Differences in ITO Interface Characteristics Change According to the Formation of Aromatic-Ring and Aliphatic Self-Assembled Monolayers

Abstract

Herein, we confirm the performance difference according to the structure of self-assembling monolayer (SAM) and investigate the characteristics of the indium tin oxide (ITO) surface when ITO substrates are deposited by (3,3,3-trifluoropropyl)trimethoxysilane (F-3SAM) and (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (F-10SAM) having different chain lengths with trifluoromethyl group as terminal functional group, as well as SAM benzoic acid (BA) and 2-naphthoic acid (NA) with benzene ring forms. Through these, it is possible to control the wetting properties, surface roughness, and work function of the ITO surface. Wetting characteristics, average roughness, and changes in work function of the ITO surface were characterized by contact angle measurement, atomic force microscopy (AFM), and UV photoelectron spectroscopy (UPS). The measured contact angles were 41.1°, 82.25°, and 118° for the bare ITO, NA, and F-10SAM, respectively, the average roughnesses of the SAM-modified surfaces were 1.377, 1.033, and 0.838 nm for the bare ITO, NA, and F-10SAM, respectively. The work function of the ITO surface modified with NA and F-10SAM increased from 0.21 and 0.36 eV to 5.01 and 5.16 eV, respectively. As a result, the surface properties of ITO were better for aliphatic SAM than for aromatic ring SAM.

Differences in ITO Surfaces According to the Formation of Aromatic Rings and Aliphatic Self-Assembled Monolayers for Organic Light-Emitting Diode Applications

“…This section describes the mechanism of SAM formation on the surface of an ITO substrate immersed in a solution. The following stages occurred during the formation process: (1) a low-density stage, in which a low SAM coverage was present on the substrate and exhibited fluidity; (2) an intermediate stage, in which the SAM coverage was greater than the threshold and the SAM molecules aligned horizontally on the surface to cause uneven condensation; and (3) a final high-density stage, in which the SAM was rearranged perpendicular to the substrate, resulting in a well-aligned SAM [13,14,24]. The hydroxyl group formed on the surface of the hydrated ITO substrate to produce a hydrophilic surface and, as the SAM deposition proceeded, the polar head group of the SAM became increasingly hydrolyzed to form hydroxyl groups.…”

“…Finally, M.G. et al [24] conducted a study on the changes in ITO interface characteristics according to the formation of aromatic rings and aliphatic self-assembled monolayers.…”