AVS 51st International Symposium
    Organic Films and Devices Thursday Sessions
       Session OF+NS-ThM

Paper OF+NS-ThM7
Electrical and Mechanical Contacts at the Atomic Scale: a Combined UHV STM/AFM Study

Thursday, November 18, 2004, 10:20 am, Room 304C

Session: Molecular Electronics
Presenter: Y. Sun, McGill University, Canada
Authors: Y. Sun, McGill University, Canada
M. Henrik, McGill University, Canada
S. Schaer, McGill University, Canada
Y. Miyahara, McGill University, Canada
A.-S. Lucier, McGill University, Canada
M.E. Ouali, McGill University, Canada
P. Grutter, McGill University, Canada
W. Hofer, University of Liverpool, United Kingdom
Correspondent: Click to Email
Understanding electrical contacts is widely considered as one of the central issues in molecular electronics. As a first step, we have measured simultaneously at the atomic scale the interaction forces and the currents between a sharp tungsten tip and a Au(111) sample using a combined ultra-high vacuum scanning tunnelling and atomic force microscope (UHV STM/AFM). Close correlation between conductance and interaction forces were observed in the regimes from weak coupling to strong interaction. In particular, the electrical and mechanical points of contact are defined as a result of the observed barrier collapse and adhesive bond formation, respectively. The points of contact as defined by force and current measurements coincide within measurement error. We find experimentally that at contact the very front atoms of the tip apex experience repulsive forces, while the total interaction force remains attractive as a consequence of competing interaction decay lengths. Ab-initio calculations of the current as a function of distance were performed for our experimental tip-sample system. We find that in the weak coupling regime the calculated electrical current as a function of distance is in quantitative agreement with experimental results only if tip and sample relaxation effects are taken into account. The calculated relaxation of the tip apex atoms is 50-100 pm. We conclude that force effects of different decay lengths cannot be excluded if a detailed understanding of atomic scale contacts is to be achieved.