RBS ANALYSIS OF THE DIFFUSION OF NANO-SIZE SPHERES IN A POLYMER MATRIX

Rutherford Backscattering Spectrometry (RBS) with 1.5 MeV He ions was employed to measure the depth distribution of gold particles sandwiche d between two poly (tell-butyl acrylate) layers following various isot hermal annealing treatments: temperatures were kept below 170 degrees C to prevent degradation of the polymer. Since PTBA also degrades when the ion beam impinges the sample, it was necessary to quantify the ma ss loss in order to obtain accurate diffusion coefficients. Although t he total mass loss was substantial (40-60%). a simple expansion of the energy-to-depth scale was sufficient to account for the beam-induced shrinkage. This result is attributed to the fact that the mass loss oc curs very rapidly, and is uniformly distributed through the depth of t he sample. The data reveal that the diffusion of the nanometer-size go ld particles is substantially slower than is predicted by a simple phy sical model (Stokes-Einstein) for noninteracting particles. This slowd own is attributed to polymer bridging interactions, in which polymer s trands bind to individual metal particles, thereby retarding their dif fusion. (C) 1998 Elsevier Science B.V.