We show direct experimental evidence that radiation effects produced by single MeV heavy ions on a polymer surface are weakened when the length of the ion track in the material is confined into layers of a few tens of nanometers. Deviation from the bulk (thick film) behavior of ion-induced craters starts at a critical thickness as large as ∼40 nm, due to suppression of long-range additive effects of excited atoms along the track. Good agreement was found between the experimental results, molecular dynamic simulations, and an analytical model.

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The electronic properties of low-dimensional materials can be engineered by doping, but in the case of graphene nanoribbons ͑GNRs͒ the proximity of two symmetry-breaking edges introduces an additional dependence on the location of an impurity across the width of the ribbon. This introduces energetically favorable locations for impurities, leading to a degree of spatial segregation in the impurity concentration. We develop a simple model to describe how the change in energy of a GNR system doped with a single impurity depends on the impurity position. The model is validated by comparing its findings with ab initio calculations. Although our results agree with previous works predicting the dominance of edge disorder in GNR, we argue that the distribution of adsorbed impurities across a ribbon may be controllable by external factors, namely, an applied electric field. We propose that this control over impurity segregation may allow manipulation and fine tuning of the magnetic and transport properties of GNRs.