Direct Imaging of Two-State Dynamics on the Amorphous Silicon Surface

Amorphous silicon is an important material, amidst a debate whether or not it is a glass. We produce amorphous Si surfaces by ion bombardment and vapor growth, and image discrete Si clusters which hop by two-state dynamics at 295 K. Independent of surface preparation, these clusters have an average diameter of ~5 atoms. Given prior results for metallic glasses, we suggest that this cluster size is a universal feature. The hopping activation free energy of 0.93 ± 0.15 eV is rather small, in agreement with a previously untested surface glass model. Hydrogenation quenches the two-state dynamics, apparently by increasing surface crystallinity

Direct measurements of magnetostrictive process in amorphous wires using scanning tunneling microscopy

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.We demonstrate a versatile capability to measure directly the magnetostrictive properties through the magnetization process on a nanometric scale using a modified scanning tunneling microscope. Single 10 mm long, 125 μm diam amorphouswires of both positive and negative magnetostriction have been studied and the data are compared with the hysteretic loops determined by both ac and SQUID magnetic measurements. This improved technique promises interesting possibilities, from both fundamental and applications points of view, in a number of scientific disciplines especially of interest in life and environmental sciences

Characterization of nanometer-sized, mechanically exfoliated graphene on the H-passivated Si(100) surface using scanning tunnelling microscopy

We have developed a method for depositing graphene monolayers and bilayers with minimum lateral dimensions of 2-10 nm by the mechanical exfoliation of graphite onto the Si(100)-2x1:H surface. Room temperature, ultra-high vacuum (UHV) tunnelling spectroscopy measurements of nanometer-sized single-layer graphene reveal a size dependent energy gap ranging from 0.1-1 eV. Furthermore, the number of graphene layers can be directly determined from scanning tunnelling microscopy (STM) topographic contours. This atomistic study provides an experimental basis for probing the electronic structure of nanometer-sized graphene which can assist the development of graphene-based nanoelectronics.Comment: Accepted for publication in Nanotechnolog

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$\times1$) 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$\sigma$ 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

Fabrication of metallic nanowires with a scanning tunneling microscope

A procedure to pattern thin metal films on a nanometer scale with a scanning tunneling microscope (STM) operating in air is reported. A 30 nm film of hydrogenated amorphous silicon (a‐Si:H) is deposited on a 10 nm film of TaIr. Applying a negative voltage between the STM tip and the a‐Si:H film causes the local oxidation of a‐Si:H. The oxide which is formed is used as a mask to wet etch the not‐oxidized a‐Si:H and subsequently, the remaining pattern is transferred into the metal film by Ar ion milling. Metal wires as narrow as 40 nm have been fabricated. Since a‐Si:H can be deposited in very thin layers on almost any substrate, the presented procedure can be applied to structure all kind of thin films on a nanometer scale

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 websit

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