Observation of hypersonic phononic crystal effects in porous silicon superlattices

Brillouin light scattering experiments were carried out on porous silicon superlattices with modulation wavelengths in the range 37–167 nm. Phonon frequencies deduced from the Brillouin spectra show good agreement with those obtained from an elastic continuum model for a system with one-dimensional periodicity. Evidence for the existence of a hypersonic phononic bandgap and zone-folded longitudinal acoustic phonons is reported

Surface functionalized spherical nanoparticles: an optical assessment of local chirality

Electromagnetic radiation propagating through any molecular system typically experiences a characteristic change in its polarization state as a result of light-matter interaction. Circularly polarized light is commonly absorbed or scattered to an extent that is sensitive to the incident circularity, when it traverses a medium whose constituents are chiral. This research assesses specific modifications to the properties of circularly polarized light that arise on passage through a system of surface-functionalized spherical nanoparticles, through the influence of chiral molecules on their surfaces. Non-functionalized nanospheres of atomic constitution are usually inherently achiral, but can exhibit local chirality associated with such surface-bound chromophores. The principal result of this investigation is the quantification of functionally conferred nanoparticle chirality, manifest through optical measurements such as circularly polarized emission. The relative position of chiral chromophores fixed to a nanoparticle sphere are first determined by means of spherical coverage co-ordinate analysis. The total electromagnetic field received by a spatially fixed, remote detector is then determined. It is shown that bound chromophores will accommodate both electric and magnetic dipole transition moments, whose scalar product represents the physical and mathematical origin of chiral properties identified in the detected signal. The analysis concludes with discussion of the magnitude of circular differential optical effects, and their potential significance for the characterization of surface-functionalized nanoparticles

Comment on 'Non-equilibrium thermodynamics of light absorption'

A recent paper by Meszéna and Westerhoff (1999 J. Phys. A: Math. Gen. 32 301) has aimed to address what is referred to as a principal question of biological thermodynamics, the possibility of describing photosynthesis in terms of non-equilibrium thermodynamics. The issue is associated with a misrepresentation of the fundamental photophysics involved, and as a result the analysis is invalid

Equation of state for hard sphere fluids with and without Kac tails

In this note, we propose a simple derivation of the one dimensional hard rod equation of state, with and without a Kac tail (appended long range and weak potential). The case of hard spheres in higher dimension is also addressed and it is shown there that our arguments --which avoid any mathematical complication-- allow to recover the virial form of the equation of state in a direct way.Comment: pedagogical pape

Interparticle interactions:Energy potentials, energy transfer, and nanoscale mechanical motion in response to optical radiation

In the interactions between particles of material with slightly different electronic levels, unusually large shifts in the pair potential can result from photoexcitation, and on subsequent electronic excitation transfer. To elicit these phenomena, it is necessary to understand the fundamental differences between a variety of optical properties deriving from dispersion interactions, and processes such as resonance energy transfer that occur under laser irradiance. This helps dispel some confusion in the recent literature. By developing and interpreting the theory at a deeper level, one can anticipate that in suitable systems, light absorption and energy transfer will be accompanied by significant displacements in interparticle separation, leading to nanoscale mechanical motion

Identifying the development in phase and amplitude of dipole and multipole radiation

The spatial variation in phase and the propagating wave-front of plane wave electromagnetic radiation are widely familiar text-book territory. In contrast, the developing amplitude and phase of radiation emitted by a dipole or multipole source generally receive less attention, despite the prevalence of these systems. There is additional complexity in such cases where, in consequence of retardation, the character and features significantly and progressively change as radiation propagates onwards, from the near-field and out towards the wave-zone. Readily developed analytical representations of the electric field, cast as a function of distance from the source, provide illuminating insights into the most prominent and distinctive properties of radiant electromagnetic emission. Graphical implementations and animations of the results prove particularly instructive in revealing the spatial form and temporal evolution of the emergent electromagnetic fields