AVS 45th International Symposium
    Organic Electronic Materials Topical Conference Tuesday Sessions
       Session OE+BI+EM-TuA

Paper OE+BI+EM-TuA5
Long Range Crystalline Order for Thin Films of an Organic Salt Grown by Low Pressure Organic Vapor Phase Deposition

Tuesday, November 3, 1998, 3:20 pm, Room 327

Session: Organic Thin Film Growth
Presenter: M. Deutsch, Princeton University
Authors: M. Deutsch, Princeton University
S.R. Forrest, Princeton University
M.C. Gerstenberg, Princeton University
H.F. Gossenberger, PD-LD Inc.
V.S. Ban, PD-LD Inc.
Correspondent: Click to Email
There is a growing interest in new organic materials with large second-order hyperpolarizabilities, ß, for use in nonlinear optical (NLO) devices. In particular, small organic-molecule salts can exhibit very large ß, due to their non-centrosymmetric crystal structure. The organometallic charge-transfer salt DAST is an ideally suited material for NLO device applications, having a large electro-optic (EO) coefficient and low dielectric constants, which eventuate in a high figure of merit. Thin films of DAST with very long-range structural ordering were grown by organic vapor phase deposition (OVPD). In this technique vapor transported precursors of the stilbazole and methyl-tosylate combine on a substrate in the heated zone of a low pressure, hot wall reactor. This method enables the stoichiometric growth of polar, multiple-component compounds with highly incongruent vapor pressures, which cannot be otherwise deposited by vacuum evaporation. The DAST films were grown on amorphous TiO2 substrates, which was pre-sputtered on thermally oxidized [111] Si wafers. The films exhibit very long-range structural ordering, limited only by substrate size. The strong azimuthal dependence of the relative second harmonic generation (SHG) efficiencies, together with polarized microscopy studies indicate that the structural ordering extends typically ~2 cm across the substrate surface. Using x-ray diffraction we have identified the films as consisting of the SHG-active crystalline phase of DAST belonging to the monoclinic space group Cc, with a well-defined [001] orientation with respect to the substrate normal. Such very long-range crystalline order is a prerequisite for realizing high-performance, low-loss NLO devices.