Fabricating high-quality ultra-thin croconic acid film using electric field guidance

A novel method for fabricating ultra-thin croconic acid (CA) films with a very low surface roughness on Si wafers is reported. With a thickness of approximately 20 nm and surface roughness of +/- 2.0 nm, the film obtained far exceeds the quality and smoothness of previously reported CA thin films. The film is prepared by applying a high electric field in situ during thermal vapor deposition, promoting alignment of the CA molecules due to their high dipole moment. The result is compared with that of the best-reported film produced via a combination of thermal evaporation at low substrate temperature with subsequent slow heating, to demonstrate the greatly enhanced uniformness of the film. In addition, the film's ferroelectric behavior is demonstrated using piezoresponse force microscopy measurements. A mechanism for film formation under electric field assisted deposition is proposed. (C) 2017 Elsevier B.V. All rights reserved.