Paper SS-ThM4
Imaging a Surface Explosion: Autocatalytic Desorption of Tartaric Acid from Cu(110)

Thursday, October 31, 2013, 9:00 am, Room 202 A

Autocatalytic reactions occur in a variety of fields and are characterized by an initiation event causing the rate of a reaction to increase non-linearly until it ceases. In addition to occurring in ambient environments, this type of reaction has been observed in a growing number of systems on single crystal surfaces (sometimes called surface explosions) under ultra high vacuum conditions but the mechanism for this process has not been fully determined. These well-controlled model surfaces allowed us to study the progression of an autocatalytic reaction, the thermal decomposition of tartaric acid (TA) on a Cu(110) single crystal surface, with molecular resolution imaging using scanning tunneling microscopy (STM) and temperature programmed reaction spectroscopy (TPRS). Using STM we progressively anneal the tartaric acid system and obtain the first molecular-scale images during a surface explosion to determine the changes occurring as a function of temperature. From these images we determine that the density of molecules slightly decreases until a critical threshold is reached when the molecules can decompose then desorb. We also observe, for the first time, a new phase of TA complexed with Cu adatoms that may play a role in the surface explosion as it occurs at the onset of the explosion. One area in which an understanding of autocatalytic reactions could be exploited is the separation of enantiomers from a heterogeneous catalyst. In this example a more complete separation of enantiomers could be achieved compared to normal desorption kinetics.