Physical Sciences and Mathematics Commons^™

Nonlinear Ordinary Differential Equations In Fluid Dynamics, John D. Ramshaw

Physics Faculty Publications and Presentations

The equivalence between nonlinear ordinary differential equations (ODEs) and linear partial differential equations (PDEs) was recently revisited by Smith, who used the equivalence to transform the ODEs of Newtonian dynamics into equivalent PDEs, from which analytical solutions to several simple dynamical problems were derived. We show how this equivalence can be used to derive a variety of exact solutions to the PDEs describing advection in fluid dynamics in terms of solutions to the equivalent ODEs for the trajectories of Lagrangian fluid particles. The PDEs that we consider describe the time evolution of non-diffusive scalars, conserved densities, and Lagrangian surfaces advected …

Frequency Multiplication In Nanowires, Marius Ghita, Ed Godshalk, Gary Goncher, Raj Solanki

Physics Faculty Publications and Presentations

Frequency multiplication in silicon and ZnO nanowire based Schottky and p-n diodes has been demonstrated at fundamental frequencies of 70 MHz and 500 MHz. Our motivation for using nanowires contacted at their tips was to minimize the spreading resistance and boundary capacitance in order to produce higher cut-off frequencies and conversion efficiencies compared to planar diodes. The data presented here are limited to the lower GHz range by the frequency response of the experimental apparatus. However, by employing microwave waveguides and higher fundamental source frequencies, it should be possible to reach much higher output frequencies with nanowire-based diodes.

Field Programmable Gate Array Based Reconfigurable Scanning Probe/Optical Microscope, Derek Brant Nowak, Andrew James Lawrence, Zechariah K. Dzegede, Justin C. Hiester, Cliff Kim, Erik J. Sánchez

Physics Faculty Publications and Presentations

The increasing popularity of nanometrology and nanospectroscopy has pushed researchers to develop complex new analytical systems. This paper describes the development of a platform on which to build a microscopy tool that will allow for flexibility of customization to suit research needs. The novelty of the described system lies in its versatility of capabilities. So far, one version of this microscope has allowed for successful near-field and far-field fluorescence imaging with single molecule detection sensitivity. This system is easily adapted for reflection, polarization (Kerr magneto-optical (MO)), Raman, super-resolution techniques, and other novel scanning probe imaging and spectroscopic designs. While collecting …

A Simple Approach To Neutral Atom Microscopy, Philip Witham, Erik J. Sánchez

Physics Faculty Publications and Presentations

Scanning surfaces using a beam of noncharged atoms or molecules allows for especially nondestructive and low-energy surface imaging, with the potential to obtain new information about surfaces that cannot be easily obtained otherwise. We have developed a new approach, operating with the sample at a close working distance from an aperture, the need for optics to focus the beam is obviated. Compared to more complex approaches, the theoretical performance has no other disadvantage than the short working distance. Resolution of 1.5 μm has been achieved, and submicron resolution appears to be practical. Construction of the microscope and results are presented, …

Whispering-Gallery Acoustic Sensing: Characterization Of Mesoscopic Films And Scanning Probe Microscopy Applications, Andres H. La Rosa, Nan Li, Rodolfo Fernandez, Xiaohua Wang, Richard Nordstrom, S. K. Padigi

Physics Faculty Publications and Presentations

Full understanding of the physics underlying the striking changes in viscoelasticity, relaxation time, and phase transitions that mesoscopic fluid-like films undergo at solid-liquid interfaces, or under confinement between two sliding solid boundaries, constitutes one of the major challenges in condensed matter physics. Their role in the imaging process of solid substrates by scanning probe microscopy (SPM) is also currently controversial. Aiming at improving the reliability and versatility of instrumentation dedicated to characterize mesoscopic films, a noninvasive whispering-gallery acoustic sensing (WGAS) technique is introduced; its application as feedback control in SPM is also demonstrated. To illustrate its working principle and potential …

Electronic Properties Of Metal-Arene Functionalized Graphene, Pavel Plachinda, David Evans, Raj Solanki

Physics Faculty Publications and Presentations

We have employed first-principles density-functional calculations to study the electronic characteristics of covalently functionalized graphene by metal-bis-arene chemistry. It is shown that functionalization with M-bis-arene (M = Ti, V, Cr, Mn, Fe) molecules leads to an opening in the bandgap of graphene (up to 0.81 eV for the Cr derivative), and as a result, transforms it from a semimetal to a semiconductor. The bandgap induced by attachment of a metal atom topped by a benzene ring is attributed to modification of π-conjugation and depends on the concentration of functionalizing molecules. This approach offers a means of tailoring the band structure …

Nonlinear Time Dependence Of Dark Current In Charge-Coupled Devices, Justin Charles Dunlap, Erik Bodegom, Ralf Widenhorn

Physics Faculty Publications and Presentations

It is generally assumed that charge-coupled device (CCD) imagers produce a linear response of dark current versus exposure time except near saturation. We found a large number of pixels with nonlinear dark current response to exposure time to be present in two scientific CCD imagers. These pixels are found to exhibit distinguishable behavior with other analogous pixels and therefore can be characterized in groupings. Data from two Kodak CCD sensors are presented for exposure times from a few seconds up to two hours. Linear behavior is traditionally taken for granted when carrying out dark current correction and as a result, …

Dark Current In An Active Pixel Complementary Metal-Oxide-Semiconductor Sensor, Justin Charles Dunlap, William Christian Porter, Erik Bodegom, Ralf Widenhorn

Physics Faculty Publications and Presentations

We present an analysis of dark current from a complementary metal?oxide?semiconductor (CMOS) active pixels sensor with global shutter. The presence of two sources of dark current, one within the collection area of the pixel and another within the sense node, present complications to correction of the dark current. The two sources are shown to generate unique and characteristic dark current behavior with respect to varying exposure time, temperature, and/or frame rate. In particular, a pixel with storage time in the sense node will show a dark current dependence on frame rate and the appearance of being a ?stuck pixel? with …

Acousto Characterization Of Fluid-Like Mesoscopic Films Under Shear, Rodolfo Fernandez, Xiaohua Wang, Andres H. La Rosa

Physics Faculty Publications and Presentations

Full understanding of the physics underlying the striking changes-in viscoelasticity, relaxation time, and phase transitions-that mesoscopic fluid-like systems undergo when placed under confinement or when adsorbed at solid surfaces constitutes a long standing scientific challenge. One of the methods used to characterize these films consists of bringing a solid boundary closer to another solid boundary (while in relative lateral periodic motion) with a liquid trapped in between. In addition, using a tapered probe (~ 50 nm apex diameter) as one of the boundaries improves the lateral resolution of the measurement. In this scenario, the dynamics of the fluid is inferred …

Crystallite Phase And Orientation Determinations Of (Mn, Ga) As/Gaas-Crystallites Using Analyzed (Precession) Electron Diffraction Patterns, Ines Häusler, Stavros Nicolopoulos, Edgar F. Rauch, K. Volz, Peter Moeck

Physics Faculty Publications and Presentations

Outline of the presentation:

1. Material system: (Mn,Ga)As/GaAs-crystallites

2. Structure analysis using Nano-beam Diffraction (NBD) Precession Electron Diffraction Technique (PED) --> Structure type I + II

3. Phase and orientation mapping using ASTAR

4. Conclusion

Computational Approach To Dark Current Spectroscopy In Ccds As Complex Systems. Ii. Numerical Analysis Of The Uniqueness Parameters Evaluation, Ionel Tunaru, Ralf Widenhorn, Dan A. Iordache, Erik Bodegom

Physics Faculty Publications and Presentations

The evaluation of the uniqueness parameters of the temperature dependence in CCDs is difficult to the considerable number of input parameters and to the strongly nonlinear (exponential) theoretical relations. For this reason, the elaborated computer programs are very sensitive to the choice of the zero-order approximations of the effective (Si) energy gap, and of the weights associated to the experimentally determined dark current. The main goal of this work was to study the rather narrow stability domains of the zero-order approximations, which lead to attractors with physical meaning. It was found that the stability domains are surrounded by (usually in …

Photoelectron Emission Control With Polarized Light In Plasmonic Metal Random Structures, Robert Campbell Word, Joseph Fitzgerald, Rolf Kӧnenkamp

Physics Faculty Publications and Presentations

The authors report on the possibility of switching the emission rate of photoelectrons by polarization changes in the plasmon excitation light. Photoelectron emission is strongly enhanced in the near-field of localized surface plasmons and occurs from areas with typical diameters of 20-70 nm. The underlying physical process involves excitation of a localized surface plasmon polariton with a femtosecond laser pulse, and a subsequent multi-photon photoemission process. The non-linearity of this process leads to a sharp polarization dependence that allows efficient switching of the emission. We demonstrate that a 90° polarization change can result in on/off ratios of ∼100 for electron …