Manoj R. Pillai

Growth of InxGa1−xAs/GaAs heterostructures using Bi as a surfactant

The effects of a bismuth surfactant layer on the molecular beam epitaxy of GaAs and InxGa1−xAs layers on GaAs (001) were studied. The InxGa1−xAs surface reconstruction changed from arsenic stabilized 2×4 to bismuth stabilized 1×3 for high enough bismuth fluxes and low enough substrate temperatures. Maintaining a bismuth stabilized surface during InxGa1−xAs growth resulted in a larger number of reflection high-energy electron diffraction (RHEED) oscillations. RHEED patterns were also streakier after InxGa1−xAs growth with Bi. Roughness measurements using atomic force microscopy showed reduced root mean square roughness with Bi, e.g., from 3.8 to 2.8 nm, for 4 nm thick In0.3Ga0.7As layers. Simulations of x-ray diffraction results from 10 period In0.5Ga0.5As/GaAs superlattices showed that Bi reduced interface roughness from 1.1 to 0.5 nm and reduced interfacial broadening from 2.8 to 2.1 nm. The latter was attributed to reduced In segregation. InxGa1−xAs/GaAs (x=0.2–0.4) multiple quantum wells grown with Bi ...

Solid oxide fuel cell with oxide anode-side support

Solid oxide fuel cells (SOFCs) with Sr 0.8 La 0.2 TiO 3 anode-side supports, along with Ni-Y 2 O 4 -stabilized ZrO 2 (YSZ) anode, YSZ electrolyte, and LSM-YSZ (LSM = La 0.8 Sr 0.2 MnO 3 ) cathode, were prepared. Button cells yielded a power density up to 1.0 W/cm 2 in humidified H 2 and air at 800°C. The cells showed much-improved stability against coking in methane compared with conventional Ni-YSZ anode-supported SOFCs. A detailed model was used to fit the SOFC electrical results and to show that the good stability in methane was a result of the high 0-to-C ratio in the Ni-YSZ anode due to the Sr 0.8 La 0.2 TiO 3 support.

Structure and interfacial stability of (111)-oriented InAsSb/InAs strained-layer multiquantum well structures

Biaxially strained InAsxSb1−x/InAs (111)-oriented multiquantum well structures with x≈0.8 have been grown by metalorganic vapor phase epitaxy. The quality of the multiquantum well structures was assessed by double-crystal x-ray diffraction (θ–2θ scans) and kinematical computer simulations. The x-ray diffraction pattern of an InAs0.79Sb0.21/InAs multiquantum well film showed eight orders of satellite peaks, with a low diffuse background, indicating that excellent (111)-oriented structures can be achieved. The simulations modeled the compositional broadening of the interfaces, layer thickness fluctuations, and lattice spacing fluctuations of the compositionally modulated structures. The simulations indicated that the InAs/InAsSb interfaces were compositionally broadened over at least 0.5 nm, and that the layer thickness fluctuations of the highest quality structure were below the detection limit of 0.1 nm. Segregation of the antimony during deposition appears to be the primary cause of the compositional bro...

Liquid-Hydrocarbon Internal Reforming In Catalyst-Assisted SOFCs

Direct internal reforming of hydrocarbon fuels such as gasoline and diesel has been problematic due to coking on Ni-based SOFC anodes. This paper describes stable direct internal reforming SOFCs (Ni-YSZ/YSZ/LSM-YSZ) using anode reforming catalysts. Button cells were tested with a separate catalyst piece placed against the anode. Button cell power densities of ~ 0.5W/cm2 at ~ 800oC have been demonstrated with n-dodecane and n-tridecane mixed with H2O-CO2-air. Life tests with n-dodecane showed stable operation for > 140 h. Flattened-tube segmented-in- series modules with 14 cells on each side were tested with a catalyst layer coating on the fuel side of the zirconia support tube. For iso-octane mixed with either air or H2O-CO2-air, a stable maximum power density of ~ 0.6W/cm2 was obtained at ~ 800oC.