Nicholas Seaton

Growth Parameters of Fully Crystallized YIG, Bi:YIG, and Ce:YIG Films With High Faraday Rotations

We report on the growth of thin films of yttrium iron garnet (YIG) on dielectric substrates. Such films have historically been challenging to grow due to either cracking or incomplete crystallization of the films. We have established the proper growth parameters by tuning seed layer thickness to an optimum of 45 nm. These films were then used as seed layers for growth of films of Bi:YIG and Ce:YIG. Bi:YIG films show a Faraday rotation of 1700 °/cm, and Ce:YIG films show a Faraday rotation of 3700 °/cm.

Lawsonite vorticity and subduction kinematics

The exceptional preservation of lawsonite in eclogite and blueschist in a subduction complex (Sivrihisar, Turkey) allows evaluation of high-pressure (H P ) deformation and exhumation using vorticity analysis of a H P index mineral. The Sivrihisar H P rocks were deformed during H P metamorphism and initial decompression by oblique (normal and/or dextral) shearing beneath serpentinized peridotite. We evaluated kinematic vorticity (W m pure shear = 0, W m simple shear = 1) using the shape fabric of lawsonite crystals in blueschist layers and meter-scale eclogite pods. Pods record dominant simple shear (W m > 0.8) in their eclogitic core and at pod margins partially transformed to blueschist; map-scale blueschist layers record a large component of pure shear (W m = 0.4–0.6), consistent with oblique extrusion at depth in the subduction zone, and local simple shear (W m = 0.8) at the fault contact with serpentinite. A combination of oblique unroofing from beneath a weak serpentinized hanging wall and pure shear extrusion in the subduction channel accounts for rapid exhumation along a low geothermal gradient and the rare preservation of lawsonite eclogite during exhumation to the Earth9s surface.

Petrofabrics of high‐pressure rocks exhumed at the slab‐mantle interface from the “point of no return” in a subduction zone (Sivrihisar, Turkey)

The highest pressure recorded by metamorphic rocks exhumed from oceanic subduction zones is ~2.5 GPa, corresponding to the maximum decoupling depth (MDD) (80 ± 10 km) identified in active subduction zones; beyond the MDD (the “point of no return”) exhumation is unlikely. The Sivrihisar massif (Turkey) is a coherent terrane of lawsonite eclogite and blueschist facies rocks in which assemblages and fabrics record P-T-fluid-deformation conditions during exhumation from ~80 to 45 km. Crystallographic fabrics and other features of high-pressure metasedimentary and metabasaltic rocks record transitions during exhumation. In quartzite, microstructures and crystallographic fabrics record deformation in the dislocation creep regime, including dynamic recrystallization during decompression, and a transition from prism   slip to activation of rhomb   and basal   slip that may be related to a decrease in water fugacity during decompression (~2.5 to ~1.5 GPa). Phengite, lawsonite, and omphacite or glaucophane in quartzite and metabasalt remained stable during deformation, and omphacite developed an L-type crystallographic fabric. In marble, aragonite developed columnar textures with strong crystallographic fabrics that persisted during partial to complete dynamic recrystallization that was likely achieved in the stability field of aragonite (P > ~1.2 GPa). Results of kinematic vorticity analysis based on lawsonite shape fabrics are consistent with shear criteria in quartzite and metabasalt and indicate a large component of coaxial deformation in the exhuming channel beneath a simple shear dominated interface. This large coaxial component may have multiplied the exhuming power of the subduction channel and forced deeply subducted rocks to flow back from the point of no return.

Quasi-Phase-Matched Faraday Rotation in Semiconductor Waveguides With a Magnetooptic Cladding for Monolithically Integrated Optical Isolators

Strategies are developed for obtaining nonreciprocal polarization mode conversion, also known as Faraday rotation, in waveguides in a format consistent with silicon-on-insulator or III-V semiconductor photonic integrated circuits. Fabrication techniques are developed using liftoff lithography and sputtering to obtain garnet segments as upper claddings, which have an evanescent wave interaction with the guided light. A mode solver approach is used to determine the modal Stokes parameters for such structures, and design considerations indicate that quasi-phase-matched Faraday rotation for optical isolator applications could be obtained with devices on the millimeter length scale.

Quartz and calcite microfabric transitions in a pressure and temperature gradient, Sivrihisar, Turkey

Interlayered quartzite and marble in the southern Sivrihisar Massif, Turkey, record metamorphic conditions ranging from high-pressure/low-temperature through a Barrovian overprint from chlorite- to sillimanite-zone conditions. This sequence was exhumed under transtension, producing macroscopic constrictional fabrics (L-tectonites) during crustal thinning. Quartz microstructures consist of dynamically recrystallized aggregates in the dislocation creep regime dominated by grain boundary migration. Quartz microstructures are relatively constant across the high metamorphic gradient, and crystallographic fabric patterns transition from plane strain to constriction strain. Calcite fabrics are characterized by progressive overprinting of a columnar texture inherited from the high-pressure polymorph aragonite. In the low-temperature Barrovian domain (<400 °C), shearing of calcite rods produced a very strong c-axis point maximum. At moderate temperature, calcite rods were partially to totally recrystallized and the strong preferred orientation maintained. At temperature >500 °C and high constriction strain, marble has no crystallographic fabric, likely reflecting a transition from dislocation creep to diffusion creep. Phengite in high-pressure/low-temperature marble and quartzite yields relatively simple age spectra with Late Cretaceous (88–82 Ma) 40Ar/39Ar ages. Barrovian muscovite records significantly younger ages (63–55 Ma). The transtension system and associated metamorphism may have occurred above a subduction zone in Paleocene–Eocene time as a precursor to intrusion of Eocene (~53 Ma) arc plutons.

Transmission Electron Backscatter Diffraction (tEBSD) analysis of Au Thin Films

Identifying and characterizing nanoscale crystallographic features is vital for understanding deformation in plasmonic devices and developing more robust plasmonic structures. Here, advanced characterization processes using transmission Electron Back Scatter Diffraction (tEBSD) were developed to analyze thin film crystal structure and its role in plasmonic device stability. The specific crystalline features of interest are film texture, grain boundary configuration and grain size. These results will hopefully contribute to the successful implementation of Heat Assisted Magnetic Recording (HAMR) as well as improve plasmonic device reliability in other applications.[1]

Optimized yttrium iron garnet growth on silicon for films with high faraday rotation

Bismuth and cerium YIG films with Faraday rotations of 4000°/cm and 10000°/cm were obtained on Si, and a complete model for the growth and crystallization required to obtain such films is presented.