Characterization of Indium−Tin Oxide Interfaces Using X-ray Photoelectron Spectroscopy and Redox Processes of a Chemisorbed Probe Molecule:  Effect of Surface Pretreatment Conditions

Abstract

Surface characterization of indium−tin oxide (ITO) thin films has been carried out with monochromatic X-ray photoelectron spectroscopy (XPS) following various solution pretreatments, RF air plasma etching or high-vacuum argon-ion sputtering. Commercially available ITO films show high concentrations of hydrolyzed oxides and oxy-hydroxides in the near-surface region, along with stoichiometric oxide (In2O3, SnO2) and variable levels of oxygen defect sites. XPS revealed that solution and vacuum treatments changed both the relative surface coverage of the hydroxides and, to a lesser extent, the concentration of oxide defect sites in the near-surface region. These pretreatments have a significant effect on both the coverage and electron-transfer rates for chemisorbed ferrocene dicarboxylic acid (Fc(COOH)2), with the air-plasma-etched ITO showing the highest surface coverage of Fc(COOH)2 and an RCA treatment showing the highest electron-transfer rates.

Determination of Anisotropic Optical Constants and Surface Coverage of Molecular Films Using Polarized Visible ATR Spectroscopy. Application to Adsorbed Cytochrome c Films

“…Indium tin oxide (ITO) films on soda lime glass (Colorado Concept Coatings) with a sheet resistance of approximately 20 ohmsper-square, and a root-mean-square (rms) surface roughness of 1-2 nm (determined using atomic force microscopy on scan areas of 1 µm 2 ) were used throughout. The ITO substrates were cleaned by scrubbing with a 2% Triton-X solution for 1 min, and then sonicating for 10 min each in 2% Triton-X, water, and ethanol, 29 followed by low-temperature air plasma cleaning (Harrick model PDC-3XG) for 15 min at 30 W. Before use, ITO substrates were soaked for 12-48 h in 10 mM phosphate buffer, pH 7. Wet chemical etching of ITO was accomplished by soaking the ITO coated substrates in a 6 M HCl/0.2 M FeCl 3 solution for 5 min.…”

New Horizons in Spectroelectrochemical Measurements: Optically Transparent Carbon Electrodes

“…Over the years, OTEs have been prepared by coating thin films of metals (e.g., gold and platinum), carbon, and metal oxides onto glass or quartz substrates. Of these, indium tin oxide (ITO) films have been the most widely used (11,12). ITO is a Sn(IV)-doped, In 2 O 3 -based n-type semiconductor, which, along with ZnO, has been extensively applied for >20 years to electrooptical devices and photovoltaics (13).…”

Environmental stability of high-mobility indium-oxide based transparent electrodes

“…Peak C at BE of 532 eV is attributed to chemisorbed OH groups on the surface, often shown as indium oxyhydroxide (InOOH). 22,27,29 This peak is indicative for the amount of chemisorbed OH in the layers, surface, and grain boundaries. The fourth peak at 533 eV, peak D, we assign to O in metal carbonates (C-O-M) 29 or molecularly chemisorbed H 2 O.…”

“…The high-resolution core-level O1s spectra were then recorded and Gauss-Lorentz fitted, which is the standard procedure for In 2 O 3 compounds. 22 The H 2 O and H 2 desorption of the films was investigated by thermal desorption spectroscopy (TDS). For this an ESCO EMD-WA1000S system operated at ultrahigh vacuum (<1.0 × 10 −9 Torr) was used in which the samples are lamp heated up to 1000 • C, with a linear temperature ramp of 20 K min −1 .…”