• Enhanced Photothermal Effect in Si Nanowires
Some nanomaterials have been found to show unusual and often unexpected properties because of their unique structures and small dimensions. In our paper published in Nano Letter in 2003, we reported that silicon nanowires ignited in air and exhibited a large photo-acoustic effect when exposed to a conventional photographic flash. Because of the enhanced photothermal effect, the microstructure of the Si nanowires was changed. This is a new property of nano-sized Si material and has not been observed previously in silicon material.
We have observed that:
(1) SiNW ignite and fiercely burn in air when exposed to a camera flash
(2) No ignition, when flashing SiNW in inert gasses, but emitting a loud pop.
(3) SiNW trap a huge amount of energy from the flash, resulting in sufficiently high temperature (>1150 oC) and hence leading to instantaneous, fierce oxidation.
Since the energy required to ignite the Si nanowires was low, it is believed that Si nanowires have a strong ability to confine photo energy from visible light. The optical absorption in Si nanowires was enhanced by their special structure because the same effect was not observed in bulk silicon material. The remaining materials obtained after burning Si nanowires were observed to consist of various forms of nanostructures, e.g., nanoparticles, amorphous wires, and nanotubes. The mechanism of the enhanced photo thermal effect in silicon nanowires is not well understood though a number of theoretical works about this were published recently. The ignition of Si nanowires is distinct, and it is the intrinsic property of Si nanowires.
Due to its unexpected ability to confine photoenergy, Si nanowires may find uses in smart ignition systems, self-destructing systems for electronic devices, nanosensors, and nanostructural or nanophase reformation (for nanotechnology). This interesting phenomenon has surprised scientists and stimulated extensive investigations experimentally and theoretically in order to understand the new phenomenon of one-dimensional nano-structural materials. This work has been reported by the overseas media as new scientific news, e.g., on the website of the American Chemistry Society.
N. Wang, B. D. Yao, Y. F. Chan and X. Y. Zhang, Nano Lett., 3 (2003) pp475-477.