As2S3 Films Research Articles

Selective wet etching of amorphous As2Se3 thin films

Photosensitivity based practical applications of chalcogenide glasses such as high resolution inorganic photoresists require thorough understanding of the relations between the glass structure and the etching kinetics. In this paper we report on the selective wet etching of thermally evaporated As2Se3 thin films carried out using amine based solutions. The relation between photo- and thermo-induced structural changes in thin As2Se3 films and the decrease of the etching rate, increase of the etching process' activation energy respectively, was determined.

Deformation of Amorphous GeSe2 Film under Uniaxial Pressure Applied at Elevated Temperatures

In an effort to evaluate the practicability of an imprinting technique for amorphous chalcogenide film in Ge-based compositions, we investigate the deformation behavior of the surface of amorphous GeSe₂ film deposited via a thermal evaporation route according to varying static loads applied at elevated temperatures. We observe that, under these static loading conditions, crystallization tends to occur on its surface relatively more easily than in As-based As₂Se₃ films. As for the present GeSe₂ film, higher processing temperatures are required in order to make its surface reflect the given stamp patterns well; however, in this case, its surface becomes partially crystallized in the monoclinic GeSe₂ phase. The increased vulnerability of this amorphous GeSe₂ film toward surface crystallization under static loading, when compared with the As₂Se₃ counterpart, is explained in terms of the topological aspects of its amorphous structure.

Infrared waveguide fabrications with an E-beam evaporated chalcogenide glass film

Chalcogenide glasses have a variety of unique optical properties due to the intrinsic structural flexibility and bonds metastability. They are desirable materials for many applications, such as infrared communication sensors, holographic grating, optical imaging, and ultrafast nonlinear optic devices. Here, we introduce a novel electron-beam evaporation process to deposit the good quality arsenic trisulfide (As2S3) films and then the As2S3 films were used to fabricate the As2S3 waveguides with three approaches. The first method is photoresist lift-off. Because of the restriction of thermal budget of photoresist, the As2S3 film must be deposited at the room temperature. The second one is the silicon dioxide lift-off process on sapphire substrates, in which the As2S3 film could be evaporated at a high temperature (>180 °C) for better film quality. The third one is the plasma etching process with a metal protective thin layer in the pattern development process.

Local surface structure and structural properties of As–Se nanolayers studied by synchrotron radiation photoelectron spectroscopy and DFT calculations

The surfaces of As20Se80, As40Se60 and As50Se50 films were studied using synchrotron radiation photoelectron spectroscopy and DFT electronic structure calculations. The composition and local structure of the surfaces were determined by curve fitting of the experimental As 3d and Se 3d core levels, and studies show significant Se-enrichment in the top surface layers of the films. The valence band spectra have been interpreted within a model of discrete structural units, giving rise to distinct peaks in the spectra. The interconnection between the surface composition, local structure formation and the features of the valence band spectra of As20Se80, As40Se60 and As50Se50 films is analyzed and discussed in detail.

On the detection of U − centers in g-As2Se3 films by thermal cycling measurements of electrical conductivity

Pinning of the Fermi level near the midgap is one of the basic properties of chalcogenide glassy semiconductors. It is assumed in most models that the pinning is due to the presence of charged defects (U− centers) that strongly polarize the lattice and have energy levels close to the Fermi level. U− centers are detected in this study by the thermal cycling method, which made it possible to markedly extend the time during which the charge released by these centers is recorded. The results of measurements of the electrical conductivity of As2Se3 films in successive cycles of sample cooling and heating are presented. This cycling leads to the appearance and evolution of two discrete peaks. A conclusion is made that at least one of these peaks is associated with negatively charged U− centers with levels near the Fermi level.

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.

Asymmetric one-dimensional photonic crystal for optical sensing in the visible spectral range

A gas sensor based on an asymmetric one-dimensional (1D) photonic band gap structure with one defect layer was designed and fabricated through layer-by-layer deposition of spin-coated poly methyl methacrylate (PMMA) and vacuum-deposited As2S3. Initially, the thickness variations, Δd, were determined of the thin films resulting from the poly methyl methacrylate exposure to chloroform vapor in the concentration range 100 – 9000 ppm. It was found that the value of Δd depends on the gas concentration and the exposure time. A two-layer structure was prepared consisting of PMMA and vacuum-deposited As2S3. Further, the permeability of thin As2S3 films to chloroform vapors was investigated. The asymmetric photonic structure consisted of 11 alternating layers of As2S3 and PMMA. The defect PMMA layer was located before the last high-refractive-index film of chalcogenide glass. The thickness of the defect layer of PMMA was pre-calculated so that the pass band be centered at the wavelength of 550 nm. An offset was observed of the position of the pass band to the larger wavelengths after exposure to chloroform vapor. The multilayered structure proposed is promising for optical sensor applications.

Binary Superimposed Gratings Formed by <I>e</I>-Beam Recording in Amorphous AsS Films

Binary Superimposed Gratings Formed by <I>e</I>-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.

RF sputtered amorphous chalcogenide thin films for surface enhanced infrared absorption spectroscopy

The primary objective of this study is the development of transparent thin film materials in the IR enabling strong infrared absorption of organic compounds in the vicinity of metal nanoparticles by the surface plasmon effect. For developing these optical micro-sensors, hetero-structures combining gold nanoparticles and chalcogenide planar waveguides are fabricated and adequately characterized. Single As2S3 and Ge25Sb10Se65 amorphous chalcogenide thin films are prepared by radio-frequency magnetron sputtering. For the fabrication of gold nanoparticles on a chalcogenide planar waveguide, direct current sputtering is employed. Fabricated single layers or hetero-structures are characterized using various techniques to investigate the influence of deposition parameters. The nanoparticles of gold are functionalized by a self-assembled monolayer of 4-nitrothiophenol. Finally, the surface enhanced infrared absorption spectra of 4-nitrothiophenol self-assembled on fabricated Au/Ge-Sb-Se thin films hetero-structures are measured and analyzed. This optical component presents a ~24 enhancement factor for the detection of NO2 symmetric stretching vibration band of 4-nitrothiophenol at 1336 cm−1.

Holographic investigation of silver electromigration in nano-sized As2S3 films**This work is dedicated to the 90th anniversary of the birth of Academician Jordan Malinowski.

Holographic gratings with a diffraction efficiency (DE) greater than 8% and a spatial resolution of 2237 mm−1 are recorded in very thin As2S3 films with a thickness of 100 nm. Silver photo-diffusion is observed during the holographic recording process while applying a corona discharge. We use the method of holographic grating relaxation spectroscopy (forced Rayleigh scattering) based on the evanescent waves to determine that the silver diffusion coefficient in the thin As2S3 film is in the range of (0.9–10.3) × 10−13 cm2 s−1 depending on the corona charge polarity.

Observation of Ag photodoping phenomena in GeS2 chalcogenide glass films by spectroscopic ellipsometry and atomic force microscopy

The anomalous diffusion process of Ag into a GeS2 film induced by the illumination of light with the photon energy near or larger than the optical gap of a GeS2 film was examined in-situ by the spectroscopic ellipsometry in the wavelength region between 450 and 850nm. The physical parameters such as the thickness and the refractive indices n and κ for each layer were derived from the ellipsometric parameters measured at respective wavelength using the simulation assuming a three layers (Ag, Ag: GeS2 and GeS2 layers) model. Two steps of doping process called the first and second stage were derived through the analyses of the optical constants, which were different from the results for As2S3 films. Especially, the first stage progressed very fast in GeS2 films in the three layers model. The in-situ observations using an atomic force microscope were also carried out to understand the doping process through the change of the surface morphology during doping of Ag and the results which supported the ellipsometric behaviors were obtained. Other simulation model assuming optical constants considering effective medium approximation for the doped layer during doping was discussed for the analysis of ellipsometric data and the difference of the doping behavior between two models was discussed.

Optics of microlenses created by irradiation of As2S3 amorphous chalcogenide films with femtosecond laser pulses

Arrays of microlenses have been created on the surface of thin amorphous films of As2S3 by localized photoexpansion induced by femtosecond laser pulses. The profile of a typical microlens has been mathematically described. Ray-tracing analysis has been performed to determine the focal points in the red and near-infrared spectrum of electromagnetic radiation. These lie at distances of 1.21 μm at λ = 650 nm and 1.33 μm at λ = 1.5 μm above the top of the microlens. It is suggested that the microlenses could be used in two-dimensional optoelectronic circuits or in fibre optics.

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.

Photoinduced scalar and vectorial optical phenomena in nano-dimensional glassy chalcogenide films and their liquid crystal photoalignment

Photoinduced (PI) scalar and vectorial optical phenomena in chalcogenide glassy films' early studies were performed on films thicker than 0.5–l μm. Recent finding of nano-dimensional (ND) As2S3 films possibility to act as a photoalignment layer for nematic liquid crystals (LCs) made careful investigation of PI anisotropy and other PI phenomena in nano-dimensional (<100 nm thick) chalcogenide films of different composition. Results of such investigation are considered in this paper. The scalar and vectorial PI phenomena having many similar characteristics are shown to exist in all studied (ND) As-containing chalcogenide glassy films both stoichiometric and non-stoichiometric. The ND Ge-containing chalcogenide glassy films are shown to have very different optical characteristics. We demonstrated that ND chalcogenide glassy films of different compositions are able to act as photoalignment layers for nematic LCs under irradiation with linearly polarized light.

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.

One dimensional photonic crystals from As2S3 and PMMA films for photonic and sensor applications

One dimensional photonic crystal (1D-PhC) in form of 19 layered stack was prepared through layer-by-layer deposition of spin coated Poly (methyl methacrylate) (n = 1.49 at 1.55 μm) and vacuum deposited As2S3 (n = 2.27 at 1.55 μm) as low and high refractive index materials, respectively. The optical properties of the single layers and the multilayered stack are studied at normal and oblique incidence of linearly polarized light. The possibility of using the 1D-PhC as an omnidirectional reflector was exploited theoretically and confirmed experimentally. Besides, the prospect of using the studied structure for chemical sensing with optical read-out is demonstrated.

Diffraction efficiency growth of nano-scale holographic recording produced in a corona discharge

The nano-scale holographic gratings ware recorded in 29 nm and 56 nm thick As2S3 films. The chalcogenide layers were deposited on a transparent chromium electrode with thickness 10 nm, produced on a glass substrate. Both chromium and chalcogenide films were deposited in one vacuum cycle by e-beam and thermal evaporation, respectively. The diode 532 nm diode laser was used as a light source in the present holographic experiments. The total internal reflection arrangement (Stetson-Nassenstein) was used in holographic recordings. The reference beam was totally reflected from the air-As2S3 boundary surface by an input glass prism. The object beam was normally incident on the recording medium. The corona charging was performed by a needle fixed at the distance of 1 cm from the holographic recording medium by applying a – 5 kV voltage. The diffraction efficiency increased from 9 to 30 times when the corona discharge was applied during the holographic recording, in comparison to the uncharged recording. The possible reason of the observed effect is discussed on the basis of the Franz-Keldysh effect and Moss rule.

Reversible Amorphous‐to‐Amorphous Transitions in Chalcogenide Films: Correlating Changes in Structure and Optical Properties

AbstractStructural transitions in materials are accompanied by appreciable and exploitable changes in physical‐chemical properties. Whereas reversible optically‐driven atomistic changes in crystal‐to‐amorphous transitions are generally known and exploited in applications, the nature of the corresponding polyamorphic transitions between two structurally distinct meta‐stable amorphous phases is an unexplored theme. Direct experimental evidence is reported for the nature of the atomistic changes during fully reversible amorphous‐to‐amorphous switching between two individual states in the non‐crystalline As50Se50 films prepared by pulsed‐laser deposition and consequent changes in optical properties. Combination of surface sensitive X‐ray photoelectron spectroscopy and spectroscopic ellipsometry show that the near‐bandgap energy illumination and annealing induce reversible switching in the material's structure by local bonding rearrangements. This is accompanied by switching in refractive index between two well‐defined states. Exploiting the pluralism of distinct structural states in a disordered solid can provide new insights into the data storage in emerging optical memory and photonic applications.

Optical and holographic properties of nano-sized As2S3 films

The theoretical background as well as the experimental results of evanescent wave holographic recording with grating periods of 3.2, 0.88 and 0.37μm (spatial frequencies of 310mm−1, 1140mm−1 and 2700mm−1) in nano-sized As2S3 films with thicknesses of 29nm, 15nm and 10nm are presented. The grating recording has been performed using the interference of surface-propagating evanescent waves, created by total internal light reflection. The maximum diffraction efficiency of 5.6×10−3% has been achieved for grating period of 0.88μm and sample thickness of 15nm. Besides, the optical characteristics as refractive index n and extinction coefficient k of the films studied have been determined from spectrophotometric measurements in 250–650nm wavelength region. Furthermore, drawing a connection to our previous morphological investigations, the existence of a strong relationship between microstructure, optical and holographic behavior of nano-sized As2S3 films has been revealed. On this basis the possibility of applying the evanescent – wave holography as a useful nano-tool for studying structures and different phenomena at nanometer scale has been outlined.