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We show that the magnetic and vacancy orders in the 122 $(A_{1-y}Fe_{2-x}Se_2)$ iron-chalcogenides can be naturally derived from the $J_1-J_2-J_3$ model with $J_1$ being the ferromagnetic (FM) nearest neighbor exchange coupling and $J_{2}, J_3$ being the antiferromagnetic (AFM) next and third nearest neighbor ones respectively, previously proposed to describe the magnetism in the 11(FeTe/Se) systems. In the 11 systems, the magnetic exchange couplings are extremely frustrated in the ordered bi-collinear antiferromagnetic state so that the magnetic transition temperature is low. In the 122 systems, the formation of iron vacancy order reduces the magnetic frustration and significantly increases the magnetic transition temperature and the ordered magnetic moment. The pattern of the 245 iron-vacancy order ($\sqrt{5}\times \sqrt{5}$) observed in experiments is correlated to the maximum reduction of magnetic frustration. The nature of the iron-vacancy ordering may hence be electronically driven. We explore other possible vacancy patterns and magnetic orders associated with them. We also calculate the spin wave excitations and their novel features to test our model.

We report density functional calculations of electronic structure and magnetic properties of ternary iron chalcogenide TlFe$_{2}$Se$_{2}$, which occurs in the ThCr$_{2}$Si$_{2}$ structure and discuss the results in relation to the iron-based superconductors. The ground state is antiferromagnetic with checkerboard order and Fe moment $\sim$ 1.90 $\mu$B. There is strong magnetoelastic coupling similar to the Fe-based superconductors, reflected in a sensitivity of the Se position to magnetism. Tl is monovalent in this compound, providing heavy electron-doping of 0.5 additional carriers per Fe relative to the parent compounds of the Fe-based superconductors. Other than the change in electron count, the electronic structure is rather similar to those materials. In particular, the Fermi surface is closely related to those of the Fe-based superconductors, except that the electron cylinders are larger, and the hole sections are suppressed. This removes the tendency towards a spin density wave.

A minority carrier device includes at least one junction of at least two dissimilar materials, at least one of which is a semiconductor, and a passivating layer on at least one surface of the device. The passivating layer includes a Group 13 element and a chalcogenide component. Embodiments of the minority carrier device include, for example, laser diodes, light emitting diodes, heterojunction bipolar transistors, and solar cells.

An experimental study established the effectiveness of chalcogenide glass composition AMTIR-1 (Ge33As12Se55) as structural material and/or coating material or windows in IR systems operating in a marine environment. Test results show that the optical and structural properties of the material are not degraded by continuous or intermittent submersion in seawater. A tremendous potential reduction in expenditures would result from its application wherever feasible.

In this review, we present a summary of the results on single crystal growth of two types of iron-chalcogenide superconductors, Fe(1+y)Te(1-x)Se(x) (11), and A(x)Fe(2-y)Se(2) (A= K, Rb, Cs, Tl, Tl/K, Tl/Rb), using Bridgman, zone-melting, vapor self-transport, and flux techniques. The superconducting and magnetic properties (the latter gained mainly from neutron scattering measurements) of these materials are reviewed to demonstrate the connection between magnetism and superconductivity. It will be shown that for the 11 system, while static magnetic order around the reciprocal lattice position (0.5, 0) competes with superconductivity, spin excitations centered around (0.5, 0.5) are closely coupled to the materials' superconductivity; this is made evident by the strong correlation between the spectral weight around (0.5, 0.5) and the superconducting volume fraction. The observation of a spin resonance below the superconducting temperature, Tc, and the magnetic-field dependence of the resonance, emphasize the important role spin excitations play in the superconductivity. Generally, these results illustrate the similarities between the iron-based and cuprate superconductors. In A(x)Fe(2-y)Se(2), superconductivity with Tc ~ 30 K borders an antiferromagnetic insulating phase; this is closer to the behavior observed in the cuprates but differs from that in other iron-based superconductors.

The high upper critical field characteristic of the recently discovered iron-based superconducting chalcogenides opens the possibility of developing a new type of non-oxide high-field superconducting wires. In this work, we utilize a buffered metal template on which we grow a textured FeSe$_{0.5}$Te$_{0.5}$ layer, an approach developed originally for high temperature superconducting coated conductors. These tapes carry high critical current densities (>1$\times10^{4}$A/cm$^{2}$) at about 4.2K under magnetic field as high as 25 T, which are nearly isotropic to the field direction. This demonstrates a very promising future for iron chalcogenides for high field applications at liquid helium temperatures. Flux pinning force analysis indicates a point defect pinning mechanism, creating prospects for a straightforward approach to conductor optimization.

Fibre optic technology offers the possibility for developing of a variety of physical sensors for a wide range of physical parameters. The main advantage of fiber optic sensors lies in their dielectric construction, providing electrical isolation, immunity from electromagnetic fields, small dimensions, and compatibility with optical fibre technology. A large number of fiber sensors in production are based on intensity modulation of the light either outside the fiber or within it. In the case of intensity sensors the physical perturbation to be measured interacts with the fibre or some device attached to the fibre to modulate the intensity of the light as it travels through the fiber. Intensity modulated fiber sensors have been demonstrated to be efficient for different applications. A variation of internal-modulation sensors are the microbending-loss sensors, which are characterized by a relatively simple construction, good performances and compatibility with multimode fibre technology. A very effective con- figuration for the microbending-loss sensors is that one based on clad mode detection. For clad modes detection the end segment of the fiber is bent and placed in an integrating sphere. The use of chalcogenide rather quartz fibre optic highly increases the Sensitivity of the sensor. Experimental set-up, transmission characteristics and technical parameters are presented.

The glass system (As2S3)1-x(Sb2S3)x, 0</-X</-0.65, has been studied by X-ray diffraction and microhardness measurements. The long-time irradiation of the samples by ultraviolet rays has been carried out and its structural effect was investigated. The substitutional model and the microphase separation model have been discarded. A new intermediate model, whose main feature is the formation of mezoscopic Sb2S3 clusters, has been advanced.

The two main purposes of the research here described are to elucidate the mechanism of threshold switching and to explore new possibilities through the use of contact materials which can be electronically altered in situ. In pursuit of these objectives, four lines of research have been followed. They are concerned with the nature of the ON-state, the effect of semiconductor electrodes and contact asymmetry on the switching process, The statistical nature of threshold switching, and scaling problems, i.e. the variation of switching parameters with thickness of the chalcogenide glass film.

The two main purposes of the research here described are to elucidate the mechanism of threshold switching and to explore new possibilities through the use of contact materials which can be electronically altered in situ. In pursuit of these objectives, four lines of research have been followed. They are concerned with the nature of the ON-state, the effect of semiconductor electrodes and contact asymmetry on the switching process, The statistical nature of threshold switching, and scaling problems, i.e. the variation of switching parameters with thickness of the chalcogenide glass film.

The possible physical origin of third-order nonlinearity of cadmium chalcogenide (Te, Se, and S) semiconductor nanocrystals were discussed based on the results of both Z-scan and degenerate four-wave mixing spectroscopies of 532, 775, 800, and 1064 nm in nanosecond, picosecond, and femtosecond time scale for nonlinear photonic applications.

The ferromagnetism and metallic conductivity of the compounds Cu(Cr2) X4, where X = S, Se, or Te, have been interpreted in terms of collective 'd' electrons of t2g symmetry from Cu(2+) ions and localized d electrons of t2g symmetry at Cr(3+) ions. Lotgering and van Stapele have studied the compounds CuCrRhSe4, CuCrTiS4, and M1-xCu(Cr2)Se4, where M = Zn, Cd, or Hg. They have asserted that their results disprove this hypothesis and strongly support the existence of Cr(4+) ions in the presence of Cu(+) ions. It is shown that these assertions are incorrect.

We present a comprehensive computational study on the properties of face-centered cubic and hexagonal chalcogenide Ge2Sb2Te5. We calculate the electronic structure using density functional theory (DFT); the obtained density of states (DOS) compares favorably with experiments, also looking suitable for transport analysis. Optical constants including refraction index and absorption coefficient capture major experimental features, aside from an energy shift owed to an underestimate of the band gap that is typical of DFT calculations. We also compute the phonon DOS for the hexagonal phase, obtaining a speed of sound and thermal conductivity in good agreement with the experimental lattice contribution. The calculated heat capacity reaches ~ 1.4 x 106 J/(m3 K) at high temperature, in agreement with experimental data, and provides insight into the low-temperature range ( < 150 K), where data are unavailable.

The absence of long range periodic order in amorphous semiconductors makes the interpretation of the usual scattering experiments, such as x-ray, neutron or electron scattering, both difficult and model dependent. For this reason information concerning the static and dynamic properties of these solids must be gathered using many different experimental techniques. In the chalcogenide (group VI) and pnictide (group V) amorphous semiconductors nuclear quadrupole resonance (NQR) spectroscopy has proved to be one of the important techniques. The NQR technique provides information on a scale of the interatomic spacings and is thus a sensitive probe of the local environments of the major constituent atoms in an amorphous semiconductor. In the specific case of 75As, analyses of the NQR lineshapes and of nuclear spin-spin phenomena yield detailed structural information concerning not only the local bonding at an arsenic site but also the presence of intermediate range order in some chalcogenide glasses. The lineshapes also provide a very sensitive probe of photo-induced polymerization in films of amorphous chalcogenides.

Intensity parameters, radiative transition probabilities and non-radiative relaxation of Ho3+ in various tellurite glasses are described. Eigenstates of Tm3+ in an intermediate coupling scheme were obtained by diagonalization of electrostatic matrices of E(1), E(2) and E(3), the configurational parameters alpha and the spin orbit matrix.

In the first part of the paper we summarize the results of our study of photoinduced optical anisotropy in thin film and bulk samples of different chalcogenide glasses. We distinguish three ranges of exciting photons energy: above-band-gap excitation, sub-band-gap excitation and super-band-gap excitation. We claim that in each of these excitation ranges, different mechanisms are responsible for appearance of photoinduced anisotropy, namely, creation and next orientation of photoinduced defects, creation of anisotropically scattering defects and orientation of main covalent bonds of the glass (in addition to creation and orientation of defects) are the main reasons of observed anisotropy in the mentioned spectral ranges. We consider also some interesting results obtained recently in different research groups-. Among them: polarization dependent photocrystallization of some amorphous films, polarization-dependent photodoping of chalcogenide films by metals, photoinduced anisotropy of photoconductivity, polarization-dependent optomechanical effect and photoinduced an isotropy in the ion-conducting amorphous chalcogenide films.

One of the most known reversible memory effect in chalcogenide glassy semiconductors (CGS) is associated with a reversible glass-crystal phase transition. In contrast to the photo-structural effect, which is associated with a reversible structural changes between two metastable disordered glassy states, the glass-crystal phase transition in CGS can be initiated and reversed not only by power light but by an electrical voltage also. These facts give us a principle opportunity to combine electric field and laser light pulses for information recording processes in CGS. The present paper is devoted to peculiarities of information recording based on glass-crystal phase transition in CGS. We discuss the differences and resemblances of the information recording by laser light and electrical voltage pulses. It is shown that recordings based on the reversible glass- crystal phase transition are similar for optical and electrical cases and the main mechanism of phase transition is determined by thermal heating.

This project focused on exploring the potential of a new heavy atom chalcogenide family of semiconductors for room temperature gamma radiation detection. Its goal was to accelerate nuclear detector material discovery and development through innovative materials design/selection, synthesis and characterization. The project succeeded in expanding the currently small portfolio of potential materials. It allowed the assessment of fundamental limits for performance of the new materials. The project also focused in delineating clear relationships between material composition, structure and properties and the targeted performance and how they evolve from one material to the next. The close coupling of experiment and theory created an accelerated fundamental materials discovery effort which is greatly needed to develop the next generation radiation detector materials. The project investigated ternary chalcogenide semiconductors using selection criteria relevant to -ray detection at room temperature. These include heavy element composition, extended structures and wide energy band gap 1.8 Eg 2.5 eV.

This project focused on exploring the potential of a new heavy atom chalcogenide family of semiconductors for room temperature gamma radiation detection. Its goal was to accelerate nuclear detector material discovery and development through innovative materials design/selection, synthesis and characterization. The project succeeded in expanding the currently small portfolio of potential materials. It allowed the assessment of fundamental limits for performance of the new materials. The project also focused in delineating clear relationships between material composition, structure and properties and the targeted performance and how they evolve from one material to the next. The close coupling of experiment and theory created an accelerated fundamental materials discovery effort which is greatly needed to develop the next generation radiation detector materials. The project investigated ternary chalcogenide semiconductors using selection criteria relevant to -ray detection at room temperature. These include heavy element composition, extended structures and wide energy band gap 1.8 Eg 2.5 eV.

Changes of optical transmittance induced by the influence of 60Co gamma-irradiation have been studied in ternary As-Ge-S, Sb-Ge-S, As-Ge-Se and As-Bi-Se systems. The characters of radiation-induced optical effects in all these systems have been compared It was shown that the compositional dependencies of such effects are almost linear for stoichiometric glasses and reveal some peculiarities connected with phase features, the "free volume" parameters and the specificity of radiation induced defects formation for non-stoichiometric families.

Changes of optical transmittance induced by the influence of 60Co gamma-irradiation have been studied in ternary As-Ge-S, Sb-Ge-S, As-Ge-Se and As-Bi-Se systems. The characters of radiation-induced optical effects in all these systems have been compared It was shown that the compositional dependencies of such effects are almost linear for stoichiometric glasses and reveal some peculiarities connected with phase features, the "free volume" parameters and the specificity of radiation induced defects formation for non-stoichiometric families.

Quasi-two-dimensional (2D) films of layered metal-chalcogenides have attractive optoelectronic properties. However, photonic applications of thin films may be limited owing to weak light absorption and surface effects leading to reduced quantum yield. Integration of 2D films in optical microcavities will permit these limitations to be overcome owing to modified light coupling with the films. Here we present tunable microcavities with embedded monolayer MoS2 or few monolayer GaSe films. We observe significant modification of spectral and temporal properties of photoluminescence (PL): PL is emitted in spectrally narrow and wavelength-tunable cavity modes with quality factors up to 7400; PL life-time shortening by a factor of 10 is achieved, a consequence of Purcell enhancement of the spontaneous emission rate. This work has potential to pave the way to microcavity-enhanced light-emitting devices based on layered 2D materials and their heterostructures, and also opens possibilities for cavity QED in a new material system of van der Waals crystals.

Motivated by the newly-discovered intercalated iron chalcogenide superconductors, we construct a single orbital tight-binding model for topological insulators on the square lattice with a perfect vacancy superstructure. We find that such lattice structure naturally accommodates a non-vanishing geometry phase associated with the next-nearest-neighbor spin-orbit interaction. By calculating the bulk band structures and the finite stripe edge states, we show that the topological insulator phases can be tuned at certain electron fillings in a wide range of the model parameters. The possible implications of these results for the iron deficient compounds $(A,Tl)_{y}Fe_{2-x}Se_2$ have been discussed.

Experimental and theoretical studies of spectral properties of chalcogenide Ge-S and As-Ge-S glasses and fibers are performed. A broad infrared (IR) luminescence band which covers the 1.2-2.3~$\mu$m range with a lifetime about 6~$\mu$s is discovered. Similar luminescence is also present in optical fibers drawn from these glasses. Arsenic addition to Ge-S glass significantly enhances both its resistance to crystallization and the intensity of the luminescence. Computer modeling of Bi-related centers shows that interstitial Bi$^+$ ions adjacent to negatively charged S vacancies are most likely responsible for the IR luminescence.

In this work is presented the research on thin films of chalcogenide glassy semiconductors as the medium for relief holograms record. The optimization of photoresist has allowed for an essential rise in sensitivity to light. As(50)Se(50) photoresist composition on which above thousandfold chemical amplification of holographic record is achieved, was used. Diffraction gratings in range of spatial frequencies 600 - 2400 mm are submitted. For natural light the magnitude of diffraction efficiency exceeds 70 - 80 % at measurements in autocollimator conditions. The probable cause of differences between continuous and pulse irradiation of thin films of chalcogenide vitreous semiconductors is discussed.

In this work is presented the research on thin films of chalcogenide glassy semiconductors as the medium for relief holograms record. The optimization of photoresist has allowed for an essential rise in sensitivity to light. As(50)Se(50) photoresist composition on which above thousandfold chemical amplification of holographic record is achieved, was used. Diffraction gratings in range of spatial frequencies 600 - 2400 mm are submitted. For natural light the magnitude of diffraction efficiency exceeds 70 - 80 % at measurements in autocollimator conditions. The probable cause of differences between continuous and pulse irradiation of thin films of chalcogenide vitreous semiconductors is discussed.

We propose a structural model that treats in a unified fashion both the atomic motions and electronic excitations in quenched melts of pnictide and chalcogenide semiconductors. In Part I (submitted to J. Chem. Phys.), we argued these quenched melts represent aperiodic $pp\sigma$-networks that are highly stable and, at the same time, structurally degenerate. These networks are characterized by a continuous range of coordination. Here we present a systematic way to classify these types of coordination in terms of discrete coordination defects in a parent structure defined on a simple cubic lattice. We identify the lowest energy coordination defects with the intrinsic midgap electronic states in semiconductor glasses, which were argued earlier to cause many of the unique optoelectronic anomalies in these materials. In addition, these coordination defects are mobile and correspond to the transition state configurations during the activated transport above the glass transition. The presence of the coordination defects may account for the puzzling discrepancy between the kinetic and thermodynamic fragility in chalcogenides. Finally, the proposed model recovers as limiting cases several popular types of bonding patterns proposed earlier, including: valence-alternation pairs, hypervalent configurations, and homopolar bonds in heteropolar compounds.

An SDW antiferromagnetic (SDW-AF) low temperature phase transition is generally observe and the AF spin fluctuations are considered to play an important role for the superconductivity paring mechanism in FeAs superconductors. However, a similar magnetic phase transition is not observed in FeSe superconductors, which has caused considerable discussion. We report on the intrinsic electronic states of FeSe as elucidated by transport measurements under magnetic fields using a high quality single crystal. A mobility spectrum analysis, an ab initio method that does not make assumptions on the transport parameters in a multicarrier system, provides very import and clear evidence that another hidden order, most likely the symmetry broken from the tetragonal C4 symmetry to the C2 symmetry nematicity associated with the selective d-orbital splitting, exists in the case of superconducting FeSe other than the AF magnetic order spin fluctuations. The intrinsic low temperature phase in FeSe is in the almost compensated semimetallic states but is additionally accompanied by Dirac cone like ultrafast electrons $\sim$ 10$^4$cm$^2$(VS)$^{-1}$ as minority carriers.

Low-temperature thermal conductivity measurements were performed on single crystals of TlNi$_2$Se$_2$, a nickel-chalcogenide heavy-electron superconductor with $T_c$ $\simeq$ 3.7 K. In zero field, the residual electronic contribution at $T$ $\rightarrow$ 0 K ($\kappa_0/T$) was well separated from the total thermal conductivity, which is less than 0.45\% of its normal-state value. Such a tiny residual $\kappa_0/T$ is unlikely contributed by the nodal quasiparticles. Nodeless gap structure is supported by the very weak field dependence of $\kappa_0(H)/T$ in low magnetic fields. In the whole field range, $\kappa_0(H)/T$ exhibits an "$S$"-shape curve, as in the case of nickel pnictides BaNi$_2$As$_2$ and SrNi$_2$P$_2$. This common feature of nickel-based superconductors can be explained by multiple nodeless superconducting gaps.

We report the synthesis and superconducting properties of a new transition-metal chalcogenide Ta$_2$PdSe$_5$. The measurements of resistivity, magnetization, and specific heat reveal that Ta$_2$PdSe$_5$ is a bulk superconductor with $T_c$ $\simeq$ 2.5 K. The zero-field electronic specific heat in the superconducting state can be fitted with a two-gap BCS model. The upper critical field $H_{c2}$ shows a linear temperature dependence, and the value of $H_{c2}$(0) is much higher than the estimated Pauli limiting field $H_{c2}^{P}$ and orbital limiting field $H_{c2}^{orb}$. All these results of specific heat and upper critical field suggest that Ta$_2$PdSe$_5$ is a multi-band superconductor.

Gallium chalcogenides are promising building blocks for novel van der Waals heterostructures. We report low-temperature micro-photoluminescence (PL) of GaTe and GaSe films with thickness ranging from from 200 nm to a single unit cell. In both materials, PL shows dramatic decrease by 10$^4$-10$^5$ when film thickness is reduced from 200 to 10 nm. Based on evidence from cw and time-resolved PL, we propose a model explaining the PL decrease as a result of non-radiative carrier escape via surface states.

We present a theoretical and experimental analysis of nonlinear thermo-optic effects in suspended chalcogenide glass nanobeam cavities. We measure the power dependent resonance peaks and characterise the dynamic nonlinear thermo-optic response of the cavity under modulated light input. Several distinct nonlinear characteristics are identified, including a modified spectral response containing periodic fringes, a critical wavelength jump and saturated time delay for modulation frequency faster than the thermal characteristic time. We reveal that the coupling to a parasitic Fabry-Perot cavity enables isolated thermal equilibrium states resulting in the discontinuous thermo-optic critical point.

Many properties of alloyed chalcogenide glasses can be closely correlated with the average coordination of these compounds. This is the case, for example, of the ultrasonic constants, dilatometric softening temperature and the vibrational densities of states. What is striking, however, is that these properties are nevertheless almost independent of the composition at given average coordination. Here, we report on some numerical verification of this experimental rule as applied to vibrational density of states.

A pronounced local in-gap zero-energy bound state (ZBS) has been observed by recent scanning tunneling microscopy (STM) experiments on the interstitial Fe impurity (IFI) and its nearest-neighboring (nn) sites in $\mathrm{FeTe_{0.5}Se_{0.5}}$ superconducting (SC) compound. By introducing a new impurity mechanism, the so-called tunneling impurity, and based on the Bogoliubove-de Gennes (BDG) equations we investigated the low-lying energy states of the IFI and the underlying Fe-plane. We found the peak of ZBS does not shift or split in a magnetic field as long as the tunneling parameter between IFI and the Fe-plane is sufficiently small and the Fe-plane is deep in the SC state. Our results are in good agreement with the experiments. We also predicted that modulation of spin density wave (SDW), or charge density wave (CDW) will suppress the intensity of the ZBS.

We have used a density-functional-based tight-binding method in order to create structural models of the canonical chalcogenide glass, amorphous (a-)As$_2$S$_3$. The models range from one containing defects that are both chemical (homopolar bonds) and topological (valence-alternation pairs) in nature to one that is defect-free (stoichiometric). The structural, vibrational and electronic properties of the simulated models are in good agreement with experimental data where available. The electronic densities of states obtained for all models show clean optical band gaps. A certain degree of electron-state localization at the band edges is observed for all models, which suggests that photoinduced phenomena in chalcogenide glasses may not necessarily be attributed to the excitation of defects of only one particular kind.

Using density-functional theory, we calculate the electronic bandstructure of single-layer graphene on top of hexagonal In_2Te_2 monolayers. The geometric configuration with In and Te atoms at centers of carbon hexagons leads to a Kekule' texture with an ensuing bandgap of 20 meV. The alternative structure, nearly degenerate in energy, with the In and Te atoms on top of carbon sites is characterized instead by gapless spectrum with the original Dirac cones of graphene reshaped, depending on the graphene-indium chalcogenide distance, either in the form of an undoubled pseudo-spin one Dirac cone or in a quadratic band crossing point at the Fermi level. These electronic phases harbor charge fractionalization and topological Mott insulating states of matter.

We demonstrate microstructuring of chalcogenide fiber end faces in order to obtain enhanced transmission due to the antireflective properties of the microstructured surfaces. A variety of molding approaches have been investigated for As2S3 and As2Se3 fibers. Transmission as high as 97% per facet was obtained in the case of As2S3 fiber, compared to the native, Fresnel-loss limited, transmission of 83%. The potential for hydrophobic character was also demonstrated by increasing the contact angle of water droplets to greater than 120?.

The optical properties of sputtered, amorphous films of GeTe, Sb2Te3, and Ge2SbTe5 grown up to several micrometers thick are influenced by the presence of oxygen impurities. The absorption edges in these glasses are sometimes broader than in standard chalcogenide glasses, such as GeSe2 and As2Se3. This result implies either that the valance band consists of high strained bonds or that large densities of defects exist. Below the optical gap the refractive index for Ge2Sb2Te5 is approximately 3.5. In samples of Ge2Sb2Te5 made with large oxygen concentrations using a hot-pressed target, there exists a large ESR signal corresponding to a defect density of 10 to the power of 19 cm to the power of -3. In samples with the lowest oxygen contamination levels (approximately 10 to the power of 19 cm to the power of -3) no ESR signal is observed, which implies that the defect density is below 10 to the power of 18 com to the power of -3. ESR signals associated with the glassy SiO2 interface with the chalcogenide films are also observed. In amorphous Ge2Sb2Te5, the average coordination numbers for Ge, Sb, and Te are approximately 4, 3, and 2.5 respectively.

We have successfully Ag-photodoped As2S3 using photographic Ag derived from evaporated AgBr. The use of evaporated AgBr has resulted in a 1000-fold increase in speed. We have shown that evaporated AgBr has very high sensitivity in the deep UV (50 microJ/cm2 at 2600 angstrnoms), at soft x-ray wavelengths (5 microJ/cm2 at 7 angstrnoms) and confirmed the previously observed e-beam sensitivity of 10-9 coulombs/cm2. We have shown the feasibility of using evaporated AgBr as the photon sensitive layer of a multi-layer photoresist system for submicron lithography. (Author)

The technique of step-by-step optically-induced diffusion and dissolution (OIDD) of Ag with As33 S67 amorphous films has allowed to design films with exact silver concentration. The photodoped films with a silver concentration of 25 at.%, i.e. with composition of the stoichiometric AgAsS2 compound were prepared. The host As33S67 films were photodoped by consecutive dissolving thin ( 10 nm) layer of silver, which resulted in a single-phase optically homogeneous films. We have analyzed affect of the silver doping in the host material on optical, thermal properties, and its structure by means of optical spectroscopy, temperature- modulated differential scanning calorimetry and Raman spectroscopy respectively. Application of such films can be foreseen for rewritable high resolution optical memories (reversible phase change "amorphous-crystalline" or film optical surface nanoshaping in dependence on intensity and silver concentration). The surface structure of optically shaped films were studied by atomic force microscopy.

A quantitative study of infrared absorption in the 250-4000/cm region of As2Se3 glasses doped with small amounts of As2O3 or purified has been carried out with particular attention ot absorption in the wavelength regions of the CO2 and CO lasers. The dependence of the relative intensities of the oxide impurity bands in the 650-1340/cm region on the total amount of As2O3 added to the glass indicates the existence of three distinct oxide impurity species. A number of higher frequency impurity bands which are due to the presence of hydrogen in the glass and whose intensities are highly dependent on the glass melting conditions have been observed and classified. Intrinsic multiphonon absorption coefficients of mixed As2Se3-GeSe2 glasses were found to be of the same magnitude at the same respective frequencies as those for pure As2Se3 glass.

This article is from Scientific Reports , volume 4 . Abstract Nanoscale inorganic electronic synapses or synaptic devices, which are capable of emulating the functions of biological synapses of brain neuronal systems, are regarded as the basic building blocks for beyond-Von Neumann computing architecture, combining information storage and processing. Here, we demonstrate a Ag/AgInSbTe/Ag structure for chalcogenide memristor-based electronic synapses. The memristive characteristics with reproducible gradual resistance tuning are utilised to mimic the activity-dependent synaptic plasticity that serves as the basis of memory and learning. Bidirectional long-term Hebbian plasticity modulation is implemented by the coactivity of pre- and postsynaptic spikes, and the sign and degree are affected by assorted factors including the temporal difference, spike rate and voltage. Moreover, synaptic saturation is observed to be an adjustment of Hebbian rules to stabilise the growth of synaptic weights. Our results may contribute to the development of highly functional plastic electronic synapses and the further construction of next-generation parallel neuromorphic computing architecture.

Se-Te based chalcogenide glasses have been found suitable for optical memory devices due to their distinct amorphous-to-crystalline transformation. In the present work alloys of Se65Ge15Te20-aSba (a = 3, 6, 9, 12, 15, 18) glasses have been synthesized using melt quench technique. Author report investigations leading to optical, thermal and topological properties of these glasses by varying the concentrations of Te and Sb. Glass transition and crystallization kinetics of alloys have been investigated using differential thermal analysis at different heating rates (5, 10, 15, and 20 Kmin-1). The results so obtained verify the usefulness of above composition.

Experimental and theoretical evidence and arguments are presented to justify a search for new superconductors, similar to the perovskite-based high temperature superconductors, but with the oxygen replaced by a chalcogen, that is sulfur, selenium or tellurium. Candidate compositions are proposed, together with methods of achieving their chemical synthesis. Safety and environmental issues were also analyzed. The work was performed as part of a Phase 1 SBIR project, sponsored by SDIO (BMDO) and managed by AFOSR. jg

High Tc superconductivity in composite system of selenium matrix with globular Y-Ba-Cu-O is discussed in relation to the experimental results.

This work investigates the feasibility of using Ge2Te2Sb5 chalcogenide films for analog memory. Thick film chalcogenide memory devices provided by Ovonyx, Inc. are characterized to determine how well the devices meet the repeatability, stability and predictability criteria needed to accurately store analog data values. Chalcogenide memory devices take advantage of the phase-shifting nature of chalcogenide materials to store the analog data as a resistance level. An automated test system was developed to characterize the material and the prototype devices with the goal to determine the 1) non-destructive readability of the device at different resistance values; 2) repeatability of programming the device; 3) stability the resistance value has over time; 4) parametric variations between devices; and 5) maximum and reliably achievable analog resolution. The results of these characterizations demonstrate that thick film chalcogenide devices possess the necessary repeatability, stability and predictability properties needed in an analog memory, with at least a 4-bit analog resolution. However, the prototype devices, as produced for this research, do not demonstrate these properties consistently. A full scale, commercial fabrication process is likely to improve the device design and manufacture so it can be used as an analog memory.

We propose an all-fiber mode-locking device which operates based on nonlinear switching in a novel concentric ring core fiber structure. The design is particularly attractive given the ease of fabrication and coupling to other components in a mode-locked fiber laser cavity. The nonlinear switching in this coupler is studied and the relative power transmission is obtained. The analysis shows that this nonlinear switch is practical for mode-locking fiber lasers and is forgiving to fabrication errors.

The toxicity and instability of some metal-halides has made it unfovarouble to be used for the development and fabrications of perovskites despite its good Power Conversion Efficiencies (PCE). The need to suggest good perovskites absorber materials that has excellent Dimensionality, optical band gap, and power conversion efficiencies to substitute lead in photovoltaic application is very essential in the recent research. This research work reviewed and suggested the combinable good perovskites absorber materials that can substitute lead in the perovskites. This research further discussed the possible alternative elements to replace lead in metal halide perovskites and the properties of the corresponding perovskite materials based on recent theoretical and experimental studies. In this research work other elements such as germanium, copper, antimony, bismuth, and the corresponding perovskite compounds are already showing promising properties.

The toxicity and instability of some metal-halides has made it unfovarouble to be used for the development and fabrications of perovskites despite its good Power Conversion Efficiencies (PCE). The need to suggest good perovskites absorber materials that has excellent Dimensionality, optical band gap, and power conversion efficiencies to substitute lead in photovoltaic application is very essential in the recent research. This research work reviewed and suggested the combinable good perovskites absorber materials that can substitute lead in the perovskites. This research further discussed the possible alternative elements to replace lead in metal halide perovskites and the properties of the corresponding perovskite materials based on recent theoretical and experimental studies. In this research work other elements such as germanium, copper, antimony, bismuth, and the corresponding perovskite compounds are already showing promising properties.

Book Source: Digital Library of India Item 2015.228929 dc.contributor.author: Bharat Kumar Pandey dc.date.accessioned: 2015-07-10T15:52:04Z dc.date.available: 2015-07-10T15:52:04Z dc.date.digitalpublicationdate: 0000-00-00 dc.identifier.barcode: 5990010117828 dc.identifier.origpath: /rawdataupload/upload/0117/830 dc.identifier.copyno: 1 dc.identifier.uri: http://www.new.dli.ernet.in/handle/2015/228929 dc.description.scanningcentre: IIIT, Allahabad dc.description.main: 1 dc.description.tagged: 0 dc.description.totalpages: 77 dc.format.mimetype: application/pdf dc.language.iso: English dc.publisher: Iit Kanpur dc.rights: Out_of_copyright dc.source.library: I I T Kanpur dc.subject.classification: Science dc.subject.classification: Engineering. Technology In General dc.subject.classification: Mechanical Engineering In General. Nuclear Technology. Electrical Engineering. Machinery dc.title: Electrical Properties Of Lead-oside Base Chalcogenide(se) Glass