IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Nanometer Structures Wednesday Sessions
       Session NS+EL-WeA

Paper NS+EL-WeA4
Conductance Switching in Single Molecules Through Conformational Changes

Wednesday, October 31, 2001, 3:00 pm, Room 133

Session: Molecular Electronics and Patterning
Presenter: K.F. Kelly, Penn State University
Authors: K.F. Kelly, Penn State University
Z.J. Donhauser, Penn State University
B.A. Mantooth, Penn State University
L.A. Bumm, Penn State University
J.D. Monnell, Penn State University
J.J. Stapleton, Penn State University
D.W. Price, Rice University
D.L. Allara, Penn State University
J.M. Tour, Rice University
P.S. Weiss, Penn State University
Correspondent: Click to Email
The viability of molecular electronics is being investigated with the aim of creating inexpensive, ultra-dense, high-capacity electronic devices. Conjugated phenylene-ethynylene oligomers have been extensively studied as candidate molecular devices. However, most experiments have required the assembly and study of these molecules in groups of thousands. We utilize self-assembly techniques in combination with scanning tunneling microscopy (STM) to study candidate molecular switches individually and in small bundles. Alkanethiol self-assembled monolayers (SAMs) on gold are used as a host two-dimensional matrix to isolate and to insulate electrically the molecular switches. The candidate molecules selectively adsorb into existing defect sites and at step edges. The molecules bind with a sulfur "alligator clip" to the underlying gold substrate, and the ordered SAM causes the molecules to adsorb nearly normal to the substrate. We then individually address and electronically probe each molecule using STM. The conjugated molecules exhibit reversible conductance switching, manifested as a change in the apparent height in STM images. The observed switching occurs randomly and reversibly, with persistence times for each state ranging from seconds (or less) to hours. Both individual molecules and bundles of molecules exhibit switching. We have demonstrated the ability to control the amount and rate of active switching by controlling the local environment of the guest molecules. Inserting the guest molecules into poorly ordered matrix films results in increased switching activity when compared to well-ordered films. Similarly, annealing the SAM after inserting the guest molecules results in decreased switching activity, when compared to unannealed SAMs. We ascribe the switching to conformational changes of the molecules that are either enhanced or reduced by the corresponding loosening or tightening of the surrounding matrix.