Showing papers by "Mallikarjuna Rao Motapothula published in 2018"

Investigating the Role of Copper Oxide in Electrochemical CO2 Reduction in Real Time.

Abstract: Copper oxides have been of considerable interest as electrocatalysts for CO2 reduction (CO2R) in aqueous electrolytes. However, their role as an active catalyst in reducing the required overpotential and improving the selectivity of reaction compared with that of polycrystalline copper remains controversial. Here, we introduce the use of selected-ion flow tube mass spectrometry, in concert with chronopotentiometry, in situ Raman spectroscopy, and computational modeling, to investigate CO2R on Cu2O nanoneedles, Cu2O nanocrystals, and Cu2O nanoparticles. We show experimentally that the selective formation of gaseous C2 products (i.e., ethylene) in CO2R is preceded by the reduction of the copper oxide (Cu2OR) surface to metallic copper. On the basis of density functional theory modeling, CO2R products are not formed as long as Cu2O is present at the surface because Cu2OR is kinetically and energetically more favorable than CO2R.

Intrinsic hydrophilic nature of epitaxial thin-film of rare-earth oxide grown by pulsed laser deposition.

Abstract: Herein, we report a systematic study of water contact angle (WCA) of rare-earth oxide thin-films. These ultra-smooth and epitaxial thin-films were grown using pulsed laser deposition and then characterized using X-Ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), and atomic force microscopy (AFM). Through both the traditional sessile drop and the novel f–d method, we found that the films were intrinsically hydrophilic (WCA < 10°) just after being removed from the growth chamber, but their WCAs evolved with an exposure to the atmosphere with time to reach their eventual saturation values near 90° (but always stay ‘technically’ hydrophilic). X-Ray photoelectron spectroscopy analysis was used to further investigate qualitatively the nature of hydrocarbon contamination on the freshly prepared as well as the environmentally exposed REO thin-film samples as a function of the exposure time after they were removed from the deposition chamber. A clear correlation between the carbon coverage of the surface and the increase in WCA was observed for all of the rare-earth films, indicating the extrinsic nature of the surface wetting properties of these films and having no relation to the electronic configuration of the rare-earth atoms as proposed by Azimi et al.

Anatase TiO2—A Model System for Large Polaron Transport

Abstract: Large polarons have been of significant recent technological interest as they screen and protect electrons from point-scattering centers. Anatase TiO2 is a model system for studying large polarons as they can be studied systematically over a wide range of temperature and carrier density. The electronic and magneto transport properties of reduced anatase TiO2 epitaxial thin films are analyzed considering various polaronic effects. Unexpectedly, with increasing carrier concentration, the mobility increases, which rarely happens in common metallic systems. We find that the screening of the electron–phonon (e–ph) coupling by excess carriers is necessary to explain this unusual dependence. We also find that the magnetoresistance could be decomposed into a linear and a quadratic component, separately characterizing the carrier transport and trapping as a function of temperature, respectively. The various transport behaviors could be organized into a single phase diagram, which clarifies the evolution of large p...

Initial Application of Selected-Ion Flow-Tube Mass Spectrometry to Real-Time Product Detection in Electrochemical CO2 Reduction

Abstract: Author(s): Lobaccaro, P; Mandal, L; Motapothula, MR; Sherburne, M; Martin, J; Venkatesan, T; Ager, JW | Abstract: Electrochemical CO2 reduction (EC-CO2R) has seen a resurgence in interest over the past several years; however, the means of analyzing catalytically produced products continues to rely on decades-old methods such as gas chromatography, high-performance liquid chromatography, and nuclear magnetic resonance. Real-time analysis of the gaseous and liquid products of this reaction is highly desirable; however, few analytical techniques have been developed thus far to meet this need. Here, we demonstrate the first use of selected-ion flow-tube mass spectrometry (SIFT-MS) as an analytical tool capable of measuring in real time both the gas- and liquid-phase products of EC-CO2R in aqueous solution. SIFT-MS uses well-understood ion–molecule reactions to enable the analysis of similar multicomponent mixtures by preventing substantial fragmentation of the analyte. We lay out the framework in which to evaluate the tool's capabilities and show that the C1–C3 hydrocarbon, alcohol, and aldehyde products of CO2R should be quantitatively detectable.

Identification of Biofilm Inhibitors by Screening Combinatorial Libraries of Metal Oxide Thin Films.

Abstract: With the rise in nosocomial infections worldwide, research on materials with an intrinsic ability to inhibit biofilm formation has been generating a great deal of interest. In the present work, we describe how thin film material libraries generated by pulsed laser deposition can be used for simultaneously screening several novel metal oxide mixtures that inhibit biofilm formation in a common human pathogen, Salmonella enterica serovar Typhimurium. We discovered that in a material library constructed using two metal oxides, the net effect on biofilm formation can be modeled as an addition of the activities of the individual oxides weighted to their relative composition at that particular point on the library. In contrast, for similar material libraries constructed using three metal oxides, there was a nonlinear relation between the amount of dominant metal oxide and the formation of Salmonella biofilms. This nonlinearity resulted in several useful metal oxide combinations that were not expected from the we...

Direct observation of anisotropic small-hole polarons in an orthorhombic structure of BiV O 4 films

Abstract: Here, we report an anisotropic small-hole polaron in an orthorhombic structure of $\mathrm{BiV}{\mathrm{O}}_{4}$ films grown by pulsed-laser deposition on yttrium-doped zirconium oxide substrate. The polaronic state and electronic structure of $\mathrm{BiV}{\mathrm{O}}_{4}$ films are revealed using a combination of polarization-dependent x-ray absorption spectroscopy at $\mathrm{V}\phantom{\rule{0.16em}{0ex}}{L}_{3,2}$ edges, spectroscopic ellipsometry, x-ray photoemission spectroscopies, and high-resolution x-ray diffraction with the support of first-principles calculations. We find that in the orthorhombic phase, which is slightly different from the conventional pucherite structure, the unoccupied V 3d orbitals and charge inhomogeneities lead to an anisotropic small-hole polaron state. Our result shows the importance of the interplay of charge and lattice for the formation of a hole polaronic state, which has a significant impact in the electrical conductivity of $\mathrm{BiV}{\mathrm{O}}_{4}$, hence its potential use as a photoanode for water splitting.

A study of small impact parameter ion channeling effects in thin crystals

Abstract: We have recorded channeling patterns produced by 1–2 MeV protons aligned with ⟨1 1 1⟩ axes in 55 nm thick silicon crystals which exhibit characteristic angular structure for deflection angles up to and beyond the axial critical angle, ψ a . Such large angular deflections are produced by ions incident on atomic strings with small impact parameters, resulting in trajectories which pass through several radial rings of atomic strings before exiting the thin crystal. Each ring may focus, steer or scatter the channeled ions in the transverse direction and the resulting characteristic angular structure beyond 0.6ψ a at different depths can be related to peaks and troughs in the nuclear encounter probability. Such “radial focusing” underlies other axial channeling phenomena in thin crystals including planar channeling of small impact parameter trajectories, peaks around the azimuthal distribution at small tilts and large shoulders in the nuclear encounter probability at tilts beyond ψ a .

Corrigendum: Robust resistive memory devices using solution-processable metal-coordinated azo aromatics.

Abstract: Nature Materials 16, 1216–1224 (2017); published online 23 October 2017; corrected after print 4 December 2017. In the version of this Article originally published, the x-axis units of Fig. 3a were incorrectly given as ms, and should have read μs. This has now been corrected. Two places in the text also needed amending to reflect this change: the penultimate sentence of Fig.