Scanning tunneling microscopy mechanism

The dangling bonds of a Si surface abstract one F atom from an incident F2 molecule while the complementary F atom is scattered back into the gas phase [20]. This abstractive mechanism leads to F adsorjDtion at single sites rather than at adjacent pairs of sites, as observed directly by scanning tunnelling microscopy [21]. Br atoms adsorb only to Ga atoms in the second layer of GaAs(001)-(2 x 4) where empty dangling bonds on the Ga atoms can be filled by electrons from the Br atoms [22]. 

The Holy Grail of catalysis has been to identify what Taylor described as the active site that is, that ensemble of atoms which is responsible for the surface reactions involved in catalytic turnover. With the advent of atomically resolving techniques such as scanning tunnelling microscopy it is now possible to identify reaction centres on planar surfaces. This gives a greater insight also into reaction kinetics and mechanisms in catalysis. In this paper two examples of such work are described, namely CO oxidation on a Rh(llO) crystal and methanol selective oxidation to formaldehyde on Cu(llO). 

Kuznetsov AM, Ulstrup J (2000) Mechanisms of in situ scanning tunnelling microscopy of organized redox molecular assemblies. J Phys Chem A 104 11531-11540... 

Lewandowski M, Groot IMN, Shaikhutdinov S, Freund HJ. Scanning tunneling microscopy evidence for the Mars-van Krevelen type mechanism of low temperature CO oxidation on an FeO(lll) film on Pt(lll). Catal. Today. 2012 181 52-55. 

The first and best known near-field technique to measure electrical properties in the nanoscale is of course Scanning Tunnelling Microscopy (STM). Since its invention by Binnig et al., STM has been used to explore the mechanisms of lots of phenomena on surfaces [289-294], ranging from experiments concerning the local work function to the use of an STM-tip to induce electropolymerisation [295]. Most of all, STM provides us with atomically resolved images of the surface structure. 

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