Simulation of Mechanical Deformation and Tribology of Nano-Thin Amorphous Hydrogenated Carbon (a:Ch) Films Using Molecular Dynamics

Molecular dynamics computer simulations are used to study the effect of substrate temperature on microstructure of deposited amorphous hydrogenated carbon (a:CH) films. A transition from dense diamond- like films to porous graphite-like films is observed between substrate temperatures of 400 and 600 K for a deposition energy of 20 eV. The dense a:CH film grown at 300 K and 20 eV has a hardness ({similar_to}50 GPa) about half that of a pure carbon (a:C) film grown under the same conditions

Molecular Dynamics Simulation of Mechanical Deformation of Ultra-Thin Amorphous Carbon Films

Amorphous carbon films approximately 20nm thick are used throughout the computer industry as protective coatings on magnetic storage disks. The structure and function of this family of materials at the atomic level is poorly understood. Recently. we simulated the growth of a:C and a:CH films 1 to 5 nm thick using Brenner`s bond-order potential model with added torsional energy terms. The microstructure shows a propensity towards graphitic structures at low deposition energy (20eV). In this paper we present simulations of the evolution of this microstructure for the dense 20eV films during a simulated indentation by a hard diamond tip. We also simulate sliding, the tip across the surface to study dynamical processes like friction, energy transport and microstructure evolution during sliding

Molecular dynamics modeling of ultrathin amorphous carbon films

Amorphous carbon films about 20 mn thick are used by the computer industry as protective coatings on magnetic disks. The structure and function of this family of materials at the atomic level is poorly understood. The growth and properties of a:C and a:CH films 1 to 5 nm thick has been simulated using classical molecular dynamics and a bond-order potential with torsional terms. Studies of quenched melts that verify the ability of this potential to reproduce known features of extended structures of carbon in two and three dimensions are briefly described. In molecular dynamics calculations the incident species were neutral atoms C, or C and H with energies up to 100 eV. The stoichiometry, chemical bonding and distribution functions within the films were analyzed using IBM`s Power Visualization System for different incident gas energies. Microscopic features such as multiple ring structures, including planar graphitic structures, were easily identified. Some preliminary studies of the nanotribology of the a:C films are described, including nano-indentation and sliding in contact with a rigid probe

Spontaneous emission between an unusual pair of plates

We compute the modification in the spontaneous emission rate for a two-level atom when it is located between two parallel plates of different nature: a perfectly conducting plate $(\epsilon\to \infty)$ and an infinitely permeable one $(\mu\to \infty)$. We also discuss the case of two infinitely permeable plates. We compare our results with those found in the literature for the case of two perfectly conducting plates.Comment: latex file 4 pages, 4 figure

Correction:The effect of a programme to improve men's sedentary time and physical activity: The European Fans in Training (EuroFIT) randomised controlled trial (PLoS medicine (2019) 16 2 (e1002736))

[This corrects the article DOI: 10.1371/journal.pmed.1002736.].status: publishe

THEORY OF SURFACE ENHANCED RAMAN SCATTERING : A PROSPECTIVE VIEW

La compréhension théorique des origines des forts signaux Raman de molécules proches de surfaces d'Ag, de Cu et d'Au rendues rugueuses, a progressé de telle façon qu'on reconnaît l'action de deux types de processus très différents. Il existe un renforcement "chimique", qui est apparent seulement pour les espèces chimisorbées, comme par exemple des anions adsorbés de façon spécifique sur des électrodes d'Ag. Le mécanisme chimique est mal compris, cependant on a avancé des idées et des concepts ingénieux, incluant la localisation d'états de paires électron-trou et le transfert de charge, commandé optiquement, entre l'adsorbat et le métal, pour modéliser des aspects du renforcement chimique. Le second processus qui est mieux compris, est le renforcement énorme à la surface des champs du rayonnement entrant et sortant, qui résulte de géométries en forme de paratonnerre et de l'excitation de modes de plasmon de surface localisés. Les calculs montrent que, pour des géométries particulières, des facteurs de renforcement très élevés (approximativement 106-108) sont possibles dans des régions confinées.Theoretical understanding of the origins of strong Raman signals from molecules near roughened Ag, Cu, and Au surfaces has progressed to the point where the action of two very different types of process are recognized. There is "chemical" enhancement that is apparent only for chemisorbed species, as for example, specifically adsorbed anions on Ag electrodes. The chemical mechanism is poorly understood, however, ingenious ideas and concepts have been advanced, including localization of electron-hole pair states and optically driven charge transfer between adsorbate and metal, to model aspects of the chemical enhancement. The second and best understood process is the enormous enhancement of the incoming and outgoing radiation fields at the surface resulting from lightening rod geometries and the excitation of localized surface plasmon modes. Calculations show that for special geometries, very high (approximately 106-108) enhancement factors are possible in confined regions

Atomistic modeling and simulation

Electrochemical Society Interface9430-32ELSI

Ab initio molecular dynamics simulation of LiBr association in water

10.1063/1.1311965Journal of Chemical Physics1132310676-10684JCPS

The electronic structure of the dizincocene core

10.1016/j.chemphys.2006.04.021Chemical Physics3272-3283-290CMPH

Electronic structure of bulk and (0 0 1) surface layers of pyrite FeS 2

10.1016/j.commatsci.2004.02.026Computational Materials Science303-4 SPEC. ISS.358-363CMMS