Among the many possible applications of laser ablation one of the more recent taken is related to nanosatellites propulsion. The study of Laser Ablation Propulsion (LAP) requires research activity on different fields like high power pulsed lasers, laser ablation itself, because it is still a problem to relate the well known mechanisms to impulse generation, and finally materials that represent the fuel in LAP. This thesis presents a research activity on LAP from its very beginning, with the development of an experimental apparatus to measure laser generated impulse and the first results on metals and polymers that paves the way to the development of future LAP materials. Chapter 1 presents an overview of the actual situation of space economy and its recent fast evolution that led in the last years to the exploitation of space for many different applications, also by private companies. The so called New Space Economy is the background on which LAP develops, as an attractive propulsion technique for nano satellites, nowadays extremely diffused in all kind of space missions, and as a possible solution for the space debris problem. In this Chapter typical results obtained in LAP are also reviewed and compared with other solutions both for space debris and propulsion, in order to obtain a better image of its applicability range. Chapter 2 deals with laser ablation. Initially the parameters that play a role in laser ablation are discussed, in particular those related to the laser source like wavelength, pulse duration and repetition rate, to give an overview of the experimental conditions involved. Then general phenomenological observations on laser ablation are presented and related to the physical mechanisms involved, both in the case of metals and polymers, highlighting the main differences between these two classes of materials. The experimental part of this thesis starts in Chapter 3, with the description of the experimental apparatus developed to measure the laser generated mechanical impulses in the order of uN s. The different strategies to perform this kind of measurements are reviewed and compared to the one adopted in this work, based on a ballistic pendulum, and main advantages and problems are discussed. A technical description of the apparatus is given, focusing in particular on all the precautions that have been taken in order to let the pendulum operate in as ideal as possible conditions. The measurement procedure developed during this work is then described in detail, by discussing data analysis and showing some examples. Chapter 4 also deals with the development of the apparatus, in particular for what concerns the estimation of the laser energy density that reaches the target material (fluence), a fundamental parameter for LAP measurements. Some measurements on metals are also presented here in order to discuss some features related to the measurements of some common LAP parameters. Chapter 5 and 6 deal with LAP using polymers, and in particular with experiments devoted to the understanding of material properties that mainly affect LAP performances. The starting material chosen for these experiments is poly(vinyl chloride)(PVC), a benchmark in LAP experiments. Chapter 5 compares localized or uniform laser absorption by PVC, that can be obtained respectively by including carbon nanoparticles in the polymer matrix or by mixing PVC with an absorbing polymer (poly(styrene sulfonate)). The comparison is carried out from the optical an thermodynamical point of view, along with impulse generation. Specific ablation mechanisms are also discussed, showing that a localized absorption of laser radiation is more energetically efficient for impulse generation. Chapter 6 then continues the work on PVC containing nanoparticles, investigating the role of their size, morphology and concentration in laser ablation and in impulse generation. Both commercial and green produced carbon nanoparticles are used for these experiments showing that, at least in the considered size range, the only parameter that affects laser ablation is the number density of absorption centers in the polymer matrix, and not size or morphology. This points the direction to follow in the development of a polymeric material for LAP applications. Some open problems and future works are presented in Chapter 7. Effects on impulse generated by irradiating multiple times the same region are discussed, showing opposite behaviours between metals and polymers, for which still there is not a clear explanation. Then experimental issues and some results on specific impulse measurements are presented, and difficulties related to this measurement in metals briefly discussed. Finally laser ablation in a confined geometry is considered as an attracting technique to enhance impulse generation. And some results on PVC are shown. As a conclusion, main results obtained in this thesis are highlighted, and possible future research activities, developments and perspectives are discussed.

No / The work presented in this paper contributes to a wider research objective aiming at gaining a better understanding of the injection moulding process at microscales. More specifically, it contributes to the development of a new modelling approach combining experimental observation and mathematical modelling to characterise thermal contact resistance that results from the imperfections present on the surfaces when two surfaces are brought in contact. Thus, this paper describes micro and nano structuring technologies (Focus Ion beam and Laser Ablation) used to structure sapphire inserts that are used as ”windows” in the injection moulding process, allowing thermal measurements with a high speed thermal camera whilst sapphire structures are filled with polymer melt. / The Engineering and Physical Sciences Research Council (EPSRC) under the grant EP/I014551/1 and the Interreg IVB project “ECOefficient LASER technology for FACTories of the future”.

No description available.

<p>Mechanical oscillating drills and saws are used in orthopaedic surgery to cut bone and develop screw-holes; however, their use causes friction resulting in significant thermal damage. Ultrashort pulsed lasers appear well-suited to replace traditional tools as they have the ability to efficiently remove bone tissue while causing only minimal collateral damage. Laser ablation also has the added advantages of: (i) no mechanical vibration; (ii) minimal invasiveness; and (iii) small focus spot size. In this thesis work, we experimentally investigated a few key aspects of ultrashort laser ablation of bone tissue.</p> <p>The ablation threshold of unaltered bone was measured using the <em>D</em>²technique and found to range from 1.66 J/cm²± 0.87 J/cm² to 2.37 J/cm²± 0.78 J/cm² depending on incident pulse number. The reduction in ablation threshold with pulse number was an indication of an incubation effect. Using a power law model, the incubation coefficient, ζ, was measured to be 0.89 ± 0.03.</p> <p>The effect of specific laser parameters and drilling protocols on ablation efficiency was also characterized. For ultrashort pulses (≤10 ps), the removal rate was found to be inversely related to the pulse duration; however, irradiation with 5-10 ps pulses were also shown to result in significant tissue removal. With a pulse repetition rate of 1 kHz, the removal rate was observed to be highest when ablating with 50-100 pulses per spot.</p> <p>Larger volumes (>1 mm³) of bone tissue were removed using laser scanning procedures. A series of scanned concentric circles produced a structure ~2.4 mm deep; however, ablated side-lobes were present at oblique angles to the incident beam. A two-layer structure subsequently produced no side-lobes. The ablative precision in trabecular bone was observed to be less than cortical bone. Using mimicked Nd:YAG laser parameters, cylindrical drilling produced craters significantly less deep than those achieved with a typical Ti:Sapphire configuration. The ability to drill large-scale holes using low average pulse energies and optimized scanning procedures will alleviate the stringent requirements for optical components in clinical practice.</p> / Master of Science (MSc)

This study was divided into two main parts as there were two kind of films studied. The method of deposition, pulsed laser ablation, was common to both SrBi₂Ta₂O₉ and TiO₂ films. The methods of investigations were also the same. There is an important race for the development of a practical ferroelectric memory. Among ferroelectrics that have attracted attention are the novel compounds with the Aurivillius layered structure. Ferroelectric films of SrBi₂Ta₂O₉, seem to have promising properties, low fatigue and good hysteresis. In this thesis, structure and crystal vibrations in the films were investigated with Raman scattering, infrared absorption, and x-ray diffraction. Similar studies were carried out on powders and crystals of these materials also. The results obtained prove that the films have the orthorhombic SrBi₂Ta₂O₉, structure, and the Raman and IR measurements (the first reported for SBT films) are demonstrated to provide valuable tools for optimizing the deposition process. TiO₂ is another important material in the domain of thin films. This work was undertaken to study its deposition with laser ablation. The TiO₂ films deposited are very unusual; we discovered that they contain the rare brookite phase. This is the first time that brookite has been obtained in laser-ablation-deposited films. This opens up a new area in thin film development with new potential applications. The absorption edge of brookite was measured, using natural crystals. The optical bandgap was found to be lower than the bandgaps of the rutile and anatase forms of TiO₂, in contradiction of a recent theoretical calculation. / Master of Science

Eine der bedeutendsten technischen Errungenschaften des letzten Jahrhunderts beinhaltet zweifelsfrei die Erfindung des Lasers. Bereits wenige Jahrzehnte nach seiner ersten technischen Umsetzung ist er heute aus so unterschiedlichen Anwendungsbereichen wie der Mess- und Regeltechnik, der Unterhaltungselektronik, sowie der industriellen Fertigung und Materialbearbeitung nicht mehr wegzudenken. Die analytische Chemie bildet hier keine Ausnahme. Die Möglichkeit mittels Laserstrahlung sowohl räumlich als auch zeitlich definiert einen maßgeschneiderten Energieeintrag in Materialsysteme vorzunehmen, wird heute umfangreich in diversen Analyseverfahren eingesetzt. Ein Meilenstein auf dem Gebiet der Laserentwicklung stellt die Einführung diodengepumpter Festkörperlaser (DPSS) dar. Diese neuartige Lasergeneration vereint die Vorteile einer begünstigten Energiebilanz durch resonante Anregung im Lasermedium mit einer erhöhten Flexibilität der zeitlichen Modulation der Laserausgangsleistung. Während DPSS Laser auf dem Gebiet der Materialbearbeitung bereits die Hälfte des Marktanteils ausmachen, finden sie bislang in den analytischen Wissenschaften nur wenig Verbreitung. Auch hier könnten die inhärenten Vorteile von DPSS Lasern bezüglich Konversionseffizienz, Stabilität, Flexibilität und Strahlprofil maßgeblich zu einer Optimierung relevanter Teilschritte beitragen. Die vorliegende Arbeit schließt diese Lücke, indem sie die Anwendbarkeit eines modernen DPSS Lasers für solch unterschiedliche Aufgaben wie der Laserablation, der Raman-Spektroskopie, der atomaren und molekularen Emissionsspektroskopie, bis hin zur Erzeugung eines neuartigen quasi-kontinuierlichen, luftgetragenen Plasmas für die Atmosphärendruck-Ionisation untersucht. In allen Studien konnten die Verbesserungen der jeweiligen analytischen Verfahren auf die Eigenschaften des verwendeten Lasers zurückgeführt werden. / Without any doubt, one of the most momentous technical achievements of the last century has been the invention of the laser. Today, merely some decades after its first technical realization, the laser has established a leading role in such broad application fields as sensing and control engineering, consumer electronics, as well as industrial production and materials processing. Analytical chemistry does not make an exception. The possibility of both spatially and temporally well-confined introduction of precisely dosed and defined energy into any material is nowadays widely exploited in a plethora of analytical techniques. A milestone in the field of laser technology was the advent of diode-pumped solid-state (DPSS) lasers. This new generation of laser systems combines the benefits of an advantageous energy balance, caused by resonant excitation of the laser medium, with an enhancement in flexibility in terms of modulation of the laser output. While DPSS lasers already account for half of the devices used in materials processing, the dissemination in the analytical sciences has so far hardly occurred. Also here, the inherent advantages of DPSS lasers regarding efficiency, reliability, flexibility, and beam profile could greatly contribute in a multitude of analytically relevant sub-steps. This thesis closes this gap by studying the applicability of a current state-of-the-art DPSS laser for as different tasks as laser ablation, Raman spectroscopy, atomic and molecular emission spectroscopy, all the way to generating a generally new quasi-continuous airborne plasma for ambient ionization. In all cases studied, the improvement of the respective analytical techniques could be ascribed to the intrinsic properties of the used laser.

Die chemische Zusammensetzung pharmazeutisch verwendeter Gläser (Ampullen, Infusionsglas, Fertigspritzenbehältnisse) wurde mit Laser-Ablation-ICP-Massenspektrometrie (LA-ICP-MS) untersucht. Dazu kam ein Nd:YAG-Laser mit einer Frequenz von 10 Hz im q-switch mode mit der Grundwellenlänge sowie der 4. Harmonischen (1064 und 266 nm) zum Einsatz. Ziel war die Identifizierung verschiedener Arten pharmazeutisch eingesetzter Gläser. Folgende Isotope wurden zur Charakterisierung bestimmt: 7Li, 11B, 23Na, 24Mg, 27Al, 28Si, 29Si, 30Si, 39K, 42Ca, 47Ti, 57Fe, 90Zr, 121Sb, 137Ba. Die quantitativen Ergebnisse zeigten relative Standardabweichungen von 1.8 % bis 8.0 %. Die Normierung der Daten erfolgte unter Bezug auf 29Si. Mit Referenzmaterial verschiedener Zusammensetzung (Natron-Kalk-Glas, Borosilikatglas und Bleiglas) wurden externe Mehrpunktkalibrationen erstellt. Für alle gemessenen Isotope konnten lineare Kalibrierfunktionen festgestellt werden. Die Richtigkeit des Verfahrens wurde durch Aufschluß des Standardmaterials wie auch der untersuchten Proben mit Flußsäure/Salpetersäure und Messung der Aufschlußlösungen nach externer Kalibration durch Multielement-Standards gezeigt. Aufschluß- und Laserablation-Ergebnisse zeigten gute Übereinstimmung und wichen um bis zu 8 % voneinander ab. Zur Prüfung repräsentativer Ablation der Proben wurden die Isotopenverhältnisse bestimmt. Auch hier zeigte sich eine ausreichende Übereinstimmung mit den theoretischen Werten. Weiterhin wurden Präzision, Empfindlichkeit, Selektivität, Nachweisgrenze, Bestimmungsgrenze und Robustheit des Verfahrens bestimmt. Im Unterschied zu den Ergebnissen unter der Grundwellenlänge führte die Verwendung der Laserwellenlänge 266 nm zu keinen signifikanten Verbesserungen der Resultate. Die Aufnahme transienter Signale sollte zur Erkennung von Elementverteilungen in Glasoberflächen dienen. Am Beispiel eines Natron-Kalk-Glases wurden in einzelnen Schichten verschiedene Elementkonzentrationen festgestellt. Weiterhin konnten mit dieser Technik Glasampullen erkannt werden, deren Oberflächen durch ein Silikonisierungsverfahren vergütet waren. Zum Abschluß der Untersuchungen wurde versucht, auf Grundlage der unnormierten Intensitätsdaten der LA-Messungen Gläser zu klassifizieren. Hierzu wurde die lineare Diskriminanzanalyse eingesetzt, mit deren Hilfe nach Variablenreduktion (8 von 13 Isotopen) alle eingesetzten Glasarten korrekt identifiziert werden konnten. Durch das entwickelte und validierte LA-ICP-MS-Verfahren steht eine leistungsfähige Technik zur quantitativen Untersuchung der chemischen Zusammensetzung von Gläsern sowie zur Identifizierung der jeweiligen Glassorte zur Verfügung. / The chemical composition of pharmaceutical glasses (ampoules, infusion bottles, plunger) has been determined by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). A Nd:YAG laser with 10 Hz repetition rate in the q-switch mode at its fundamental wavelength and its 4th harmonic (1064 and 266 nm) was used to identify common types of pharmaceutical glasses. The following isotopes were used for measurements: 7Li, 11B, 23Na, 24Mg, 27Al, 28Si, 29Si, 30Si, 39K, 42Ca, 47Ti, 57Fe, 90Zr, 121Sb, 137Ba. Relative standard deviations between 1.8 % and 8.0 % of the quantitative results were obtained. 29Si was used as internal standard. Standard reference materials (soda-lime-, lead- and borosilicate glasses) were used for external calibration of laser sampling. Linear calibration functions for each isotope were found. The accuracy was determined by digestion of all samples and standard materials in a two-step-procedure by nitric/fluoric acid, measurement and external calibration by ICP-MS with multi-elemental standard solutions. Digestion and laser ablation results agreed within 8 % with the certified values. The proof of representative ablation was given by sufficient agreement of intensity ratios of most isotopes with the corresponding theoretical values. Further precision, sensititivity, selectivity, limit of detection, limit of quantitation and robustness were determined. In contrast to the fundamental wavelength the laserablation technique with 266 nm showed no significant improvement in the quality of the results. By measuring transient signals element concentrations of surface layers should be detected. Differing concentrations could be determined in soda-lime-glass samples. Also different surface-treated borosilicate-glass ampoules were examined by this method. Silicon-treated glass surfaces could be identified. Finally raw data of LA measurements were used for applying linear discriminant analysis. After reduction of the used variables (8 of 13 isotopes) all types of glasses could be distinguished only by their intensity data of LA measurements. The developed LA-ICP-MS method is a powerful technique to distinguish different types of pharmaceutical glasses and to examine their chemical composition.

The present research work mainly focuses on fabrication of compositionally modulated multilayers of (l−x) Pb(Mgi/3N2/3)O3 - x PbTiO3 (PMNPT) through multi target pulsed laser ablation technique. Heterostructures like compositionally varying multilayers; multilayers with graded interface and a ferroelectric [PbTiO3 (PT)] and relaxor (PMN) superlattices of different periodicities were fabricated. Role of artificially enhanced chemical heterogeneity and strain on enhancement of physical property was studied. Dimensional dependent ferroelectric and antiferroelectric type of polarization behavior was observed in the case of both compositionally varying multilayers and the superlattice structures fabricated. The dimensional dependence of various ferroelectric interactions like long-range, short-range and interfacial coupling among the layers was studied. The phase transition behavior and dielectric studies were carried out on these heterostructures. An artificial superlattice of a relaxor ferroelectric with a ferromagnetic layer was also fabricated for magnetoelectric applications. Chapter 1 provides a brief introduction to ferroelectric (FE) heterostructures, their technological applications and the fundamental physics involved in ferroelectric heterostructures. Initially an introduction to the technological importance and advantages of ferroelectric heterostructures is provided. A brief introduction to relaxor ferroelectrics and their characteristic structural features are discussed. A brief review of the ferroelectric heterostructures both from fundamental science and technological point of view is provided. Finally the specific objectives of the current research are outlined. Chapter 2 deals with the various experimental studies carried out in this research work. It gives the details of the experimental set up and the basic operation principles of various structural and physical characterizations of the materials prepared. A brief explanation of material fabrication, structural, micro structural and physical property measurements is discussed. Chapter 3 addresses the problem of phase formation of PMNPT over platinum substrates and the role of the template over the phase formation, micro structural evolution and polarization behavior. The surface modifications of bare Pt under the processing conditions used to fabricate PMNPT was also studied. An intermediate roughening mechanism was observed. The role of LSCO over the micro structural evolution of PMNPT, the minimum thickness of LSCO required for phase formation of PMNPT, role of LSCO on phase formation and its effect on the polarization behavior of PMNPT of constant thickness are discussed. Chapter 4 deals with fabrication of different types of relaxor based heterostructures studied in this work. Three different types of PMNPT based heterostructures was fabricated using a multi target laser ablation chamber. The first type of heterostructure is a compositionally modulated multilayer thin film with four different compositions of (1-x) PMN - x PT (x = 0.0, 0.1, 0.2, 0.3 at.%) and is represented as PMNPT multilayer (ML) further in this thesis. PMNPT ML with different individual layer thickness was fabricated (30, 40, 60, 80, 100 and 120 nm). The second type of heterostructure is the PMNPT ML of same dimensions, but associated with a post deposition annealing to achieve a graded interface between the multilayers present and will be named as PMNPT graded or simply graded, further in this thesis. The third type of heterostructure is an artificial superlattice of a simple relaxor ferroelectric (PMN) and a normal ferroelectric (PT), which will be named as PMN-PT superlattice (SL) further in this thesis. The crystallinity, micro structural features and the nature of the interface present in the fabricated heterostructures were studied using various experimental techniques. Chapter 5 deals with the FE studies of compositionally modulated PMNPT ML thin films and PMNPT graded thin films. The ML with individual layer thickness of 120nm exhibited a clear FE behavior but with a reduced remnant polarization and reduced non linear behavior in capacitance - voltage (C-V) characteristics. But on varying the dimensions of the individual layers (30, 40, 60, 80, 100 and 120nm) a large dielectric tunability of around 74% was observed at lOOnm. The polarization behavior of these ML exhibited an interesting size dependent polarization behavior. A FE behavior was observed at low dimensions of 40 and 30nm. An AFE type of loop was observed at 60 and 80nm of individual layer thickness and at lOOnm it showed a clear paraelectric kind of behavior both in polarization hysteresis (P-E) and C-V studies. Graded films exhibited clear FE behavior at all dimensions fabricated and hence the role of interface in developing a critical polarization behavior in the case of ML was confirmed. Apart from the fundamental physics these ML and graded films permits the tunability of their physical properties on just varying the individual layer thickness. The dimensional dependence of dielectric tunability of ML and graded films were studied and it was found that in the case of a ML the dielectric tunability was high at lOOnm individual layer thickness and at 40nm in the case of a graded film. Thus the interfacial strain, interfacial coupling and chemical heterogeneity give an opportunity to engineer the physical property depending on the requirements. Chapter 6 deals with ferroelectric studies (P-E, C-V) of PMN-PT superlattice structures with different periodicities. The dimensional range in which, the interfacial coupling dominates the overall polarization behavior of the system was analyzed. A dimensional dependent FE and AFE behavior was observed in the PMN-PT SL structures. The dimensional dependent tunability of physical properties was achieved. The different interactions like short range, long range and the interfacial coupling and their dimensional dependent behavior was studied. The dimensional dependent tunability of the P-E and C-V behavior was observed both in symmetric and asymmetric SL structures. Chapter 7 deals with the relaxor behavior of the fabricated PMNPT ML, graded and PMN-PT SL structures. The dielectric phase transition of a PMNPT ML exhibited local maxima in the real part of dielectric constant with temperature. The local maxima correspond to the temperature regime at which, the individual layer dielectric maxima dominates the phase transition behavior of the ML structure. In the case of graded films an averaged behavior of all the compositions, with an enhanced diffusivity was observed. All the characteristic features of a relaxor ferroelectric were observed in the phase transition behavior of a graded thin film. The dielectric maxima exhibited a Vogel-Fulcher type of behavior with frequency, A similar averaged behavior was observed in the phase transition behavior of PMNPT ML at low dimensions (< 40 nm) of the individual layer. The dielectric phase transition behavior of PMN-PT SL structures of different periodicities was studied. No characteristic of a relaxor ferroelectric was observed for the periodicities in the range of 10 to 50 nm. At 60 nm periodicity the individual layer dominance was observed in the phase transition behavior of the SL structure. The phase transition behavior was found to be insensitive to the interfacial coupling in both the PMNPT ML and PMN-PT SL. Chapter 8 deals with the dielectric response, impedance spectroscopy and the DC leakage characteristics of the relaxor heterostructures. All the relaxor heterostructures fabricated, exhibited low frequency dispersion, similar to that of the Jonscher's universal type of relaxation behavior. The anomalous dispersion common of a relaxor ferroelectric was observed in the imaginary dielectric constant at high frequencies. A.multi debye type of relaxation behavior was observed in the impedance analysis and the relaxation time was found to obey Vogel-Fulcher type of relation with temperature. The leakage current of all the heterostructures were found to be few orders less than the homogeneous single layer thin films. A space charge limited conduction was observed in all the heterostructures fabricated. Chapter 9 deals with an attempt of realizing the magnetoelectric effect in an artificial superlattice structure consisting ferromagnetic [Lao.6Sro.4Mn03 (LSMO)] and ferroelectric (PMNPT 70-30) layers. Both symmetric and asymmetric SL structures were fabricated and the asymmetric SL exhibited both room temperature ferromagnetic and ferroelectric behavior. A weak influence of magnetic field over the polarization behavior was observed. The magnetic behavior and its influence over electrical behavior were found to be dominated by the interface and were confirmed from the Maxwell-Wagner type of relaxation. Chapter 10 gives the summary and conclusions of the present study and also discusses about the future work that could give more insight into the understanding of the relaxor heterostructures.

Fabrication of artificially structured superlattices, when controlled on a nanoscale level, can exhibit enhanced dielectric properties over a wide temperature range. Possible fabrication of new functional devices based on the parametric values of dielectric constants of these heterostructures was the major motivation behind the work. Chapter 1 gives a brief overview of ferroelectrics; their defining features and their commercial importance to electronic industry. An introduction to ferroelectric superlattices, their technological application and fundamental physics that influence the behavior of superlattices are provided. Chapter 2 deals with the various experimental studies carried out in this research work. It gives the details of the experimental set up and the basic operation principles of various structural and physical characterizations of the materials prepared. A brief explanation of material fabrication, structural, micro structural and physical property measurements is discussed. Chapter 3 involves fabrication of two-component ferroelectric superlattices consisting of Barium Titanate (BTO), and Strontium Titanate (STO) with nanoscale control of superlattice periodicities by high-pressure multi target pulsed laser deposition on Pt (111)/Ti/SiO2/Si (100) substrate. Superlattices with varying periodicities were fabricated and their compositional variation across the thin film and the interface width were studied using Secondary Ion Mass Spectrometry (SIMS). Fabrications of superlattice structure were supported by observation of satellite peaks in XRD corresponding to the coherent heterostructures. The microstructural analysis was carried out using cross-sectional scanning electron microscopy (SEM), and contact mode-AFM was used to image surface morphology and root-mean-square (rms) roughness of the thin film heterostructure. Chapter 4 deals with ferroelectric studies of BTO/STO superlattices. The size dependent polarization behaviors of the superlattices are shown. The experimental realization of the dimensional range in which, the long-range coupling interaction dominates the overall polarization behavior of the system was studied. The dependence of average spontaneous polarization on the individual layer thickness, temperature and the dimensional range of interaction are discussed. The enhanced non-linear behaviors of the films were measured in terms of tunability. The dielectric phase transition behavior of superlattice structures of different periodicities was studied. Chapter 5 focuses on fabrication of three-component ferroelectric superlattices consisting of Barium Titanate (BTO), Calcium Titanate (CTO) and Strontium Titanate (STO). The fabrications of superlattice structures were confirmed by the presence of satellite reflections in XRD analysis and a periodic concentration of Sr, Ba and Ca throughout the film in Depth profile of SIMS analysis. The microstructural analysis was carried out using cross-sectional scanning electron microscopy (SEM), and contact mode-AFM was used to image surface morphology and root-mean-square (rms) roughness of the thin film heterostructure. The dielectric characteristic and polarization properties of the system are discussed. Large variations of lattice distortion in the consisting layers were achieved by varying the stacking sequence and superlattice periodicity. The influence of interfacial strain on enhancement of ferroelectric polarization was studied. The size dependence and the role of interfaces in the observed enhancements of the dielectric behaviors were highlighted. The tunability of about 55% was achieved in these systems and was higher than any of the single polycrystalline thin film of the constituent materials reported till date. The enhanced dielectric properties were thus discussed in terms of the interfacial strain driven polar region due to high lattice mismatch and electrostatic coupling due to polarization mismatch between individual layers. Chapter 6 deals with the dielectric response, impedance spectroscopy and the DC leakage characteristics of the superlattice structures. All the heterostructures fabricated, exhibited low frequency dispersion, similar to that of the Jonscher’s universal type of relaxation behavior. The anomalous dispersion was observed in the imaginary dielectric constant at high frequencies. A Debye type relaxation behavior was observed in the impedance analysis at low temperatures, whereas, a departure from ideal ‘Debye’ type was noticed as the temperature was increased. The leakage currents of all the heterostructures were found to be a few orders less than the homogeneous single layer thin films. A space charge limited conduction was observed in al the superlattice structures fabricated. Chapter 7 summarizes the present study and discusses about the future work that could give more insight into the understanding of the ferroelectric perovskite heterostructures.

Lo scopo della tesi è di caratterizzare i rischi per la salute umana, che derivano dall’inquinamento delle acque (acque sotterranee) e dal cibo (riso) tramite l’applicazione e lo sviluppo di nuove tecniche analitiche. La tecnica “diffusive gradients in thin films (DGT)” con resina a base di ferrihydrite, è stata studiata per l'accumulo delle forme inorganiche (As(III) e As(V)) e organiche (DMA(V) e MMA(V)) di Arsenico in matrici acquose. I DGT sono stati applicati su campioni di acque sotterranee, raccolti in sei diverse città del Nord Italia, dove la concentrazione di As è molto alta. Antimonio (Sb) è associato all’As in diversi studi perché le proprietà fisiche e chimiche di questi due elementi sono simili, ed esso è stato recentemente riconosciuto come contaminante dell'acqua. In questa tesi per la prima volta sono state riportate le prestazioni dettagliate dei DGT con ferrihydrite, impiegati in soluzioni acquose di Sb(III) e Sb(V). L’analisi delle forme chimiche di Sb(III) e Sb(V) in campioni acquosi è stata realizzata con l’applicazione della diluizione isotopica. In generale il riso, a differenza di altri prodotti alimentari di origine terrestre, contiene quantità significative di Arsenico inorganico. L’analisi della speciazione di As è stata realizzata in 70 campioni di riso italiano, rappresentativo di diversi tipi di coltivazione. Le forme più abbondanti nel riso erano As(III) e DMA(V). Inoltre è stato interessante studiare la localizzazione dell’As nel chicco di riso, sottoposto a diversi processi di lavorazione (risone, riso integrale e lavorato con o senza parboiling), perché sia la distribuzione che la presenza delle diverse forme chimiche nel chicco sono fattori chiave che controllano la biodisponibilità del contaminante. La distribuzione dell’ As nei chicchi di riso di due varietà (Gladio e Ronaldo) sottoposti a diversi processi, è stato determinato con Laser Ablation ICP-MS. In realtà il contenuto di As era più alto nei chicchi di riso non-parboiled rispetto a quello parboiled. La relazione tra intensità dell’As e le varie parti del chicco di riso ha rivelato che i livelli di As diminuisco dalla parte esterna verso la posizione centrale, mentre i valori di As sembrano essere simili tra la parte media e interna dei non parboiled. / The aim of this thesis was to explore new analytical techniques as well as to carry out further characterisations of human health risks, which derive from water pollution, in particular groundwater, and food, in particular rice. The prevention of water pollution is an environmental aspect, that includes monitoring of both natural enrichment and outside pollution with routine analysis but also with new techniques, e.g. the application of passive sampling techniques and advanced technologies. The diffusive gradients in thin films (DGT) technique with ferrihydrite adsorbent, has been investigated for the accumulation of different species of Arsenic (As), like Inorganic Species (arsenite and arsenate) and Organic Arsenic (dimethylarsinic and monomethylarsenate) in aqueous matrix. To evaluate the performance of DGT method for accumulation of arsenic species, after deployment in synthetic solutions, DGT devices were carried out on groundwaters collected in six different towns in the North of Italy, where the As concentration is very high. Recently, health effects at arsenic exposures have been observed in areas where levels of inorganic As in drinking water are not excessive. Antimony (Sb) is associated to As in several studies because the physical and chemical properties of these two elements are similar, and it has been recently recognized as water contaminant. In this thesis I reported for the first time detailed performance characteristics of the Fe-oxide gel associated to DGT devices deployed in known aqueous solutions of trivalent and pentavalent Sb. Speciation analysis of Sb(III) and Sb(V) in aqueous samples was performed through extraction and on-line determination of isotope dilution concentration after a chromatographic separation. Generally rice, unlike food products of terrestrial origin, contains significant amounts of inorganic arsenic. Recently some Government Organizations (e.g. EFSA) debated the possibility to set an upper limit for total and inorganic arsenic in rice. Arsenic speciation was realized in 70 Italian rice samples from different representative cultivation conditions. The most abundant forms in rice were As(III) and DMA(V). After that, it was fundamental to investigate the localization of As in rice grains in different processes (raw, brown and milled rice with or without parboiling technique), because both speciation and distribution throughout the grain are key factors controlling bioavailability of the contaminant. The As distribution in rice grains of two varieties (Gladio and Ronaldo) from different processes, was determined by LA-ICP-MS. The distribution of As varied between the various parts of the grains (exterior, medium and interior part). During parboiling, the partial boiling of food as the first step in the cooking process, arsenic might have released from the grain to the boiling water. Thus, parboiling of rice grain may reduce the magnitude of arsenic intake in human body. Actually the As content was higher in non-parboiled rice grain than in parboiled rice. The relationship between As intensities and the different parts of rice grain revealed that As levels decreased from the external part towards the middle position, and then the intensity values seem to be similar between medium and internal part in non parboiled products.