Photoelectrochemistry at New Mexico Tech


Figure 1: A schematic of the photoelectrochemical apparatus used for measuring photocurrents and photovoltages on metals immersed in a liquid.
Figure 2: The photocurrents are result from light exciting electrons in the oxide film, in the presence of a Schottky barrier. The electrons are excited from the valence band (V.B.) to the conduction band (C.B.) where they flow down hill under the influence of the electric field. The electric field is a result of the mismatch of the Fermi levels of the electrolyte and the metal.


What is Photoelectrochemistry (also known as Photocurrent Spectroscopy)?

Photocurrent spectroscopy (PCS), also known as photoelectrochemistry (PEC), is the science of measuring and interpreting the weak electric currents which is generated by illumination a metal in an electrolyte. In a typical experiment, light from a xenon arc lamp is chopped by a rotating blade into pulses, then a wavelength is selected using a diffraction grating. Next the pulsed, monochromated light is focussed through a quartz window onto a metal sample immersed in an electrolyte. A potential can be applied to the sample, and the current on the sample is monitored. A lock-in amplifier measures the magnitude of the pulsed photocurrent, and the results are recorded.

Why use Photocurrent Spectroscopy?

PCS can be used to determine semiconductor properties of the oxide films on the metal sample. Properties such as the quantum efficiency, the bandgap, and the flatband potential. As these properties are generally unique to certain oxides, a type of "fingerprinting" can be used to identify these oxides with this information. PEC is also helpful in determining the growth rate of such oxides, as well as how and how fast they corrode. A current application to determine the mechanism(s) that create the oxide layer and the mechanism(s) that destroy it is also being developed.

Examples

Photoelectrochemistry has been applied to the study of oxides of titanium and aluminum. It has been used to examine various kinds of oxides, their growth, corrosion resistance and rates, bandgaps, and flatband potentials for such samples. The defect structure of aluminum has also been examined, along with the effect of inhibitors on different steels.

Specialized Photocurrent Spectroscopy Equipment

  • Oriel 150-W Xenon Arc Lamp
  • Oriel Light Intensity Controller, Model 68850
  • Universal Power Supply, Model 68805
  • Arc Lamp Housing, Model 68855
  • Monochromator, Model GM252
  • Controller, Model 789A
  • PARC Light Chopper, Model 125A
  • PAR Potentiostats, Models 263A,363, 173, 371
  • PAR Lock-in Amplifier, Model 5210
  • Kipp & Zonen X-Y-Y' Plotter
  • Computers
  • EG&G 398 Electrochemical Impedance Spectroscopy Software
  • EG&G 352 Corrosion Software
  • PAR PowerSuite Electrochemistry Software
  • PARSTAT 2263 Potentiostat
  • TecNu 10V-25A Power Supply

    Contact Information:

    Dr. T. D. Burleigh
    Associate Professor
    Materials and Metallurgical Engineering Department
    New Mexico Tech, Socorro, NM 87801 USA
    Telephone: (505) 835-5831, Fax: (505) 835-5626
    e-mail: burleigh@nmt.edu


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