This research studies the effects of RuO4 exposure on various samples of poly(styrene) (PS). Transmission electron energy-loss spectroscopy (EELS) shows a decrease in the 7 eV pi-pi * transition characteristic of aromatic rings in PS indicating that RuO4 covalently alters aromatic character. Imaging and selected-area electron diffraction show that a layer of RuO2 solid forms on the surface of bulk PS specimens exposed to RuO4. Hi.-h-resolution TEM imaging (HREM) shows that RuO2 nanocrystals consistently condense on specimen surfaces, independent of the chemical nature of the specimen below. These nanocrystals modulate contrast at length scales on the order of 2-5 run in TEM images and limit resolution at nanometer length scales.