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Radiative energy and momentum transfer for various spherical shapes: a single sphere, a bubble, a spherical shell and a coated sphere

We use fluctuational electrodynamics to determine emissivity and van der Waals contribution to surface energy for various spherical shapes, such as a sphere, a bubble, a spherical shell and a coated sphere, in a homogeneous and isotropic medium. Near-field radiative transfer and momentum transfer between flat plates and curved surfaces have been studied for the past decades, however the investigation of radiative heat transfer and van der Waals stress due to fluctuations of electromagnetic fields for a single object is missing from literature. The dyadic Green's function formalism of radiative energy and fluctuation-induced van der Waals stress for different spherical configurations have been developed. We show (1) emission spectra of micro and nano-sized spheres display several emissivity sharp peaks as the size of object reduces, and (2) surface energy becomes size dependent due to van der Waals phenomena when size of object is reduced to a nanoscopic length scale.