The growth mechanism and characterization of few-layer diphenyl dinaphthothienothiophene films prepared by vacuum deposition

Abstract

The growth mechanism of 2,9-diphenyl-dinaphtho [2,3-b:2′,3′-f]thieno [3,2-b]thiophene (DPh-DNTT) thin-films prepared by vacuum deposition was investigated based on the morphological crystallinity of the obtained films. In addition to atomic force microscopy, which is commonly used for imaging surface morphology, optical microscopy was also positively used for the same purpose. The technique allows the quick and easy evaluation of thin films. The optical microscopy images show that DPh-DNTT films grew according to a layer-by-layer growth mode. Each layer grew as flat two-dimensional (2D) islands with a thickness of about 2.3 nm, where DPh-DNTT molecules stand almost vertically on the substrate. The height difference between layers provided a color contrast in these images, which visualizes the initial 2D island on the Si substrate with thermally grown SiO2 and fractal-shape 2D islands on top surface. By using the method, a monolayer of isolated and round 2D islands, with a diameter of approximately 4 μm, formed at a high substrate temperature on a SiO2 surface that had been previously treated with O2 plasma or UV-O3. The presence of a DPh-DNTT layer on the substrate was also confirmed by micro-Raman measurement.