171 research outputs found
Tunneling images of a 2D electron system in a quantizing magnetic field
We have applied a scanning probe method, Subsurface Charge Accumulation (SCA)
imaging, to resolve the local structure of the interior of a semiconductor
two-dimensional electron system (2DES) in a tunneling geometry. Near magnetic
fields corresponding to integer Landau level filling, submicron scale spatial
structure in the out-of-phase component of the tunneling signal becomes
visible. In the images presented here, the structure repeats itself when the
filling factor is changed from nu=6 to nu=7. Therefore, we believe the images
reflect small modulations in the 2DES density caused by the disorder in the
sample.Comment: 2 pages, 2 color figures, submitted to LT23 proceeding
Modeling single- and multiple-electron resonances for electric-field-sensitive scanning probes
We have developed a modeling method suitable to analyze single- and
multiple-electron resonances detected by electric-field-sensitive scanning
probe techniques. The method is based on basic electrostatics and a numerical
boundary-element approach. The results compare well to approximate analytical
expressions and experimental data.Comment: 10 pages, 4 figure
Subsurface Charge Accumulation Imaging
Contains an introduction and a list of publications.Joint Services Electronics Program Grant DAAH04-95-1-0038National Science Foundation Young Investigator AwardU.S. Navy - Office of Naval Research Grant N00014-93-1-063
Scanning-probe spectroscopy of semiconductor donor molecules
Semiconductor devices continue to press into the nanoscale regime, and new
applications have emerged for which the quantum properties of dopant atoms act
as the functional part of the device, underscoring the necessity to probe the
quantum structure of small numbers of dopant atoms in semiconductors[1-3].
Although dopant properties are well-understood with respect to bulk
semiconductors, new questions arise in nanosystems. For example, the quantum
energy levels of dopants will be affected by the proximity of nanometer-scale
electrodes. Moreover, because shallow donors and acceptors are analogous to
hydrogen atoms, experiments on small numbers of dopants have the potential to
be a testing ground for fundamental questions of atomic and molecular physics,
such as the maximum negative ionization of a molecule with a given number of
positive ions[4,5]. Electron tunneling spectroscopy through isolated dopants
has been observed in transport studies[6,7]. In addition, Geim and coworkers
identified resonances due to two closely spaced donors, effectively forming
donor molecules[8]. Here we present capacitance spectroscopy measurements of
silicon donors in a gallium-arsenide heterostructure using a scanning probe
technique[9,10]. In contrast to the work of Geim et al., our data show
discernible peaks attributed to successive electrons entering the molecules.
Hence this work represents the first addition spectrum measurement of dopant
molecules. More generally, to the best of our knowledge, this study is the
first example of single-electron capacitance spectroscopy performed directly
with a scanning probe tip[9].Comment: In press, Nature Physics. Original manuscript posted here; 16 pages,
3 figures, 5 supplementary figure
Direct observation of micron-scale ordered structure in a two-dimensional electron system
We have applied a novel scanned probe method to directly resolve the interior
structure of a GaAs/AlGaAs two-dimensional electron system in a tunneling
geometry. We find that the application of a perpendicular magnetic field can
induce surprising density modulations that are not static as a function of the
field. Near six and four filled Landau levels, stripe-like structures emerge
with a characteristic wave length ~2 microns. Present theories do not account
for ordered density modulations on this length scale.Comment: 5 pages, 4 figures. To appear in Phys. Rev.
Modifying the surface electronic properties of YBa2Cu3O7-delta with cryogenic scanning probe microscopy
We report the results of a cryogenic study of the modification of
YBa2Cu3O7-delta surface electronic properties with the probe of a scanning
tunneling microscope (STM). A negative voltage applied to the sample during STM
tunneling is found to modify locally the conductance of the native degraded
surface layer. When the degraded layer is removed by etching, the effect
disappears. An additional surface effect is identified using Scanning Kelvin
Probe Microscopy in combination with STM. We observe reversible surface
charging for both etched and unetched samples, indicating the presence of a
defect layer even on a surface never exposed to air.Comment: 6 pages, 4 figures. To appear in Superconductor Science and
Technolog
Modeling Subsurface Charge Accumulation Images of a Quantum Hall Liquid
Subsurface Charge Accumulation imaging is a cryogenic scanning probe
technique that has recently been used to spatially probe incompressible strips
formed in a two-dimensional electron system (2DES) at high magnetic fields. In
this paper, we present detailed numerical modeling of these data. At a basic
level, the method produces results that agree well with the predictions of
models based on simple circuit elements. Moreover, the modeling method is
sufficiently advanced to simulate the spatially resolved measurements. By
comparing directly the simulations to the experimentally measured data, we can
extract quantitatively local electronic features of the 2DES. In particular, we
deduce the electron density of states inside the incompressible strips and
electrical resistance across them.Comment: 11 pages, 3 figure
Single-Electron Spectroscopy
Contains an introduction, reports on four research projects and a list of publications,Joint Services Electronics Program Grant DAAH04-95-1-0038National Science Foundation Young Investigator AwardU.S. Navy - Office of Naval Research Grant N00014-93-1-063
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