&lt;title&gt;Atmospheric rf plasma coating of indium and tin oxide films&lt;/title&gt;

Williams, James A.; Lee, D. H.; Vuong, K.D.; Tenpas, E.; Wu, Victor Wei‐Keh; Moss, R.W.; Condrate, R. A.; Wang, Xing Wu

doi:10.1117/12.217342

Cited by 2 publications

(1 citation statement)

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“…The reactivity of these natively clean or freshly activated metal oxides is not surprising, inasmuch as reactive defects are intentionally introduced into these materials to promote electrical conductivity without sacrificing optical transparency . The hydrolysis chemistry of both indium and tin oxides also suggests that reactions of the oxide surface with water will quickly lead to hydroxides or even oligomeric hydroxides, although indium oxides are somewhat more reactive than tin oxides. ,, Having now characterized both IO and ITO films prepared and analyzed under in vacuo conditions, it is clear that the intrinsic photoemission line shapes for ITO are asymmetric as a result of both the high degree of surface heterogeneity and the high density of states near the conduction band edge causing energy-loss processes brought about by the coupling of escaping photoelectrons with these states. − Being able to distinguish the O 1s intrinsic line shapes for clean IO and ITO films, however, allows us to identify more precisely (a) asymmetry due to energy-loss peaks correlated with near-surface Sn content in these films, (b) new higher-BE O 1s peaks correlated primarily with the presence of surface hydroxides, and (c) asymmetry in the fitted components of the O 1s spectra associated with both chemical and morphological surface heterogeneity. This approach will see wider use when molecular modifiers are added to the ITO surface, as a way of controlling the effective work function, to allow the identification of their binding modes …”

Section: Discussionmentioning

confidence: 99%

Surface Composition and Electrical and Electrochemical Properties of Freshly Deposited and Acid-Etched Indium Tin Oxide Electrodes

et al. 2007

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We compare the near-surface composition and electroactivity of commercial indium tin oxide (ITO) thin films, activated by plasma cleaning or etching with strong haloacids, with ITO films that have been freshly deposited in high vacuum, before and after exposure to the atmosphere or water vapor. Conductive-tip AFM, X-ray photoelectron spectroscopy (XPS), and the electrochemistry of probe molecules in solution were used to compare the relative degrees of electroactivity and the near-surface composition of these materials. Brief etching of commercial ITO samples with concentrated HCl or HI significantly enhances the electrical activity of these oxides as revealed by C-AFM. XPS was used to compare the composition of these activated surfaces, focusing on the intrinsically asymmetric O 1s line shape. Energy-loss processes associated with photoemission from the tin-doped, oxygen-deficient oxides complicate the interpretation of the O 1s spectra. O 1s spectra from the stoichiometric indium oxide lattice are accompanied by higher-binding-energy peaks associated with hydroxylated forms of the oxide (and in some cases carbonaceous impurities) and overlapping photoemission associated with energy-loss processes. Characterization of freshly sputter-deposited indium oxide (IO) and ITO films, transferred under high vacuum to the surface analysis environment, allowed us to differentiate the contributions of tin doping and oxygen-vacancy doping to the O 1s line shape, relative to higher-binding-energy O 1s components associated with hydroxyl species and carbonaceous impurities. Using these approaches, we determined that acid activation and O2 plasma etching create an ITO surface that is still covered with an average of one to two monolayers of hydroxide. Both of these activation treatments lead to significantly higher rates of electron transfer to solution probe molecules, such as dimethyferrocene in acetonitrile. Solution electron-transfer events appear to occur at no more than 4x10(7) electroactive sites per cm2 (each with diameters of ca. 50-200 nm) (i.e., a small fraction of the geometric area of the electrode). Electron-transfer rates correlate with the near-surface tin dopant concentration, suggesting that these electroactive sites arise from near-surface tin enrichment.

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