Oxygen vacancies (V(O)) have profound effects on the physical and chemical performance of devices based on oxide materials. This is particularly true in the case of oxide-based resistive random access memories, in which memory switching operation under an external electrical stimulus is closely associated with the migration and ordering of the oxygen vacancies in the oxide material. In this paper, we report on a reliable approach to in situ control of the oxygen vacancies in TiOx films. Our strategy for tight control of the oxygen vacancy is based on the utilization of plasma-enhanced atomic layer deposition of titanium oxide under precisely regulated decomposition of the precursor molecules (titanium (IV) tetraisopropoxide, Ti[OCH(CH₃)₂]₄) by plasma-activated reactant mixture (N₂+O₂). From the various spectroscopic and microstructural analyses by using Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, confocal Raman spectroscopy, and spectroscopic ellipsometry, we found that the precursor decomposition power (R(F)) of plasma-activated reactant mixture determines not only the oxygen vacancy concentration but also the crystallinity of the resulting TiO(x) film: nanocrystalline anatase TiO(x) with fewer oxygen vacancies under high R(F), while amorphous TiOx with more oxygen vacancies under low RF. Enabled by our controlling capability over the oxygen vacancy concentration, we were able to thoroughly elucidate the effect of oxygen vacancies on the resistive switching behavior of TiO(x)-based memory capacitors (Pt/TiO(x)/Pt). The electrical conduction behavior at the high resistance state could be explained within the framework of the trap-controlled space-charge-limited conduction with two characteristic transition voltages. One is the voltage (V(SCL)) for the transition from Ohmic conduction to space-charge-limited conduction, and the other is the voltage (V(TFL)) for transition from space-charge-limited conduction to trap-filled-limited conduction. In this work, we have disclosed for the first time the dependence of these two characteristic transition voltages (i.e., V(SCL) and V(TFL)) on the oxygen vacancy concentration.

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In this work, Au nanomesh was fabricated by dint of sacrificial wet-etching of Ag layer of Au/Ag/AAO. Scheme S1 describes the detail for preparation of Au nanomesh. Au/Ag-coated AAO membrane was floated on the surface of HNO 3 solution (60%) to selectively etch away Ag layer from Au/Ag/AAO membrane. Within 10 min, Au layer separated from AAO replication master was floating on the surface of HNO 3 solution. Afterward, weakly bound metal nanoparticles (NPs) at the edges of holes of Au nanomesh were removed by floating the resulting Au mesh on the surface of diluted aqua regia. Finally, Au mesh was transferred onto a substrate after replacing aqua regia with de-ionized (DI) water in order to rinse Au mesh.Scheme S1 Schematic diagram for transfer of Au mesh on a substrate by (i) selectively dissolving Ag sacrificial layer of Au/Ag-coated AAO by HNO 3 and (ii) extirpating undesired metal nanoparticles (NPs) from the bottom side of the mesh after replacing HNO 3 with aqua regia, followed by (iii) transfer of Au nanomesh after DI water rinsing.

A generic top-down approach for the preparation of extended arrays of high-aspect ratio GaAs nanowires (NWs) with different crystallographic orientations (i.e., [100] or [111]) and morphologies (i.e., porous, nonporous, tapered, or awl-like NWs) is reported. The method is based on the anodically induced chemical etching (AICE) of GaAs wafers in an oxidant-free aqueous HF solution at room temperature by using a patterned metal mesh and allows us to overcome the drawbacks of conventional metal-assisted chemical etching (MACE) processes. Local oxidative dissolution of GaAs in contact with a metal is achieved by externally injecting holes (h + ) into the valence band (VB) of GaAs through the metal mesh. It is found that injection of holes (h + ) through direct GaAs contact, rather than the metal mesh, does not yield uniform nanowires but porosify GaAs wafers due to the high cell potential. On the basis of experiments and numerical simulation for the spatial distribution of an electric field, a phenomenological model that explains the formation of GaAs NWs and their porosification behaviors is proposed. GaAs NWs exhibit excellent terahertz (THz) wave emission properties, which vary with either the length or the shape of the nanowires. By taking advantage of controlled porosification and easy transfer of GaAs NWs to foreign substrates, a flexible THz wave emitter is realized.

Photo-corrosion of anode participating in photo-electrochemical (PEC) water splitting is one of the obstacles for the long-term stability. To prevent the photo-corrosion, "electrically leaky" thick TiO2 film was deposited onto...