Growth-rate induced epitaxial orientation of CeO2 on Al2O3(0001)

High-quality CeO2 films were grown on Al2O3(0001) substrates using oxygen plasma-assisted molecular beam epitaxy. The epitaxial orientation of the films is found to be CeO2(100) and CeO2(111) at low ( \u3c 8 A/min) and higher growth rates ( \u3e 12 A/min), respectively. CeO2(100) film grows as three-dimensional islands, while CeO2(111) film grows as two-dimensional layers. The CeO2(100) film exhibits better epitaxial quality compared to CeO2(111) film. However, the CeO2(100) film on Al2O3(0001) shows three in-plane domains at 30 degrees to each other. While the epitaxial quality is attributed to the close match between oxygen sublattices of CeO2(100) and Al2O3(0001), the three in-plane domains in CeO2(100) are attributed to the threefold symmetry of the substrate. The relative stability of different epitaxial orientations of CeO2 films on Al2O3(0001) obtained from molecular dynamics simulations strongly supports the experimental observations

Identification and thermochemical analysis of high-lignin feedstocks for biofuel and biochemical production

Background - Lignin is a highly abundant biopolymer synthesized by plants as a complex component of plant secondary cell walls. Efforts to utilize lignin-based bioproducts are needed. Results - Herein we identify and characterize the composition and pyrolytic deconstruction characteristics of high-lignin feedstocks. Feedstocks displaying the highest levels of lignin were identified as drupe endocarp biomass arising as agricultural waste from horticultural crops. By performing pyrolysis coupled to gas chromatography-mass spectrometry, we characterized lignin-derived deconstruction products from endocarp biomass and compared these with switchgrass. By comparing individual pyrolytic products, we document higher amounts of acetic acid, 1-hydroxy-2-propanone, acetone and furfural in switchgrass compared to endocarp tissue, which is consistent with high holocellulose relative to lignin. By contrast, greater yields of lignin-based pyrolytic products such as phenol, 2-methoxyphenol, 2-methylphenol, 2-methoxy-4-methylphenol and 4-ethyl-2-methoxyphenol arising from drupe endocarp tissue are documented. Conclusions - Differences in product yield, thermal decomposition rates and molecular species distribution among the feedstocks illustrate the potential of high-lignin endocarp feedstocks to generate valuable chemicals by thermochemical deconstruction

Oxygen Pressure-Tuned Epitaxy and Optoelectronic Properties of Laser-Deposited ZnO Films on Sapphire

Influence of oxygen pressure on the epitaxy, surface morphology, and optoelectronic properties has been studied in the case of ZnO thin films grown on sapphire ~0001! by pulsed-laser deposition. Results of Rutherford backscattering and ion channeling in conjunction with atomic force microscopy clearly indicate that the growth mode, degree of epitaxy, and the defect density strongly depend on the oxygen background pressure during growth. It is also found that the growth mode and the defects strongly influence the electron mobility, free-electron concentration, and the luminescence properties of the ZnO films. By tuning the oxygen pressure during the initial and the final growth stages, smooth and epitaxial ZnO films with high optical quality, high electron mobility, and low background carrier concentration have been obtained. The implication of these results towards the fabrication of superlattices and controlled n- and p-type doping is discussed