Single-walled carbon nanotubes (SWNTs) exhibit a range of unusual mechanical and electronic properties because of their unique structure and dimensions. Here we report another unusual property. We accidentally discovered that SWNTs ignite when exposed to a conventional photographic flash. This photoeffect occurs for SWNTs prepared by the carbon arc, laser ablation, or chemical vapor deposition upon exposure to a camera flash at close range (several cm away from the sample). Ignition did not occur for multiwalled nanotubes, graphite powder, fluffy carbon soot, or C60.

Frames taken from a real-time video recording of burning SWNTs after the application of the photoflash (Fig. 1, A and B) show red hot spots immediately after the flash (Fig. 1B). The sample burns down in air, generating CO and CO2 and leaving behind oxidized catalyst particles (such as Ni-Y or Fe, used for SWNT synthesis) and traces of disordered carbonaceous materials. The effect we describe occurs only on dry,“fluffy,” as-prepared nanotube samples (see below). After flashing SWNTs, we observed an associated large photoacoustic effect caused by the absorption of incident light on the SWNT samples, in which acoustic waves are caused by the expansion and contraction of trapped gases (1). Ignition and burning occur when local increases in temperature are sufficient to initiate the oxidation of the carbon and propagate as more heat is released by this exothermic reaction. Flashlight consists of a combination of various wavelengths, which intend to emulate sunlight (without the ultraviolet light). In air, the average light power needed to ignite SWNTs was found to be 100 mW cm 2 (20 mW) for a sample density of about 0.2 g cm 3 (pulse rise time: 50 s; decay time: 1.2 ms). When the sample is compacted to higher densities, larger power is needed to ignite SWNTs; for densities 1 g cm 3, ignition occurs at about 300 mW cm 2. At higher densities, the tubes are less prone to catching fire because of the lack of oxygen access and loss of heat into the bulk of the sample.