Characterization of Indium−Tin Oxide Interfaces Using X-ray Photoelectron Spectroscopy and Redox Processes of a Chemisorbed Probe Molecule: Effect of Surface Pretreatment Conditions
TL;DR: In this article, a monochromatic X-ray photoelectron spectroscopy (XPS) was used for surface characterization of indium−tin oxide (ITO) thin films.
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.
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TL;DR: Combustion processing is now reported as a new low-temperature route for the deposition of diverse metal oxide films, and high-performance transistors are demonstrated using this method as discussed by the authors.
Abstract: Solution-deposited metal oxides show great potential for large-area electronics, but they generally require high annealing temperatures, which are incompatible with flexible polymeric substrates. Combustion processing is now reported as a new low-temperature route for the deposition of diverse metal oxide films, and high-performance transistors are demonstrated using this method.
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TL;DR: PA modification of ITO has resulted in materials that are more stable and more compatible with subsequently deposited organic materials, an effective work function that can be tuned by over 1 eV, and energy barriers to hole injection (OLED) or hole-harvesting (OPV) that can been well matched to the frontier orbital energies of the organic active layers, leading to better overall device properties.
Abstract: Transparent metal oxides, in particular, indium tin oxide (ITO), are critical transparent contact materials for applications in next-generation organic electronics, including organic light emitting diodes (OLEDs) and organic photovoltaics (OPVs). Understanding and controlling the surface properties of ITO allows for the molecular engineering of the ITO–organic interface, resulting in fine control of the interfacial chemistries and electronics. In particular, both surface energy matching and work function compatibility at material interfaces can result in marked improvement in OLED and OPV performance. Although there are numerous ways to change the surface properties of ITO, one of the more successful surface modifications is the use of monolayers based on organic molecules with widely variable end functional groups. Phosphonic acids (PAs) are known to bind strongly to metal oxides and form robust monolayers on many different metal oxide materials. They also demonstrate several advantages over other functi...
291 citations
TL;DR: In this article, the molecular nature of surface attachment and changes in electronic and wetting properties were characterized by X-ray photoelectron spectroscopy (XPS), UV-photoelectron (UPS), photoelastic modulation infrared reflection−absorption spectrograph (PM-IRRAS), and contact angle measurements using both water and hexadecane.
Abstract: Indium−tin oxide (ITO) electrodes have been modified with both fluorinated alkyl and aryl phosphonic acids [n-hexylphosphonic acid (HPA) and n-octadecylphosphonic acid (ODPA); 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl phosphonic acid (FHOPA), pentafluorobenzyl phosphonic acid (PFBPA), and tetrafluorobenzyl-1,4-diphosphonic acid (TFBdiPA)]. These are modifiers designed to control both wetting properties toward nonpolar molecular solids and to provide a wide range of tunability in effective surface work function. The molecular nature of surface attachment and changes in electronic and wetting properties were characterized by X-ray photoelectron spectroscopy (XPS), UV-photoelectron spectroscopy (UPS), photoelastic modulation infrared reflection−absorption spectroscopy (PM-IRRAS), and contact angle measurements using both water and hexadecane. Interface dipoles from the PA modifiers contribute to shifts in the low kinetic energy regions of UPS spectra (local vacuum level shifts, which translate into change...
231 citations
TL;DR: It is shown that structural relaxation and densification by In(3+) and Sn(4+) mixing is effective in reducing carrier trap sites and in creating carrier-generating oxygen vacancies.
Abstract: Films of the high-performance solution-processed amorphous oxide semiconductor a-ZnIn4Sn4O15, grown from 2-methoxyethanol/ethanolamine solutions, were used to fabricate thin-film transistors (TFTs) in combination with an organic self-assembled nanodielectric as the gate insulator. This structurally dense-packed semiconductor composition with minimal Zn2+ incorporation strongly suppresses transistor off-currents without significant mobility degradation, and affords field-effect electron mobilities of ∼90 cm2 V−1 s−1 (104 cm2 V−1 s−1 maximum obtained for patterned ZITO films), with Ion/Ioff ratio ∼105, a subthreshhold swing of ∼0.2 V/dec, and operating voltage <2 V for patterned devices with W/L = 50. The microstructural and electronic properties of ZITO semiconductor film compositions in the range Zn9−2xInxSnxO9+1.5x (x = 1−4) and ZnIn8−xSnxO13+0.5x (x = 1−7) were systematically investigated to elucidate those factors which yield optimum mobility, Ion/Ioff, and threshold voltage parameters. It is shown tha...
227 citations
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TL;DR: In this article, the equation of the linear potential sweep voltammogram is derived for any degree of reversibility of the electrochemical reaction for the following methods: surface voltammetry when both the oxidized and the reduced forms are strongly adsorbed, and a Langmuir isotherm is obeyed, thin layer voltamometry, and linear potential sweeping coulometry.
5,920 citations
TL;DR: In this paper, the effect of hydrogen plasma treatment on indium tin oxide (ITO), fluorine-doped tin dioxide (FTO), and indium doped zinc oxide (IZO) films has been studied.
Abstract: The effect of hydrogen plasma treatment on indium tin oxide (ITO), fluorine‐doped tin oxide (FTO), and indium‐doped zinc oxide (IZO) films has been studied. X‐ray photoelectron spectroscopy analysis shows that ITO and FTO surfaces get reduced to yield elemental indium and tin, respectively. Annealing of the plasma treated films in air leads to re‐oxidation of the reduced surface and the electro‐optical properties are recovered. In contrast, IZO films are not reduced by plasma treatment and show no changes in the electrical and optical properties. The surface of plasma treated IZO films shows a higher binding energy O(1s) peak probably due to OH or OH...O species which appear to form a protective layer against plasma degradation.
584 citations
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24 Aug 1999
TL;DR: Theoretical modeling of the solid-liquid interface of metal-electrolyte interfaces has been studied in this article, using Monte Carlo methods for equilibrium and nonequilibrium problems of polyatomic oxyanions adsorbed on metal surfaces.
Abstract: Theory and modelling: theoretical modelling of the solid-liquid interface - chemically specific simulation methods theory of the metal-electrolyte interface structure of water at the water-metal interface - molecular dynamics computer simulations Monte Carlo methods for equilibrium and nonequilibrium problems in interfacial electrochemistry electronic structure calculations of polyatomic oxyanions adsorbed on metal surfaces. electrochemical surface science: electro-chemical processes involving H adsorbed at metal electrode surfaces reconstruction of gold surfaces in situ surface X-ray scattering studies of electrosorption atomic-scale aspects of anodic dissolution of metals - studies by in situ scanning funnelling microscopy Auger spectroscopy of electrode surfaces. Nonmetallic and semiconductor electrodes: electrochemical properties of carbon surfaces bulk and surface states of reactive oxide films - an extended semiconductor model with Ti, Ni, and Fe as examples solid-state voltammetry conducting polymer films as electrodes photoelectrochemistry of nanostructured semiconductors - the case of anatase TiO2. Electrocatalysis: interfacial electrochemistry of conductive oxides for electrocatalysis kinetic modelling of electrocatalytic reactions - methanol oxidation on platinum electrodes properties of bimetallic electrodes - spectroscopic characterization and electrocatalysis electrocatalysis as well-defined surfaces - kinetics of oxygen reduction and hydrogen oxidation/evolution on Pr(hkl) electrodes mechanism of methanol electro-oxidation. (Part contents).
505 citations
TL;DR: In this article, the anodes were doped with a variety of polymer and monomer-based acids and cast from either water or organic solvents to determine the effect of the dopant and solvent on the hole-injection properties.
Abstract: We have studied polyaniline and polyethylenedioxythiophene transparent electrodes for use as hole-injecting anodes in polymer light emitting diodes. The anodes were doped with a variety of polymer and monomer-based acids and cast from either water or organic solvents to determine the effect of the dopant and solvent on the hole-injection properties. We find that the anodes with polymeric dopants have improved device quantum efficiency and brightness relative to those with small molecule dopants, independent of conductivity, solvent, or type of conducting polymer. For the most conducting polymer anodes [σ>2(Ωcm)−1], diodes could be made without an indium tin oxide underlayer. These diodes show substantially slower degradation.
424 citations