Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session P38: Sensors and Signal Analysis |
Hide Abstracts |
Sponsoring Units: GIMS Chair: Charles Agosta, Clark University Room: Colorado Convention Center 501 |
Wednesday, March 7, 2007 11:15AM - 11:27AM |
P38.00001: An Ultra-Wideband Cross-Correlation Radiometer for Mesoscopic Experiments Ryan Toonen, Cyrus Haselby, Hua Qin, Mark Eriksson, Robert Blick We have designed, built and tested a cross-correlation radiometer for detecting statistical order in the quantum fluctuations of mesoscopic experiments at sub-Kelvin temperatures.~ Our system utilizes a fully analog front-end--operating over the X- and Ku-bands (8 to 18 GHz)--for computing the cross-correlation function.~ Digital signal processing techniques are used to provide robustness against instrumentation drifts and offsets.~ The economized version of our instrument can measure, with sufficient correlation efficiency, noise signals having power levels as low as 10 fW.~ We show that, if desired, we can improve this performance by including cryogenic preamplifiers which boost the signal-to-noise ratio near the signal source.~ By adding a few extra components, we can measure both the real and imaginary parts of the cross-correlation function--improving the overall signal-to-noise ratio by a factor of sqrt[2].~ We demonstrate the utility of our cross-correlator with noise power measurements from a quantum point contact. [Preview Abstract] |
Wednesday, March 7, 2007 11:27AM - 11:39AM |
P38.00002: Monochromatic Photo-Field Electron Emission Sources Theodore Vecchione, Gary Hembree, Uwe Weierstall, John Spence, Nigel Browning Laser-pulsed photo-field-emission sources with high coherence and brightness are needed for time-resolved electron microscopy. Our ongoing work explores the possibility of using sharpened semiconductor electron emitters to achieve this goal. Intrinsic GaAs field-emission sources have been prepared from cleaved needles that are clipped into refractory metal holders. These needles are chemically sharpened and surface cleaned by field-desorption and electron-bombardment heating. Field emission I-V curves have been analyzed, with and without laser illumination, which demonstrate a range of metallic and semiconductor characteristics. He-Ne laser illumination has been observed to increase field emission currents by more then an order of magnitude. The band structure of a semiconductor can be used to create a lower bound on the energy of photo-excited field-emitted electrons, producing a beam whose energy width is E=Eg-h$\nu $ (bandgap Eg). Energy analysis is planned using a hemispherical analyzer, aimed at achieving an energy spread less than the 0.26 eV of conventional W tips. Calculations are underway to understand complications arising from surface effects and bulk transport. NNSA award DE-PS52-05NA funds this research. [Preview Abstract] |
Wednesday, March 7, 2007 11:39AM - 11:51AM |
P38.00003: Design and Fabrication of Piezoresistive Microcantilevers for Low Temperature Torque Magnetometry Dan J. Hills, Jack K. Luo, Christoph Bergemann Piezoresistive microcantilevers provide an experimentally simple and highly sensitive way of measuring the magnetization of small (\,$<\!(100\,\mu\mathrm{m})^3$\,) samples. These devices --- micromachined from crystalline silicon --- were originally designed as probes for atomic force microscopy, but were implemented by several researchers as torque sensors. Here we present newly designed and fabricated levers with properties optimized for torque measurements, including specifically those at low temperatures. In particular they may be used for de Haas- van Alphen measurements in high magnetic fields. Torque magnetometry detection of quantum oscillations is a potentially advantageous method for materials with anisotropic Fermi surfaces, existing in very small crystals or platelets. In addition, several other potential applications exist for torque measurements using levers of the same or similar design. Our designs couple high sensitivity with very small lever deflections in order to minimise torque interaction effects arising from field corrections introduced by the cantilever movement. Lever heat-sinking is also considered so as to maximise the sensing current that may be used, and hence the sensitivity, while maintaining the sample at low temperature. [Preview Abstract] |
Wednesday, March 7, 2007 11:51AM - 12:03PM |
P38.00004: New de Haas-van Alphen effect measurement electronics Patrick Rourke, Alix McCollam, Stephen Julian We have implemented a new data collection infrastructure for measurements of de Haas-van Alphen oscillations in metals. Traditionally, such measurements required large banks of costly lock-in amplifiers, in order to measure on several harmonics of a fundamental excitation frequency at once for a given crystal sample. By moving to a high-quality analog-to-digital-converter/software lock-in algorithm set-up we are able to realize significant improvements in parallel data collection, configurability, data quality and cost. These performance gains will be illustrated through examples of measurements we have performed on various strongly correlated electron systems. [Preview Abstract] |
Wednesday, March 7, 2007 12:03PM - 12:15PM |
P38.00005: Permanent Magnet with Very Low Field Gradient (0.1G/mm) for NMR Spectroscopy Ognjen Ilic, David Issadore, Tom Hunt, Robert Westervelt Nuclear Magnetic Resonance (NMR) is a powerful analytical tool for obtaining chemical, physical and structural information. To produce the uniform fields required, NMR experiments typically employ large, expensive electromagnets and shimming coils. We have developed a small permanent magnet with an iron yoke that produces a field of $\sim $10 kG with gradient $<$ 0.1G/mm across a 6 mm region for a total field homogeneity of 10 ppm. The system consists of two parallel cylindrical NdFe permanent magnets, 50mm in diameter and 25mm thick, separated by 4mm. The magnets are surrounded by hollow low-carbon steel cylinders with steel caps on each end of the yoke. By adjusting the distance between the yoke caps and the magnet we cancel first-order field strength variations, as shown in simulations. This design is an important innovation for low cost, benchtop NMR systems. *Supported by the NCI MIT-Harvard CCNE. [Preview Abstract] |
Wednesday, March 7, 2007 12:15PM - 12:27PM |
P38.00006: Identifying the Constituents of and Transformations in Diatomaceous Earth and Polysiloxane Foams Through the Use of Electron Paramagnetic Resonance Spectroscopy Michael Blair, Ross Muenchausen, Bryan Bennett, James Smith, Thomas Stephens, Wayne Cooke The chemical aging of polymeric materials is largely governed by the characteristics of the storage environment. For polysiloxane foams, the diatomaceous earth (DE) filler is a small component of the foam, but it plays a large role in the handling of water in the system. The DE filler can act as either a ``source'' or a ``sink'' for water via both chemical hydroxylation/ dehydroxylation and physical adsorption/ desorption processes, depending on the processing history and storage conditions. We have used electron paramagnetic resonance (EPR) spectroscopy to examine composite foam material as well as the DE filler alone. Intense, broad (400 Gauss) resonances were recorded at room temperature as a function of the microwave power at X-band frequency. The observed spectra have been assigned to the iron oxide compounds goethite, lepidocrocite, hematite, and magnetite based upon the measured EPR spectra of these minerals. As the presence or absence of free H$_{2}$O and the temperature of processing and storage also affects the interconversion of these various iron oxides, we indicate how this process can be followed by monitoring changes in the EPR spectra. [Preview Abstract] |
Wednesday, March 7, 2007 12:27PM - 12:39PM |
P38.00007: Time resolved measurements of single electron tunneling events Julie Love, Michel Devoret, Robert Schoelkopf We have observed time resolved single electron tunneling events in a metallic thin film circuit. Using a radio frequency single electron transistor (RF-SET) capacitively coupled to a single electron trap (a circuit consisting two small metallic islands and two tunnel junctions) we are able to measure tunneling events on the 10 microsecond time scale. In the 400 microsecond average lifetime of the charge state with one excess electron on the trap island, 80 data points with SNR=10 can be obtained. We will present these measurements along with comparisons to cotunneling (quantum tunneling) and Orthodox (thermal tunneling) theories. The dynamics of cotunneling has never before been studied in an experimental system. These time domain measurements also demonstrate the possibility of measuring the higher moments of charge noise in a metallic system. [Preview Abstract] |
Wednesday, March 7, 2007 12:39PM - 12:51PM |
P38.00008: Noise Characteristics of Nanocluster-Based Chemiresistors Walter Kruppa, Ronald Rendell, Arthur Snow, Edward Foos, Mario Ancona Thin films of metallic nanoclusters interspersed between interdigitated electrodes are the basis of a promising chemiresistor technology known as MIME sensors. The chemical vapor detection limit of these sensors is set by their signal-to-noise ratio at low frequencies where the noise is found to be 1/f in nature. In this work we explore the experimental dependences of the 1/f noise on various material parameters such as nanocluster core diameter, shell thickness and shell composition. Among other things, we find that the 1/f noise decreases by more than three orders of magnitude as the core diameter increases and the shell thickness decreases, observations that are expected to be important for sensor design. The data are found to fit the well-known Hooge formula and this allows the intrinsic strength of the 1/f noise to be gauged using the Hooge parameter. For the interpretation one needs to know the number of electrons participating in the transport and we discuss how this can be obtained through simulation using the orthodox theory of Coulomb blockade. This factor is then shown to be crucial for understanding the trends in our noise data. [Preview Abstract] |
Wednesday, March 7, 2007 12:51PM - 1:03PM |
P38.00009: Stray Light Correction as a Deblurring Problem John Hornstein The problem of correcting for stray light is shown to be a type of deblurring problem. When the optical system is linear, correcting for stray light reduces to a generalization of a deconvolution problem. As such, it is an ill-posed inverse problem, in which the goal is to estimate the true radiances incident on the instrument's entrance aperture from the signals registered by its detectors. Optical ghosts and out of field and out of band stray light are all included in this formulation. They are due to the non-ideal character of the optical impulse response function, which, in turn, is proportional to the system's point spread function. Backgrounds due to thermal emission within the optical system or from the radioactivity of its components are not included, since they are independent of the true scene. Several standard techniques of solving ill-posed inverse problems are being tested for correcting for stray light in spectral imagers. Results obtained via Backus-Gilbert estimation are reported here. [Preview Abstract] |
Wednesday, March 7, 2007 1:03PM - 1:15PM |
P38.00010: The Physical Origin of the Forward Character of the Electromagnetic Optical Theorem Matthew Berg, Christopher Sorensen, Amit Chakrabarti Particles or scatterers, both spherical and nonspherical in shape, are often encountered in the natural environment. Examples include atmospheric clouds and aerosols. The scattering of sun light by these particles produces radiative forcing effects that influence the Earth's climate. Additionally, electromagnetic scattering can offer an unintrusive way to study the physical properties of a scatterer including its shape, size and composition. Extinction is the process by which radiant energy is removed from an incident field due to the scattering and absorption of the field by a system of scatterers. The extinction cross section $\sigma^{ext}$ measures the total power removed from the incident light and hence, is a quantity of interest in many electromagnetic scattering applications. A well-known relationship, called the optical theorem, relates $\sigma^{ext}$ and the amplitude of the scattered field in the exact forward direction. This work investigates the physical origin of the forward character of the optical theorem using computer simulations of simple scattering systems. The conclusion is that the optical theorem derives its forward character from the interference of the incident and scattered fields. This energy flow is seen to consist of opposing directions of flow that cancel each other in all but the forward direction when integrated to yield $\sigma^{ext}$. [Preview Abstract] |
Wednesday, March 7, 2007 1:15PM - 1:27PM |
P38.00011: Generating, and Processing, Quadrature Signals in Interferometry David Van Baak The Michelson interferometer is well-known for its ability to produce sinusoidal signals or `fringes' in response to changes in the optical path difference between its arms. Less well known is the `other output' of a Michelson interferometer, where a second set of fringes can be observed. In the simplest case of a lossless interferometer, these standard and non standard output signals are complementary, and therefore redundant. This presentation points out that the use of a lossy metal-film beamsplitter in an interferometer renders the two output signals non-redundant; they can in practice be made to occur in phase quadrature. This immediately makes a Michelson interferometer sensitive to the direction, as well as the rate, of change of optical path difference. Remarkably simple modelling makes it possible to extract the phase shift of the beamsplitter, and the instantaneous phase difference in the interferometer, from the pair of output signals. The method is illustrated via the quantification of magnetostriction by interferometry. [Preview Abstract] |
Wednesday, March 7, 2007 1:27PM - 1:39PM |
P38.00012: The effect of the energy and the momentum resolution on the extraction of Eliashberg function from angle-resolved photoemission spectroscopy TeYu Chien, Hong Liu, Ward Plummer The effects of energy and momentum resolution on the extraction of Eliashberg function from angle-resolved photoemission spectroscopy(ARPES) have been examined. The advantage of ARPES is that it can obtain the information of the dispersion of quasiparticles with energy and momentum resolutions. Moreover, recently, Eliashberg function can be directly extracted from the ARPES data by means of Maximum Entropy Method (MEM). The data near the Fermi energy are very important for the extracting procedure, and, unfortunately, are severely affected by the energy resolution. The case study here is the electron phonon coupling system -- Be(0001) surface. MEM works improper when the energy resolution is larger than 10 meV. A truncation method was proposed to make MEM can work with worse energy resolution up to 30 -- 40 meV. This method reduces the needs of ultra-high energy resolution of the instrument used in ARPES experiment. [Preview Abstract] |
Wednesday, March 7, 2007 1:39PM - 1:51PM |
P38.00013: Spectral Weight Oracle: Model-Independent Sum Rule Analysis Based on Limited-Range Spectral Data Alexey Kuzmenko, Dirk van der Marel, Fabrizio Carbone, Frank Marsiglio Partial sum rules are widely used in physics to separate low- and high-energy degrees of freedom of complex dynamical systems. Their application, though, is challenged in practice by the always finite spectrometer bandwidth and is often performed using risky model-dependent extrapolations. We show that, given spectra of the real and imaginary parts of any causal frequency-dependent response function (for example, optical conductivity, magnetic susceptibility, acoustical impedance etc.) in a limited range, the sum-rule integral from zero to a certain cutoff frequency inside this range can be safely derived using only the Kramers-Kronig dispersion relations without any extra model assumptions. This implies that experimental techniques providing both active and reactive response components independently, such as ellipsometry in optics or simultaneous measurement of attenuation and speed of sound in acoustics, allow an extrapolation-independent determination of spectral weight 'hidden' below the lowest accessible frequency. [Preview Abstract] |
Wednesday, March 7, 2007 1:51PM - 2:03PM |
P38.00014: Experimental Confirmation of Backscattering Enhancement Induced by a Photonic Jet. Alexander Heifetz, Kevin Huang, Alan Sahakian, Xu Li, Allen Taflove, Vadim Backman We report experimental confirmation of backscattering enhancement induced by a photonic jet emerging from a dielectric sphere, a phenomenon recently predicted by theoretical solutions of Maxwell's equations. To permit relatively straightforward laboratory measurements at microwave frequencies rather than visible light, we appropriately scaled the original conceptual dimensions of the dielectric microsphere and its adjacent perturbing nanoparticle (located within the microsphere's photonic jet). Our experiments verified the existence of enhanced position-dependent backscattering perturbations by the adjacent particle. Our measured backscattering perturbations agreed well with prior theory and with additional finite-difference time-domain computational models of the complete microwave test geometry. [Preview Abstract] |
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