344 research outputs found
Nanomechanical detection of nuclear magnetic resonance using a silicon nanowire oscillator
We report the use of a silicon nanowire mechanical oscillator as a
low-temperature nuclear magnetic resonance force sensor to detect the
statistical polarization of 1H spins in polystyrene. Under operating
conditions, the nanowire experienced negligible surface-induced dissipation and
exhibited a nearly thermally-limited force noise of 1.9 aN^2/Hz in the
measurement quadrature. In order to couple the 1H spins to the nanowire
oscillator, we have developed a new magnetic resonance force detection protocol
which utilizes a nanoscale current-carrying wire to produce large
time-dependent magnetic field gradients as well as the rf magnetic field.Comment: 14 pages, 5 figure
Langevin-like giant magnetoresistance in Co-Cu superlattices
We present evidence for a new type of giant magnetoresistance in (111) cobalt-copper superlattices with atomically smooth interfaces. We propose that the lowered dimensionality of the structure leads to an enhancement of the scattering of conduction electrons from paramagnetic interfaces obeying a Langevin-like saturation at very high fields, well beyond the switching field of the Co layers. The findings help to explain similarities in magnetotransport behavior with recently reported granular systems as well as differences with antiferromagnetically coupled multilayers
Low temperature properties of a quantum particle coupled to dissipative environments
We study the dynamics of a quantum particle coupled to dissipative (ohmic)
environments, such as an electron liquid. For some choices of couplings, the
properties of the particle can be described in terms of an effective mass. A
particular case is the three dimensional dirty electron liquid. In other
environments, like the one described by the Caldeira-Leggett model, the
effective mass diverges at low temperatures, and quantum effects are strongly
suppressed. For interactions within this class, arbitrarily weak potentials
lead to localized solutions. Particles bound to external potentials, or moving
in closed orbits, can show a first order transition, between strongly and
weakly localized regimes.Comment: 10 page
Quantum Diffusion of H/Ni(111) through the Monte Carlo Wave Function Formalism
We consider a quantum system coupled to a dissipative background with many
degrees of freedom using the Monte Carlo Wave Function method. Instead of
dealing with a density matrix which can be very high-dimensional, the method
consists of integrating a stochastic Schrodinger equation with a non-hermitian
damping term in the evolution operator, and with random quantum jumps. The
method is applied to the diffusion of hydrogen on the Ni(111) surface below 100
K. We show that the recent experimental diffusion data for this system can be
understood through an interband activation process, followed by quantum
tunnelling.Comment: In press at Phys.Rev.Let
Biofunctionalized Zinc Oxide Field Effect Transistors for Selective Sensing of Riboflavin with Current Modulation
Zinc oxide field effect transistors (ZnO-FET), covalently functionalized with single stranded DNA aptamers, provide a highly selective platform for label-free small molecule sensing. The nanostructured surface morphology of ZnO provides high sensitivity and room temperature deposition allows for a wide array of substrate types. Herein we demonstrate the selective detection of riboflavin down to the pM level in aqueous solution using the negative electrical current response of the ZnO-FET by covalently attaching a riboflavin binding aptamer to the surface. The response of the biofunctionalized ZnO-FET was tuned by attaching a redox tag (ferrocene) to the 3′ terminus of the aptamer, resulting in positive current modulation upon exposure to riboflavin down to pM levels
Morphology of epitaxial core-shell nanowires
We analyze the morphological stability against azimuthal, axial, and general
helical perturbations for epitaxial core-shell nanowires in the growth regimes
limited by either surface diffusion or evaporation-condensation surface
kinetics. For both regimes, we find that geometric parameters (i.e., core
radius and shell thickness) play a central role in determining whether the
nanowire remains cylindrical or its shell breaks up into epitaxial islands
similar to those observed during Stranski-Krastanow growth in thin epilayers.
The combination of small cores and rapid growth of the shell emerge as key
ingredients for stable shell growth. Our results provide an explanation for the
different core-shell morphologies reported in the Si-Ge system experimentally,
and also identify a growth-induced intrinsic mechanism for the formation of
helical nanowires.Comment: In press, Nano Letters (7 pages, 4 figures
Probing quantum confinement within single core-multishell nanowires
Theoretically core-multishell nanowires under a cross-section of hexagonal geometry should exhibit peculiar confinement effects. Using a hard X-ray nanobeam, here we show experimental evidence for carrier localization phenomena at the hexagon corners by combining synchrotron excited optical luminescence with simultaneous X-ray fluorescence spectroscopy. Applied to single coaxial n-GaN/InGaN multiquantum-well/p-GaN nanowires, our experiment narrows the gap between optical microscopy and high-resolution X-ray imaging and calls for further studies on the underlying mechanisms of optoelectronic nanodevices. © 2012 American Chemical Society.The authors thank Irina Snigireva and Armando Vicente Sole for their assistance with the SEM measurements and data processing using PyMca, respectively. We thank Remi Tocoulou and Peter Cloetens for their help and the ESRF for the beam time allocated. We also thank Andrei Rogalev for the valuable discussions and Gary Admans for the critical reading of the manuscript. This work has been partially supported by the NANOWIRING Marie Curie ITN (EU project no. PITN-GA-2010-265073), as well as by the EPIC-NANOTICS (TEC2011-29120-C05-04) and Q&C-LIGHT (S2009ESP-1503) from Spanish MEC and CAM, respectively.Martínez Criado, G.; Homs Puron, AA.; Alen, B.; Sans Tresserras, JÁ.; Segura Ruiz, J.; Molina Sánchez, A.; Susini, J.... (2012). Probing quantum confinement within single core-multishell nanowires. Nano Letters. 12(11):5829-5834. https://doi.org/10.1021/nl303178uS58295834121
Ge/Si nanowire mesoscopic Josephson junctions
The controlled growth of nanowires (NWs) with dimensions comparable to the
Fermi wavelengths of the charge carriers allows fundamental investigations of
quantum confinement phenomena. Here, we present studies of proximity-induced
superconductivity in undoped Ge/Si core/shell NW heterostructures contacted by
superconducting leads. By using a top gate electrode to modulate the carrier
density in the NW, the critical supercurrent can be tuned from zero to greater
than 100 nA. Furthermore, discrete sub-bands form in the NW due to confinement
in the radial direction, which results in stepwise increases in the critical
current as a function of gate voltage. Transport measurements on these
superconductor-NW-superconductor devices reveal high-order (n = 25) resonant
multiple Andreev reflections, indicating that the NW channel is smooth and the
charge transport is highly coherent. The ability to create and control coherent
superconducting ordered states in semiconductor-superconductor hybrid
nanostructures allows for new opportunities in the study of fundamental
low-dimensional superconductivity
Synthesis of Novel Double-Layer Nanostructures of SiC–WOxby a Two Step Thermal Evaporation Process
A novel double-layer nanostructure of silicon carbide and tungsten oxide is synthesized by a two-step thermal evaporation process using NiO as the catalyst. First, SiC nanowires are grown on Si substrate and then high density W18O49nanorods are grown on these SiC nanowires to form a double-layer nanostructure. XRD and TEM analysis revealed that the synthesized nanostructures are well crystalline. The growth of W18O49nanorods on SiC nanowires is explained on the basis of vapor–solid (VS) mechanism. The reasonably better turn-on field (5.4 V/μm) measured from the field emission measurements suggest that the synthesized nanostructures could be used as potential field emitters
- …