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Nano letters 2010 Dec;
Intrinsic Optical Properties of Vanadium Dioxide near the Insulator-Metal Transition.
We studied the insulator-metal transition (IMT) in single-domain, single crystalline vanadium dioxide (VO(2)) microbeams with infrared microspectroscopy. The unique nature of such samples allowed us to probe the intrinsic behavior of both insulating ... expand abstractand metallic phases in the close vicinity of IMT, and investigate the IMT driven by either strain or temperature independently. We found that the VO(2) insulating band gap narrows rapidly upon heating, and the infrared response undergoes an abrupt transition at both strain- and temperature-induced IMT. The results are consistent with recent studies attributing the opening of VO(2) insulating band gap to a correlation-assisted Peierls transition. collapse abstract
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Analytical chemistry 2010 Sep;
Synchrotron IR Spectromicroscopy: Chemistry of Living Cells.
Advanced analytical capabilities of synchrotron IR spectromicroscopy meet the demands of modern biological research for studying molecular reactions in individual living cells. (To listen to a podcast about this article, please go to the Analytical C... expand abstracthemistry multimedia page at pubs.acs.org/page/ancham/audio/index.html .). collapse abstract
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Surface-Enhanced Infrared Absorption-Reflectance (SEIRA) Microspectroscopy – A ChemicalBiological Probe for Bacteria Localization in Geologic Materials
Pollution of subsurface geologic zones and the possibility of using the intrinsic endolithic (rock/mineral-inhabiting) bacteria to either detoxify or immobilize the pollutants have stimulated new interests in the exploration of endolithic bacteria an... expand abstractd their long-term survival in the geologic environment. The location of bacteria within rocks and minerals affects the type and intensity of collapse abstract
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The first synchrotron infrared beamlines at the Advanced Light Source: microspectroscopy and fast timing,quot; presented at the
A set of new infrared (IR) beamlines on the 1.4 bending magnet port at the Advanced Light Source, LBNL, are described. Using a synchrotron as an IR source provides considerable brightness advantages, which manifests itself most beneficially when perf... expand abstractorming spectroscopy on a microscopic length scale. Beamline (BL) 1.4.3 is a dedicated microspectroscopy beamline, where the much smaller focused spot size using the synchrotron source is utilized. This enables an entirely new set of experiments to be performed where spectroscopy on a truly microscopic scale is now possible. BL 1.4.2 consists of a vacuum FTIR bench with a wide spectral range and step-scan capabilities. The fast timing is demonstrated by observing the synchrotron electron storage pattern at the ALS. collapse abstract
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4 Axis Implementation of the Active Feedback Mirror System for the IR
After extensive passive noise re-mediation Beamline 1.4.3 still had low frequency noise spikes on the IR spectrum, and broadband noise over the whole spectrum. 1-4 To address low frequency acoustic noise, technology adapted from a design used at Lawr... expand abstractence Livermore Laboratory was implemented--two dual axis Physik Instrumente tip/tilt PZT mirror holders with 1 mm thick collapse abstract
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Active Feedback Mirror System for the IR Beamline 1.4.x Complex
The IR beamlines, due mainly to the interferometric selection of wavelength, have proven to be the most sensitive to microscopic motions of the ALS beam. Even after a long series of beam noise abatement projects in collaboration with ALS accelerator ... expand abstractand engineering staff, 1-4 the IR photon beam still moves in angle with an rms magnitude of a few microradians. This motion, collapse abstract
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Multilayered structure of
Superconductivity is a phenomenon of matter where below a defined temperature (T) the electrical resistance drops dramati-c cally and the specific resistance is zero. Therefore, electric currents can propagate for many years without energy loss. ”Cla... expand abstractssical” superconductors, with T between c 4- 23 K, require liquid helium for cooling which is not feasible for many technological applications. High-temperature superconductors with T of around 100 K would be far c more suitable since liquid nitrogen can be used for cooling. However, the production of these compounds for technological applications is still unsolved since they are ceramic oxides which cannot be manufactured like metal wires. Most high temperature superconductors are multilayer structures of metal oxides, like the collapse abstract
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Tracking chemical changes in a live cell: Biomedical Applications of SR-
Synchrotron radiation-based Fourier transform infrared (SR-FTIR) spectromicroscopy is a newly emerging bioanalytical and imaging tool. This unique technique provides mid-infrared (IR) spectra, hence chemical information, with high signal-to-noise at ... expand abstractspatial resolutions as fine as 3 to 10 microns. Thus it enables researchers to locate, identify, and track specific chemical events within an individual living mammalian cell. Mid-IR photons are too low in energy (0.05-0.5 eV) to either break bonds or to cause ionization. In this review, we show that the synchrotron IR beam has no detectable effects on the short- and long-term viability, reproductive integrity, cell-cycle progression, and mitochondrial metabolism in living human cells, and produces only minimal sample heating (< 0.5°C). We will then present several examples demonstrating the application potentials of SR-FTIR spectromicroscopy in biomedical research. These will include monitoring living cells progressing through the cell cycle, including death, collapse abstract
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JBO LETTERS Mid-infrared reflectivity of experimental atheromas
Abstract. We report that the pathologic components present within the atheromatous plaques of ApoE knockout mice can reflect significant amounts of mid-infrared �mid-IR � light. Furthermore, the reflected light spectra contained the unique signatures... expand abstract of a variety of biologic features including those found in unstable or “vulnerable” plaque. This discovery may represent a unique opportunity to develop a new intravascular diagnostic modality that can detect and characterize sites of atherosclerosis. collapse abstract
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The first infrared beamline at the ALS: design, construction, and initial commissioning
The bright continuous spectrum of radiation from all storage rings extends into the infrared (IR) region of the spectrum. In fact, within about two orders of magnitude, all synchrotron radiation sources provide an essentially similar source of IR lig... expand abstractht. While synchrotrons do not provide as much flux as a typical laboratory source, the highly collimated nature of the light allows more light collapse abstract
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TERAHERTZ COHERENT SYNCHROTRON RADIATION FROM FEMTOSECOND LASER MODULATION OF THE ELECTRON BEAM AT THE ADVANCED LIGHT SOURCE
At the Advanced Light Source (ALS), the ‘femtoslicing ’ beamline is in operation since 1999 for the production of x-ray synchrotron radiation pulses with femtosecond duration. The mechanism used for generating the short x-ray pulses induces at the sa... expand abstractme time temporary structures in the electron bunch longitudinal distribution with very short characteristic length. Such structures emit intense coherent synchrotron radiation (CSR) in the terahertz frequency range. These CSR pulses were first observed at the ALS, and the measurement of their intensity is now routinely used as a diagnostics for the tune-up of the femtoslicing x-ray experiments. At the same time, these CSR pulses synchronous with the modulating laser, represent a potential source of terahertz radiation with very interesting features. Several measurements have been performed for their characterization and in this paper we present an updated description of the experimental results and of their interpretation. In particular, we include more data on the interesting interaction, previously observed at the ALS, between the slicing and the microbunching instability (MBI), where under particular circumstances, the slicing seems to trigger the onset of the instability. collapse abstract
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A Dedicated Storage Ring For Far-IR Coherent Synchrotron Radiation at the ALS
In the last few years an always-increasing interest of the accelerator community has been addressed to coherent synchrotron radiation (CSR). Just as an example, people working in linear collider projects are carefully investigating the potentially da... expand abstractngerous effects that CSR can have on their bunch compressor schemes [1]. Others are instead interested in CSR as a new powerful collapse abstract
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Noise reduction efforts for the ALS infrared beamlines
The quality of infrared microscopy and spectroscopy data collected at synchrotron-based sources is strongly dependent on signal-to-noise. We have successfully identified and suppressed several noise sources affecting Beamlines 1.4.2, 1.4.3, and 1.4.4... expand abstract at the Advanced Light Source (ALS), resulting in a significant increase in the quality of FTIR spectra obtained. Noise reduction for this collapse abstract
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Coherent Far IR Bursts Measured at BL 1.4.2
We have performed the first measurements at the ALS of coherent far-IR bursts coming from instabilities within a high-current single electron bunch. The 2-bunch mode operations of the ALS afforded us the opportunity to use the machine while it was tu... expand abstractned for high currents in individual electron bunches. We have used a number of collapse abstract
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Contrib Mineral Petrol DOI 10.1007s00410-008-0327-8 ORIGINAL PAPER
Diffusion-controlled spherulite growth in obsidian inferred from H 2O concentration profiles
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The Review of scientific instruments 2009 Nov; 80(12)
Improved spatial resolution for reflection mode infrared microscopy.
Standard commercial infrared microscopes operating in reflection mode use a mirror to direct the reflected light from the sample to the detector. This mirror blocks about half of the incident light, however, and thus degrades the spatial resolution b... expand abstracty reducing the numerical aperture of the objective. Here, we replace the mirror with a 50% beamsplitter to allow full illumination of the objective and retain a way to direct the reflected light to the detector. The improved spatial resolution is demonstrated using two different microscopes capable of diffraction-limited resolution: the first microscope is coupled to a synchrotron source and utilizes a single point detector, whereas the second microscope has a standard blackbody source and uses a focal plane array detector. collapse abstract
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Nature nanotechnology 2009 Dec; 5(1)
A tunable phonon-exciton Fano system in bilayer graphene.
Fano resonances are features in absorption, scattering or transport spectra resulting from the interaction of discrete and continuum states. They have been observed in a variety of systems. Here, we report a many-body Fano resonance in bilayer graphe... expand abstractne that is continuously tunable by means of electrical gating. Discrete phonons and continuous exciton (electron-hole pair) transitions are coupled by electron-phonon interactions, yielding a new hybrid phonon-exciton excited state. It may also be possible to control the phonon-exciton coupling with an optical field. This tunable phonon-exciton system could allow novel applications such as phonon lasers. collapse abstract
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Chem. Phys. Lett. 255, 309 1996
Motional diminishing of optical activity: a novel method for studying molecular dynamics in liquids and plastic crystals
Molecular dynamics calculations and optical spectroscopy measurements of weakly active infrared modes are reported. The results are qualitatively understood in terms of the "motional diminishing" of IR lines, a process analogous to the motional nar... expand abstractrowing of a nuclear magnetic resonance (NMR) signal. In molecular solids or liquids where the appropriate intramolecular resonances are observable, motional diminishing can be used to study the fluctuations of the intermolecular interactions having time scales of 1psec to 100psec. collapse abstract
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Appl. Phys. Lett. 66, 1015 (1995).
Polymeric alkali fullerides are stable in air
Infrared transmission, electron spin resonance, and X-ray diffraction measurements show unambiguously that RbC$_{60}$ and KC$_{60}$ are stable in air, in contrast to Rb$_{6}$C$_{60}$ which decomposes rapidly upon exposure. The specimens studied trans... expand abstractform into pure C$_{60}$ and other byproducts when heated above $100\dd $C, approximately the temperature of the orthorhombic-fcc phase transition. The stability of these compounds raises the possibility of applying them as protective layers for the superconducting fullerides. collapse abstract
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Phys. Rev. B 53, 14285 (1996).
Magnetism and Structural Distortion in the La0.7Sr0.3MnO3 Metallic Ferromagnet
Neutron scattering studies on a single crystal of the highly-correlated electron system, La1-xSrxMnO3 with x~0.3, have been carried out elucidating both the spin and lattice dynamics of this metallic ferromagnet. We report a large measured value of... expand abstract the spin wave stiffness constant, which directly shows that the electron transfer energy of the d band is large. The spin dynamics, including magnetic critical scattering, demonstrate that this material behaves similar to other typical metallic ferromagnets such as Fe or Ni. The crystal structure is rhombohedral, as previously reported, for all temperatures studied (below ~425K). We have observed new superlattice peaks which show that the primary rhombohedral lattice distortion arises from oxygen octahedra rotations resulting in an R-3c structure. The superlattice reflection intensities which are very sensitive to structural changes are independent of temperature demonstrating that there is no primary lattice distortion anomaly at the magnetic transition temperature, Tc = 378.1 K, however there is a lattice contraction. collapse abstract
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Phys. Rev. B 53, R14713 1996.
Temperature Dependence of the Spin-Peierls Energy Gap and Anomalous Line Shapes in CuGeO_3
Neutron scattering measurements on a large single crystal of CuGeO$_3$ have been used to determine the temperature-dependence of the spin-Peierls energy gap. While the power law behavior of the intensity of structural superlattice peaks is well fit... expand abstract by $I({\rm T})\propto ({\rm T}_c - {\rm T})^{2\beta}$ with an exponent of $\beta =0.33$, the exponent for the temperature dependence of the energy gap is significantly smaller than expected for conventional spin-Peierls materials. Usual scaling relations relate the energy gap to the superlattice reflection intensity as $\Delta({\rm T}) \propto I^a$ with $a=1/3$; the present results suggest an exponent of $a\approx 1/6$ for CuGeO$_3$. Additional scattering cross-section is observed in constant-$q$ and constant-$E$ scans creating a long `tail' extending to higher energies relating to a proposed scattering continuum. collapse abstract
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Phys. Rev. B 54, R6835 (1996)
New phase diagram of Zn-doped CuGeO3
A series of high-quality single crystals of Cu$_{1-x}$Zn$_x$GeO$_3$ have been examined by neutron scattering techniques. An antiferromagnetic (AF) ordering is confirmed for samples with $x\geq 0.02$, in complete agreement with previous reports. We ... expand abstractshow that the spin-Peierls (SP) phase transition persists to 6\% Zn, whereas previous magnetic susceptibility measurements reported a deterioration of the SP transition above 2\% Zn. We present some details of the successive transitions upon lowering temperature into the spin-Peierls phase which is followed by a transition into an antiferromagnetically ordered phase. Below the N\'eel temperature we observe the coexistence of the SP lattice dimerization and AF states. collapse abstract
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Phys. Rev. Lett. 77, 4082 (1996).
Energy gap in superconducting fullerides: optical and tunneling studies
Tunneling and optical transmission studies have been performed on superconducting samples of Rb3C60. At temperatures much below the superconducting transition temperature Tc the energy gap is 2 Delta=5.2 +- 0.2meV, corresponding to 2 Delta/kB Tc = ... expand abstract4.2. The low temperature density of states, and the temperature dependence of the optical conductivity resembles the BCS behavior, although there is an enhanced ``normal state" contribution. The results indicate that this fulleride material is an s-wave superconductor, but the superconductivity cannot be described in the weak coupling limit. collapse abstract
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Phys. Rev. B 47, 14607 (1993)
In-Situ Infrared Transmission Study of Rb- and K-Doped Fullerenes
We have measured the four IR active $C_{60}$ molecular vibrations in $M_{x}C_{60}$ $(M = K, Rb)$ as a function of doping $x$. We observe discontinuous changes in the vibrational spectra showing four distinct phases (presumably $x = 0, 3, 4$, and 6)... expand abstract. The $1427cm^{-1}$ and $576cm^{-1}$ modes show the largest changes shifting downward in frequency in four steps as the doping increases. Several new very weak modes are visible in the $x=6$ phase and are possibly Raman modes becoming weakly optically active. We present quantitative fits of the data and calculate the electron-phonon coupling of the $1427cm^{-1}$ IR mode. collapse abstract
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Phys. Rev. Lett. 70, 2629 (1993)
No Far-Infrared-Spectroscopic Gap in Clean and Dirty High-T_C Superconductors
We report far infrared transmission measurements on single crystal samples derived from Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$. The impurity scattering rate of the samples was varied by electron-beam irradiation, 50MeV $^{16}$O$^{+6}$ ion irradiation, h... expand abstracteat treatment in vacuum, and Y doping. Although substantial changes in the infrared spectra were produced, in no case was a feature observed that could be associated with the superconducting energy gap. These results all but rule out ``clean limit'' explanations for the absence of the spectroscopic gap in this material, and provide evidence that the superconductivity in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ is gapless. collapse abstract
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