We imitated the sandwich structure of TMR(Tunneling Magnetoresistance) to apply to CMR(Colossal Magnetoresistance) material . We choose one of the Colossal Magnetoresistance material La0.67Sr0.33MnO3(113) to be the Ferromagnetic(FM) layers as top and bottom layer in sandwich structure and use La0.67Sr0.33MnO3 ¡P SrO(214) to be middle layer which have Antiferromagnetic(AFM) property to form FM-AFM-FM structure. The FM and AFM layer can match their lattice in interface joint. What its purpose is to use this structure to enhance SPT (Spin Polarization Tunneling) effect and let spintronics can periodical spin-flip in supper lattice structure of antiferromagnetic. Upon this compose we try to show increase the LFMR (Low Field Magnetoresistance) by use CMR. The experiment result shows maybe the film structure damage occurred in our made TMR tunneling device process (ex. Ion etching process), so we should improvement the process to get the exactly experiment data. Additional, due to the alignment of the moment of La0.67Sr0.33MnO3 is unstable, the back and forth hysteresis loop can¡¦t overlap, So that afterwards we can use the more stable material La0.67Ca0.33MnO3 which have more stable moment.

This understanding of nanocellulose can be directly applied in future formulation design to use nanocellulose in polymer nanocomposites, foams, emulsions, latexes, gels and biomedical materials. / In this study, the potential of nanocellulose as a reinforcing agent in composite materials was investigated using atomic force microscopy (AFM). AFM was used to probe the mechanical properties of nanocelluloses and to investigate their interactions and adhesion in liquid media. Amplitude modulated-frequency modulated AFM was used to map the mechanical properties of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs). Results showed Young’s moduli of 90 GPa and 120 GPa for CNCs and CNFs, respectively, which are comparable to literature values determined using other methods. Additionally, colloid probe AFM was implemented to observe the interactions (attractive, repulsive, steric, adhesive) between cellulose and silica colloid probes with anionic CNCs (containing either a Na+ or H+ counterion) and cationic CNCs. Colloid probe AFM measurements were carried out in five different liquid media: two salt solutions (NaCl and CaCl2) and three surfactant solutions (cationic cetyltrimethylammonium bromide, CTAB; anionic sodium dodecyl sulfate, SDS; and nonionic Triton X100). It was found that low salt concentrations resulted in electrostatic repulsion and high adhesion, whereas the reverse was observed at high salt concentrations. On the contrary, an increased surfactant concentration and increased number of surfactant aggregates (micelles, bilayers, etc.) resulted in increased adhesion. Surprisingly, the interactions were strongly dependent on the CNC counterion as surfactant adsorption seemed to be primarily driven by electrostatic interactions; CTAB adsorbed more to anionic CNCs, SDS adsorbed more to cationic CNCs and Triton X100 adsorbed minimally to all CNCs. Electrophoretic mobility and particle size data showed complementary results to colloid probe AFM, indicating that interactions between surfactants and CNC films and CNCs in suspension are closely related. This research suggests that CNCs have potential as reinforcing agents due to their high strength and the tunability of their interactions through the simple addition of salts or surfactants. This understanding can be directly applied in future formulation design to use nanocellulose in polymer nanocomposites, foams, emulsions, latexes, gels and biomedical materials. / Thesis / Master of Applied Science (MASc) / Nanocellulose is a sustainable nanomaterial most commonly extracted from plants and trees. In recent research, nanocellulose has been shown to have potential as a reinforcing agent for materials such as plastics, foams, paints and adhesives. In this study, the potential of nanocellulose was investigated using atomic force microscopy (AFM). As predicted, AFM measurements indicated that nanocellulose has a high stiffness, supporting the substitution of this biobased material in the place of metals and synthetic fibres. AFM was also used to examine particle interactions in salt and soap-like (surfactant) solutions; changes in nanocellulose size and charge were used to support the findings. Negatively charged nanocellulose interacted more with positively charged surfactants and vice versa. Low salt and high surfactant concentrations led to high adhesion and better material compatibility, which is preferred. This understanding can help us design better nanocellulose materials for future applications.

Un microscope à force atomique (AFM) est utilisé pour caractériser des matériaux isolant ou semi-conducteur avec une résolution pouvant atteindre l'échelle atomique. Ce microscope est constitué d'un capteur de force couplé à une électronique de contrôle pour pouvoir correctement caractériser ces matériaux. Parmi les différents modes (statique et dynamique), nous nous focalisons essentiellement sur le mode dynamique et plus particulièrement sur le fonctionnement sans contact à modulation de fréquence (FM-AFM). Dans ce mode, le capteur de force est maintenu comme un oscillateur harmonique par le système d'asservissement. Le projet ANR Pnano2008 intitulé : ”Cantilevers en carbure de silicium à piézorésistivité métallique pour AFM dynamique à très haute fréquence" a pour objectif d'augmenter significativement les performances d'un FM-AFM en développant un nouveau capteur de force très haute fréquence. Le but est d'augmenter la sensibilité du capteur et de diminuer le temps nécessaire à l'obtention d'une image de la surface du matériau. Le système de contrôle associé doit être capable de détecter des variations de fréquence de 100mHz pour une fréquence de résonance de 50MHz. Etant donné que les systèmes présents dans l'état de l'art ne permettent pas d'atteindre ces performances, l'objectif de cette thèse fut de développer un nouveau système de contrôle. Celui-ci est entièrement numérique et il est implémenté sur une carte de prototypage basée sur un FPGA. Dans ce mémoire, nous présentons le fonctionnement global du système ainsi que ses caractéristiques principales. Elles portent sur la détection de l'écart de fréquence de résonance du capteur de force. / An atomic force microscope (AFM) is used to characterize insulating materials or semiconductors with a resolution up to the atomic length scale. The microscope includes a force sensor linked to a control electronic in order to properly characterize these materials. Among the various modes (static and dynamic), we focus mainly on the dynamic mode and especially on the frequency modulation mode (FM-AFM). In this mode, the force sensor is maintained as a harmonic oscillator by the servo system. The research project ANR Pnano2008 entitled: "metal piezoresistivity silicon carbide cantilever for very high frequency dynamic AFM" aims to significantly increase the performance of a FM-AFM by developing new very high frequency force sensors. The goal is to increase the sensitivity of the sensor and to decrease the time necessary to obtain topography images of the material. The control system of this new sensor must be able to detect frequency variations as small as 100mHz for cantilevers with resonance frequencies up to 50MHz. Since the state-of-the-art systems doe not present these performances, the objective of this thesis was to develop a new control system. It is fully digital and it is implemented on a FPGA based prototyping board. In this report, we present the system overall functioning and its main features which are related to the cantilever resonant frequency detection. This detection is managed by a phase locked loop (PLL) which is the key element of the system.

Different methods for the determination of cantilever properties in non-contact atomic force microscopy (NC-AFM) are under investigation. A key aspect is the determination of the cantilever stiffness being essential for a quantitative NC-AFM data analysis including the extraction of the tip-surface interaction force and potential. Furthermore, a systematic analysis of the displacement noise in the cantilever oscillation detection is performed with a special focus on the thermally excited cantilever oscillation. The propagation from displacement noise to frequency shift noise is studied under consideration of the frequency response of the PLL demodulator. The effective Q-factor of cantilevers depends on the internal damping of the cantilever as well as external influences like the ambient pressure and the quality of the cantilever fixation. While the Q-factor has a strong dependence on the ambient pressure between vacuum and ambient pressure yielding a decrease by several orders of magnitude, the pressure dependence of the resonance frequency is smaller than 1% for the same pressure range. On the other hand, the resonance frequency highly depends on the mass of the tip at the end of the cantilever making its reliable prediction from known cantilever dimensions difficult. The cantilever stiffness is determined with a high-precision static measurement method and compared to dimensional and dynamic methods. Dimensional methods suffer from the uncertainty of the measured cantilever dimensions and require a precise knowledge its material properties. A dynamic method utilising the measurement of the thermally excited cantilever displacement noise to obtain cantilever properties allows to characterise unknown cantilevers but requires an elaborative measurement equipment for spectral displacement noise analysis. Having the noise propagation in the NC-AFM system fully characterised, a proposed method allows for spring constant determination from the frequency shift noise at the output of the PLL demodulator with equipment already being available in most NC-AFM setups.