Abstract:Nanoscale control of the metal-insulator transition in LaAlO 3 / SrTiO 3 heterostructures can be achieved using local voltages applied by a conductive atomic-force microscope probe. One proposed mechanism for the writing and erasing process involves an adsorbed H 2 O layer at the top LaAlO 3 surface. In this picture, water molecules dissociates into OH -and H + which are then selectively removed by a biased AFM probe. To test this mechanism, writing and erasing experiments are performed in a vacuum AFM using various gas mixtures. Writing ability is suppressed in those environments where H 2 O is not present. The stability of written nanostructures is found to be strongly associated with the ambient environment. The self-erasure process in air can be strongly suppressed by creating a modest vacuum or replacing the humid air with dry inert gas. These experiments provide strong constraints for theories of both the writing process as well as the origin of interfacial conductance. an insulating state. We refer to this process as a "water cycle" because it permits multiple writing and erasing without physical modification of the oxide heterostructure.Here we investigate the writing and erasing process on 3uc-LAO/STO heterostructures under a variety of atmospheric conditions, in order to constrain physical models of the writing and erasing procedure and the origin of the interfacial electron gas. Thin films (3 u.c.) of LaAlO 3 were deposited on a TiO 2 -terminated (001) SrTiO 3 substrates by pulsed laser deposition with in situ high pressure reflection high energy electron diffraction (RHEED) [18]. Growth was at a temperature of 550°C and O 2 pressure of 1×10 -3 Torr. 4After growth, electrical contacts to the interface were prepared by milling 25nm deep trenches via an Ar-ion mill and filling them with Au/Ti bilayer (2nm adhesion Ti layer and 23nm Au layer).To perform c-AFM experiments, a vacuum AFM ( FIG. 1(a)) is employed that is capable of operation down to 10 -5 Torr and allows controlled introduction of various gases. Writing and erasing experiments (

As a room-temperature multiferroic, BiFeO 3 has been intensively investigated for both magnetoelectric devices and non-volatile ferroelectric memory applications. [1][2][3] BiFeO 3 , having a rhombohedral unit cell, has antiferromagnetic, ferroelectric and ferroelastic order parameters. Since BiFeO 3 exhibits coupling between spontaneous electric polarization in the [111] direction and the (111) antiferromagnetic planes, control of the magnetic order can be achieved by ferroelectric domain reorientation resulting from polarization switching by an external electric fi eld. [ 4 ] This possibility of controlling the magnetism by an electric fi eld has been demonstrated at room temperature in single crystals [ 5 , 6 ] and thin fi lms. [ 4 , 7 ] In addition, BiFeO 3 has the largest remanent polarization ( P r ∼ 100 μ C cm − 2 ) along the [111] polar direction among all known ferroelectrics, [1][2][3] which is a promising feature as a lead-free material for ferroelectric random access memory (FeRAM). Utilizing the large remanent polarization of BiFeO 3 would enable further reduction of the cell size limited by conventional ferroelectrics such as BaTiO 3 and Pb(Zr,Ti)O 3 .Both magnetoelectric and ferroelectric memory devices have the same control knob: polarization switching by an applied electric fi eld. [1][2][3][4][5][6][7] Due to the rhombohedral symmetry of BiFeO 3 , there are four ferroelastic variances and three different polarization switching events: (1) 71 ° switching from r1 − to r3 + , (2) 109 ° switching from r1 − to r2 + (or r4 + ), and (3) 180 o switching from r1 − to r1 + (the superscript + and -stand for up and down polarization, respectively). Each switching path is coupled to a different reorientation of the BiFeO 3 unit cell, and hence different coupling to the magnetic order [ 4 ] as well as different magnitudes of switchable polarization. [ 8 , 9 ] A degradation of the ferroelectric properties of BiFeO 3 will result in losing controllability of magnetic order switching in magnetoelectric devices and capacity for information storage in ferroelectric memory devices. Especially, polarization fatigue [ 10 , 11 ] will directly restrict the reliability of the actual devices. Hence it is important to understand the intrinsic fatigue behavior of each polarization switching path in BiFeO 3 thin fi lms. In this communication, we report polarization fatigue in BiFeO 3 that depends on switching path, and propose a fatigue model which will broaden our understanding of the fatigue phenomenon in low-symmetry materials.Previously, there were reports on fatigue characteristics of rhombohedral ferroelectrics: ferroelastic domain evolution with polarization fatigue in textured fi lms [ 12 , 13 ] and ceramics [ 14 , 15 ] of PZN-PT, and orientation dependence showing (111)-oriented samples are more easily fatigued than (001)-oriented ones in PZN-PT [16][17][18] and BiFeO 3 . [ 19 ] In order to study the intrinsic behavior of switching-path dependent fatigue, it is crucial (1) to control a single polarization sw...

The resistance switching current-voltage (I-V) characteristics in polycrystalline NiO films were investigated in the temperature range of 10K<T<300K. Very clear reversible resistive switching phenomena were observed in the entire temperature range. An analysis of the temperature dependence of the resistance switching transport revealed additional features, not reported in previous studies, that weak metallic conduction and correlated barrier polaron hopping coexist in the high-resistance off state and that relative dominance depends on the temperature and defect configuration. In addition, the authors propose that metallic Ni defects, existing near polycrystalline (or granular) boundaries, play a key role in the formation of a metallic channel.

Devices that confine and process single electrons represent an important scaling limit of electronics. Such devices have been realized in a variety of materials and exhibit remarkable electronic, optical and spintronic properties. Here, we use an atomic force microscope tip to reversibly 'sketch' single-electron transistors by controlling a metal-insulator transition at the interface of two oxides. In these devices, single electrons tunnel resonantly between source and drain electrodes through a conducting oxide island with a diameter of ∼1.5 nm. We demonstrate control over the number of electrons on the island using bottom- and side-gate electrodes, and observe hysteresis in electron occupation that is attributed to ferroelectricity within the oxide heterostructure. These single-electron devices may find use as ultradense non-volatile memories, nanoscale hybrid piezoelectric and charge sensors, as well as building blocks in quantum information processing and simulation platforms.

NiO films were prepared on Pt∕Ti∕SiO2∕Si substrates by rf reactive sputtering. The voltage-current characteristics of the Pt∕NiO∕Pt structures showed reproducible resistive switching behaviors at room temperature. The high- and low-resistance states were retained without applying an external bias voltage; the high- to low-resistance ratio was greater than 10. To investigate the influence of the oxygen content on the electrical properties, voltage-current characteristics of NiO films grown at various oxygen contents were investigated. As oxygen content increased from 5% to 10%, the resistance value of the NiO film drastically increased, and a resistive switching behavior was observed. However, as the oxygen content increased to 20%, the resistive switching behavior disappeared. The change in switching behavior was discussed in terms of Ni vacancies and compensating holes inside the NiO film. In addition, the memory properties of NiO-based resistive random-access memory were also investigated.