Direct Observation of a Semiconductor/Liquid Junction by Operando X-Ray Photoelectron Spectroscopy (XPS)

Lichterman, M. F. et al. Direct Observation of the Energetics at a Semiconductor/Liquid Junction by Operando X-Ray Photoelectron Spectroscopy. Energy Environ. Sci., 2015, DOI: 10.1039/C5EE01014D (2015).

Scientific Achievement

We demonstrated that the operandoXPS technique, applied to a semiconductor/liquid junction, can directly measure the positions of the electronic states of the electrode and the electrolyte at the solid/liquid interface.

Significance & impact

The operando XPS investigation provides insight into the working principles of protective coatings on semiconductors that are critical to stable operation of solar-fuel devices.

 

Top:  Diagram of the Operando XPS experiment.

Bottom:  (a) XPS peak positions of O 1s and Ti 2p3/2 signals for H2O liq. and TiO2 as a function of the potential (U) of a bare p+–Si/TiO2 electrode in 1.0 M KOH(aq).  A solid line corresponding to a slope of Δ = −1 eV·V−1 has been drawn through the water O 1s data; a solid line drawn as a visual guide is shown for the titania data.   (b) Analogous XPS peak positions vs. electrode potential for a p+–Si/TiO2/Ni (deposited by 60 s of Ni sputtering) interface were measured.

 Adapted from Lichterman, M. F. et al. Direct Observation of the Energetics at a Semiconductor/Liquid Junction by Operando X-Ray Photoelectron Spectroscopy. Energy Environ. Sci., 2015, DOI: 10.1039/C5EE01014D (2015) with permission of…

 

Adapted from Lichterman, M. F. et al. Direct Observation of the Energetics at a Semiconductor/Liquid Junction by Operando X-Ray Photoelectron Spectroscopy. Energy Environ. Sci., 2015, DOI: 10.1039/C5EE01014D (2015) with permission of The Royal Society of Chemistry.

Research Details

  • Operando ambient-pressure XPS was used to directly characterize the semiconductor/liquid junction at room temperature under real-time electrochemical control.
  • The use of tender X-rays allowed for the direct evaluation of the energetics for the electrode surface, the electrochemical double layer, and the adjacent bulk water.
  • TiO2-protected p+–Si, prepared by Atomic Layer Deposition (ALD), was used in 1.0 M KO(aq).

Contact: bsb@caltech.edu, nslewis@caltech.edu,lewerenz@caltech.edu, zliu2@lbl.gov

 

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