Investigation of Clean Ferroelectric Surface in Ultra High Vacuum (UHV): Surface Conduction and Scanning Probe Microscopy in UHV

We discuss the controversies related with an intrinsic screening effect of the ferroelectric surface and report experiments of electron (e −)/hole (h +) layer on the clean surface of insulating pure BaTiO3 single crystals in ultra high vacuum, which is a follow-up of the first report on the intrinsic surface carrier layer on ferroelectric [Y. Watanabe et al., Phys. Rev. Lett. 86, 332 (2001)]. The experiments verify that both accumulation and inversion occur and the surface carrier layer is intrinsic, i.e., mainly due to spontaneous polarization P S not to impurities or defects. We show also that the surface carrier layer is consistent with the 180° domains, the theory for the polarization (D-E) curves of ferroelectric FET [S. L. Miller and P. J. McWhorter, J.Appl. Phys. 72, 5999 (1992)], the invisibility of the carrier layer in the dynamic response of ferroelectric. Especially, the electrostatic and the piezoelectric-response images by UHV-AFM show directly an intrinsic screening effect in 180° domains.