532 research outputs found
Water Resources Planning and Management in Advanced Economies: The Case Study of Western Skane, Sweden - A Background Report
This is a Working Paper intended to give background information on the Western Skane case study of water resource planning and management which is being pursued jointly by IIASA and Lund University. The paper is primarily intended to be read by a non-Swedish public. We have, however, also included some discussion of the most important analytical and policy-oriented problems of the Skane area, which means that some of the information is also of interest to a Swedish public.
The presentation in this paper is based on currently available published information on the economic and administrative structure and environmental conditions related to water planning in the region.
A preliminary version of the paper was distributed for review to planning agencies at the central and regional level of decision making. Our interpretation of their comments have been included in this final version.
We have abstained from including discussions about modeling and other methodological issues at this stage. Such methodological issues will be presented in separate papers.
It is also the intention to present a research plan based on this paper and other methodological research currently pursued at IIASA. The research plan is intended to cover a working period of approximately two years at IIASA and to be fitted into a four to five year research plan for the group working with these issues in Sweden
Analyzing capacitance-voltage measurements of vertical wrapped-gated nanowires
The capacitance of arrays of vertical wrapped-gate InAs nanowires are
analyzed. With the help of a Poisson-Schr"odinger solver, information about the
doping density can be obtained directly. Further features in the measured
capacitance-voltage characteristics can be attributed to the presence of
surface states as well as the coexistence of electrons and holes in the wire.
For both scenarios, quantitative estimates are provided. It is furthermore
shown that the difference between the actual capacitance and the geometrical
limit is quite large, and depends strongly on the nanowire material.Comment: 15 pages, 6 Figures included, to appear in Nanotechnolog
Measuring Temperature Gradients over Nanometer Length Scales
When a quantum dot is subjected to a thermal gradient, the temperature of
electrons entering the dot can be determined from the dot's thermocurrent if
the conductance spectrum and background temperature are known. We demonstrate
this technique by measuring the temperature difference across a 15 nm quantum
dot embedded in a nanowire. This technique can be used when the dot's energy
states are separated by many kT and will enable future quantitative
investigations of electron-phonon interaction, nonlinear thermoelectric
effects, and the effciency of thermoelectric energy conversion in quantum dots.Comment: 6 pages, 5 figure
Coherent Single Charge Transport in Molecular-Scale Silicon Nanowire Transistors
We report low-temperature electrical transport studies of molecule-scale
silicon nanowires. Individual nanowires exhibit well-defined Coulomb blockade
oscillations characteristic of charge addition to a single nanostructure with
length scales up to at least 400 nm. Further studies demonstrate coherent
charge transport through discrete single particle quantum levels extending the
whole device, and show that the ground state spin configuration follows the
Lieb-Mattis theorem. In addition, depletion of the nanowires suggests that
phase coherent single-dot characteristics are accessible in a regime where
correlations are strong.Comment: 4 pages and 4 figure
GaAs:Mn nanowires grown by molecular beam epitaxy of (Ga,Mn)As at MnAs segregation conditions
GaAs:Mn nanowires were obtained on GaAs(001) and GaAs(111)B substrates by
molecular beam epitaxial growth of (Ga,Mn)As at conditions leading to MnAs
phase separation. Their density is proportional to the density of catalyzing
MnAs nanoislands, which can be controlled by the Mn flux and/or the substrate
temperature. Being rooted in the ferromagnetic semiconductor (Ga,Mn)As, the
nanowires combine one-dimensional properties with the magnetic properties of
(Ga,Mn)As and provide natural, self assembled structures for nanospintronics.Comment: 13 pages, 6 figure
Correlating the nanostructure and electronic properties of InAs nanowires
The electronic properties and nanostructure of InAs nanowires are correlated
by creating multiple field effect transistors (FETs) on nanowires grown to have
low and high defect density segments. 4.2 K carrier mobilities are ~4X larger
in the nominally defect-free segments of the wire. We also find that dark field
optical intensity is correlated with the mobility, suggesting a simple route
for selecting wires with a low defect density. At low temperatures, FETs
fabricated on high defect density segments of InAs nanowires showed transport
properties consistent with single electron charging, even on devices with low
resistance ohmic contacts. The charging energies obtained suggest quantum dot
formation at defects in the wires. These results reinforce the importance of
controlling the defect density in order to produce high quality electrical and
optical devices using InAs nanowires.Comment: Related papers at http://pettagroup.princeton.ed
Unintentional high density p-type modulation doping of a GaAs/AlAs core-multi-shell nanowire
Achieving significant doping in GaAs/AlAs core/shell nanowires (NWs) is of
considerable technological importance but remains a challenge due to the
amphoteric behavior of the dopant atoms. Here we show that placing a narrow
GaAs quantum well in the AlAs shell effectively getters residual carbon
acceptors leading to an \emph{unintentional} p-type doping. Magneto-optical
studies of such a GaAs/AlAs core multi-shell NW reveal quantum confined
emission. Theoretical calculations of NW electronic structure confirm quantum
confinement of carriers at the core/shell interface due to the presence of
ionized carbon acceptors in the 1~nm GaAs layer in the shell.
Micro-photoluminescence in high magnetic field shows a clear signature of
avoided crossings of the Landau level emission line with the Landau
level TO phonon replica. The coupling is caused by the resonant hole-phonon
interaction, which points to a large 2D hole density in the structure.Comment: just published in Nano Letters
(http://pubs.acs.org/doi/full/10.1021/nl500818k
One-dimensional Weak Localization of Electrons in a Single InAs Nanowire
We report on low temperature (2-30K) electron transport and magneto-transport
measurements of a chemically synthesized InAs nanowire. Both the temperature,
T, and transverse magnetic field dependences of the nanowire conductance are
consistent with the functional forms predicted in one-dimensional (1D) weak
localization theory. By fitting the magneto-conductance data to theory, the
phase coherence length of electrons is determined to be tens of nanometers with
a T-1/3 dependence. Moreover, as the electron density is increased by a gate
voltage, the magneto-conductance shows a possible signature of suppression of
weak localization in multiple 1D subbands
Observation of degenerate one-dimensional sub-bands in cylindrical InAs nanowires
One-dimensional (1D) sub-bands in cylindrical InAs nanowires (NWs) are
electrically mapped as a function of NW diameter in the range of 15-35 nm. At
low temperatures, stepwise current increases with the gate voltage are clearly
observed and attributed to the electron transport through individual 1D
sub-bands. The two-fold degeneracy in certain sub-band energies predicted by
simulation due to structural symmetry is experimentally observed for the first
time. The experimentally obtained sub-band energies match the simulated
results, shedding light on both the energies of the sub-bands as well as the
number of sub-bands populated per given gate voltage and diameter. This work
serves to provide better insight into the electrical transport behavior of 1D
semiconductors.Comment: 20 pages, 5 figures, supporting information include
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