Amorphization of TiNi induced by high-pressure torsion

Using high-resolution electron microscopy, we investigated the initial stages of high-pressure-torsion-induced crystalline-to-amorphous transformation of TiNi. It is found that the deformation-induced amorphization initiated from dislocation core regions in the interior of grains and from grain boundaries. It is believed that both the energy stored in the dislocations and the energy stored in the grain boundaries contribute significantly to driving the crystalline-to-amorphous transformation.     

Temperature-dependent crack surface tension

The fracture surface energy is calculated for a one-dimensional, exactly solvable model of a crack. The temperature dependence of the crack surface tension is determined on the basis of a self-consistent Einstein approach. It is found that lattice vibrations result in a strong reduction in the crack surface tension.     

The effect of hydrogen plasma on the properties of a-Si:H/a-Si1-xNx:H superlattices

Abstract

A hydrogen plasma introduced during the interrupting interval when alternating two gases affects the properties of a-Si:H/a-Si_1-xN_x:H superlattices resulting in the creation of fewer interface defects than the superlattices prepared without the hydrogen plasma.     

Potential fluctuations in phase change memory materials

Long-range potential fluctuations have been quantified in amorphous and crystallised thin films of a family of Ge–Sb–Te (GST) chalcogenide glasses. Among the compositions studied, the width of the potential fluctuations is the smallest for amorphous Ge₂Sb₂Te₅. This is also the most robust material in terms of the number of write–erase cycles for GST films when used as phase change memory materials. A plausible explanation for this observation is given and a criterion for selecting suitable compositions in optical memory devices is proposed.     

Effect of lithium-ion irradiation on the crystallization kinetics of glassy Se98In2

Differential scanning calorimetry (DSC) has been used to study the crystallization kinetics of glassy Se₉₈In₂ both before and after irradiation of the alloy with high-energy (50 MeV) lithium ions. After the ion-irradiation, significant changes in the kinetic parameters of crystallization of the glass were observed. The results are explained in terms of a model involving irradiation-induced defects.     

Long-term metastability of light-induced defects in hydrogenated amorphous silicon

The decay of the peak intensity of the electron spin resonance signal associated with light-induced dangling bonds in a-Si(H) has been measured at room temperature as a function of time during very long intervals such as 3400 days after the intense pulsed illumination was turned off. The decay curve is fitted by an exponential function with a decay constant of 393 days and reaches a steady-state value smaller than the value taken before illumination. Such a long-term metastability of light-induced dangling bonds in a-Si:H is discussed in terms of reconstruction of the amorphous network occurring through hydrogen motion.     

Thermal stability and glass-forming ability of Se80− x Te20Ag x (x = 0, 3, 5, 7 and 9) chalcogenide glasses

The thermal stability and glass-forming ability (GFA) of Se_{80? x} Te₂₀Ag _x (x?=?0,?3,?5,?7 and 9) chalcogenide glasses have been investigated using differential scanning calorimetry (DSC). The DSC runs have been taken at five different heating rates (10, 20, 30, 40 and 50?K/min) under non-isothermal condition. The thermal stability and GFA are monitored through determination of the temperature difference ΔT?=?T _c???T _g, where T _c is the onset crystallization temperature, T _g is the glass transition temperature, H ^l is the stability parameter, ΔH _c is the enthalpy released during crystallization and F _i is the fragility index. The activation energy of crystallization E _c and crystallization rate factor K have also been determined as indicators of the thermal stability of the above-mentioned samples. It is found that Se₇₁Te₂₀Ag₉ is the most stable among all the samples of the series.     

In situ simultaneous measurements of photodarkening and photoinduced defect creation in amorphous As2Se3 films

To understand the direct correlation between photodarkening (PD) and photoinduced defect creation (PDC) observed in amorphous chalcogenides, in situ simultaneous measurements of PD and photocurrent (PC) have been performed on amorphous As₂Se₃ films. The time evolution of PD and PDC during light excitations are empirically described by a stretched exponential function; 1 ??exp[?(t/τ) ^β ], where τ is the effective response time and β the dispersion parameter. The value of τ for the PDC is very much smaller than that for the PD, suggesting that there is no direct correlation between the two.     

Highly inhomogeneous compressive plasticity in nanocrystal-toughened Zr–Cu–Ni–Al bulk metallic glass

A Zr₆₂Cu_15.5Al₁₀Ni_12.5 bulk metallic glass with a large supercooled liquid region of 90 K, produced by copper-mould casting, exhibits a high strength of 1730 MPa and superior but highly inhomogeneous plasticity under uniaxial compression at ambient temperature. Micro-X-ray diffraction shows that compressive loading facilitates crystallization in the monolithic glassy alloy, resulting in room-temperature plasticity. The plastic deformation of the Zr₆₂Cu_15.5Al₁₀Ni_12.5 BMG may be attributed to in situ precipitation of nanocrystals during compression in heavily deformed areas.