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Mitin, Vladimir; Antipov, Andrei; Sergeev, Andrei; Vagidov, Nizami; Eason, David; Strasser, Gottfried |
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Quantum Dot Infrared Photodetectors: Photoresponse Enhancement Due to Potential Barriers |
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2011 |
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Nanoscale Research Letters |
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Nanoscale res lett |
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6 |
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1 |
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6 |
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Quantum dots; Infrared detectors; Photoresponse; Doping; Potential barriers; Capture processes |
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Potential barriers around quantum dots (QDs) play a key role in kinetics of photoelectrons. These barriers are always created, when electrons from dopants outside QDs fill the dots. Potential barriers suppress the capture processes of photoelectrons and increase the photoresponse. To directly investigate the effect of potential barriers on photoelectron kinetics, we fabricated several QD structures with different positions of dopants and various levels of doping. The potential barriers as a function of doping and dopant positions have been determined using nextnano3 software. We experimentally investigated the photoresponse to IR radiation as a function of the radiation frequency and voltage bias. We also measured the dark current in these QD structures. Our investigations show that the photoresponse increases ~30 times as the height of potential barriers changes from 30 to 130 meV. |
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RPLAB @ gujma @ |
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712 |
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Parrott, Edward P. J.; Zeitler, J. Axel; Fris<cc><152>c<cc><152>ic<cc><81>, Tomislav; Pepper, Michael; Jones, William; Day, Graeme M.; Gladden, Lynn F. |
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Testing the sensitivity of terahertz spectroscopy to changes in molecular and supramolecular structure: a study of structurally similar cocrystals |
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2009 |
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Crystal Growth & Design |
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Crystal Growth & Design |
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9 |
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3 |
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1452-1460 |
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supramolecular recognition, infrared, terahertz, IR, THz, TDS |
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Terahertz time-domain-spectroscopy (THz-TDS) has emerged as a versatile spectroscopic technique, and an alternative to powder X-ray diffraction in the characterization of molecular crystals. We tested the ability of terahertz spectroscopy to distinguish between chiral and racemic hydrogen-bonded cocrystals that are similar in molecular and supramolecular structure. Terahertz spectroscopy readily distinguished between the isostructural cocrystals of theophylline with chiral and racemic forms of malic acid which are almost identical in molecular structure and supramolecular architecture. Similarly, the cocrystals of theophylline with chiral and racemic forms of tartaric acid, which are similar at the molecular level but dissimilar in crystal packing, were distinguished unequivocally. The investigation of the same cocrystals using X-ray powder diffraction and Raman spectroscopy suggested that THz-TDS is comparable in sensitivity to diffraction methods and more sensitive than Raman spectroscopy to changes in cocrystal architecture. The differences in spectra acquired by THz-TDS could be further enhanced by cooling the samples to 109 K. |
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1528-7483 |
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Kawakami, A; Saito, S.; Hyodo, M. |
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Fabrication of nano-antennas for superconducting Infrared detectors |
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2011 |
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IEEE Trans. Appl. Supercond. |
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21 |
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3 |
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632-635 |
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optical antennas, NbN/MgO/NbN/TiN/Al HEB, dipole antennas, IR, infrared |
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To improve the response performance of superconducting infrared detectors, we have developed a fabrication process for nano-antennas. A nano-antenna consists of a dipole antenna, and a superconducting thin film strip placed in the antenna's center. By measuring the transition temperature of the superconducting strips, we confirmed that their superconductivity maintained a good condition after the nano-antenna fabrication process. We also evaluated nano-antenna characteristics using Fourier transform infrared spectroscopy. The evaluated antenna length and width were respectively set at around 2400 nm and 400 nm, and the antennas were placed at intervals of several micrometers around the area of 1 mm2 . In an evaluation of spectral transmission characteristics, clear absorption caused by antenna effects was observed at around 1400 cm-1. High polarization dependencies were also observed. |
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761 |
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Krasnopolsky, Vladimir A.; Maillard, Jean Pierre; C. Owen, Tobias |
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Detection of methane in the martian atmosphere: evidence for life? |
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2004 |
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Icarus |
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Icarus |
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172 |
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2 |
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537-547 |
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FTS, Mars atmosphere, methane absorption lines, IR spectroscopy, infrared spectroscopy, landfill gas |
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Using the Fourier Transform Spectrometer at the Canada–France–Hawaii Telescope, we observed a spectrum of Mars at the P-branch of the strongest CH4 band at 3.3 μm with resolving power of 180,000 for the apodized spectrum. Summing up the spectral intervals at the expected positions of the 15 strongest Doppler-shifted martian lines, we detected the absorption by martian methane at a 3.7 sigma level which is exactly centered in the summed spectrum. The observed CH4 mixing ratio is 10±3 ppb. Total photochemical loss of CH4 in the martian atmosphere is equal to View the MathML source, the CH4 lifetime is 340 years and methane should be uniformly mixed in the atmosphere. Heterogeneous loss of atmospheric methane is probably negligible, while the sink of CH4 during its diffusion through the regolith may be significant. There are no processes of CH4 formation in the atmosphere, so the photochemical loss must therefore be balanced by abiogenic and biogenic sources. Outgassing from Mars is weak, the latest volcanism is at least 10 million years old, and thermal emission imaging from the Mars Odyssey orbiter does not reveal any hot spots on Mars. Hydrothermal systems can hardly be warmer than the room temperature at which production of methane is very low in terrestrial waters. Therefore a significant production of hydrothermal and magmatic methane is not very likely on Mars. The calculated average production of CH4 by cometary impacts is 2% of the methane loss. Production of methane by meteorites and interplanetary dust does not exceed 4% of the methane loss. Methane cannot originate from an extinct biosphere, as in the case of “natural gas†on Earth, given the exceedingly low limits on organic matter set by the Viking landers and the dry recent history which has been extremely hostile to the macroscopic life needed to generate the gas. Therefore, methanogenesis by living subterranean organisms is a plausible explanation for this discovery. Our estimates of the biomass and its production using the measured CH4 abundance show that the martian biota may be extremely scarce and Mars may be generally sterile except for some oases. |
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879 |
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Marsili, F.; Bitauld, D.; Divochiy, A.; Gaggero, A.; Leoni, R.; Mattioli, F.; Korneev, A.; Seleznev, V.; Kaurova, N.; Minaeva, O.; Gol’tsman, G.; Lagoudakis, K.G.; Benkahoul, M.; Lévy, F.; Fiore, A. |
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Superconducting nanowire photon number resolving detector at telecom wavelength |
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Conference Article |
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2008 |
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CLEO/QELS |
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CLEO/QELS |
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Qmj1 (1 to 2) |
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PNR SSPD; SNSPD; Detectors; Infrared; Low light level; Diode lasers; Photons; Scanning electron microscopy; Superconductors; Ti:sapphire lasers |
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We demonstrate a photon-number-resolving (PNR) detector, based on parallel superconducting nanowires, capable of resolving up to 5 photons in the telecommunication wavelength range, with sensitivity and speed far exceeding existing approaches. |
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Optical Society of America |
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978-1-55752-859-9 |
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1243 |
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