As2S3 Films Research Articles

Fs Laser Patterning of Amorphous As2S3 Thin Films.

This study investigates the morphological changes induced by femtosecond (fs) laser pulses in arsenic trisulfide (As2S3) thin films and gold-arsenic trisulfide (Au\As2S3) heterostructures, grown by pulsed laser deposition (PLD). By means of a direct laser writing experimental setup, the films were systematically irradiated at various laser power and irradiation times to observe their effects on surface modifications. AFM was employed for morphological and topological characterization. Our results reveal a clear transition threshold between photoexpansion and photoevaporation phenomena under different femtosecond laser power regimes, occurring between 1 and 1.5 mW, irrespective of exposure time. Notably, the presence of a gold layer in the heterostructure minimally influenced this threshold. A maximum photoexpansion of 5.2% was obtained in As2S3 films, while the Au\As2S3 heterostructure exhibited a peak photoexpansion of 0.8%. The study also includes a comparative analysis of continuous-wave (cw) laser irradiation, confirming the efficiency of fs laser pulses in inducing photoexpansion effects.

Femtosecond laser induced damage threshold incubation and oxidation in AS2S3 and AS2Se3 thin films

Laser surface structuring has emerged as a versatile technology for precise and localized material processing. When dealing with femtosecond lasers, thermal effects and collateral damage are reduced due to nonlinear light-matter interaction, improving the processing. This study explores the fabrication of microstructures using femtosecond pulses on thin films of chalcogenide glasses, which can be used for photonics applications, such as waveguides, fiber lasers, and photonic crystals. Moreover, the photoinduced changes in chalcogenide glasses have opened up new possibilities in optoelectronics, data storage, and other applications. Femtosecond laser machining of amorphous thin films of As2S3 and As2Se3 using femtosecond laser pulses is investigated through various microscopy techniques and spectroscopy tools, focusing on the impact of incubation effects and controlled photo-oxidation. This research contributes to a deeper understanding of the interaction of ultrafast pulses with chalcogenide glasses, promoting further advancements in photonics and optoelectronic applications.

Hierarchical Surface Structures and Large-Area Nanoscale Gratings in As2S3 and As2Se3 Films Irradiated with Femtosecond Laser Pulses.

Chalcogenide vitreous semiconductors (ChVSs) find application in rewritable optical memory storage and optically switchable infrared photonic devices due to the possibility of fast and reversible phase transitions, as well as high refractive index and transmission in the near- and mid-infrared spectral range. Formed on such materials, laser-induced periodic surface structures (LIPSSs), open wide prospects for increasing information storage capacity and create polarization-sensitive optical elements of infrared photonics. In the present work, a possibility to produce LIPSSs under femtosecond laser irradiation (pulse duration 300 fs, wavelength 515 nm, repetition rate up to 2 kHz, pulse energy ranged 0.03 to 0.5 μJ) is demonstrated on a large (up to 5 × 5 mm2) area of arsenic sulfide (As2S3) and arsenic selenide (As2Se3) ChVS films. Scanning electron and atomic force microscopy revealed that LIPSSs with various periods (170-490 nm) and orientations can coexist within the same irradiated region as a hierarchical structure, resulting from the interference of various plasmon polariton modes generated under intense photoexcitation of nonequilibrium carriers within the film. The depth of the structures varied from 30 to 100 nm. The periods and orientations of the formed LIPSSs were numerically simulated using the Sipe-Drude approach. A good agreement of the calculations with the experimental data was achieved.

Surface-enhanced Raman scattering of As2S3 and Se thin films formed on Au nano-structures

The effect of plasmonic nanostructures (NSs) on the Raman spectra and underlying structural changes in thin chalcogenide films is investigated. Several tens of nanometers thick As 2 S 3 and Se films were deposited by thermal sputtering on glass and surface-enhanced Raman spectroscopy (SERS) substrates based on gold nanostructures for comparison. The films on glass were practically not detectable by the Raman spectroscopy. Using gold NSs as the substrates enabled reliable registration of the Raman spectra of both the As 2 S 3 and Se films. The registered Raman spectra contained all the features usually present in the films with the thicknesses ~1 μm or more. Based on our analysis of the spectra obtained at different excitation wavelengths, we may conclude that the SERS chemical mechanism makes the main contribution to the enhancement of the Raman signal from chalcogenide films. Adjustment of the parameters of SERS substrates to tune their plasmon band position in resonance with the excitation laser radiation enables increasing the plasmonic enhancement contribution. Besides the effect of enhancement, localized plasmon resonance in the gold NSs causes local heating of the chalcogenide film around them leading to local structural transformations, which can be controlled using the Raman spectra.

Photo-induced solid-state reaction on the interface of As2S3–Ge30Se70 thin films

The laser-induced solid-state reaction in double-layer As2S3 and Ge30Se70 thin films evaporated on each other on substrates was studied. The extent of the solid-state reaction on the interface of two films was evaluated as a shift of the short-wavelength absorption edge, which was significantly higher for the illuminated/annealed double-layer in comparison with the sum of shifts of the individual virgin films. The presence of a newly created intermix layer was proved by FTIR, AFM and ellipsometry.

Electro-Optical properties of photoaligned Liquid Crystal cells prepared with obliquely irradiated Chalcogenide glasses

We report the effect of oblique irradiation of thin As2S3 chalcogenide glass films on the photoalignment of Nematic liquid crystals and their electro optical properties. After depositing 60 nm As2S3 films on ITO coated substrates, the substrates were irradiated with polarized blue light (436 nm) at angles 0°, 5°, 20° and 48° of the light propagation direction with respect to the substrate plane. Then, the substrates were assembled and filled with the liquid crystal. The device LC-20° exhibits good extinction, and lower threshold voltage when compared to all other devices. The contrast ratio of LC-20° almost double that of the LC-5° and LC-48° devices. The response time increases with the angle, so for LC-20° slightly longer than for LC-5° but shorter than that of LC-48°. It is evident from the observations that the obliquely irradiated cells show good photoalignment and enhanced electro optical properties, although no pretilt is generated due to the oblique irradiation. Therefore, contrary to the photoalignment using photosensitive polymers, chalcogenide glasses have the advantage of providing photoalignment with little sensitivity to the irradiation angle. This fact led us to propose a model for the photoinduced alignment on chalcogenide glasses based on directional structural changes, not related to oriented dipoles generation as in the case of photoalignment with polymers.

Mass transport in amorphous As2S3 films due to directional light scattering under illumination by an oblique tightly focused beam

Photoinduced deformation of an amorphous As2S3 film surface under illumination by sub-bandgap (638 nm) and above-bandgap (532 nm) polarized laser light at oblique incidence are studied by atomic force microscopy performed directly after the film exposure to the laser beam. Photoinduced expansion as well as directional mass transport from the laser spot are observed. The photodeformation character under sub-bandgap and above-bandgap illumination are discussed in view of the optical forces (gradient force and scattering force) due to the interaction of light with the amorphous As2S3 film .

Gold nanoparticle assisted synthesis and characterization of As–S crystallites: Scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray and Raman spectroscopy combined with DFT calculations

Gold nanoparticle assisted thermally initiated chemical vapor deposition was used to synthesize nanostructured As-S films. The nanostructures were grown on heated Si substrates covered by spherical gold nanoparticles of different (5, 20, 40 and 60 nm) sizes. In contrast to polycrystalline As-S films prepared by ordinary thermal evaporation and chemical vapor deposition of As2S3 glass without the use of gold nanoparticles, the gold nanoparticle assisted synthesis leads to growth of particular type of crystal-like As-S nanostructures. The As-S micro-crystallites with well-defined size and shape were obtained with 43.9 and 56.1 at% As and S atomic content, respectively. The local structure of the As-S microcrystallites was investigated by Raman and/or surface-enhanced Raman spectroscopy. To assist the interpretation of the experimental Raman spectra and to identify the structure of the crystallites, the vibrational spectra of different cage-like nanocluster models were also calculated by using the density functional theory. Results show that at specific deposition conditions a stimulated formation of As4S5 molecules occurs which activates the growth of micro-crystallites on the gold nanoparticle coated Si surface with well distinguished shape. The structure and properties of nanostructured As-S films synthesized with and without the use of gold nanoparticles were investigated and the gold nanoparticle assisted selective growth of a new type of As–S microcrystallite is discussed.

Formation of holographic diffraction gratings in thin films of chalcogenide glassy semiconductors

The paper presents a study of the formation of holographic diffraction gratings in thin films of chalcogenide glassy semiconductors. The recording process of holographic gratings at the argon-laser radiation wave length 488 nm and the process of chemical etching that enables the formation of а relief holographic grating are analysed. The optimum conditions for the formation of diffraction gratings in films of arsenic sulfide As2S3 are defined. It is shown that at the 488 nm wave length of an argon laser the optimum exposure comes to ∼5–8 J/cm2. At the recording stage a quasi-phase (relief-phase) grating is formed, with the diffraction efficiency on the order of a few per cent. Etching of the exposed sample with a solution of NaOH alkali in deionised water and isopropanol makes it possible to increase considerably the relief depth and to improve the diffraction efficiency of a thin diffraction grating approximately up to 20 % for the red spectral region, and to approach the maximal value ∼34 % for the near infra-red region. The results of the study considered look promising for the creation of relief holographic gratings which are essential in present-day optical instrument building (production of spectral devices, holographic sights, and the like).

Mössbauer 57Fe and 129I Spectra, as Well as the Local Environment of Atoms, in Chalcogenide CuI–AgI–As2Se3 and CuI–PbI2–SbI3–As2Se3 Films Deposited from Glass Solutions in N-Butylamine

Mössbauer 57Fe and 129I Spectra, as Well as the Local Environment of Atoms, in Chalcogenide CuI–AgI–As2Se3 and CuI–PbI2–SbI3–As2Se3 Films Deposited from Glass Solutions in N-Butylamine

Utilization of As50Se50 thin films in electron beam lithography

Chalcogenide glass of As50Se50 composition have been intensively studied for its interesting physical and chemical properties. Presented manuscript explores the applicability of As50Se50 thermally evaporated thin films in electron beam lithography exploiting wet etching in amine based solution. As50Se50 films proved to be highly sensitive negative resist. Decrease of the etching selectivity with increasing accelerating voltage and its increase with increasing exposure dose were observed. Height irregularities of prepared structures connected with the electron beam scattering and preferential etching of upper edges were observed and thoroughly studied. Comparison of photoinduced chemical resistance changes showed same trends as in case of electron beam induced changes – chemical resistance significantly increased with increasing exposure dosages.

Optical Parameters of Both As2S3 and As2Se3 Thin Films from Ultraviolet to the Near-Infrared via Variable-Angle Spectroscopic Ellipsometer

In the UV-visible-near infrared regions from 245 to 1000 nm, variable-angle spectroscopic ellipsometer (VASE) was used to investigate optical functions of As2S3 and As2Se3 thin films. In the entire measured spectral range, data were analyzed by assembly from several dispersion models. These assemblies comprise individual Tauc–Lorentz supplemented by several Lorentz (TL-group) or single Cody–Lorentz with several Lorentz (CL-group) models. For As2S3 and As2Se3 thin films, the optical parameters were quantified. The model parameters, such as the Lorentz amplitude, resonance frequency, oscillator width, extinction coefficients, refractive indices, and Urbach and optical band energy of both films were obtained. The band gap energy Eg was experimentally determined using the obtained data of CL-group from (αhν)1/2 vs. hν plots. It is found that the band gap energies of As2Se3 and As2S3 were 1.796 and 2.349 eV, respectively. The Eg values for the films were theoretically investigated by the bond statistics of the random covalent network model (CRNM) with the aid of Manca’s relation. Plausible agreement between the experimental and calculated Eg values for both samples was obtained.

Ab initio investigation of optical properties of As2S3 and Ag doped As2S3

The density functional theory along with generalized gradient approximation is used to calculate the optical properties of As2S3 and Ag0.25As1.75S3. The effective band gap of Ag0.25As1.75S3 is reduced as compared to As2S3. The scissor correction of 1 eV is used to calculate the optical properties. The dielectric function of Ag0.25As1.75S3 enhances significantly at low energies while at higher energies there is constant shift in the peak positions of Ag0.25As1.75S3 as compared to As2S3. Similar enhancements at low energies and shift at higher energies are found in the refractive index, optical conductivity, absorption coefficient and reflectance of Ag0.25As1.75S3 as compared to As2S3. The optical parameters are found more anisotropic at low energies however at higher energies the anisotropy nearly vanishes. The Ag0.25As1.75S3 is found more birefringent than As2S3. The calculated results closely agree with the available experimental estimates of crystalline, amorphous and thin films of As2S3 and Ag0.25As1.75S3.

SURFACE PLASMON RESONANCE IN As2Se3 PLANAR WAVEGUIDES FOR THE IR SPECTRAL REGION

The surface plasmon resonance (SPR) four layers configuration that contains prism of BK7-gold metal film-As2Se3 waveguide-air was realized. As2Se3 thin films with low roughness were obtained by thermal evaporation using cvasi-closed evaporator. The surface roughness’s was less than 2.5 nm. The SPR curves shape calculated by MATLAB solver were identical to these one calculated by matrix method. The As2Se3 films were characterized by ellipsometric spectroscopy and the obtained optical constants were used for calculations. Experimentally obtained SPR curves at the 1064 nm wavelength shown sharp resonance and are in accordance with calculus.

Raman study of laser-induced formation of II–VI nanocrystals in zinc-doped As–S(Se) films

Zn-doped As2Se3 and As2S3 films were prepared by thermal evaporation. Their amorphous structure was confirmed by Raman spectroscopy. Zinc chalcogenide nanocrystals can be formed in the films under laser irradiation due to the photoenhanced diffusion of atoms in the arsenic chalcogenide films, which enables aggregation of Zn and S(Se) atoms in nanocrystals. For As2S3:Zn films, not only ZnS, but also ZnO crystallites can be formed under irradiation with UV laser light due to oxidation of the film surface with abundant zinc atoms.

SPECTRAL DEPENDENCE OF PHOTOINDUCED FORMATION OF SURFACE RELIEF GRATINGS IN AMORPHOUS CHALCOGENIDES

The surface relief grating formation in As2S3 and As40S15Se45 films under laser wavelengths λ = 491, 532, 561, 594 and 633 nm light influence was examined. The studies of spectral dependence of photoinduced birefringence and its development during the holographic recording in studied chalcogenide films showed that photoinduced birefringence plays an important role in SRG formation process.

Can the copper completely suppress the photodarkening effect in As-Se films

Photodarkening (PD) effect in Cu-doped As-Se films with various structures has been investigated to see whether the copper can completely suppress the PD effect in the As-Se films. Under the illumination of 655 nm light, it was found that, the minimum PD can be found in the homogeneously doped As-Se films. This is in sharp contrast with the previous results where it was claimed that PD can be completely suppressed in Cu-doped As2Se3 bulk glasses. Further experiments in the films illuminated by the light with different power elucidate that PD in the Cu-doped As2Se3 films is sensitive to photon energy and power level used in the experiments.

Electroconductivity and Electrode Properties of Amorphous PbS–Ag2S–As2S3 and PbS–AgI–As2S3 Films Deposited from Solutions of Glass in n-Butylamine

The parameters of the specific electroconductivity and electrode properties of massive glass and amorphous films of PbS–AgI–As2S3 and PbS–Ag2S–As2S3 are studied. It is established that the lower detection limit of Pb2+ cations is 10–7 mol/L for most of the studied membranes, while the Nernst region of the electrode function is 10–6–10–1 mol/L. The response time of the best film membranes Pb-ISE is 30–40 s in diluted solutions and 5–10 s in 0.01–0.1 M stirred solutions of Pb(NO3)2.

Impact of composition and ex-situ laser irradiation on the structure and optical properties of As-S-based films synthesized by PECVD

Synthesis of amorphous chalcogenide As-S-based films with arsenic content from 35 to 55 at. % by a PECVD method is achieved. The composition-structure-optical properties relationship is revealed. Varying the composition of the films from As35S65 to As55S45 is accompanied by a change of the dominant structural units: from AsS3/2 pyramids to cage-like As4S4 and As4S3 units, causing a considerable decrease of the optical band gap from 2.42 to 1.87 eV. It has been found out that modification by a focused laser irradiation (473 nm) leads to formation of micro/nanocrystalline inclusions feasible for applications in medicine, optoelectronics and integrated optics. The type of inclusions depends on the dominant structural units of the initial films. In case of the As55S45 film appearance of the dimorphite crystalline phase (α-As4S3) is observed. The ex-situ laser modification of the As-S films leads to appearance of a photoluminescence emission, and its maximum position shifts from 1.8 to 2.05 eV depending on the initial film stoichiometry.

Exploring the Optical Dynamics in the ITO/As2Se3 Interfaces

In this work, the effects of indium tin oxide (ITO) substrates on the structural, compositional, optical dielectric and optical conduction properties of arsenic selenide thin films are investigated. The As2Se3 films which are prepared by the thermal deposition technique under vacuum pressure of 10−5 mbar exhibit an induced crystallization process, improved stoichiometry, increased optical transmittance in the visible range of light and increased dielectric response in the infrared range of light upon replacement of glass substrates by ITO. The ITO/As2Se3 interfaces exhibit conduction and valence band offset values of 0.46 eV and 0.91 eV, respectively. The experimental optical conductivity spectra are theoretically reproduced with the help of the Drude–Lorentz approach for optical conduction. In accordance with this approach, owing to the improved crystallinity of the arsenic selenide, the deposition of As2Se3 onto ITO substrates increases the drift mobility value from ∼ 17.6 cm2/Vs to 34.6 cm2/Vs. It also reduces the density of free carriers by one order of magnitude. The ITO/As2Se3/C heterojunction devices which are tested as band filters which may operate in the frequency domain of 0.01–3.0 GHz revealed low pass filter characteristics below 0.35 GHz and band pass filter characteristics in the remaining spectral range.