Physics Commons^™

Apertureless Near-Field/Far-Field Cw Two-Photon Microscope For Biological And Material Imaging And Spectroscopic Applications, Derek Brant Nowak, Andrew James Lawrence, Erik J. Sánchez

Physics Faculty Publications and Presentations

We present the development of a versatile spectroscopic imaging tool to allow for imaging with single-molecule sensitivity and high spatial resolution. The microscope allows for near-field and subdiffraction-limited far-field imaging by integrating a shear-force microscope on top of a custom inverted microscope design. The instrument has the ability to image in ambient conditions with optical resolutions on the order of tens of nanometers in the near field. A single low-cost computer controls the microscope with a field programmable gate array data acquisition card. High spatial resolution imaging is achieved with an inexpensive CW multiphoton excitation source, using an apertureless probe …

Bandwidth Tuning Triggers Interplay Of Charge Order And Superconductivity In Two-Dimensional Organic Materials, S. Kaiser, M. Dressel, Y. Sun, A. Greco, J. A. Schlueter, Gary L. Gard, N. Drichko

Chemistry Faculty Publications and Presentations

We observe charge-order fluctuations in the quasi-two-dimensional organic superconductor β″-(BEDT-TTF)₂SF₅CH₂CF₂SO₃, both by means of vibrational spectroscopy, locally probing the fluctuating charge order, and by investigating the in-plane dynamical response by infrared reflectance spectroscopy. The decrease of the effective electronic interaction in an isostructural metal suppresses both charge-order fluctuations and superconductivity, pointing to their interplay. We compare the results of our experiments with calculations on the extended Hubbard model.

Accurate Description Of The Optical Response Of A Multilayered Spherical System In The Long Wavelength Approximation, H. Y. Chung, G. Y. Guo, Hai-Pang Chiang, D. P. Tsai, P.T. Leung

Physics Faculty Publications and Presentations

The optical response of a multilayered spherical system of unlimited number of layers (a “matryoshka”) in the long wavelength limit can be accounted for from the knowledge of the static multipole polarizability of the system to first-order accuracy. However, for systems of ultrasmall dimensions or systems with sizes not-too-small compared to the wavelength, this ordinary quasistatic long wavelength approximation (LWA) becomes inaccurate. Here we introduce two significant modifications of the LWA for such a nanomatryoshka in each of the two limits: the nonlocal optical response for ultrasmall systems (<10 >nm), and the “finite-wavelength corrections” for systems ∼100 nm. This is …

Systems For Assessing And Enhancing The Performance Of Scanning Electron Microscopes By Quantifying And Enforcing Symmetries And Periodicities In Two Dimensions, Peter Moeck

Physics Faculty Publications and Presentations

Scanning probe microscope (SPM) images are enhanced by enforcing one or more symmetries that can be selected based on suitable Fourier coefficient amplitude or phase angle residuals, and/ or geometric Akaike information criteria, and/ or cross correlation techniques. Alternatively, this selection can be based on prior knowledge of specimen characteristics. In addition, a scanning microscope point spread function is obtained based on the evaluation of a calibration image by enforcing at least one symmetry and can be applied to other image acquisitions.

Contribution Of Membrane Elastic Energy To Rhodopsin Function, Olivier Soubias, Walter E. Teague, Kirk G. Hines, Drake C. Mitchell, Klaus Gawrisch

Physics Faculty Publications and Presentations

We considered the issue of whether shifts in the metarhodopsin I (MI)-metarhodopsin II (MII) equilibrium from lipid composition are fully explicable by differences in bilayer curvature elastic stress. A series of six lipids with known spontaneous radii of monolayer curvature and bending elastic moduli were added at increasing concentrations to the matrix lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and the MI-MII equilibrium measured by flash photolysis followed by recording UV-vis spectra. The average area-per-lipid molecule and the membrane hydrophobic thickness were derived from measurements of the 2H NMR order parameter profile of the palmitic acid chain in POPC. For the series of ethanolamines …

Photoemission From Localized Surface Plasmons In Fractal Metal Nanostructures, Robert Campbell Word, Rolf Könenkamp, T. T. Dornan

Physics Faculty Publications and Presentations

We use photoemission microscopy to characterize localized surface plasmon distributions in nanostructured gold layers on indium-tin-oxide/glass substrates. The Au films have a fractal dimension of ∼1.3 and smallest feature sizes of ∼100 nm. We use femtosecond laser pulses at a wavelength of ∼800 nm for the plasmon excitation. Photoelectron emission occurs by a three-photon process in localized areas of indium-tin-oxide with ∼70 nm diameter. In these areas the photoemission rate is enhanced several thousand fold compared to nonstructured surface areas. The results show that plasmon enhanced photoemission can be induced in a nonabsorbing material in proximity to a plasmon-active metal …

Remote Plasma Assisted Growth Of Graphene Films, Gopichand Nandamuri, Sergei Rouvimov, Raj Solanki

Physics Faculty Publications and Presentations

Single and multiple layers of graphene films were grown on 111 oriented single crystals of nickel and polycrystalline nickel films using remote plasma assisted chemical vapor deposition. Remote plasma was employed to eliminate the effect of the plasma electrical field on the orientation of the grown graphene films, as well as to reduce the growth temperature compared to conventional chemical vapor deposition. The electrical and optical properties, including high resolution transmission electron microscopy of these films, suggest that this approach is both versatile and scalable for potential large area optoelectronic applications.

Charge Diffusion In The Field-Free Region Of Charge-Coupled Devices, Ralf Widenhorn, Alexander Weber-Bargioni, Morley M. Blouke, Albert J. Bae, Erik Bodegom

Physics Faculty Publications and Presentations

The potential well in back-illuminated charge-coupled devices (CCDs) does not reach all the way to the back surface. Hence, light that is absorbed in the field-free region generates electrons that can diffuse into neighboring pixels and thus decreases the spatial resolution of the sensor. We present data for the charge diffusion from a near point source by measuring the response of a back-illuminated CCD to light emitted from a submicron diameter glass fiber tip. The diffusion of electrons into neighboring pixels is analyzed for different wavelengths of light ranging from 430 to 780 nm. To find out how the charge …

Correction Of Dark Current In Consumer Cameras, Justin Charles Dunlap, Erik Bodegom, Ralf Widenhorn

Physics Faculty Publications and Presentations

A study of dark current in digital imagers in digital singlelens reflex (DSLR) and compact consumer-grade digital cameras is presented. Dark current is shown to vary with temperature, exposure time, and ISO setting. Further, dark current is shown to increase in successive images during a series of images. DSLR and compact consumer cameras are often designed such that they are contained within a densely packed camera body, and therefore the digital imagers within the camera frame are prone to heat generated by the sensor as well as nearby elements within the camera body. It is the scope of this work …

Automated Nanocrystal Orientation And Phase Mapping In The Transmission Electron Microscope On The Basis Of Precession Electron Diffraction, Edgar F. Rauch, Joaquin Portillo, Stavros Nicolopoulos, Daniel Bultreys, Sergei Rouvimov, Peter Moeck

Physics Faculty Publications and Presentations

An automated technique for the mapping of nanocrystal phases and orientations in a transmission electron microscope is described. It is primarily based on the projected reciprocal lattice geometry that is extracted from electron diffraction spot patterns. Precession electron diffraction patterns are especially useful for this purpose. The required hardware allows for a scanning-precession movement of the primary electron beam on the crystalline sample and can be interfaced to any older or newer mid-voltage transmission electron microscope (TEM). Experimentally obtained crystal phase and orientation maps are shown for a variety of samples. Comprehensive commercial and open-access crystallographic databases may be used …

Gauge Invariance And Reciprocity In Quantum Mechanics, P.T. Leung, K. Young

Physics Faculty Publications and Presentations

Reciprocity in wave propagation usually refers to the symmetry of the Green's function under the interchange of the source and the observer coordinates, but this condition is not gauge invariant in quantum mechanics, a problem that is particularly significant in the presence of a vector potential. Several possible alternative criteria are given and analyzed with reference to different examples with nonzero magnetic fields and/or vector potentials, including the case of a multiply connected spatial domain. It is shown that the appropriate reciprocity criterion allows for specific phase factors separable into functions of the source and observer coordinates and that this …

Emissions Of Anaerobically Produced Methane By Trees, Andrew L. Rice, Christopher Lee Butenhoff, Martha J. Shearer, Doaa Teama, Todd N. Rosenstiel, M. A. K. Khalil

Physics Faculty Publications and Presentations

Recent studies indicate that plants may be a previously overlooked but significant source of atmospheric CH₄, though there is considerable disagreement on the mechanism of production. Our work sought to verify that woody deciduous trees grown under inundated conditions had the capacity for transporting CH₄ from an anaerobic subsurface to the atmosphere and to consider if such a source could be important globally. Here, we report results from a greenhouse mesocosm study that indicate significant emissions of anaerobically produced CH₄ transmitted to the atmosphere through broadleaf riparian tree species grown under flooded conditions. Using a leaf area normalized mean emission …

Thin Film Group Ii-Vi Solar Cells Based On Band-Offsets, James Keith Walton

Dissertations and Theses

The amount of traditional energy sources are finite and the ecological impact of continuing to produce energy using fossil fuels will only exacerbate the carbon footprint. It is for these reasons that photovoltaic modules are becoming a larger and more necessary part the world's electricity production paradigm.

Photovoltaic (PV) semiconductor modules are grouped into three categories. 'First generation' monocrystalline and polycrystalline silicon modules that consist of p-n junctions created via the addition of impurities known as dopants. Almost 85% of solar cells produced at this time are 'first generation' and it is the high production costs of silicon PV modules …

Investigation Of The Sources And Sinks Of Atmospheric Methane, Christopher Lee Butenhoff

Dissertations and Theses

The work presented here represents a number of independent studies that investigated various components of the CH₄ budget, namely the sources and sinks. We used a chemical-tracer model and created unique long-term time series of atmospheric CH₄, carbon monoxide (CO), molecular hydrogen (H₂), and methylchloroform (CH₃CCl₃) measurements at marine background air to derive histories of atmospheric hydroxyl radical (OH) - the main chemical oxidant of CH₄, biomass burning - an important source of CH₄ in the tropics, and emissions of CH₄ from rice paddies - one of …

Characterization And Correction Of Dark Current In Compact Consumer Cameras, Justin Charles Dunlap, Erik Bodegom, Ralf Widenhorn

Physics Faculty Publications and Presentations

A study of dark current in digital imagers within consumer grade digital cameras is presented. Dark current is shown to vary with temperature, exposure time, and ISO setting. Further, dark current is shown to increase in successive images during a series of images. Consumer cameras are often designed to be as compact as possible and therefore the digital imagers within the camera frame are prone to heat generated by nearby elements within the camera body. It is the scope of this work to characterize the dark current in such cameras and to show that the dark current, in part due …

Study Of The Numerical Modeling Of The Temperature Dependence Of The Dark Current In Charge Coupled Devices, Ralf Widenhorn, Ionel Tunaru, Erik Bodegom, Dan A. Iordache

Physics Faculty Publications and Presentations

As it is well known, the classical works of the Dark Current Spectroscopy method allow - using some not too accurate theoretical relations, but huge numbers of dark current values for thousands of pixels - the evaluation of a reduced number of basic impurities parameters. Unlike these works, this paper tries to obtain--by means of some better approximations of the Shockley-Read-Hall (SRH) model--more information about the studied impurities, as well as the study of the compatibility of the used theoretical model SRH relative to the experimental data. In this manner, both the compatibility SRH model with the studied experimental data …