Hot Microcontact Printing for Patterning ITO Surfaces. Methodology, Morphology, Microstructure, and OLED Charge Injection Barrier Imaging

Abstract

A soft lithographic microcontact printing (μCP) procedure is successfully applied for the first time to form densely packed organosilane self-assembled monolayers (SAMs) on the surface of ITO (Sn-doped In2O3) coated glass via a thermally activated deposition process. Hot microcontact printing (HμCP) enables localized transfer with 1.0−40 μm feature sizes of dense docosyltrichlorosilane (CH3(CH2)20CH2SiCl3 = DTS) monolayer patterns onto ITO, which reacts sluggishly under conventional μCP conditions. X-ray reflectivity measurements yield a thickness of 12.1 ± 0.1 Å and a surface roughness of 2.8 ± 0.1 Å for HμCP printed DTS films, which is well within the range for self-assembled monolayer formation, while the weak reflected intensity from conventionally prepared DTS films indicates a poorly organized monolayer structure. Noncontact mode AFM studies reveal that HμCP creates uniform SAMs over a wide area with excellent line edge resolution, while the original patterns are poorly transferred by conventional μCP, presumably due to the slow Si−O bond formation. Cyclic voltammetry of 1,1‘-ferrocenedimethanol solutions using HμCP-derived, DTS SAM coated ITO working electrodes evidences good barrier properties, consistent with dense films. The DTS SAM patterns can be imaged by fabricating organic light-emitting diode (OLED) heterostructures on the patterned ITO. The DTS SAM role as a hole injection blocking layer enables patterned luminescence from the hot contact printed ITO surfaces.