56 research outputs found
Energy-Resolved Femtosecond Hot Electron Dynamics in Single Plasmonic Nanoparticles
Efficient excitation and harvesting of hot carriers are central to a variety
of emerging nanoplasmonic applications, but ballistic carrier extraction
remains a challenge. To elucidate the relevant dynamics as a function of
nanoscale geometry, we perform femtosecond two-color pump-probe photoemission
studies of single gold nanorods and gold/silica nanoshells with simultaneous
time, energy, and vector momentum resolution. Angle-resolved photoelectron
momentum distributions elucidate the dominant intraband photoexcitation
mechanism and subsequent ballistic dynamics within the gold nanoparticle
volume, as verified via Monte Carlo photoemission modeling. Energy-averaged hot
electron lifetimes around 30 fs are measured in the ~1-2 eV excitation energy
range, while energy-resolved measurements reveal good agreement with Fermi
liquid theory behavior based on electron-electron inelastic scattering, as well
as more detailed kinetic Boltzmann modeling including the effects of electron
cascading from higher energy levels and quasi-elastic electron phonon
scattering. These results directly demonstrate the predominance of bulk-like
hot electron dynamical behaviors (including volume-like excitation and bulk
inelastic scattering rates) in metal nanoparticles with dimensions as small as
10 nm, which should contribute to the design of more efficient hot carrier
devices
Temperature dependence of the thermal boundary resistivity of glass-embedded metal nanoparticles
The temperature dependence of the thermal boundary resistivity is
investigated in glass-embedded Ag particles of radius 4.5 nm, in the
temperature range from 300 to 70 K, using all-optical time-resolved
nanocalorimetry. The present results provide a benchmark for theories aiming at
explaining the thermal boundary resistivity at the interface between metal
nanoparticles and their environment, a topic of great relevance when tailoring
thermal energy delivery from nanoparticles as for applications in nanomedicine
and thermal management at the nanoscaleComment: 4 pages, 3 figure
Water filling in carbon nanotubes with different wettability and implications on nanotube/water heat transfer via atomistic simulations
The peculiar heat and mass transfer properties of Carbon Nanotubes (CNTs) envision promising applications in nanoengineering and nanofluidic devices, such as heat sinks and desalination membranes. However, a comprehensive understanding of the intertwined effects of mass transfer (entrance and exit of liquid molecules inside CNTs) and heat transfer mechanisms (thermal exchange at the CNT/solvent interface) as a function of the properties of CNT surface is currently incomplete. In this work, we use molecular dynamics simulations to study heat and mass transfer in single wall CNTs with (5,5) and (10,10) chirality immersed in water. We present a sensitivity analysis where, starting from different choices of interaction potentials between CNTs and water molecules, we deduce the corresponding CNT/water wetting parameters, we model fill-in and fill-out water dynamics and arrangement of water molecules at the equilibrium. Spontaneous water entrance into CNTs is examined and a single energy parameter to model water filling is introduced. Secondly, we compute the CNT/water thermal boundary resistance for the different wetting properties. In perspective, this work supports a more rational design of CNT-based devices operating in nanothermal and nanobiological environments
Cooling dynamics and thermal interface resistance of glass-embedded metal nanoparticles
The cooling dynamics of glass-embedded noble metal nanoparticles with
diameters ranging from 4 to 26 nm were studied using ultrafast pump-probe
spectroscopy. Measurements were performed probing away from the surface plasmon
resonance of the nanoparticles to avoid spurious effects due to glass heating
around the particle. In these conditions, the time-domain data reflect the
cooling kinetics of the nanoparticle. Cooling dynamics are shown to be
controlled by both thermal resistance at the nanoparticule?glass interface, and
heat diffusion in the glass matrix. Moreover, the interface conductances are
deduced from the experiments and found to be correlated to the acoustic
impedance mismatch at the metal/glass interface
Ultrafast nano generation of acoustic waves in water via a single carbon nanotube
Generation of ultra high frequency acoustic waves in water is key to nano resolution sensing, acoustic imaging and theranostics. In this context water immersed carbon nanotubes (CNTs) may act as an ideal optoacoustic source, due to their nanometric radial dimensions, peculiar thermal properties and broad band optical absorption. The generation mechanism of acoustic waves in water, upon excitation of both a single -wall (SW) and a multi-wall (MW) CNT with laser pulses of temporal width ranging from 5 ns down to ps, is theoretically investigated via a multiscale approach. We show that, depending on the combination of CNT size and laser pulse duration, the CNT can act as a thermophone or a mechanophone. As a thermophone, the CNT acts as a nanoheater for the surrounding water, which, upon thermal expansion, launches the pressure wave. As a mechanophone, the CNT acts as a nanopiston, its thermal expansion directly triggering the pressure wave in water. Activation of the mechanophone effect is sought to trigger few nanometers wavelength sound waves in water, matching the CNT acoustic frequencies. This is at variance with respect to the commonly addressed case of water-immersed single metallic nano-objects excited with ns laser pulses, where only the thermophone effect significantly contributes. The present findings might be of impact in fields ranging from nanoscale non-destructive testing to water dynamics at the meso to nanoscale
Anisotropy effects on the time-resolved spectroscopy of the acoustic vibrations of nanoobjects
International audienceThe impact of spherical symmetry breaking and rystallinity on the response of the vibrational acoustic modes of a nanoobject in frequency- and time-domain experiments is investigated using the finite-element analysis method. The results show that introduction of shape anisotropy, i.e., evolution from a nanosphere to a nanorod, modifies the periods of the fundamental radial and quadrupolar modes and leads to activation of a quadrupolar-like mode in time-domain studies. In contrast, crystallinity is shown to have a negligible impact on the breathing mode frequency of a nanosphere formed by a cubic crystal and does not activate any quadrupolar mode. The effect of an anisotropic excitation in time-resolved measurements of a large nanosphere is also discussed
Time-domain investigation of the acoustic vibrations of metal nanoparticles: Size and encapsulation effects
International audienc
Advances in femto-nano-optics: ultrafast nonlinearity of metal nanoparticles
With the recent advances of experimental techniques, the nonlinear ultrafast optical
response of metal nano-objects can now be investigated both on ensembles and on single
nanoparticles. Its connection with the metal electronic and lattice kinetics is studied on
the basis of a model describing the wavelength and time-dependent modifications of the
object material dielectric function. Its application is illustrated in the case of single
silver nanospheres and gold nanorods, as well as on ensembles of noble metal nanoparticles
and metal-semiconductor nano-hybrids. This quantitative analysis also permits to elucidate
the physical mechanisms at the origin of ultrafast nonlinearities in confined metals at
different timescales
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