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The cation ratio, crystal structure, and ferroelectric properties of TbMnO3 films on (010) oriented YAlO3 substrates grown by pulsed laser deposition were investigated. We found that the cation ratio is altered by the background gas pressure, and that stoichiometric films have larger critical thicknesses than Tb-rich films. The ferroelectric order was severely disturbed in Tb-rich films showing a lower transition temperature and a smaller polarization. In addition, frequency dispersion was observed in the dielectric response of relaxed stoichiometric TbMnO3 films, which may be introduced by defects due to strain relaxation.

9 págs.; 8 figs., The aim of this work is to demonstrate that single-photon photoionization processes make a significant difference in the expansion and temperature of the plasma produced by laser ablation of ceramic Al2O3 in vacuum as well as to show their consequences in the kinetic energy distribution of the species that eventually will impact on the film properties produced by pulsed laser deposition. This work compares results obtained by mass spectrometry and optical spectroscopy on the composition and features of the plasma produced by laser ablation at 193 nm and 248 nm, i.e., photon energies that are, respectively, above and below the ionization potential of Al, and for fluences between threshold for visible plasma and up to ≈2 times higher. The results show that the ionic composition and excitation of the plasma as well as the ion kinetic energies are much higher at 193 nm than at 248 nm and, in the latter case, the population of excited ions is even negligible. The comparison of Maxwell-Boltzmann temperature, electron temperatures, and densities of the plasmas produced with the two laser wavelengths suggests that the expansion of the plasma produced at 248 nm is dominated by a single population. Instead, the one produced at 193 nm is consistent with the existence of two populations of cold and hot species, the latter associated to Al+ ions that travel at the forefront and produced by single photon ionization as well as Al neutrals and double ionized ions produced by electron-ion impact. The results also show that the most energetic Al neutrals in the plasma produced at the two studied wavelengths are in the ground state. © 2013 AIP Publishing LLC., This work has been partially supported by project IZK0Z2 of the Swiss National Science Foundation. R.P. acknowledges a grant from the JAE-doc program, co-funded by European Social Fund.

Films of LiMn2O4 prepared by pulsed laser ablation deposition are typically lithium deficient when grown at background pressures ranging between 10−4 and 20 Pa. The deficiency of light atomic species such as lithium in LiMn2O4 thin films occurs as a result of the different behavior of the species during plume expansion and the deposition of the film at elevated deposition temperatures. The plasma plume evolution in vacuum and 20 Pa oxygen pressure are studied using two spectroscopic techniques: emission spectroscopy and plume imaging. Higher velocities and a wider spatial distribution of lithium atoms are observed in vacuum when compared with manganese and oxygen species. Plume species are slowed down due to collisions with gas molecules when ablating LiMn2O4 in an oxygen atmosphere. As a result, a strong deceleration of the plasma front occurs, and the effect is more pronounced for the light species, e.g., Li. Comparing the spatial manganese and lithium distribution within the plasma, the lithium species...

Single-phase samples of La1−xCaxMnO3−δ (LCMO), x≈0.3, prepared by pulsed reactive crossed beam laser ablation on SrTiO3 (STO) substrates, and soft chemistry synthesized powders were studied by various methods. The precise study of the crystal structure and microstructures by a combination of electron diffraction and high-resolution electron microscopy revealed a monoclinic distortion of the GdFeO3-type structure, P21/c space group, in both types of materials, i.e., the thin films and powder compound. The analysis of the LCMO/STO interface showed nonhomogeneous stress states and a composition that results in a different superstructure from the usual detected structure. The temperature-dependent thermoelectric power in the case of thin films presented an anomalous behavior compared to those from the powder compound. A structural transition at high temperature (T≈750 K) influences the thermopower behavior as well as the thermal conductivity values.