Fig. 1
From: Artificial two-dimensional polar metal by charge transfer to a ferroelectric insulator
Piezoresponse force microscopy characterization of a 10 unit cells of Ba0.2Sr0.8TiO3 thin film at room temperature. a Schematic diagram of the geometry for the piezoresponse force microscopy (PFM) setup, the red arrow indicates the as-grown polarization direction of Ba0.2Sr0.8TiO3 (BST). The Nb-doped SrTiO3 (Nb:STO, 0.1 wt% Nb doping) substrate is used as the bottom electrode. b Local PFM phase hysteresis loops and, c butterfly-like amplitude loops of the BST/Nb:STO sample, different colors stand for different voltage scans, the solid lines are guides for the eyes. d, e PFM amplitude (d) and phase (e) images (5 × 5 µm2) of the piezoelectric domains after application of −8 and 8 V tip bias to the 3 × 3 and 1 × 1 µm2 regions, respectively. Yellow region corresponds to as-grown downward polarization, purple region represents switched upward polarization. The same color between the as-grown 5 × 5 µm2 region and the central 1 × 1 µm2 region indicates that the as-grown BST has a downward polarization. The scale bars in d and e are 1 µm
