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We report the study of anatase TiO2(001)-oriented thin films grown by pulsed laser deposition on LaAlO3(001). A combination of in situ and ex situ methods has been used to address both the origin of the Ti(3+)-localized states and their relationship with the structural and electronic properties on the surface and the subsurface. Localized in-gap states are analyzed using resonant X-ray photoelectron spectroscopy and are related to the Ti(3+) electronic configuration, homogeneously distributed over the entire film thickness. We find that an increase in the oxygen pressure corresponds to an increase in Ti(3+) only in a well-defined range of deposition pressure; outside this range, Ti(3+) and the strength of the in-gap states are reduced.

The indirect effect of oxygen background gas on the La/Al ratio during the growth of LaAlO3 (LAO) films by pulsed laser deposition (PLD) is analyzed, in a pressure range between 10^-3 and 10^-1 mbar. We resort to two complementary investigation methods: Rutherford backscattering spectroscopy and spectrally resolved, time-gated imaging of the laser plume. The first technique allows us to analyze the stoichiometry of the deposited films, and the latter allows us to analyze the plume expansion phase of the PLD process by collecting chemically resolved two-dimensional images of the relevant atomic/molecular species. The comparison between the results obtained by the two techniques allows us to highlight the role of the plume-gas interaction in affecting cations stoichiometry. Our results indicate that, in the considered pressure range, the background oxygen pressure affects the cations stoichiometry of the LAO films, besides determining their oxygen content.

Segregation and competition of Y-based impurities in Y-rich biepitaxial YBCO samples is investigated. The analysis of distribution and microstructure of the precipitates is performed by high resolution electron microscopy (HREM). Y 2 O 3 precipitates are found in (103) YBCO films grown on (110) SrTiO 3 (STO) substrates. On the same biepitaxial samples, Y 2 BaCuO 5 (Y211) precipitates are found in (001) YBCO films deposited on an intermediate (110) MgO seed layer. Agglomeration of Y211 precipitates is observed near the edge in the MgO seed layer. The experimental data are discussed in the context of phase competition, nucleation, epitaxy and surface migration in the Y–Ba–Cu–O system. It is deduced that the change of supersaturation and surface energy, also governed by the favorable epitaxy of the secondary phase with the substrate or the YBCO matrix, plays a major role in determining the segregation of either Y211 or Y 2 O 3 precipitates.

By a combination of optical second harmonic generation and transport measurements, we have investigated interfaces formed by either crystalline or amorphous thin films of LaAlO3 grown on TiO2-terminated SrTiO3(001) substrates. Our approach aims at disentangling the relative role of intrinsic and extrinsic doping mechanisms in the formation of the two-dimensional electron gas. The different nature of the two mechanisms is revealed when comparing the sample response variation as a function of temperature during annealing in air. However, before the thermal treatment, the two types of interfaces show almost the same intensity of the second harmonic signal, provided the overlayer thickness is the same. As we will show, the second harmonic signal is proportional to the depth of the potential well confining the charges at the interface. Therefore, our result demonstrates that this depth is about the same for the two different material systems. This conclusion supports the idea that the electronic properties of the two-dimensional electron gas are almost independent of the doping mechanism of the quantum well.

LaAlO$_{3}$ and NdGaO$_{3}$ thin films of different thickness have been grown by pulsed laser deposition on TiO$_2$-terminated SrTiO$_{3}$ single crystals and investigated by soft X-ray photoemission spectroscopy. The surface sensitivity of the measurements has been tuned by varying photon energy $h\nu$ and emission angle $\Theta$. In contrast to the core levels of the other elements, the Sr $3d$ line shows an unexpected splitting for higher surface sensitivity, signaling the presence of a second strontium component. From our quantitative analysis we conclude that during the growth process Sr atoms diffuse away from the substrate and segregate at the surface of the heterostructure, possibly forming strontium oxide.

The plume expansion dynamics strongly affects the growth and the chemistry of pulsed laser deposited thin films. The interaction with the background gas determines the kinetic energy of the species impinging on the substrate, their angular broadening, the plasma chemistry, and eventually the cations stoichiometric ratio in oxide films. Here, we exploit two-dimensional, spectrally resolved plume imaging to characterize the diverse effects of the oxygen background pressure on the expansion dynamics of La, Ga, and LaO species during pulsed laser deposition of LaGaO3. The propagation of the ablated species towards the substrate is studied for background oxygen pressures ranging from high vacuum up to ≈10−1 mbar. Our experimental results show specie-dependent effects of the background gas on the angular distribution of the precursors within the plume. These findings suggest that even in the presence of a stoichiometric ablation and of a globally stoichiometric plume, cations off-stoichiometry can take place in the forefront portion of the plume impinging on the substrate. We show that such effect can be compensated by a proper choice of process parameters.

We investigate pulsed laser ablation of LaAlO 3 and LaGaO 3 with a focus on the influence of oxygen background gas pressure on the plume expansion dynamics and deposition rate. The ablation plume is characterized by exploiting fast photography and time- and space-resolved optical emission spectroscopy. The variation of the deposition rate with the oxygen background pressure was obtained at 800 °C by reflection high-energy electron diffraction, and compared to that measured at room temperature by means of a quartz crystal microbalance. The experimental findings allow one to address the various stages of plume expansion as a function of the background oxygen pressure as well as the changes induced on the plume species kinetic energy and composition. On the base of our experimental results, the possible influence of various mechanisms, such as subplantation and oxygen vacancy formation, on the growth of oxides interfaces is addressed.

The properties of thin films of complex oxides, such as La1−xDxMnO3− D=Ba, Ca, Sr, etc., produced by pulsed laser deposition depend critically on the experimental parameters in which laser ablation is carried out. Here, we report a comparative analysis of the pulsed laser ablation process of La0.7Ba0.3MnO3−, in oxygen background, in the ambient pressure range from 10−2 to 1 mbar, typically employed in pulsed laser deposition of manganites. The laser ablation plume was studied by using time-gated imaging and optical emission spectroscopy techniques. It was found that at a pressure of 10−2 mbar, the plume species arriving at the substrate are characterized by hyperthermal kinetic energy 10 eV, and high degree of excitation. On the contrary, at larger oxygen pressure 0.1–1 mbar, the velocity of plume species reaching the substrate, and their degree of excitation are much reduced by the confining effects of the background gas. These features explain why an appropriate choice of the experimental conditions in which the deposition process is carried out leads to better quality films, providing helpful indications to improve control over the growth process of both La1−xDxMnO3− and other perovskitic oxides.

Superconductive thin films of Y-Ba-Cu-O have been grown in situ by r.f. magnetron sputtering from a single stoichiometric target on Al2O3 substrates. Zero-resistivity temperatures as high as 73 K have been achieved. X-ray and EDS analyses have been performed on the samples. The dependence of film features on deposition conditions is also discussed.

A study of the 2D vs 3D growth in c-axis Nd 1+x Ba 2x Cu 3 O 7−δ films and a study of the crossover between a-axis to c-axis growth in the Re 1+x Ba 2−x Cu 3 O 7−δ (RBCO) family is reported. We found that c-axis stoichiometric Nd 1 Ba 2 Cu 3 O 7 films exhibit a 3D layered island-growth, possibly originated by screw and half loop dislocations. On the contrary, a continuous 2D growth is found in off-stoichiometry films, characterized by Nd excess. The amount of a-axis in Nd 1+x Ba 2−x Cu 3 O 7 films deposited at different temperatures has been carefully determined by XRD. The experimental results are interpreted in the framework of a theoretical model of the nucleation of RBCO films. The model provides a quantitative description and a satisfactory fit of experimental data from our experiment and from the current litterature.

TlBaCaCuO superconducting films have been fabricated on LaAlO3 (100) buffer layers, grown by metal-organic chemical vapour deposition (MOCVD) on SrTiO3 (100) substrates. The usual two step procedure, involving the MOCVD deposition of BaCaCuO(F) matrices and a thallium vapour diffusion process, has been adopted for the preparation of the TlBaCaCuO films. The films grown on the LaAlO3 (100)/SrTiO3 (100) substrates area-axis oriented as indicated by both X-ray diffraction measurements and scanning electron micrographs. The morphological nature of the LaAlO3 buffer layer seems to be responsible for the formation ofa-axis-oriented domains, since simultaneous fabrications of TlBaCaCuO films on commercial LaAlO3 (100) and LaAlO3 (100)/SrTiO3 (100) substrates givec-axis anda-axis-oriented films, respectively. The MOCVD grown LaAlO3 buffer layers are highly (100) oriented, the full width at half maximum (FWHM) of the rocking curve of the (100) peak being as small as 0.16°.

(110) MgO thin films have been deposited by RF sputtering on (110) SrTiO3 and used as buffer layers for YBCO deposition. The MgO films show high morphological quality, as confirmed by X-ray specular reflectivity, and narrow (approximate to 1 degrees) X-ray diffraction peaks in the rocking curves measurements. These results are discussed in the framework of an ionic oxide growth model. XRD analyses performed on the bilayer YBCO/MgO (110) confirm the epitaxial growth of the films. with cool) YBCO//(110) MgO. XRD, AFM, SEM measurements are compared with data relative to bilayers deposited on (100) SrTiO3.

Superconducting thin-films containing randomly disordered layers of and have been synthesized through a combined approach of metal-organic chemical vapour deposition (MOCVD) and thallium vapour diffusion. The BaCaCu matrices have been deposited onto yttria stabilized zirconia (YSZ) substrates using the second generation tetraglyme and tetraglyme (hfa denotes hexafluoroacetylacetonate), and the (acac denotes acetylacetonate) as volatile metal-organic precursors. BaCaCu precursor films of composition 2:2:3 were annealed in the presence of a mixture of thallium (III), barium, calcium and copper oxides at temperatures of 840 - and oxygen partial pressure varying from 0.04 - 0.5 atm. The formation of an oriented () intergrowth structure has been observed in narrow temperature and oxygen partial pressure ranges. The electrical resistivity data show which, in accordance with the scanning electron microscopy image, appears indicative of a material with weakly linked grains.

Superconductivity of Y 1 Ba 2 Cu 3 O 7− d c -axis epitaxial films is always depressed when the films thickness is reduced to few unit cells. Here we report a detailed study of the structure, morphology and transport properties of Y(Nd 0.05 Ba 1.95 )Cu 3 O 7− d films deposited by high pressure diode oxygen sputtering. Films having thickness between 9 and 250 unit cells deposited on LaAlO 3 substrates have been investigated. It is shown that both T c and J c are reduced by decreasing the film thickness. The effect is quite evident even in relatively thick Y(Nd 0.05 Ba 1.95 )Cu 3 O 7− d films made of 32 unit cells. Moreover it is shown that the a and b axes of the films approach one to each other with decreasing thickness. A nine unit cell film is almost tetragonal. Application of a simple elasticity theory to account for the structural changes fails to explain the experimental results. Inelastic strain induced by an oxygen disordering in the Cu(1)–O chains may explain the experimental results.

A theroretical analysis of the behaviour of an STJ detector in the non equilibrium regime induced by some external radiation has been carried, based on the kinetic equations for both junction electrodes. The analytical expression of the tunnel times and of the non equilibrium current has been obtained. The effect of the backtunneling process on the amount of collected charge is shown.

Epitaxial (001)-oriented ultrathin YBCO films of different thicknesses are deposited by Inverted Cylindrical Magnetron Sputtering (ICMS) on (100) MgO single-crystal substrates. The mean films stoichiometry is determined by Rutherford Backscattering (RBS). Auger Electron Spectroscopy (AES), X-ray Photoemission Spectroscopy (XPS) and Scanning Electron Microscopy (SEM) are employed in order to analyse film growth, and identify spurious phases present in the samples.

Superconducting thin films of the TlBaCaCuO family have been prepared through a combined approach of MOCVD and thallium vapour diffusion. A three-step process has been adopted involving i) the synthesis of Ba−Ca−Cu−O films by MOCVD using «second-generation» barium and calcium sources, ii) the hydrolysis of the fluoride phases by annealing in water vapour-saturated oxygen and iii) the annealing in the presence of a thallium source. Reproducible results, in terms of phase formation, are discussed depending on the different conditions of the preannealing process. The superconducting films consist predominantly of single-phase Tl2Ba2Ca2Cu3Ox(2223). Preferential orientation of the crystallitec-axes perpendicular to the substrate surface has been observed. The films exhibit superconducting onset temperatures of 115–120 K with zero resistance higher than 100 K.

We investigate the effects of ambient pressure and substrate temperature on the deposition rate of oxides grown by pulsed laser deposition in oxygen atmosphere. The deposition rate of LaGaO3 (LGO) and LaAlO3 (LAO) is studied at room temperature by means of a quartz crystal microbalance and at 800 °C by exploiting reflection high energy electron diffraction. We observe a clear dependence of the deposition rate on temperature for an oxygen pressure between 10−2 and 1 mbar. A simple model based on multiple-elastic-scattering processes thoroughly describes the observed dependence of the deposition rate on the pressure/density of the background gas.

International audience; Two kinds of epitaxial structures were grown by standard pulsed laser deposition on (001) Si, namely La0.7Sr0.3MnO3/Bi4Ti3O12/CeO2/YSZ/Si (BTO-based), and La0.7Sr0.3MnO3/SrTiO3/ CeO2 /YSZ/Si (STO-based) multilayers. The samples were investigated by means of x-ray diffraction, transmission electron microscopy, magnetic and transport measurements. The Curie temperature TC of the BTO-based samples was found to be higher (360 K) than for the typical reference epitaxial LSMO film grown on (001) SrTiO3 single crystal (345 K), due to high compressive in-plane strain. The STO-based samples show high structural quality, low roughness and high TC (350 K), making them interesting candidates for use in innovative LSMO-based bolometers or spintronic devices operating at room temperature. (Some figures in this article are in colour only in the electronic version)

A simple technique for the growth of SrO-terminated SrTiO3 surfaces is reported. High quality SrTiO3 epitaxial films were grown by reflection high energy electron diffraction assisted pulsed laser deposition on suitably prepared NdGaO3 (110) substrates. The surface properties, analyzed within a growth/characterization multichamber ultrahigh vacuum system by photoemission spectroscopy performed on the core-level spectra of Sr and Ti, low energy electron diffraction-, scanning tunneling-, and atomic force microscopy, are fully consistent with a single Sr oxide termination. The availability of such high quality SrO-terminated SrTiO3 surfaces is of major importance for the controlled growth of oxide epilayers and interfaces.

The authors prepared Mo/sub 60/Re/sub 40/ thin films by single target magnetron sputtering. All the films analyzed exhibited a sharp superconductive transition and values of the critical temperature T/sub c/ up to 13 K were achieved. Structural analyses (EDS and X-rays) were performed on the samples. A15 phase was obtained even at low deposition temperatures. From the measured low temperature resistivity O/sub c/ and critical temperature T/sub c/ an estimate of the theoretical BCS surface resistance is inferred and compared with that of niobium. >

Experimental results on stable point-contact Nb/Y-Ba-Cu-O structures are reported. Reproducible current-voltage characteristics showing Josephson coupling are obtained. Measurements of dV/dI give an estimate for the energy-gap value of the high-T/sub c/ superconductor Y-Ba-Cu-O ..delta.. = 19.5 +- 2.0 mV, corresponding to a ratio (2..delta..(0)/k/sub B/T/sub c/) = 4.8 in agreement with previous results obtained by a different technique.