31 research outputs found
Observation of strong surface state effects in the nonlinear magneto-optical response of Ni(110)
Spectroscopic magnetization induced optical Second Harmonic Generation (MSHG)
measurements from a clean Ni(110) surface reveal strong resonance effects near
2.7 eV that can be attributed to the presence of an empty surface state. The
good agreement with model calculations shows the potential of MSHG to probe
spin polarized interface band structures.Comment: REVTeX/EPS figures/Authors's single Postsript file, to appear in PRL,
our new phase-sensitive detection technique is used (see PRB, 58, R16020
(1998)), for more details see http://www.sci.kun.nl/tvs/people/petukhov
Atom lithography with two-dimensional optical masks
With a two-dimensional (2D) optical mask, nanoscale patterns are created for
the first time in an atom lithography process using metastable helium atoms.
The internal energy of the atoms is used to locally damage a hydrofobic resist
layer, which is removed in a wet etching process. Experiments have been
performed with several polarizations for the optical mask, resulting in
different intensity patterns, and corresponding nanoscale structures. The
results for a linear polarized light field show an array of holes with a
diameter of 260 nm, in agreement with a computed pattern. With a circularly
polarized light field a line pattern is observed with a spacing of 766 nm.
Simulations taking into account many possible experimental imperfections can
not explain this pattern.Comment: 5 pages, 4 figure
Transition from tunneling to direct contact in tungsten nanojunctions
We apply the mechanically controllable break junctions technique to
investigate the transition from tunneling to direct contact in tungsten. This
transition is quite different from that of other metals and is determined by
the local electronic properties of the tungsten surface and the relief of the
electrodes at the point of their closest proximity. The conductance traces show
a rich variety of patterns from the avalanche-like jump to a mesoscopic contact
to the completely smooth transition between direct contact and tunneling. Due
to the occasional absence of an adhesive jump the conductance of the contact
can be continuously monitored at ultra-small electrode separations. The
conductance histograms of tungsten are either featureless or show two distinct
peaks related to the sequential opening of spatially separated groups of
conductance channels. The role of surface states of tungsten and their
contribution to the junction conductance at sub-Angstrom electrode separations
are discussed.Comment: 6 pages, 6 figure
Raman spectroscopy as a tool to determine the thermal maturity of organic matter : application to sedimentary, metamorphic and structural geology
Raman spectrometry is a rapid, non-destructive alternative to conventional tools employed to assess the thermal alteration of organic matter (OM). Raman may be used to determine vitrinite reflectance equivalent OM maturity values for petroleum exploration, to provide temperature data for metamorphic studies, and to determine the maximum temperatures reached in fault zones. To achieve the wider utilisation of Raman, the spectrum processing method, and the positions and nomenclature of Raman bands and parameters, all need to be standardized. We assess the most widely used Raman parameters as well as the best analytical practices that have been proposed. Raman band separation and G-band full-width at half-maximum are the best parameters to estimate the maturity for rocks following diagenesis–metagenesis. For metamorphic studies, the ratios of band areas after performing deconvolution are generally used. Further work is needed on the second-order region, as well as assessing the potential of using integrated areas on the whole spectrum, to increase the calibrated temperature range of Raman parameters. Applying Raman spectroscopy on faults has potential to be able to infer both temperature and deformation processes. We propose a unified terminology for OM Raman bands and parameters that should be adopted in the future. The popular method of fitting several functions to a spectrum is generally unnecessary, as Raman parameters determined from an un-deconvoluted spectrum can track the maturity of OM. To progress the Raman application as a geothermometer a standardized approach must be developed and tested by means of an interlaboratory calibration exercise using reference materials
Laser-focused nanofabrication: Beating of two atomic resonances
Contains fulltext :
92604.pdf (publisher's version ) (Open Access
Deposition of magnetic nanostructures of atomic lithography: Semiclassical simulation
Contains fulltext :
92670.pdf (publisher's version ) (Open Access