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In recent years, hematite's potential as a photoanode material for solar hydrogen production has ignited a renewed interest in its physical and interfacial properties, which continues to be an active field of research. Research on hematite photoanodes provides new insights on the correlations between electronic structure, transport properties, excited state dynamics, and charge transfer phenomena, and expands our knowledge on solar cell materials into correlated electron systems. This research news article presents a snapshot of selected theoretical and experimental developments linking the electronic structure to the photoelectrochemical performance, with particular focus on optoelectronic properties and charge carrier dynamics.

Transparent Fe1-xNixOOH overlayers (~2 nm thick) were deposited photoelectrochemically on (001) oriented heteroepitaxial Sn-and Zn-doped hematite (α-Fe2O3) thin film photoanodes. In both cases, the water photo-oxidation performance was improved by the co-catalyst overlayers. Intensity modulated photocurrent spectroscopy (IMPS) was applied to study the changes in the hole current and recombination current induced by the overlayers. For the Sn-doped hematite photoanode, the improvement in performance after deposition of the Fe1-xNixOOH overlayer was entirely due to reduction in the recombination current, leading to a cathodic shift in the onset potential. For the Zn-doped hematite photoanode, in addition to a reduction in recombination current, an increase in the hole current to the surface was also observed after the overlayer deposition, leading to a cathodic shift in the onset potential as well as an enhancement in the plateau photocurrent. These results demonstrate that Fe1-xNixOOH cocatalysts can play different roles depending on the underlying hematite photoanode. The effect of the cocatalyst is not always limited to changes in the surface properties, but also to an increase in hole current from the bulk to the surface that indicates a possible crosslink between surface and bulk processes. Manuscript Hematite (-Fe2O3) is an attractive material for solar water splitting based on its favorable properties as a photoanode material in photoelectrochemical (PEC) cells. 1 However, the performance of state-of-theart hematite photoanodes 2-5 is still far short of the maximum theoretical efficiency, both in terms of photocurrent and photovoltage. One route for improving photoanode performance is through use of various co-catalysts which reduce the overpotential for water photo-oxidation, thereby leading to a cathodic shift in the applied bias. 6-9 One of the most promising materials for use as a co-catalyst is earth abundant Fe1-xNixOOH. For the remainder of the manuscript, we will refer to Fe1-xNixOOH as "FeNiOx", a commonly used abbreviation. FeNiOx overlayers have shown similar improvements in photoelectrochemical performance as more expensive IrOx based co-catalysts. 10 FeNiOx overlayers can be produced easily by a variety of methods 11-15 and they are stable in alkaline solutions, 12 as the oxyhydroxide phase Fe1-xNixOOH. 16 In addition, it has recently been shown 17 that using a photoelectrochemical deposition method, very thin and transparent FeNiOx overlayers can be deposited to avoid optical (absorption) losses in the photoanode. Significant cathodic shifting of the onset potential for water photo-oxidation is typically observed for FeNiOx coated hematite photoanodes. 18,19 Generally, the changes in performance have been attributed to a reduction in the surface recombination either as a result of surface passivation, 20 hole storage in the overlayer, 21 or p-n junction formation. 22 For ultrathin photoelectrodeposited FeNiOx overlayers, improved catalysis has been suggested as the reason for improvement. 17 I...

Spintronics seeks to functionalize antiferromagnetic materials to develop memory and logic devices operating at terahertz speed and robust against external magnetic field perturbations. To be useful, such functionality needs to be developed in thin film devices. The key functionality of long-distance spin-transport has, however, so far only been reported in bulk single crystal antiferromagnets, while in thin films, transport has so far been limited to a few nanometers. In this work, we electrically achieve a long-distance propagation of spin-information in thin films of the insulating antiferromagnet hematite. Through transport and magnetic imaging, we demonstrate a strong correlation between the efficiency of the transport of magnons, which carry spin-information, and the magnetic domain structure of the films. In thin films with large domains, magnons propagate over micrometer distances whilst they attenuate over much shorter distances in multidomain thin films. The governing factor of the attenuation is related to scattering at domain walls, and we demonstrate that we can reduce this through training by field

Ti-doped, undoped, and Zn-doped hematite (-Fe2O3) thick (~1 m) films were found to be n-type, weak n-type, and p-type, respectively. Heterogeneous doping profiles were generated in 30 nm thick hematite stacks on F:SnO2 coated glass substrates with 25 nm thick SnO2 underlayers in order to investigate the effect of different doping profiles on photoelectrochemical performance and compare with homogenously-doped counterpart photoelectrodes. Among the homogenously-doped photoelectrodes, the Ti-doped sample displayed the highest plateau photocurrent but also the highest onset potential, whereas the Zn-doped one had the lowest onset potential and the lowest plateau photocurrent. Heterogeneouslydoped photoelectrodes displayed both high plateau photocurrent and low onset potential, with the highest performance achieved for the specimen with Ti-doped, undoped and Zn-doped layers at the bottom, center and top parts of the stack, respectively. This demonstrates the potential of heterogeneous doping to improve the performance of hematite photoelectrodes for solar water splitting. The most critical bottleneck towards the technological advancement of photoelectrochemical (PEC) cells for use in solar water splitting is the photoelectrode material, which must meet the requirements of being inexpensive, efficient, robust, and stable for water photoelectrolysis. One of the most promising materials for use as a photoanode for water splitting is hematite (-Fe2O3) due to its vast abundance, low cost, light absorption characteristics and stability in the conditions needed for water oxidation. 1 Indeed, a reported working stability of at least 1000 hours has very recently been reported. 2 But hematite photoanodes also display some prominent