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ABSTRACT: We report measurements of the energy resolution of ultra-sensitive superconducting bolometric detectors. The device is a superconducting titanium nanobridge with niobium contacts. A fast microwave pulse is used to simulate a single higher-frequency photon, where the absorbed energy of the pulse is equal to the photon energy. This technique allows precise calibration of the input coupling and avoids problems with unwanted background photons. Present devices have an intrinsic full-width at half-maximum energy resolution of approximately 23 terahertz, near the predicted value due to intrinsic thermal fluctuation noise. Comment: 11 pages (double-spaced), 5 figures; minor revisions
Applied Physics Letters 02/2010; 96(8):083505. · 3.84 Impact Factor
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ABSTRACT: We are presenting experimental results on the electrical noise in small titanium hot-electron nanobolometers with the critical temperature above 300 mK. The noise data demonstrate good agreement with the conventional bolometer theory prediction. The noise is dominated by the thermal energy fluctuations (phonon noise) when the operating temperature is set just a few mK below the superconducting transition. The corresponding noise equivalent power (NEP) is about 3 times 10<sup>-18</sup> W/Hz<sup>1/2</sup> for the smallest measured device. The relative NEP's for the two devices measured scale roughly as the square root of the device volume as one would expect from the theory. Therefore an additional factor of 2-3 reduction of NEP may be feasible if the length and width of our device are further reduced. The demonstrated combination of the low NEP and the relatively high operating temperature is attractive for submillimeter low-background applications.
IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
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ABSTRACT: We have measured the conductivity of high-mobility (001) Si
metal-oxide-semiconductor field effect transistors (MOSFETs) over wide ranges
of electron densities n=(1.8-15)x10^11cm^2, temperatures T=30mK-4.2K, and
in-plane magnetic fields B=0-5T. The experimental data have been analyzed using
the theory of interaction effects in the conductivity of disordered 2D systems.
The parameters essential for comparison with the theory, such as the
intervalley scattering time and valley splitting, have been measured or
evaluated in independent experiments. The observed behavior of the
conductivity, including its quasi-linear increase with decreasing T down to
~0.4K and its downturn at lower temperatures, is in agreement with the theory.
The values of the Fermi- liquid parameter obtained from the comparison agree
with the corresponding values extracted from the analysis of Shubnikov-de Haas
oscillations based on the theory of magnetooscillations in interacting 2D
systems.
09/2008;
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ABSTRACT: Self-assembled monolayers (SAMs) are widely used in a variety of emerging applications for surface modification of metals and oxides. Here, we demonstrate a new type of molecular self-assembly: the growth of organosilane SAMs at the surface of organic semiconductors. Remarkably, SAM growth results in a pronounced increase of the surface conductivity of organic materials, which can be very large for SAMs with a strong electron-withdrawing ability. For example, the conductivity induced by perfluorinated alkyl silanes in organic molecular crystals approaches 10(-5) S per square, two orders of magnitude greater than the maximum conductivity typically achieved in organic field-effect transistors. The observed large electronic effect opens new opportunities for nanoscale surface functionalization of organic semiconductors with molecular self-assembly. In particular, SAM-induced conductivity shows sensitivity to different molecular species present in the environment, which makes this system very attractive for chemical sensing applications.
Nature Material 02/2008; 7(1):84-9. · 32.84 Impact Factor
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ABSTRACT: We report on an infrared spectroscopy study of mobile holes in the accumulation layer of organic field-effect transistors based on rubrene single crystals. Our data indicate that both transport and infrared properties of these transistors at room temperature are governed by light quasiparticles in molecular orbital bands with the effective masses m* comparable to free electron mass. Furthermore, the m* values inferred from our experiments are in agreement with those determined from band structure calculations. These findings reveal no evidence for prominent polaronic effects, which is at variance with the common beliefs of polaron formation in molecular solids.
Physical Review Letters 08/2007; 99(1):016403. · 7.37 Impact Factor
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ABSTRACT: We are developing hot-electron superconducting transition-edge sensors (TES) capable of counting THz photons and operating at . We fabricated superconducting Ti nanosensors with Nb contacts with a volume of on planar Si substrates and have measured the thermal conductance in the material, G=4times10<sup>-3</sup> W/K at 0.3 K, caused predominantly by the weak electron-phonon coupling. The corresponding phonon-noise NEP=3times10<sup>-19</sup> W/Hz<sup>1/2</sup> . Detection of single optical photons (1550 nm and 670 nm wavelength) has been demonstrated for larger devices and yielded the thermal time constants of 30 mus at 145 mK and of 25 mus at 190 mK. This hot-electron direct detector (HEDD) is expected to have a small enough energy fluctuation noise for detecting individual photons with v>THz where NEP~3times10<sup>-20</sup> W/Hz<sup>1/2</sup> is needed for spectroscopy in space.
IEEE Transactions on Appiled Superconductivity 07/2007; · 1.04 Impact Factor
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ABSTRACT: We have measured the weak localization magnetoresistance in (001)-oriented Si MOS structures with a wide range of mobilities. For the quantitative analysis of the data, we have extended the theory of weak-localization corrections in the ballistic regime to the system with two equivalent valleys in electron spectrum. This theory describes the observed magnetoresistance and allows the extraction of the phase breaking time tau_phi and the intervalley scattering time tau_v. The temperature dependences tau_phi(T) for all studied structures are in good agreement with the theory of electron-electron interaction effects in two-dimensional systems. The intervalley scattering is elastic and rather strong: tau_v is typically only an order of magnitude greater than the transport time, tau. It is found that the intervalley scattering rate is temperature-independent and the ratio tau_v/tau decreases with increasing the electron density. These observations suggest that the roughness of the Si-SiO2 interface plays the major role in intervalley scattering.
02/2007;
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Advanced Materials 05/2006; 18(12):1552 - 1556. · 13.88 Impact Factor
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ABSTRACT: We report on the effect of monochromatic microwave (MW) radiation on the weak-localization corrections to the conductivity of quasi-one-dimensional silver wires. Because of the improved electron cooling in the wires, the MW-induced dephasing is observed without a concomitant overheating of electrons over wide ranges of the MW power P(MW) and frequency f. The observed dependences of the conductivity and MW-induced dephasing rate on P(MW) and f are in agreement with the theory by Altshuler, Aronov, and Khmelnitsky [Solid State Commun. 39, 619 (1981)]. Our results suggest that in the low-temperature experiments with 1D wires, saturation of the temperature dependence of the dephasing time can be caused by an MW electromagnetic noise with a sub-pW power.
Physical Review Letters 04/2006; 96(8):086801. · 7.37 Impact Factor
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ABSTRACT: We have observed the Hall effect in the field-induced accumulation layer on the surface of single-crystal samples of a small-molecule organic semiconductor rubrene. The Hall mobility muH increases with decreasing temperature in both the intrinsic (high-temperature) and trap-dominated (low-temperature) conduction regimes. In the intrinsic regime, the density of mobile field-induced charge carriers extracted from the Hall measurements, nH, coincides with the density n calculated using the gate-channel capacitance and becomes smaller than n in the trap-dominated regime. The Hall data are consistent with the diffusive bandlike motion of field-induced charge carriers between trapping events.
Physical Review Letters 12/2005; 95(22):226601. · 7.37 Impact Factor
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ABSTRACT: In order to reveal the effects of disorder in the vicinity of the apparent metal-insulator transition in 2D, we studied electron In order to reveal the effects of disorder in the vicinity of the apparent metal-insulator transition in 2D, we studied electron
transport in the same Si device after cooling it down to 4 K at different fixed values of the gate voltage V transport in the same Si device after cooling it down to 4 K at different fixed values of the gate voltage V
cool. Different V cool. Different V
cool did not significantly modify either the momentum relaxation rate or the strength of electron-electron interactions. However, cool did not significantly modify either the momentum relaxation rate or the strength of electron-electron interactions. However,
temperature dependences of the resistance and the magnetoresistance in parallel magnetic fields in the vicinity of the 2D temperature dependences of the resistance and the magnetoresistance in parallel magnetic fields in the vicinity of the 2D
metal-insulator transition carry a strong imprint of the quenched disorder determined by V metal-insulator transition carry a strong imprint of the quenched disorder determined by V
cool. This demonstrates that the observed transition between the metallic and insulating regimes, besides the universal effects cool. This demonstrates that the observed transition between the metallic and insulating regimes, besides the universal effects
of electron-electron interaction, depends on the sample-specific localized states (disorder). We report on evidence for a of electron-electron interaction, depends on the sample-specific localized states (disorder). We report on evidence for a
weak exchange of electrons between the reservoirs of extended and resonant localized states that occur at low densities. The weak exchange of electrons between the reservoirs of extended and resonant localized states that occur at low densities. The
strong cool-down dependent variations of ρ(T), we believe, are evidence for a developing spatially inhomogeneous state in the critical regime. strong cool-down dependent variations of ρ(T), we believe, are evidence for a developing spatially inhomogeneous state in the critical regime.
JETP Letters 08/2005; 82(6):371-376. · 1.35 Impact Factor
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ABSTRACT: Photoinduced charge transfer of positive and negative charges across the interface between a single-crystal organic semiconductor and a polymeric insulator is observed in electric field-effect experiments. Immobilization of the transferred charge by deep traps in the polymer results in a shift of the threshold of field-induced conductivity along the semiconductor-polymer interface, which allows for direct measurements of the charge transfer rate. The transfer occurs when the photon energy exceeds the absorption edge of the semiconductor. The direction of the transverse electric field at the interface determines the sign of the transferred charge; the transfer rate is controlled by the field magnitude and light intensity.
Physical Review Letters 08/2005; 95(1):016602. · 7.37 Impact Factor
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ABSTRACT: Using single-crystal organic field-effect transistors with the conduction channel exposed to environmental agents we have observed generation of electronic defects at the organic surface in the high-vacuum environment. Rapid decrease of the source-drain current of an operating device is observed upon exposure of the channel to the species generated by high-vacuum gauges. We attribute this effect to interaction of the organic surface with electrically neutral free radicals produced in the process of hydrocarbon cracking on hot filaments with a relatively low activation energy Ea ~ 2.5 eV (240 kJ/mol). The reported results might be important for optimizing the high-vacuum processes of fabrication and characterization of a wide range of organic and molecular electronic devices. Comment: submitted to Appl. Phys. Lett
05/2005;
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Applied Physics Letters 01/2005; 86(12):1-3. · 3.84 Impact Factor
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Advanced Materials 12/2004; 16(23‐24):2097 - 2101. · 13.88 Impact Factor
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ABSTRACT: Photo-induced charge transfer of positive and negative charges across the interface between an ordered organic semiconductor and a polymeric insulator is observed in the field-effect experiments. Immobilization of the transferred charge in the polymer results in a shift of the field-effect threshold of polaronic conduction along the interface in the semiconductor, which allows for direct measurements of the charge transfer rate. The transfer occurs when the photon energy exceeds the absorption edge of the semiconductor. The direction of the transverse electric field at the interface determines the sign of the transferred charge; the transfer rate is controlled by the field magnitude and light intensity.
11/2004;
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ABSTRACT: The air-gap field-effect technique enabled realization of the intrinsic (not limited by static disorder) polaronic transport on the surface of rubrene (C42H28) crystals over a wide temperature range. The signatures of this intrinsic transport are the anisotropy of the carrier mobility, mu, and the growth of mu with cooling. Anisotropy of mu vanishes in the activation regime at low temperatures, where the transport is dominated by shallow traps. The deep traps, introduced by x-ray radiation, increase the field-effect threshold without affecting mu, an indication that the filled traps do not scatter polarons.
Physical Review Letters 09/2004; 93(8):086602. · 7.37 Impact Factor
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ABSTRACT: We report observation of the unexpected negative and nonmonotonic magnetoresistance of 2D electrons in Si-MOSFET subjected to a varying in-plane magnetic field superimposed on a constant
perpendicular field component. We show that this nonmonotonic magnetoresistance is irrelevant to the energy spectrum of mobile
2D electrons. We also observed variations of the density of mobile electrons with the in-plane field. We argue that both variations
of the negative magnetoresistance and of the density of mobile electrons originate from the band of localized states. The
latter coexist and interact with mobile electrons even at relatively high density, a factor of 1.5 higher than the critical
density of the apparent metal-insulator transition.
JETP Letters 08/2004; 80(5):359-362. · 1.35 Impact Factor
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ABSTRACT: We report on observation of a light-induced switching of the conductance in the back-gated organic field-effect transistors (OFETs) with built-in conduction channel. In the studied devices, the built-in channel is formed owing to the self-sensitized photo-oxidation of rubrene surface. In the dark, the back gate controls the charge injection from metal contacts into the built-in channel: the high-current ON state corresponds to zero or negative back-gate voltage; the low-current OFF state - to a positive back-gate voltage that blocks the Schottky contacts. Illumination of the OFET in the OFF state with a short pulse of light switches the device into the ON state that persists in the dark for days. The OFF state can be restored by cycling the back gate voltage. The observed effect can be explained by screening of the back-gate electric field by the charges photo-generated in the bulk of organic semiconductor. Comment: 3 pages
06/2004;
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ABSTRACT: We report on fabrication of field-effect transistors (FETs) based on transition metal dichalcogenides. The unique structure of single crystals of these layered inorganic semiconductors enables fabrication of FETs with intrinsically low field-effect threshold and high charge carrier mobility, comparable to that in the best single-crystal Si FETs (up to 500 cm<sup>2</sup>/V s for the p-type conductivity in the WSe <sub>2</sub> -based FETs at room temperature). These FETs demonstrate ambipolar operation. Owing to mechanical flexibility, they hold potential for applications in “flexible” electronics. © 2004 American Institute of Physics.
Applied Physics Letters 05/2004; · 3.84 Impact Factor
