Development and Characterization of Novel Garnet and Gold Thin Films for Photonic and Plasmonic Applications

University of Minnesota Ph.D. dissertation. August 2017. Major: Material Science and Engineering. Advisor: Bethanie Stadler. 1 computer file (PDF); xv, 135 pages.The massive amount of data that we produce and share today is the result of advancements made in the semiconductor and magnetic recording industries. As the number of transistors per unit area in integrated circuits continues to rise, power dissipation is reaching alarming levels. Photonics, which essentially is a marriage of semiconductor with laser technology has shown great promise in tackling the issue of power dissipation. The first part of this work focuses on optical isolators, which are essential to halt back-reflections that interfere with the laser source of the photonic systems. Novel terbium iron garnet thin-film optical isolators have been developed on semiconductor platforms and their magneto-optical properties are explored. Modesolver and finite-difference simulations are done to assess their device-feasibility and efficiency. Subsequently, a new photonic device has been developed using current semiconductor microelectronic fabrication techniques. Advancement in magnetic recording is equally vital to keep up with the demand for more data at faster speeds as the current perpendicular recording technique is fast-approaching its areal density limitations. Heat assisted magnetic recording (HAMR) is the next step in the evolution of hard drives. HAMR involves heating of magnetic media using plasmonic near field transducers (NFTs), which must be able to withstand elevated temperatures for extended times. The second part of this work presents a statistical crystallographic study of thermally induced deformation of Au NFTs. Subsequently, the most thermally stable crystallographic orientation for Au NFT has been determined that could lead to significant improvements in HAMR drive reliability

Optimized magneto-optical isolator designs inspired by seedlayer-free terbium iron garnets with opposite chirality

Simulations demonstrate that undoped yttrium iron garnet (YIG) seedlayers cause reduced Faraday rotation in silicon-on-insulator (SOI) waveguides with Ce-doped YIG claddings. Undoped seedlayers are required for the crystallization of the magneto-optical Ce:YIG claddings, but they diminish the interaction of the Ce:YIG with the guided modes. Therefore new magneto-optical garnets, terbium iron garnet (TIG) and bismuth-doped TIG (Bi:TIG), are introduced that can be integrated directly on Si and quartz substrates without seedlayers. The Faraday rotations of TIG and Bi:TIG films at 1550nm were measured to be +500 and -500°/cm, respectively. Simulations show that these new garnets have the potential to significantly mitigate the negative impact of the seedlayers under Ce:YIG claddings. The successful growth of TIG and Bi:TIG on low-index fused quartz inspired novel garnet-core waveguide isolator designs, simulated using finite difference time domain (FDTD) methods. These designs use alternating segments of positive and negative Faraday rotation for push-pull quasi phase matching in order to overcome birefringence in waveguides with rectangular cross-sections

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

High-gyrotropy seedlayer-free Ce:TbIG for monolithic laser-matched SOI optical isolators

Monolithic optical isolators that provide modal (transverse electric, TE) and dimensional (500 nm core) matching to on-chip lasers have been realized with “one step” seedlayer-free garnets. To date, seedlayer-free garnet claddings have required thinner (< 340 nm) silicon-on-insulator (SOI) cores because mode-cladding interactions were too weak for laser-matched cores. However, laser matching is important because tapers, and/or mode converters between the laser and the isolator can cause detrimental reflections prior to isolation. This paper reports the use of cerium-doped terbium iron garnet (Ce:TbIG) in a quasi-phase matched non-reciprocal mode conversion (NRMC) isolator that operates on both TE and TM modes. A key innovation presented here is a repeatable process for foundry-friendly sputter deposition of Ce:TbIG, which enables this high Faraday rotation material (-3200°/cm) to be synthesized in any isolator design that would benefit from one-step lithographical manufacturing. A proof-of-feasibility 500 nm-SOI NRMC device is demonstrated with seedlayer-free Ce:TbIG that achieves an isolation ratio of 11 dB. With an optimal length, this NRMC design can provide greater than 30 dB isolation

Monolithically-integrated TE-mode 1D silicon-on-insulator isolators using seedlayer-free garnet

The first experimental TE-mode silicon-on-insulator (SOI) isolators using Faraday Rotation are here realized to fill the ‘missing link’ in source-integrated near infrared photonic circuits. The isolators are simple 1D 2-element waveguides, where garnet claddings and longitudinal magnetic fields produce nonreciprocal mode conversion, the waveguide equivalent of Faraday Rotation (FR). Quasi-phase matched claddings are used to overcome the limitations of birefringence. Current experimental SOI isolators use nonreciprocal phase shift (NRPS) in interferometers or ring resonators, but to date NRPS requires TM-modes, so the TE-modes normally produced by integrated lasers cannot be isolated without many ancillary polarisation controls. The presented FR isolators are made via lithography and sputter deposition, which allows facile upscaling compared to the pulsed laser deposition or wafer bonding used in the fabrication of NRPS devices. Here, isolation ratios and losses of 11 dB and 4 dB were obtained, and future designs are identified capable of isolation ratios >30 dB with losses <6 dB

Antibiogram of Salmonella spp Isolates from Raw Chicken Meat of Kathmandu Valley

Salmonella is one of the pathogenic microbe responsible in food borne diseases. In developing countries like Nepal,  Salmonellosis is one of the leading food-borne disease. The present study was conducted with an objective to enumerate coliform and to find the prevalence of Salmonella species in chicken meat along with their antimicrobial susceptible profile. A total of 30 chicken meat samples were collected and examined following the standard techniques and procedures at the Med Micro Lab from January 2020 to April 2020. The study was performed following the conventional methods for the detection of Salmonella spp. Biochemical methods were implied for the detection of isolates and Antibiotic Susceptibility Test were performed by modified Kirby Bauer disc diffusion test [1]. Out of the 30 samples, 12(40%) sample showed positive for Salmonella spp. Salmonella spp 2(16.67%) were found to be resistant to Ciprofloxacin, Chloramphenicol 1 (0.33%), Cotrimoxazole 2(16.66%), Nalidixic acid 7 (58.33%) Ampicillin 3 (25%) and Ceftriaxone (0%). Salmonella was found to be 100% sensitive towards Ceftriaxone. The highest resistance was observed towards Nalidixic acid (58.33%) followed by Ampicillin (25%) and Cotrimoxazole (16.67%). Finally, the result of the study recommended that the use of standardized procedures in slaughtering and handling of chicken meat, provision of training on best practice of handling of meat for handlers and raising the level of awareness of people about the healthy consumption of chicken meat should be increased

Si-integrated ultrathin films of phase-pure Y3Fe5O12 (YIG) via novel two-step rapid thermal anneal

Traditional one-step annealing of ultrathin amorphous Y–Fe–O films on Si has been reported to yield ‘incomplete crystallization’. Here, it is shown that films produced by standard anneals (e.g.: 800°C, 3 min) actually contain yttrium iron garnet (YIG) crystallites in a nanocrystalline non-garnet matrix. During in situ TEM laser annealing, a low-temperature pre-anneal enabled subsequent YIG crystallization at velocities of 280 nm/s that prevented the formation of the nanocrystalline matrix. From these results, a two-step rapid thermal anneal was identified (400°C, 3 min; 800°C, 3 min) that successfully produces phase-pure garnet films on SiO2 on Si

37 elementare axiomatische Charakterisierungen des reellen Zahlkoerpers

enl. ed.Available from TIB Hannover: RR 9398(87) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Si-integrated ultrathin films of phase-pure Y₃Fe₅O₁₂ (YIG) via novel two-step rapid thermal anneal

<p>Traditional one-step annealing of ultrathin amorphous Y–Fe–O films on Si has been reported to yield ‘incomplete crystallization’. Here, it is shown that films produced by standard anneals (e.g.: 800°C, 3 min) actually contain yttrium iron garnet (YIG) crystallites in a nanocrystalline non-garnet matrix. During <i>in situ</i> TEM laser annealing, a low-temperature pre-anneal enabled subsequent YIG crystallization at velocities of 280 nm/s that prevented the formation of the nanocrystalline matrix. From these results, a two-step rapid thermal anneal was identified (400°C, 3 min; 800°C, 3 min) that successfully produces phase-pure garnet films on SiO₂ on Si.</p> <p><b>IMPACT STATEMENT</b></p> <p>A novel two-step anneal discovered through <i>in situ</i> TEM laser annealing produces phase-pure, fully crystallized ultrathin YIG films grown on SiO₂ on Si.</p