Polarization landscape effects in soft X-ray-induced surface chemical decomposition of lead zirco-titanate, evidenced by photoelectron spectromicroscopy

Abstract

The stability of thin films of lead zirco-titanate (PZT) under intense soft X-ray beams is investigated by time-resolved photoelectron spectromicroscopy with a lateral resolution below 1 micrometer. Surface dissociation is observed when samples are irradiated with intense (5 × 10 photons per s per m) soft X-rays, with promotion of reduced lead on the surface. On areas exhibiting outwards polarization (P), the reduced lead is formed at the expense of P-PZT. On areas presenting co-existing P states with areas without out-of-plane polarization (P), the reduced lead is formed at the expense of the P-PZT component, while the P-PZT remains constant. The main dissociation mechanism was found to be triggered by 'hot' electrons in the conduction band, with energies exceeding the surface dissociation energies. Dissociation occurs basically when the electron affinity is larger than the dissociation energy of PbO (for P areas) or PbO (for P areas). Such mechanisms may be adapted for dissociation of other molecules on surfaces of ferroelectric thin films or for quantifying the stability of ferroelectric surfaces interacting with other radiation, with applications in the fields of photocatalysis or photovoltaic devices.

Resistance hysteresis correlated with synchrotron radiation surface studies in atomic sp2 layers of carbon synthesized on ferroelectric (001) lead zirconate titanate in an ultrahigh vacuum

“…This may be attributed to the formation of metallic Pb during carbon deposition. 45,57 One also observes that, just aer the carbon deposition, all core levels are shied to larger binding energies with about 2 eV (less for Zr) and also the occurrence of narrow low BE peaks in the Pb spectra, attribute to the formation of metal Pb on the surface. The atomically clean sample evidenced an inward electric polarization P (À) , as in other experiments.…”

“…Release of metal lead from PZT(001) subject to a high beam ux ($5 Â 10 11 photons per (s mm 2 )) was reported and analysed in ref. 45. In the actual case, the beam ux is in the range of 10 9 photons per (s mm 2 ), but the photon energy is larger and several de-excitation channels with respect to that outlined from the above reference may contribute to the creation of 'hot electrons' which induce Pb-O surface dissociation.…”

“…The second hypothesis involve the fact that carbon deposition was followed-up by PES, thus the sample at high temperature was continuously irradiated with a high intensity synchrotron radiation beam. Release of metal lead from PZT(001) subject to a high beam flux (∼5 × 10 11 photons per (s μm 2 )) was reported and analysed in ref. 45 .…”

“…Photoelectron spectroscopy is able to derive the surface composition of the substrate, the chemical states of the different atomic species and, moreover, is able also to assess the surface polarization through a model implying intrinsic or extrinsic charge compensation. 34,35,37,38,[42][43][44][45] The asymmetry parameter of the C 1s spectrum recorded with high resolution is also a ngerprint of graphene-like structure. 13,46,47 Near-edge absorption spectroscopy (NEXAFS) with angular resolution is able to assess the proportion of in-plane sp 2 bonds, thus to give a global ngerprint of carbon organized in graphene-like layers.…”

Self-consistently derived sample permittivity in stabilization of ferroelectricity due to charge accumulated at interfaces

“…As soon the polar material or the heterostructure comprising such a material is able to produce some charge accumulation at the extremities of the film, this phenomenon is likely to be produced accompanied with a transition towards ferroelectricity, due to the interaction of the field produced by the accumulated charges with the dipoles formed inside the material. The fact that even by using photoelectron spectromicroscopy with submicrometer resolution one is able to identify inhomogeneous band bending at surfaces [9][10][11] may be brought as an argument that the model of stabilization induced by charges accumulated at surfaces or interfaces might be valid even in the case of thicker samples, inside each individual domain with welldefined ferroelectric polarization.…”