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We report on the properties of laser-induced plasma plumes generated by ns pulsed excimer lasers as used for pulsed laser deposition to prepare thin oxide films. A focus is on the time and spatial evolution of chemical species in the plasma plume as well as the mechanisms related to the plume expansion. The overall dynamics of such a plume is governed by the species composition in particular if three or more elements are involved. We studied the temporal evolution of the plume, the composition of the chemical species in the plasma, as well as their electric charge. In particular, ionized species can have an important influence on film growth. Likewise, the different oxygen sources contributing to the overall oxygen content of an oxide film are presented and discussed. Important for the growth of oxide thin films is the compositional transfer of light element such as oxygen or Li. We will show and discuss how to monitor these light elements using plasma spectroscopy and plasma imaging and outline some consequences of our experimental results., Applied Physics A, 129 (2), ISSN:0947-8396, ISSN:1432-0630, ISSN:0340-3793

The disposal of pollutants in the surface, underground, and public water supply is an important problem, which is why it is necessary to study more efficient photocatalysts in the treatment of wastewater. In this context, thin films of TiO2, Mn2O3 and TiO2/Mn2O3 were prepared by the hydrolysis of precursors in the presence of citric acid and ethylene glycol, to evaluate the photocatalytic performance in the degradation of methylene blue dye and the hormone 17a-ethinylestradiol (EE2), the measurements were repeated 10 times in a period of 300 min. Thin films were deposited by spin-coating on Si (100) substrates and calcined at 500 °C and 600 °C for 2 h. Nanocomposites were characterized by X-ray diffraction, atomic force microscopy, scanning electron microscopy, UV–visible spectroscopy, photocatalytic activity, and photoluminescence. X-ray diffraction results revealed that no other phase was formed besides anatase and bixbite, indicating that there was no chemical interaction between the TiO2 and Mn2O3 layers. The results show the degradation values of methylene blue in approximately 57% and for the 17a-ethinylestradiol a degradation around 82%, showing that the studied photocatalysts are promising, mainly for the degradation of 17a-ethinylestradiol.

10 pags., 5 figs., 1 tab., Thin films of silicon carbide (SiC) on Si (100) and SrTiO (100) substrates have been grown by nanosecond pulsed laser deposition (PLD) with a Q-switched Nd:YAG laser operating at the wavelengths of 1064, 532 and 266 nm. The deposits obtained consisted of smooth and uniform layers of amorphous SiC, free of holes and cracks, with thicknesses in the range of 30–100 nm and average roughness substantially lower than 1 nm. The role of laser wavelength and of substrate temperature (300 K vs. 1025 K) on morphology, crystallinity and composition of the deposits was assessed. The films were analyzed by X-ray diffraction, micro-Raman spectroscopy and X-ray photoelectron spectroscopy. In addition, optical emission spectroscopy was employed to evaluate the characteristics of the ablation plasma and its correlation with the film growth., This research was supported by the Spanish State Research Agency (AEI) and European Regional Development (FEDER) through Projects PID2019-106125GB-I00/AEI/0.13039/501100011033 and PID2019-104124RB-I00/AEI/0.13039/501100011033. Thanks are given to the Soft and Polymeric Matter group (IEM-CSIC) for the use of AFM. We are grateful to M. Furió from MNCN-CSIC and P. Gonzalez from ICTP-CSIC for Raman and X-ray difraction technical assistance, respectively. Funding Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature.

Fluoride perovskites have recently attracted great attention due to their unique optical properties. The present study reports for the first time the fabrication of fluoride-based perovskite, CsCaF3, in form of thin films through a combined sol–gel/spin-coating approach using β-diketonate fluorinated precursors. The entire sol–gel process has been carried out in ethanol solution under acid-catalyzed conditions starting from the β-diketonate complexes, Cs(hfa) and Ca(hfa)2•diglyme•H2O (Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; diglyme = 2–Methoxyethylether), which act as single sources for metal ions and fluorine. A careful optimization of the process parameters, such as molar ratio of the starting mixture, aging time and annealing temperature, has allowed to produce for the first time, selectively and reproducibly, transparent and pure CsCaF3 films. Field-emission scanning electron microscopy and energy dispersive X-ray analyses highlight the formation of films with compact morphologies having a 1:1 stoichiometric ratio of Cs:Ca, uniform throughout the film and compatible with the CsCaF3 phase identified through X-ray diffraction analysis.

The Ge-Bi-Se thin films of varied compositions (Ge content 0-32.1 at. %, Bi content 0-45.7 at. %, Se content 54.3-67.9 at. %) have been prepared by rf magnetron (co)-sputtering technique. The present study was undertaken in order to investigate the clusters generated during the interaction of laser pulses with Ge-Bi-Se thin films using laser ablation time-of-flight mass spectrometry. The stoichiometry of the clusters was determined in order to understand the individual species present in the plasma plume. Laser ablation of Ge-Bi-Se thin films accompanied by ionization produces about 20 positively and/or negatively charged unary, binary and ternary (Ge-x(+), Bi-y(+), Se-z(+/-), GexSez+/-, BiySez+/- and GexBiySez-) clusters. Furthermore, we performed the laser ablation experiments of Ge:Bi:Se elemental mixtures and the results were compared with laser ablation time-of-flight mass spectrometry analysis of thin films. Moreover, to understand the geometry of the generated clusters, we calculated structures of some selected binary and ternary clusters using DFT. The generated clusters and their calculated possible geometries can give important structural information, as well as help to understand the processes present in the plasma processes exploited for thin films deposition. Tenké vrstvy Ge-Bi-Se s různým složením (Ge 0-32,1 at. %, Bi 0-45,7 at. %, Se 54,3-67,9 at. %) byly připraveny RF magnetronovým vícekatodovým naprašováním. Současná studie byla provedena pomocí time-of-flight hmotnostní spektrometrie s laserovou ablací za účelem zkoumání klastrů generovaných během interakce laserových pulzů s tenkými vrstvami Ge-Bi-Se. K pochopení přítomnosti jednotlivých částic v plazmatu byla určena stechiometrie klastrů. Laserová ablace tenkých vrstev Ge-Bi-Se spojená s ionizací produkuje kolem 20 kladně a/nebo negativně nabitých unárních, binárních a ternárních (Ge-x(+), Bi-y(+), Se-z(+/-), GexSez+/-, BiySez+/- and GexBiySez-) klastrů. Dále jsme provedli experimenty s laserovou ablací prvkových směsí Ge:Bi:Se a výsledky byly porovnány s time-of-flight hmotnostní spektrometrií s laserovou ablací tenkých vrstev. Pro pochopení geometrie generovaných klastrů jsme navíc vypočetli struktury několika vybraných binárních a ternárních klastrů pomocí DFT. Generované klastry a jejich vypočtené možné geometrie mohou poskytnout důležité strukturní informace a mohou pomoci porozumět dějům přítomným v plazmatických procesech využívaných pro depozice tenkých vrstev.

The subject of this thesis is the systematic study of the impact of pulsed laser deposition (PLD) conditions on the growth mode, strain state and film composition of ferroelectric NaNbO3 and KxNa1-xNbO3 thin films and superlattices. Lattice mismatched (011)NdGaO3, (001)SrTiO3, (011)DyScO3, (011)TbScO3 and (011)NdScO3 single crystalline substrates have been used in order to induce tensile or compressive biaxial lattice strain of different magnitude in the films. Coherent 2D growth of thin NaNbO3 films was achieved by optimizations of the growth process. The key interests were to adjust the deposition conditions allowing for near stoichiometric film growth and to analyze the dependence of ferroelectric domain formation and local hysteresis loops on the composition of films, incorporating different biaxial lattice strains. The amount of sodium and oxygen vacancies in the films was found to be critically affected by the oxygen background pressure and the Na/Nb ratio in the applied targets. By increasing the oxygen pressure from 0.05 mbar to 2 mbar or the Na/Nb ratio in the targets up to 1.17, a substantial reduction of sodium and oxygen vacancies was achieved. No extended defects were found in fully tensilely strained films deposited under thus optimized deposition conditions. In contrast, in compressively strained films deposited under otherwise identical conditions, the presence of columnar defects was observed, which provide stress relief in compressively strained films. In films incorporating full tensile lattice strain, regular lateral ferroelectric a1/a2 domain patterns were obtained only in the case of near-stoichiometric growth. In ferroelectric films under partially relaxed tensile lattice strain, typically a1/c/a2/c patterns are observed. In partially relaxed PLD-grown NaNbO3 films, additionally a vertical polarization evolves, resulting in an a1c/a2c domain pattern. Distinct local ferroelectric hysteresis loops were observed in near-stoichiometric films under low compressive lattice strain. Thus, it was confirmed that a ferroelectric room temperature phase can be induced by biaxial lattice strain in NaNbO3, which is antiferroelectric in the unstrained state. In the case of KxNa1-xNbO3, the key interest was to investigate the impact of K/Na ratio and biaxial lattice strain on local piezoelectric coefficients. It was found that the thickness up to which KxNa1-xNbO3 films could be deposited in a 2D-growth mode is lower compared to NaNbO3 films, which is correlated to the amount of incorporated K. As a promising alternative to the growth of single films, superlattices with alternating layers under compressive and tensile lattice strain were deposited on DyScO3 substrates. This way, both 2D growth and full in-plane lattice strain of the individual layers were retained for remarkably increased thicknesses compared to single films. In agreement with theoretical predictions made for ferroelectric/ferroelectric superlattices, 2D-grown, fully strained NaNbO3/K0.5Na0.5NbO3 superlattices on DyScO3 substrates were found to exhibit very promising local piezo/ferroelectric properties., Das Ziel dieser Arbeit war die systematische Untersuchung des Einflusses von Wachstumsbedingungen der Laserstrahlverdampfung (PLD) auf den Wachstumsmodus, den Verspannungszustand und die Zusammensetzung von NaNbO3- und KxNa1-xNbO3-Dünnschichten und Übergittern. Einkristalline (011)NdGaO3, (001)SrTiO3, (011)DyScO3, (011)TbScO3 und (011)NdScO3 Substrate mit kontrollierter Gitter-Fehlanpassung wurden verwendet, um biaxial kompressive oder tensile Gitterverspannungen in den Filmen zu erzeugen. Im Fall von NaNbO3 lag der Fokus auf der Erforschung von Abscheidebedingungen, die ein nahezu stöchiometrisches, 2D Film-Wachstum ermöglichen. Es wurde untersucht, wie sich Sauerstoff- und Natriumvakanzen auf (i) die ferroelektrische Domänenbildung in tensil und (ii) lokale Hysteresen in kompressiv verspannten Filmen auswirken. Es wird gezeigt, dass die Dichte von Natrium- und Sauerstoffvakanzen kritisch von dem Sauerstoffhintergrunddruck während des Wachstums und dem Na/Nb-Verhältnis des verwendeten Targets abhängt. Eine signifikante Verringerung dieser Vakanzdichte konnte sowohl durch Anheben des Sauerstoff-Hintergrunddruckes von 0,05 auf 2 mbar, als auch durch die Verwendung eines Targets mit einem Na/Nb-Verhältnis von 1,17 erreicht werden. In nahezu stöchiometrischen, tensil verspannten Filmen wurden keine ausgedehnten Defekte beobachtet. Im Gegensatz dazu sind säulenartige Defekte in kompressiv verspannten Filmen präsent, die unter ansonsten identischen Wachstums-Bedingungen abgeschieden wurden. Es wurde ermittelt, dass dieser Defekt-typ in der Lage ist, kompressive Verspannung in den Filmen abzubauen. In tensil verspannten Filmen konnten gut geordnete laterale ferroelektrische a1/a2 Domänen nur beobachtet werden, wenn die Filme nahezu stöchiometrisch waren. Die Art der Domänenkonfiguration in Filmen unter reduzierter tensiler Verspannung (a1c/a2c) weicht deutlich von üblicherweise beobachteten a1/c/a2/c Domänen ab. Gut ausgeprägte lokale ferroelektrische Hysteresen konnten in nahezu stöchiometrischen Filmen unter geringer kompressiver Verspannung nachgewiesen werden. Damit wurde bestätigt, dass bei Raumtemperatur durch Gitterverspannung eine stabile ferroelektrische Phase in NaNbO3 erzeugt werden kann, welches im relaxierten Zustand antiferroelektrisch ist. Im Fall von KxNa1-xNbO3 lag das Hauptaugenmerk auf der Untersuchung des Zusammenhanges zwischen dem K/Na-Verhältnis und Gitterverspannungen auf der einen und den lokalen piezoelektrischen Koeffizienten auf der anderen Seite. Dabei wurde 2D-Wachstum von voll kompressiv verspannten Filmen gegenüber nahezu stöchiometrischer Film-Abscheidung priorisiert. Die Dicke, bis zu der glatte KxNa1-xNbO3-Schichten abgeschieden werden konnten war deutlich geringer als im Fall von ähnlich verspannten NaNbO3 Filmen. Als alternativer Ansatz wurde die Abscheidung von Übergittern mit alternierenden Schichten unter kompressiver und tensiler Verspannung auf DyScO3 Substraten verfolgt. Auf diese Weise war es möglich sowohl 2D-Wachstum als auch voll kompressiv verspannte Systeme für signifikant dickere Schicht-Stapel im Vergleich zu Einzelschichten zu erreichen. Theoretische Vorhersagen lassen auf exzellente ferro/piezoelektrische Eigenschaften von Übergittern aus zwei ferroelektrischen Materialien schließen. In dieser Arbeit wird gezeigt, dass 2D-gewachsene und voll kompressiv verspannte NaNbO3/K0.5Na0.5NbO3-Übergitter auf DyScO3 Substraten viel versprechende lokale piezoelektrische Eigenschaften haben.

Made available in DSpace on 2013-08-12T19:00:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-10-01 Made available in DSpace on 2013-09-30T18:04:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-10-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T13:26:22Z No. of bitstreams: 0 Made available in DSpace on 2014-05-20T13:26:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-10-01 The absorption edge and the bandgap transition of sol-gel-dip-coating SnO2 thin films, deposited on quartz substrates, are evaluated from optical absorption data and temperature dependent photoconductivity spectra. Structural properties of these films help the interpretation of bandgap transition nature, since the obtained nanosized dimensions of crystallites are determinant on dominant growth direction and, thus, absorption energy. Electronic properties of the bulk and (110) and (101) surfaces are also presented, calculated by means of density functional theory applied to periodic calculations at B3LYP hybrid functional level. Experimentally obtained absorption edge is compared to the calculated energy band diagrams of bulk and (110) and (101) surfaces. The overall calculated electronic properties in conjunction with structural and electro-optical experimental data suggest that the nature of the bandgap transition is related to a combined effect of bulk and (101) surface, which presents direct bandgap transition. State Univ São Paulo UNESP, Adv Mat Grp, BR-17033360 São Paulo, Brazil State Univ São Paulo UNESP, Defects Semicond & Insulators Grp, BR-17033360 São Paulo, Brazil State Univ São Paulo UNESP, Dept Phys FC, BR-17033360 São Paulo, Brazil State Univ São Paulo UNESP, Modeling & Mol Simulat Grp DM FC, BR-17033360 São Paulo, Brazil Fed Univ Minas Gerais UFMG, Lab Nanomat, BR-31270901 Belo Horizonte, MG, Brazil State Univ São Paulo UNESP, Adv Mat Grp, BR-17033360 São Paulo, Brazil State Univ São Paulo UNESP, Defects Semicond & Insulators Grp, BR-17033360 São Paulo, Brazil State Univ São Paulo UNESP, Dept Phys FC, BR-17033360 São Paulo, Brazil State Univ São Paulo UNESP, Modeling & Mol Simulat Grp DM FC, BR-17033360 São Paulo, Brazil

International audience; In this paper, starting from the classical 3D micromagnetic energy, we determine, via an asymptotic analysis, the free energy of two joined ferromagnetic thin films. We distinguish different regimes depending on the limit of the ratio between the small thicknesses of the two films.