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Phototransients are investigated for CuSbS2 films with varying the illumination energy. The generation and recombination of photocarriers, which are manifested as changes in the sheet conductivity of the films, take place almost instantaneously for excitation wavelengths of 970 and 633 nm. These rapid responses are, in contrast, absent for the illumination at wavelengths of 375 and 280 nm. In particular, roughly no photoconduction occurs in the case of 280 nm. The sheet conductivity develops thereby random two-level fluctuations following the illumination. Ultraviolet irradiation is thus suggested to generate crystalline defects, giving rise to the quenching of the instantaneous photoresponse caused by their trapping of the photocarriers. The photoresponse in simultaneous illumination at multiple wavelengths is dependent upon the relative intensities of the ultraviolet and visible/infrared components in a nonlinear fashion unless the photo-generated defects are overwhelmed by photocarriers.

Electrically induced resistive switching resulting from ionic transport and electrochemical redox reactions is promising for future generation non-volatile memory devices and artificial neural computing. The key ingredient for the highly efficient neural computing in this context is a memristor, which is a special type of a resistive two-terminal element whose electrical properties depend on not only the state of the element but also how the state has been achieved in its history. Memristor characteristics are demonstrated in a bilayer junction of Al and a Bi–Cu–S alloy utilizing electrically reversible generation of an insulating interface. The high resistance due to the interface layer drops abruptly by orders of magnitude when the barrier is annihilated electrochemically under a bias. The barrier is made to be robust by applying a reverse bias, giving rise to a controllable memory effect on the switching phenomenon. The switching mechanism based on the manipulation of a barrier, which is complementary to conventional bridging conductive filaments, will open the way for new functionalities as device elements. [ABSTRACT FROM AUTHOR]

Diffuse boundary reflection of electrons in the presence of a magnetic field is demonstrated to induce a rectification effect in circular-shaped ballistic nano-channels. The effect is robust as the rectification is associated with a transmission asymmetry in the equilibrium transmission predicted by the billiard model, which is possible as the time reversal symmetry is broken by the magnetic field. The rectified current exhibits antisymmetric dependence on the magnetic field despite the two-terminal geometry due to the inherent nonlinearity of the rectification. Unambiguous identification of the origin of the current based on this antisymmetric dependence reveals the rectification effect being sensitive to the extent that extraction of electrical energy out of environmental non-equilibrium noises is achieved. [ABSTRACT FROM AUTHOR]

Hot-wall-epitaxy growth of Bi2Se3, Bi2Te3 and Sb2Te3 films is carried out on Si as well as GaAs surfaces. For Bi2Se3, self-assembled dots are formed at the initial stage of the growth due to the large lattice mismatch. The dots expand in a way to fill the whole substrate surface with (0 0 0 1)-oriented domains. While no in-plane epitaxial orientation relationship is established between the films and the substrates, the influence of the substrates is reflected in the morphology of the films. Throughout the growth, micrometer-size free-standing disks are spontaneously generated and eventually cover the whole surface. The disk geometry manifests that the Bi2Se3 crystal grows preferentially in the in-plane directions of the (0 0 0 1)-plane. For Bi2Te3 and Sb2Te3, we experience thermal decomposition. Although nanowires can be generated under low source-flux intensities, they are solely composed of Te as a consequence. Owing to different solidification temperatures, we obtain Bi2Te3 islands when the substrate temperature is raised. The surface of these islands is remarkably flat and the typical thickness is less than 10 nm. [ABSTRACT FROM AUTHOR]

We report on the gating in GaAs-(Al,Ga)As heterostructures using the electrical double layer of ionic liquids. We employ tetrabutylammonium bis(trifluoromethylsulfonyl)imide for the ionic liquid, which has a melting point of 92 degC. As the 'ionic liquid' is solid at room temperature, the device operation is more stable compared to when an aqueous electrolyte is used. Hysteretic behavior appeared in the variation of the resistance when the negative gate bias exceeded [?][?]3 V, which is considered to be the electrochemical window of the ionic liquid. Temporary gate degradation occurred when the positive gate bias was larger than 8 V. We attribute these characteristics to the generation of space charge and its slow dissipation in the ionic liquid. The gating ceases to function at low temperatures with a transition range of 100-200 K due to the freezing of ions. [ABSTRACT FROM AUTHOR]