Vacuum vapor deposited thin films of a perylene dicarboximide derivative: Microstructure versus deposition parameters

Abstract

The microscopic physical structure in thin films of vapor deposited, large heterocyclic organic molecules is strongly dependent on the deposition parameters. The scale of the microstructure can vary enormously compared to inorganic systems, strongly affecting the macroscopic properties. Multiple polymorphs frequently characterize these systems. We have extended our previous work with the perylene dicarboximides to include a phenethyl derivative. Films in the 300–1000 Å thickness range, deposited on metal and transparent substrates at varying rates and substrate temperatures from −165 to 155 °C, with and without vacuum annealing, have been characterized by scanning electron microscopy, ultraviolet/visible, and infrared (IR) spectroscopies, and polarization modulation reflectivity changes. Evidence is presented for a critical substrate temperature between −22 and −32 °C. Also a polymorphic phase sensitivity to deposition substrate temperature and rate is demonstrated, consistent with an exothermic peak observed by differential scanning calorimetry of the vapor deposited material, and an annealing induced molecular reorientation observed by reflection absorption IR.