46 research outputs found
Parametric study of temperature distribution in plasmon-assisted photocatalysis
Recently, there has been a growing interest in the usage of mm-scale
composites of plasmonic nanoparticles for enhancing the rates of chemical
reactions; the effect was shown recently to be predominantly associated with
the elevated temperature caused by illumination. Here, we study the parametric
dependence of the temperature distribution in these samples, and provide
analytic expressions for simple cases. We show that since these systems are
usually designed to absorb all the incoming light, the temperature distribution
in them is weakly-dependent on the illumination spectrum, pulse duration,
particle shape, size and density. Thus, changes in these parameters yield at
most modest quantitative changes. We also show that the temperature
distribution is linearly dependent on the beam radius and the thermal
conductivity of the host. Finally, we study the sensitivity of the reaction
rate to these parameters as a function of the activation energy and interpret
various previous experimental reports. These results would simplify the
optimization of photocatalysis experiments, as well as for other energy-related
applications based on light harvesting for heat generation
Theory of Non-equilibrium "Hot" Carriers in Direct Band-gap Semiconductors Under Continuous Illumination
The interplay between the illuminated excitation of carriers and subsequent
thermalization and recombination leads to the formation of non-equilibrium
distributions for the "hot" carriers and to heating of both electrons, holes
and phonons. In spite of the fundamental and practical importance of these
processes, there is no theoretical framework which encompasses all of them and
provides a clear prediction for the non-equilibrium carrier distributions.
Here, a self-consistent theory accounting for the interplay between excitation,
thermalization, and recombination in continuously-illuminated semiconductors is
presented, enabling the calculation of non-equilibrium carrier distributions.
We show that counter-intuitively, distributions deviate more from equilibrium
under weak illumination than at high intensities. We mimic two experimental
procedures to extract the carrier temperatures and show that they yield
different dependence on illumination. Finally, we provide an accurate way to
evaluate photoluminescence efficiency, which, unlike conventional models,
predicts correctly the experimental results. These results provide a starting
point towards examining how non-equilibrium features will affect properties
hot-carrier based application.Comment: Version accepted in New Journal of Physic