√2×√2 R45∘ surface reconstruction and electronic structure of BaSnO 3 film

Abstract

We studied the surface and electronic structures of barium stannate (BaSnO3) thin films by low-energy electron diffraction (LEED) and angle-resolved photoemission spectroscopy (ARPES) techniques. BaSnO3/Ba0.96La0.04SnO3/SrTiO3 (10 nm/100 nm/0.5 mm) samples were grown using the pulsed-laser deposition (PLD) method and were ex situ transferred from the PLD chamber to ultrahigh vacuum (UHV) chambers for annealing, LEED, and ARPES studies. UHV annealing starting from 300 degrees C up to 550 degrees C, followed by LEED and ARPES measurements, show 1 x 1 surfaces with nondispersive energy-momentum bands. The 1 x 1 surface reconstructs into a root 2. x root 2R45 degrees one at an annealing temperature of 700 degrees C where the ARPES data show clear dispersive bands with a valence band maximum located around 3.3 eV below the Fermi level. While the root 2 x root 2R45 degrees surface reconstruction is stable under further UHV annealing, it is reversed to a 1 x 1 surface by annealing the sample in 400 mTorr oxygen at 600 degrees C. Another UHV annealing at 600 degrees C, followed by LEED and ARPES measurements, suggests that LEED root 2 x root 2R45 degrees surface reconstruction and ARPES dispersive bands are reproduced. Our results provide a better picture of the electronic structure of BaSnO3 surfaces and are suggestive of the role of oxygen vacancies in reversible root 2 x root 2R45 degrees surface reconstruction.