Exposure of thin films of as-prepared single-walled carbon nanotubes (SWNT) to nitric acid induces dramatic bleaching of the first and second interband transitions of semiconducting tubes (S1 and S2). These near-IR absorption features can be restored by annealing of treated SWNT films to elevated temperatures. Annealing may also be accomplished by visible laser irradiation thus allowing for spatially resolved modifications to SWNT thin film optical absorption.

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In ten years fullerenes have gone from structural speculation to single crystals as ever more efficient preparation and separation procedures have been developed. Today fullerene solids comprise an extensive family of all‐carbon materials assembled from a large number of different ∼ 1 nm sized subunits. We discuss a number of issues related to the unique electronic and geometric structure of these molecular subunits.