Probing Heat In Molecular Junctions

Israeli researchers have directly measured the effective temperature of current-carrying molecular junctions in an electronic device by using surface-enhanced Raman spectroscopy (SERS) (Nat. Nanotechnol., DOI: 10.1038/nnano.2008.304). Molecular junctions, which are circuit structures that consist of a few or even just one molecule straddling a pair of electrodes, offer extreme miniaturization advantages for electronic device designers. But these junctions are fragile and sensitive to temperature, which varies with current flow. Only indirect methods for gauging junction temperatures have been reported so far. For example, some methods are based on measuring the rate at which chains of metal atoms rupture. Tel Aviv University chemists Ori Cheshnovsky, Yoram Selzer, and coworkers have now prepared temperature-probe devices in which 4,4'-biphenyldithiol molecules form junctions with silver electrodes. The team used a SERS microscope to measure Raman scattering while current flowed through those junctions. Then from the intensity of the measured Raman signals, which are associated with molecular vibrations, the group determined the junction temperature as a function of applied voltage.