Liquid As2Se3 Research Articles

Transient photodarkening induced by a nanosecond pulsed laser in amorphous and liquid As2Se3: fractal characteristics in relaxation dynamics

Transient photodarkening induced by a nanosecond pulsed laser in amorphous and liquid As2Se3: fractal characteristics in relaxation dynamics

Viscoelastic anomaly accompanying anti-crossing behaviour in liquid As2Se3

We investigate the dynamic structure factor of the melt of the well known glass former, As2Se3, using inelastic x-ray scattering for temperatures, T, K and momentum transfers Q from nm−1. An anomaly was observed at Q = 2.7 nm−1 ( K) with, in the context of a simple model, both an abrupt change in frequency and an increased linewidth reminiscent of an anti-crossing in a solid. Comparison with structural information from reverse Monte Carlo modeling of x-ray diffraction data allows us to associate the disappearance of the anomaly at higher temperatures with a drop in the number of mechanical constraints per atom, nmc, to reminiscent of the threshold applicable for glass formation in rigidity theory. It is inferred that the surprising jump in the dispersion in the liquid may be correlated with a stiffness transition in a network glass.

Chemical order in liquid As2Se3 at high temperatures obtained by X-ray scattering and reverse Monte Carlo modeling

X-ray scattering experiments for liquid As2Se3 were carried out at high temperatures up to 1673K at 6MPa, using synchrotron radiation at SPring-8 in Japan, and the structure factor with reasonably nice statistics is obtained. The first peak position in the pair distribution function slightly shifts to smaller distance and the first minimum at 2.7Å develops, as the metallic properties are enhanced with increasing temperatures. A first sharp diffraction peak at 1.2Å−1 in the structure factor becomes broad with an increasing temperature. The partial structure factors in liquid As2Se3 were deduced by Reverse Monte Carlo modeling constrained by partial coordination number fractions reported by the first principles molecular dynamics simulations. Chemical order correlated with the medium range order expected by the first sharp diffraction peak is discussed on the basis of results from the Reverse Monte Carlo modeling.

Inelastic x-ray scattering measurements of dynamical cross-over in liquid As2Se3 at high temperature and high pressure

Liquid As2Se3 undergoes the semiconductor-metal transition with increasing temperature when pressure is applied to avoid evaporation of the liquid. To investigate the atomic dynamics of liquid As2Se3, we have carried out inelastic x-ray scattering experiments of this system at 1073 K and 6 MPa and obtained the dynamic structure factor S(Q,E), from approximately 1.6 nm−1 to 11 nm−1, where Q and E are momentum and energy transfer, respectively. The excitation energy in the semiconducting state at 1073 K disperses as fast as the ultrasonic sound velocity at Q 2.9 nm−1 it disperses approximately 1.8 times faster. We analyzed S(Q,E) at 1073 K using a simple viscoelastic model and discussed Q dependence of the propagation of the acoustic mode.

Fast Photodarkening in Amorphous and Liquid Chalcogenide

AbstractTransient photo-induced optical absorption in amorphous and liquid As2Se3 was investigated using a nanosecond pulsed laser and a specially designed optical cell. The measurements have been performed in the second and minute domain and the nanosecond and microsecond domain. From the measurements in the second and minute domain using repeated illumination, we observed the accumulation of photo-induced absorption and the decay after stopping the illumination. The durable photodarkening was also observed after the decay. The accumulated photoinduced change becomes smaller with increasing temperature and approaches to be zero around the glass transition temperature. From the measurements in the nanosecond and microsecond domain, the transient photodarkening in the time domain responded for each pulsed laser was observed. This fast photodarkening was observed even in the liquid state. This is contrast to the cases of the durable photodarkening and the transient photodarkening in the second and minute domain. The origin of the observed photoinduced changes is discussed.

Atomic and electronic structures in liquid arsenic telluride by ab initio moleculardynamics simulations

The temperature dependence of atomic and electronic structures in the liquidAs2Te3 is studied by means of ab initio molecular dynamics simulations. Themicroscopic mechanism of the semiconductor–metal transition in this liquidmixture with increasing temperature and pressure is discussed compared withthat in the liquid As2Se3. It is shown that the structure of the liquid As2Te3 doesnot change qualitatively with increasing temperature in the sense that most of theAs and Te atoms continue to have three-and twofold coordination, respectively,which is contrast with the structural change from the network structure to thechain-like structure seen in the liquid As2Se3 at high temperatures. It is clarifiedthat the electronic states around Te atoms contribute importantly to themetallization.

Semiconductor-Metal Transition in Liquid As2Se3 at High Temperatures under Pressure

Semiconductor-Metal Transition in Liquid As2Se3 at High Temperatures under Pressure

Short- and Intermediate-Range Atomic Structure of Glassy and Liquid As2Se3 ? An Anomalous X-Ray Scattering Study

An anomalous X-ray scattering experiment has been performed for glassy (g-) and liquid (l-) As2Se3 in order to clarify the role of each constituent for the short- and intermediate-range order (SRO and IRO). The differential structure factors ΔiS(Q) close to the As and Se K edges have been obtained from a detailed analysis. The first nearest-neighbour distances around both As and Se are about 2.4 Å for both g- and l-As2Se3, which would support the SRO model that g- and l-As2Se3 have an SRO similar to the corresponding crystal. The pre-peak in S(Q) for g- and l-As2Se3, is dominated by a partial structure factor SAsAs(Q), which reveals the existence of the As–As IRO with a correlation length of about 5.2 Å.

The electronic and structural changes in the supercooled liquid and glassy As2Se3

We have measured extended X-ray absorption fine structure (EXAFS) and dc conductivity σ of the liquid and glassy As2Se3. Each |F(r)|, the magnitude of the Fourier transform of EXAFS oscillations around As and Se atoms, has a symmetric peak around 2.5 Å. The curve fitting analysis indicates the presence of chemical order and no homopolar As–As and Se–Se bonds. When liquid As2Se3 is cooled to the glassy state through the supercooled state, the inter-layer correlation increases and the two-dimensional (2D) As2Se3 network structure transforms to a three-dimensional (3D) one. This transformation is the reason for the change in the temperature variation of the coordination number N around 300°C whose temperature is higher than Tg(=181°C). The change in the slope of log σ versus 1/T around 300°C is assumed to be associated with the appearance of broadened and localized charged defect states near the band tail.

Optical absorption spectra of liquid As2S3 and As2Se3 over a wide temperature range

The authors have measured the optical absorption coefficient of liquid As2S3 and As2Se3 up to 900 degrees C in a wide absorption range up to about 3*105 cm-1. They have developed an optical cell of their own design with a sample thickness of about 2000 AA. The optical gap obtained from the spectra decreases rapidly with increasing temperature, eventually becoming zero at about 950 degrees C for liquid As2Se3, where the semiconductor-to-metal transition starts to occur.

The influence of electric and magnetic fields on the crystallization of supercooled liquids

We have measured extended X-ray absorption fine structure (EXAFS) and dc conductivity σ of the liquid and glassy As2Se3. Each |F(r)|, the magnitude of the Fourier transform of EXAFS oscillations around As and Se atoms, has a symmetric peak around 2.5 Å. The curve fitting analysis indicates the presence of chemical order and no homopolar As–As and Se–Se bonds. When liquid As2Se3 is cooled to the glassy state through the supercooled state, the inter-layer correlation increases and the two-dimensional (2D) As2Se3 network structure transforms to a three-dimensional (3D) one. This transformation is the reason for the change in the temperature variation of the coordination number N around 300°C whose temperature is higher than Tg(=181°C). The change in the slope of log σ versus 1/T around 300°C is assumed to be associated with the appearance of broadened and localized charged defect states near the band tail.