arXiv subjects

R. Stanley Williams

Publications and source records attributed to R. Stanley Williams.

23 records · Page 2Linked to original sources

arXiv2010

Molecular dynamics simulations of oxide memory resistors (memristors)

Reversible bipolar nano-switches that can be set and read electronically in a solid-state two-terminal device are very promising for applications. We have performed molecular-dynamics simulations that mimic systems with oxygen vacancies interacting via realistic potentials and driven by an external bias voltage. The competing short- and long-range interactions among charged mobile vacancies lead to density fluctuations and short-range ordering, while illustrating some aspects of observed experimental behavior, such as memristor polarity inversion.

cond-mat.mes-hall↗

arXiv2009

Molecular Scale Imaging with a Smooth Superlens

We demonstrate a smooth and low loss silver (Ag) optical superlens capable of resolving features at 1/12th of the illumination wavelength with high fidelity. This is made possible by utilizing state-of-the-art nanoimprint technology and intermediate wetting layer of germanium (Ge) for the growth of flat silver films with surface roughness at sub-nanometer scales. Our measurement of the resolved lines of 30nm half-pitch shows a full-width at half-maximum better than 37nm, in excellent agreement with theoretical predictions. The development of this unique optical superlens lead promise to parallel imaging and nanofabrication in a single snapshot, a feat that are not yet available with other nanoscale imaging techniques such as atomic force microscope or scanning electron microscope.

physics.optics↗

arXiv2007

Modulation of Negative Index Metamaterials in the Near-IR Range

Optical modulation of the effective refractive properties of a "fishnet" metamaterial with a Ag/Si/Ag heterostructure is demonstrated in the near-IR range and the associated fast dynamics of negative refractive index is studied by pump-probe method. Photo excitation of the amorphous Si layer at visible wavelength and corresponding modification of its optical parameters is found to be responsible for the observed modulation of negative refractive index in near-IR.

cond-mat.mtrl-sci↗

arXiv2007

Quantum Conductance Oscillations in Metal/Molecule/Metal Switches at Room Temperature

Conductance switching has been reported in many molecular junction devices, but in most cases has not been convincingly explained. We investigate conductance switching in Pt/stearic acid monolayer/Ti devices using pressure-modulated conductance microscopy. For devices with conductance G>>G_Q or G<<G_Q, where GQ=2e^2/h is the conductance quantum, pressure-induced conductance peaks <30 nm in diameter are observed, indicating the formation of nanoscale conducting pathways between the electrodes. For devices with G~ 1- 2 G_Q, in addition to conductance peaks we also observed conductance dips and oscillations in response to localized pressure. These results can be modeled by considering interfering electron waves along a quantum conductance channel between two partially transmitting electrode surfaces. Our findings underscore the possible use of these devices as atomic-scale switches.

cond-mat.mes-hall↗

arXiv2007

Alloying mechanisms for epitaxial nanocrystals

The different mechanisms involved in the alloying of epitaxial nanocrystals are reported in this letter. Intermixing during growth, surface diffusion and intra-island diffusion were investigated by varying the growth conditions and annealing environments during chemical vapor deposition. The relative importance of each mechanism was evaluated in determining a particular composition profile for dome-shaped Ge:Si (001) islands. For samples grown at a faster rate, intermixing during growth was reduced. Si surface diffusion dominates during H$_2$ annealing whereas Ge surface diffusion and intra-island diffusion prevail during annealing in a PH$_3$ environment.

cond-mat.mtrl-sci↗