Excitation-wavelength-dependent small polaron trapping of photoexcited carriers in α-Fe2O3

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Abstract

The effect of polaron formation on photoconversion efficiency for oxide photocatalysts is not well known. Femtosecond extreme-ultraviolet measurements suggest that polaron localization is responsible for ultrafast trapping of photoexcited carriers in haematite.

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Solar water splitting: progress using hematite (α-Fe(2) O(3) ) photoelectrodes.

Kevin Sivula, Florian Le Formal, Michael Grätzel (2011)

Photoelectrochemical (PEC) cells offer the ability to convert electromagnetic energy from our largest renewable source, the Sun, to stored chemical energy through the splitting of water into molecular oxygen and hydrogen. Hematite (α-Fe(2)O(3)) has emerged as a promising photo-electrode material due to its significant light absorption, chemical stability in aqueous environments, and ample abundance. However, its performance as a water-oxidizing photoanode has been crucially limited by poor optoelectronic properties that lead to both low light harvesting efficiencies and a large requisite overpotential for photoassisted water oxidation. Recently, the application of nanostructuring techniques and advanced interfacial engineering has afforded landmark improvements in the performance of hematite photoanodes. In this review, new insights into the basic material properties, the attractive aspects, and the challenges in using hematite for photoelectrochemical (PEC) water splitting are first examined. Next, recent progress enhancing the photocurrent by precise morphology control and reducing the overpotential with surface treatments are critically detailed and compared. The latest efforts using advanced characterization techniques, particularly electrochemical impedance spectroscopy, are finally presented. These methods help to define the obstacles that remain to be surmounted in order to fully exploit the potential of this promising material for solar energy conversion. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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The CTM4XAS program for EELS and XAS spectral shape analysis of transition metal L edges.

Eli Stavitski, Frank M.F de Groot (2010)

The CTM4XAS program for the analysis of transition metal L edge Electron Energy Loss Spectroscopy (EELS) or X-ray Absorption Spectra (XAS) is explained. The physical background of the calculations is briefly discussed. The program consists of three theoretical components, based on, respectively, atomic multiplet theory, crystal field theory and charge transfer theory. The theoretical concepts are explained and a number of examples are presented. The calculation of the 2p EELS and XAS spectra of transition metal ions, is given in detail, including their Magnetic Circular Dichroism (MCD). In addition, examples of 1s, 2s, 3s, 2p and 3p X-ray Photoemission Spectroscopy (XPS) are given.