We have examined the effect of the post-processing of spin-coated tetracene and DAST (4'-dimethylamino-N-methyl-4-stilbazolium tosylate) films in their solvent vapor to examine the possibility of precisely controlling the vapor pressure and studying the effect of applying electric fields to their structural properties. It was demonstrated that the solvent concentration in the vapor phase can be monitored by infrared spectroscopy. The thickness uniformity of the tetracene films was improved by the formation of a mixture of the tetracene crystals with the saturated solution ("solution ultrathin film") on the surface. Crystals with an ordered orientation were obtained by additionally applying an electric field during the vapor exposure of the DAST. The present technique for monitoring the solvent vapor pressure is also applicable for controlling the drying speed during the inkjet printing of functional organic materials. (c) 2006 Elsevier B.V. All rights reserved.