Morphology-properties studies in laser synthesized nanostructured materials

Synthesis of well-defined nanostructures by pulsed laser melting is an interesting subject from both a funda- mental and technological point of view. In this thesis, the synthesis and functional properties of potentially useful materials were studied, such as tin dioxide nanostructured arrays, which have potential applications in hydrogen gas sensing, and ferromagnetic Co nanowire and nanomagnets, which are fundamentally im- portant towards understanding magnetism in the nanoscale. First, the formation of 1D periodic tin dioxide nanoarrays was investigated with the goal of forming nanowires for hydrogen sensing. Experimental obser- vations combined with theoretical modeling successfully explained the mechanisms of structure formation. One of the primary findings was that evaporation of tin dioxide was the most significant contributor to the pattern formation. Next, the spontaneous liquid film spinodal dewetting process under pulsed laser melting was modeled using the viscous dissipation approach. We found that the fluid condition for spinodal dewet- ting is where the film-substrate tangential stress is zero. Following this, the remainder of the thesis focused on synthesis and characterization of magnetic nanostructures. We first successfully installed a home-built Surface Magneto-optical Kerr Effect (SMOKE) system. Using SMOKE we measured the Kerr rotation from potential plasmonic-ferromagnetic magneto-optical materials made from Co-Ag thin films and nanoparti- cles as a function of composition. We found that films made by co-deposition of Co and Ag showed higher Kerr rotation in contrast to bilayer film structures with same effective amount of Co and Ag. Next, we inves- tigated the shape and size dependence of magnetic properties of nanostructures, specifically hemispherical nanoparticles, nanowires and nanorods, prepared by the pulsed laser process. The magnetic anisotropy was studied by using the SMOKE system complemented with magnetic force microscopy (MFM) analy- sis. Results from magnetic hysteresis measurements of the nanostructures in different geometries showed coercivity and remanence that could be attributed to magnetic shape anisotropy. MFM analysis showed that domain orientation was found to depend on the aspect ratio of the nanostructure. These investigations generally helped advance the science of nanostructure synthesis using nanosecond pulsed laser techniques as well demonstrate that SMOKE is a promising method to investigate nanostructure magnetism

Optical isolator for TE polarized light realized by adhesive bonding of Ce:YIG on silicon-on-insulator waveguide circuits

An optical isolator for transverse electric (TE) polarized light is demonstrated by adhesive bonding of a ferrimagnetic garnet die on top of a 380 nm thick silicon waveguide circuit. Polarization rotators are implemented in the arms of a nonreciprocal Mach-Zehnder interferometer to rotate the polarization to transverse magnetic in the nonreciprocal phase shifter regions. Calculation of the nonreciprocal phase shift (NRPS) as a function of bonding layer thickness experienced by the TM mode in the interferometer arms is presented, together with the simulation of the robustness of the polarization rotator. Experimentally, 32 dB isolation is measured at 1540.5 nm wavelength using a magnetic field transverse to the light propagation directions. This paves the way to the cointegration of laser diodes and optical isolators on a silicon photonics platform

The Use of Remote Monitoring for Internal Cardioverter Defibrillators (ICDS): The Infusion of Information Technology and Medicine

The clinical use of automated implantable cardioverter defibrillators (AICDs) has been rapidly increasing since the results of several randomized trials confirmed the efficacy of AICDs in the secondary and primary prevention of sudden cardiac death. Patients with AICDs require high-quality care and intense follow-up to ensure safe and effective device performance. According to international guidelines these patients should be followed at 1- to 4 month intervals, depending on the device model and the patient’s clinical status (Schoenfeld, 2004). Given the expanding indications for use and the complexity of these devices, there is an urgent need to develop new means of ICD follow-up, so as to optimize patient safety and the use of healthcare resources. An internet-based remote-monitoring system could provide a practical substitute to time-consuming and expensive in-office visits. Although the initial experience with these systems has been favorable, many practical issues remain. In particular, more information is required on the usability and safety of remote monitoring for patient-initiated transmissions and cost effectiveness of the system as a substitute for routine in-office visits during long-term follow-up

Thermodynamic approach to the dewetting instability in ultrathin films

The fluid dynamics of the classical dewetting instability in ultrathin films is a non-linear process. However, the physical manifestation of the instability in terms of characteristic length and time scales can be described by a linearized form of the initial conditions of the films's dynamics. Alternately, the thermodynamic approach based on equating the rate of free energy decrease to the viscous dissipation [de Gennes, C. R. Acad. Paris.v298, 1984] can give similar information. Here we have evaluated dewetting in the presence of thermocapillary forces arising from a film-thickness (h) dependent temperature. Such a situation can be found during pulsed laser melting of ultrathin metal films where nanoscale effects lead to a local h-dependent temperature. The thermodynamic approach provides an analytical description of this thermocapillary dewetting. The results of this approach agree with those from linear theory and experimental observations provided the minimum value of viscous dissipation is equated to the rate of free energy decrease. The flow boundary condition that produces this minimum viscous dissipation is when the film-substrate tangential stress is zero. The physical implication of this finding is that the spontaneous dewetting instability follows the path of minimum rate of energy loss.Comment: 8 pages, 3 figures. Under revie

Muscle Plasticity and β2-Adrenergic Receptors: Adaptive Responses of β2-Adrenergic Receptor Expression to Muscle Hypertrophy and Atrophy

We discuss the functional roles of β2-adrenergic receptors in skeletal muscle hypertrophy and atrophy as well as the adaptive responses of β2-adrenergic receptor expression to anabolic and catabolic conditions. β2-Adrenergic receptor stimulation using anabolic drugs increases muscle mass by promoting muscle protein synthesis and/or attenuating protein degradation. These effects are prevented by the downregulation of the receptor. Endurance training improves oxidative performance partly by increasing β2-adrenergic receptor density in exercise-recruited slow-twitch muscles. However, excessive stimulation of β2-adrenergic receptors negates their beneficial effects. Although the preventive effects of β2-adrenergic receptor stimulation on atrophy induced by muscle disuse and catabolic hormones or drugs are observed, these catabolic conditions decrease β2-adrenergic receptor expression in slow-twitch muscles. These findings present evidence against the use of β2-adrenergic agonists in therapy for muscle wasting and weakness. Thus, β2-adrenergic receptors in the skeletal muscles play an important physiological role in the regulation of protein and energy balance