arXiv subjects

Rishmali Sooriyagoda

Publications and source records attributed to Rishmali Sooriyagoda.

4 recordsLinked to original sources

arXiv2022

Structure-Property-Performance Relationships of Cuprous Oxide Nanostructures for Dielectric Mie Resonance-Enhanced Photocatalysis

Nanostructured metal oxides, such as Cu2O, CeO2, α-Fe2O3, and TiO2 can efficiently mediate photocatalysis for solar-to-chemical energy conversion and pollution remediation. In this contribution, we report a novel approach, dielectric Mie resonance-enhanced photocatalysis, to enhance the catalytic activity of metal oxide photocatalysts. Specifically, we demonstrate that Cu2O nanostructures exhibiting dielectric Mie resonances can exhibit up to an order of magnitude higher photocatalytic rate as compared to Cu2O nanostructures not exhibiting dielectric Mie resonances. Our finite-difference time-domain (FDTD) simulation and experimental results predict a volcano-type relationship between the photocatalytic rate and the size of Cu2O nanospheres and nanocubes. Using transient absorption measurements, we reveal that a coherent electronic process associated with dielectric Mie resonance-mediated charge carrier generation is dominant in Cu2O nanostructures that exhibit higher photocatalytic rates. Although we experimentally demonstrate dielectric Mie resonance-enhanced photocatalysis using Cu2O particles here, based on our FDTD simulations, we anticipate the same can be achieved with other metal oxide photocatalysts, including CeO2, α-Fe2O3, and TiO2.

physics.app-ph↗

arXiv2021

Hot-carrier dynamics in InAs/AlAsSb multiple-quantum wells

A type-II InAs/AlAs$_{0.16}$Sb$_{0.84}$ multiple-quantum well sample is investigated for the photoexcited carrier dynamics as a function of excitation photon energy and lattice temperature. Time-resolved measurements are performed using a near-infrared pump pulse, with photon energies near to and above the band gap, probed with a terahertz probe pulse. The transient terahertz absorption is characterized by a multi-rise, multi-decay function that captures long-lived decay times and a metastable state of for an excess-photon energy of $>100$ meV. For sufficient excess-photon energy, excitation of the metastable state is followed by a transition to the long-lived states. Excitation dependence of the long-lived states map onto a near-direct band gap ($E{_g}$) density of states with an Urbach tail below $E{_g}$. As temperature increases, the long-lived decay times increase $ E{_g}$. Additionally, Auger (and/or trap-assisted Auger) scattering above the onset of the plateau may also contribute to longer hot-carrier lifetimes. Meanwhile, the initial decay component shows strong dependence on excitation energy and temperature, reflecting the complicated initial transfer of energy between valence-band and defect states, indicating methods to further prolong hot carriers for technological applications.

cond-mat.mtrl-sci↗

arXiv2020

Experimental and Computational Studies of the Optical Properties of CuAl1-xFexO2

Delafossites are promising candidates for photocatalysis applications because of their chemical stability and absorption in the solar region of the electromagnetic spectrum. For example, CuAlO2 has good chemical stability but has a large indirect bandgap (~3 eV), so that efforts to improve its absorption in the solar region through alloying are investigated. The effect of dilute alloying on the optical absorption of powdered CuAl1-xFexO2 (x = 0.0-1.0) is measured and compared to electronic band structures calculations using a generalized gradient approximation with Hubbard exchange-correlation parameter and spin. A new absorption feature is observed at 1.8 eV for x = 0.01, which redshifts to 1.4 eV for x = 0.10. This feature is associated with transitions from the L-point valence band maximum to the Fe-3d state that appears below the conduction band of the spin-down band structure. The feature increases the optical absorption below the bandgap of pure CuAlO2, making dilute CuAl1-xFexO2 alloys better suited for solar photocatalysis.

cond-mat.mtrl-sci↗

arXiv2020

Carrier transport and electron-lattice interactions of nonlinear optical crystals CdGeP$_2$, ZnGeP$_2$ and CdSiP$_2$

Terahertz time-domain spectroscopy is employed to investigate temperature-dependent properties of bulk chalcopyrite crystals (CdGeP$_2$, ZnGeP$_2$ and CdSiP$_2$). The complex spectra provide the refraction and absorption as a function of temperature, from which electron-phonon coupling and average phonon energies are extracted and linked to the mechanics of the A- and B-site cations. Also, AC conductivity spectra provide carrier densities and electron scattering times, the temperature dependence of which is associated with unintentional shallow dopants. Temperature dependence of the scattering time is converted into carrier mobility and modeled with microscopic transport mechanisms such as polar optical phonon, acoustic phonons, deformation potential, ionized impurity and dislocation scattering. Hence, analysis links the THz optical and electronic properties to relate microscopic carrier transport and carrier-lattice interactions.

cond-mat.mtrl-sci↗