18,544 research outputs found
Phononics: Manipulating heat flow with electronic analogs and beyond
The form of energy termed heat that typically derives from lattice
vibrations, i.e. the phonons, is usually considered as waste energy and,
moreover, deleterious to information processing. However, with this colloquium,
we attempt to rebut this common view: By use of tailored models we demonstrate
that phonons can be manipulated like electrons and photons can, thus enabling
controlled heat transport. Moreover, we explain that phonons can be put to
beneficial use to carry and process information. In a first part we present
ways to control heat transport and how to process information for physical
systems which are driven by a temperature bias. Particularly, we put forward
the toolkit of familiar electronic analogs for exercising phononics; i.e.
phononic devices which act as thermal diodes, thermal transistors, thermal
logic gates and thermal memories, etc.. These concepts are then put to work to
transport, control and rectify heat in physical realistic nanosystems by
devising practical designs of hybrid nanostructures that permit the operation
of functional phononic devices and, as well, report first experimental
realizations. Next, we discuss yet richer possibilities to manipulate heat flow
by use of time varying thermal bath temperatures or various other external
fields. These give rise to a plenty of intriguing phononic nonequilibrium
phenomena as for example the directed shuttling of heat, a geometrical phase
induced heat pumping, or the phonon Hall effect, that all may find its way into
operation with electronic analogs.Comment: 24 pages, 16 figures, modified title and revised, accepted for
publication in Rev. Mod. Phy
Schottky nanocontacts on ZnO nanorod arrays
We report on fabrication and electrical characteristics of ZnO nanorod Schottky diode arrays. High quality ZnO nanorods were grown for the fabrication of the Schottky diodes using noncatalytic metalorganic vapor phase epitaxy and Au was evaporated on the tips of the vertically well-aligned ZnO nanorods. I-V characteristics of both bare ZnO and Au/ZnO heterostructure nanorod arrays were measured using current-sensing atomic force microscopy. Although both nanorods exhibited nonlinear and asymmetric I-V characteristic curves, Au/ZnO heterostructure nanorods demonstrated much improved electrical characteristics: the reverse-bias breakdown voltage was improved from -3 to -8 V by capping a Au layer on the nanorod tips. The origin of the enhanced electrical characteristics for the heterostructure nanorods is suggested. (C) 2003 American Institute of Physics.X11326sciescopu
Large-signal model of the Metal-Insulator-Graphene diode targeting RF applications
We present a circuit-design compatible large-signal compact model of
metal-insulator-graphene (MIG) diodes for describing its dynamic response for
the first time. The model essentially consists of a voltage-dependent diode
intrinsic capacitance coupled with a static voltage-dependent current source,
the latter accounts for the vertical electron transport from/towards graphene,
which has been modeled by means of the Dirac-thermionic electron transport
theory through the insulator barrier. Importantly, the image force effect has
been found to play a key role in determining the barrier height, so it has been
incorporated into the model accordingly. The resulting model has been
implemented in Verilog A to be used in existing circuit simulators and
benchmarked against an experimental 6-nm TiO2 barrier MIG diode working as a
power detector.Comment: 4 pages, 5 figures, 1 tabl
Nanoscale Torsional Optomechanics
Optomechanical transduction is demonstrated for nanoscale torsional
resonators evanescently coupled to optical microdisk whispering gallery mode
resonators. The on-chip, integrated devices are measured using a fully
fiber-based system, including a tapered and dimpled optical fiber probe. With a
thermomechanically calibrated optomechanical noise floor down to 7 fm/sqrt(Hz),
these devices open the door for a wide range of physical measurements involving
extremely small torques, as little as 4x10^-20 N*m.Comment: 4 pages, 4 figures - Accepted to APL Oct 22nd, 2012. To appear in
February 4th issue - as cover articl
Near-field electrospinning of conjugated polymer light-emitting nanofibers
The authors report on the realization of ordered arrays of light-emitting
conjugated polymer nanofibers by near-field electrospinning. The fibers, made
by poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene], have diameters of
few hundreds of nanometers and emission peaked at 560 nm. The observed
blue-shift compared to the emission from reference films is attributed to
different polymer packing in the nanostructures. Optical confinement in the
fibers is also analyzed through self-waveguided emission. These results open
interesting perspectives for realizing complex and ordered architectures by
light-emitting nanofibers, such as photonic circuits, and for the precise
positioning and integration of conjugated polymer fibers into light-emitting
devices.Comment: 11 pages, 6 figures Nanoscale, 201
Enhancing fluorescence excitation and collection from the nitrogen-vacancy center in diamond through a micro-concave mirror
We experimentally demonstrate a simple and robust optical fibers based method
to achieve simultaneously efficient excitation and fluorescence collection from
Nitrogen-Vacancy (NV) defects containing micro-crystalline diamond. We
fabricate a suitable micro-concave (MC) mirror that focuses scattered
excitation laser light into the diamond located at the focal point of the
mirror. At the same instance, the mirror also couples the fluorescence light
exiting out of the diamond crystal in the opposite direction of the optical
fiber back into the optical fiber within its light acceptance cone. This part
of fluorescence would have been otherwise lost from reaching the detector. Our
proof-of-principle demonstration achieves a 25 times improvement in
fluorescence collection compared to the case of not using any mirrors. The
increase in light collection favors getting high signal-to-noise ratio (SNR)
optically detected magnetic resonance (ODMR) signals hence offers a practical
advantage in fiber-based NV quantum sensors. Additionally, we compacted the NV
sensor system by replacing some bulky optical elements in the optical path with
a 1x2 fiber optical coupler in our optical system. This reduces the complexity
of the system and provides portability and robustness needed for applications
like magnetic endoscopy and remote-magnetic sensing.Comment: 6 pages, 8 figure
Single photon emission and detection at the nanoscale utilizing semiconductor nanowires
We report recent progress toward on-chip single photon emission and detection
in the near infrared utilizing semiconductor nanowires. Our single photon
emitter is based on a single InAsP quantum dot embedded in a p-n junction
defined along the growth axis of an InP nanowire. Under forward bias, light is
emitted from the single quantum dot by electrical injection of electrons and
holes. The optical quality of the quantum dot emission is shown to improve when
surrounding the dot material by a small intrinsic section of InP. Finally, we
report large multiplication factors in excess of 1000 from a single Si nanowire
avalanche photodiode comprised of p-doped, intrinsic, and n-doped sections. The
large multiplication factor obtained from a single Si nanowire opens up the
possibility to detect a single photon at the nanoscale.Comment: 11 pages, 7 figure
Heterojunction Hybrid Devices from Vapor Phase Grown MoS
We investigate a vertically-stacked hybrid photodiode consisting of a thin
n-type molybdenum disulfide (MoS) layer transferred onto p-type silicon.
The fabrication is scalable as the MoS is grown by a controlled and
tunable vapor phase sulfurization process. The obtained large-scale p-n
heterojunction diodes exhibit notable photoconductivity which can be tuned by
modifying the thickness of the MoS layer. The diodes have a broad
spectral response due to direct and indirect band transitions of the nanoscale
MoS. Further, we observe a blue-shift of the spectral response into the
visible range. The results are a significant step towards scalable fabrication
of vertical devices from two-dimensional materials and constitute a new
paradigm for materials engineering.Comment: 23 pages with 4 figures. This article has been published in
Scientific Reports. (26 June 2014, doi:10.1038/srep05458
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