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Resistive random access memory (RRAM) technologies based on non-volatile resistive filament redox switching oxides have the potential of drastically improving the performance of future mass-storage solutions. However, the physico-chemical properties of the TiN bottom metal electrode (BME) can significantly alter the resistive switching (RS) behavior of the oxygen-vacancy RRAM devices, yet the correlation between RS and the physico-chemical properties of TiN and HfOx/TiN interface remains unclear. Here, we establish this particular correlation via detailed material and electrical characterization for the purpose of achieving further performance enhancement of the stack integration. Two types of RRAM stacks were fabricated where the TiN BME was fabricated by physical vapor deposition (PVD) and atomic layer deposition (ALD), respectively. The HfOx layer in HfOx/PVD-TiN is more oxygen deficient than that of the HfOx/ALD-TiN because of more defective PVD-TiN and probably because pristine ALD-TiN has a thicker TiO2 overlayer. Higher concentration of oxygen vacancies induces a larger magnitude of band bending at the HfOx/PVD-TiN interface and leads to the formation of a higher Schottky barrier. Pulsed endurance measurements of up to 106 switches, with 10 μA ± 1.0 V pulses, demonstrate the potential of the studied ultra-thin-HfOx/TiN device stack for dense, large scale, and low-power memory integration.

InGaAs nanowires grown by Metalorganic Vapor Phase Epitaxy (MOVPE) are promising candidates in future device technologies. The control of the chemical composition of InGaAs nanowires is not trivial due to the In atom diffusion from the substrate, which causes significant variations in the chemical composition along the nanowire. In this work, we report on the growth of InGaAs nanowires on (111)B InAs substrates followed by the characterization using high-resolution x-ray diffraction (HRXRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) as well as scanning transmission electron microscopy (STEM) in combination with energy dispersive X-ray spectroscopy (EDS). By detailed analyses of the HRXRD spectra and their variations with nanowires grown for different times, fundamental insight was gained into tapering formation and chemical composition gradient of the nanowires. The measurements show that acceptable uniformity of In and Ga concentrations along InGaAs nanowires can be achieved, and the maximum achievable nanowire length without tapering depends on the nanowire density. Finally, by carefully choosing the growth conditions, the morphology of the InGaAs nanowire can be further optimized. (C) 2 013 Elsevier B.V. All rights reserved (Less)

We propose a geometric model to estimate the contribution of substrate surface diffusion to growth of dense nanowire arrays using metalorganic vapour phase epitaxy. It is shown that the nanowire mantle area becomes the most significant collector of growth material when the nanowire diameter is large and the inter-nanowire pitch is small. It is concluded that this growth regime is important for the array geometries typically used for optoelectronic and photovoltaic applications of nanowires. The growth rate under these conditions is also not constant with time, due to the growing nanowire mantle area. This result was confirmed by experiments in which dense arrays of InAs nanowires were grown and the nanowire growth rate was measured as a function of time. (C) 2013 Elsevier B.V. All rights reserved. (Less)

Summary The highly conserved ClpP protease consists of two heptameric rings that interact by the interdigitation of an α-helix β strand handle domain motif to form a tetradecameric cylinder. We previously proposed that protease dynamics results in the temporary unstructuring of interacting pairs of handle domains, opening transient equatorial side pores that allow for peptide egress. Here, we report the structure of an Escherichia coli ClpP mutant in which each opposing pair of protomers is linked by a disulfide bond. This structure resembles the compact structures of Streptococcus pneumoniae , Mycobacterium tuberculosis , and Plasmodium falciparum ClpPs, rather than the active, extended structures that have previously been determined for E. coli ClpPs. The structural data, along with normal mode analysis, support a model whereby the ClpP cylinder switches dynamically between an active extended state required for substrate degradation and an inactive compact state allowing peptide product release.

Adsorption of 0.2 ML Na on Al(1 0 0) at room temperature yields a disordered Al(1 0 0)-(1 x 1)-Na phase, which transforms reversibly to a well-ordered Al(1 0 0)-(root5 x root5)R27degrees-Na phase on cooling below 250 K. Based on low energy electron diffraction (LEED) and high resolution core-level spectroscopy (HRCLS) measurements, and on ab initio calculations, it is concluded that the structure of the Al(1 0 0)-(root5 x root5-)R27degrees-Na phase consists of Na atoms occupying substitutional sites. The structural parameters obtained from LEED and density functional theory analyses are in quantitative agreement. Adsorption of 0.2 ML Na at 100 K yields an Al(1 0 0)-c(2 x 2)-Na island structure, which transforms irreversibly into the (root5 x root5)R27degrees-Na structure by annealing above 190 K. The nature of the reversible and irreversible phase transformations to the (root5 x root5)R27degrees structure is investigated by HRCLS and LEED. (C) 2002 Elsevier Science B.V. All rights reserved.

We have studied the CO/Mo(1 1 0) adsorption system at different sample temperatures by high-resolution core-level spectroscopy and near-edge X-ray-absorption fine-structure measurements. We demonstrate that CO molecules having different tilt angles with respect to the surface normal may be assigned to different components of the C 1s core-level spectra. The tilt of the CO molecules is shown to depend on the CO coverage. The thermally induced dissociation of CO is studied and is shown to differ at low and high initial CO coverages. At low coverage CO dissociation starts already at temperatures as low as 125 K whereas at saturation CO coverage no dissociation occurs below 280 K. The reasons for this difference in dissociation behavior are discussed and it is concluded that steric effects play a large role.

High resolution core level photoemission is used to measure the equilibrium coverages of CO on Rh(1 1 1) at different sample temperatures and CO background pressures. Use of the chemical shifts of the C 1s binding energy allows us to divide the total CO coverage into separate coverages for the different adsorption sites of CO on Rh(1 1 1). A Clausius–Clapeyron analysis of isosteres constructed from the measured isotherms for the total CO coverage is used to derive the coverage dependence of the isosteric heat of adsorption E ads for this adsorption system. The present results are found to agree well with a recent calculation of the adsorption energy for the Rh(1 1 1)-(2×2)-1CO structure at 0.25 ML (monolayer, ML). Furthermore, the present determination of E ads is consistent with a recent measurement of the zero coverage limit E ads ( θ =0 ML) but is inconsistent with some previous determinations of this quantity. The coverage variation of the isosteric heat of adsorption is briefly discussed and put in relation to the relative occupations of different sites by the CO molecules.

High-resolution core-level photoemission at an energy resolution better than the intrinsic width of the C 1s level has been used to study the CO/Rh(1 1 1) overlayer system. C 1s spectra have been measured in a large CO coverage range; from low coverages, where the CO molecules only adsorb in on-top positions, to saturation coverage, where CO molecules occupy both on-top and threefold hollow sites. Fine structure components due to vibrational excitation of the C–O stretch mode are clearly resolved in the emission peak from each site. The vibrational splittings and intensity ratios are found to be different for the different adsorption sites. A third C 1s component, which has not been resolved earlier, is found at intermediate CO coverages. Some possible explanations for the origin of this extra component are discussed. In the light of its binding energy and vibrational energy in photoemission, together with supporting evidence from high-resolution electron energy loss spectroscopy data and photoelectron diffraction, this is assigned to bridging CO species at intermediate coverages.

By combining high-resolution X-ray photoelectron and electron energy loss spectroscopies a comprehensive analysis of the adsorption of CO on Pd(1 1 1) at 300 K has been performed. The characteristic fingerprints for various CO‐ Pd(1 1 1) bonding configurations have been identified from the decomposition analysis of the adsorbate C 1s and the substrate Pd 3d5=2 core-level photoemission spectra obtained after CO adsorption at 120 K. The cO4 2U structure at 0.5 monolayer (ML) and theO2 2U-3CO structure at 0.75 ML formed at low temperature have been used for calibration purposes. The core-level results are consistent with CO adsorbing in a mixture of fcc and hcp threefold hollow sites in the cO4 2U structure and of hollow and on-top sites in theO2 2U structure, as reported in the literature. For CO adsorption at 300 K, a diAerent site occupation is evidenced by the presence of two components in the C 1s and Pd 3d5=2 core-level and C‐O stretching vibration lineshapes. At coverages up to 0.1 ML only fcc threefold hollow sites in a O AAA