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.Comment: 8 pages, 3 figure
