Xiaoyuan Qi

Integrating yttrium iron garnet onto nongarnet substrates with faster deposition rates and high reliability

Magneto-optical garnets (Y3Fe5O12 or YIG) were grown monolithically by a novel reactive radio-frequency sputtering method that used a partial pressure differential to increase sputtering rates. MgO and quartz substrates were used as they are good buffer layers and optical claddings for integration. A wide single-phase field for annealed YIG was found (26.9–43.2at% Y), and the magnetic properties were measured. The films had refractive indices of 2.1 and out-of-plane Faraday rotations up to 0.2°∕μm at 633nm. The dielectric matrix was used to calculate the difference in the propagation constants of forward and backward traveling light (Δβ=1.999×10−5).

Large-scale ordering of porous Si using anodic aluminum oxide grown by directed self-assembly

Porous Si with perfect long range order (mm2 scale) was obtained using an integrated mask of ordered anodic aluminum oxide (AAO). This represents an increase of many orders of magnitude in the ordered domain size compared with porous Si made with self-assembled AAO masks. Here, master stamps composed of silicon nitride posts (180nm diameter, 400nm spacing) were imprinted into Al films that were grown onto nitride-coated Si wafers. The Al films were then anodized and the resulting ordered, nanoporous pattern was transferred into the Si using reactive ion etching. The stamps could be reused a multitude of times to produce exact replicas.

Si-doping of Co/Pd multilayers for improved signal to noise in perpendicular magnetic recording media

Co/Pd-based multilayers have been Si doped in order to enhance their potential for extremely high-density perpendicular magnetic recording (PMR) media. Co/Pd multilayers have high interface-induced perpendicular anisotropy, high coercivity, and high remnant squareness, all of which make them excellent candidates for PMR. Dopants can be utilized to reduce grain size as well as to reduce magnetic coupling between grains via compositional segregation to the grain boundaries. Here, Si was chosen for a dopant because the phase diagrams indicated that Si may migrate to form silicides at the grain boundaries. An additional benefit of Si as a dopant is that it can be detected chemically, unlike the more common dopant B, which is a much lighter element. A significant difference between the current doping and all other doping in PMR media is that Si was added into the Pd layers rather than the Co layers, which keeps the magnetic layer pure and improves the magnetic properties. This media was also made at room temperature, which yields smaller grains and reduces interfacial diffusion. The static magnetic properties of the Si-doped multilayers were very promising as measured by vibrating sample magnetometry: Hc= 5400 Oe, Ms= 160 emu/cm/sup 3/, and /spl alpha/=4/spl pi/dM/dH/spl ap/1. The fact that the latter term was unity suggests that the grains are magnetically decoupled which promises low transition noise. The samples were measured by atomic force and magnetic force microscopy (AFM/MFM) and by X-ray scattering. They were found to have 12-nm grains. In addition, Si-doped multilayer media that were spin-stand tested showed an increase in signal-to-noise ratio of 5 dB compared to high-performing B-doped media.

Effects and microstructures of indium tin oxide seed layers for perpendicular magnetic recording media

Co/Pd multilayers have been shown to exhibit fcc structures and they have good recording properties with ITO as a seed layer. The microstructures of extremely thin indium–tin–oxide (ITO) grown in pure Ar, and the effects of this ITO as seed layers for Co/Pd and Co75B25/Pd multilayers, have been studied. The magnetic properties of the multilayers have been correlated with the crystallinity of the ITO. TEM analysis showed that this ITO has a crystalline structure instead of the amorphous structure reported by other researchers. Both heated and unheated films had what appeared to be metallic fcc structures with lattice constants of 4.88 A. Heating ITO seed layers led to increased coercivity (from 5.5 kOe to 7 kOe) in Co/Pd multilayers that were grown at room temperature.

Integration of magneto-optic garnet waveguides and polarizers for optical isolators

YIG waveguides and polarizers were integrated monolithically onto semiconductors. The waveguide losses were 1.55 dB/mm with Faraday rotations of 0.2 dB/mm. Birefringence was minimized by optimized etching. Photonic crystal polarizers and biasing films completed the isolator.

Garnet Waveguides and Polarizers for Integrated Optical Isolators on Si Substrates

High quality YIG waveguides and photonic crystal polarizers were fabricated on Si with various cladding/buffer layers. The structures were designed for optical isolation at 1.55 mum with the waveguide acting as a Faraday rotator with an integrated magnetic biasing film.

Fabrication of Garnet Waveguides and Polarizers for Integrated Optical Isolators

YIG waveguides and photonic crystal polarizers were successfully integrated with Si using SiO2 claddings. The films were grown by room temperature reactive RF sputtering and rapid thermal annealing. Faraday rotations of 0.2deg/mum were achieved.

Opening hybrid band gaps in two-dimensional photonic crystals of Pb(Mg 1/3 Nb 1/3 )O 3 -PbTiO 3 having very low refractive index contrast

The effect of anisotropy on photonic crystals of Pb(Mg_1/3Nb_1/3)O₃-PbTiO₃ rods in air matrices was analyzed. Despite a low refractive index contrast (n=1.47), hybrid photonic bandgaps were achieved after optimization of the structure and the anisotropy.

Analysis of one-dimensional photonic band gap structure to design tunable electro-optic filters for DWDM

A DWDM tunable electro-optic filter using photonic bandgaps was designed. The tuning range and minimum channel spacing was controlled by an electro-optic defect, Pb (Mg_1/3Nb_1/3)O₃-PbTiO₃, or by including the EO material within the reflecting stacks.

Opening of Hybrid Bandgaps in Two-Dimensional Photonic Crystals of Pb(Mg

The effect of anisotropy on two-dimensional photonic crystals of hexagonally arranged Pb(Mg1/3Nb1/3)O3-PbTiO3 (PMNT) rods in air background was analyzed using a finite-difference time-domain method. The refractive index contrast between PMNT (n = 2.47) and air is low compared to conventional semiconductor-air photonic crystals. Yet, hybrid (polarization-independent) photonic bandgaps were achieved for anisotropic PMNT rods by adjusting the structural parameters and the anisotropy. The maximum bandwidth found was 20 nm. It was possible to engineer the center wavelength of this bandgap to 980, 1300, and 1550 nm, for potential applications as switches, electrooptic filters, and modulators in this region.