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Compositional and fabrication method dependences of laser-induced geometrical surface relief formation in Ge Se amorphous layers were investigated with the aim to determine the possible role of initial conditions in the mechanism and efficiency of optical recording. The results show that pulsed laser deposition has some advantages in composition preservation and surface relief formation in comparison with thermal evaporation for producing layers with high sensitivity and efficiency of surface relief grating formation, especially in layers with Ge 24 Se 76 composition. It was shown that modulation depth of the created surface structures increases with increasing Se content in Ge Se amorphous chalcogenide layers. Thermal annealing has essential influence on the recording parameters, enabling additional insight into the possible mechanisms of light induced surface patterning in this type of light-sensitive amorphous chalcogenides. Raman spectroscopy was used to identify local structure of produced surface patterns.

The knowledge of viscosity, which determines the flow of material under applied stresses, is important for many processes of the material production. Data on viscosity of thin amorphous films are necessary for development of molding technology, which allows fast fabrication of various components for integrated optics. Chalcogenide films attract great attention due to their non-linear optical properties and possibility of viscosity variation by light illumination. Despite of importance of data on the film viscosity, no methods of their direct measurements were reported. We propose such method and apply it for measurements of viscosity of As20Se80 chalcogenide films in a temperature range 378–403 K. We have obtained that coefficients of viscosity vary in the range 3 × 107–1010 Pa·s, with the activation energy 2.9 eV. The thin film viscosity coefficients are 2–5 times smaller compared to those for massive glasses.

In this paper, the plasmon field enhanced light-induced changes are investigated in the amorphous Ge24Se76 layer incorporating Au nanoparticles. The presence of gold nanoobjects in amorphous chalcogenide/gold heterostructure influences the optical and structural properties, as well as volume changes of the material. It also enhances the Raman signal of the structure through surface enhancement, which allows clearer and better investigation of the glass structure and understanding of the mechanisms of surface plasmon stimulated transformations. In addition, it also enhances the recording of the optical grating pattern into the layer.

We have detected that surface relief gratings (SRG) in amorphous chalcogenide films As20Se80 can be optically recorded at low temperature, such as 77 K. A diffusion mechanism of photo-induced (PI) mass transport is proposed. A driving force of PI mass transport is a lateral steady state electric field induced by light interference. The kinetics of PI SRG growth depends on temperature due to temperature dependence of PI diffusion coefficients and concentration of radiation defects. By comparison of low temperature kinetics with that at 300 K we estimated diffusion activation energy, which turned out 0.09 eV. We present a model that explains low diffusion activation energy.

Direct surface relief recording in amorphous chalcogenide semiconductors like As20Se80 and other compositions from As(Ge)–S(Se) systems essentially depends on the chemical composition, technology, and the recording conditions, resulting discrepancies in the results and interpretations. We have developed a method of direct comparison of the relief height and form in a combined thin film samples made of the reference and investigated compositions, as well as simple way of determining the efficiency of mass transport at surface relief recording. Selection of the a-Se as reference layer enables consideration of the possible role of composition, temperature, polarization in the recording process for any other chalcogenide or other material, which possess similar relief recording effects.

Nonlinear refractive indices of simple and composite chalcogenide glasses with gold nanoparticles are measured by the Z-scan method using a femtosecond Ti:sapphire laser with a central wavelength of 800 nm and a pulse duration of 40 fs. It is shown that introduction of nanoparticles into thin layers of amorphous GeS2, As30Ge20S50, and As3Ge35S62 leads to a decrease in the total nonlinear refractive index due to additional absorption of femtosecond laser radiation without efficient excitation of localized plasmons outside the resonance region. For example, the nonlinear refractive index decreases with addition of gold nanoparticles from 16.1 × 10–12 to 13.0 × 10–12 cm2/W for GeS2, from 3.9 × 10–12 to 3.2 × 10–12 cm2/W for As30Ge20S50, and from 5.8 × 10–12 to 4.7 × 10–12 cm2/W for As3Ge35S62.

Surface reliefs in the form of dots and surrounding rings were recorded by focused laser beam on bulk amorphous selenium samples with an aim to separate the possible contributions of pure light- and thermally stimulated effects to the relief formation process. It is concluded, that heating by the light beam can be cross-linked with light induced mass transport in the gradient of illumination and temperature fields and so with surface relief formation, influencing its efficiency and quality. Such thermal effects should be taken into account in light sensitive chalcogenide glasses with low softening temperatures and possible crystallization effects.

The focus of this work is on the formation of a lithography-free redox conductive bridge memristor array, comprised of different compositions of GexSe1−x chalcogenide glasses with the aim of selecting the chalcogenide material that provides the best performance. Various memristive arrays were fabricated on a metal–chalcogenide–metal stack. This structure offers high device density with the simplest configuration and allows access to each nano redox conductive bridge device. It was found that the device stability and threshold voltage were a function of the chalcogenide glass composition, with the Ge-rich film contributing to the best device performance, which is attributed to the formation of rigid structure and the availability of Ge–Ge bonds. Additionally, these parameters were dependent on the thickness and the surface roughness of the chalcogenide glass. Application of a nonlithography method for fabricating the array structure offered excellent yield, stable ON–OFF states and good uniformity. This demonstration, along with success achieved at the single cell level, suggests that the redox conductive bridge memristor is well positioned for ultrahigh performance memory and logic applications.

The influence of the localized surface plasmon fields on the light stimulated transformations in amorphous chalcogenide films was investigated. It was established that both in the gold nanoparticle array-chalcogenide film and in the gold film with nanohole array-chalcogenide film composites the plasmon fields, induced during the laser illumination of the structures, increase the efficiency of structural transformations, the related photo-darkening or bleaching, as well as of the volume change, surface deformations. The results, obtained for structures with As 20 Se 80 amorphous layer, can be applied for other selected chalcogenide layers and fabrication of locally driven information recording media.

Patterning processes in amorphous Se and $$\hbox {As}_{20}\hbox {Se}_{80}$$ films at short electron beam pulses (from 200 ns to 100 ms) were studied for the first time. The surface reliefs occurring as after-pulses effects were recorded and analysed. Giant hillock formation was detected at about $$200\,\upmu \hbox {s}$$ pulses while very small changes in surface morphology were observed at other pulse durations. The obtained data indicate that the strong increase in e-beam sensitivity of mechanical response (giant surface hillock formation) at about $$200\,\upmu \hbox {s}$$ is due to some resonance effect. A qualitative description is given, relating these times to the characteristic generation and relaxation time of the defects in these materials, which illuminates the process of e-beam induced structural rearrangement. The measurement has been performed at room temperature and at $$-120\,^{\circ }\hbox {C}$$ and only a 20% change in the maximal pattern height has been detected.

Here we demonstrate a plasmon enhanced optical recording in As-Se layers, which are among the most applicable for processing with He-Ne or other red light emitting lasers. Gold nanoparticles deposited on the silica glass substrate and covered by an amorphous chalcogenide layer satisfy the conditions of efficient surface plasmon resonance in this spectral region. The enhancement of photo-induced transformations results in an increased rates of photo-darkening, followed by bleaching and localized volume changes. These experimental results support the importance of localized electric fields in photo-structural transformations of chalcogenide glasses as well as suggest new approaches for improving the performance of these recording media. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The photo-stimulated interdiffusion within chalcogenide based nano-layered structures (NLS) produces large changes in properties, which have potential application in optical pattern recording. The mechanism of these changes is investigated for two NLS consisting of 100 alternate layers of antimony and As 2 S 3 , but of different relative thicknesses, by high-resolution X-ray photoelectron spectroscopy. The results suggest the formation of Sb–S bonds at the expense of As–S bonds, with a consequent increase in the refractive index but minimal change in thickness. The role of oxygen in photoinduced transformations, especially in the top layers, is characterized and discussed.

The light and heat induced changes in the optical band gap of Sb/As 2 S 3 nanomultilayered chalcogenide film has been studied. Even though the changes in optical bandgap are attributed to the light and heat induced interdiffusion, the diffusional intermixing between the layers is rather different with light and heat. The observed difference in the light and heat induced interdiffusion is due to unequal diffusion coefficients of light and heat predicted by thermal spike model.

Investigations of light-induced volume expansion and surface pattern recording in amorphous chalcogenide layers and nano-layered structures (NLS) were extended to direct electron-beam recording on Se/As 2 S 3 and Sb/As 2 S 3 NLS. Light as well as e-beam induced bleaching occurs in all NLS, while volume expansion occurs only in chalcogenide–chalcogenide NLS and in homogeneous Se or As 2 S 3 layers. Comparison of these two phenomena revealed the possible role of purely electronic and thermal processes in the interdiffusion and relief formation. The latter is supposed to be connected with radiation-induced defect creation, free volume increase under the increased fluidity conditions as well as with the possible additional influence of electrostatic forces and stress.

The high spatial resolution of the localized structural transformations induced by different irradiations in amorphous chalcogenides, as well as the possibility of inducing volume expansion, promotes applications of these inorganic resists for optical recording, data storage and makes them attractive for nanolithography. This paper focuses on the fabrication of surface reliefs at submicrometer length scales in a direct, one-step process of recording by light or ion beam on Se layers or Se/As2S3 nanolayered films due to induced volume expansion.

Thin As2Se3 amorphous chalcogenide films have been studied by nanoindentation and atomic force microscopy in darkness and under illumination by band-gap light. The combination of these two methods has been used to study the peculiarities of the photoplastic effect in amorphous semiconductors. It has been shown by multiple loading indentation experiments that a non-linear mechanism of the formation of the strain response is realized in the As2Se3 films subjected to the combined action of light and external mechanical loading. We have observed that light illumination alters the internal friction of the films and their shear modulus. These observations have been considered in the frame of the two-phase model of chalcogenide glasses. Some arguments in favor that the self-organization processes take place in the structure of irradiated film are given.

The technology of light-sensitive amorphous chalcogenide layers, made from As-Ge-Se raw glasses, thick layers of acrylic polymers, made from mixture of isomers as well as two types of nanocomposites of these materials with gold nanoparticles was developed. These layers were used for direct, one-step surface geometrical and optical (amplitude-phase) relief recording by laser- or electron-beams. Investigations were directed to the establishment of giant geometrical relief formation processes, which resulted elements like bumps, single lines and diffractive gratings applicable as elements of integrated optics. The mechanism of the recording processes, which include excitation of electron-hole processes, structural transformation or polymerization, as well as mass-transport component was accepted for explanation of comparable effects at light- and electron beam recording. Selection of the materials and recording conditions with best resulting parameters was done.

Homogeneous, 200 – 3000 nm thick layers of chalcogenide glasses, 1 – 2 mm thick plane-parallel plates as well as nanocomposite structures, containing gold nanoparticles have been produced and used for in situ surface optical and geometrical relief fabrication by optical- or electron-, ion-beam recording. Investigations were focused on the formation of giant (height modulation from nanometers up to micrometers) geometrical reliefs and elements (dots, lines and diffractive elements) applicable in the 0.5 – 10 micrometer spectral range. Recording parameters were compared with available data on acrylic polymer nanocomposites. The mechanism of the recording processes, which include thermal, electron and mass-transport components were explained and the selection of the materials from As(Ge)-S(Se) binary systems with best recording parameters was done.

The influence of nanostructuring on photo- and thermo-stimulated structural transformations and related changes of optical, thermodynamical and electrophysical parameters were investigated in Se 0.6 Te 0.4 /SiO x nano-multilayer structures and compared with the same changes in single amorphous Se 0.6 Te 0.4 films. It was established that stimulated crystallization processes in an amorphous Se 0.6 Te 0.4 model material that easily undergo stimulated crystallization depend on the presence of matrix in the nano-layered structure which enables additional operation of the optical recording in this type of chalcogenide materials for data storage.

The effect of hydrostatic pressure on photo-induced interdiffusion in Se/As 2 S 3 and As 0.2 Se 0.8 /As 0.2 S 0.8 nanomultilayers has been studied in the pressure range of 0-0.9 GPa. The photo-bleaching due to the mixing was in situ detected and used to follow the interdiffusion kinetics. We have observed that the applied pressure suppressed the diffusion rate. The activation volumes of the interdiffusion process in both systems are in the range of 0.40-0.45 in average atomic volume units.

Enhanced intermixing, induced by a laser beam, has been recently observed in amorphous Se/As2S3 and similar multilayers. We report a model, based on the concept of thermal spikes, which can consistently describe experimental observations. The concentration dependence of the light absorption properties causes the photo-stimulated diffusion to be non-linear even when a concentration independent coefficient of thermo-stimulated diffusion is assumed.

Structural transformations, stimulated by illumination or heating are related to the interdiffusion processes in nanolayered structures, which were prepared by cyclic thermal evaporation or magnetron sputtering from Si, Ge, Se semiconductors and some As2S3, SexTe1–x-type chalcogenide glasses. It is shown that the intermixing velocity and the related changes of optical parameters depend on the period of the multilayer and intensity of illumination. Volume extension can be stimulated at the illuminated regions and used for the surface relief formation.

Surface relief gratings produced on a surface of amorphous chalcogenide films As 20 Se 80 are flatten at room temperature under illumination by a near-bandgap polarized light ( λ = 650 nm). The rates of the profiles flattening are dependent on the light intensity, polarization direction, and grating period. Two possible flattening mechanisms are selected: viscous flow and volume diffusion, and the flattening rates are calculated for both of them. From the comparison of the theory with the experiments, it is concluded that the process is controlled by anisotropic volume diffusion. The effective photo-induced diffusion coefficients, D xx , along E -vector of the light polarization, obtained from the flattening kinetics are proportional to the light intensity ( D xx = β x I ) with β x = 2.5 × 10 − 18 m 4 /J. The diffusion coefficients D yy along perpendicular direction are four times smaller, independently of the light intensity.

The conductive bridge non-volatile memory technology is an emerging way to replace traditional charge based memory devices for future neural networks and configurable logic applications. An array of the memory devices that fulfills logic operations must be developed for implementing such architectures. A scheme to fabricate these arrays, using ion bombardment through a mask, has been suggested and advanced by us. Performance of the memory devices is studied, based on the formation of vias and damage accumulation due to the interactions of Ar+ ions with GexSe1-x (x=0.2, 0.3 and 0.4) chalcogenide glasses as a function of the ion energy and dose dependence. Blanket films and devices were created to study the structural changes, surface roughness, and device performance. Raman Spectroscopy, Atomic Force Microscopy (AFM), Energy Dispersive X-Ray Spectroscopy (EDS) and electrical measurements expound the Ar+ ions behavior on thin films of GexSe1-x system. Raman studies show that there is a decrease in area ratio between edge-shared to corner-shared structural units, revealing occurrence of structural reorganization within the system as a result of ion/film interaction. AFM results demonstrate a tendency in surface roughness improvement with increased Ge concentration, after ion bombardment. EDS results reveal a compositional change in the vias, with a clear tendency of greater interaction between ions and the Ge atoms, as evidenced by greater compositional changes in the Ge rich films.

The surface patterning on amorphous chalcogenide nanomultilayers was successfully performed employing laser-irradiation or electron-beam recording. Significant changes of thickness reaching up to 10% of initial values investigated by AFM are accompanied by modifications of optical transmittance and refractive index. Observed phenomena can be used for the one-step fabrication of micro-optical elements.

Two types of amorphous materials with the same functional purpose – direct optical recording of optical amplitude–phase surface reliefs – were investigated with the aim to establish the influence of incorporated gold nanoparticles on the recording efficiency. It was shown that the laser recording of optical reliefs on the basis of photo-polymerization of the selected acrylates or on the basis of structural polymerization–destruction like processes in chalcogenides with photo-plastic effects can be enhanced in the presence of Au nanoparticles (AuNPs). The lateral mass-transport processes at the molecular and nanoparticle levels are initiated by the non-uniformly, periodically distributed recording optical fields and increase the resulting surface reliefs in these materials, which can be used as microstructured optical elements, holographic gratings.

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.

The technology problems of fabricating different, nanometers sized gold particles in the layered composites like light-sensitive chalcogenide glass/gold nanoparticles/transparent substrate or titanium/titanium oxide/gold nanoparticles were investigated in our work. Combination of ion implantation, plasma deposition with annealing processes results physical routes for creation of gold nanoparticles in the mentioned structures, which possess plasmon effects. These functionalized structures are planned to use for investigations of optical recording processes, biocompatibility of titanium implants.

Laser-matter coupling results specific structural changes in amorphous chalcogenide semiconductor layers which originate from electron-hole excitations, defect creation or modification and subsequent atomic motions. These changes can be influenced by plasmon fields. Plasmon enhanced photo-darkening and bleaching, optical recording in thin As x Se 1 − x films have been demonstrated in this paper, specifically in As 20 Se 80 and As 2 Se 3 compositions which revealed the best effects of stimulated expansion or optical darkening respectively due to the He–Ne laser (λ = 633 nm) illumination. Gold nanoparticles deposited on the silica glass substrate and covered by an amorphous chalcogenide film satisfy the conditions of efficient surface plasmon resonance in this spectral region. These experimental results support the importance of localized electric fields in photo-structural transformations of chalcogenide glasses as well as suggest better approaches for improving the performance of these optical recording media.

The role of the composition and of the related changes of the structure in the formation of the surface of amorphous As x Se 1− x (0 x x ⩽ 0.3, where the maximum light stimulated surface deformations (localized expansion) occurs. Both relate to the rigidity percolation range and the maximum photoplastic effects, which are not directly connected to the known photodarkening effect, since it is minimal for these compositions.

Investigations of direct one-step optical recording of surface optical and geometrical patterns in homogeneous and nanostructured chalcogenide layers were extended towards e-beam recording. Our aim was to establish the common features of the two processes, and to develop some optimum materials for prototypic micro- and nanosized elements for optoelectronics. Experiments were conducted on Se/As2S3 and Sb/As2S3 nanolayered structures (NLS) as well as on uniform Se, Sb and As2S3 layers. Both green laser light (λ = 535 nm) and e-beam (5-20 pA, 10-30 keV) induced bleaching in all NLS. The optical change was more efficient in Sb-containing NLS. In contrast, volume expansion occurred only in chalcogenide-chalcogenide NLS and the homogeneous Se or As2S3 layers. Its magnitude was larger for the NLS (Δd /d ≥10%); no volume change was detected in Sb layer. A comparison of the two types of recording revealed the role of interdiffusion and induced free volume aggregation in a giant relief formation under the increased fluidity conditions. It was shown that these effects could be used to fabricate micro lenses, amplitude-phase optical modulating and guiding elements. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Cyclic pulsed laser deposition technique was used for the fabrication of chalcogenide GeSe/GeS nanomultilayers with ∼10 nm modulation period. Low-angle X-ray diffraction technique revealed good periodicity of prepared multilayered materials. The films are sensitive to annealing and illumination by 532 nm laser; both processes lead to refractive index decrease and blue shift of the short-wavelength absorption edge, respectively, connected with interdiffusion processes between the individual layers. Light-induced bleaching of the films is accompanied by giant volume-changes (up to 10% expansion) as observed by atomic force microscopy. These can be used for direct surface patterning and relief formation.

Investigations of $a-Se/As_2S_3$-type chalcogenide nanomultilayers (NML) were extended towards the metal-containing $Bi(Sb)/As_2S_3$ structures. It was shown that essential changes of optical parameters (transmission, refraction and reflection) and of the electrical conductivity occur due to the interdiffusion stimulated by direct heating or by the influence of the intensive laser beam unlike the chalcogenide–chalcogenide nanostructures, where the photo-induced effects may dominate. Low temperature solid-phase synthesis, phase separation can be performed this way. Stimulated structural changes in these multilayers may be used for efficient amplitude-phase modulated optical relief recording as well as for creating surface patterns with modified electrical parameters.

The effect of irradiation on the optical absorption edge and thickness of AsSe and As2S3 thin films has been investigated for different doses of 12H, 11H accelerated to energies of 80 and 180 keV. The kinetics and value of the stimulated changes were compared with photo-induced effects of laser illumination at 0.51 and 0.63 μm. It was observed that the optical band gap decreases and the thickness increases for both cases. The penetration length and depth profile of implanted ions with different energies were calculated and proposed for creating layer structures with depth-profiled optical parameters.

Diffusion mass transfer in thin chalcogenide films under illumination by a focused Gaussian beam have been studied both experimentally and theoretically. It is demonstrated that depending on the light intensity, waist of the beam, and the film thickness, one can obtain formation of either hillocks or dips in the illuminated regions. By comparison of the kinetics of hillock or dip formation on a surface of As20Se80 glass films with the results of our theoretical analysis, we have estimated the photo-induced diffusion coefficients, D, at various light intensities, I, and found D to be proportional to I (D = βI), with β ≈ 1.5 × 10−18 m4/J.

The kinetics of photoinduced variations in surface profile in chalcogenide glass films under illumination is described. It is demonstrated that the competition between the stress-induced atomic flux (toward irradiated regions of the film) and the diffusion flux induced by an increase in the bulk energy due to broken bonds (and directed from irradiated to dark regions) can result in either a positive or negative net mass transfer in the irradiated region. Depending on the light intensity, one can obtain either formation of bumps or depressions in the illuminated regions.