Direct evidence for ferroelectric polar distortion in ultrathin lead titanate perovskite films

Abstract

X-ray photoelectron diffraction is used to directly probe the intra-cell polar atomic distortion and tetragonality associated with ferroelectricity in ultrathin epitaxial PbTiO3 films. Our measurements, combined with ab-initio calculations, unambiguously demonstrate non-centro-symmetry in films a few unit cells thick, imply that films as thin as 3 unit cells still preserve a ferroelectric polar distortion, and also show that there is no thick paraelectric dead layer at the surface.

X-ray photoelectron diffraction study of relaxation and rumpling of ferroelectric domains in BaTiO3(001)

“…The interlayer relaxation tends to zero going into the bulk, corresponding to a constant ferroelectric distortion, as expected far from the polarization discontinuity of the surface. These conclusions are in qualitative agreement with the results of Despont et al 16 who found that the surface relaxation and rumpling also acted against the ferroelectric distortion in epitaxially strained PbTiO 3 films. The structural changes over the first two unit cells will modify the near-surface electronic environment; this aspect should be confirmed by more systematic experiments and calculations.…”

“…14 Berlich et al have investigated the surface chemistry of paraelectric BTO, 15 while Despont et al have published high-resolution XPD and x-ray diffraction (XRD) studies of the FE distortion in a PbTiO 3 thin film. 16,17 By using synchrotron radiation, the kinetic energy of the photoelectrons can be tuned so as to favor the more bulk-sensitive, forward scattering, or the more surface-sensitive multiple scattering regimes. 18 One experimental study of the atomic rumpling and relaxation for P + polarization in a thin film has been published using LEED.…”

Monodomain to polydomain transition in ferroelectric PbTiO3 thin films with La0.67Sr0.33MnO3 electrodes

“…This effect is discussed in Ref. 9 where experiments varying the x-ray intensity did not reveal any change in the material tetragonality, suggesting that the modification of the domain structure ͑or switching of the polarization͒ occurs in the initial stage of the experiments.…”

“…[1][2][3][4][5][6][7][8][9] The depolarization field, which results from the imperfect screening of the polarization, has been shown theoretically to play a critical role. 6,10,11 In uniformly polarized ͑monodomain͒ thin PbTiO 3 epitaxial films prepared on Nb-doped SrTiO 3 substrates, it was experimentally shown that the increase of the depolarization field as the film thickness decreases leads to a reduction of the polarization accompanied by a continuous reduction of the film tetragonality c / a.…”

Giant tunnel electroresistance with PbTiO3 ferroelectric tunnel barriers

“…Due to tremendous technological advances in the growth of oxide thin films over the last decade, ferroelectric thin films of a few unit-cells are now achievable. This critical thickness ͑t c ͒ was determined for common ferroelectric materials such as the perovskite BaTiO 3 ͑BTO͒, PbTiO 3 ͑PTO͒, and BiFeO 3 ͑BFO͒ using x-ray photoemission diffraction, 4 x-ray scattering, 5 and piezoresponse force microscopy ͑PFM͒. 6 Besides the nature of the ferroelectric material, t c also depends on several factors, such as the electrode materials ͑through their ability to efficiently screen polarization charges͒, the strain state, or the ambient atmosphere giving rise to partial or complete screening on the ferroelectric surface.…”