20 research outputs found
Optically driven ultra-stable nanomechanical rotor
Nanomechanical devices have attracted the interest of a growing
interdisciplinary research community, since they can be used as highly
sensitive transducers for various physical quantities. Exquisite control over
these systems facilitates experiments on the foundations of physics. Here, we
demonstrate that an optically trapped silicon nanorod, set into rotation at MHz
frequencies, can be locked to an external clock, transducing the properties of
the time standard to the rod's motion with the remarkable frequency stability
of . While the dynamics of
this periodically driven rotor generally can be chaotic, we derive and verify
that stable limit cycles exist over a surprisingly wide parameter range. This
robustness should enable, in principle, measurements of external torques with
sensitivities better than 0.25zNm, even at room temperature. We show that in a
dilute gas, real-time phase measurements on the locked nanorod transduce
pressure values with a sensitivity of 0.3%.Comment: 5 pages, 4 figure
Cavity-assisted manipulation of freely rotating silicon nanorods in high vacuum
Optical control of nanoscale objects has recently developed into a thriving
field of research with far-reaching promises for precision measurements,
fundamental quantum physics and studies on single-particle thermodynamics.
Here, we demonstrate the optical manipulation of silicon nanorods in high
vacuum. Initially, we sculpture these particles into a silicon substrate with a
tailored geometry to facilitate their launch into high vacuum by laser-induced
mechanical cleavage. We manipulate and trace their center-of-mass and
rotational motion through the interaction with an intense intra-cavity field.
Our experiments show optical forces on nanorotors three times stronger than on
silicon nanospheres of the same mass. The optical torque experienced by the
spinning rods will enable cooling of the rotational motion and torsional
opto-mechanics in a dissipation-free environment.Comment: 8 page
Full rotational control of levitated silicon nanorods
We study a nanofabricated silicon rod levitated in an optical trap. By
manipulating the polarization of the light we gain full control over the
ro-translational dynamics of the rod. We are able to trap both its
centre-of-mass and align it along the linear polarization of the laser field.
The rod can be set into rotation at a tuned frequency by exploiting the
radiation pressure exerted by elliptically polarized light. The rotational
motion of the rod dynamically modifies the optical potential, which allows
tuning of the rotational frequency over hundreds of Kilohertz. This ability to
trap and control the motion and alignment of nanoparticles opens up the field
of rotational optomechanics, rotational ground state cooling and the study of
rotational thermodynamics in the underdamped regime.Comment: 5 pages, 4 figures, 4 Supplementary pages, 4 Supplementary figure
The multi-configurational time-dependent Hartree method for bosons: Many-body dynamics of bosonic systems
The evolution of Bose-Einstein condensates is amply described by the
time-dependent Gross-Pitaevskii mean-field theory which assumes all bosons to
reside in a single time-dependent one-particle state throughout the propagation
process. In this work, we go beyond mean-field and develop an essentially-exact
many-body theory for the propagation of the time-dependent Schr\"odinger
equation of interacting identical bosons. In our theory, the time-dependent
many-boson wavefunction is written as a sum of permanents assembled from
orthogonal one-particle functions, or orbitals, where {\it both} the expansion
coefficients {\it and} the permanents (orbitals) themselves are {\it
time-dependent} and fully determined according to a standard time-dependent
variational principle. By employing either the usual Lagrangian formulation or
the Dirac-Frenkel variational principle we arrive at two sets of coupled
equations-of-motion, one for the orbitals and one for the expansion
coefficients. The first set comprises of first-order differential equations in
time and non-linear integro-differential equations in position space, whereas
the second set consists of first-order differential equations with
time-dependent coefficients. We call our theory multi-configurational
time-dependent Hartree for bosons, or MCTDHB(), where specifies the
number of time-dependent orbitals used to construct the permanents. Numerical
implementation of the theory is reported and illustrative numerical examples of
many-body dynamics of trapped Bose-Einstein condensates are provided and
discussed.Comment: 30 pages, 2 figure
Nanodicing Single Crystalline Silicon Nanowire Arrays
Here,
we demonstrate a novel method for the production of single-crystal
Si nanowire arrays based on the top-down carving of Si-nanowall structures
from a donor substrate, and their subsequent controlled and selective
harvesting into a sacrificial solid material block. Nanosectioning
of the nanostructures-embedding block by ultramicrotome leads to the
formation of size, shape, and orientation-controlled high quality
nanowire arrays. Additionally, we introduce a novel approach that
enables transferring the nanowire arrays to any acceptor substrate,
while preserving their orientation, and placing them on defined locations.
Furthermore, crystallographic analysis and electrical measurements
were performed, proving that the quality of the sectioned nanowires,
which derive from their original crystalline donor substrate, are
remarkably preserved
Controlled Formation of Radial Core–Shell Si/Metal Silicide Crystalline Heterostructures
The
highly controlled formation of “radial” silicon/NiSi
core−shell nanowire heterostructures has been demonstrated
for the first time. Here, we investigated the “radial”
diffusion of nickel atoms into crystalline nanoscale silicon pillar
11 cores, followed by nickel silicide phase formation and the creation
of a well-defined shell structure. The described approach is based
on a two-step thermal process, which involves metal diffusion at low
temperatures in the range of 200–400 °C, followed by a
thermal curing step at a higher temperature of 400 °C. In-depth
crystallographic analysis was performed by nanosectioning the resulting
silicide–shelled silicon nanopillar heterostructures, giving
us the ability to study in detail the newly formed silicide shells.
Remarkably, it was observed that the resulting silicide shell thickness
has a self-limiting behavior, and can be tightly controlled by the
modulation of the initial diffusion-step temperature. In addition,
electrical measurements of the core–shell structures revealed
that the resulting shells can serve as an embedded conductive layer
in future optoelectronic applications. This research provides a broad
insight into the Ni silicide “radial” diffusion process
at the nanoscale regime, and offers a simple approach to form thickness-controlled
metal silicide shells in the range of 5–100 nm around semiconductor
nanowire core structures, regardless the diameter of the nanowire
cores. These high quality Si/NiSi core–shell nanowire structures
will be applied in the near future as building blocks for the creation
of utrathin highly conductive optically transparent top electrodes,
over vertical nanopillars-based solar cell devices, which may subsequently
lead to significant performance improvements of these devices in terms
of charge collection and reduced recombination
Controlled Formation of Radial Core–Shell Si/Metal Silicide Crystalline Heterostructures
The
highly controlled formation of “radial” silicon/NiSi
core−shell nanowire heterostructures has been demonstrated
for the first time. Here, we investigated the “radial”
diffusion of nickel atoms into crystalline nanoscale silicon pillar
11 cores, followed by nickel silicide phase formation and the creation
of a well-defined shell structure. The described approach is based
on a two-step thermal process, which involves metal diffusion at low
temperatures in the range of 200–400 °C, followed by a
thermal curing step at a higher temperature of 400 °C. In-depth
crystallographic analysis was performed by nanosectioning the resulting
silicide–shelled silicon nanopillar heterostructures, giving
us the ability to study in detail the newly formed silicide shells.
Remarkably, it was observed that the resulting silicide shell thickness
has a self-limiting behavior, and can be tightly controlled by the
modulation of the initial diffusion-step temperature. In addition,
electrical measurements of the core–shell structures revealed
that the resulting shells can serve as an embedded conductive layer
in future optoelectronic applications. This research provides a broad
insight into the Ni silicide “radial” diffusion process
at the nanoscale regime, and offers a simple approach to form thickness-controlled
metal silicide shells in the range of 5–100 nm around semiconductor
nanowire core structures, regardless the diameter of the nanowire
cores. These high quality Si/NiSi core–shell nanowire structures
will be applied in the near future as building blocks for the creation
of utrathin highly conductive optically transparent top electrodes,
over vertical nanopillars-based solar cell devices, which may subsequently
lead to significant performance improvements of these devices in terms
of charge collection and reduced recombination
Optically transparent vertical silicon nanowire arrays for live-cell imaging
Programmable nano-bio interfaces driven by tuneable vertically configured nanostructures have recently emerged as a powerful tool for cellular manipulations and interrogations. Such interfaces have strong potential for ground-breaking advances, particularly in cellular nanobiotechnology and mechanobiology. However, the opaque nature of many nanostructured surfaces makes non-destructive, live-cell characterization of cellular behavior on vertically aligned nanostructures challenging to observe. Here, a new nanofabrication route is proposed that enables harvesting of vertically aligned silicon (Si) nanowires and their subsequent transfer onto an optically transparent substrate, with high efficiency and without artefacts. We demonstrate the potential of this route for efficient live-cell phase contrast imaging and subsequent characterization of cells growing on vertically aligned Si nanowires. This approach provides the first opportunity to understand dynamic cellular responses to a cell-nanowire interface, and thus has the potential to inform the design of future nanoscale cellular manipulation technologies
Supplement 1: Full rotational control of levitated silicon nanorods
Supplement 1 Originally published in Optica on 20 March 2017 (optica-4-3-356
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Optically transparent vertical silicon nanowire arrays for live-cell imaging
Programmable nano-bio interfaces driven by tuneable vertically configured nanostructures have recently emerged as a powerful tool for cellular manipulations and interrogations. Such interfaces have strong potential for ground-break-ing advances, particularly in cellular nanobiotechnology and mechanobiology. However, the opaque nature of many nanostructured surfaces makes non-destructive, live-cell characterization of cellular behavior on vertically aligned nanostructures challenging to observe. Here, a new nanofabrication route is proposed that enables harvesting of vertically aligned silicon (Si) nanowires and their subsequent transfer onto an optically transparent substrate, with high efficiency and without artefacts. We demonstrate the potential of this route for efficient live-cell phase contrast imaging and subsequent characterization of cells growing on vertically aligned Si nanowires. This approach provides the first opportunity to understand dynamic cellular responses to a cell-nanowire interface, and thus has the potential to inform the design of future nanoscale cellular manipulation technologies