Fractal nature of π-bonded nanocrystalline clusters:: A N+ beam-induced phenomenon in poly(2,6-dimethyl-1,4-phenylene oxide)

Formation of nanosized carbonaceous clusters has been investigated in 100 keV N+ irradiated poly(2,6-dimethyl-1,4-phenylene oxide) [PPO] thin films, using Fourier transform (FT)-Raman, transmission electron microscopy and UV-Vis spectroscopy in the fluence range of 1x10(15)-5x10(16) ions/cm(2). Above a critical fluence of similar to 1x10(16) ions/cm(2), the energy density transferred to the implanted layer resulted in a molecular construction/self-organization process with the evolution of graphitelike clusters of varying size similar to 2 -50 nm. Electron diffraction analysis of these clusters shows a close resemblance to the formation of single crystalline graphite phase with a zone axis [070]. The deduced band gaps from the optical spectra using Tauc's approximation provided information on the electronic structure of the fused hexagonally clustered aromatic rings with varying sizes; the number of the rings varying from similar to 20-170. Evidence for the signature of fractal patterns, with dimension 1.37 +/- 0.02, during aggregation of small particlelike clusters in the polymer implanted layer is presented; analysis of the data suggests the growth process to follow a diffusion-limited-aggregation model. [S0163-1829(99)05715-X].