carrier injection effects. It is thought that the capacitance value decreases with increasing polarization and more carriers are introduced in the structure. Also, the measured capacitance (C m ) and conductance (Gm/w) values have been corrected to obtain the real diode capacitance (C c ) and conductance (G c /w).

Effect of thermal annealing on the band gap and optical properties of chemical bath deposited PbS-CuS thin films

Abstract: Thin films of PbS-CuS have been grown on glass substrate by chemical bath deposition technique at room temperature. The films were annealed between 423K and 623K. The structure of the films was studied by x-ray diffraction measurement. UV-VIS spectrophotometric measurement showes a direct allowed band gap lying in the range 2.2 - 2.5eV for the annealed films and 1.7eV for the as-deposited film. The band gap increases with increasing annealing temperature.

Experimental evidence of an optical shuttering action in cholesteric phase of a double hydrogen bonded ferroelectric liquid crystal

Abstract: A novel series of double hydrogen bonded liquid crystals have been isolated. Hydrogen bond was formed between non mesogen chiral ingredient levo tartaric acid (LTA) and mesogenic undecyloxy benzoic acids (11BA). Thermal and electrical properties exhibited by levo tartaric acid and undccyloxy benzoic acid (LTA+11BA) were discussed. Interesting feature of the present investigation was observation of an optical shuttering action in LTA+11BA hydrogen bonded complex on application of a stipulated applied dc bias voltage. By enhancement of the dc bias voltage the mesogen behaves like an optical shutter, thus this hydrogen bonded complex mesogen acts as an effective light modulator. It was noticed that this action of shuttering was reversible, in the sense that when applied bias voltage was removed the original texture was restored. Experimental results relating to textures, optical tilt, dielectric studies and optical shuttering action were presented. This optical shutter property of the mesogen can be exploited for commercial and display device applications.

Optical and spectroscopic studies of ZnO-Bi 2 O 3 -B 2 O 3 glasses

Abstract: The effect of zinc oxide on the structural, physical and optical properties of bismuth borate glasses system has been investigated by means of infrared and optical absorption spectroscopic techniques. The samples were prepared by normal melt-quench technique. The formation of tetrahedral coordination of Zn (i.e. ZnO4) is not observed in glasses under study. The fundamental absorption edge for all the glass samples has been identified using the theory proposed by Davis and Mott. The optical band gap is found to increase with increase in ZnO content. The theoretical optical basicity has been reported as a function of Bi2O3. The density and molar volume of the present glass system are found to depend on ZnO substitution.

Silver/amorphous As2S3 heterostructure

Abstract: The heterostructure Ag/As 2 S 3 was deposited on glass substrate in two configurations: Ag/As 2 S 3 /glass and As 2 S 3 /Ag/glass. The effect of light emitted by a halogen lamp has been investigated by optical microscopy and X-ray diffraction. Particular morphological and structural aspects were revealed. Lateral diffusion rate of Ag has been determined.