Strong Light-Matter Interaction in ZnO Nanowires

Experimental Sections

The details of ZnO nanowire synthesis and optical mea-surements have been reported elsewhere.16,18 The sol-gel solutions of ZnO were prepared by dissolving zinc acetate dihydrate (Zn(CH3COO)2·2H2O) in methanol and mixing with monoethanolamine at a volume ratio of 1:5. The seed layers were prepared by spin coating of sol-gel solutions onto silicon wafer substrates, where ZnO nanowires were grown by a chemical vapor transport method. The source mixture of Zn (1.0 g) and ZnO (1.0 g) was placed in an alumina boat and loaded inside a horizontal tube furnace. The seed film was placed 40 mm downstream of the source boat, where the temperature was 820 °C. The growth was carried out under flow of N2 (140 sccm) and O2 (5 sccm) for 10 min. The shapes and lengths of the nanostructures were characterized by scanning electron microscopy. The dia-meters of the nanowires were 200-250 nm and the lengths were in the range of 3-4 mm (Figure 1(a)). The nanowires were sonicated in methanol to isolate individual nanowires and drop coated onto silicon wafer substrates. An isolated single nanowire was selectively excited by 355 nm through an ultraviolet microscope objective. The normal photo-luminescence and lasing emissions were collected by the same objective, resolved spectrally by a monochromator, and detected by a photomultiplier.