| AVS 58th Annual International Symposium and Exhibition | |
| Thin Film Division | Thursday Sessions |
| Session TF+EM+SS-ThA |
| Session: | Applications of Self Assembled Monolayers |
| Presenter: | Sujitra Pookpanratana, National Institute of Standards and Technology |
| Authors: | S. Pookpanratana, National Institute of Standards and Technology M.A. Walsh, National Institute of Standards and Technology C.A. Richter, National Institute of Standards and Technology C.A. Hacker, National Institute of Standards and Technology |
| Correspondent: | Click to Email |
Molecular electronics is attractive for next-generation applications because of the flexibility in tailoring the organic functionality and the facile formation of uniform monolayers by using thiol-Au chemistry for self-assembly. Added functionality can be achieved by using thiol self-assembled monolayers (SAMs) containing terminal carboxylic acid functional groups to chelate with metal ions [1], and thus can incorporate d-orbital transition metals with the SAMs. One challenge in molecular electronics has been the reliable formation of a top contact to the organic layer. Fabrication techniques involving metal evaporation of the top contact often result in penetration to the substrate [2] or into the SAM [3], either of which influences the measured electrical properties across the junction. Here, we utilize flip chip lamination (FCL), a soft metallization technique by nanotransfer printing, to form a top contact onto SAMs on Au [4].
Based on previous work by Ulman et al. [5] and Allara et al. [6], we have incorporated metal ions (Cu and Ni) with mercaptohexadecanoic acid (MHA) and formed a molecular junction by FCL. SAMs of MHA were prepared on Au on Si and Au on polyethylene terephthalate (PET) substrates. The MHA/Au/Si was exposed to metal ion (M) containing solution. The M-MHA/Au/Si samples were then laminated to MHA/Au/PET to create a ‘molecular sandwich’ which resulted in the following structure: PET/Au/MHA-M-MHA/Au/Si where the PET substrate is removable.
The SAMs on Au were investigated by using X-ray photoelectron spectroscopy (XPS) and p-polarized reflection absorption infrared spectroscopy (p-RAIRS), and both methods confirm the initial presence of carboxylic acid on the (pre-FCL) surface. Successful incorporation of metal ions into the SAM were directly confirmed by XPS (occupying 30-50% of the –COOH sites), and indirectly by p-RAIRS with the appearance of C=O bands in an acid salt environment. Electrical and physical characterization (using backside p-RAIRS and near edge X-ray absorption fine structure (NEXAFS)) measurements to investigate the monolayer after FCL are currently ongoing. With these results, we are able to obtain a thorough picture linking electrical properties with physical characterization of the buried molecular junctions.
[1] A. C. Templeton et al., Langmuir, 2000, 16, 6682-6688.
[2] A. V. Walker et al., J. Am. Chem. Soc., 2004, 126, 3954-3963.
[3] C. A. Richter et al., Solid-State Electron., 2006, 50, 1088-1096.
[4] M. Coll et al., J. Am. Chem. Soc. 2009, 131, 12451-12457.
[5] S. D. Evans et al., J. Am. Chem. Soc., 1991, 113, 5866-5868.
[6] T. A. Daniel et al., Langmuir, 2007, 23, 638-648.