1,654 research outputs found
Spectral Function in Mott Insulating Surfaces
We show theoretically the fingerprints of short-range spiral magnetic
correlations in the photoemission spectra of the Mott insulating ground states
realized in the triangular silicon surfaces K/Si(111)-B and SiC(0001). The
calculated spectra present low energy features of magnetic origin with a
reduced dispersion ~10-40 meV compared with the center-of-mass spectra
bandwidth ~0.2-0:3 eV. Remarkably, we find that the quasiparticle signal
survives only around the magnetic Goldstone modes. Our findings would position
these silicon surfaces as new candidates to investigate non-conventional
quasiparticle excitations.Comment: 5 pages, 4 figures. To be published in Journal of Physics: Condensed
Matte
Extended Classical Over-Barrier Model for Collisions of Highly Charged Ions with Conducting and Insulating Surfaces
We have extended the classical over-barrier model to simulate the
neutralization dynamics of highly charged ions interacting under grazing
incidence with conducting and insulating surfaces. Our calculations are based
on simple model rates for resonant and Auger transitions. We include effects
caused by the dielectric response of the target and, for insulators, localized
surface charges. Characteristic deviations regarding the charge transfer
processes from conducting and insulating targets to the ion are discussed. We
find good agreement with previously published experimental data for the image
energy gain of a variety of highly charged ions impinging on Au, Al, LiF and KI
crystals.Comment: 32 pages http://pikp28.uni-muenster.de/~ducree
Interaction of Silicon Dangling Bonds with Insulating Surfaces
We use first principles density functional theory calculations to study the interaction of a model dangling bond silicon tip with the surfaces of CaF2, Al2O3, TiO2, and MgO. In each case the strongest interaction is with the highest anions in the surface. We show that this is due to the onset of chemical bonding with the surface anions, which can be controlled by an electric field across the system. Combining our results and previous studies on semiconductor surfaces suggests that using dangling bond Si tips can provide immediate identification of surface species in atomically resolved noncontact atomic force microscopy and facilitate selective measurements of short-range interactions with surface sites.Peer reviewe
Sessile water droplets on insulating surfaces subject to high AC stress effect of contact angle
Surface pollution of outdoor high-voltage insulators is an important cause of flashover. We have undertaken an experimental study of electrical breakdown at the edges of a sessile water droplet on a planar, polymeric, insulating surface when subject to AC stress, parallel to the insulator surface, up to 2MV/m. The static contact angle between droplet and surface was varied by controlling the physical properties of the droplet and by inclining the insulator plane from the horizontal. The partial discharge activity from the water droplet was investigated using a combination of high-speed video camera, operated at up to 3,000 frames per second, and an electrical partial discharge detection system. We have used this to examine the location of partial discharge at the edges of the water droplet
Electrostatic stability of insulating surfaces: Theory and applications
We analyze the electrostatic stability of insulating surfaces in the
framework of the bulk modern theory of polarization. We show that heuristic
arguments based on a fully ionic limit find formal justification at the
microscopic level, even in solids where the bonding has a mixed ionic/covalent
character. Based on these arguments, we propose simple criteria to construct
arbitrary non-polar terminations of a given bulk crystal. We illustrate our
ideas by performing model calculations of several LaAlO3 and SrTiO3 surfaces.
We find, in the case of ideal LaAlO3 surfaces, that cleavage along a
higher-index (n10) direction is energetically favorable compared to the polar
(100) orientation. In the presence of external adsorbates or defects the
picture can change dramatically, as we demonstrate in the case of
H2O/LaAlO3(100).Comment: 18 pages, 10 figure
Towards chemical identification in atomic-resolution noncontact AFM imaging with silicon tips
In this study we use ab initio calculations and a pure silicon tip to study the tip-surface interaction with four characteristic insulating surfaces: (i) the narrow gap TiO2 (110) surface, (ii) the classic oxide MgO (001) surface, (iii) the ionic solid CaCO3 (101ÂŻ4) surface with molecular anion, and (iv) the wide gap CaF2 (111) surface. Generally we find that the tip-surface interaction strongly depends on the surface electronic structure due to the dominance of covalent bond formation with the silicon tip. However, we also find that in every case the strongest interaction is with the highest anion of the surface. This result suggests that, if the original silicon tip can be carefully controlled, it should be possible to immediately identify the species seen as bright in images of insulating surfaces. In order to provide a more complete picture we also compare these results to those for contaminated tips and suggest how applied voltage could also be used to probe chemical identity.Peer reviewe
Observation of individual molecules trapped on a nanostructured insulator
For the first time, ordered polar molecules confined in monolayer-deep
rectangular pits produced on an alkali halide surface by electron irradiation
have been resolved at room temperature by non-contact atomic force microscopy.
Molecules self-assemble in a specific fashion inside pits of width smaller than
15 nm. By contrast no ordered aggregates of molecules are observed on flat
terraces. Conclusions regarding nucleation and ordering mechanisms are drawn.
Trapping in pits as small as 2 nm opens a route to address single molecules
The role of potential barrier formation in spacecraft charging
The role of potential barrier formation in spacecraft charging at geosynchronous orbit is discussed. The evidence for, and understanding of, spacecraft charging and its hazards to spacecraft operation in the early 1970's are summarized. Theoretical and experimental advances which have changed the basic understanding of the role of barrier formation in charging phenomenology are described. Potential barriers are found to play a fundamental role in the dynamics of spacecraft charging. The consequences for structural and differential charging and for discharging are described
Surface phenomena in plasma environments
Plasma interactions and their effects on materials depend on a number of factors, including the pre-existing environment, the properties of surface materials and the characteristics of the system. An additional dimension is the question of mission: some payloads may be much more sensitive to plasma interactions than others. As an example, a payload whose objective is to measure the ambient environment will be more sensitive to any effects than will a power system. Material specific effects include charging and its associated effects, which can result in short- and long-term damage. Selection of materials for a particular application requires consideration of all factors and assessment of effects due to all causes. Proper selection and suitability determination requires analysis to identify the actual environment combined with testing under exposure to single and combined environment factors
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