4,682 research outputs found
Color changes upon cooling of Lepidoptera scales containing photonic nanoarchitectures, and a method for identifying the changes
The effects produced by the condensation of water vapor from the environment in the various intricate
nanoarchitectures occurring in the wing scales of several Lepidoptera species were
investigated by controlled cooling (from 23° C, room temperature to -5 to -10° C) combined with
in situ measurements of changes in the reflectance spectra. It was determined that all photonic
nanoarchitectures giving a reflectance maximum in the visible range and having an open
nanostructure exhibited alteration of the position of the reflectance maximum associated with the
photonic nanoarchitectures. The photonic nanoarchitectures with a closed structure exhibited little
to no alteration in color. Similarly, control specimens colored by pigments did not exhibit a
color change under the same conditions. Hence, this method can be used to identify species with
open photonic nanoarchitectures in their scales. For certain species, an almost complete disappearance
of the reflectance maximum was found. All specimens recovered their original colors
following warming and drying. Cooling experiments using thin copper wires demonstrated that
color alterations could be limited to a width of a millimeter or less. Dried museum specimens did
not exhibit color changes when cooled in the absence of a heat sink due to the low heat capacity
of the wings
Colour changes upon cooling of Lepidoptera scales containing photonic nanoarchitectures
The effects produced by the condensation of water vapours from the ambient in
the various intricate nanoarchitectures occurring in the wing scales of several
Lepidoptera species were investigated by controlled cooling (from room
temperature to -5 - -10 {\deg}C) combined with in situ measurement of changes
in the reflectance spectra. It was determined that, due to this procedure, all
photonic nanoarchitectures giving a reflectance maximum in the visible range
and having an open nanostructure exhibited alteration of the position of the
reflectance maximum associated with the photonic nanoarchitectures. The
photonic nanoarchitectures with a closed structure exhibited little to no
alteration in colour. Similarly, control specimens coloured by pigments did not
exhibit a colour change under the same conditions. Hence, this effect can be
used to identify species with open photonic nanoarchitectures in their scales.
For certain species, an almost complete disappearance of the reflectance
maximum was found. All specimens recovered their original colours following
warming and drying. Cooling experiments using thin copper wires demonstrated
that colour alterations could be limited to a millimetre, or below. Dried
museum specimens do not exhibit colour changes when cooled in the absence of a
heat sink due to the low heat capacity of the wings.Comment: 18 pages, 9 figures, including supplemen
Strongly anisotropic ballistic magnetoresistance in compact three-dimensional semiconducting nanoarchitectures
We establish theoretically that in nonmagnetic semiconducting bilayer or
multilayer thin film systems rolled up into compact quasi-one-dimensional
nanoarchitectures, the ballistic magnetoresistance is very anisotropic:
conductances depend strongly on the direction of an externally applied magnetic
field. This phenomenon originates from the curved open geometry of rolled-up
nanotubes, which leads to a tunability of the number of quasi-one-dimensional
magnetic subbands crossing the Fermi energy. The experimental significance of
this phenomenon is illustrated by a sizable anisotropy that scales with the
inverse of the winding number, and persists up to a critical temperature that
can be strongly enhanced by increasing the strength of the external magnetic
field or the characteristic radius of curvature, and can reach room
temperature.Comment: 5 pages, 4 figures, one supplemental materia
Colloidal Assemblies of Oriented Maghemite Nanocrystals and their NMR Relaxometric Properties
Elevated-temperature polyol-based colloidal-chemistry approach allows for the
development of size-tunable (50 and 86 nm) assemblies of maghemite iso-oriented
nanocrystals, with enhanced magnetization. 1H-Nuclear Magnetic Resonance (NMR)
relaxometric experiments show that the ferrimagnetic cluster-like colloidal
entities exhibit a remarkable enhancement (4 to 5 times) in the transverse
relaxivity, if compared to that of the superparamagnetic contrast agent
Endorem, over an extended frequency range (1-60 MHz). The marked increase of
the transverse relaxivity r2 at a clinical magnetic field strength (1.41 T),
which is 405.1 and 508.3 mM-1 s-1 for small and large assemblies respectively,
allows to relate the observed response to the raised intra-aggregate magnetic
material volume fraction. Furthermore, cell tests with murine fibroblast
culture medium confirmed the cell viability in presence of the clusters. We
discuss the NMR dispersion profiles on the basis of relaxivity models to
highlight the magneto-structural characteristics of the materials for improved
T2-weighted magnetic resonance images.Comment: Includes supporting informatio
Optical properties of bioinspired disordered photonic nanoarchitectures
Bioinspired 1+2D nanoarchitectures inspired by the quasi-ordered structures occurring in
photonic nanoarchitectures of biological origin, like for example butterfly scales, were
produced by depositing a layer of SiO2 nanospheres (156 nm and 292 nm in diameter) on Si
wafers, over which a regular multilayer composed from three alternating layers of SiO2 and
TiO2 was deposited by physical vapor deposition. Flat multilayers were deposited in the same
run on oxidized Si (324 nm SiO2 thickness) for comparison. Different types of disorder (in
plane and out of plane) were purposefully allowed in the 1+2D nanoarchitectures. The
positions of the specular reflection maxima for the flat multilayer and for the two different
bioinspired nanoarchitectures were found to be similar. Additionally to this, the bioinspired
nanoarchitectures exhibited angle independent diffuse reflection too, which was absent in the
flat multilayer. Different model calculations were made to explain the specular and diffuse
optical properties of the samples. Satisfactory agreement was obtained between experimental
data and model calculations
ToPoliNano: Nanoarchitectures Design Made Real
Many facts about emerging nanotechnologies are yet to be assessed. There are still major concerns, for instance, about maximum achievable device density, or about which architecture is best fit for a specific application. Growing complexity requires taking into account many aspects of technology, application and architecture at the same time. Researchers face problems that are not new per se, but are now subject to very different constraints, that need to be captured by design tools. Among the emerging nanotechnologies, two-dimensional nanowire based arrays represent promising nanostructures, especially for massively parallel computing architectures. Few attempts have been done, aimed at giving the possibility to explore architectural solutions, deriving information from extensive and reliable nanoarray characterization. Moreover, in the nanotechnology arena there is still not a clear winner, so it is important to be able to target different technologies, not to miss the next big thing. We present a tool, ToPoliNano, that enables such a multi-technological characterization in terms of logic behavior, power and timing performance, area and layout constraints, on the basis of specific technological and topological descriptions. This tool can aid the design process, beside providing a comprehensive simulation framework for DC and timing simulations, and detailed power analysis. Design and simulation results will be shown for nanoarray-based circuits. ToPoliNano is the first real design tool that tackles the top down design of a circuit based on emerging technologie
On-Surface Hydrogen-Induced Covalent Coupling of Polycyclic Aromatic Hydrocarbons via a Superhydrogenated Intermediate
The activation and subsequent covalent coupling of polycyclic aromatic
hydrocarbons (PAHs) are of great interest in fields like chemistry, energy,
biology, or health, among others. However, this is not a trivial process. So
far, it is based on the use of catalysts that drive and increase the efficiency
of the reaction. Here, we report on an unprecedented method in which the
dehydrogenation and covalent coupling is thermally activated in the presence of
atomic hydrogen and a surface. This mechanism, which requires of the
superhydrogenation of the PAHs, has been characterized by high-resolution
scanning tunnelling microscopy (STM) and rationalized by density functional
theory (DFT) calculations. This work opens a door toward the formation of
covalent, PAH-based, macromolecular nanostructures on low-reactive surfaces,
thus facilitating its applicability.Comment: This manuscript version is made available under the CC-BY-NC-ND 4.0
licens
Quantum mechanics of a spin-orbit coupled electron constrained to a space curve
We derive the effective one-dimensional Schrodinger-Pauli equation for
electrons constrained to move on a space curve. The electrons are confined
using a double thin-wall quantization procedure with adiabatic separation of
fast and slow quantum degrees of freedom. This procedure is capable of yielding
a correct Hermitian one-dimensional Schrodinger-Pauli operator. We find that
the torsion of the space curve generates an additional quantum geometric
potential, adding to the well-known curvature-induced one. Finally, we derive
an analytic form of the one-dimensional Hamiltonian for spin-orbit coupled
electrons in a nanoscale helical wire.Comment: 5 pages, no figure
Mechanical properties of mesoporous ceria nanoarchitectures
Architectural constructs are engineered to impart desirable mechanical properties facilitating bridges spanning a thousand meters and buildings nearly 1 km in height. However, do the same 'engineering-rules' translate to the nanoscale, where the architectural features are less than 0.0001 mm in size? Here, we calculate the mechanical properties of a porous ceramic functional material, ceria, as a function of its nanoarchitecture using molecular dynamics simulation and predict its yield strength to be almost two orders of magnitude higher than the parent bulk material. In particular, we generate models of nanoporous ceria with either a hexagonal or cubic array of one-dimensional pores and simulate their responses to mechanical load. We find that the mechanical properties are critically dependent upon the orientation between the crystal structure (symmetry, direction) and the pore structure (symmetry, direction). This journal i
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