5,389 research outputs found
Formation and Thermal Stability of sub-10 nm Carbon Templates on Si(100)
We report a lithographic process for creating high-resolution (<10 nm) carbon
templates on Si(100). A scanning electron microscope, operating under low
vacuum (10E-6 mbar), produces a carbon-containing deposit ("contamination
resist") on the silicon surface via electron-stimulated dissociation of ambient
hydrocarbons, water and other adsorbed molecules. Subsequent annealing at
temperatures up to 1320 K in ultra-high vacuum removes SiO2 and other
contaminants, with no observable change in dot shape. The annealed structures
are compatible with subsequent growth of semiconductors and complex oxides.
Carbon dots with diameter as low as 3.5 nm are obtained with a 200 us
electron-beam exposure time.Comment: 13 pages, 4 figure
Development and Performance of the Nanoworkbench: A Four Tip STM for Electrical Conductivity Measurements Down to Sub-micrometer Scales
A multiple-tip ultra-high vacuum (UHV) scanning tunneling microscope (MT-STM)
with a scanning electron microscope (SEM) for imaging and molecular-beam
epitaxy growth capabilities has been developed. This instrument (nanoworkbench)
is used to perform four-point probe conductivity measurements at micrometer
spatial dimension. The system is composed of four chambers, the multiple-tip
STM/SEM chamber, a surface analysis and preparation chamber, a molecular-beam
epitaxy chamber and a load-lock chamber for fast transfer of samples and
probes. The four chambers are interconnected by a unique transfer system based
on a sample box with integrated heating and temperature-measuring capabilities.
We demonstrate the operation and the performance of the nanoworkbench with STM
imaging on graphite and with four-point-probe conductivity measurements on a
silicon-on-insulator (SOI) crystal. The creation of a local FET, whose
dimension and localization are respectively determined by the spacing between
the probes and their position on the SOI surface, is demonstrated.Comment: 39 pages, 15 figure
Low temperature silicon epitaxy on hydrogen terminated Si(100) surfaces
Si deposition on H terminated Si(100)-2x1 and 3x1 surfaces at temperatures
300-530 K is studied by scanning tunneling microscopy. Hydrogen apparently
hinders Si adatom diffusion and enhances surface roughening. The post-growth
annealing effect is analyzed. Hydrogen is shown to remain on the growth front
up to at least 10 ML. The dihydride units on the 3x1 surfaces further suppress
the Si adatom diffusion and increase surface roughness.Comment: 26 pages, 9 figure
Kondo temperature of magnetic impurities at surfaces
Based on the experimental observation, that only the close vicinity of a
magnetic impurity at metal surfaces determines its Kondo behaviour, we
introduce a simple model which explains the Kondo temperatures observed for
cobalt adatoms at the (111) and (100) surfaces of Cu, Ag, and Au. Excellent
agreement between the model and scanning tunneling spectroscopy (STS)
experiments is demonstrated. The Kondo temperature is shown to depend on the
occupation of the d-level determined by the hybridization between adatom and
substrate with a minimum around single occupancy.Comment: 4 pages, 2 figure
Assessing the effectiveness and cost effectiveness of subcutaneous nerve stimulation in patients with predominant back pain due to failed back surgery syndrome (SubQStim study): study protocol for a multicenter randomized controlled trial
This is a freely-available open access publication. Please cite the published version which is available via the DOI link in this record.Chronic radicular pain can be effectively treated with spinal cord stimulation, but this therapy is not always sufficient for chronic back pain. Subcutaneous nerve stimulation (SQS) refers to the placement of percutaneous leads in the subcutaneous tissue within the area of pain. Case series data show that failed back surgery syndrome (FBSS) patients experience clinically important levels of pain relief following SQS and may also reduce their levels of analgesic therapy and experience functional well-being. However, to date, there is no randomized controlled trial evidence to support the use of SQS in FBSS.Medtronic Inc
(Meta-)stable reconstructions of the diamond(111) surface: interplay between diamond- and graphite-like bonding
Off-lattice Grand Canonical Monte Carlo simulations of the clean diamond
(111) surface, based on the effective many-body Brenner potential, yield the
Pandey reconstruction in agreement with \emph{ab-initio}
calculations and predict the existence of new meta-stable states, very near in
energy, with all surface atoms in three-fold graphite-like bonding. We believe
that the long-standing debate on the structural and electronic properties of
this surface could be solved by considering this type of carbon-specific
configurations.Comment: 4 pages + 4 figures, Phys. Rev. B Rapid Comm., in press (15Apr00).
For many additional details (animations, xyz files) see electronic supplement
to this paper at http://www.sci.kun.nl/tvs/carbon/meta.htm
Optical Pulse-Phased Photopolarimetry of PSR B0656+14
We have observed the optical pulse profile of PSR B0656+14 in 10 phase bins
at a high signal-to-noise ratio, and have measured the linear polarization
profile over 30% of the pulsar period with some significance. The pulse profile
is double-peaked, with a bridge of emission between the two peaks, similar to
gamma-ray profiles observed in other pulsars. There is no detectable unpulsed
flux, to a 1-sigma limit of 16% of the pulse-averaged flux. The emission in the
bridge is highly (~ 100%) polarized, with a position angle sweep in excellent
agreement with the prediction of the Rotating Vector Model as determined from
radio polarization observations. We are able to account for the gross features
of the optical light curve (i.e., the phase separation of the peaks) using both
polar cap and outer gap models. Using the polar cap model, we are also able to
estimate the height of the optical emission regions.Comment: 27 pages, 11 figures, accepted by ApJ (scheduled v597 n2, November
10, 2003
Influence of Mature Overstory Trees on Adjacent 12-Year Regeneration and the Woody Understory: Aggregated Retention versus Intact Forest
Retention harvesting, an approach that intentionally retains legacy features such as mature overstory trees, provides options for achieving ecological objectives. At the same time, retained overstory trees may compete with the nearby recovering understory for resources, and much remains to be learned about potential trade-offs with regeneration objectives, particularly over extended time periods. We assessed the influence of aggregated retention (reserved mature overstory and understory patches) versus intact forest on structure and productivity (standing biomass) of the adjacent woody understory and regeneration 12 years after harvest in northern Minnesota, USA. Each site was dominated by Populus tremuloides Michx., a species that regenerates prolifically via root sprouts following disturbance. Overall, fewer differences than expected occurred between the effects of intact forest and aggregated retention on regeneration, despite the small size (0.1 ha) of aggregates. Instead, harvest status and distance from harvest edge had a greater influence on structure and standing woody biomass. Proximity to aggregates reduced large sapling biomass (all species, combined) relative to open conditions, but only up to 5 m into harvested areas. This suggests the trade-off for achieving productivity objectives might be minimal if managers use retention aggregates in this region to achieve ecological objectives and meet management guidelines
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