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1.
The radial distribution analyses for GeTe and As2Te3 are made at temperatures above the melting point in the range of momentum transfer between 0.7 and 10.0 Å?1 by the neutron diffraction technique. Furthermore, the local order in amorphous GeTe is determined by analyzing the intensity data of the electron diffraction of its thin film. The result for the amorphous film indicates that the local distribution of atoms in amorphous GeTe is not characteristic of the structure of its crystalline state. The shape of the peaks of the intensity curve for liquid GeTe differs from that for the amorphous and crystalline states. However, the short bond length and the small coordination number determined from liquid RDF suggest that the covalent-like bonding between nearest-neighbor atoms remains unbroken when melting. The general form of the structure factor for liquid As2Te3 is similar to that for the amorphous material reported previously. The position of the first peak of RDF in the liquid state is observed to be shifted to a shorter distance than the average of nearest-neighbor atoms in crystalline As2Te3. The structure of GeTe differs considerably between the crystalline, amorphous and liquid states, whereas the local order in the liquid As2Te3 is similar to that in the amorphous state but not in the crystalline state.  相似文献   

2.
A study of infrared absorption in the 250–4000 cm?1 region has been carried out for 0.5 As2Se30.5 GeSe2 glasses quantitatively doped with oxide impurity. The frequencies of the intrinsic 2- and 3-phonon absorption bands at 490 and 690 cm?1 correspond well to those predicted from combinations of the high frequency bands in the first order IR and Raman spectra of As2Se3 and GeSe2 glasses.Glasses doped with As2O3 exhibit the same oxide impurity absorptionbands as those doped with GeO2. Unlike As2Se3 glass, at impurity concentrations up to 1000 ppm As2O3, 0.5 As2Se30.5 GeSe2 glass exhibits only one major oxide impurity species, characterized by absorption bands at 780 and 1260 cm?1 and due to oxygen bonded to network Ge. The observation of a much weaker network AsO vibration band at 670 cm?1 confirms that oxygen bonds preferentially to Ge in this glass. The same minor oxide species appears to determine excess IR absorption at the CO2 laser wavelength of 10.6 μm in both As2Se3 and 0.5 As2Se3 0.5 GeSe2 glasses. The frequencies and intensities of absorption bands due to hydrogen impurities are also quite comparable for these two materials.  相似文献   

3.
Thin amorphous films from system (As2Se3)80−x(As2Te3)x(SnTe)20 were prepared by pulsed laser deposition (PLD) from their bulk glasses and their optical properties were studied by spectral ellipsometry. Spectral dependencies of refractive index, absorption and extinction coefficient and optical gap (1.41–1.66 eV for (As2Se3)80−x(As2Te3)x(SnTe)20 with x = 20 resp. x = 0) were calculated from optical tansmittance, from ellipsometric data by Tauc method. High values of refractive index n0 (2.49–2.60) and of non-linear χ(3) coefficient of index of refraction (4.9–7.5 × 10−12 esu for the glass (As2Se3)80−x(As2Te3)x(SnTe)20 with x = 0 resp. x = 20) made studied thin films of system (As2Se3)80−x(As2Te3)x(SnTe)20 promising candidates for application in optics and optoelectronics.  相似文献   

4.
An analysis of the atomic radial distribution function of Al0.20As0.30Te0.30, Al0.10As0.40Te0.50 and Al0.10As0.20Te0.70 amorphous alloys obtained from quenching of the molten mixture of the elements was performed. A structure in which all the Al atoms are tetrahedrally bonded to the other types of atoms in the material, would satisfy the requirements of the experimental curve. Tetrahedral groups might be linked to each other by As and Te atoms, or directly through a Te or As atom belonging to more than one tetrahedra.  相似文献   

5.
Amorphous thin films from the system As2Se3-Ag4SSe-SnTe were prepared by thermal vacuum evaporation from the corresponding bulk glassy samples. The film structure and surface morphology were investigated by scanning electron microscopy and atomic force microscopy; the results revealed uniform, smooth and homogeneous coatings. The amorphous chalcogenide films are transparent in a wide spectral range as shown by transmission and reflection measurements in the VIS and NIR regions. The optical band gap was determined and its compositional dependence is discussed in terms of structural considerations and the formation of charged defect centers.  相似文献   

6.
Amorphous As2Se1Te2 (a-As2Se1Te2) films, into which Cu or Cd ions were doped by thermal diffusion below the glass transition temperature exhibited the increase of conductivity by several orders of magnitude. In addition, these samples exhibited enhanced photoconductivity and the activation type conduction. From the measurements of the thermoelectric power, it was found that Cu doped samples were p-type and Cd doped samples were n-type. The impurities was also studied by SIMS.  相似文献   

7.
This study identifies and characterizes the phase transitions induced thermally in bulk amorphous and crystalline As2Te3. In addition, it examines the nature and the electrical properties of the various As2Te3 phases, and attempts to correlate the memory electrical switching exhibited by these materials with their phase transitions.  相似文献   

8.
75As Nuclear Quadrupole Resonance (NQR) lineshape measurements for the amorphous mixed chalcogenide system As2SxSe3?x are reported. The line-shapes are asymmetric and approximately 8 MHz in width (full width at half maximum). The peak resonance frequency is observed to increase approximately linearly with x. The NQR results indicate the presence of mixed As2(S, Se)3 pyramidal structural units and are thus not consistent with models that predict the occurrence of anion subsite segregation. NQR measurements performed on crystalline As2SSe2 lend support to the structural model proposed for the glasses.  相似文献   

9.
Polarized room temperature Raman spectra of glassy As2SxSe3-x for 0≦×≦3 have been measured. Spectra for crystalline As2S1Se2 are reported. The polarization and intensity dependence upon composition are consistent with mixed pyramids of composition As2SnSe3-n and preclude phase separation in the glassy system.  相似文献   

10.
The liquid structures of As2Se3 and GeSe2 have been investigated using the neutron diffraction patterns. In both cases the structure factor showed a low first peak maximum which follows a weak but apparent pre-peak at very low momentum transfer. It was also observed that the radial distribution function of both materials are characterized by the well-defined first neighbor shell because of the deep minimum on its right-hand side although in the liquid state. These results indicate that strong covalent bondings between unlike atoms in the solid state still remain when melting. Both the structure factor and the distribution curves of these alloys are, on the whole, similar to those in the amorphous phase which have already been examined. A slight difference in the coordination number, however, is found between amorphous and liquid phases of these materials.  相似文献   

11.
Some experimental results of the vitreous As2Se3 investigation (the photoconductivity spectrum of volume examples, the temperature dependence of the thermoelectric E.M.F., the shift of the optical edge under the temperature and pressure) may be explained by the use of fluctuations of an internal potential field. A hypothesis about the nature of chaotic potential field is proposed, which is based on a negligible magnitude of the gap deformation potential Dg = Dc ? Dv, where Dc and Dv are deformation potentials of band edges. By this hypothesis the fluctuations of the substance density in glass generate the chaotic potential field of magnitude about a half of the gap Eg, while the gap magnitude fluctuates only slightly within some per cent of Eg. It is shown that the displacement of the optical edge at As2Se3 amorphization may be a demonstration of the deformation nature of the chaotic potential field in this material.  相似文献   

12.
A spherical-shaped model of Al0.20As0.50Te0.30, Al0.10As0.40Te0.50 and Al0.10As0.20Te0.70 amorphous alloys has been performed by the random Monte Carlo method. These models describe quite well the experimental radial distribution functions and abide by the expected coordination numbers apart from the threefold coordinated Te, of which an excess has appeared. The structures are formed, basically, of distorted tetrahedra around the Al atoms whose corners are occupied by As or Te atoms. Also, a separated phase model for Al0.10As0.20Te0.70 alloy has been built taking into account the results of thermodynamical study on this amorphous alloy system. The fitting of this model was better than that of the model generated under the hypothesis of a continuous phase.  相似文献   

13.
A quantitative study of infrared absorption in the 250–4000 cm?1 region of As2Se3 glasses doped with small amounts of As2O3 or purified by various procedures has been carried out with particular attention to 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?1 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 in the 400–1100 cm?1 region has been interpreted in terms of combination and overtone bands of the two highest-frequency fundamental vibrational modes. Absorption coefficients of As2Se3 glass in the 920–1090 cm?1 CO2 laser region are limited by intrinsic multiphonon absorption to values of around 10?2 cm?1. The lowest absorption coefficients measured in the 1700–2000 cm?1 CO laser region were around 2 × 10?3 cm?1 and may contain contributions from hydrogen-impurity bands.  相似文献   

14.
The structure of the semiconducting glassy As2Se3Hgx system was investigated in a composition range x = 0.005?0.12. An explanation of the anomalous behaviour of the macroscopic density is proposed, based on the analysis of radial electron density distribution curves. A formula is given which correlates quantitatively the magnitude of coordination spheres with the experimental macroscopic density.  相似文献   

15.
Data are presented on the dc conductivity, thermopower and optical absorption of glasses in the CuAs2Se3 system. The electronic properties of the alloys differ markedly from those of As2Se3, but variations in composition do not introduce significant changes in properties, until the atomic percent of copper is greater than 25. The results are interpreted in terms of small polaron transport.  相似文献   

16.
Velocities of 30 MHz longitudinal and shear ultrasonic waves have been measured in As2S3 and As2Se3 glasses as a function of hydrostatic pressure up to 1.5 kbar at 195 K and 3 kbar at 296 K. The elastic stiffness moduli are found to have relatively large, positive, pressure dependences which are about the same at both temperatures for both glasses. This behavior is attributed to the weakness of bonding between layers comprised of AsS3 and AsS3 pyramids.Inspection of data for a variety of glasses reveals a correlation between the value of CL/3CT and whether the elastic moduli are increased or decreased by pressure. (CL is the longitudinal modulus and CT the shear modulus.)Using the pressure dependences of the elastic moduli obtained in the present work, it is found that volume change is responsible for most of the temperature dependences of the moduli. In addition elastic gammas are obtained which are consistent with thermal Grüneisen gammas at 12 K. The pressure dependence of the volume of As2S3 glass at 296 K is calculated using the present results in the Murnagham equation. Agreement with volumetric data of Weir is obtained.  相似文献   

17.
We have measured the specific heats of amorphous and crystalline specimens of Te0.81Ge0.15As0.04 between 0.2 and 20 K, and of crystalline Te0.93As0.07 between 1 and 20 K. Amorphous Te0.81Ge0.15As0.04 shows a low-temperature linear specific heat anomaly whose magnitude, 0.027 mJ/mol-K2, is similar to that of other amorphous insulators. Crystalline Te0.81Ge0.15As0.04 exists as a two-phase material comprised of GeTe and As-doped Te. The specific heat of this material is analyzed in terms of a weighted average of the properties of its two constituents.  相似文献   

18.
The effect of temperature on the crystallization kinetics of bulk amorphous selenium and the alloy As0.005Se0.995 has been studied using differential scanning calorimetry. A time-temperature-transformation (TTT) curve has been plotted from isothermal results over the temperature range 320 to 490 K, and shows the presence of two minima for both materials. Using the empirical Avrami expression for solid-state transformations, a number of kinetic parameters has been determined.  相似文献   

19.
Photoinduced diffusion in Se/As2S3 and Sb/As2S3 nanomultilayered thin films are studied by X-ray photoelectron spectroscopy (XPS). The XPS measurements show the atomic movements during photoinduced diffusion in Se/As2S3 and Sb/As2S3 nanomultilayered film. The analysis of experimental data describes the nature of light induced changes in different structural units.  相似文献   

20.
We discuss the atomic displacements of the optically active vibrational modes of vitreous (v-)As2O3 through comparisons of the infrared (ir) and Raman response with the corresponding spectra of the two crystalline polymorphs, claudetite, a layer crystal similar to orpiment, and arsenolite, a molecular crystal based on the As4O6 molecule. We conclude from these comparisons that the structure of the glass is composed of AsO32 pyramidal units that are corner connected to form a continuous random network. The character of the strong ir and polarized Raman modes in the vitreous form, suggests that the interconnection of these pyramidal units cannot be described by a random distribution of dihedral angles, but rather has peaks at angles characteristic of the different ordering in two-dimensional macromolecular layer basis of claudetite, and the As4O6 molecule. The comparisons are extended to v-As2S3 and vAs2Se3 where we conclude the dihedral angle distributions characteristic of an As4O6-like local geometry are less prevalent.  相似文献   

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