Implantation of heavy inert gas ions such as Kr and Xe are found to form nanometer-size bubbles/cavities in thermally grown silicon dioxide. Implantation energies were chosen to produce the same projected range R-p similar to 125 nm for the two ions. The bubble/cavity distribution and size are found to be ion-mass-dependent. After thermal annealing the SiO2 layer implanted with Kr is bubble free while thermal growth of bubbles/cavities is observed for the sample implanted with Xe. These bubbles/cavities created in SiO2 are reflected by significant reduction in its dielectric constant, thus offering the prospect for an original way of generating low-k materials. (C) 2007 The Electrochemical Society.