Conventional computing faces a huge technical challenge as traditional transistors will soon reach their size limitations. This will halt progress in reaching faster processing speeds and to overcome this problem, require an entirely new approach. Quantum computing (QC) is a natural solution offering a route to miniaturisation by, for example, storing information in electron or nuclear spin states, whilst harnessing the power of quantum physics to perform certain calculations exponentially faster than its classical counterpart. However, QCs face many difficulties, such as, protecting the quantum-bit (qubit) from the environment and its irreversible loss through the process of decoherence. Hybrid systems provide a route to harnessing the benefits of multiple degrees of freedom through the coherent transfer of quantum information between them. In this thesis I show coherent qubit transfer between electron and nuclear spin states in a ¹⁵N@C₆₀ molecular system (comprising a nitrogen atom encapsulated in a carbon cage) and a solid state system, using phosphorous donors in silicon (Si:P). The propagation uses a series of resonant mi- crowave and radiofrequency pulses and is shown with a two-way fidelity of around 90% for an arbitrary qubit state. The transfer allows quantum information to be held in the nuclear spin for up to 3 orders of magnitude longer than in the electron spin, producing a ¹⁵N@C₆₀ and Si:P ‘quantum memory’ of up to 130 ms and 1.75 s, respectively. I show electron and nuclear spin relaxation (T₁), in both systems, is dominated by a two-phonon process resonant with an excited state, with a constant electron/nuclear T₁ ratio. The thesis further investigates the decoherence and relaxation properties of metal atoms encapsulated in a carbon cage, termed metallofullerenes, discovering that exceptionally long electron spin decoherence times are possible, such that these can be considered a viable QC candidate.

Les matériaux ferroélectriques suscitent beaucoup d’intérêt du fait de leurs propriétés physiques telles que la piézoélectricité, la ferroélectricité ou encore leur permittivité élevée. Ainsi, on cherche à les intégrer dans les micro- et nano-systèmes dans lesquels on les retrouve généralement sous forme de couche mince dans une configuration de type capacité plane. En particulier, l’oxyde de plomb, titane et zirconium (PZT) est un matériau très attractif pour les applications RF capacitives du fait de sa grande permittivité. Son intégration sur des électrodes métalliques, i.e. les lignes coplanaires constituant le guide d’onde, implique de maîtriser sa croissance en film mince. L’application d’une tension dans un dispositif RF actif impose également de contrôler les propriétés électriques : nature des courants de fuite et comportement ferroélectrique du PZT. Dans ce contexte, les couches minces de PZT sont déposées par ablation laser (PLD) sur un empilement La₀.₆₇Sr₀.₃₃MnO₃ (LSMO) / Pt (111) déposé sur un substrat monocristallin de saphir. La couche d’accroche conductrice LSMO est nécessaire afin d’éviter la formation d’une phase pyrochlore paraélectrique. Le contrôle de l’orientation cristalline de la couche de LSMO permet de contrôler la texturation de la couche de PZT. Les courants de fuite au travers de l’empilement Pt/PZT/LSMO/Pt ont ensuite été étudiés dans l’intervalle de température 220-330K de façon à déterminer les mécanismes de conduction. Une transition a été mise en évidence entre, autour de la température ambiante, un mécanisme contrôlé par la diffusion des charges en volume et, à basse température, un mécanisme contrôlé par l’injection des charges aux interfaces électrode/PZT. Un mécanisme par sauts a été identifié au-dessus de 280K en cohérence avec la présence de défauts étendus et la structure colonnaire du PZT. Afin de contrôler ces courants de fuite, différentes stratégies ont été utilisées. La première consiste à insérer une couche d’oxyde isolante à l’interface supérieure Pt/PZT modifiant ainsi l’injection des charges et permettant de réduire les courants de fuite. La seconde stratégie consiste, quant à elle, à modifier la structure de la couche de PZT en volume en élaborant des composites diélectrique/PZT multicouches ou colonnaires. Ainsi, une couche d’oxyde isolante a été insérée au milieu de la couche de PZT et a permis de réduire les courants de fuite. Le contrôle de la nucléation du PZT a également permis par nanofabrication d’élaborer un composite colonnaire pérovskite PZT/pyrochlore. La densité de piliers de pyrochlore dans la phase ferroélectrique permet de moduler la densité de courant dans la structure. Le PZT et les hétérostructures permettant de réduire les courants de fuite ont ensuite été intégrés dans une structure RF capacitive avec des lignes coplanaires d’or. Les performances RF en termes d’isolation et de pertes par insertion ainsi que la compatibilité de ces différents matériaux ont été étudiées et ont montré que les solutions développées dans le cadre du contrôle des courants de fuite sont prometteuses pour être intégrées dans les dispositifs RF capacitifs. En outre, on a cherché à extraire la permittivité à haute fréquence du PZT lorsque celui-ci est inséré dans une structure capacitive. Cette étude a notamment permis de mettre en évidence les points techniques à modifier concernant la structure du dispositif afin de parvenir à exploiter les propriétés physiques du PZT à haute fréquence. / Ferroelectric materials are raising a lot of interest due to their physical properties such as piezoelectricity, ferroelectricity or high dielectric constant. Thus, they are generally integrated in micro- and nano-systems as thin films in a capacitive configuration. Especially, the lead zirconate titanate oxide (PZT) is an attractive material for capacitive RF applications due to its high dielectric constant. The growth of the PZT thin film has to be controlled on metallic electrodes for its integration on coplanar transmission lines. Moreover, electrical properties such as leakage current and ferroelectric behavior of PZT have to be monitored upon application of a dc voltage bias for RF device operation. In this context, PZT thin films were grown by the pulsed laser deposition technique (PLD) on a La₀.₆₇Sr₀.₃₃MnO₃ (LSMO) / Pt (111) electrode on a monocrystalline sapphire substrate. The LSMO buffer layer is mandatory to avoid the formation of the paraelectric pyrochlore phase. The control of the crystalline orientation of the LSMO layer allows for the control of the PZT layer texture. Leakage currents through the Pt/PZT/LSMO/Pt stack were then studied in the 220-330K temperature range to determine the conduction mechanisms. A transition is evidenced between a bulk-controlled mechanism near room temperature and an interface-controlled mechanism at low temperature. A hopping mechanism is identified above 280K in line with the presence of extended defects and the columnar structure of the PZT layer. Several strategies were tested to control leakage currents. The first one consists in inserting an insulating oxide layer at the top Pt/PZT interface. In this way, charge injection was modified and leakage currents were reduced. The second strategy consists in changing the PZT layer bulk structure by elaborating a layered or columnar dielectric/PZT composite. Thus, an insulating oxide layer was inserted in the middle of the PZT layer and permitted to reduce leakage currents. Moreover, the control of the PZT nucleation allowed for the elaboration of a columnar PZT/pyrochlore composite. The leakage currents in this composite can be tuned through the pyrochlore pillars density among the ferroelectric matrix. Then, PZT and the heterostructures for leakage current control were integrated in a capacitive RF structure with gold coplanar transmission lines. RF performances in terms of isolation and insertion loss of these materials were studied and gave good results. In particular the heterostructures developed to control the leakage currents are promising for their integration in capacitive RF devices. Besides, I tried to extract the permittivity of PZT at high frequency with the PZT layer in a capacitive configuration. This study highlighted the essential modifications of the capacitive structure that have to be made in order to be able to exploit PZT properties at high frequency.

The present research work mainly focuses on the fabrication and characterization of single and multilayer thin films based on Bismuth Vanadate (BVO) and Bismuth Titanate (BTO). The multi-target laser ablation technique was used to fabricate single layer thin films of BVO, BVN and BTO; and multilayers composed of BVO and BTO in different structures. The fabricated thin films exhibited dense microstructure and a sharp interface with the substrate. The lattice strain, surface roughness and grain size could be varied as functions of composition and individual layer thickness in different structure fabricated. The optical properties were studied by spectroscopic ellipsometry and optical transmission spectra. The various models that were used for ellipsometric data analysis gave an excellent fitting to the experimental data. The optical constants were determined through multilayer analyses of the films. The band gap of these films was studied by spectroscopic ellipsometry and optical transmission. The optical studies carried out on BVO-BTO bilayer indicated the presence of an interfacial layer in between the BVO and BTO layer, whose refractive index was different from that of the individual layers and is attributed to different nature of the interfacial layer. The ferroelectric nature of BVO films was confirmed by P-E hysteresis loop studies under different applied fields and at various probing frequencies. The same was corroborated via the C-V measurements of these BVO films which exhibited butterfly shaped C-V characteristics. Fatigue studies in these films indicated that the switchable polarization is essentially constant through 105 cycles, after which it starts increasing probably due to the ionic conduction in BVO thin films. The dielectric response of undoped and Nb doped BVO as well as BVBT ML thin films were studied over a wide range of temperatures. The BVO films exhibited remarkable dielectric dispersion at low frequencies especially in the high temperature regime. Further, the frequency and temperature dependence of the dielectric, impedance, modulus and conductivity spectra of these films were investigated in detail. The ac conductivity was found to obey well the double power law in case of ML, indicating the different contributions to the conductivity, the low frequency conductivity being due to the short range translational hopping and the high frequency conductivity is due to the localized or reorientational hopping motion. DC leakage conduction in BVO, BVN and BVBT ML thin films was studied over a wide range of temperatures and applied electric fields. The experimental data were analyzed in light of different models to investigate the dc conduction mechanism in these films which were broadly classified into electrode limited and bulk limited conduction processes. In the case of BVO thin films the dc leakage current exhibited an ohmic nature at low electric fields followed by an onset of the space charge limited conduction (>1). Further in case of BVN films, three distinct regions were observed in I-V characteristics signifying different types of conduction processes in these films. In case of BVBT ML thin films, bulk limited PF mechanism was found to determine the conduction behavior at moderate electric fields. At higher electric fields, a trap filled region was observed which was followed by SCL conduction at higher fields. Therefore the present observation indicates the presence of more than one bulk limited conduction process in BVBT ML thin films. BVO thin films exhibiting good structure and dense morphology were successfully prepared on p-type Si by chemical solution decomposition technique. The C-V characteristics were evaluated for Au/BVO/Si MFS structure which showed a typical high frequency feature of a conventional MFIS structure.

Semi conductors are of technological importance and attracted many of the re-searchers. ZnO belongs to the family of II-VI semiconductors and has material properties well suitable to UV light emitters, varistors, Schottky diodes, gas sensors, spintronics, ferroelectric devices and thin film transistors. It has been considered as a competitor to GaN, which belongs to the family of III-V semiconductors. This is due to the fact that ZnO of high quality can be deposited at lower growth temperatures than GaN, leading to the possibility of transparent junctions on less expensive substrates such as glass. This will lead to low-cost UV lasers with important applications in high-density data storage systems etc. One of the most popular growth techniques of ZnO is physical sputtering. As compared to sol-gel and chemical-vapor deposition, the magnetron sputtering is a preferred method because of its simplicity and low operating temperatures. Hence, detailed investigations were carried out on undoped and doped ZnO thin films primarily deposited by magnetron sputtering. The obtained results in the present work are presented in the form of a thesis. Chapter 1: A brief discussion on the crystal structure of ZnO material and its possible applications in the different areas such as Schottky diodes, spintronics, ferroelectric devices and thin film transistors are presented. Chapter 2: This chapter deals with various deposition techniques used in the present study. It includes the magnetron sputtering, thermal oxidation, pulsed-laser ablation and sol-gel technique. The experimental set up details and the deposition procedures are described in detail i.e., the deposition principle and the parameters that will affect the film properties. A brief note on the structural characterization equipments namely, X-ray diffraction, scanning electron microscopy, atomic force microscopy, transmission electron microscopy and the optical characterization equipments namely, transmission spectroscopy is presented. The transport properties of the films were studied which include Dielectric studies, impedance studies, device characterization and are discussed. Chapter 3: The optimization of ZnO thin films for Schottky diode formation and The characterization of various Schottky diodes is presented in this chapter. P-type conductivity in ZnO was implemented by the variation of partial pressure of oxygen during the sputtering and are discussed. A method to achieve low series resistance hetero-junction was achieved using thermal oxidation method and the detailed transport properties were studied. The optical investigation carried out on the ZnO thin films under various growth conditions are also presented. Chapter 4: This chapter deals with the processing, structural, electrical, optical and magnetic properties of Mn doped ZnO thin films grown by pulsed laser ablation. Structural investigations have shown that the Mn incorporation increases the c-axis length due to the relatively larger ionic size of the Mn ions. Studies conducted both at low and high concentration region of Zn1¡xMnxO thin films showed that the films are anti-ferromagnetic in nature. The transport measurements revealed that the electrical conductivity is dominated by the presence of shallow traps. Optical investigations suggested the absence of midgap absorption and confirm the uniform distribution of Mn in wurtzite structure. Chapter 5: Carrier induced ferromagnetism in Co doped ZnO thin films were studied and the results are presented in this chapter. High density targets were prepared by solid state reaction process and the thin films were deposited by pulsed laser ablation technique. Two compositions were studied and it was found that with increase in substrate temperature, c-axis length decreases. Optical studies suggested a strong mid gap absorption around 2eV and could be attributed to the d-d transitions of tetrahedral coordinated Co2+. The presence of ferromagnetism in these films makes them potential candidates for spintronics applications. Chapter 6: It has been reported in literature that o®-centered polarization will drive ferroelectric phase transition. Motivated by such results, substitution of Lithium in ZnO was studied in detail. The structural and electrical properties were investigated over a wide range of composition (0-25%). The ferroelectric studies were carried out both in metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) configuration and are presented in this chapter. The appearance of Ferro electricity in these films makes them potential candidates for ferroelectric memory devices. Chapter 7: This chapter describes the studies conducted on Mg doped ZnO Thin films grown by multi-magnetron sputtering. The hexagonal phases of the films were evaluated. All the films exhibited c-axis preferred orientation towards (002) orientation. Micro structural evolutions of the films were carried out through scanning electron microscopy and atomic force microscopy. Ferroelectric properties were investigated in both metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) configurations. It was observed that the Mg concentration increases the band gap and the details on optical investigations are also presented in this chapter. Chapter 8: ZnO based thin film transistors have been fabricated and characterized using ZnO as active channel layer and Mg doped ZnO as dielectric layer. Excellent leakage properties of the gate dielectric were studied and presented in this chapter. These studies demonstrated that Mg doped ZnO thin films are suitable candidates for gate dielectric applications. Conclusions: This section presents the conclusions derived out of the present work. It also includes a few suggestions on future work on this material.

We have embarked on a systematic study of novel charge states at oxide interfaces. We have performed pulsed laser deposition (PLD) growth of epitaxial oxide thin films on single crystal oxide substrates. We studied the effects of epitaxial strain and rare-earth composition of the metal oxide thin films. We have successfully created TiO₂ terminated SrTiO₃ (STO) substrates and have grown epitaxial thin films of LaAlO₃ (LAO), LaGaO₃ (LGO), and RAlO₃ on STO using a KrF pulsed excimer laser. Current work emphasizes the importance of understanding the effect of both epitaxial strain and R³+ magnetism on the interface between RAlO₃ and STO. We have demonstrated that the interfaces between LAO/STO and LGO/STO are metallic with carrier concentrations of 1.1 x 10¹⁴ cm[superscript -2] and 4.5 x 10¹⁴ cm[superscript −2], respectively. Rare-earth aluminate films, RAlO₃, with R = Ce, Pr, Nd, Sm, Eu, Gd, and Tb, were also grown on STO. Conducting interfaces were found for R = Pr, Nd and Gd, and the results indicate that for R [does not equal] La the magnetic nature of the R³+ ion causes increased scattering with decreasing temperature that is modeled by the Kondo effect. Epitaxial strain between the polar RAlO₃ films and STO appears to play a crucial role in the transport properties of the metallic interface, where a decrease in the R³+ ion size causes an increase in sheet resistance and an increase in the onset temperatures for increased scattering. / text

No description available.

System on Chip (SoC) and System in Package (SiP) are two electronic technologies that involve integrating multiple functionalities onto a single platform. When the platform is a single wafer, as in SOC, it requires the ability to deposit various materials that enable the different functions on to an underlying substrate that can host the electronic circuitry. Transition metal oxides which have a wide range of properties are ideal candidates for the functional material. Si wafer on which micro-electronics technology is widely commercialized is the ideal host platform. Integrating oxides with Si, generally in the form of thin films as required by microelectronics technology, is however a challenge. It starts with the fact that the properties of crystalline oxides to be exploited in performing various functions are direction dependent. Thus, thin films of these oxides need to be deposited on Si in certain crystallographic orientations. Even if a suitably oriented Si wafer surface were available, it does not always provide for epitaxial growth a critical requirement for controlling the crystalline orientation of thin films. This is because Si surface is covered by an amorphous oxide of Si (SiOx). Thus, during growth of the functional oxide, an ambience in which the Si itself will not oxidize needs to be provided. In addition, during thin film growth on either Si or SiOx surface stresses are generated from various sources. Stress and its relaxation are also associated with the formation and evolution of defects. Both, stress and defects need to be managed in order to harness their beneficial effects and prevent detrimental ones. Given the requirement of SoC technology and the problem associated, the research work reported in this thesis was hence concerned with the precise controlling the stress and microstructure in oxide thin films deposited on Si substrates. In order to do so a versatile, ultra high vacuum (UHV) thin film with a base pressure of 10-9 Torr was designed and built as part of this study. The chamber is capable of depositing films by both sputtering (RF & DC) and pulsed laser ablation (PLD). The system has been designed to include an optical curvature measurement tool that enabled real-time stress measurement during growth. Doped zirconia, ZrO2, was chosen as the first oxide to be deposited, as it is among the few oxides that is more stable than SiOx. It is hence used as a buffer layer. It is shown in this thesis that a change in the growth rate at nucleation can lead to (100) or (111) textured films. These two are among the most commonly preferred orientation. Following nucleation a change in growth rate does not affect orientation but affects stress. Thus, independent selection of texture and stress is demonstrated in YSZ thin films on Si. A quantitative model based on the adatom motion on the growth surface and the anisotropic growth rates of the two orientations is used to explain these observations. This study was then subsequent extended to the growth on platinized Si another commonly used Si platform.. A knowledge of the stress and microstructure tailoring in cubic zirconia on Si was then extended to look at the effect of stress on electrical properties of zirconia on germanium for high-k dielectric applications. Ge channels are expected to play a key role in next generation n-MOS technology. Development of high-k dielectrics for channel control is hence essential. Interesting stress and property relations were analyzed in ZrO2/Ge. Stress and texture in pulsed laser deposited (PLD) oxides on silicon and SrTiO3 were studied. It is shown in this thesis that stress tuning is critical to achieve the highest possible dielectric constant. The effect of stress on dielectric constant is due to two reasons. The first one is an indirect effect involving the effect of stress on phase stability. The second one is the direct effect involving interatomic distance. By stress control an equivalent oxide thickness (EOT) of 0.8 nm was achieved in sputter deposited ZrO2/Ge films at 5 nm thickness. This is among the best reported till date. Finally, the effect of growth parameters and deposition geometry on the microstructural and stress evolution during deposition of SrTiO3 on Si and BaTiO3 on SrTiO3 by pulsed laser deposition is the same chamber is described.

Abstract Although gain-switching is a simple, well-established technique for obtaining ultrashort optical pulses generated with laser diodes, the optical energy in a pulse achievable from commercial structures using this technique is no more than moderate and the ‘spiking’ behaviour seen at turn-on is likely to evolve into trailing oscillations. This thesis investigates, develops and improves laser diodes in order to offer experimentally verified solutions for maximizing the optical energy so as to achieve a peak power of several watts in a single optical pulse of picosecond-range duration in the gain-switching operation regime, and for suppressing the energy located in any trailing pulses to a negligible level relative to the total optical pulse energy. This was addressed by means of either (i) an ultrashort pump current pulse with an amplitude range ~(1–10) A or (ii) custom laser diode structures, both options being capable of operating uncooled at room temperature (23±3°C). For the first solution a unique superfast gallium arsenide (GaAs) avalanche transistor was utilized as a switch in order to achieve an injection current pulse with a duration of < 1 ns, which is short enough to generate only a first optical ‘spike’ when pumping a commercial laser diode. The most promising structure with regard to the second solution was an edge-emitting semiconductor laser having a strongly asymmetric broadened double heterostructure with a relatively thick active layer. Laser pulses with full width at half maximum (FWHM) of ~100 ps and an optical energy of >3 nJ but with some trailing oscillations were achieved in experiments employing injection current pulses in the nanosecond range with an amplitude of ≤17 A, generated using inexpensive silicon (Si) electronics. The performance was improved by introducing a saturable absorber (SA) into the laser cavity, which suppressed the formation of trailing oscillations, resulting in a single optical pulse. / Tiivistelmä ”Gain switching” (vahvistuskytkentä) on tunnettu tekniikka lyhyiden (<100 ps) optisten pulssien generoimiseen laserdiodeilla. Kaupallisia laserdiodirakenteita käyttäen optinen energia rajoittuu kuitenkin 10…100 pJ:n tasolle. Tällöinkin, erityisesti suurilla energiatasoilla, optisessa pulssissa ilmenee voimakkaita jälkioskillaatioita. Tässä väitöskirjassa tutkittiin ja kehitettiin kokeellisesti varmennettuja laserdiodilähetinrakenteita tavoitteena saavuttaa >1 nJ:n optisen pulssin energia ja ~100 ps:n pulssinpituus gain-switching -toimintamoodissa. Tavoitteena oli myös minimoida jälkipulssien energia. Tutkimuksen pääsisältönä on kaksi toimintaperiaatetta: Toisessa tekniikassa päähuomio kohdistuu laseridiodin virta-ajuriin, johon kehitettiin elektroniikka, joka kykenee tuottamaan nopeita virtapulsseja laajalla pulssivirta-alueella. Virtapulssin nopeuden kasvattamisen (<1 ns) osoitettiin edistävän gain switching -ilmiötä. Toisena tekniikkana tutkittiin räätälöityä laserdiodirakennetta, joka sisäisen toimintansa perusteella tuottaa dynaamisessa ohjaustilanteessa tehokkaan ja nopean laserpulssin. Kummankin periaatteen osoitettiin toimivan huonelämpötilassa (23±3°C) ilman erillistä jäähdytystä. Ensimmäisessä ratkaisussa käytettiin nopeaa gallium-arsenidi (GaAs) -avalanchetransistoria virtakytkimenä, jolla saavutettiin <1 ns FWHM injektiovirtapulssi 10 A:n virtatasolla. Tällainen virtapulssi on riittävän lyhyt virittämään ”gain switching” -ilmiön nJ-energiatasolla. Lupaavin rakenne toiseksi ratkaisuksi oli reunaemittoiva puolijohdelaseri, jossa epäsymmetrinen aaltoputki ja aktiivinen alue ovat sijoitettu normaalista laserdiodirakenteesta poiketen rinnakkain. Tällä rakenteella voitiin tuottaa ~100 ps levyisiä (FWHM) ja >3 nJ optisen kokonaisenergian omavia laserpulsseja edullisella pii-pohjaisella (Si) elektroniikalla luoduilla 1.5–2 ns:n (FWHM) ≤17 A injektiovirtapulsseilla. Suorituskykyä saatiin edelleen parannettua istuttamalla saturoiva absorbaattori (SA) laserin optiseen onteloon. Tämän osoitettiin vähentävän jälkioskillaatioiden muodostumista.

Spintronics (spin based electronics) is a relatively new topic of research which is important both from the fundamental and technological point of view. In conventional electronics charge of the electron is manipulated and controlled to realize electronic devices. Spintronics uses charge as well as the spin degree of freedom of electrons, which is completely ignored in the charge based devices. This new device concept brings in a whole new set of device possibilities with potential advantages like higher speed, greater efficiency, non-volatility, reduced power consumption etc. The first realization of the spintronic device happened in 1989, owing to the discovery of the Giant Magneto-resistive (GMR) structure showing a large resistance change by the application of an external magnetic field. Nobel Prize in Physics is awarded for this discovery in 2007. In less than ten years, such devices moved from the lab to commercial devices, as read head sensors in hard disc drives. This new sensor led to an unprecedented yearly growth in the area l density of bits in a magnetic disc drive. Since 2005, another spintronic device known as Magnetic Tunnel Junction (MTJ) which shows a better performance replaced the existing GMR structures in the read heads. Another device which can potentially replace Si based Dynamic Random Access Memory (DRAM) is Magneto-resistive Random Access Memory (MRAM). Being magnetic it is non-volatile, which means not only it retains its memory with the power turned off but also there is no constant power required for frequent refreshing. This can save a lot of power(~ 10-15 Watts in a DRAM), which is quite significant amount for any portable device which runs under battery. Prototype of a commercial MRAM is also made during 2004-2005 by Infineon and Freescale Semiconductors. Recent development has shown switching of magnetic moment by spin-polarised currents (known as spin transfer torque), electric fields, and photonic fields. Instead of Oersted field switching in the conventional MRAM devices, spin torque effect can also be used to switch a magnetic element more efficiently. Recently Spin-Torque MRAM has gained lot of interest due to it’s less power consumption during the writing process. A continuous research effort is going on in realizing other proposed spintronic devices, such as Spin Torque Oscillator, Spin Field Effect Transistor , Race Track Memory etc. which are yet to get realized or yet to make their entry in the commercial devices. Spintronics can be divided in to two broad subfields viz.(1) Semiconductor Spintronics and (2) Metallic Spintronics. Most of the devices belong to the second class whereas the former one is rich in fundamental science and not yet cleared its path towards the world of application. Any spintronic device requires ferromagnetic material which is generally the source of spin polarized electrons. For semiconductor spintronic devices, the main obstacle is the non-existence of the ferromagnetic semiconductor above room temperature (RT). So the development in this direction is very much dependent on the material science research and discovery of novel material systems. Almost a decade back, Dilute Magnetic Semiconductors (DMS) are proposed to behaving RT ferromagnetism. As a result an intense theoretical and experimental research is being carried out since then on these materials. Still a general consensus is lacking both in terms of theory as well as experiment. There are many methodologies and thin film deposition protocols have been followed by different research groups to realize spintronic device concepts. The deposition techniques such as magnetron sputtering, molecular beam epitaxy have been found very efficient for growing metallic spintronic devices. For semiconductor spintronics especially in the area of Dilute Magnetic Semiconductors (DMS) pulsed laser ablation is also considered to be a viable technique. Even though pulsed laser ablation is a very powerful technique to prepare stoichiometric multi-component oxide films, it’s viability for the growth of metallic films and multilayer is considered to be limited. In this regard, we have used pulsed laser ablation to prepare pure and Co doped ZnO films, to examine the magnetic and magneto-transport behavior of these oxides. In addition extensive work has been carried out to optimize and reproducibly prepare metallic multilayer by Pulsed Laser Deposition to realize Spin Valve (SV) effect, which proves the viability of this technique for making metallic multilayer. This thesis deals with the study of Pulsed Laser Deposition(PLD) deposited DMSs and metallic SVs. The thesis is organized into seven chapters as described below: • Chapter:1 This chapter gives an introduction to Spintronics and the different device structures. It is followed by a brief description of the motivation of the present work. Since magnetism is at the heart of the spintronics, next we attempt to introduce some of the basic concepts in magnetism, which are related to the topics discussed in the following chapters. We discuss about various exchange interactions responsible for the long range ferromagnetic ordering below Curie temperature in different compounds. Other magnetic properties are also discussed. Then another important phenomenon called magnetic anisotropy is brought in. We discuss the origin of different types of anisotropy in materials. These anisotropies are also responsible for magnetic domain formation. Then a description of the different types of domain walls are introduced. Unlike conventional electronics, spintronics deals with spin polarized current. A short description of spin polarization from the band picture and concept of half-metal is introduced. The next part (Section-I) of this chapter gives an overview of the challenges in semiconductor spintronics. The spin injection efficiency from a ferromagnetic metal to a semiconductor is found to be poor. This problem is attributed to the conductivity mismatch at the interface. DMS materials can be potential candidates in order to solve this problem. Ferromagnetism in these proposed materials cannot be explained in terms of the standard exchange mechanisms. A model was first proposed for the hole doped system based on Zener model. A more apt model for the n-doped high dielectric materials is then proposed based on Bound Magnetic Polarons (BMP). These models for the unusual ferromagnetism are briefly discussed. Although ferromagnetism is observed by different groups, often questions are raised about the intrinsic origin of this behavior and the topic is still under debate. In this study we have tried to correlate the magnetic property with the transport property as the transport properties are generally not affected much by the presence of external impurities and probes the intrinsic property of the material. Transport and the magneto-transport in disordered materials in general are discussed. A specific model proposed for degenerate semiconductors, which is used for fitting our experimental data is explained. As the ferromagnetism in these materials are generally found to be related to the defects, different types of possible defects are described. Section-II deals with the metallic SV devices. In the history of spintronics, this is one of the most basic and most studied structures, but still having a lot of interest both fundamentally and technologically. A brief history of this discovery and a chronological progress in the device structure is discussed. Our work focuses on the metallic spin valve (SV) structures. Different types of SVs and their properties are explained. In a SV structure one of the ferromagnets (FM) is pinned using an adjuscent antiferromagnetic layer by an effect called exchange bias. A brief description of exchange bias and the effects of different parameters is given. This is followed by a discussion about the theory of GMR which deals with the spin dependent scattering at the bulk and at the interfaces, their relative contributions, effect of the band matching etc. A simple resistor model is used to explain the qualitative behavior of these SVs. The chapter is concluded with a brief summery and applications. • Chapter:2 This chapter provides a brief description of some of the experimental apparatus that are used to perform various experiments. The chapter is organized according to the general functionality of the techniques. This includes different thin film deposition techniques which are used depending on the requirements and also for comparing the properties of the samples, grown by different techniques. Structural, spectroscopic, magnetic and different microscopy techniques which are extensively used throughout, are discussed and their working principles are explained. This work also involves nano/microstructuring of devices. Mainly two structuring techniques are used viz. e-beam lithography and optical lithography by laser writer. In this section we will be discussing about these two techniques and other associated techniques like lift-off, etching etc. Effect of different parameters on the device structures are highlighted. • Chapter:3 Chapter-3 deals with the synthesis and characterization of the pure and 5% Co doped ZnO bulk samples. First a brief introduction about the ZnO crystal structure, band structure and other properties are given followed by the synthesis technique followed in our study. Synthesis is done by low temeperature in organic co-precipitation method. This liquid phase synthesis gives better homogeniety. As-grown sample is also sintered at a higher temperature. Structural study confirms the proper synthesis of the intended compound. Spectroscopic as well as magnetic study of the bulk doped sample indicates the presence of Co nano clusters in the low temperature synthesized sample, whereas after sintering indication of Co2+ is observed which reflects in the magnetic property as well. These samples are used as target material for laser ablation. • Chapter:4 Chapter-4 presents the results of the pure and Co doped ZnO thin film samples. Thin films are grown by PLD method on r-plane Sapphire substrates. Details of the growth technique and the deposition parameters are explained. Our result shows that 5% Co doped ZnO thin film is ferromagnetic in nature as expected in a DMS material, although the film is grown using a paramagnetic target. We also report that pure ZnO grown in an oxygen deficient condition giving ferromagnetic behavior. Not only that, the obtained saturation moment is much higher compared to the Co doped sample. We have demonstrated that the FM can be tuned by tuning the oxygen content and FM disappears when the film is annealed in an oxygen environment .But for the Co doped sample magnetic property could not be tuned much as Co doping stabilizes the surface states. To exclude the possibilities of the extrinsic origin we have done a detailed magneto-transport study for both doped and undoped films. For ZnO, we have shown a one to one correlation of the magnetic and magneto-transport data which further supports the fact that the obtained magnetic behavior is intrinsic. Fitting of the magnetorsistance (MR) data for the pure and Co doped ZnO samples is done using a semi-empirical formula, consisting of both positive and negative MR terms originally proposed for degenerate semiconductors .Excellent agreement of the experimental data is found with the formula. For pure ZnO sample we have extracted the mobility, carrier concentration etc .by Hall measurement. The fabrication steps of Hall bar sample which involves optical lithography and ion beam etching are discussed. 3D e-e interaction induced transport mechanism is found to be dominant in case of oxygen deficient pure ZnO. • Chapter:5 Chapter-5 demonstrates the tuning of band gap of ZnO by alloying with MgO. By changing the ZnO:MgO ratio in PLD grown films, we could tune the band gap over a wide range. Composition alanalysis is done by Rutherford Back-Scattering. Structural and spectroscopic studies are carried out, which shows tuning of band gap upon alloying with MgO. We could tune ZnO band gap from 3.3eV to 3.92eV by30% MgO alloying, while retaining the Wurtzite crystal structure. • Chapter:6 Chapter-6 demonstrates the metallic Pseudo Spin Valve (PSV) structures grown by sputtering and by PLD. Main focus of this chapter is to show that, PLD can be aviable technique for making metallic PSV and Spin Valve (SV) structures. This is almost an unexplored technique for growing metallic thin film SVs, as it is evident in the literature. NiFe and Co are used as the soft and hard FM layers respectively, Au and Cu are used as the spacer layer. FeMn is used for pinning the Co layer in case of the SV structures. The first section describes the properties of these materials and then substrate preparation, deposition parameters etc. are explained in details. Properties of sputter deposited PSV structures are also described. Thickness variation of different layers, double PSV structure and angular variation of the MR properties are presented. Generally two measurement geometries are followed for the SV measurements viz.(1) Current In Plane (CIP) and (2) Current Perpendicular to Plane(CPP). We have carried out MR studies in both the measurement geometries. Measurement in CPP geometry is much more involved than CIP and need structuring with multiple lithography steps. CPP measurement geometry scheme and the process steps are discussed. For this measurement a special ac bridge technique is followed which is also discussed. In the next part we have demonstrated PSV and SV structures, grown, using PLD in an Ultra High Vacuum (UHV) system. Not only that, we have obtained a CIPMR as high as 3.3%. PLD is generally thought to be a technique for oxide deposition and metallic multilayers are not deposited due to particulate formation, high enegy of the adatom species which can lead to inter-mixing at the interface etc. But in this study we have shown that by properly tuning the deposition parameters, it is possible to grow SVs using PLD. We have found the roughness of the PLD grown films are much lower compared to the sputtered films. For top SV structures we have obtained exchange bias even in the absence of applied field during deposition. This effect is observed by performing magnetic and magneto-resistance measurements. Effect of different layer thicknesses, field annealing etc. are discussed. Two different spacer layers are used and their properties are compared. We have found that the interface engineered structures are giving highest MR among the different samples. Then a conclusion of our study is presented followed by a discussion on the difficulties and challenges faced for optimizing the PLD grown SVs. • Chapter:7 Finally, in Chapter-7, various results are summarized and a broad outlook is given. Perspectives for the continuation of the present work is also given.

Les matériaux métalliques sont utilisés dans des conditions de plus en plus sévères et doivent présenter une parfaite intégrité sur des périodes de plus en plus longues. L’objectif de ce travail de thèse est d’évaluer le potentiel d'un traitement de refusion laser pour améliorer la résistance à la corrosion d'un acier inoxydable de type 304L ; l’utilisation du laser dans le domaine des traitements de surface constituant un procédé en pleine évolution à cause des changements récents dans la technologie des lasers. Dans le cadre de ce travail, le choix du laser s’est porté sur un laser nano-impulsionnel à fibre dopée ytterbium dont les caractéristiques permettent la fusion quasi-instantanée sur quelques microns de la surface traitée, immédiatement suivie d'une solidification ultra-rapide avec des vitesses de refroidissement pouvant atteindre 1011 K/s. La combinaison de ces processus favorise l'élimination des défauts surfaciques, la formation de phases hors équilibre, la ségrégation d’éléments chimiques et la formation d’une nouvelle couche d’oxyde dont les propriétés sont gouvernées par les paramètres laser. Afin de les corréler avec la réactivité électrochimique de la surface, l’influence de deux paramètres laser sur les propriétés physico-chimiques de la surface a été étudiée : la puissance du laser et le taux de recouvrement des impacts laser. Pour clarifier ces relations, la résistance à la corrosion par piqûration des surfaces traitées a été déterminée par des tests électrochimiques. Pour des paramètres laser spécifiques, le potentiel de piqûration d'un acier inoxydable de type 304L augmente de plus de 500 mV traduisant ainsi une meilleure tenue à la corrosion localisée en milieu chloruré. L’interdépendance des différents phénomènes résultant du traitement laser a rendu complexe la hiérarchisation de leur effet sur la sensibilité de l’alliage testé. Cependant, il a été montré que la nature de l’oxyde thermique formé au cours de la refusion laser et ses défauts sont du premier ordre pour l’amorçage des piqûres. / Metallic materials are more and more used in severe conditions with particularly strong request for improving their behavior in aggressive environment and especially over long periods. The objective of this PhD work is to estimate the potentiality of a laser surface melting treatment on the improvement of the stainless steel 304L corrosion resistance, surface treatments by laser can be revisited on the basis of a recent change in the laser technology. In the frame of this work, a nano-pulsed laser fiber was chosen : it allows the treated surface to be melted for few microns in depth, followed by an ultra-fast solidification occuring with cooling rates up to 1011 K/s. The combination of these processes leads to the elimination of the surface defects, the formation (trapping) of metastable phases, the segregation of chemical elements and the growth of a new oxide layer which properties are governed by the laser parameters. To correlate these latter to the electrochemical reactivity of the surface, the influence of two laser parameters on the physico-chemical properties of the surface was studied : the laser power and the overlap of the laser impacts. To support this approach, the pitting corrosion resistance of the samples was determined by standard electrochemical tests. For specific laser parameters, the pitting potential of a 304L stainless steel was increased by more than 500 mV corresponding to an important enhancement in localized corrosion resistance in chloride environment. The interdependence of the different phenomena resulting from the laser treatment lead to a quite complex prioritization of their role on the sensibility of the 304L. However, it was demonstrated that the nature of the thermal oxide formed during the laser surface melting and the induced defects are first-order parameters for the initiation of pits.