Metastable liquid lamellar structures in binary and ternary mixtures of Lennard-Jones fluids

We have carried out extensive equilibrium molecular dynamics (MD) simulations to investigate the Liquid-Vapor coexistence in partially miscible binary and ternary mixtures of Lennard-Jones (LJ) fluids. We have studied in detail the time evolution of the density profiles and the interfacial properties in a temperature region of the phase diagram where the condensed phase is demixed. The composition of the mixtures are fixed, 50% for the binary mixture and 33.33% for the ternary mixture. The results of the simulations clearly indicate that in the range of temperatures $78 < T < 102 ^{\rm o}$K, --in the scale of argon-- the system evolves towards a metastable alternated liquid-liquid lamellar state in coexistence with its vapor phase. These states can be achieved if the initial configuration is fully disordered, that is, when the particles of the fluids are randomly placed on the sites of an FCC crystal or the system is completely mixed. As temperature decreases these states become very well defined and more stables in time. We find that below $90 ^{\rm o}$K, the alternated liquid-liquid lamellar state remains alive for 80 ns, in the scale of argon, the longest simulation we have carried out. Nonetheless, we believe that in this temperature region these states will be alive for even much longer times.Comment: 18 Latex-RevTex pages including 12 encapsulated postscript figures. Figures with better resolution available upon request. Accepted for publication in Phys. Rev. E Dec. 1st issu

Towards Oxide Electronics:a Roadmap

At the end of a rush lasting over half a century, in which CMOS technology has been experiencing a constant and breathtaking increase of device speed and density, Moore's law is approaching the insurmountable barrier given by the ultimate atomic nature of matter. A major challenge for 21st century scientists is finding novel strategies, concepts and materials for replacing silicon-based CMOS semiconductor technologies and guaranteeing a continued and steady technological progress in next decades. Among the materials classes candidate to contribute to this momentous challenge, oxide films and heterostructures are a particularly appealing hunting ground. The vastity, intended in pure chemical terms, of this class of compounds, the complexity of their correlated behaviour, and the wealth of functional properties they display, has already made these systems the subject of choice, worldwide, of a strongly networked, dynamic and interdisciplinary research community. Oxide science and technology has been the target of a wide four-year project, named Towards Oxide-Based Electronics (TO-BE), that has been recently running in Europe and has involved as participants several hundred scientists from 29 EU countries. In this review and perspective paper, published as a final deliverable of the TO-BE Action, the opportunities of oxides as future electronic materials for Information and Communication Technologies ICT and Energy are discussed. The paper is organized as a set of contributions, all selected and ordered as individual building blocks of a wider general scheme. After a brief preface by the editors and an introductory contribution, two sections follow. The first is mainly devoted to providing a perspective on the latest theoretical and experimental methods that are employed to investigate oxides and to produce oxide-based films, heterostructures and devices. In the second, all contributions are dedicated to different specific fields of applications of oxide thin films and heterostructures, in sectors as data storage and computing, optics and plasmonics, magnonics, energy conversion and harvesting, and power electronics

Strong absorption and ultrafast localisation in NaBiS2 nanocrystals with slow charge carrier recombination

I V VI2 ternary chalcogenides are gaining attention as earth abundant, nontoxic, and air stable absorbers for photovoltaic applications. However, the semiconductors explored thus far have slowly rising absorption onsets, and their charge carrier transport is not well understood yet. Herein, we investigate cation disordered NaBiS2 nanocrystals, which have a steep absorption onset, with absorption coefficients reaching gt;105 cm amp; 8722;1 just above its pseudo direct bandgap of 1.4 eV. Surprisingly, we also observe an ultrafast picosecond time scale photoconductivity decay and long lived charge carrier population persisting for over onemicrosecond in NaBiS2 nanocrystals. These unusual features arise because of the localised, non bonding S p character of the upper valence band, which leads to a high density of electronic states at the band edges, ultrafast localisation of spatially separated electrons and holes, as well as the slow decay of trapped holes. Thiswork reveals the critical role of cation disorder in these systems on both absorption characteristics and charge carrier kinetic

Technical note: The heterogeneous Zeldovich factor

International audienceIn this technical note we present the exact form of the Zeldovich factor for heterogeneous nucleation on spherical pre-existing particles. We study the error caused by planar pre-existing surface approximations, which have been used in our earlier heterogeneous nucleation model and elsewhere in the literature. We also test the significance of widely used approximations for cluster surface area and circumference. We conclude that the approximations do not affect the predicted onset saturation. Especially for small pre-existing particles the nucleation rates calculated with the exact and approximative models differ significantly

Effect of ammonium bisulphate formation on atmospheric water-sulphuric acid-ammonia nucleation

The effect of formation of stable ammonium bisulphate clusters on the ternary water-sulphuric acid-ammonia nucleation was investigated by means of the classical thermodynamics. The performed calculations show that most of the sulphuric acid in the atmosphere is likely to be bound to stable ammonium bisulphate clusters. Consequently the nucleation rates calculated with the new model are orders, sometimes even tens of orders, of magnitude lower than the rates produced by the previous ternary model which neglected the formation of these clusters. The new nucleation rates compare favourably with the available experimental results, unlike the old ones, which are far too high. In contrast to the old ternary model, the revised model does not predict significant nucleation rates that would explain new particle formation events every time they are observed, and we have to look for other nucleation mechanisms like multi-component nucleation involving organics or ion induced nucleation to understand atmospheric new particle formation