Thermal conductivity of GexSb(As)ySe100‐x‐y glasses measured by Raman scattering spectra

We systematically measured thermal conductivity of Ge_xSb(As)₁₀Se_90−x, Ge_xSb₁₅Se_85−x, and Ge_xSb(As)₂₀Se_80−x chalcogenide glasses by measuring their Stokes and anti‐Stokes Raman scattering spectra and estimating the temperature raised by laser irradiation via the ratio of Stoke and anti‐Stokes scattering cross‐section. We aimed at demonstrating the viability of Raman scattering method for thermal conductivity measurements, and understanding the role of chemical composition in determining thermal conductivity of the chalcogenide glasses. We found that, while the values of the thermal conductivity measured in the paper are in a range from ~0.078 to 1.120 Wm^‐1K^‐1 that are in agreement with those reported data in the literatures, thermal conductivity increases before it reaches a maximum at the glass with chemically stoichiometric composition, and then decreases with increasing Ge content. We ascribed the threshold behavior of the thermal conductivity to the demixing of the structural units like GeSe₂, As₂Se₃ and Sb₂Se₃ from the main glass network. The present study demonstrated that Raman scattering method is simple and easy to measure thermal conductivity of the material. Copyright © 2014 John Wiley & Sons, Ltd.     

Advances in Photonic Devices Based on Optical Phase-Change Materials

Phase-change materials (PCMs) are important photonic materials that have the advantages of a rapid and reversible phase change, a great difference in the optical properties between the crystalline and amorphous states, scalability, and nonvolatility. With the constant development in the PCM platform and integration of multiple material platforms, more and more reconfigurable photonic devices and their dynamic regulation have been theoretically proposed and experimentally demonstrated, showing the great potential of PCMs in integrated photonic chips. Here, we review the recent developments in PCMs and discuss their potential for photonic devices. A universal overview of the mechanism of the phase transition and models of PCMs is presented. PCMs have injected new life into on-chip photonic integrated circuits, which generally contain an optical switch, an optical logical gate, and an optical modulator. Photonic neural networks based on PCMs are another interesting application of PCMs. Finally, the future development prospects and problems that need to be solved are discussed. PCMs are likely to have wide applications in future intelligent photonic systems.     

An investigation of structural parameters and magnetic and optical properties of EuLn2Q4 (Ln=Tb-Lu, Q=S, Se)

EuLn₂Q₄ (Ln=Tb-Lu; Q=S, Se) has been synthesized using Sb₂Q₃ (Q=S, Se) fluxes at 1000 °C. These compounds crystallize in a CaFe₂O₄-type three-dimensional channel structure that is built from edge-shared double rutile chains of [LnQ₆] octahedra running down the b-axis. Each double chain is connected at the vertices to four other double chains to form open channels where bicapped trigonal prismatic Eu²⁺ ions reside. All of these compounds show antiferromagnetic ordering with Neel temperatures, T_N∼3-4 K. The optical band gaps for EuTb₂Se₄, EuDy₂Se₄, EuHo₂Se₄, EuEr₂Se₄, EuTm₂Se₄, EuYb₂Se₄ EuLu₂Se₄, and EuYb₂S₄ are found to be 2.0, 1.8, 1.8, 1.7, 1.8, 1.3, 1.7, and 1.6 eV, respectively.     

Rayleigh and Mandelstam-Brillouin light scattering in chalcogenide glasses of the As-S system

The Rayleigh light scattering in chalcogenide glasslike alloys of the As-S system is investigated. The velocities of longitudinal hypersound, elasto-optical constants, extinction coefficients, and scattering losses have been determined. It is shown that an increase in the amount of sulfur in alloys leads to an increase in chemical differentiation and, as a result, to an increase in the intensity of Rayleigh scattering and in inherent optical losses.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, 823–826, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Liquid Film Deposition of Chalcogenide Thin Films

Thin films of MoS _x were prepared by liquid film deposition of MoS₄ ^2– solutions in 1,2-diaminoethane (en) and 1,2-diaminopropane (pn) and subsequent thermolysis at temperatures up to 800°C under N₂. As the coatings show a high carbon content of up to 30 at.% that influences the morphology and the physical properties, the precursor thermolysis and the solution properties were analysed in detail and correlated to the coating properties. A reduction of the intermediately formed MoS₃ by organic residues at approx. 300°C was made out as the main cause of the carbon contamination during the thermolysis of the precursor salts (enH₂)MoS₄ and (pnH₂)MoS₄, leading to an immobilisation of the organic carbon. In the corresponding solutions cations of the form [RNH₂...H...NH₂R]⁺ could be detected, that result in an incorporation of additional diamine with 3–4 molecules per MoS₄ ^2– ion in the wet films. This cross-linked structure on the one hand reduces the tendency of the precursor salts to crystallise and thus makes it easier to obtain amorphous precursor films, but on the other hand increases the content of organic residues before thermolysis.     

A distinct hollow spindle-like CdIn2S4 photocatalyst for high-efficiency tetracycline removal

Due to the massive release of antibiotics into the environment, it is of great emergency to find an effective approach to deal with antibiotic-containing wastewater. Photocatalytic technology, benefiting from its low cost and high efficiency, is deemed to be an appealing strategy. Photocatalytic-induced production of reactive oxygen species (ROS) is a promising but challenging prospect in water purification and environmental remediation. Herein, we fabricated a spindle-like hollow CdIn₂S₄ (HCIS) photocatalytic system for high-efficiency tetracycline removal. Targeting MIL-88A (Fe) as a template, the obtained CdIn₂S₄ photocatalysts reserved intrinsic spindle-like morphology. Compared with Bulk CdIn₂S₄ (BCIS), this unique hollow structure enhanced light absorption capacity and boosted carriers separation. As a result, the photodegradation efficiency reached over 94.5% within 40 min under visible light illumination. The degradation rate constant was four times higher than that of pristine CdIn₂S₄. We believe this work will endow some lights for the design of hollow catalysts in other environmental applications.     

Bond constraint theory and the quest for the glass computer

Electronic switching in amorphous chalcogenide semiconductors has been observed and studied for nearly forty years. Technological exploitation of this phenomenon has most recently emerged in DVD’s where GST, a compound of germanium, antimony, and tellurium, is used to store information. We explain how GST behaves as a switch and how X-ray absorption fine structure can be used to unlock the specifics of the switching process. The tool that leads to this deeper understanding is the bond constraint theory. We explain how this theory leads to an explanation of switching and of the behavior and properties of amorphous materials in general. Finally, the prospects for developing GST-related materials into non-volatile memory media that could be the basis for glass computers are discussed.      

Photoinduced transformations in (As1–xBix)2S3 glass observed by Raman spectroscopy

Raman spectra of (As_1–xBi_x)₂S₃ glass samples with x ≤ 0.2 measured at the excitation with above-bandgap (532 nm) laser light at a relatively low power density (P_exc = 4 kW/cm²) clearly confirm the amorphous character, thereby markedly extending the known compositional interval of existence of the (As_1–xBi_x)₂S₃ glass previously known (x ≤ 0.06). Spectra measured at an increased P_exc (40 kW/cm²) reveal a photostructural transformation in the illuminated area of the glass leading to an additional contribution of Bi–S bonds as well as to an increasing number of cage-type As₄S₄ units with homopolar As–As bonds. A number of new features in a broad range up to about 1,000 cm⁻¹, which emerge in the Raman spectra of the (As_1–xBi_x)₂S₃ glasses with high (x ≥ 0.14) Bi content and increase in intensity with the exposure time, are related to a photochemical transformation, namely, oxidation of arsenic and sulphur on the (As_1–xBi_x)₂S₃ glass surface with formation of units containing arsenate AsO₄³⁻ and sulphate SO₄²⁻ ions. These processes are irreversible and occur only in the presence of a sufficient amount of bismuth.