AVS 50th International Symposium
    Organic Films and Devices Wednesday Sessions
       Session OF+NS-WeM

Paper OF+NS-WeM4
Observation of Negative Differential Resistance Measured through Individual Molecules on Silicon at Room Temperature

Wednesday, November 5, 2003, 9:20 am, Room 318/319

Session: Molecular Electronics
Presenter: N.P. Guisinger, Northwestern University
Authors: N.P. Guisinger, Northwestern University
R. Basu, Northwestern University
A.S. Baluch, Northwestern University
M.C. Hersam, Northwestern University
Correspondent: Click to Email
In recent years, substantial progress has been made in the emerging field of molecular electronics. In particular, metal-molecule-metal junctions have been widely studied. In this paper, charge transport through molecule-semiconductor junctions is considered. The presence of the energy band gap in semiconductors provides opportunities for resonant tunneling through individual molecules, leading to interesting effects such as negative differential resistance (NDR). The ultra-high vacuum (UHV) scanning tunneling microscope (STM) allows individual molecules to be imaged, addressed, and manipulated on semiconducting surfaces with atomic resolution at room temperature. This paper considers two distinct chemistries on the Si(100) surface. Styrene reacts with Si(100) via a covalent silicon-carbon bond. On degenerately n-type Si(100), STM current-voltage characteristics on individual styrene molecules show clear NDR at negative sample biases of approximately -2.5 V and -4 V. However, at positive sample bias, the styrene is liberated from the surface via inelastic electron stimulated desorption (ESD). In an effort to minimize perturbation via ESD, individual 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) molecules were bound to degenerately n-type Si(100). The exceptional stability of the silicon-oxygen bond allows charge transport measurements on TEMPO at high biases up to ±5 volts without ESD. Similar to styrene, NDR is clearly observable at negative sample biases of approximately -3 V, -4 V, and -4.5 V. These effects will be explained by considering the energy band diagram of the semiconductor-molecule junction.