PHYSICAL AND ELECTRICAL CHARACTERIZATION OF METAL INCORPORATED MOLECULAR ELECTRONIC JUNCTIONS
S. Pookpanratana, C.A. Richter, and C. A. Hacker
Self-assembled monolayers (SAMs) are attractive as components integrated into Si-based electronic devices. One of the challenges with their implementation is forming physical and electrical contacts to the molecular layer. To circumvent that challenge, we have utilized flip chip lamination (FCL), a soft metallization technique base on nanotransfer printing, to form a top contact to molecular electronic junctions .
Molecular monolayers are formed by self-assembly by utilizing Au-thiol chemistry or by grafting them photochemically onto Si. Carboxylic acid-terminated monolayers (CAM) were prepared on Au/Si and/or Au/polyethylene terephthalate (PET) substrates, and then exposed to Cu ion containing solution. The Cu-CAM/Au/PET samples were then FCL-processed to CAM/Si to create a ‘molecular sandwich’ (i.e., CAM-Cu-CAM).
The SAMs were investigated by using X-ray photoelectron spectroscopy (XPS) and p-polarized reflection absorption infrared spectroscopy. Both methods confirm the initial presence of carboxylic acid on the (pre-FCL) surface. Successful incorporation of metal ions onto the SAM was confirmed by XPS. Electrical measurements of these molecular electronic junctions show that the current through the molecular junction is attenuated as the effective molecular layer thickness is increased. With these results, we are able to obtain a picture linking electrical properties with physical characterization of the buried molecular junctions.
 M. Coll et al., J. Am. Chem. Soc. 2009, 131, 12451-12457.