Physics (Scholarly Publications)
http://hdl.handle.net/2262/222
Physics (Scholarly Publications)Wed, 23 Oct 2019 07:25:53 GMT2019-10-23T07:25:53Z2D foams above the jamming transition: Deformation matters
http://hdl.handle.net/2262/89855
2D foams above the jamming transition: Deformation matters
Hutzler, Stefan; Weaire, Denis; Moebius, Matthias
Jammed soft matter systems are often modelled as dense packings of overlapping soft spheres, thus ignoring particle deformation. For 2D (and 3D) soft disks packings, close to the critical packing fraction ϕc, this results in an increase of the average contact number Z with a square root in ϕ − ϕc. Using the program PLAT, we find that in the case of idealised two-dimensional foams, close to the wet limit, Z increases linearly with ϕ − ϕc, where ϕ is the gas fraction. This result is consistent with the different distributions of separations for soft disks and foams at the critical packing fraction. Thus, 2D foams close to the wet limit are not well described as random packings of soft disks, since bubbles in a foam are deformable and adjust their shape. This is not captured by overlapping circular disks.
PUBLISHED
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/2262/898552017-01-01T00:00:00ZInfluence of plasmonic array geometry on non-radiative energy transfer from a quantum well to a quantum dot layer
http://hdl.handle.net/2262/89754
Influence of plasmonic array geometry on non-radiative energy transfer from a quantum well to a quantum dot layer
Bradley, Louise
M. Marciniak
The influence of ordered plasmonic arrays on energy transfer from a quantum well to a quantum dot layer has been investigated. The ordered arrays are comprised of nanostructures of different geometries, including boxes, disks and rings. Despite no signature of non-radiative energy transfer in the absence of an array, an efficiency of ~51% is observed for a ring array, though strong emission quenching yields an overall increase of only ~ 14% of the QD emission. The QD emission is enhanced by ~25% for disk arrays, and was found to be relatively insensitive to the gap between disks. In contrast, the QD emission enhancement decreases from ~70% to 40% as the separation between boxes increases from 100 nm to 160 nm. The largest increase in QD emission of ~70% is due to a non-radiative energy transfer efficiency of ~25% coupled with a QD emission enhancement factor of ~1.4. The results demonstrate the flexibility offered by plasmonic arrays to optimise non-radiative energy transfer or to benefit from a combination of energy transfer and enhanced radiative emission, relevant to sensing and colour conversion applications.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/2262/897542017-01-01T00:00:00ZQuantum control of excitons for reversible heat transfer
http://hdl.handle.net/2262/89660
Quantum control of excitons for reversible heat transfer
Eastham, Paul
Lasers, photovoltaics, and thermoelectrically-pumped light emitting diodes are thermodynamic machines which use excitons (electron-hole pairs) as the working medium. The heat transfers in such devices are highly irreversible, leading to low efficiencies. Here we predict that reversible heat transfers between a quantum-dot exciton and its phonon environment can be induced by laser pulses. We calculate the heat transfer when a quantum-dot exciton is driven by a chirped laser pulse. The reversibility of this heat transfer is quantified by the efficiency of a heat engine in which it forms the hot stroke, which we predict to reach 95% of the Carnot limit. This performance is achieved by using the time-dependent laser-dressing of the exciton to control the heat current and exciton temperature. We conclude that reversible heat transfers can be achieved in excitonic thermal machines, allowing substantial improvements in their efficiency.
PUBLISHED
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/2262/896602019-01-01T00:00:00ZEquipartition of Energy Defines the Size-Thickness Relationship in Liquid-Exfoliated Nanosheets.
http://hdl.handle.net/2262/89629
Equipartition of Energy Defines the Size-Thickness Relationship in Liquid-Exfoliated Nanosheets.
Coleman, Jonathan
Liquid phase exfoliation is a commonly used method to produce 2D nanosheets from a range of layered crystals. However, such nanosheets display broad size and thickness distributions and correlations between area and thickness, issues that limit nanosheet application potential. To understand the factors controlling the exfoliation process, we have liquid-exfoliated 11 different layered materials, size-selecting each into fractions before using AFM to measure the nanosheet length, width, and thickness distributions for each fraction. The resultant data show a clear power-law scaling of nanosheet area with thickness for each material. We have developed a simple nonequilibrium thermodynamics-based model predicting that the power-law prefactor is proportional to both the ratios of in-plane-tearing/out-of-plane-peeling energies and in-plane/out-of-plane moduli. By comparing the experimental data with the modulus ratio calculated from first-principles, we find close agreement between experiment and theory. This supports our hypothesis that energy equipartition holds between nanosheet tearing and peeling during sonication-assisted exfoliation.
PUBLISHED
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/2262/896292019-01-01T00:00:00Z