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We have investigated photoinduced effects in as-deposited Ge 40−x Sb x Se 60 (x = 8, 15, and 20) films via in situ measurements of transmission spectra for wavelengths λ = 500 to 950 nm. The absorption coefficient increases initially, indicating the photodarkening (PD) effect, which rapidly saturates in tens of seconds. Then the absorption coefficient starts decreasing representing photobleaching (PB). The evolution of PD and PB can be described by stretched exponential function, yielding the time constants for the changes in absorption coefficients. The kinetics of PD is faster than that of PB. The coexistence of PB and PD suggests that the Sb and Ge based structural units of Ge-Sb-Se films respond to bandgap radiation independently. The structural origins of the observed opposing photoinduced effects are discussed. [ABSTRACT FROM AUTHOR]

The dynamics and reversibility of Ag nanoparticle photodissolution into As2S3 chalcogenide thin films have uniquely been directly measured by continuous AFM imaging during patterned optical illumination. The surface morphology, roughness and particle size distribution have thus been spatially and statistically monitored as a function of time, both during and following optical exposure. Photodissolution was observed to proceed via two mechanisms. In one case, nanoparticles abruptly and nearly completely disappeared along a sharp dissolution front traveling laterally at ~0.19 μm s-1. Following illumination, similarly sized nanoparticles uniformly reformed on the surface. A more inhomogeneous photodissolution process was separately recorded, clearing irregular ~1-2 μm patches that grew with time until most of the surface was free of nanoparticles. Post-illumination, surface nanoparticle development and coverage were similarly inhomogeneous, with larger but 50% fewer particles in the final distribution. In every experiment, an initial roughening was detected before the nanoparticle surface coverage visually diminished, indicating the onset of photodissolution at widely distributed energetically and kinetically favored sites which temporarily enhances nanoscale roughness. Such direct studies of surface dynamics are crucial to understanding and ultimately optimizing chalcogenide film applications such as photomasks, optoelectronics media and bio-chemical sensors. [ABSTRACT FROM AUTHOR]

High-resolution X-ray photoelectron spectroscopy is used to identify the mechanism of X-ray-induced Ag diffusion into Ge30Se70 chalcogenide glass thin films, which are prepared in situ to avoid oxygen contamination. From the analysis of Ge 3d, Se 3d, and Ag 3d core levels, and valence band spectra, changes in the electronic structure are determined as Ag diffuses gradually with increasing irradiation. The ternary phase based on Ge2Se6 units, which contains homopolar Ge–Ge bonds, forms when diffusion approaches equilibrium where Ag content ∼30 at.%. The formation of a Se-rich composition is indicated in the near-surface region at the initial stage of the process, but the previously assumed Ag2Se phase is not detected. [ABSTRACT FROM AUTHOR]

We report a dramatic change in effective three-photon absorption coefficient of amorphous Ge16As29Se55 thin films, when its optical band gap decreases by 10 meV with 532 nm light illumination. This large change provides valuable information on the higher excited states, which are otherwise inaccessible via normal optical absorption. The results also indicate that photodarkening in chalcogenide glasses can serve as an effective tool to tune the multiphoton absorption in a rather simple way. [ABSTRACT FROM AUTHOR]

We report a detailed investigation of the charge carrier transport in polycrystalline n-type impurity-doped zinc oxide (ZnO) thin films grown by spray pyrolysis over a wide range of carrier concentrations. Particular attention is devoted to a study of the composition-dependent metal-insulator transition (MIT) in this transparent conducting oxide (TCO). In order to describe the flow of electrons in these impurity-doped thin films over this full range of conditions, it is necessary to consider multiple electronic conduction processes. The first conduction process arises from current carriers thermally excited from impurity states into the (host) ZnO conduction band. The second involves thermally-activated, quantum-mechanical tunnelling within an impurity band located close to the host conduction band. The latter conduction process predominates at low temperatures whilst the former dominates at high temperatures. We find that a MIT occurs at a critical carrier concentration between 2 and 6 × 1019 cm-3. At higher concentrations in this metallic regime, the impurity band merges with the ZnO conduction band. The location of the MIT was determined from low temperature resistivity data and the results are discussed in terms of the Mott and Ioffe-Regel models. In addition, the overriding importance of grain boundaries is highlighted for these polycrystalline thin films; this is a key factor in determining and limiting electronic conduction in these samples, particularly at high temperatures. These results highlight the practical importance of understanding both the MIT and also grain boundary effects in determining the electrical performance of polycrystalline TCO films. [ABSTRACT FROM AUTHOR]

Abstract: 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/As2S3 and Sb/As2S3 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 As2S3 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. [Copyright &y& Elsevier]

Abstract Chalcogenide glass – silver heterostructures are candidates for photoresist and diffractive optical applications. To optimize their processing, we report the kinetics of Ag photo-dissolution in As 2 S 3 matrix using in-situ optical transmission/reflection measurements and real time atomic force microscopy (AFM) imaging under optical illumination. The results indicate that photo-dissolution occurs in three stages with the extent and kinetics of each stage depending strongly on Ag film thickness. By contrast, the photo-dissolution is found to be independent of As 2 S 3 matrix thickness. The extent of three stages also depends strongly on the laser dose and can be reduced to two stages at higher laser fluence. A comparative study of two oppositely stacked sample configurations: As 2 S 3 /Ag/glass and Ag/As 2 S 3 /glass show that the heterostructures respond differently to light illumination. For the former, Ag dissolves completely into As 2 S 3 matrix at a faster rate than for the latter case. The origin of this difference is established by energy dispersive X-ray spectroscopy and AFM measurements. Highlights • We resolve three different stages of Ag photo-dissolution in As 2 S 3 matrix. • The kinetics and extent of each stage depend strongly on Ag film thickness and laser fluence. • Ag photo-dissolution is found to be independent of As 2 S 3 matrix film thickness. • The sequence of Ag and As 2 S 3 films within stacked heterostructure strongly affects Ag photo-dissolution. • In situ AFM imaging shows real time evolution of morphological changes resulting from Ag dissolution into As 2 S 3 matrix [ABSTRACT FROM AUTHOR]

We employ EXAFS spectroscopy to refine the local atomic arrangements of evaporation-deposited equiatomic GeSe film. Amorphous structure of the as-deposited GeSe film turns out to satisfy mainly the 4:2 structural model. The crystallized GeSe film, however, consists of the orthorhombic GeSe crystals with the 3:3 atomic arrangements and quasi-crystalline Ge clusters. Its temperature-dependent electrical resistance is explained in connection with this structural difference, which exemplifies significance of the chemical environments on the electrical switching phenomena observed from amorphous chalcogenide solids. [ABSTRACT FROM AUTHOR]

Abstract: The use of high resolution X-ray photoelectron spectroscopy to study chalcogenide glass thin films is analyzed. It is shown that the method is an effective tool to explore different chemical environments in the films and control chemical composition of the surface. Examples of the method applications such as kinetics study of induced silver dissolution in the thin films and investigation of oxidation on the surface of the thin film are presented. Limitations of the method are shown on the example of photoinduced structural transformations in chalcogenide glass thin films. [Copyright &y& Elsevier]

Abstract: The role of structure in the crystallization of Ge x Te100− x model system suitable for phase-change applications is established by determining the local environment of each constituent using EXAFS analysis. Across the compositional spectrum, both constituents satisfy the (8-N) rule in the amorphous state except that the Ge atoms are surrounded by ∼3.4 neighbors in the stoichiometric composition. The estimation of homopolar Ge–Ge and Te–Te bonds indicates that chemical order is preserved less for Ge than for Te atoms. The crystallized stoichiometric film consists of Ge clusters in addition to GeTe crystals, implying that the latter has appreciable concentration of Ge vacancies. [Copyright &y& Elsevier]

Abstract: Changes of electronic and atomic structure during silver photodissolution in As2S3 thin film are studied using a combination of high-resolution X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) methods. It is shown that the photodiffusion process starts already under the influence of Al Kα and synchrotron X-ray probe radiations, forming a highly disordered metastable structure. Concurrent irradiation with UV/VIS light leads to the formation of a stable uniform ternary phase. The mechanisms of structural transformations and final chemical products are proposed. The influence of surface oxidation on the structure of Ag/As2S3 bilayer is also investigated. [Copyright &y& Elsevier]

Abstract: GeSe2 and Ge28Sb12Se60 chalcogenide glass thin films have been deposited on single crystal silicon substrates by vacuum thermal evaporation. The surface morphology of these films has been investigated by field emission-scanning electron microscopy and atomic force microscopy, revealing heterogeneities in their microstructure consisting of granular regions ∼15–50nm in size, which were coarser in the case of the GeSe2 films. Typical RMS film surface roughness values were ∼0.9–1.3nm. [Copyright &y& Elsevier]