55 research outputs found
A graphene electron lens
International audienceAn epitaxial layer of graphene was grown on a pre patterned 6H-SiC(0001) crystal. The graphene smoothly covers the hexagonal nano-holes in the substrate without the introduction of small angle grain boundaries or dislocations. This is achieved by an elastic deformation of the graphene by ~0.3% in accordance to its large elastic strain limit. This elastic stretching of the graphene leads to a modification of the band structure and to a local lowering of the electron group velocity of the graphene. We propose to use this effect to focus two-dimensional electrons in analogy to simple optical lenses
Structure and Stability of Si(114)-(2x1)
We describe a recently discovered stable planar surface of silicon, Si(114).
This high-index surface, oriented 19.5 degrees away from (001) toward (111),
undergoes a 2x1 reconstruction. We propose a complete model for the
reconstructed surface based on scanning tunneling microscopy images and
first-principles total-energy calculations. The structure and stability of
Si(114)-(2x1) arises from a balance between surface dangling bond reduction and
surface stress relief, and provides a key to understanding the morphology of a
family of surfaces oriented between (001) and (114).Comment: REVTeX, 4 pages + 3 figures. A preprint with high-resolution figures
is available at http://cst-www.nrl.navy.mil/papers/si114.ps . To be published
in Phys. Rev. Let
Decay of isolated surface features driven by the Gibbs-Thomson effect in analytic model and simulation
A theory based on the thermodynamic Gibbs-Thomson relation is presented which
provides the framework for understanding the time evolution of isolated
nanoscale features (i.e., islands and pits) on surfaces. Two limiting cases are
predicted, in which either diffusion or interface transfer is the limiting
process. These cases correspond to similar regimes considered in previous works
addressing the Ostwald ripening of ensembles of features. A third possible
limiting case is noted for the special geometry of "stacked" islands. In these
limiting cases, isolated features are predicted to decay in size with a power
law scaling in time: A is proportional to (t0-t)^n, where A is the area of the
feature, t0 is the time at which the feature disappears, and n=2/3 or 1. The
constant of proportionality is related to parameters describing both the
kinetic and equilibrium properties of the surface. A continuous time Monte
Carlo simulation is used to test the application of this theory to generic
surfaces with atomic scale features. A new method is described to obtain
macroscopic kinetic parameters describing interfaces in such simulations.
Simulation and analytic theory are compared directly, using measurements of the
simulation to determine the constants of the analytic theory. Agreement between
the two is very good over a range of surface parameters, suggesting that the
analytic theory properly captures the necessary physics. It is anticipated that
the simulation will be useful in modeling complex surface geometries often seen
in experiments on physical surfaces, for which application of the analytic
model is not straightforward.Comment: RevTeX (with .bbl file), 25 pages, 7 figures from 9 Postscript files
embedded using epsf. Submitted to Phys. Rev. B A few minor changes made on
9/24/9
The first stages of the formation of the interface between gold and silicon (100) at room temperature
Highly-Conformal TiN Thin Films Grown by Thermal and Plasma-Enhanced Atomic Layer Deposition
Cross characterization by scanning electron microscopy and atomic force microscopy of Ag islands grown on Si (111) 7×7
Two types of microscopy, scanning electron (SEM) and atomic force microscopy (AFM), have been used in a comparative way to study very big (10 - 40 μm) Ag islands grown on a Si(111)√3 x √3 interface. The signals used for image formation are of very different nature; secondary electrons emitted from the sample, in SEM and, in AFM, light deflected from the system probing the surface. In the present study, both microscopes were used in similar magnification ranges. A rather irregular morphology of the islands and a surface topography with large inhomogeneities on the top face were observed. The size distribution of the islands was found to be very wide. AFM and SEM, for minor differences, basically give access to the same results.Deux types de microscopies, la microscopie électronique à balayage (SEM) et la microscopie à force atomique (AFM), ont été utilisées d'une façon comparative pour étudier des ilots d'Ag de très grande taille (10 - 40 μm) formés sur l'interface Si(111)√3 x √3-Ag. Les images sont de nature très différente dans les deux cas: Electrons secondaires émis par l'échantillon en SEM, lumière réfléchie par la sonde balayant la surface en AFM. Les deux microscopes ont été utilisés dans des gammes de grossissement comparables. Une morphologie plutôt irrégulière et une topographie de surface démontrant de grandes inhomogenéités ont pu être mises en évidence sur les îlots dont la distribution de taille est par ailleurs très large. Les résultats obtenus en AFM et SEM sont, mis à part des différences mineures, principalement identiques
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