The whispering gallery modes (WGM) of a 500 nm radius silver core shell particle are investigated using general Mie theory. The increase in the shell thickness leads to narrow WGM resonances and a blue shift in the resonance wavelengths. The light propagation within a vacuum cavity with a thickness of less than 1% of the incident wavelength is demonstrated, in which only the transverse electric modes are excited. The discovered phenomena can be of assistance in the investigations of controllable electromagnetic wave propagation in a subwavelength space or in the development of novel nanosensors. (c) 2008 Elsevier B.V. All rights reserved.