230 results found
Chang V, Noakes TCQ, Harrison NM, 2018, Work function and quantum efficiency study of metal oxide thin films on Ag(100), Physical Review B, Vol: 97, ISSN: 2469-9950
© 2018 American Physical Society. Increasing the quantum efficiency (QE) of metal photocathodes is in the design and development of photocathodes for free-electron laser applications. The growth of metal oxide thin films on certain metal surfaces has previously been shown to reduce the work function (WF). Using a photoemission model B. Camino [Comput. Mater. Sci. 122, 331 (2016)CMMSEM0927-025610.1016/j.commatsci.2016.05.025] based on the three-step model combined with density functional theory calculations we predict that the growth of a finite number of MgO(100) or BaO(100) layers on the Ag(100) surface increases significantly the QE compared with the clean Ag(100) surface for a photon energy of 4.7 eV. Different mechanisms for affecting the QE are identified for the different metal oxide thin films. The addition of MgO(100) increases the QE due to the reduction of the WF and the direct excitation of electrons from the Ag surface to the MgO conduction band. For BaO(100) thin films, an additional mechanism is in operation as the oxide film also photoemits at this energy. We also note that a significant increase in the QE for photons with an energy of a few eV above the WF is achieved due to an increase in the inelastic mean-free path of the electrons.
Jong U-G, Yu C-J, Ri G-C, et al., 2018, Influence of water intercalation and hydration on chemical decomposition and ion transport in methylammonium lead halide perovskites, Publisher: ROYAL SOC CHEMISTRY
Savazzi F, Risplendi F, Mallia G, et al., 2018, Unravelling Some of the Structure-Property Relationships in Graphene Oxide at Low Degree of Oxidation, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, Vol: 9, Pages: 1746-1749, ISSN: 1948-7185
Adjiman CS, Harrison NM, Weider SZ, 2017, Molecular science and engineering: a powerful transdisciplinary approach to solving grand challenges, Briefing paper, 1
The concept of molecular science and engineering – melding a deep understanding of molecular science with an engineering mind-set – is emerging as a powerful way to create novel, effective and sustainable solutions to global grand challenges, such as the growing threat of antimicrobial resistance. By blurring the boundaries between scientificand engineering disciplines, in this holistic approach, final function and end-use requirements become an integral part of the underlying scientific research. Commercially ready materials can thus become a reality in an accelerated, flexible and economic manner. In other words, molecular science and engineering can fundamentally alter the way molecules are identified and designed for real-world usage. It is not enough to simply make molecules; we must make molecules work for a complex world.The notion of bringing researchers, industry and government communities together to work on grand challenges has a long and illustrious history – think, for instance, of the Manhattan Project, the industrial scale-up of penicillin and the Moon landings. More recently, the idea of ‘convergence’ – tackling grand challenges with a multifaceted array of scientists, engineers, clinicians and beyond – has become more formally recognised as a valuable way to stimulate societally important and ground-breaking research. Molecular science and engineering is a specific, yet far-reaching, part of this convergence landscape.Within the growing worldwide molecular science and engineering community, the Institute for Molecular Science and Engineering (IMSE) was founded in 2015 as Imperial College London’s newest Global Institute. The Institute’s overarching aim is to bring the College’s engineers, scientists, medics and business researchers together with awide array of external stakeholders – and to remove the boundaries between these disciplines – to find innovative molecular-based scie
Jong UG, Yu CJ, Ri GC, et al., 2017, Influence of water intercalation and hydration on chemical decomposition and ion transport in methylammonium lead halide perovskites, Journal of Materials Chemistry A, Vol: 6, Pages: 1067-1074, ISSN: 2050-7496
The application of methylammonium (MA) lead halide perovskites, CH3NH3PbX3 (X = I, Br, Cl), in perovskite solar cells has made great recent progress in performance efficiency during recent years. However, the rapid decomposition of these materials in humid environments hinders outdoor application, and thus, a comprehensive understanding of the degradation mechanism is required. We investigate the effect of water intercalation and hydration of the decomposition and ion migration of CH3NH3PbX3 using first-principles calculations. We find that water interacts with PbX6 and MA through hydrogen bonding, and the former interaction increases gradually, while the latter hardly changes when going from X = I to Br and to Cl. Thermodynamic calculations indicate that water exothermically intercalates into the perovskite, and suggest that the water intercalated and monohydrated compounds are stable with respect to decomposition. More importantly, the water intercalation reduces the activation energies for vacancy-mediated ion migration, which become higher going from X = I to Br and to Cl. Our work indicates that hydration of halide perovskites must be avoided to prevent the degradation of solar cells upon moisture exposure.
Tautschnig MP, Harrison NM, Finnis MW, 2017, A model for time-dependent grain boundary diffusion of ions and electrons through a film or scale, with an application to alumina, ACTA MATERIALIA, Vol: 132, Pages: 503-516, ISSN: 1359-6454
Wells MP, Zou B, Doiron BG, et al., 2017, Tunable, Low Optical Loss Strontium Molybdate Thin Films for Plasmonic Applications, ADVANCED OPTICAL MATERIALS, Vol: 5, ISSN: 2195-1071
Busayaporn W, Duncan DA, Allegretti F, et al., 2016, Structure of a Model Dye/Titania Interface: Geometry of Benzoate on Rutile-TiO2 (110)(1 x 1), JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 120, Pages: 14690-14698, ISSN: 1932-7447
Camino B, Noakes TCQ, Surman M, et al., 2016, Photoemission simulation for photocathode design: theory and application to copper and silver surfaces, COMPUTATIONAL MATERIALS SCIENCE, Vol: 122, Pages: 331-340, ISSN: 0927-0256
Carta D, Salaoru I, Khiat A, et al., 2016, Investigation of the Switching Mechanism in TiO2-Based RRAM: A Two-Dimensional EDX Approach, ACS APPLIED MATERIALS & INTERFACES, Vol: 8, Pages: 19605-19611, ISSN: 1944-8244
Korotana RK, Mallia G, Fortunato NM, et al., 2016, A combined thermodynamics and first principles study of the electronic, lattice and magnetic contributions to the magnetocaloric effect in La0.75Ca0.25MnO3, JOURNAL OF PHYSICS D-APPLIED PHYSICS, Vol: 49, ISSN: 0022-3727
Martinez-Casado R, Chen VH-Y, Mallia G, et al., 2016, A hybrid-exchange density functional study of the bonding and electronic structure in bulk CuFeS2, JOURNAL OF CHEMICAL PHYSICS, Vol: 144, ISSN: 0021-9606
Parkes MA, Tompsett DA, d'Avezac M, et al., 2016, The atomistic structure of yttria stabilised zirconia at 6.7 mol%: an ab initio study, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 18, Pages: 31277-31285, ISSN: 1463-9076
Ahmad EA, Tileli V, Kramer D, et al., 2015, Optimizing Oxygen Reduction Catalyst Morphologies from First Principles, Journal of Physical Chemistry C, Vol: 119, Pages: 16804-16810, ISSN: 1932-7455
Catalytic activity of perovskites for oxygen reduction (ORR) wasrecently correlated with bulk d-electron occupancy of the transition metal. Weexpand on the resultant model, which successfully reproduces the high activity ofLaMnO3 relative to other perovskites, by addressing catalyst surface morphology asan important aspect of the optimal ORR catalyst. The nature of reaction sites onlow index surfaces of orthorhombic (Pnma) LaMnO3 is established from FirstPrinciples. The adsorption of O2 is markedly influenced by local geometry andstrong electron correlation. Only one of the six reactions sites that result from experimentally confirmed symmetry-breakingJahn−Teller distortions is found to bind O2 with an intermediate binding energy while facilitating the formation of superoxide, animportant ORR intermediate in alkaline media. As demonstrated here for LaMnO3, rational design of the catalyst morphology topromote specific active sites is a highly effective optimization strategy for advanced functional ORR catalysts.
Chen VH-Y, Mallia G, Martinez-Casado R, et al., 2015, Surface morphology of CuFeS2: The stability of the polar (112)/((112)over-bar) surface pair, PHYSICAL REVIEW B, Vol: 92, ISSN: 1098-0121
Inkpen MS, Du S, Hildebrand M, et al., 2015, The Unusual Redox Properties of Fluoroferrocenes Revealed through a Comprehensive Study of the Haloferrocenes, ORGANOMETALLICS, Vol: 34, Pages: 5461-5469, ISSN: 0276-7333
Parkes MA, Refson K, d'Ayezac M, et al., 2015, Chemical Descriptors of Yttria-Stabilized Zirconia at Low Defect Concentration: An ab Initio Study, JOURNAL OF PHYSICAL CHEMISTRY A, Vol: 119, Pages: 6412-6420, ISSN: 1089-5639
Syrnianakis E, Malko D, Ahmad E, et al., 2015, Electrochemical Characterization and Quantified Surface Termination Obtained by Low Energy Ion Scattering and X-ray Photoelectron Spectroscopy of Orthorhombic and Rhombohedral LaMnO3 Powders, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 119, Pages: 12209-12217, ISSN: 1932-7447
Tautschnig MP, Blanca-Romero A, Patel M, et al., 2015, Study of corrosion scale formation from quantum mechanics simulations to a continuum model
Tseng H-H, Serri M, Harrison NM, et al., 2015, Thin film properties of tetracyanoquinodimethane (TCNQ) with novel templating effects, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 3, Pages: 8694-8699, ISSN: 2050-7526
Webster R, Bernasconi L, Harrison NM, 2015, Optical properties of alkali halide crystals from all-electron hybrid TD-DFT calculations., Journal of Chemical Physics, Vol: 142, Pages: 214705-214705, ISSN: 1089-7690
We present a study of the electronic and optical properties of a series of alkali halide crystals AX, with A = Li, Na, K, Rb and X = F, Cl, Br based on a recent implementation of hybrid-exchange time-dependent density functional theory (TD-DFT) (TD-B3LYP) in the all-electron Gaussian basis set code CRYSTAL. We examine, in particular, the impact of basis set size and quality on the prediction of the optical gap and exciton binding energy. The formation of bound excitons by photoexcitation is observed in all the studied systems and this is shown to be correlated to specific features of the Hartree-Fock exchange component of the TD-DFT response kernel. All computed optical gaps and exciton binding energies are however markedly below estimated experimental and, where available, 2-particle Green's function (GW-Bethe-Salpeter equation, GW-BSE) values. We attribute this reduced exciton binding to the incorrect asymptotics of the B3LYP exchange correlation ground state functional and of the TD-B3LYP response kernel, which lead to a large underestimation of the Coulomb interaction between the excited electron and hole wavefunctions. Considering LiF as an example, we correlate the asymptotic behaviour of the TD-B3LYP kernel to the fraction of Fock exchange admixed in the ground state functional cHF and show that there exists one value of cHF (∼0.32) that reproduces at least semi-quantitatively the optical gap of this material.
Harrison N, 2014, Computational characterisation of catalysts in reactive environments: Phase stability, surface compostion, structure, and reaction sites, 247th National Spring Meeting of the American-Chemical-Society (ACS), Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Korotana R, Mallia G, Gercsi Z, et al., 2014, Hybrid density functional study of structural, bonding, and electronic properties of the manganite series La1-xCaxMnO3 (x=0, 1/4, 1), PHYSICAL REVIEW B, Vol: 89, ISSN: 2469-9950
Martinez-Casado R, Usvyat D, Mallia G, et al., 2014, Diffraction of helium on MgO(100) surface calculated from first-principles, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 16, Pages: 21106-21113, ISSN: 1463-9076
Martinez-Casado R, Usvyat D, Maschio L, et al., 2014, Approaching an exact treatment of electronic correlations at solid surfaces: The binding energy of the lowest bound state of helium adsorbed on MgO(100), PHYSICAL REVIEW B, Vol: 89, ISSN: 2469-9950
Patel M, Sanches FF, Mallia G, et al., 2014, A quantum mechanical study of water adsorption on the (110) surfaces of rutile SnO2 and TiO2: investigating the effects of intermolecular interactions using hybrid-exchange density functional theory, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 16, Pages: 21002-21015, ISSN: 1463-9076
Sanches FF, Mallia G, Liborio L, et al., 2014, Hybrid exchange density functional study of vicinal anatase TiO2 surfaces, PHYSICAL REVIEW B, Vol: 89, ISSN: 1098-0121
Serri M, Wu W, Fleet LR, et al., 2014, High-temperature antiferromagnetism in molecular semiconductor thin films and nanostructures, NATURE COMMUNICATIONS, Vol: 5, ISSN: 2041-1723
Tomic S, Bernasconi L, Searle BG, et al., 2014, Electronic and Optical Structure of Wurtzite CuInS2, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 118, Pages: 14478-14484, ISSN: 1932-7447
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