Ellipsometric Study of Nb O 2 Grown by

Ellipsometric Study of Nb. O 2 Grown by MBE on LSAT from 77 to 800 K T. Nathan Nunley 1, Stefan Zollner 1, T. Hadamek 2, A. B. Posadas 2, A. O’Hara 2, A. A. Demkov 2 1. Dept. of Physics, New Mexico State University, Las Cruces, NM 2. Dept. of Physics, University of Texas, Austin, TX

Ellipsometry: How does it work ? We measure the change in the polarization state of light, when it is reflected by a flat surface. detector Monochromator or Interferometer (l) CINT polarizer analyzer Φ Sample NMSU

Spectroscopic Ellipsometry: Theory Linearly Polarized light to Elliptically Polarized light

Our Cryostat setup is special Heater and built-in TC up here LN 2 Arm 77 K Built-in Thermocouple Heater Control 800 K Windows 70 o Incidence Second Thermocouple behind here Turbo Pump 10 -8 torr (UHV)

LSAT, the substrate of interest • (La. Al. O 3)0. 3 (Sr 2 Al. Ta. O 6)0. 35 • Insulating perovskite • Good substrate properties

Dielectric Function of LSAT, Nice and Boring

Nb. O 2 on LSAT • This sample was grown by MBE at UT Austin • Special because dimerization axis is in plane • The dimerization causes an anisotropy

Nb. O 2 epitaxial layer (36. 8 nm on LSAT) Band gap plot Pseudo-dielectric function Substrate effects removed numerically Indirect gap: 0. 7 e. V Direct gap: 1. 3 e. V Nb 2 O 5 O’Hara et al. J. Appl. Phys. 116, 213705 (2014)

Nb. O 2: Comparison with Theory Experimentally Obtained Theory (average) Theoretically Obtained DBG IBG O’Hara et al. J. Appl. Phys. 116, 213705 (2014)

Experimental data of Nb. O 2/LSAT at varying Temperatures

Dielectric function of Nb. O 2 at different temperatures

Nb. O 2: Temperature Dependence of the band gap Dielectric function versus temperature

Conclusion • We have characterized both LSAT and Nb. O 2 • We have analyzed the temperature dependence of the dielectric function • We have been able to characterize the band gap with respect to temperature.

My Research Group NSF (DMR-1104934) DOE (DEAC 04 -94 AL 85000) SRC Contract 2012 -VJ-2299 Texas Advanced Computing Center ellipsometry. nmsu. edu