Self-Assembled Monolayers for Future Molecular Nanoelectronics

Takao Ishida

Institute for Mechanical Systems Engineering (IMSE), National Institute of Advanced Industrial Science and Technology (AIST), and PRESTO-Japan Science and Technology Corporation Tsukuba, Ibaraki 305-8564, Japan.

Organic molecules can be synthesized with unique properties that could be used to promote their self-assembly to one another and to specific surfaces, and to perform functions that can provide device operations. For the realization of molecular device, new conductive conjugated molecular wires are newly found or synthesized. Self-assembled monolayer (SAM) is a convenient technique to fix these functionalized organic molecules on suitable metal or semiconductor substrates. Especially, SAMs made from organosulfur compounds on Au surface have been utilized for the future nano-molecular electronics device demonstration so far. In the present HOME PAGE, I will show the our recent progress of SAMs, mainly in related to recent molecular nanoelectronics.

First, STM observations of conjugated molecular SAMs will be reported. We have confirmed the influence of the methylene spacers on the molecular arrangement as well as on monolayer electrical conduction.

We found the various size of domains of conjugated molecule, TP in insulative alkanethiol SAMs, and evaluated both the vertical and lateral conductivities of TP domains using a conducting disk model where the intermolecular interaction may increase the electrical conduction.

SAM
SAM
SAM
Secondly, We further measured the electrical conduction of SAMs made from several kinds of phenylene oligomers with thiol groups, using AFM with a conductive tip, with the objective of understanding the molecular structural effects as well as observing the influence of the load value on the electrical conduction. We found that the load affected the electrical conduction of the terphenyl molecules differently from that of other conjugated SAMs. In addition, we found that the direct contact of conjugated ring onto Au surface further reduce the tunneling resistance.
SAM
Thermal stability of the SAMs is one of the important issues for the future molecular device. We succeeded in the increase in the thermal stability of the SAMs using TP derivatized thiols.　
SAM