AVS 53rd International Symposium
    Surface Science Friday Sessions
       Session SS-FrM

Paper SS-FrM6
Growth and Properties of High-Quality Epitaxial N-doped TiO@sub 2@(110) Grown by Molecular Beam Epitaxy

Friday, November 17, 2006, 9:40 am, Room 2002

Session: Oxide Surfaces and Interfaces
Presenter: S.H. Cheung, Pacific Northwest National Laboratory
Authors: S.H. Cheung, Pacific Northwest National Laboratory
D.E. McCready, Pacific Northwest National Laboratory
A.G. Joly, Pacific Northwest National Laboratory
S.A. Chambers, Pacific Northwest National Laboratory
Correspondent: Click to Email
N-doped TiO@sub 2@ is of potential interest for bandgap reduction and enhanced visible light absorption for water splitting. Despite a plethora of papers, typically lacking adequate materials characterization, very little is known about the fundamental properties of N:TiO@sub 2@. To this end, we have undertaken a study of TiO@sub 2-x@N@sub x@ films grown on rutile TiO@sub 2@(110) by molecular beam epitaxy. A mixed beam of atomic N and O was prepared in an electron cyclotron resonance plasma source while Ti was supplied using an effusion cell. Due to the interplay between substitutional N (an acceptor) and interstitial Ti (a donor), the conductivity and majority carrier type depend sensitively on the three atomic fluxes during growth. N incorporation at O sites appears to be thermodynamically limited to less than 2 at. % unless heavily defective material is deliberately made, in which case higher concentrations can be achieved. Optical absorption shows that substitutional N results in a new broad feature at the top of the valence band which functionally reduces the rutile bandgap by ~0.5 eV. The high degree of structural quality was evidenced by observations of finite thickness fringes in the vicinity of the (330) Bragg peak in high-resolution X-ray diffraction. Lattice expansions of 0.5% along the a axis and 0.8% along the c axis accompanies N substitution for O. A preliminary investigation of N-doped anatase grown on LaAlO@sub 3@(001) reveals that the same limited extent of N incorporation occurs for anatase as for rutile.