Karl W. Frese

Bulk and Surface Characterization of the Silicon Electrode

Abstract The properties of silicon as an electrode are investigated. Techniques for reproducible measurement of the doping level are described, techniques designed to avoid surface films associated with fluoride ions. A peak in the capacity/voltage curve that appears near the flatband voltage for both n- and p-type silicon is characterized in detail and shown to be associated with interface states between a surface oxide layer and the silicon. The possible chemical origin of the interface states when the electrode is in solution is discussed.

Electrochemical Studies of Photocorrosion of n ‐ CdSe

Rotating-ring-disk studies of the photoelectrochemical corrosion of n-CdSe (1120) have been made. Flatband potentials for CdSe as a function of light intensity and redox potential were determined. The studies focused on the role of the Se corrosion layer. Evidence is presented to show that the nominally Se layer is a good hole conducto with an active energy level for holes at +0.76V vs. SCE. The Marcus-Gerischer reactivity pattern was found by an analysis of stabilization efficiency with various reducing agents.

Theoretical Models of Hot Carrier Effects at Metal‐Semiconductor Electrodes

The physical and electrochemical properties of hot carriers at metallized semiconductor electrodes in contact with a redox electrolyte are described. Theoretical ballistic mean-free paths, L B , for hot carriers in Ag, Cu, Au, Al, Ru, Pd and Pt, were calculated as a function of excess energy above the Fermi energy. At 0.5 eV hot, L B was 580 A for Ag, 420 A for Cu and Au, 90 to 130 A for the remaining metals, with Pt having the lowest value

Passivation and interface state studies on n-GaAs☆

Abstract The surface preparation of GaAs with HCl solutions is shown to be very important in determining anodic oxidation characteristics as well as resulting interface state densities on oxidized samples. Auger data and chemical thermodynamic arguments are used to show that the HCl pretreatment selectively removes Ga while leaving elemental arsenic on the GaAs surface. Interface state densities are compared for various HCl pretreatment times. Growth of the anodic oxides in neutral electrolytes containing KF are beneficial for the interface state density.

The influence of surface oxide films on the stabilization of n-Si photoelectrode

Abstract We have provided direct evidence of the enhanced effectiveness of stabilizing agents due to thin surface oxide films, ca. 15–25 A, on n-Si photoelectrode. Rotating ring disc electrode and ellipsometric experiments are combined to show the stabilization efficiency of potassium ferrocyanide improves with oxide thickness. A band model describing the observed effect is given.

Hot Electron Reduction at n‐Si/Au Thin Film Electrodes

Schottky barrier electrodes were prepared by deposition of thin films of Au on device quality n-Si. Barrier heights for fourteen day old films, determined by high frequency capacitance measurements at open circuit in the presence of 0.3 M each K 4 Fe(CN) 6 /K 3 Fe(CN) 6 , were found to be 0.60 eV in the thickness range of 200 to 1000 A. The exchange current densities were determined as a function of film thickness and aging time up to about one month after deposition

Hot Hole Oxidation at p‐Si/Ag Thin Film Electrodes

Hot hole oxidation of ferrous ethylenediaminetetraacetic acid (EDTA) was observed in the dark at 22 o C using thin Ag films on p-Si substrates. Schottky barrier electrodes were prepared by magnetron sputter deposition of 99.9% Ag on device quality p-Si (100), N A =1.6×10 14 cm -3 . The Schottky barrier height, as measured by open-circuit space-charge-capacitance measurements, was 0.57 eV and was independent of film thickness from 25 to 1000 A. Interface-state densities at open circuit ranged from 4×10 12 to 6×10 10 cm -2 eV -1 for film thicknesses from 25 to 125 A, and remained constant to 1000 A

Analysis of Current/Voltage Curves at n ‐ Si / SiO2 / Pt Electrodes Evidence for Hot Electron Reduction

Current voltage curves for reduction of iron ferricyanide at room temperature using thin Pt films on n-Si (100)/25 A SiO 2 /Pt electrodes are explained by the action of hot electrons and interface states. The exchange current for electron transfer was determined as a function of Pt film thickness in 0.3M each potassium Fe(CN) 6 -3/-4 pH 6.0. The current density-thickness plots had maxima at 160 to 180 A at η=0 to 0.5 V overpotential. The energy loss, δ, defined as the difference between qV cb and the energy level of the electron at the metal/electrolyte interface surface varied from 0.05 at 25 A to 0.84 eV at t≥250 A and remained constant to 400 A signifying fully cooled electrons for such thicker films