Noncarbon support materials for polymer electrolyte membrane fuel cell electrocatalysts.

High-resolution x-ray photoelectron spectroscopy (XPS) was applied to characterize the electronic structures for a series of high-k materials (HfO2)x(Al2O3)1−x grown on (100) Si substrate with different HfO2 mole fraction x. Al 2p, Hf 4f, O 1s core levels spectra, valence band spectra, and O 1s energy loss all show continuous changes with x in (HfO2)x(Al2O3)1−x. These data are used to estimate the energy gap (Eg) for (HfO2)x(Al2O3)1−x, the valence band offset (ΔEν) and the conduction band offset (ΔEc) between (HfO2)x(Al2O3)1−x and the (100) Si substrate. Our XPS results demonstrate that the values of Eg, ΔEν, and ΔEc for (HfO2)x(Al2O3)1−x change linearly with x.

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Energy gap and band alignment for (HfO2)x(Al2O3)1−x on (100) Si

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...

Phosphonic Acid Modification of Indium−Tin Oxide Electrodes: Combined XPS/UPS/Contact Angle Studies†

An ultrathin layer of nickel oxide (NiO) was deposited on the indium tin oxide (ITO) anode to enhance the hole injections in organic light-emitting diode (OLED) devices. A very low turn-on voltage (3 V) was actually observed for the device with NiO on ITO. The enhancement of hole injections by depositing NiO on the ITO anode was further verified by the hole-only devices. The excellent hole-injection ability of NiO was also demonstrated by devising a device with patterned NiO on the ITO anode. Our results suggest that the NiO/ITO anode is an excellent choice to enhance hole injections of OLED devices.

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Enhanced hole injections in organic light-emitting devices by depositing nickel oxide on indium tin oxide anode

Interface modification of ITO thin films: organic photovoltaic cells

X-ray photoelectron spectroscopy (XPS) has been used to study the electronic structures of indium tin oxide (ITO) surfaces treated by O+, Ar+, and NHx+ plasmas. The XPS data show that there is a significant change in core level energies (In 3d5/2 O 1s, and Sn 3d5/2), in donor concentration (Sn4+), in valence band maximums (VBM), and in work functions on ITO surfaces being treated by O+ and NHx+ plasmas, compared with that of virgin and Ar+ plasma treated surfaces. Based on these experimental data, a surface band-bending theory is proposed. The theory explains that when Fermi energy of the plasma-treated surface is shifted towards the middle of the band gap: core levels will shift their energies to lower binding energies, VBM will bend upward, and work function will increase, as observed.

H. Y. Yu

Papers

Surface electronic structure of plasma-treated indium tin oxides