AVS 50th International Symposium
    Contacts to Organic Materials Topical Conference Monday Sessions
       Session OM-MoA

Paper OM-MoA10
A General Soft Contact Evaporation Method for Molecule-Based (Opto) Electronic Devices

Monday, November 3, 2003, 5:00 pm, Room 318/319

Session: Contacts to Molecules and Molecular Films (II)
Presenter: H. Haick, Weizmann Institute of Science, Israel
Authors: H. Haick, Weizmann Institute of Science, Israel
J. Ghabboun, Weizmann Institute of Science, Israel
D. Cahen, Weizmann Institute of Science, Israel
Correspondent: Click to Email
Hybrid devices, in which molecular functionality is used to influence the characteristics of established electronic devices, but that do not require electronic charge transfer through the molecules, is an alternative approach to more established ones to molecule-based electronics. It is worth pursuing because of stability issues and the ability to use established technology as much as possible at this stage of molecule-based electronics. One such hybrid approach is based on controlling electronic properties of semiconductor devices by placing molecules, whose dipole can, synthetically, be changed systematically, at the device interface. Because mostly one can not insert molecules into a ready-made device interface, construct-ing such device structures requires device completion by making a sold electrical contact to a surface with the organic molecules on it. This is problematic because a process such as ther-mal evaporation or sputtering easily damages the molecules, especially molecules that have sensitive functional groups exposed. Earlier we overcame this by successful use of soft, al-ternative methods. Still, the clear technological advantages of vacuum evaporation led us to search for ways to adapt this method to meet the challenge. The result, which we will present here is Indirect, Collision-Induced, Cooled Evaporation (ICICE), with which we prepared, among others, GaAs/molecule/Au diodes. ICICE decreases drastically the temperature and, thus, the kinetic energy of the evaporated particles/atoms arriving at the surface and assures that irradiation emitted from the crucible does not reach the modified samples. Based on TOF SIMS, XPS, STM and (I-V) electrical measurements, we find that ICICE provides intimate contacts without damaging the (~ 1-3 nm wide monolayer of) organic ligands and their func-tional groups. This is best expressed by the clear molecular effect on the resulting Au/GaAs barrier heights; they vary with the functionalilty of the adsorbed molecules. To understand the limiting steps for contacting by means of metal evaporation, we com-pared results obtained in our experimental system with ICICE, and another popular one, known as Direct Evaporation Under Cryogenic Cooling (DEUCC). While, indeed use of the DEUCC mode leaves the organic ligands beneath the metal contacts, it does damage their functional groups. This finding, for which we will present an explanation, has very signifi-cant implications as it shows that while the often-used criterion of absence of shorts in metal/molecule/metal junctions is indeed a necessary condition for successful contacting molecules, it is not a sufficient one. We thank the Israel Ministry of Science (Eshkol fellowship to HH and tashtyoth project and the Israel Science Foundation (Jerusalem) for partial support.