Electric-pulse induced resistance hysteresis switching loops for Pr0.7Ca0.3MnO3 perovskite oxide films were found to exhibit an additional sharp "shuttle tail" peak around the negative pulse maximum for films deposited in an oxygen-deficient ambient. The resistance relaxation in time of this "shuttle tail" peak as well as resistance relaxation in the transition regions of the resistance hysteresis loop show evidence of oxygen diffusion under electric pulsing, and support a proposed oxygen diffusion model with oxygen vacancy pileup at the metal electrode interface region as the active process for the nonvolatile resistance switching effect in transition-metal oxides.

We report the first direct measurements of the micro scale resistance profile between the terminals of a two terminal symmetric thin film Pr0.7Ca0.3MnO3 electrical pulse induced resistance change device composed of a Pr0.7Ca0.3MnO3 active layer. The symmetric device is one in which the electrode shape, size, composition, and deposition processing are identical. We show that under certain limitations of pulse switching voltage, such a symmetric electrical pulse induced resistance change device can exhibit either no net device resistance switching at room temperature, or bipolar switching with the resistance hysteresis curve exhibiting a "table leg" structure. The resistance measurements are made using surface scanning Kelvin probe microscopy, which allows for the measurement of the profile of resistance from one electrode, across the Pr0.7Ca0.3MnO3 material and into the second electrode, both before resistance switching and after switching. The results show that resistance switching in the symmetric device occurs primarily in the interface region within about 1 to 3 micron of the electrical contact surface. Resistance switching is also observed in the bulk Pr0.7Ca0.3MnO3 material although at a lower level. Symmetry considerations for a two terminal symmetric device that can switch resistance are discussed, and the data reported here is consistent with the symmetric model previously developed.[*]

We report the direct observation of the electric pulse induced resistancechange (EPIR) effect at the nano scale on La 1-x Sr x MnO 3 (LSMO) thin films by the current measurement AFM technique. After a switching voltage of one polarity is applied across the sample by the AFM tip, the conductivity in a local nanometer region around the AFM tip is increased, and after a switching voltage of the opposite polarity is applied, the local conductivity is reduced. This reversible resistance switching effect is observed under both continuous and short pulse voltage switching conditions. It is important for future nanoscale non-volatile memory device applications.[*]

Recent research on the resistance switching effect in manganite oxide based electric-pulse-induced resistance (EPIR) devices is being reviewed. The EPIR effect encompasses the reversible change of resistance of a thin oxide film such as Pr 1-x Ca x MnO 3 (PCMO) under the application of short, low voltage pulses. Two groups of EPIR devices have been investigated: one with the PCMO layer sandwiched between a top and a bottom electrode; the other with both electrodes on top of the PCMO thin films, which were grown on insulating substrates. I-V switching characteristics, electric pulse switching hysteresis, as well as the dynamic resistance during nano second switching pulses of the EPIR devices were measured. Temperature studies showed similar activation energies for both high and low resistance states. Resistance profile microanalysis showed resistance switching both in the interface regions of the oxide film near the electrode, as well as in the bulk of PCMO film with the major resistance change from the interface regions. The resistance switching mechanism is discussed.

Low-energy electron diffraction (LEED) is the most important technique for studying the atomic structures of crystalline surfaces. This review aims to give an introduction into the experimental, theoretical and analytical procedures needed for a successful structure determination. After a brief introduction that gives some historical background and sets the problem in perspective, the experiment is described. The fundamentals of two-dimensional crystallography are discussed and their application to LEED are described. The calculation of diffracted intensities requires the development of N-beams dynamical theory, which is discussed next, together with the need for appropriate computer programs. Since the analysis is based on trial-and-error methods some attention is paid to the development of structure models, the problems caused by the co-existence of equivalent domains, and the procedures for evaluating the postulated models. Finally, a brief discussion of the accomplishments is given which, rather than comprehensive, is an assessment of the present state of the art in surface crystallography.