Imaging Molecules and Chemical Reactions

Systems of adsorbed molecules on metal surfaces have been subjects of intensive investigation for many years because of their applicability to important chemical reactions relating to catalysis, corrosion, etching, microelectronics fabrication and electrochemistry. An improved understanding of the reaction mechanisms should allow advances in the relevant technologies. Recently the STM has been used to identify individual molecular species and even distinguish among molecular isomers in mixed overlayers on a surface, leading to the hope that one may soon be able to follow reactants, intermediates and products in more complicated chemical reactions.

Our research focuses on the use of STM to image selected molecular adsorbate systems and to make real-space observations of chemical reactions. Some model adsorbate systems, involving small aromatic molecules on single crystal metal surfaces, will be studied experimentally and theoretically to better understand the STM imaging mechanisms and to ascertain the limits of the technology for real-space and real-time observation of chemical reactions. Various molecular adsorption parameters (ie. molecular orientation, binding site, molecular organization, sticking coefficients, diffusivity) on the surface will be measured. An important catalytic reaction, the cyclization of acetylene to benzene, thiophene and furan on clean, sulfided and oxidized Pd(111) will be studied to determine details of the reaction mechanism and information on the surfacxe kinetics. The reactivity will be correlated with the observation of defects and steps on the surface. The same reaction will also be studied on some bimetallic catalysits to help elucidate the catalytic mechanism.

Related Publications:

S. Chiang in Scanning Tunneling Microscopy I, second edition, ed. H.-J. Guntherodt and R. Wiesendangerm (Springer-Verlag, Berlin 1994) pp. 181-205, pp. 258-267.
V.M. Hallmark, S. Chiang, K.-P. Meinhardt and K. Hafner, Physical Review Letters 70 3740 (1993).
V.M. Hallmark and S. Chiang, Surface Science 286 190 (1993).
V.M. Hallmark, S. Chiang, J.K. Brown and Ch. Woll, Physical Review Letters 66 48 (1991).
H. Ohtani, R.J. Wilson, S. Chiang and C.M. Mate, Physical Reveiw Letters 60 2398 (1988