429 research outputs found
Do methanethiol adsorbates on the Au(111) surface dissociate?
The interaction of methanethiol molecules CHSH with the Au(111) surface
is investigated, and it is found for the first time that the S-H bond remains
intact when the methanethiol molecules are adsorbed on the regular Au(111)
surface. However, it breaks if defects are present in the Au(111) surface. At
low coverage, the fcc region is favored for S atom adsorption, but at saturated
coverage the adsorption energies at various sites are almost iso-energetic. The
presented calculations show that a methanethiol layer on the regular Au(111)
surface does not dimerize.Comment: 4 pages, 2 figures, 4 tables, submitted to Phys. Rev. Let
Isotropic Oscillator Under a Magnetic and Spatially Varying Electric Field
We investigate the energy levels of a particle confined in the isotropic oscillator potential with a magnetic and spatially varying electric field. Here we are able to exactly solve the Schrodinger equation, using matrix methods, for the first excited states. To this end we find that the spatial gradient of the electric field acts as a magnetic field in certain circumstances. Here we present the changes in the energy levels as functions of the electric field, and other parameters
Spin Filter Properties of Armchair Graphene Nanoribbons with Substitutional Fe Atoms
The spin filter capability of a (0,8) armchair graphene nanoribbon with Fe
atoms at substitutional sites is investigated by density functional theory in
combination with the non-equilibrium Greens function technique. For specific
arrangements, a high degree of spin polarization is achieved. These include a
single substitution at an edge position or double substitution in the central
sector of the transmission element. The possibility of switching between
majority and minority spin polarization by changing the double substitution
geometry is predicted. Including the bias dependence of the transmission
function proves to be essential for correct representation of the spin-resolved
current-voltage profiles
Coverage dependence of the 1-propanol adsorption on the Si(001) surface and fragmentation dynamics
The geometric, electronic, energetic, and dynamic properties of 1-propanol
adsorbed on the Si(001)-2x1 surface are studied from first principles by use of
a slab approach. The 1-propanol molecule initially interacts with the Si
surface through formation of a dative bond, subsequently the physisorbed
1-propanol molecule reacts with the surface by cleavage of the O-H bond, and
the Si(001)-2x1 surface undergoes further reconstruction as a result of the
adsorption of the organic species. The band structure and density of states
(DOS) are first analyzed for this system. The band gap of the Si/1-propanol
film increases as the coverage level is enhanced. Good agreement is found with
available experimental data.Comment: 29 pages, 15 figures, 8 tables, submitted to Phys. Rev.
Vacancy patterning and patterning vacancies: controlled self-assembly of fullerenes on metal surfaces
A density functional theory study accounting for van der Waals interactions reveals the potential of metal surface vacancies as anchor points for the construction of user-defined 2D patterns of adsorbate molecules via a controlled self-assembly process. Vice versa, energetic criteria indicate the formation of regular adsorbate-induced vacancies after adsorbate self-assembly on clean surfaces. These processes are exemplified by adsorbing C60 fullerene on Al(111), Au(111), and Be(0001) surfaces with and without single, triple, and septuple atom pits. An analysis of vacancy-adatom formation energetics precedes the study of the adsorption processes
The CH3SH molecule deposited on Cu(111) and deprotonation
We demonstrate for the first time that when a methanethiol adsorbed on the
regular Cu(111) surface, the dissociative structure is thermodynamically more
stable than the intact one. The computational results show that at low
temperature the methanethiol adsorbate prefers the atop site of the regular
Cu(111) surface. As the temperature is increased, the S-H bond is broken and
the methylthiolate favors the hollow sites. On the defected Cu(111) surface,
the dissociative configuration is still thermodynamically more stable than the
nondissociative one. The calculation indicates that the hydrogen initially
attached to the sulfur would like to form a bond with the copper surface rather
than desorb from it. Even though both copper and gold are the noble metal, the
stability of the methanethiol adsorption on the Cu(111) substrate is almost the
reverse of that on the Au(111).Comment: 13 pages, 7 figures, submitted to Phys. Rev.
Highly Stable [C\u3csub\u3e60\u3c/sub\u3eAuC\u3csub\u3e60\u3c/sub\u3e]\u3csup\u3e+/-\u3c/sup\u3e Dumbbells
Ionic complexes between gold and C60 have been observed for the first time. Cations and anions of the type [Au(C60)2]+/- are shown to have particular stability. Calculations suggest that these ions adopt a C60-Au-C60 sandwich-like (dumbbell) structure, which is reminiscent of [XAuX]+/- ions previously observed for much smaller ligands. The [Au(C60)2]+/- ions can be regarded as Au(I) complexes, regardless of whether the net charge is positive or negative, but in both cases, the charge transfer between the Au and C60 is incomplete, most likely because of a covalent contribution to the Au-C60 binding. The C60-Au-C60 dumbbell structure represents a new architecture in fullerene chemistry that might be replicable in synthetic nanostructures.
Ordered Phases of Ethylene Adsorbed on Charged
In spite of extensive investigations of ethylene adsorbed on graphite, bundles of nanotubes, and crystals of fullerenes, little is known about the existence of commensurate phases; they have escaped detection in almost all previous work. Here we present a combined experimental and theoretical study of ethylene adsorbed on free C60 and its aggregates. The ion yield of measured by mass spectrometry reveals a propensity to form a structurally ordered phase on monomers, dimers and trimers of C60 in which all sterically accessible hollow sites over carbon rings are occupied. Presumably the enhancement of the corrugation by the curvature of the fullerene surface favors this phase which is akin to a hypothetical 1 × 1 phase on graphite. Experimental data also reveal the number of molecules in groove sites of the C60 dimer through tetramer. The identity of the sites, adsorption energies and orientations of the adsorbed molecules are determined by molecular dynamics calculations based on quantum chemical potentials, as well as density functional theory. The decrease in orientational order with increasing temperature is also explored in the simulations whereas in the experiment it is impossible to vary the temperature
Search for supersymmetry with a dominant R-parity violating LQDbar couplings in e+e- collisions at centre-of-mass energies of 130GeV to 172 GeV
A search for pair-production of supersymmetric particles under the assumption
that R-parity is violated via a dominant LQDbar coupling has been performed
using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV.
The observed candidate events in the data are in agreement with the Standard
Model expectation. This result is translated into lower limits on the masses of
charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, for
m_0=500 GeV/c^2 and tan(beta)=sqrt(2) charginos with masses smaller than 81
GeV/c^2 and neutralinos with masses smaller than 29 GeV/c^2 are excluded at the
95% confidence level for any generation structure of the LQDbar coupling.Comment: 32 pages, 30 figure
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