A. Da Costa

PDB_REDO: automated re-refinement of X-ray structure models in the PDB.

The majority of previously deposited X-ray structures can be improved by applying current refinement methods.

Substrate effect on the magnetic microstructure of La0.7Sr0.3MnO3 thin films studied by magnetic force microscopy

Colossal magnetoresistive La0.7Sr0.3MnO3 thin films have been grown under tensile strains on (100)-SrTiO3 substrates and compressive strains on (100)-LaAlO3 and (110)-NdGaO3 substrates by pulsed laser deposition. Using magnetic force microscopy (MFM), a “feather-like” magnetic pattern, characteristic of films with an in-plane magnetization, is observed for films deposited on both SrTiO3 and NdGaO3 while a “bubble” magnetic pattern, typical of films with an out-of-plane magnetization, is recorded for LaAlO3. We show that the shape of the magnetic pattern imaged by MFM is fully correlated to the easy direction of the magnetization in the film.

NANOSCALE INVESTIGATIONS OF ELECTRICAL PROPERTIES IN RELAXOR Pb(Mg1/3Nb2/3)O3-PbTiO3 THIN FILMS DEPOSITED ON PLATINUM AND LaNiO3 ELECTRODES BY MEANS OF LOCAL PIEZOELECTRIC RESPONSE

ABSTRACT At very low temperature (450°C), (111)-oriented and polycrystalline 0.7Pb(Mg1/3Nb2/3) O3-0.3PbTiO3 (PMN-PT) thin films have been grown on platinum (Pt) and lanthium niobate (LaNiO3) bottom electrodes respectively. Macroscopic measurements reveal lower coercive fields for PMN-PT grown on LaNiO3 compared to on platinum, while the piezoelectric coefficient d 33 is greater. At the nanometer scale, local piezoelectric hysteresis loops show that the voltages required for domain switching and piezoelectric response are the highest for PMN-PT deposited on LaNiO3. The electrical results can be explained by taking into account the effects induced by both electrodes on the surface morphology and structural properties of the films.

Constrained ferroelectric domain orientation in (BiFeO3)m(SrTiO3)n superlattice

Ferroelectric domains were investigated using piezoresponse force microscopy in superlattices composed of multiferroic BiFeO3 and SrTiO3 layers. Compared to single BiFeO3 thin films, a reduction in the domains size and a suppression of the in-plane orientation of domains are observed in a superlattice of (BiFeO3)4(SrTiO3)8, suggesting a constrained ferroelectric domain orientation along the out-of-plane ⟨001⟩ direction. Such modification of domain size and orientation in BiFeO3-based heterostructures could play a vital role on engineering the domains and domain wall mediated functional properties necessary for device applications.

Nanoscale investigations of switching properties and piezoelectric activity in ferroelectric thin films using piezoresponse force microscopy

With respect to nanoscale ferroelectric thin films research, piezoresponse force microscopy (PFM) for domain imaging and local piezoelectric spectroscopy for switching properties and piezoelectric activity measurements require the control of experimental conditions associated to the experimental set-up. To avoid any misinterpretation of the results, stiffness of the cantilever, or frequency and amplitude of the driving AC voltage have to be carefully investigated. In this paper, optimal working conditions determined with our experimental set-up are described in order to evidence the architecture of domains, to measure the coercive voltage and to evaluate the piezoelectric activity of Pb(Zr, Ti)O3 thin films. Illustrations are carried out on highly oriented, unetched and ion beam etched tetragonal films; explanations of the behaviour of the ferroelectric material at the nanoscale level are given.

UV induced permanent gratings in Ce3+ or Eu2+ doped PZG glass thin-film waveguides deposited on CaF2 substrates

Abstract Ce 3+ or Eu 2+ doped PZG (PbF 2 , ZnF 2 , GaF 3 ) glass thin films fabricated by vapor phase deposition on CaF 2 substrates have been shown to possess high photosensitivity. As an illustration, strong permanent gratings have been written in the PZG glass by using a continuous wave UV laser ( λ = 244 nm). The kinetics of the grating growths were monitored by probing the efficiencies of the holograms at a wavelength of 633 nm. The mechanisms that could form the gratings have been analyzed. The UV induced changes in absorption coefficient at 633 nm or the UV induced surface modulation turned out to be too low to explain the order of magnitude of the grating efficiency. The gratings are assumed to come from changes in refractive index as high as 1.3 × 10 −2 and 3.9 × 10 −3 in the Eu 2+ and Ce 3+ doped samples respectively.

Scanning tunneling microscopy investigation of an inclusion complex between the β-cyclodextrin and the sodium salt of the trisulfonated triphenylphosphine

Scanning tunneling microscopy has been used to image on a highly orientated pyrolytic graphite substrate an inclusion complex between the sodium salt of the trisulfonated triphenylphosphine (TPPTS) and the β-cyclodextrin (CyD). The images were in very good agreement with the structure that has been reported for this inclusion complex and it is postulated that β-CyD/TPPTS inclusion complex lies on the apolar graphite substrate by its primary face. A correlation of image contrast with the frontier orbitals of the inclusion complex is also clearly established for the first time in the case of CyD-based supramolecular assemblies. The self-assembly of the inclusion complexes on the graphic surface is also discussed.

Enhancement in nanoscale electrical properties of lead zirconic titanate island fabricated by focused ion beam

Lead zirconic titanate (PZT) microscale island (1 μm–100 nm) was fabricated by focused ion beam before its crystallization, followed by the annealing treatment at the crystallization temperature. Local electrical properties were evaluated by piezoresponse force microscopy technique. Compared to the PZT island fabricated after crystallization, the result shows that there is noticeable enhancement in nanoscale electrical properties of PZT island fabricated before crystallization, especially when the island size decreases. Raman spectra and Kelvin force microscopy result both show that there are little degradations on the PZT surface after this amorphous etching process. The mechanism will be discussed in this paper. These results are very beneficial to the development of the ferroelectric film applications in the dynamic random access memory, ferroelectric random access memory, and micro-electro-mechanical system field.

Analysis of the degradation induced by focused ion Ga3+ beam for the realization of piezoelectric nanostructures

Piezoelectric nanostructures (islands of dimensions in the lateral size range 50–500 nm) have been fabricated by focused Ga3+ ion beam (FIB) etching on PbZr0.54Ti0.46O3 thin films obtained by magnetron sputtering. The degradation induced by the etching process is investigated through the evolution of electromechanical activity measured by means of local piezoelectric hysteresis loops produced by piezoresponse force microscopy. The analysis of surface potential is performed by kelvin force microscopy and the measurement of current-voltage curves is carried out by conducting atomic force microscopy. Two kinds of structures, namely one based on crystallized films and the other based on amorphous ones, were studied. In this latter case, the amorphous films are postannealed after etching to obtain crystallized structure. For the structures based on the crystallized and then etched films, no piezoelectric signal was registered that evidences a serious degradation of material induced by Ga3+ ion implantation. Fo...

Local Piezoelectric Hysteresis Loops for the Study of Electrical Properties of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 Thin Films : Bottom Electrode Dependence and Film Thickness Effect

0.7Pb(Mg 1/3 Nb 2/3 )O 3 –0.3PbTiO 3 (PMN–PT 70/30) thin films, 400 and 600 nm thick, have been grown on Pt and LaNiO 3 (LNO) bottom electrodes by rf magnetron sputtering. For each thickness, local piezoelectric hysteresis loops evidence that the individual PMN-PT grains deposited on LNO always require much higher voltage than the ones grown on Pt for switching. The average piezoelectric activity of grains is shown to be the highest for LNO electrode. For each electrode, film thickness has no significantly effect on the average coercive voltage and piezoelectric activity measured on the loops. A simple charge model explains this result.