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 …

Radical Constructivism Has An Answer - But This Answer Is Not An Easy One, Dewey I. Dykstra

Physics Faculty Publications and Presentations

>Context • In spite of its advantages and its ability to make valid responses to objections, radical constructivism is not mainstream.

>Problem • Extolling the virtues of radical constructivism and responding logically to the objections does not work. We know this from the evidence of many attempts. Our theoretical stance, radical constructivism, also suggests this approach is not likely to have much influence on realists. We cannot transmit understanding in the signals with which we attempt to communicate. How can we in radical constructivism enable those outside of RC to understand our explanation of human knowing?

>Method • Examine our …

What Can We Learn From The Misunderstandings Of Radical Constructivism?: Commentary On Slezak’S “Radical Constructivism: Epistemology, Education And Dynamite”, Dewey I. Dykstra

Physics Faculty Publications and Presentations

>Problem • What alternative strategies from our experiences using a Piaget-based radical constructivist pedagogy might have more and better results than the current practice of responding in debate form, each side trying to prove the other wrong?

>Method • Use of Slezak’s paper to illuminate the point that the central problem with the interpretation of RC generally used in such writing is that the authors seem not to be able to operate from the central tenet of RC, which is the opposite of that used in realism. Description of how this failure to use the central tenet of RC results …

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 …

Ferroelectricity In Non-Stoichiometric Srtio3 Films Studied By Ultraviolet Raman Spectroscopy, Dmitri A. Tenne, A. K. Farrar

Physics Faculty Publications and Presentations

Homoepitaxial Sr_1+xTiO_3+δ films with -0.2 ≤ x ≤ 0.25 grown by reactive molecular-beam epitaxy on SrTiO₃ (001) substrates have been studied by ultraviolet Raman spectroscopy. Non-stoichiometry for strontium- deficient compositions leads to the appearance of strong first-order Raman scattering at low temperatures, which decreases with increasing temperature and disappears at about 350 K. This indicates the appearance of a spontaneous polarization with a paraelectric-to-ferroelectric transition temperature above room temperature. Strontium-rich samples also show a strong first-order Raman signal, but the peaks are significantly broader and exhibit a less pronounced temperature dependence, indicating a stronger contribution …

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.

Transition Metal Dopants Essential For Producing Ferromagnetism In Metal Oxide Nanoparticles, Lydia M. Johnson, Aaron Thurber, Joshua Anghel, Maryam Sabetian, Mark H. Engelhard, Dmitri A. Tenne, Charles B. Hanna, Alex Punnoose

Physics Faculty Publications and Presentations

Recent claims that ferromagnetism can be produced in nanoparticles of metal oxides without the presence of transition metal dopants have been challenged in this work by investigating 62 high quality well-characterized nanoparticle samples of both undoped and Fe doped (0-10% Fe) ZnO. The undoped ZnO nanoparticles showed zero or negligible magnetization, without any dependence on the nanoparticle size. However, chemically synthesized Zn_1-xFe_xO nanoparticles showed clear ferromagnetism, varying systematically with Fe concentration. Furthermore, the magnetic properties of Zn_1-xFe_xO nanoparticles showed strong dependence on the reaction media used to prepare the samples. The zeta …

Multiferroic Pb(Fe1/2Nb1/2)O3 Single Crystals: A Raman Scattering Study, A. F. García-Flores, Dmitri A. Tenne, W. J. Ren, X. X. Xi., S.-W. Cheong

Physics Faculty Publications and Presentations

No abstract provided.

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 …

Ferroelectricity In Strain-Free Srtio3 Thin Films, Dmitri A. Tenne

Physics Faculty Publications and Presentations

Biaxial strain is known to induce ferroelectricity in thin films of nominally non-ferroelectric materials such as SrTiO₃. However, even strain-free SrTiO₃ films and the paraelectric phase of strained films exhibit bulk frequency-dependent polarization hysteresis loops on the nanoscale at room temperature, and stable switchable domains at 50 K. By a direct comparison of the strained and strain-free SrTiO₃ films using dielectric, ferroelectric, Raman, nonlinear optical and nanoscale piezoelectric property measurements, we conclude that SrTiO₃ films and bulk crystals are relaxor ferroelectrics, and the role of strain is to stabilize longer-range correlation of preexisting nanopolar regions, …

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 …

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 …