9 research outputs found
Universal behavior of highly-confined heat flow in semiconductor nanosystems: from nanomeshes to metalattices
Nanostructuring on length scales corresponding to phonon mean free paths
provides control over heat flow in semiconductors and makes it possible to
engineer their thermal properties. However, the influence of boundaries limits
the validity of bulk models, while first principles calculations are too
computationally expensive to model real devices. Here we use extreme
ultraviolet beams to study phonon transport dynamics in a 3D nanostructured
silicon metalattice with deep nanoscale feature size, and observe dramatically
reduced thermal conductivity relative to bulk. To explain this behavior, we
develop a predictive theory wherein thermal conduction separates into a
geometric permeability component and an intrinsic viscous contribution, arising
from a new and universal effect of nanoscale confinement on phonon flow. Using
both experiments and atomistic simulations, we show that our theory is valid
for a general set of highly-confined silicon nanosystems, from metalattices,
nanomeshes, porous nanowires to nanowire networks. This new analytical theory
of thermal conduction can be used to predict and engineer phonon transport in
boundary-dominated nanosystems, that are of great interest for next-generation
energy-efficient devices
Recommended from our members
A General and Predictive Understanding of Thermal Transport from 1D- and 2D-Confined Nanostructures : Theory and Experiment
Altres ajuts: Acord transformatiu CRUE-CSICHeat management is crucial in the design of nanoscale devices as the operating temperature determines their efficiency and lifetime. Past experimental and theoretical works exploring nanoscale heat transport in semiconductors addressed known deviations from Fourier's law modeling by including effective parameters, such as a size-dependent thermal conductivity. However, recent experiments have qualitatively shown behavior that cannot be modeled in this way. Here, we combine advanced experiment and theory to show that the cooling of 1D- and 2D-confined nanoscale hot spots on silicon can be described using a general hydrodynamic heat transport model, contrary to previous understanding of heat flow in bulk silicon. We use a comprehensive set of extreme ultraviolet scatterometry measurements of nondiffusive transport from transiently heated nanolines and nanodots to validate and generalize our ab initio model, that does not need any geometry-dependent fitting parameters. This allows us to uncover the existence of two distinct time scales and heat transport mechanisms: an interface resistance regime that dominates on short time scales and a hydrodynamic-like phonon transport regime that dominates on longer time scales. Moreover, our model can predict the full thermomechanical response on nanometer length scales and picosecond time scales for arbitrary geometries, providing an advanced practical tool for thermal management of nanoscale technologies. Furthermore, we derive analytical expressions for the transport time scales, valid for a subset of geometries, supplying a route for optimizing heat dissipation
Recommended from our members
Temporal and spectral multiplexing for EUV multibeam ptychography with a high harmonic light source
We demonstrate temporally multiplexed multibeam ptychography implemented for the first time in the EUV, by using a high harmonic based light source. This allows for simultaneous imaging of different sample areas, or of the same area at different times or incidence angles. Furthermore, we show that this technique is compatible with wavelength multiplexing for multibeam spectroscopic imaging, taking full advantage of the temporal and spectral characteristics of high harmonic light sources. This technique enables increased data throughput using a simple experimental implementation and with high photon efficiency.
</p
Full Characterization of the Mechanical Properties of 11–50 nm Ultrathin Films: Influence of Network Connectivity on the Poisson’s Ratio
Precise characterization
of the mechanical properties of ultrathin
films is of paramount importance for both a fundamental understanding
of nanoscale materials and for continued scaling and improvement of
nanotechnology. In this work, we use coherent extreme ultraviolet
beams to characterize the full elastic tensor of isotropic ultrathin
films down to 11 nm in thickness. We simultaneously extract the Young’s
modulus and Poisson’s ratio of low-<i>k</i> a-SiC:H
films with varying degrees of hardness and average network connectivity
in a single measurement. Contrary to past assumptions, we find that
the Poisson’s ratio of such films is not constant but rather
can significantly increase from 0.25 to >0.4 for a network connectivity
below a critical value of ∼2.5. Physically, the strong hydrogenation
required to decrease the dielectric constant <i>k</i> results
in bond breaking, lowering the network connectivity, and Young’s
modulus of the material but also decreases the compressibility of
the film. This new understanding of ultrathin films demonstrates that
coherent EUV beams present a new nanometrology capability that can
probe a wide range of novel complex materials not accessible using
traditional approaches