Monitoring Heat At The Molecular Level

In conventional electronic devices, heat diffuses through bulk materials such as wires via quantized lattice vibrations, which can be detected by a thermometer. But when it comes to molecular electronics in which single molecules are components of the circuitry, heat transfer occurs through discrete vibrations of the individual molecules and is difficult to measure. Zhaohui Wang, Dana D. Dlott, David G. Cahill, and coworkers at the University of Illinois, Urbana-Champaign, now have demonstrated a spectroscopic technique for measuring this type of energy transfer (Science 2007, 317, 787). They use gold substrates studded with alkane chains, and with laser pulses they heat the substrate to about 800 ^oC. As the thermal energy migrates down the alkane chains, their growing disorder can be quantified using vibrational spectroscopy as a "molecular thermometer" to detect the intensity of carbon-hydrogen stretching of the terminal alkane methyl groups. The method is expected to help monitor the stability and performance of molecular electronic devices and guide development of nanotechnology applications.