Journal of Crystal Growth 203 (1999) 412}420 Macroscopically ordered thin "lms of an organic salt grown by low-pressure organic vapor-phase deposition M. Deutsch!, M.C. Gerstenberg", H.F. Gossenberger#, V.S. Ban#, S.R. Forrest!,* !Department of Electrical Engineering, Center for Photonics and Optoelectronic Materials (POEM), Princeton Materials Institute, Princeton University, Princeton, NJ 08544, USA "Department of Chemistry and Princeton Materials Institute, Princeton University, Princeton, NJ 08544, USA #PD-LD Inc., 209 Wall Street, Princeton, NJ 08540, USA Received 27 October 1998; accepted 28 January 1999 Communicated by T.F. Kuech Abstract We demonstrate the process of low-pressure organic vapor-phase deposition (LP-OVPD) for the growth of crystalline thin "lms of the organic charge-transfer salt 4@-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) on amorphous TiO 2 substrates. LP-OVPD grown "lms exhibit polycrystallinity with long-range structural ordering limited only by substrate size. Film surface coverage and macroscopic ordering are strongly determined by the preparation of the TiO 2 surface prior to growth. The morphology and ordering of the "lms are also found to depend on the deposi- tion temperature and the composition of the precursor molecules. These results suggest that LP-OVPD "lms are of su$cient quality for use in optical waveguide and related photonic devices. ( 1999 Elsevier Science B.V. All rights reserved. 1. Introduction There is considerable interest in new organic materials with large second-order hyperpolarizabil- ities, b, for use in nonlinear optical (NLO) devices such as frequency converters and electro-optic (EO) modulators. In particular, molecular organic salts can exhibit a very large b due to their noncen- trosymmetric crystal structure [1]. Such crystalline materials can be more stable than polymers which require electric-"eld poling to attain spatial asym- metry and the ensuing NLO properties [2]. The crystalline organometallic charge-transfer salt, 4@- * Corresponding author. Fax: #1-609-258-0119. dimethylamino-N-methyl-4-stilbazolium tosylate (DAST), is a particularly interesting material for NLO device applications due to its large EO coef- "cient and a low-dielectric constant, giving rise to a high modulator "gure of merit [2]. It is desirable to grow optical quality thin "lms of DAST and other organic salts for integrated opto-electronic devices. Previous attempts to de- posit DAST by heating in vacuum were un- successful, resulting in molecular decomposition prior to evaporation [3,4]. Furthermore, the highly incongruent vapor pressures of the DAST neutral precursors 4@-dimethylamino-4-stilbazole (DAS) and methyl-tosylate (MT), result in uncontrollably rapid evaporation of MT and nonstoichiometric growth, rendering double-source co-evaporation in vacuum unfeasible. 0022-0248/99/$ - see front matter ( 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 0 2 4 8 ( 9 9 ) 0 0 0 8 0 - 9