Optical polarization driven giant relief modulation in amorphous chalcogenide glasses

We report on the observation of giant relief modulation in amorphous chalcogenide As2S3 glass under polarization modulated near band gap light illumination. We show that these periodic modulations are created as a result of the photoinduced mass transport despite the very low and uniform intensity light illumination. A phenomenological model, based on a photoinduced alignment of anisotropic microvolumes within the glass, is proposed to explain the phenomenon.     

Faceting during the transformation of amorphous to crystalline ice

We study the thermally activated transition from amorphous to crystalline ice (D2O) on Cu(111) with high-resolution scanning tunneling microscopy. Annealing of amorphous solid water up to the desorption temperature of 149 K results subsequently in monomer decorated double bilayers with different superstructure, a faceted surface, pyramidal islands, and nanocrystallites of distinct height at different coverages. Though all structures are truncations from crystalline water ice, for none of them is the ice bilayer found to be the terminating surface.     

非晶态As2S8半导体薄膜的光致结构变化效应研究

实验研究了非晶态As2S8半导体薄膜在光照、退火-光照和退火-光照-退火-光照关连作用下的光折变效应及淀积态与退火态两种膜系光致体积变化现象.采用棱镜耦合技术、Raman光谱和X线衍射测试技术,确认了As2S8薄膜经紫外光辐照后薄膜密度增高、折射率增大的现象.实验表明,淀积态As2S8薄膜经紫外光照后,折射率变化的最大增量可达到0.06,而退火态As2S8薄膜经紫外光照射后,其折射率最大变化比前者要小一个数量级,约为0.005 7.淀积态和退火态两种膜系紫外光照后,体积缩小,这与As2S3非晶态薄膜的情况不同,体积变化率分别为－3.5%和－2.1%.实验还显示,退火态的As2S8薄膜存在折射率完全可逆现象.     

New type of charged defect in amorphous chalcogenides

We report on density-functional-based tight-binding simulations of a series of amorphous arsenic sulfide models. In addition to the charged coordination defects previously proposed to exist in chalcogenide glasses, a novel defect pair, [As(4)](-)-[S(3)](+), consisting of a fourfold coordinated arsenic site in a seesaw configuration and a threefold coordinated sulfur site in a near-planar trigonal configuration, was found in several models. The valence-alternation pairs [S(3)](+)-S-1 are converted into [As(4)](-)-[S(3)](+) pairs under HOMO-to-LUMO electronic excitation. This structural transformation is accompanied by a decrease in the size of the HOMO-LUMO band gap, which suggests that such transformations could contribute to photodarkening in these materials.     

Electronic structure of As4S5 as a local structural model for amorphous As2S3 film

We have studied the electronic structure of As₄S₅ molecule as a model of the local pyramidal structure in amorphous As₂S₃ film. Emphasis has been put on the analysis of the behaviour of a trapped electron in this model concerning the consequent structural relaxation. It has been found that As₄S₅ species has affinity for an excess electron, and that the attachment of an excess electron promotes the cleavages of specific As-S bonds.     

Temperature dependence of EXAFS in amorphous arsenic

EXAFS measurements at different temperatures on amorphous arsenic are reported. The low values of the EXAFS mean square relative displacement σ² for the first coordination shell are consistent with a distribution of As₄ pyramidal units throughout the amorphous network, giving a locally very ordered first shell, whose disorder is essentially dynamic in character. The temperature dependence of the vibrational contribution to the EXAFS Debye-Waller factor is well described by an Einstein oscillator model.     

Micro‐Raman spectroscopic investigations of extremely scarce Pb–As sulfosalt minerals: baumhauerite,dufrénoysite,gratonite, sartorite,and seligmannite

The overmuch rare lead arsenic sulfosalts, baumhauerite (Pb₃As₄S₉), dufrénoysite (Pb₂As₂S₅), gratonite (Pb₉As₄S₁₅), sartorite (PbAs₂S₄), and seligmannite (PbCuAsS₃), were investigated by Raman spectroscopy. Raman spectra of the investigated minerals arise from the stretching and bending modes of the isolated and interconnected AsS₃ pyramidal groups. The As–S stretching vibrations of the studied minerals occur between 390 and 340 cm⁻¹, whereas those of S–As–S bending modes between 335 and 220 cm⁻¹. The shorter bond distances of the As–S readily elucidate the blue shift from seligmannite to gratonite, sartorite, dufrénoysite, and baumhauerite and the increase in full width at half maximum in similar modes. Copyright © 2016 John Wiley & Sons, Ltd.     

过渡区p型氢化硅氧薄膜结构和光电特性的研究

采用射频等离子体增强化学气相沉积技术,利用二氧化碳(CO_2)、氢气(H_2)、硅烷(SiH_4)和乙硼烷(B_2H_6)作为气源,制备出一系列p型氢化硅氧薄膜.利用拉曼光谱、傅里叶变换红外光谱和暗电导测试,研究了不同二氧化碳流量对薄膜材料结构和光电特性的影响,获得了从纳米晶相向非晶相转变的过渡区P层.研究表明:随着二氧化碳流量从0增加到1.2 cm~3·min~(-1),拉曼光谱的峰值位置从520 cm~(-1)逐渐移至480 cm~(-1).材料红外光谱表明,随着二氧化碳流量的增加,薄膜中的氧含量逐渐增加,氢键配置逐渐由硅单氢键转换为硅双氢键.P层SiO:H薄膜电导率从3S/cm降为8.3×10~(-6)S/cm.所有p型SiO:H薄膜的光学带隙(Eopt)都在1.82—2.13 eV之间变化.在不加背反射电极的条件下,利用从纳米晶相向非晶相转变的过渡区P层作为电池的窗口层,且在P层和I层之间插入一定厚度的缓冲层,制备出效率为8.27%的非晶硅薄膜电池.     

Impact of amorphous titanium oxide film on the device stability of Al/TiO2/Al resistive memory

We have investigated the role of amorphous titanium oxide film in the reliable bipolar resistive switching of Al/TiO₂/Al resistive random access memory devices. As TiO₂ deposition temperature decreased, a more stable endurance characteristic was obtained. We proposed that the degradation of the bipolar resistive switching property of Al/TiO₂/Al devices is closely related to the imperfect migration of oxygen ions between the top insulating interface layer and the oxygen-deficient titanium oxide during the set and reset operations. In addition, the dependence of the TiO₂ film thickness on the switching property was also studied. As the thickness of the film increased, a reduction in the resistance of the high resistance state rapidly appeared. We attribute the improved endurance performance of thin and low-temperature grown TiO₂ devices to the amorphous state with a low film density.     

基于掺锡As2S8条波导的全光逻辑门研究

实验研究了掺锡As2S8条波导的光阻断效应,提出一种新型的基于掺锡As2S8波导的全光逻辑门方案,并试制了掺锡As2S8条波导全光逻辑门,实验结果显示该逻辑门具有良好的波形特性,表明该材料适合做全光逻辑门,具有一定的应用潜力.     

The specific heat of bulk amorphous arsenic

The specific heat of bulk amorphous arsenic deposited from the vapor at 415°K has been measured between 1.8 and 20°K. A comparison with compacted amorphous As films deposited at room temperature reveals appreciable differences in the form of C/T³. The results indicate a relative increase in the density of low frequency vibrational modes in the bulk amorphous As. The specific heat measurements support x-ray and Raman scattering studies that suggest variations in the local structure of amorphous As prepared under different deposition conditions. A comparison with neutron scattering measurements in bulk amorphous As also indicates an underestimate of the low frequency density of states.     

Chemical states of GeTe thin-film during structural phase-change by annealing in ultra-high vacuum

The chemical states of GeTe thin film are investigated using high-resolution X-ray photoelectron spectroscopy (HRXPS) with synchrotron radiation, during amorphous to crystalline structural phase transition. As the temperature increases from 250 to 400 °C, we observe the rock-salt crystalline structure and phase with X-ray diffraction (XRD) and transmission electron microscopy (TEM). Spin-orbit splitting of the Ge 3d core-level spectrum clearly appears after annealing at 400 °C for 5 min. However, the binding energy of the Ge 3d_5/2 core-level peak of 29.8 eV does not change in the amorphous to crystalline structural phase transition. In the case of the Te 4d core-level, change in binding energy and peak shapes is also negligible. We assume that the Te atom is fixed at a site between the amorphous and crystalline phases. Although the structural environment of the Ge atoms changes during the structural phase transition, the chemical environment does not.     

Mixed solid electrolytes based on poly(ethylene oxide)

Polymer solid electrolytes from a PEO-NaI system were mixed with Nasicon and Al₂O₃ powders. As a result an increase of ionic conductivity exceeding 10^–1 S/cm at room temperature was observed for both cases. This increase was due to a higher concentration of amorphous phase which resulted apparently from a higher nucleation rate during the solidification process. The samples were studied using impedance spectroscopy, X-ray diffraction, electron microscopy, NMR, and other techniques.     

Chalcogenide glass waveguides integrated with quantum cascade lasers for on-chip mid-IR photonic circuits

We demonstrate on-chip hybrid integration of chalcogenide glass waveguides and quantum cascade lasers (QCLs). Integration is achieved using an additive solution-casting and molding method to directly form As(2)S(3) strip waveguides on an existing QCL chip. Integrated As(2)S(3) strip waveguides constructed in this manner display strong optical confinement and guiding around 90° bends, with a NA of 0.24 and bend loss of 12.9dB at a 1mm radius (λ=4.8μm).     

Demonstration of chalcogenide glass racetrack microresonators

We have demonstrated what we believe to be the first chalcogenide glass racetrack microresonator using a complementary metal-oxide semiconductor-compatible lift-off technique with thermally evaporated As(2)S(3) films. The device simultaneously features a small footprint of 0.012 mm x 0.012 mm, a cavity Q (quality factor) of 10,000, and an extinction ratio of 32 dB. These resonators exhibit a very high sensitivity to refractive index changes with a demonstrated detection capability of Dn(As(2)S(3)=(4.5 x 10(-6)+/-10%) refractive index unit. The resonators were applied to derive a photorefractive response of As(2)S(3) to lambda=550 nm light. The resonator devices are a versatile platform for both sensing and glass material property investigation.     

Independence of magnetic texture and hyperfine data from Mössbauer spectra of a ferromagnetic metallic glass

We analysed the Mössbauer spectra of ferromagnetic 2605 S2 metglas submitted to various external stresses; it is concluded that the hyperfine parameters and their correlations do not depend on the state of the magnetic texture. Thus the amorphous alloy can be considered as an isotropic material submitted to a small field of stresses; also, methods based on linear combination of spectra can be used.     

Thermal and complex impedance analysis of amorphous and crystalline lithium salt mixtures

Amorphous electrolytes consisting of the lithium salts, Li[R-NSO₂CF₃] were prepared and the attendant low ionic conductivities of the lithium salt mixtures (1×10⁻⁶ S cm⁻¹ at room temperature) are attributed to high glass transition temperatures. An example is the novel amorphous salt, Li[18-C-6NSO₂CF₃] which produces an amorphous salt mixture with Li[N(SO₂CF₃)₂] (LiTFSI).     

Synthesis of ZnO nanospheres with uniform nanopores by a hydrothermal process

ZnO nanospheres were successfully synthesized by a hydrothermal process (S1 sample) and a wet-chemical method (S2 sample). Following synthesis, calcination treatment at 450 °C was performed for the sample prepared by the wet-chemical method (S3 sample). All of the samples possessed a regular spherical shape. A polycrystalline wurtzite structure was confirmed in the S1 and S3 samples by X-ray diffraction and selected area electron diffraction, whereas a mixture of ZnO nanoparticles and amorphous materials was observed in the sample S2. The surface area and pore structure of the samples were investigated by nitrogen adsorption–desorption measurements. Uniform nanopores with a diameter of 4.07 nm were present in the S1 sample while a broad pore size distribution was obtained for the S2 and S3 samples. The highest surface area was obtained for the S1 sample and a possible formation mechanism was studied.     

Stability of Thin-Film Cu–As2S3 and Ag–As2S3 Structures

Technical Physics - Thin-film Cu–As2S3 and Ag–As2S3 structures obtained by successively evaporating Cu(Ag) and As2S3 in vacuum on glass substrates have been studied. Samples of these...     

Spectral variations in the optical transition matrix element and their impact on the optical properties associated with hydrogenated amorphous silicon

Using an empirical model for the density of states functions associated with hydrogenated amorphous silicon, in conjunction with an elementary model for the optical transition matrix elements, we aim to explore how variations in the matrix elements impact upon the spectral dependence of the optical properties associated with this material. We also wish to ascertain as to whether or not the hydrogenated amorphous silicon mobility gap result suggested by Jackson et al. [W.B. Jackson, S.M. Kelso, C.C. Tsai, J.W. Allen, S.-J. Oh, Phys. Rev. B 31 (1985) 5187] is consistent with the results of the experiment. We find that the mobility gap value suggested by Jackson et al. is too large. An upper bound on the mobility gap associated with hydrogenated amorphous silicon of 1.68 eV is suggested instead. Electrical measurements performed on undoped hydrogenated amorphous silicon yield a mobility gap value that is consistent with this bound.