1,018 research outputs found
Structural Properties and Relative Stability of (Meta)Stable Ordered, Partially-ordered and Disordered Al-Li Alloy Phases
We resolve issues that have plagued reliable prediction of relative phase
stability for solid-solutions and compounds. Due to its commercially important
phase diagram, we showcase Al-Li system because historically density-functional
theory (DFT) results show large scatter and limited success in predicting the
structural properties and stability of solid-solutions relative to ordered
compounds. Using recent advances in an optimal basis-set representation of the
topology of electronic charge density (and, hence, atomic size), we present DFT
results that agree reasonably well with all known experimental data for the
structural properties and formation energies of ordered, off-stoichiometric
partially-ordered and disordered alloys, opening the way for reliable study in
complex alloys.Comment: 7 pages, 2 figures, 2 Table
Anodic dissolution of metals in oxide-free cryolite melts
The anodic behavior of metals in molten cryolite-alumina melts has been investigated mostly for use as inert anodes for the Hall-Héroult process. In the present work, gold, platinum, palladium, copper, tungsten, nickel, cobalt and iron metal electrodes were anodically polarized in an oxide-free cryolite melt (11%wt. excess AlF3 ; 5%wt. CaF2) at 1273 K. The aim of the experiments was to characterize the oxidation reactions of the metals occurring without the effect of oxygen-containing dissolved species. The anodic dissolution of each metal was demonstrated, and electrochemical reactions were assigned using reversible potential calculation. The relative stability of metals as well as the possibility of generating pure fluorine is discussed
High-fidelity simulations of CdTe vapor deposition from a new bond-order potential-based molecular dynamics method
CdTe has been a special semiconductor for constructing the lowest-cost solar
cells and the CdTe-based Cd1-xZnxTe alloy has been the leading semiconductor
for radiation detection applications. The performance currently achieved for
the materials, however, is still far below the theoretical expectations. This
is because the property-limiting nanoscale defects that are easily formed
during the growth of CdTe crystals are difficult to explore in experiments.
Here we demonstrate the capability of a bond order potential-based molecular
dynamics method for predicting the crystalline growth of CdTe films during
vapor deposition simulations. Such a method may begin to enable defects
generated during vapor deposition of CdTe crystals to be accurately explored
Study of Oxidation and Combustion Characteristics of Iron Nanoparticles under Idealized and Enginelike Conditions
This document is the Accepted Manuscript version of a Published Work that appeared in final form in
Energy Fuels, copyright © American Chemical Society after peer review and technical editing by the publisher.[EN] The present work includes findings from proof-of-principle feasibility studies on iron nanopowder combustion under idealized, enginelike, and real engine conditions. The study was conducted under the scope of recent interest in metallic nanoparticles as alternative fuels for internal combustion engines. More specifically, Fe nanoparticles with different morphologies and average primary particle sizes ranging from 25 to 85 nm were studied with respect to their oxidation characteristics via thermogravimetric analysis as well as in customized shock tube, constant-volume vessel, and compression-ignition (CI) engine configurations. Combusted powder samples were in all cases examined via in situ and ex situ techniques for the identification of combustion products and their morphologies. The findings facilitated the determination of the main phenomena involved during oxidation. The results verified that combustion of Fe nanoparticles in a slightly modified CI engine is feasible, albeit with various technological challenges related to ignition and scavenging that inhibit combustion quality.The authors thank the European Commission for partial
funding of this work through the Project “COMETNANO”
(FP7-NMP4-SL-2009-229063).Mandilas, C.; Karagiannakis, G.; Konstandopoulos, AG.; Beatrice, C.; Lazzaro, M.; Di Blasio, G.; Molina, S.... (2016). Study of Oxidation and Combustion Characteristics of Iron Nanoparticles under Idealized and Enginelike Conditions. Energy and Fuels. 30(5):4318-4330. https://doi.org/10.1021/acs.energyfuels.6b00121S4318433030
Epitaxial Zn(x)Fe(3-x)O(4) Thin Films: A Spintronic Material with Tunable Electrical and Magnetic Properties
The ferrimagnetic spinel oxide Zn(x)Fe(3-x)O(4) combines high Curie
temperature and spin polarization with tunable electrical and magnetic
properties, making it a promising functional material for spintronic devices.
We have grown epitaxial thin films with 0<=x<=0.9 on MgO(001) substrates with
excellent structural properties both in pure Ar atmosphere and an Ar/O2 mixture
by laser molecular beam epitaxy. We find that the electrical conductivity and
the saturation magnetization can be tuned over a wide range during growth. Our
extensive characterization of the films provides a clear picture of the
underlying physics of this spinel ferrimagnet with antiparallel Fe moments on
the A and B sublattice: (i) Zn substitution removes both Fe3+ moments from the
A sublattice and itinerant charge carriers from the B sublattice, (ii) growth
in finite oxygen partial pressure generates Fe vacancies on the B sublattice
also removing itinerant charge carriers, and (iii) application of both Zn
substitution and excess oxygen results in a compensation effect as Zn
substitution partially removes the Fe vacancies. A decrease (increase) of
charge carrier density results in a weakening (strengthening) of double
exchange and thereby a decrease (increase) of conductivity and the saturation
magnetization. This scenario is confirmed by the observation that the
saturation magnetization scales with the longitudinal conductivity. The
combination of tailored films with semiconductor materials such as ZnO in
multi-functional heterostructures seems to be particularly appealing.Comment: 13 pages, 8 figures, Hall effect data removed, anti-phase boundary
discussion added, accepted for publication in PRB79 (2009
Edge Contacts to Atomically Precise Graphene Nanoribbons.
Bottom-up-synthesized graphene nanoribbons (GNRs) are an emerging class of designer quantum materials that possess superior properties, including atomically controlled uniformity and chemically tunable electronic properties. GNR-based devices are promising candidates for next-generation electronic, spintronic, and thermoelectric applications. However, due to their extremely small size, making electrical contact with GNRs remains a major challenge. Currently, the most commonly used methods are top metallic electrodes and bottom graphene electrodes, but for both, the contact resistance is expected to scale with overlap area. Here, we develop metallic edge contacts to contact nine-atom-wide armchair GNRs (9-AGNRs) after encapsulation in hexagonal boron-nitride (h-BN), resulting in ultrashort contact lengths. We find that charge transport in our devices occurs via two different mechanisms: at low temperatures (9 K), charges flow through single GNRs, resulting in quantum dot (QD) behavior with well-defined Coulomb diamonds (CDs), with addition energies in the range of 16 to 400 meV. For temperatures above 100 K, a combination of temperature-activated hopping and polaron-assisted tunneling takes over, with charges being able to flow through a network of 9-AGNRs across distances significantly exceeding the length of individual GNRs. At room temperature, our short-channel field-effect transistor devices exhibit on/off ratios as high as 3 × 105 with on-state current up to 50 nA at 0.2 V. Moreover, we find that the contact performance of our edge-contact devices is comparable to that of top/bottom contact geometries but with a significantly reduced footprint. Overall, our work demonstrates that 9-AGNRs can be contacted at their ends in ultra-short-channel FET devices while being encapsulated in h-BN
Wettability of amorphous and nanocrystalline Fe78B13Si9 substrates by molten Sn and Bi
The wettability of amorphous and annealing-induced nanocrystalline Fe78B13Si9 ribbons by molten Sn and Bi at 600 K was measured using an improved sessile drop method. The results demonstrate that the structural relaxation and crystallization in the amorphous substrates do not substantially change the wettability with molten Bi because of their invariable physical interaction, but remarkably deteriorate the wettability and interfacial bonding with molten Sn as a result of changing a chemical interaction to a physical one for the atoms at the interface
Seeking legitimacy through CSR: Institutional Pressures and Corporate Responses of Multinationals in Sri Lanka
Arguably, the corporate social responsibility (CSR) practices of multinational enterprises (MNEs) are influenced by a wide range of both internal and external factors. Perhaps most critical among the exogenous forces operating on MNEs are those exerted by state and other key institutional actors in host countries. Crucially, academic research conducted to date offers little data about how MNEs use their CSR activities to strategically manage their relationship with those actors in order to gain legitimisation advantages in host countries. This paper addresses that gap by exploring interactions between external institutional pressures and firm-level CSR activities, which take the form of community initiatives, to examine how MNEs develop their legitimacy-seeking policies and practices. In focusing on a developing country, Sri Lanka, this paper provides valuable insights into how MNEs instrumentally utilise community initiatives in a country where relationship-building with governmental and other powerful non-governmental actors can be vitally important for the long-term viability of the business. Drawing on neo-institutional theory and CSR literature, this paper examines and contributes to the embryonic but emerging debate about the instrumental and political implications of CSR. The evidence presented and discussed here reveals the extent to which, and the reasons why, MNEs engage in complex legitimacy-seeking relationships with Sri Lankan institutions
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