Determination of Conduction and Valence Band Electronic Structure of LaTiOxNyThin Film.
The nitrogen substitution into the oxygen sites of several oxide materials leads to a reduction of the band gap to the visible-light energy range, which makes these oxynitride semiconductors potential photocatalysts for efficient solar water splitting. Oxynitrides typically show a different crystal structure compared to the pristine oxide material. As the band gap is correlated to both the chemical composition and the crystal structure, it is not trivial to distinguish which modifications of the electronic structure induced by the nitrogen substitution are related to compositional and/or structural effects. Here, X-ray emission and absorption spectroscopy are used to investigate the electronic structures of orthorhombic perovskite LaTiOxNythin films in comparison with films of the pristine oxide LaTiOxwith similar orthorhombic structure and cationic oxidation state. Experiment and theory show the expected upward shift in energy of the valence band maximum that reduces the band gap as a consequence of the nitrogen incorporation. This study also shows that the conduction band minimum, typically considered almost unaffected by nitrogen substitution, undergoes a significant downward shift in energy. For a rational design of oxynitride photocatalysts, the observed changes of both the unoccupied and occupied electronic states have to be taken into account to justify the total band-gap narrowing induced by the nitrogen incorporation.
Research with Neutrons and Muons Division, Paul Scherrer Institut, 5232, Villigen-PSI, Switzerland.
Markus
M
Pichler
Paul Scherrer Institut, 5232, Villigen-PSI, Switzerland.|Institute of Physics, Jan Kochanowski University, Kielce, Poland.
Jakub
J
Szlachetko
Theory and Simulation of Materials and National Centre for Computational Design and Discovery of Novel Materials (MARVEL), École Polytechnique Fédérale de Lausanne, 1015, Lausanne, Switzerland.
Ivano E
IE
Castelli
Theory and Simulation of Materials and National Centre for Computational Design and Discovery of Novel Materials (MARVEL), École Polytechnique Fédérale de Lausanne, 1015, Lausanne, Switzerland.
Nicola
N
Marzari
Ion Beam Physics, ETH Zurich, 8093, Zurich, Switzerland.
Max
M
Döbeli
Research with Neutrons and Muons Division, Paul Scherrer Institut, 5232, Villigen-PSI, Switzerland.
Alexander
A
Wokaun
Research with Neutrons and Muons Division, Paul Scherrer Institut, 5232, Villigen-PSI, Switzerland.
Daniele
0000-0002-6231-0237
D
Pergolesi
Research with Neutrons and Muons Division, Paul Scherrer Institut, 5232, Villigen-PSI, Switzerland.|Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093, Zurich, Switzerland.
Thomas
T
Lippert
D017610:Calcium Compounds; D002384:Catalysis; D004583:Electrons; D009584:Nitrogen; D010087:Oxides; D012666:Semiconductors; D013052:Spectrometry, X-Ray Emission; D014025:Titanium; D056928:X-Ray Absorption Spectroscopy
D017610:Calcium Compounds; D010087:Oxides; C059910:perovskite; D014025:Titanium; D009584:Nitrogen
electronic structure; oxynitrides; pulsed laser deposition; solar water splitting; spectroscopy