Development of a Controlled Environment Near-Field Optical Microscope for Organic Thin Film Studies

The requirements of a microscope differ greatly from field to field and with the sample being studied Organic thin films are highly sensitive to environmental conditions being rapidly photobleached in the presence of oxygen In this paper we introduce the design of a low cost near field optical microscope suitable for environmentally controlled studies. We demonstrate that reducing ambient pressure to similar to 10 mTorr (1 3 Pa) of nitrogen (a pressure accessible with a mechanical pump) significantly reduces photo-bleaching on a typical experimental timescale. In addition, we introduce a novel non-optical feedback control mechanism combining a piezoelectric diaphragm with a tuning fork. The morphology of thin films of MEH-PPV spin cast from the polymer dissolved in chlorobenzene is investigated These films are shown to be featureless on a 100 nm length scale in terms of topology, PL intensity and PL spectrum both before and during photo-bleaching. As far as we are aware these are the first reported thin films of MEH-PPV grown in which similar to 100 nm sized domains arc absent. We believe that the ability to control environment will not only allow better optical characterization of thin films but also opens up the possibility of the production of novel two dimensional organic photonic crystals through a combination of mechanical disruption, photo-bleaching and photo-conjugation of polymers.