Electron transport at model membrane interfaces

COLL 321

Denis Scaini, denis.scaini@elettra.trieste.it1, J. Liang, jliang@princeton.edu2, Silvano de Franceschi3, Martina Dell'Angela1, Matteo Castronovo, castronovo@tasc.infm.it4, Loredana Casalis, loredana.casalis@elettra.trieste.it5, and G. Scoles, gscoles@princeton.edu6. (1) Physics Department, University of Trieste, P. Europa 1, I-34127 Trieste, Italy, (2) Department of Chemistry, Princeton University, Washington Road, Princeton, NJ 08544, (3) TASC National Laboratory, SS 14 Km 163,5, Basovizza, I-34012 Trieste, Italy, (4) ELETTRA Nanostructure Laboratory and SISSA, I-34127 Trieste, Italy, (5) Sincrotrone Trieste, SS 14 Km. 163,5, Basovizza, I-34012 Trieste, Italy, (6) Princeton University and SISSA (Trieste, Italy), Princeton, NJ 08544
Conductive Tip AFM (CT-AFM) is commonly used for electrical characterisation of organic and inorganic surface systems. One of the more promising applications concerns the study of metal-molecule-metal junctions: Understanding the transport properties of these key systems is in fact of great importance for the advancement of both organic and molecular electronics. Despite the non negligible number of experimental data in this field, however, the accumulated data sets are often not consistent with each other, due to the scarce reproducibility of the metal tip-molecule contact at a microscopic level. Nanografting, an AFM-assisted nanolithography technique, has been proved to be a very useful method to compare transport properties of different molecules on the same substrate with the same probing tip. Differential measurements of this kind have been useful to distinguish conductivity differences between molecules with subtle structural differences. We will discuss here in detail the case of differential conductivity at model membrane interfaces, in particular the case of patches of alkyl- or aromatic-thiols nanografted into a matrix of alkyl-thiol self-assembled monolayer (SAM) made of different length molecules. By differentially comparing the “conductivities” of different molecules we will show that the discrepancies present in the literature are due to the fact that the metallic tip of the CT-AFM gets invariably coated by the molecules of the monolayers so that most measurements relate to the tunneling of current through TWO monolayers instead of one. We will also address specifically the very important point of the influence of the degree of order in the nanografted patches and the surrounding SAM on the transport properties of the measured metal-molecule-metal junction. We will show that, if the tip of the CT-AFM Is smaller than the average SAM domain our technique allows the unequivocal determination of the SAM “defect free conductivity”.
 

Chemistry at Membrane Interfaces
6:00 PM-8:00 PM, Monday, 11 September 2006 Moscone Center -- Room 104, Poster

Division of Colloid & Surface Chemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006