Modification of Hematite Electronic Properties with Trimethyl Aluminum to Enhance the Efficiency of Photoelectrodes

The electronic properties of hematite were investigated by means of synchrotron radiation photoemission (SR-PES) and X-ray absorption spectroscopy (XAS). Hematite samples were exposed to trimethyl aluminum (TMA) pulses, a widely used Al-precursor for the atomic layer deposition (ALD) of Al2O3. SR-PES and XAS showed that the electronic properties of hematite were modified by the interaction with TMA. In particular, the hybridization of O 2p states with Fe 3d and Fe 4s4p changed upon TMA pulses due to electron inclusion as polarons. The change of hybridization correlates with an enhancement of the photocurrent density due to water oxidation for the hematite electrodes. Such an enhancement has been associated with an improvement in charge carrier transport. Our findings open new perspectives for the understanding and utilization of electrode modifications by very thin ALD films and show that the interactions between metal precursors and substrates seem to be important factors in defining their electronic and photoelectrocatalytic properties.

Funding from the German Research Foundation (DFG) with the project SCHM 745/31-1, the German Ministry for Education and Research (BMBF) with the grant 03IN2 V4A, the Spanish Ministry of Economy and Competitiveness (MINECO) through the project MAT2012-37676 (FONDOS FEDER), the Finnish Centre of Excellence in Atomic Layer Deposition (CoE ALD), and the Estonian Research Agency (ETAg) with the project PUT170 is acknowledged. D.C. is grateful to MINECO for the award of an FPI grant.