75 research outputs found
Soliton effects in dangling-bond wires on Si(001)
Dangling bond wires on Si(001) are prototypical one dimensional wires, which
are expected to show polaronic and solitonic effects. We present electronic
structure calculations, using the tight binding model, of solitons in
dangling-bond wires, and demonstrate that these defects are stable in
even-length wires, although approximately 0.1 eV higher in energy than a
perfect wire. We also note that in contrast to conjugated polymer systems,
there are two types of soliton and that the type of soliton has strong effects
on the energetics of the bandgap edges, with formation of intra-gap states
between 0.1 eV and 0.2 eV from the band edges. These intra-gap states are
localised on the atoms comprising the soliton.Comment: 6 pages, 3 figures, 3 tables, submitted to Phys. Rev.
STM induced hydrogen desorption via a hole resonance
We report STM-induced desorption of H from Si(100)-H(2) at negative
sample bias. The desorption rate exhibits a power-law dependence on current and
a maximum desorption rate at -7 V. The desorption is explained by vibrational
heating of H due to inelastic scattering of tunneling holes with the Si-H
5 hole resonance. The dependence of desorption rate on current and bias
is analyzed using a novel approach for calculating inelastic scattering, which
includes the effect of the electric field between tip and sample. We show that
the maximum desorption rate at -7 V is due to a maximum fraction of
inelastically scattered electrons at the onset of the field emission regime.Comment: 4 pages, 4 figures. To appear in Phys. Rev. Let
Silicon Atomic Quantum Dots Enable Beyond-CMOS Electronics
We review our recent efforts in building atom-scale quantum-dot cellular
automata circuits on a silicon surface. Our building block consists of silicon
dangling bond on a H-Si(001) surface, which has been shown to act as a quantum
dot. First the fabrication, experimental imaging, and charging character of the
dangling bond are discussed. We then show how precise assemblies of such dots
can be created to form artificial molecules. Such complex structures can be
used as systems with custom optical properties, circuit elements for
quantum-dot cellular automata, and quantum computing. Considerations on
macro-to-atom connections are discussed.Comment: 28 pages, 19 figure
Towards the fabrication of phosphorus qubits for a silicon quantum computer
The quest to build a quantum computer has been inspired by the recognition of
the formidable computational power such a device could offer. In particular
silicon-based proposals, using the nuclear or electron spin of dopants as
qubits, are attractive due to the long spin relaxation times involved, their
scalability, and the ease of integration with existing silicon technology.
Fabrication of such devices however requires atomic scale manipulation - an
immense technological challenge. We demonstrate that it is possible to
fabricate an atomically-precise linear array of single phosphorus bearing
molecules on a silicon surface with the required dimensions for the fabrication
of a silicon-based quantum computer. We also discuss strategies for the
encapsulation of these phosphorus atoms by subsequent silicon crystal growth.Comment: To Appear in Phys. Rev. B Rapid Comm. 5 pages, 5 color figure
Scanning Tunneling Microscopy Study and Nanomanipulation of Graphene-Coated Water on Mica
We study interfacial water trapped between a sheet of graphene and a
muscovite (mica) surface using Raman spectroscopy and ultra-high vacuum
scanning tunneling microscopy (UHV-STM) at room temperature. We are able to
image the graphene-water interface with atomic resolution, revealing a layered
network of water trapped underneath the graphene. We identify water layer
numbers with a carbon nanotube height reference. Under normal scanning
conditions, the water structures remain stable. However, at greater electron
energies, we are able to locally manipulate the water using the STM tip.Comment: In press, 5 figures, supplementary information at Nano Letters
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Exchange Reactions between Alkanethiolates and Alkaneselenols on Au{111}
When alkanethiolate self-assembled monolayers on Au{111} are exchanged with alkaneselenols from solution, replacement of thiolates by selenols is rapid and complete, and is well described by perimeter-dependent island growth kinetics. The monolayer structures change as selenolate coverage increases, from being epitaxial and consistent with the initial thiolate structure to being characteristic of selenolate monolayer structures. At room temperature and at positive sample bias in scanning tunneling microscopy, the selenolate-gold attachment is labile, and molecules exchange positions with neighboring thiolates. The scanning tunneling microscope probe can be used to induce these place-exchange reactions
Nanoscale STM-patterning and chemical modification of the Si(100) surface
Nanoscale patterning of the Si(100)-2x1:H monohydride surface has been achieved using an ultrahigh vacuum (UHV) scanning tunneling microscope (STM). The monohydride surface, prepared in UHV by exposure of a heated sample (650 K) to an atomic hydrogen flux, serves as an effective resist for STM patterning and exposure to O 2 and NH 3. Operating the STM in field emission causes hydrogen to be desorbed from the surface, exposing atomically clean silicon. There is no evidence for repassivation of the surface after patterning, suggesting that hydrogen may desorb as H 2. Hydrogen desorption can also be achieved at tunneling biases (~3-4 V) by using larger currents. Nanometer-scale linewidths can be achieved with this technique; single dimer rows have in fact been depassivated. The patterned areas display the same chemical reactivity as clean Si, suggesting the possibility of selective chemical modification of the surface at nanometer scales. This STM-depassivation technique shows considerable potential as a means for nanostructure fabrication
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