Understanding the electrical properties of defect-free nanowires with different structures and their responses under deformation are essential for design and applications of nanodevices and strain engineering. In this study, defect-free zinc-blende- and wurtzite-structured InAs nanowires were grown using molecular beam epitaxy, and individual nanowires with different structures and orientations were carefully selected and their electrical properties and electromechanical responses were investigated using an electrical probing system inside a transmission electron microscope. Through our careful experimental design and detailed analyses, we uncovered several extraordinary physical phenomena, such as the electromechanical characteristics are dominated by the nanowire orientation, rather than its crystal structure. Our results provide critical insights into different responses induced by deformation of InAs with different structures, which is important for nanowire-based devices.

Opposite electrical responses have been observed in the same individual ZnO nanowire (NW) during bending via changes in the contact modes between the NW and the tungsten tips. We herein discuss the piezoresistive and piezoelectric effects on the transport properties during these two deformation processes.

•V doped Ge2Sb2Te5 films were characterized by XRD, EDS and in situ TEM.•V dopants improved the thermal stability and crystalline sheet resistance.•V dopants improved the thermal stability and crystalline sheet resistance.A series of V-doped Ge2Sb2Te5 films were prepared via magnetron co-sputtering. The V content ranged from 3.3 to 20.1 at%, as determined via energy-dispersive spectrometry. The influence of the V content on the crystallization behavior and electrical properties was investigated using X-ray diffraction, electrical resistivity measurements and in situ transmission electron microscope annealing. The results indicated that adding V to Ge2Sb2Te5 films within a certain amount enhances the electrical resistance and thermal stability. These results also indicate that V doping leads to aphase change from being amorphous to a face-centered cubic (fcc) structure below 350 °C. As a result, V doped Ge2Sb2Te5 composite films can be considered as a promising material for phase change memory.

We quantified the size-dependent energy bandgap modulation of ZnO nanowires under tensile strain by an in situ measurement system combining a uniaxial tensile setup with a cathodoluminescence spectroscope. The maximal strain and corresponding bandgap variation increased by decreasing the size of the nanowires. The adjustable bandgap for the 100 nm nanowire caused by a strain of 7.3% reached approximately 110 meV, which is nearly double the value of 59 meV for the 760 nm nanowire with a strain of 1.7%. A two-step linear feature involving bandgap reduction caused by straining and a corresponding critical strain was identified in ZnO nanowires with diameters less than 300 nm. The critical strain moved toward the high strain level with shrunken nanowires. The distinct size effect of strained nanowires on the bandgap variation reveals a competition between core-dominated and surface-dominated bandgap modulations. These results could facilitate potential applications involving nanowire-based optoelectronic devices and band-strain engineering.

Phase change memory, which is based on the reversible switching of phase change materials between amorphous and crystalline states, is one of the most promising bases of nonvolatile memory devices. However, the transition mechanism remains poorly understood. In this study, via in situ transmission electron microscopy with an externally applied DC voltage and nanosecond electrical pulses, for the first time we revealed a reversible structural evolution of Ge2Sb2Te5 thin films from an amorphous state to a single-crystal state via polycrystals as an intermediate state. This transition is different from the traditional understanding of structural changes in Ge2Sb2Te5, i.e., from an amorphous structure to a hexagonal close-packed structure via face-centered cubic as an intermediate structure. In situ observations indicate that this poly-to-single crystal structural transition is caused by coalescence of neighbouring grains induced by an electric field, in which a fast heating/cooling rate is found to be essential. Our study opens a new avenue for the realization of the multi-level operation of phase change materials.