102 research outputs found
Lifetime enhanced transport in silicon due to spin and valley blockade
We report the observation of Lifetime Enhanced Transport (LET) based on
perpendicular valleys in silicon by transport spectroscopy measurements of a
two-electron system in a silicon transistor. The LET is manifested as a
peculiar current step in the stability diagram due to a forbidden transition
between an excited state and any of the lower energy states due perpendicular
valley (and spin) configurations, offering an additional current path. By
employing a detailed temperature dependence study in combination with a rate
equation model, we estimate the lifetime of this particular state to exceed 48
ns. The two-electron spin-valley configurations of all relevant confined
quantum states in our device were obtained by a large-scale atomistic
tight-binding simulation. The LET acts as a signature of the complicated valley
physics in silicon; a feature that becomes increasingly important in silicon
quantum devices.Comment: 4 pages, 4 figures. (The current version (v3) is the result of
splitting up the previous version (v2), and has been completely rewritten
A hybrid double-dot in silicon
We report electrical measurements of a single arsenic dopant atom in the
tunnel-barrier of a silicon SET. As well as performing electrical
characterization of the individual dopant, we study series electrical transport
through the dopant and SET. We measure the triple points of this hybrid double
dot, using simulations to support our results, and show that we can tune the
electrostatic coupling between the two sub-systems.Comment: 11 pages, 6 figure
Stark tuning of the charge states of a two-donor molecule in silicon
Gate control of phosphorus donor based charge qubits in Si is investigated
using a tight-binding approach. Excited molecular states of P2+ are found to
impose limits on the allowed donor separations and operating gate voltages. The
effects of surface (S) and barrier (B) gates are analyzed in various voltage
regimes with respect to the quantum confined states of the whole device.
Effects such as interface ionization, saturation of the tunnel coupling,
sensitivity to donor and gate placement are also studied. It is found that
realistic gate control is smooth for any donor separation, although at certain
donor orientations the S and B gates may get switched in functionality. This
paper outlines and analyzes the various issues that are of importance in
practical control of such donor molecular systems.Comment: 8 pages, 9 figure
Level Spectrum of Single Gated As Donors
We study the electrical transport through single As donors incorporated in the channel of a FinFET, i.e. a donor in a three-terminal geometry. By means of spectroscopic measurements in conjuction with a NEMO-3D model, we can identify the excited states and associate them with either the donors Coulomb potential, a triangular well at the interface or a hybridized combination of the two. The correspondence between the transport measurements, the theoretical model and the local environment provides an atomic understanding of actual gated donors in a nanostructure
Does phosphoglucoisomerase display anomeric specificity or selectivity towards α-d-glucose 6-phosphate? An assessment by two-dimensional phase-sensitive 31P exchange spectroscopy (EXSY) n.m.r
Electric field reduced charging energies and two-electron bound excited states of single donors in silicon
We present atomistic simulations of the D0 to D- charging energies of a gated
donor in silicon as a function of applied fields and donor depths and find good
agreement with experimental measure- ments. A self-consistent field large-scale
tight-binding method is used to compute the D- binding energies with a domain
of over 1.4 million atoms, taking into account the full bandstructure of the
host, applied fields, and interfaces. An applied field pulls the loosely bound
D- electron towards the interface and reduces the charging energy significantly
below the bulk values. This enables formation of bound excited D-states in
these gated donors, in contrast to bulk donors. A detailed quantitative
comparison of the charging energies with transport spectroscopy measurements
with multiple samples of arsenic donors in ultra-scaled FinFETs validates the
model results and provides physical insights. We also report measured D-data
showing for the first time the presence of bound D-excited states under applied
fields
APEX status pt.1: instrument development and performance
ESA APEX (Airborne Prism EXperiment) is a project for the realisation of an airborne dispersive pushbroom imaging spectrometer, a dedicated data Processing and Archiving Facility (PAF, hosted at VITO) and a Calibration Home Base (CHB, hosted at DLR) for instrument calibration operation. It has been developed by a joint Swiss-Belgian consortium.
The APEX instrument is facing its finalisation phase undergoing intense experimental activities in view of its validation and performance assessment. Environmental tests were executed to simulate flight environment conditions. The first APEX airborne campaign has been held in June 2009 covering a variety of water targets over Switzerland and Belgium. Extensive pre- and postflight characterisation and calibration campaigns were accomplished. Instrument data evaluation, performance analysis and optimisation of the data processing schemes adopted have followed.
This paper outlines the activities performed and presents the first products achieved
Evaluation of the atmospheric correction procedure for the APEX level 2/3 processor
The Airborne Prism Experiment (APEX) is a hyperspectral instrument built in a Swiss - Belgian collaboration within the ESA-PRODEX program [1]. It aims at highest possible accuracy of its delivered surface reflectance image data products.
The atmospheric correction of hyperspectral imagery is a critical element of a complete processing chain towards
unbiased reflectance and for the creation of higher level products. As the first data of APEX is expected to become
available in 2009, an appropriate processing chain for higher level processing needs to be defined and evaluated.
Standard products have been identified in all application fields of hyperspectral imaging, i.e., geology, vegetation,
cryosphere, limnology and atmosphere. They are being implemented at the APEX science center [2]. The according
processing procedures rely on data of well-defined processing states which range from calibrated at-sensor radiance to(bihemispherical) spectral albedo.
In this paper, the atmospheric processing which is implemented as part of the automated data processing chain for level 2 in the APEX processing and archiving facility (PAF) [3] is evaluated together with the ATCOR-4 atmospheric correction program [4],[5]. The evaluation is done regarding flexibility, reflectance output accuracy and processing efficiency. Two test data sets are taken for this purpose: a well-documented set of HYMAP data [6] and a high resolution HYSPEX data set [7]. Both data sets exhibit areas of overlap, which are taken for self-contained analysis of the atmospheric correction procedure. The accuracy tests include plausibility checks on selected regions of interest including a variety of known surfaces in the imagery. As some of the observed effects are related to BRDF differences, the results also give an indication for the inaccuracy related to these reflectance anisotropies. Speed measurements of the processing are then
compared to the demand for operational processing of series of data acquisition. Further comparison information is
drawn from the by-products of atmospheric correction such as water vapor distribution maps.
The study shows performance and limitations of atmospheric correction using the state-of-the-art technology, which are
mainly found in the field of BRDF effects. This points towards improvements to be implemented in course of the further development of the higher level processing chain for the APEX sensor
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