S. W. Li

Resistive dependence of magnetic properties in nonvolatile Ti/Mn:TiO2/SrTi0.993Nb0.007O3/Ti memory device

We report the relationship of the magnetic properties of the Mn-doped TiO 2 ( Mn : TiO 2 ) thin film on SrTi 0.993 Ti 0.007 O 3 substrate to the different resistance states of the Ti / Mn : TiO 2 / Nb : SrTiO 3 / Ti device. Initially, the device showed paramagnetic behavior without applying voltage. When the device was switched to low resistance state after applying a positive voltage, robust ferromagnetism was observed. In contrast, when a negative voltage was applied to switch to high resistance state, the device exhibited weak ferromagnetism. This electrically controllable ferromagnetism should be attributed to the tunability of oxygen-vacancy concentration in the Mn : TiO 2 film by electric field.

Uniaxial strain modulated band gap of ZnO nanostructures

Influence of the uniaxial strain on the electronic structures of ZnO nanowires (NWs) and nanotubes (NTs) has been studied using the density functional theory. It was found that the uniaxial compress strain can lead to a band gap transition from direct to indirect band for both ZnO NWs and NTs. Under the same strain, the phase transition of the thick NW is easier than that of the thin one, and the phase transition of NWs seems easier than that of NTs. These results suggested the uniaxial strain can be used to tune the band structures of ZnO nanostructures, which may be help for design of ZnO-based nanodevices.

N-derived signals in the x-ray photoelectron spectra of N-doped anatase TiO2

The plasma-assisted molecular beam epitaxial anatase TiO2−xNx (x<0.3) films were chosen to investigate the N-derived variation in the x-ray photoelectron spectroscopy (XPS). With increasing nitrogen concentration, the small chemical shift and the shoulder of the main peak emerge in the N 1s, O 1s, or Ti 2p3/2 core level spectra. In combination with the experimental results obtained from x-ray diffraction and atomic force microscopy, the variations in the spectra could be ascribed to the microstructural distortion. This distortion, induced by the N3− substitution for lattice O2−, could slightly decrease the average ionicity of the Ti–O (or N) bonds. In addition, the other N 1s features (at 399.8 and 401.8 eV) and the oxygen vacancy are also discussed. For the N-doped TiO2, this work introduces a correlation between the microstructural properties and the XPS signals.

Universal scaling of semiconductor nanowires bandgap

We have established an analytical model to investigate the bandgap energy of III-V and II-V semiconductor nanowires (NWs) by taking size and surface effect into account and found that there is a universal scaling of bandgap between bandgap energy Eg and structural factor K of NWs, Eg∼K−1, which meaning that the bandgap energy of semiconductor NWs usually increases with the structural factor decreasing. This scaling rule has a general insight into the basic physics involved in size effect of semiconductor NWs bandgap.

Extrinsic anomalous Hall effect in epitaxial Mn4N films

Anomalous Hall effect (AHE) in ferrimagnetic Mn4N epitaxial films grown by molecular-beam epitaxy is investigated. The longitudinal conductivity σxx is within the superclean regime, indicating Mn4N is a highly conducting material. We further demonstrate that the AHE signal in 40-nm-thick films is mainly due to the extrinsic contributions based on the analysis fitted by ρAH=a′ρxx0+bρxx2 and σAH∝σxx. Our study not only provide a strategy for further theoretical work on antiperovskite manganese nitrides but also shed promising light on utilizing their extrinsic AHE to fabricate spintronic devices.

Direct evidences of filamentary resistive switching in Pt/Nb-doped SrTiO3 junctions

The first concerned question on the fundamental physics of the resistive switching (RS) effect in metal/Nb-doped SrTiO3 junctions is whether the RS does take place at the whole interface or at some local regions of the interface. Even though several investigations provide the clues of the filamentary nature of the RS, direct evidences are still required. Moreover, there is obvious inconsistency between the possible filamentary feature and the observed capacitance-voltage (C-V) hysteresis loops. Here, we report direct evidences of a filamentary RS effect in Pt/Nb-doped SrTiO3 junctions. The virgin Pt/NSTO junctions show an initial RS effect. The current-voltage (I-V) characteristic of the initial RS and the C-V characteristic in the virgin junctions are interpreted by using the theory of metal/semiconductor contacts. The correspondence between the initial RS and the C-V hysteresis loops is also discussed. The most important is that an electroforming process is observed at a large forward voltage, which is ...

Electrical field induced direct-to-indirect bandgap transition in ZnO nanowires

As a wide bandgap (3.37 eV) compound semiconductor with the exciton binding energy of 60 meV, ZnO nanowires have attracted considerable interest because of great potential applications in micro-optoelectronics and nano-optoelectronics. However, ZnO nanowires as basic units of microelectronic and optoelectronic nanodevices usually work in the circumstance of the electrical field. Therefore, the influence of electrical field on the electronic structure of ZnO nanowires partly determines the performance of nanodevices. For this issue, we inhere have studied the effects of the applied electrical field on the electronic structure of ZnO nanowires using the density functional theory. It was found that the applied electrical field cannot only effectively modulate the bandgap of ZnO nanowires but also leads to the bandgap transition from direct to indirect. Meanwhile, the above effects of electrical field depend on the size and shape of ZnO nanowires. The physical understanding of the electrical field effects of ...

Enlarged Mn 3s splitting and room-temperature ferromagnetism in epitaxially grown oxygen doped Mn2N0.86 films

Single-phase and oxygen doped Mn2N0.86 thin films have been grown on MgO (111) by plasma-assisted molecular beam epitaxy. The films grow under tensile strain and, remarkably, they show ferromagnetic-like interactions at low temperature and ferromagnetic ordering agreed well with the Bloch-law T3/2 at room-temperature. We further demonstrate the enlarged Mn 3s splitting (6.46 eV) and its possible relation to the observed ferromagnetism. Our study not only provide a strategy for further theoretical work on oxygen doped manganese nitrides, but also shed promising light on utilizing its room-temperature FM property to fabricate spintronic devices.

Room-temperature ferromagnetism in (Mn, N)-codoped TiO2 films grown by plasma assisted molecular beam epitaxy

(Mn, N)-codoped TiO2 films have been fabricated by plasma assisted molecular beam epitaxy. X-ray diffraction and x-ray photoelectron spectroscopy studies indicate the incorporation of both Mn and N ions into the TiO2 lattice but without Mn metal clusters. Ferromagnetism with clear hysteresis at 300 K is observed in (Mn, N)-codoped TiO2 films, whereas the films without nitrogen show paramagnetic behavior. It is demonstrated experimentally that the intentional nitrogen doping plays an important role in realizing dominant ferromagnetic ordering in Mn-doped TiO2 films.

Golgi-associated LC3 lipidation requires V-ATPase in noncanonical autophagy

Autophagy is an evolutionarily conserved catabolic process by which cells degrade intracellular proteins and organelles in the lysosomes. Canonical autophagy requires all autophagy proteins (ATGs), whereas noncanonical autophagy is activated by diverse agents in which some of the essential autophagy proteins are dispensable. How noncanonical autophagy is induced and/or inhibited is still largely unclear. In this study, we demonstrated that AMDE-1, a recently identified chemical that can induce canonical autophagy, was able to elicit noncanonical autophagy that is independent of the ULK1 (unc-51-like kinase 1) complex and the Beclin1 complex. AMDE-1-induced noncanonical autophagy could be specifically suppressed by various V-ATPase (vacuolar-type H+-ATPase) inhibitors, but not by disturbance of the lysosome function or the intracellular ion redistribution. Similar findings were applicable to a diverse group of stimuli that can induce noncanonical autophagy in a FIP200-independent manner. AMDE-1-induced LC3 lipidation was colocalized with the Golgi complex, and was inhibited by the disturbance of Golgi complex. The integrity of the Golgi complex was also required for multiple other agents to stimulate noncanonical LC3 lipidation. These results suggest that the Golgi complex may serve as a membrane platform for noncanonical autophagy where V-ATPase is a key player. V-ATPase inhibitors could be useful tools for studying noncanonical autophagy.