The energetic positions of the surface states in α-Fe₂O₃ treated with Co−Pi, in which the photo-generated holes were trapped, were determined by the charge carrier-selective heterodyne transient grating (CS-HD-TG) technique.

Abstract

Near-field heterodyne transient grating (NF-HD-TG) responses of hematite (α-Fe₂O₃) treated with cobalt phosphate (Co−Pi) were measured with the burn lasers inducing the depletion of the response by the removal of the trapped charge carriers in the target state, which is called charge carrier-selective heterodyne transient grating (CS-HD-TG) spectroscopic technique. We found that two distinct trap states co-existed in Co−Pi loaded on the surface of α-Fe₂O₃. One of them named r-SS2, of which potential was similar to that of r-SS1 in the surface of α-Fe₂O₃, acted as a recombination centre but could increase the lifetime of the trapped holes by the charge separation. We also revealed that the energetic position of the other (i-SS2), which has been regarded as the intermediate state for oxygen evolution reaction with low overpotential, was higher than that of i-SS1 in α-Fe₂O₃ but lower than those of r-SS1 and r-SS2.