David O. Scanlon

Bio: David O. Scanlon is an academic researcher from University College London. The author has contributed to research in topics: Band gap & Density functional theory. The author has an hindex of 64, co-authored 295 publications receiving 14766 citations. Previous affiliations of David O. Scanlon include Boston College & Trinity College, Dublin.

Band alignment of rutile and anatase TiO2

Abstract: The most widely used oxide for photocatalytic applications owing to its low cost and high activity is TiO2. The discovery of the photolysis of water on the surface of TiO2 in 19721 launched four decades of intensive research into the underlying chemical and physical processes involved2, 3, 4, 5. Despite much collected evidence, a thoroughly convincing explanation of why mixed-phase samples of anatase and rutile outperform the individual polymorphs has remained elusive6. One long-standing controversy is the energetic alignment of the band edges of the rutile and anatase polymorphs of TiO2 (ref. 7). We demonstrate, through a combination of state-of-the-art materials simulation techniques and X-ray photoemission experiments, that a type-II, staggered, band alignment of ~ 0.4 eV exists between anatase and rutile with anatase possessing the higher electron affinity, or work function. Our results help to explain the robust separation of photoexcited charge carriers between the two phases and highlight a route to improved photocatalysts.

On the application of the tolerance factor to inorganic and hybrid halide perovskites: a revised system

Abstract: The tolerance factor is a widely used predictor of perovskite stability. The recent interest in hybrid perovskites for use as solar cell absorbers has lead to application of the tolerance factor to these materials as a way to explain and predict structure. Here we critically assess the suitability of the tolerance factor for halide perovskites. We show that the tolerance factor fails to accurately predict the stability of the 32 known inorganic iodide perovskites, and propose an alternative method. We introduce a revised set of ionic radii for cations that is anion dependent, this revision is necessary due to increased covalency in metal–halide bonds for heavier halides compared with the metal-oxide and fluoride bonds used to calculate Shannon radii. We also employ a 2D structural map to account for the size requirements of the halide anions. Together these measures yield a simple system which may assist in the search for new hybrid and inorganic perovskites.

Theoretical and Experimental Study of the Electronic Structures of MoO3 and MoO2

Abstract: The geometric and electronic structures of MoO3 and MoO2 have been calculated using the generalized gradient approximation to density functional theory. The calculated cross-section weighted densities of states are compared with high-resolution X-ray photoemission spectra. There is very good agreement between the calculated structures and those determined previously by X-ray diffraction and between the computed densities of states and the present photoemission measurements. MoO2 is shown to be a metallic material, as is found experimentally, but the Fermi level sits in a distinct trough in the density of states. Satellite peaks found in core photoemission spectra of MoO2 are shown to derive from final state screening effects in this narrow band metallic material.

Self‐Regulation Mechanism for Charged Point Defects in Hybrid Halide Perovskites

Abstract: Hybrid halide perovskites such as methylammonium lead iodide (CH3NH3PbI3) exhibit unusually low free-carrier concentrations despite being processed at low-temperatures from solution. We demonstrate, through quantum mechanical calculations, that an origin of this phenomenon is a prevalence of ionic over electronic disorder in stoichiometric materials. Schottky defect formation provides a mechanism to self-regulate the concentration of charge carriers through ionic compensation of charged point defects. The equilibrium charged vacancy concentration is predicted to exceed 0.4% at room temperature. This behavior, which goes against established defect conventions for inorganic semiconductors, has implications for photovoltaic performance.

Can Pb-Free Halide Double Perovskites Support High-Efficiency Solar Cells?

Abstract: The methylammonium lead halides have become champion photoactive semiconductors for solar cell applications; however, issues still remain with respect to chemical instability and potential toxicity. Recently, the Cs2AgBiX6 (X = Cl, Br) double perovskite family has been synthesized and investigated as stable nontoxic replacements. We probe the chemical bonding, physical properties, and cation anti-site disorder of Cs2AgBiX6 and related compounds from first-principles. We demonstrate that the combination of Ag(I) and Bi(III) leads to the wide indirect band gaps with large carrier effective masses owing to a mismatch in angular momentum of the frontier atomic orbitals. The spectroscopically limited photovoltaic conversion efficiency is less than 10% for X = Cl or Br. This limitation can be overcome by replacing Ag with In or Tl; however, the resulting compounds are predicted to be unstable thermodynamically. The search for nontoxic bismuth perovskites must expand beyond the Cs2AgBiX6 motif.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

The European commission

Abstract: 2 1 The innovative transport systems and the CityMobil project 10 1.1 The research questions 10 2 The state of art in the field of automatic transport systems 12 2.1 Case studies and demand studies for innovative transport systems 12 3 The design and implementation of surveys 14 3.1 Definition of experimental design 14 3.2 Questionnaire design and delivery 16 3.3 First analyses on the collected sample 18 4 Calibration of Logit Multionomial demand models 21 4.1 Methodology 21 4.2 Calibration of the “full” model. 22 4.3 Calibration of the “final” model 24 4.4 The demand analysis through the final Multinomial Logit model 25 5 The analysis of interaction between the demand and socioeconomic attributes 31 5.1 Methodology 31 5.2 Application of Mixed Logit models to the demand 31 5.3 Analysis of the interactions between demand and socioeconomic attributes through Mixed Logit models 32 5.4 Mixed Logit model and interaction between age and the demand for the CTS 38 5.5 Demand analysis with Mixed Logit model 39 6 Final analyses and conclusions 45 6.1 Comparison between the results of the analyses 45 6.2 Conclusions 48 6.3 Answers to the research questions and future developments 52

Research Design: Qualitative, Quantitative, and Mixed Method Approaches

Abstract: หนงสอเรอง การออกแบบการวจย: วธการวจยเชงคณภาพ วธการวจยเชงปรมาณ และวธการวจยแบบผสม (Research Design: Qualitative, Quantitative, and Mixed Method Approaches) เปนหนงสอทเรยบเรยงเพออธบายเกยวกบความแตกตางของกระบวนทศนการวจยทง 2 แบบ ไดแก การวจย เชงปรมาณ และการวจยเชงคณภาพ และความจำเปนของประเดนปญหาการวจยทตองนำกระบวนทศนทง 2 มารวมกนหาขอคนพบเพอนำไปสผลการวจยทสามารถนำผลการวจยไปใชประโยชนไดอยางจรงมากยงขน เรยกวา “การวจยแบบผสมผสาน” ซงเปนหนงสอทอธบายวธการวจยทง 2 ประเภทไดอยางชดเจน และการรวมกนของกระบวนทศนการวจยทง 2 แบบอยางลงตว