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| Author | 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 | Type | Journal Article | ||
| Year | 2009 | Publication | J. Vac. Sci. Technol. A | Abbreviated Journal  |
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| Volume | 27 | Issue | 4 | Pages | 6 |
| Keywords | Annealing | ||||
| Abstract | 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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| Notes | Annealing | Approved | no | ||
| Call Number | RPLAB @ gujma @ | Serial | 690 | ||
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| Author | Ожегов, Р.В.; Окунев, О.В.; Гольцман, Г.Н. | ||||
| Title | Флуктуационная чувствительность сверхпроводящего болометрического смесителя на эффекте разогрева электронного газа | Type | Journal Article | ||
| Year | 2009 | Publication | Радиотехника | Abbreviated Journal |
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| Volume | Issue | 3 | Pages | 120-124 | |
| Keywords | смеситель на горячих электронах; флуктуационная чувствительность; тепловизор терагерцевого диапазона частот; hot-electron bolometer mixer; Imaging system; Noise equivalent temperature difference; Heterodyne receiver; Terahertz range | ||||
| Abstract | Interest in research in the terahertz range is driven by a great number of various applications, where terahertz instruments may play a leading role. To name just a few, such applications include study of the cosmic microwave background radiation and the distribution of the dark matter, medicine, navigation, fire alarm, security systems and environmental monitoring. The paper discusses the possibility of using a receiver based on the hot-electron effect in superconducting films as an imaging system. We present the results of the noise equivalent temperature difference (NETD) measurements performed with a hot-electron bolometer mixer made from a thin superconducting film. The receiver with a noise temperature of ~ 3800 K at a local oscillator frequency of 300 GHz a bandwidth of 500 MHz and an integration time of 1 s has offered an NETD of 0.5 K. We have also developed a technique that enabled us to reduce the contribution of the mixer gain fluctuations to the overall system instability. As of this writing, the above value of the NETD is the lowest value offered for this type of receiver, which indicates the possibility to use such receivers in real-time imaging systems. The technique offered in the paper for achieving the limiting value of the NETD offers an alternative to the phase-locking scheme. Представены результаты измерения флуктуационной чувствительности (NETD – noise equivalent temperature difference) болометрического смесителя на эффекте разогрева электронного газа в тонких сверхпроводящих пленках. Получено предельное значение NETD, равное 0,5 К, при шумовой температуре приемника 3800 К, ширине полосы преобразования 500 МГц, постоянной времени 1 с и частоте гетеродина 300 ГГц. Разработана методика достижения предельной флуктуационной чувствительности, позволяющая избежать влияния нестабильности коэффициента преобразования смесителя. |
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| Notes | Approved | no | |||
| Call Number | RPLAB @ gujma @ | Serial | 728 | ||
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| Author | Pekker, David; Shah, Nayana; Sahu, Mitrabhanu; Bezryadin, Alexey; Goldbart, Paul M. | ||||
| Title | Stochastic dynamics of phase-slip trains and superconductive-resistive switching in current-biased nanowires | Type | Journal Article | ||
| Year | 2009 | Publication | Phys. Rev. B | Abbreviated Journal |
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| Volume | 80 | Issue | Pages | 214525 (1 to 17) | |
| Keywords | superconducting nanowire, phase-slip, order parameter, HEB distributed model, HEB model | ||||
| Abstract | Superconducting nanowires fabricated via carbon-nanotube templating can be used to realize and study quasi-one-dimensional superconductors. However, measurement of the linear resistance of these nanowires have been inconclusive in determining the low-temperature behavior of phase-slip fluctuations, both quantal and thermal. Thus, we are motivated to study the nonlinear current-voltage characteristics in current-biased nanowires and the stochastic dynamics of superconductive-resistive switching, as a way of probing phase-slip events. In particular, we address the question: can a single phase-slip event occurring somewhere along the wire—during which the order-parameter fluctuates to zero—induce switching, via the local heating it causes? We explore this and related issues by constructing a stochastic model for the time evolution of the temperature in a nanowire whose ends are maintained at a fixed temperature. We derive the corresponding master equation as a tool for evaluating and analyzing the mean switching time at a given value of current (smaller than the depairing critical current). The model indicates that although, in general, several phase-slip events are necessary to induce switching via a thermal runaway, there is indeed a regime of temperatures and currents in which a single event is sufficient. We carry out a detailed comparison of the results of the model with experimental measurements of the distribution of switching currents, and provide an explanation for the rather counterintuitive broadening of the distribution width that is observed upon lowering the temperature. Moreover, we identify a regime in which the experiments are probing individual phase-slip events, and thus offer a way of unearthing and exploring the physics of nanoscale quantum tunneling of the one-dimensional collective quantum field associated with the superconducting order parameter. | ||||
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| Notes | Recommended by Klapwijk | Approved | no | ||
| Call Number | Serial | 923 | |||
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| Author | Ovchinnikov, Yu. N.; Varlamov, A. A. | ||||
| Title | Fluctuation-dissipative phenomena in a narrow superconducting channel carrying current below critical | Type | Journal Article | ||
| Year | 2009 | Publication | arXiv | Abbreviated Journal |
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| Volume | 0910.2659v1 | Issue | Pages | 1-4 | |
| Keywords | superconducting nanowire, resistance calculation | ||||
| Abstract | The theory of current transport in a narrow superconducting channel accounting for thermal fluctuations is developed. These fluctuations result in the appearance of small but finite dissipation in the sample. The value of corresponding voltage is found as the function of temperature (close to transition temperature) and arbitrary bias current. It is demonstrated that the value of the activation energy (exponential factor in the Arrenius law) when current approaches to the critical one is proportional to (1-J/Jc)^(5/4). This result is in concordance with the one for the affine phenomenon of the Josephson current decay due to the thermal phase fluctuations, where the activation energy proportional (1-J/J_c)^(3/2)(the difference in the exponents is related to the additional current dependence of the order parameter). Found dependence of the activation energy on current explains the enormous discrepancy between the theoretically predicted before and the experimentally observed broadening of the resistive transition. | ||||
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| Notes | arXiv:0910.2659v1; 4 pages, 3 figures | Approved | no | ||
| Call Number | Serial | 931 | |||
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| Author | Khosropanah P.; Baryshev A.; Zhang W.; Jellema W.; Hovenier J.N.; Gao G.R.; Klapwijk T.M; Paveliev D.G.; Williams B.S.; Kumar S.; Hu Q.; Reno J.L.; Klein B.; Hesler J.L. | ||||
| Title | Phase-locking of a 2.7-THz quantum cascade laser to a microwave reference | Type | Journal Article | ||
| Year | 2009 | Publication | Optics Letters | Abbreviated Journal |
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| Volume | 34 | Issue | Pages | 2958-2960 | |
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| Abstract | We demonstrate the phase locking of a 2.7 THz metal–metal waveguide quantum cascade laser (QCL) to an external microwave signal. The reference is the 15th harmonic, generated by a semiconductor superlattice nonlinear device, of a signal at 182 GHz, which itself is generated by a multiplier chain (X12) from a microwave synthesizer at ~ 15 GHz. Both laser and reference radiations are coupled into a bolometer mixer, resulting in a beat signal, which is fed into a phase-lock loop. The spectral analysis of the beat signal con-firms that the QCL is phase locked. This result opens the possibility to extend heterodyne interferometers into the far-infrared range. |
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| Notes | Approved | no | |||
| Call Number | RPLAB @ atomics90 @ | Serial | 966 | ||
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