1,721,092 research outputs found
Infrared studies under pressure at the infrared beamline SISSI at ELETTRA
No full textTransition metal oxides often display insulator to metal transitions (MIT) with conductivity jumps up to several orders of magnitude, which makes them very attractive both for technological applications and for the several fundamental issues they raise. Information about the mechanism inducing the MIT may be gained by means of infrared (IR) spectroscopy. We present here the capabilities of the IR synchrotron source SISSI (Synchrotron Infrared Source for Spectroscopy and Imaging), at the Italian storage ring ELETTRA. We demonstrate SISSI to be a powerful source for optical studies of pressure-induced insulator-to-metal transitions, reporting on V3O5 and (V0.989Cr0.011)2O3 as examples
Plasmon-enhanced Ge-based metal-semiconductor-metal photodetector at near-IR wavelengths
Full text linkWe demonstrate the use of plasmonic effects to boost the near-infrared sensitivity of metal-semiconductor-metal detectors. Plasmon-enhanced photodetection is achieved by properly optimizing Au interdigitated electrodes, micro-fabricated on Ge, a semiconductor that features a strong near IR absorption. Finite-difference time-domain simulations, photocurrent experiments and Fourier-transform IR spectroscopy are performed to validate how a relatively simple tuning of the contact geometry allows for an enhancement of the response of the device adapting it to the specific detection needs. A 2-fold gain factor in the Ge absorption characteristics is experimentally demonstrated at 1.4 µm, highlighting the potential of this approach for optoelectronic and sensing applications.QCD/Scappucci La
Raman Spectroscopy in Ionic Liquids Under Variable Thermodynamic and Environmental Conditions.
No full textFar infrared properties of the rare-earth scandate DyScO3
No full textWe present reflectance measurements in the infrared region on a single crystal the rare-earth scandate DyScO3. Measurements performed between room temperature and 10 K allow us to determine the frequency of the infrared-active phonons, never investigated experimentally, and to get information on their temperature dependence. A comparison with the phonon peak frequency resulting from ab initio computations is also provided. We finally report detailed data on the frequency dependence of the complex refractive index of DyScO3 in the terahertz region, which is important in the analysis of terahertz measurements on thin films deposited on DyScO3
Intrinsic linewidth of the plasmonic resonance in a micrometric metal mesh
No full textThe intrinsic linewidth and angular dispersion of Surface Plasmon Polariton resonance of a micrometric metal mesh have been measured with a collimated mid-infrared beam, provided by an External Cavity tunable Quantum Cascade Laser. We show that the use of a collimated beam yields an observed resonance linewidth gamma = 12 cm(-1) at the resonance frequency nu(0) = 1658 cm-1, better by an order of magnitude than with a non-collimated beam. The extremely narrow plasmon resonance attained by our mesh is then exploited to reconstruct, by varying the QCL angle of incidence theta, the angular intensity distribution f(theta) of a globar at the focal plane of a conventional imaging setup. We thus show that f (theta) is better reproduced by a Gaussian distribution than by a uniform one, in agreement with ray-tracing simulation. (C) 2013 Optical Society of Americ
Protein clustering in chemically stressed HeLa cells studied by infrared nanospectroscopy
Full text linkPhoto-Thermal Induced Resonance (PTIR) nanospectroscopy, tuned towards amide-I absorption, was used to study the distribution of proteic material in 34 different HeLa cells, of which 18 were chemically stressed by oxidative stress with Na3AsO3. The cell nucleus was found to provide a weaker amide-I signal than the surrounding cytoplasm, while the strongest PTIR signal comes from the perinuclear region. AFM topography shows that the cells exposed to oxidative stress undergo a volume reduction with respect to the control cells, through an accumulation of the proteic material around and above the nucleus. This is confirmed by the PTIR maps of the cytoplasm, where the pixels providing a high amide-I signal were identified with a space resolution of ∼300 × 300 nm. By analyzing their distribution with two different statistical procedures we found that the probability to find protein clusters smaller than 0.6 μm in the cytoplasm of stressed HeLa cells is higher by 35% than in the control cells. These results indicate that it is possible to study proteic clustering within single cells by label-free optical nanospectroscopy
Time-resolved investigation of nanometric cell membrane patches with a mid-infrared laser microscope
Full text linkThe proton pump Bacteriorhodopsin (BR) undergoes repeated photocycles including reversible conformational changes upon visible light illumination. Exploiting the sensitivity of infrared (IR) spectra to the conformation, we have determined the reaction kinetic parameters of the conductive intermediate M for the wild-type protein and for its slow mutant D96N during its photocycle. Time-resolved IR micro-spectroscopy using an in-house developed confocal laser microscope operating in the mid-IR is employed to record absorption changes of 10−4 at wavelengths λ1 = 6.08 μm and λ2 = 6.35 μm, assigned to backbone and retinal structural modifications, respectively. Protein samples were embedded in dried lipid bilayers deposited on ultraflat gold supports to enhance the surface field. The signals were analyzed according to a simplified photocycle model with only two dominant states: the dark-adapted state BR* and the intermediate M. We obtained the excitation and relaxation times of the intermediate M from exponential fits to the absorption change time traces. Our results constitute a first step towards future plasmonic-assisted nanoscale time-resolved mid-IR spectrometers for the characterization of bioelectronic and light-harvesting nanodevices based on BR
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