Amorphous As2S3 Research Articles

Thin films of amorphous Ga2S3 and rare-earth sulphides

The aim of this research is to prepare amorphous thin films of undoped gallium sulphide and doped with rare-earth sulphides, of rare-earth sulphides and to investigate their physical properties. We have prepared thin amorphous films of Ga2S3, EuS, Er2S3, Gd2S3, and Ga2S3 doped with rare-earth sulphides (Ga2S3:EuS, Ga2S3:Er2S3, Ga2S3:Gd2S3) by Pulsed Laser Deposition (PLD). The corresponding targets for preparation of amorphous thin films were obtained by Spark Plasma Sintering (SPS) from commercially available powders of binary sulphides. The structural results for the undoped and doped Ga2S3 thin films indicate a packing of disordered layers similar to that of amorphous As2S3. Femtosecond laser irradiation of the Ga2S3 thin films shows a photoexpansion effect at low laser power (85–100mW) and an ablation effect at higher laser power (above 105mW). The threshold between low power and high power pulses is situated at higher value for Ga2S3 (100mW) in comparison with the case of As2S3 thin films (20mW).

Field effect transistors based on semiconductive microbially synthesized chalcogenide nanofibers

Microbial redox activity offers a potentially transformative approach to the low-temperature synthesis of nanostructured inorganic materials. Diverse strains of the dissimilatory metal-reducing bacteria Shewanella are known to produce photoactive filamentous arsenic sulfide nanomaterials by reducing arsenate and thiosulfate in anaerobic culture conditions. Here we report in situ microscopic observations and measure the thermally activated (79kJmol−1) precipitation kinetics of high yield (504mg per liter of culture, 82% of theoretical maximum) extracellular As2S3 nanofibers produced by Shewanella sp. strain ANA-3, and demonstrate their potential in functional devices by constructing field effect transistors (FETs) based on individual nanofibers. The use of strain ANA-3, which possesses both respiratory and detoxification arsenic reductases, resulted in significantly faster nanofiber synthesis than other strains previously tested, mutants of ANA-3 deficient in arsenic reduction, and when compared to abiotic arsenic sulfide precipitation from As(III) and S2−. Detailed characterization by electron microscopy, energy-dispersive X-ray spectroscopy, electron probe microanalysis and Tauc analysis of UV-vis spectrophotometry showed the biogenic precipitate to consist primarily of amorphous As2S3 nanofibers with an indirect optical band gap of 2.37eV. X-ray diffraction also revealed the presence of crystalline As8S9-x minerals that, until recently, were thought to form only at higher temperatures and under hydrothermal conditions. The nanoscale FETs enabled a detailed characterization of the charge mobility (∼10−5cm2V−1s−1) and gating behavior of the heterogeneously doped nanofibers. These studies indicate that the biotransformation of metalloids and chalcogens by bacteria enables fast, efficient, sustainable synthesis of technologically relevant chalcogenides for potential electronic and optoelectronic applications.

Light-induced switching of a chalcogenide-coated side-polished fiber device

In this report, we describe light-induced switching of the state of polarization of a side-polished fiber (SPF) coated with a chalcogenide (ChG) film, amorphous As2Se3 (a-As2Se3). The transient photodarkening effect produced by a-As2Se3 under 532-nm laser illumination modulated the refractive index of the coated ChG, changed the refractive index of the a-As2Se3-coated SPF device, and controlled and switched the phase retardation. When this design was used, a 70° phase change coupled with an optical loss of <0.2dB was achieved at a probe-beam wavelength of 1550nm; moreover, the extinction ratio achieved using an inline fiber polarizer was 22.8dB.

Surface relief grating formation in amorphous As40S15Se45 and As2S3 films under 0.532 μm wavelength illumination

In this research we have studied the influence of λ = 0.532 μm laser light illumination on the formation and properties of surface relief gratings in amorphous As2S3 and As40Se15Se45 films, as well as a bulk As2S3 sample. The surface relief grating formation was studied for a wide range of grating periods (∼1 – ∼80 μm) for the variable thicknesses of the samples. The examination of the relief depth, Δh, and its dependence on the grating period at constant exposures shows that the impact of sample thickness could manifest itself as a shift in the optimal grating period at holographic surface relief formation (As2S3) and affect the process itself.

Binary Superimposed Gratings Formed by &lt;I&gt;e&lt;/I&gt;-Beam Recording in Amorphous AsS Films

Binary Superimposed Gratings Formed by &lt;I&gt;e&lt;/I&gt;-Beam Recording in Amorphous AsS Films

Photo-induced formation of surface relief in amorphous As2S3 films

In this report we study the formation of surface relief in arsenic trisulfide films under laser light radiation with modulated polarization direction. The formation of surface relief is obtained with method what is different from holographic recording – only one laser beam with modulated polarization direction was used. Samples with different thickness were made using vacuum evaporation. The photo-induced changes on the surface were initiated by DPSS laser light (λ = 532nm). Profiles of surface reliefs were observed and relief depth dependence on film thickness and exposure was studied.

Terahertz-induced Kerr effect in amorphous chalcogenide glasses

We have investigated the terahertz-induced third-order (Kerr) nonlinear optical properties of the amorphous chalcogenide glasses As2S3 and As2Se3. Chalcogenide glasses are known for their high optical Kerr nonlinearities which can be several hundred times greater than those of fused silica. We use high-intensity, single-cycle terahertz pulses with a maximum electrical field strength exceeding 400 kV/cm and frequency content from 0.2 to 3.0 THz. By optical Kerr-gate sampling, we measured the terahertz-induced nonlinear refractive indices at 800 nm to be n2=1.746×10−14cm2/W for As2S3 and n2=3.440×10−14 cm2/W for As2Se3.

Photo-induced changes in a-AS2S3/gold nanoparticle composite layer structures

Optical parameters of pristine As2S3 amorphous chalcogenide layers are compared with those of layer structures which consist of gold nanoparticles on silica glass substrate, covered by the layer of amorphous As2S3. The localized plasmon resonances are measured and modeled in dependence on the nanocomposite structure. It is shown, that plasmon fields can be excited in these structures by laser irradiation, complementing the action of light on this light sensitive chalcogenide glass and influencing structural transformations in the glass as well as changes of its optical parameters. The enhancement of the light stimulated changes of optical parameters used for laser recording of photonic structures in selected chalcogenide nanocomposites follows from the results.

Ultralow-frequency photoelectric response of amorphous As2Se3 layers

The results of studying the photodielectric effect in amorphous layers of As2Se3 are reported. Agreement between the experimental and theoretical functions of the relative variation in the conductivity in the infralow-frequency region is observed. The dispersion of the recombination coefficient exhibits a minimum. Possible causes of the observed dependences are discussed.

Conduction Mechanism in Amorphous As&lt;sub&gt;2&lt;/sub&gt;S&lt;sub&gt;3&lt;/sub&gt;

The conduction mechanism in amorphous As2S3 has been studied by investigating the variation of the electrical resistivity over the temperature range 300 – 450 K. The electrical resistivity is characterised by a mobility gap of 2.15 eV over the temperature range investigated. The dc conductivity provides evidence of conduction by excitation of charge carriers into the band edges near the mobility edges. The results also give the possibility of conduction by a phonon-assisted hopping of polarons between localised states.Keywords: Amorphous semiconductor, hopping, mobility edge

Possible mechanism of Ag photodiffusion in a‐As2S3 thin films

Abstractmagnified imageMonitoring the silver photodiffusion in thin amorphous As2S3 film is addressed with a new experimental setup. A possible photo‐diffusion mechanism of silver into the a‐As2S3 thin film under green laser diode light (λ = 532 nm) irradiation is proposed. The proposed mechanism is based on a gradual filling of the structural voids existing in the network of the thin chalcogenide layer. This mechanism is supported by XRD measurements, optical absorption, and modeling data.

Imaging ellipsometry mapping of photo-induced refractive index in As2S3 films

Photoinduced diffraction grating formation in amorphous As2S3 thin films has been studied using imaging ellipsometry. We first have applied the ACCURION Nanofilm-EP3SE Imaging Spectroscopic Ellipsometer to obtain mapping of diffraction gratings in amorphous As2S3 thin films based on different photoinduced phenomena, namely photodarkening and photoinduced changes of refractive index.The profile and absolute value of refractive index in gratings were studied as a function of exposure. It is shown that underexposure led to the formation of a sinusoidal profile of the refractive index. The proper exposure produced results close to the cycloidal profile. Overexposure led to the same cycloidal profile but with reduced amplitude of refractive index variation in comparison with that obtained under proper exposure.

Specific features of the photodielectric effect in amorphous As2Se3 layers

The photodielectric effect (PDE) in amorphous arsenic triselenide (As2Se3) layers has been studied in a weakly varying electric field. As the field frequency decreases in the infra-low-frequency range, the experimentally measured function of relative conductivity coincides with the theoretically predicted behavior. It is established that the frequency dependence of the recombination coefficient exhibits a minimum.

Photo-Induced Mass Transport in Thin Films of Amorphous As2S3

Abstract In this report direct photo-induced formation of surface relief gratings (SRG) in thin layers of arsenic sulfide (As 2 S 3 ) are shown. This anisotropic light-induced mass transfer phenomenon has been discussed with the special attention focused on the polarization and intensity of the corresponding light. The experimental setup for the SRG recording is straight-forward consisting of ~10 μm optical slit through which an unfocused beam of light is projected on the surface of sample. The evolution of surface relief in dependence from the recording time and polarization has been investigated in detail. The processes of SRG formation and mass transfer which are based on the photo-induced plasticity have discussed.

Optical field-induced surface relief formation on chalcogenide and azo-benzene polymer films

The dependence of the surface relief formation in amorphous As2S3 and Disperse Red 1dye grafted polyurethane polymer films on the polarization state of recording light was studied. It is shown that the direction of mass transport on the film surface is determined by the direction of light electric vector and photoinduced anisotropy in the film. We propose a photoinduced dielectropfhoretic model to explain the photoinduced mass transport in amorphous films. Model is based on the photoinduced softening of the matrix, formation of defects with enhanced or decreased polarizability, and their drift under the electrical field gradient of light.

Photoexpansion and nano-lenslet formation in amorphous As2S3 thin films by 800 nm femtosecond laser irradiation

Two step laser processing has been used for the formation of nano-lenslets transmitting in red/infrared region of the optical spectrum on the surface of arsenic sulphide glass films. In the first step the films were obtained by pulsed laser deposition (248 nm), while in the second step the lenslets were created by low power femtosecond (800 nm) laser irradiation. Photoexpansion of the material along with simultaneous migration of chalcogen atoms in the irradiated area was the main phenomena involved in the generation of these structures. The maximum photoexpansion observed was 5.1%. At higher laser power, material ablation was evidenced.

Evaluation of Arsenic Availability in Sulfidic Materials from Gold Mining Areas in Brazil

This study is aimed at evaluating the availability and mobility of arsenic in sulfidic materials from gold mining areas in Minas Gerais State, Brazil. Eight extraction media were employed in a sequential extraction scheme, as follows: exchangeable As; strongly adsorbed As; As coprecipitated with acid-volatile sulfide, carbonates, MnO2, and Al2O3; As coprecipitated with amorphous iron; As linked to crystalline iron oxide; As coprecipitated with silicates; As coprecipitated with amorphous FeS2 and As2S3, and residual As, which was determined by GFAAS. Results demonstrated that in spite of differences in arsenic concentrations, the availability of the metalloid was found to be low for all samples. In general, arsenic was found in less available forms. Nevertheless, most of the arsenic in the environment is retained in the fractions 3, 4, and 5 which are susceptible to dissolution in acid medium, which in turn might be due to oxidation of the sulfide present in the samples.

On the ultraviolet light induced oxidation of amorphous As2S3 film

Illumination of amorphous As2S3 film by ultraviolet light with an overall light intensity on the sample surface of around 10Wcm−2 leads to extensive film oxidation. After 2min of illumination most of As2S3 film of an original thickness at around 0.425μm was converted into a cubic form of As2O3-arsenolite. A considerable amount of arsenolite microcrystals were found at a height of around 2μm and more which indicated a growth of As2O3 microcrystalline particles from the vapor phase.

Plasmon-Assisted Transformations in Metal-Amorphous Chalcogenide Light-Sensitive Nanostructures

Laser irradiation induced changes of optical parameters in the layered structures which consist of gold nanoparticles and amorphous As2S3 were investigated and modelled in the framework of Bruggeman approximation for localised plasmons with aim to show the influence of plasmon fields on the optical recording process.

Investigation of the structure of an amorphous As-Se semiconductor system by relaxation methods

The results of a complex investigation into dark-current relaxation in the long-time region of an MIM structure based on an As-Se thin-film chalcogenide system are presented. The values of parameters describing the electronic processes ocurring in the contact layers of the investigated compounds are estimated. The coincidence of the nature of conductivity and charge-accumulation mechanisms is revealed. The relaxation-time distribution function is calculated, and its structural sensitivity to such technological factors as the change in the composition stoichiometry and the method for manufacturing experimental samples is established.