We report the fabrication of a double Schottky barrier (DSB) device by self-assembly of nanowires (NWs). The operating principle of the device is governed by the surface depletion effects of the NWs. High DSBs were formed at the contact interface of ZnO NWs self-assembled into bascule nanobridge (NB) structures. The bascule NB structures exhibited high sensitivity and fast response to UV illumination, having a photocurrent to dark current ratio > 10(4) and a recovery time as short as approximately 3 s. The enhanced UV photoresponse of the bascule NB structure is ascribed to the DSB, whose height is tunable with UV light, being high (approximately 0.77 eV) in dark and low under UV. The bascule NB structure provides a new type of optical switch for spectrally selective light sensing applications ranging from environmental monitoring to optical communication.

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High-temperature shape memory alloys are promising candidates for actuator applications at elevated temperatures. Ternary nickeltitanium-based alloys either contain noble metals which are very expensive, or suffer from poor workability. Titanium-tantalum shape memory alloys represent a promising alternative if one can avoid the cyclic degradation due to the formation of the omega phase. The current study investigates the functional fatigue behavior of Ti-Ta and introduces a new concept providing for pronounced fatigue life extension.Keywords: Omega phase; martensite; phase transformation; microstructure; shape memory effect.Conventional shape memory alloys (SMAs) have been intensely investigated over the last decades due to their extraordinary properties. 1-6 Different metallic alloys can show a shape memory effect, e.g. Cu-based 5 and Fe-based systems, 6 but Ni-Ti is still the most widely used conventional SMA 3 due to good functional and structural properties. Unfortunately, the transformation temperatures of Ni-Ti are limited to below 100 ○ C, thus hindering applications in elevated and high-temperature regimes. 7 As shape memory actuators allow for designing devices characterized by high compactness and efficiency, a large effort has been spent to develop high-temperature shape memory alloys (HTSMAs). For actuation in a medium temperature range of about 100-400 ○ C, mainly Ni-Ti based ternary (Ni-Ti-X) systems have been proposed. [8][9][10] These alloys show promising shape memory characteristics, i.e. actuation strain and microstructural stability, but at the same time suffer from two main drawbacks, i.e. poor workability and/or high amounts of noble metals. 8,9,11 Titanium-tantalum SMAs represent a promising alternative to overcome all these issues if one can avoid the cyclic degradation due to the formation of the !-phase. The current study investigates the functional fatigue behavior of Ti-Ta and introduces a new concept providing pronounced fatigue life extension. The cyclic deformation behavior of a polycrystalline titanium-tantalum (Ti-Ta) alloy containing 30 at.% Ta under iso-stress loading during thermal cycling employing temperatures ranging from 50 ○ C to 600 ○ C was investigated. In order to reveal the most detrimental factor leading to a change of transformation temperatures and a loss of transformation strain, fatigue tests were conducted with differing heating and cooling rates and aging treatments. Using X-ray diffraction (XRD) it could be clearly shown that stabilization of the high-temperature parent phase (β-phase) and the concomitant evolution of the !-phase led to functional degradation. The results of the current study suggest that both phases are mainly induced through aging during high temperature exposure and not by martensitic transformation events during cycling. A new concept employing single-step short-time annealing for regeneration of the initial transformation behavior is introduced.As shown and intensively discussed in a series of studies published by Buenconsejio et al.,[12]...

Ti-Ta based alloys are an interesting class of high-temperature shape memory materials. When fabricated as thin films, they can be used as high-temperature micro-actuators with operation temperatures exceeding 100°C. In this study, microstructure, shape memory effect and thermal cycling stability of room-temperature sputter deposited Ti 67 Ta 33 thin films are investigated. A disordered a 00 martensite (orthorhombic) phase is formed in the as-deposited Ti 67 Ta 33 films. The films show a columnar morphology with the columns being oriented perpendicular to the substrate surface. They are approximately 200 nm in width. XRD texture analysis reveals a martensite fiber texture with {120} and {102} fiber axes. The XRD results are confirmed by TEM analysis, which also shows columnar grains with long axes perpendicular to the {120} and {102} planes of a 00 martensite. The shape memory effect is analyzed in the temperature range of -10 to 240°C using the cantilever deflection method, with special emphasis placed on cyclic stability. Ti 67 Ta 33 thin films undergo a forward martensitic transformation at M s % 165°C, with a stress relaxation of approximately 33 MPa during the transformation. The actuation response of the film actuators degrades significantly during thermal cycling. TEM analysis shows that this degradation is related to the formation of nanoscale v precipitates (5-13 nm) which form above the austenite finish temperature. These precipitates suppress the martensitic transformation, as they act as obstacles for the growth of martensite variants.