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Lecture Maciej Gutowski


17 november 2004 FWN-Building 5118.-156, Nijenborgh 4, 9747 AG, Groningen
Speaker: Dr. Maciej Gutowski
Affiliation: Fundamental Science Directorate, Pacific Northwest National Laboratory, Richland, WA, USA
Title: Control of electronic structure of type II heterojunctions through nanoengineering
Date: Wed Nov 17, 2004
Start: 11.00
Location: FWN-Building 5118.-156
Host: J. Knoester
Telephone: +31 50 363 4369


Type II heterojunctions can be used to separate electron/hole pairs generated via non-thermal excitations and promote photochemical reactions. We demonstrate that electronic structure of epitaxial interfaces depends on fine details of interfacial atomic structure. In turn, the interfacial atomic structure can be controlled through nanoengineering. The epitaxial alpha-Fe2O3/alpha-Cr2O3 heterojunction has been studied at the density-functional level of theory. We identified two epitaxial and isomeric interfaces between Fe2O3 and Cr2O3 (''oxygen-divided'' and ''split metal''), which are characterized by similar thermodynamic stability but different valence band offsets (chromia above hematite by 0.4 and 0.6 eV for oxygen-divided and split metal, respectively). Depending on the growth conditions either the former or the latter interface can develop. The non-commutativity raises the possibility of a spontaneous average electric potential gradient across several periods of the superlattice. Such a structure could efficiently separate electrons and holes in, for example, a photoelectrochemical device. Indeed, the recent experimental results from PNNL demonstrate an enhanced photocatalytic activity of Cr2O3/Fe2O3, with chromia in the top layer, in comparison with Cr2O3(0001). We also demonstrate that a buffer monolayer of another metal oxide M2O3 (M=Al, Ga, Sc, Ti, V, Mn, Co) can further modify the electronic and magnetic properties of the Fe2O3/Cr2O3 heterojunction. The valence band offset can be changed from +0.62 eV (split metal; no interfactant) up to +0.90 eV with a monolayer of Sc2O3, and down to -0.51 eV (i. the alpha-Fe2O3/alpha-Cr2O3 heterojunction changes from Type II to Type I) with the Ti2O3 interfactant, due to a massive interfacial charge transfer. Thus, nanoscale engineering through layer-by-layer growth will strongly affect the macroscopic properties of this system.
Laatst gewijzigd:22 oktober 2012 14:30