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Author |
Bulaevskii, L. N.; Graf, M. J.; Batista, C. D.; Kogan, V. G. |
Title |
Vortex-induced dissipation in narrow current-biased thin-film superconducting strips |
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Journal Article |
Year |
2011 |
Publication |
Phys. Rev. B |
Abbreviated Journal |
Phys. Rev. B |
Volume |
83 |
Issue |
14 |
Pages |
9 |
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Abstract |
A vortex crossing a thin-film superconducting strip from one edge to the other, perpendicular to the bias current, is the dominant mechanism of dissipation for films of thickness d on the order of the coherence length ξ and of width w much narrower than the Pearl length Λâ‰<ab>wâ‰<ab>ξ. At high bias currents I*<I<Ic the heat released by the crossing of a single vortex suffices to create a belt-like normal-state region across the strip, resulting in a detectable voltage pulse. Here Ic is the critical current at which the energy barrier vanishes for a single vortex crossing. The belt forms along the vortex path and causes a transition of the entire strip into the normal state. We estimate I* to be roughly Ic/3. Furthermore, we argue that such “hot†vortex crossings are the origin of dark counts in photon detectors, which operate in the regime of metastable superconductivity at currents between I* and Ic. We estimate the rate of vortex crossings and compare it with recent experimental data for dark counts. For currents below I*, that is, in the stable superconducting but resistive regime, we estimate the amplitude and duration of voltage pulses induced by a single vortex crossing. |
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RPLAB @ gujma @ |
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688 |
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Dorenbos, S. N.; Heeres, R.W.; Driessen, E.F.C; Zwiller, V. |
Title |
Efficient and robust fiber coupling of superconducting single photon detectors |
Type |
Journal Article |
Year |
2011 |
Publication |
arXiv |
Abbreviated Journal |
arXiv |
Volume |
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Issue |
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Pages |
6 |
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SSPD |
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We applied a recently developed fiber coupling technique to superconducting single photon detectors (SSPDs). As the detector area of SSPDs has to be kept as small as possible, coupling to an optical fiber has been either inefficient or unreliable. Etching through the silicon substrate allows fabrication of a circularly shaped chip which self aligns to the core of a ferrule terminated fiber in a fiber sleeve. In situ alignment at cryogenic temperatures is unnecessary and no thermal stress during cooldown, causing misalignment, is induced. We measured the quantum efficiency of these devices with an attenuated tunable broadband source. The combination of a lithographically defined chip and high precision standard telecommunication components yields near unity coupling efficiency and a system detection efficiency of 34% at a wavelength of 1200 nm. This quantum efficiency measurement is confirmed by an absolute efficiency measurement using correlated photon pairs (with $\lambda$ = 1064 nm) produced by spontaneous parametric down-conversion. The efficiency obtained via this method agrees well with the efficiency measured with the attenuated tunable broadband source. |
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arXiv:1109.5809 |
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RPLAB @ gujma @ |
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689 |
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Venkatasubramanian, Chandrasekaran; Cabarcos, Orlando M.; Allara, David L. Horn, Mark W.; Ashok, S. |
Title |
Correlation of temperature response and structure of annealed VOx thin films for IR detector applications |
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Journal Article |
Year |
2009 |
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J. Vac. Sci. Technol. A |
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27 |
Issue |
4 |
Pages |
6 |
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Annealing |
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The effects of thermal annealing on vanadium oxide (VOx) thin films prepared by pulsed-dc magnetron sputtering were studied to explore methods of improving the efficiency of uncooled IR imaging microbolometers, particularly with respect to maximizing the temperature coefficients of resistance (TCR) (typically ~2%) while minimizing resistivity values (typically 0.05–5 Ω cm). Since high TCR values are usually associated with high resistivities, the experiments were designed to find processing conditions that provide an optimal balance in these properties and to then determine the underlying structural correlations which would enable rational design of thin films for this specific application. VOx films of different compositions were deposited by pulsed-dc reactive sputtering from a vanadium target at different oxygen flow rates. The deposited films were further modified by annealing in inert (nitrogen) and oxidizing (oxygen) atmospheres at four different temperatures for 10, 20, or 30 min at a time. The resistivities of the as-deposited films ranged from 0.2 to 13 Ω cm and the TCR values varied from –1.6% to –2.2%. Depending on the exact annealing conditions, several orders of magnitude change in resistance and significant variations in TCR were observed. Optimal results were obtained with annealing in a nitrogen atmosphere. Structural characterization by x-ray diffraction, field emission scanning electron microscopy, atomic force microscopy, and Raman spectroscopy indicated changes in the film crystallinity and phase for annealing conditions over 300 °C with the onset and extent of the changes dependent on which annealing atmosphere was used. |
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RPLAB @ gujma @ |
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690 |
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Mannino, Giovanni; Spinella, Corrado; Ruggeri, Rosa; La Magna, Antonino; Fisicaro, Giuseppe; Fazio, Enza; Neri, Fortunato; Privitera, Vittorio |
Title |
Crystallization of implanted amorphous silicon during millisecond annealing by infrared laser irradiation |
Type |
Journal Article |
Year |
2010 |
Publication |
Applied Physics Letters |
Abbreviated Journal |
Appl. Phys. Lett. |
Volume |
97 |
Issue |
2 |
Pages |
3 |
Keywords |
Annealing |
Abstract |
We investigated the homogenous nucleation of crystalline grains in amorphous Si during transient temperature pulse of few milliseconds IR laser irradiation. The crystallized volume fraction is ~80%. Significant crystallization occurs in nonsteady regime because of the rapid temperature variation (106 °C/s). Our model combines the time evolution of the crystal grain population with the consumption of the amorphous volume due to the growth of grains. Thanks to the experimental approach based on a laser source to heat α-Si and the theoretical model we extended the description of the spontaneous crystallization up to 1323 K or 250 K above the temperature investigated by conventional annealing. |
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RPLAB @ gujma @ |
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691 |
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Author |
Jang, Young Rae; Yoo, Keon-Ho; Park, Seung Min |
Title |
Rapid thermal annealing of ZnO thin films grown at room temperature |
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Journal Article |
Year |
2010 |
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J. Vac. Sci. Technol. A |
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Volume |
28 |
Issue |
2 |
Pages |
4 |
Keywords |
Annealing |
Abstract |
The authors successfully obtained high quality ZnO thin films by growing them at room temperature (RT) and postannealing by rapid thermal annealing (RTA). The thin films were grown by pulsed laser deposition on Si (100) substrates at RT, and RTA was performed under various temperatures and ambient conditions. Based on the UV emission to visible emission ratio in RT photoluminescence (PL) spectra, the optimum film was obtained at annealing temperature ~700 °C in an ambient of Ar, N2, or O2 at 0.1 Torr, while the optimum annealing temperature was above 1100 °C in the air ambient at atmospheric pressure. The morphology and structure of the films in different RTA conditions were investigated by using field emission scanning electron microscopy and grazing incidence x-ray diffraction, and were discussed in conjunction with the PL data. |
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RPLAB @ gujma @ |
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692 |
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