The morphology and optical response of Au and Ag
nanoparticles capped with dielectric amorphous Si3N4,
BN, and Al2O3 layers are studied. Quantitative analysis
of high-angle annular dark-field images obtained in a scanning
transmission electron microscope and simulations of optical
transmittance spectra are used to investigate the dependence of
the morphology of the nanoparticles on the particle size and on
the capping material. It is demonstrated that capping-layer
effects induce a size-dependent and cap-dependent reshaping of the
nanoparticles.