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ASU Scholarship Showcase


This growing collection consists of scholarly works authored by ASU-affiliated faculty, students and community members, and contains many open access articles. ASU-affiliated authors are encouraged to Share Your Work in the ASU Digital Repository.


Date Range
2014 2016


To probe the nature of metal-catalysed processes and to design better metal-based catalysts, atomic scale understanding of catalytic processes is highly desirable. Here we use aberration-corrected environmental transmission electron microscopy to investigate the atomic scale processes of silver-based nanoparticles, which catalyse the oxidation of multi-wall carbon nanotubes. A direct semi-quantitative estimate of the oxidized carbon atoms by silver-based nanoparticles is achieved. A mechanism similar to the Mars–van Krevelen process is invoked to explain the catalytic oxidation process. Theoretical calculations, together with the experimental data, suggest that the oxygen molecules dissociate on the surface of silver nanoparticles and diffuse through the …

Contributors
Yue, Yonghai, Yuchi, Datong, Guan, Pengfei, et al.
Created Date
2016-07-13

The development of non-volatile logic through direct coupling of spontaneous ferroelectric polarization with semiconductor charge carriers is nontrivial, with many issues, including epitaxial ferroelectric growth, demonstration of ferroelectric switching and measurable semiconductor modulation. Here we report a true ferroelectric field effect—carrier density modulation in an underlying Ge(001) substrate by switching of the ferroelectric polarization in epitaxial c-axis-oriented BaTiO[subscript 3] grown by molecular beam epitaxy. Using the density functional theory, we demonstrate that switching of BaTiO[subscript 3] polarization results in a large electric potential change in Ge. Aberration-corrected electron microscopy confirms BaTiO[subscript 3] tetragonality and the absence of any low-permittivity interlayer …

Contributors
Ponath, Patrick, Fredrickson, Kurt, Posadas, Agham B., et al.
Created Date
2015-01-01

The compositional dependence of the lowest direct and indirect band gaps in Ge[subscript 1−y]Sn[subscript y] alloys has been determined from room-temperature photoluminescence measurements. This technique is particularly attractive for a comparison of the two transitions because distinct features in the spectra can be associated with the direct and indirect gaps. However, detailed modeling of these room temperature spectra is required to extract the band gap values with the high accuracy required to determine the Sn concentration y[subscript c] at which the alloy becomes a direct gap semiconductor. For the direct gap, this is accomplished using a microscopic model that allows …

Contributors
Jiang, L., Gallagher, J. D., Senaratne, Charutha Lasitha, et al.
Created Date
2014-11-01

Earth-abundant sustainable inorganic thin-film solar cells, independent of precious elements, pivot on a marginal material phase space targeting specific compounds. Advanced materials characterization efforts are necessary to expose the roles of microstructure, chemistry, and interfaces. Herein, the earth-abundant solar cell device, Cu[subscript 2]ZnSnS[subscript (4–x)]Se[subscript x], is reported, which shows a high abundance of secondary phases compared to similarly grown Cu[subscript 2]ZnSnSe[subscript 4].

Contributors
Aguiar, Jeffery A., Patel, Maulik, Aoki, Toshihiro, et al.
Created Date
2016-02-02

Vibrational spectroscopy in the electron microscope would be transformative in the study of biological samples, provided that radiation damage could be prevented. However, electron beams typically create high-energy excitations that severely accelerate sample degradation. Here this major difficulty is overcome using an ‘aloof’ electron beam, positioned tens of nanometres away from the sample: high-energy excitations are suppressed, while vibrational modes of energies <1 eV can be ‘safely’ investigated. To demonstrate the potential of aloof spectroscopy, we record electron energy loss spectra from biogenic guanine crystals in their native state, resolving their characteristic C–H, N–H and C=O vibrational signatures with no …

Contributors
Rez, Peter, Aoki, Toshihiro, March, Katia, et al.
Created Date
2016-03-10

The emission properties of GeSn heterostructure pin diodes have been investigated. The devices contain thick (400–600 nm) Ge [subscript 1− y] Sn [subscript y] i-layers spanning a broad compositional range below and above the crossover Sn concentration y [subscript c] where the Ge [subscript 1− y] Sn [subscript y] alloy becomes a direct-gap material. These results are made possible by an optimized device architecture containing a single defected interface thereby mitigating the deleterious effects of mismatch-induced defects. The observed emission intensities as a function of composition show the contributions from two separate trends: an increase in direct gap emission as …

Contributors
Gallagher, J. D., Senaratne, Charutha Lasitha, Sims, Patrick, et al.
Created Date
2015-03-02

Novel hydride chemistries are employed to deposit light-emitting Ge [subscript 1- y] Sn [subscript y] alloys with y ≤ 0.1 by Ultra-High Vacuum Chemical Vapor Deposition (UHV-CVD) on Ge-buffered Si wafers. The properties of the resultant materials are systematically compared with similar alloys grown directly on Si wafers. The fundamental difference between the two systems is a fivefold (and higher) decrease in lattice mismatch between film and virtual substrate, allowing direct integration of bulk-like crystals with planar surfaces and relatively low dislocation densities. For y ≤ 0.06, the CVD precursors used were digermane Ge [subscript 2]H[subscript 6] and deuterated stannane …

Contributors
Senaratne, Charutha Lasitha, Gallagher, J. D., Jiang, Liying, et al.
Created Date
2014-10-07

The pore- and micro-structural features of a novel binding material based on the carbonation of waste metallic iron powder are reported in this paper. The binder contains metallic iron powder as the major ingredient, followed by additives containing silica and alumina to facilitate favorable reaction product formation. Compressive strengths sufficient for a majority of concrete applications are attained. The material pore structure is investigated primarily through mercury intrusion porosimetry whereas electron microscopy is used for microstructural characterization. Reduction in the overall porosity and the average pore size with an increase in carbonation duration from 1 day to 4 days is …

Contributors
Das, Sumanta, Stone, David, Convey, Diana, et al.
Created Date
2014-12-01

The Ni/NiO core/shell structure is one of the most efficient co-catalysts for solar water splitting when coupled with suitable semiconducting oxides. It has been shown that pretreated Ni/NiO core/shell structures are more active than pure Ni metal, pure NiO or mixed dispersion of Ni metal and NiO nanoparticles. However, Ni/NiO core/shell structures on TiO2 are only able to generate H2 but not O2 in aqueous water. The nature of the hydrogen evolution reaction in these systems was investigated by correlating photochemical H2 production with atomic resolution structure determined with aberration corrected electron microscopy. It was found that the core/shell structure …

Contributors
Crozier, Peter, Zhang, Liuxian, Aoki, Toshihiro, et al.
Created Date
2015

We present two-dimensional Mg(OH)[subscript 2] sheets and their vertical heterojunctions with CVD-MoS[subscript 2] for the first time as flexible 2D insulators with anomalous lattice vibration and chemical and physical properties. New hydrothermal crystal growth technique enabled isolation of environmentally stable monolayer Mg(OH)[subscript 2] sheets. Raman spectroscopy and vibrational calculations reveal that the lattice vibrations of Mg(OH)[subscript 2] have fundamentally different signature peaks and dimensionality effects compared to other 2D material systems known to date. Sub-wavelength electron energy-loss spectroscopy measurements and theoretical calculations show that Mg(OH)[subscript 2] is a 6 eV direct-gap insulator in 2D, and its optical band gap displays …

Contributors
Tuna, Aslihan, Wu, Kedi, Sahin, Hasan, et al.
Created Date
2016-02-05