Scientific Publications 2004
2004. "Studies of Two-and Three-Dimensional ZnO:Co Structures Through Different Sythetic Routes." Journal of Applied Physics 95(11):7393-7395 Part 2. Abstract Multilayers of Co and ZnO, with nominal layer thicknesses on the atomic scale with up to 25 bilayers, were deposited by ion beam sputtering on silicon and glass substrates at ambient temperature. Thick epitaxial CoxZn₁-xO films on A1₂O₃(012) substrates were grown by metalorganic chemical vapor deposition using a liquid precursor delivery system. All were co-doped with A₁. Comparative analysis of magnetization, resistivity, and magnetoresistance measurements, performed in the temperature range 2.5-300K, is presented. At small thickness of Co layers in the multilayer samples, these structures are diluted magnetic semiconductor (DMS) superlattices, with properties close to the epitaxial films. A crossover from DMS to discontinuous magnetic metal/semiconductor multilayers is observed with increasing metal content in the multilayers. This leads to changes in conduction mechanisms, with increasing contribution of quasi-three-dimensional or quasi-two-dimensional inter-granular hopping, and superparamagnetism.
2004. "Prospects for Enhancing Carbon Sequestration and Reclamation of Degraded Lands with Fossil-fuel Combustion By-products." Advances in Environmental Research 8(3-4):425-438. Abstract Concern for the potential global change consequences of increasing atmospheric CO2 has prompted interest in the development of mechanisms to reduce or stabilize atmospheric CO2 .During the next several decades, a program focused on terrestrial sequestration processes could make a significant contribution to abating CO2 increases.The reclamation of degraded lands, such as mine-spoil sites, highway rights-of-way, and poorly managed lands, represents an opportunity to couple C sequestration with the use of fossil-fuel and energy by-products and other waste material, such as biosolids and organic wastes from human and animal sewage treatment facilities, to improve soil quality. Degraded lands are often characterized by acidic pH, low levels of key nutrients, poor soil structure, and limited moisture-retention capacity.Much is known about the methods to improve these soils, but the cost of implementation is often a limiting factor.However, the additional financial and environmental benefits of C sequestration may change the economics of land reclamation activities.The addition of energy-related by-products can address the adverse conditions of these degraded lands through a variety of mechanisms, such as enhancing plant growth and capturing of organic C in long-lived soil C pools.This review examines the use of fossil-fuel combustion by-products and organic amendments to enhance C sequestration and identifies the key gaps in information that still must be addressed before these methods can be implemented on an environmentally meaningful scale.
2004. "Modeling field-scale dense nonaqueous phase liquid dissolution kinetics in heterogeneous aquifers." Water Resources Research 40(W05109):, doi:10.1029/2003WR002807 Abstract This study investigates field-scale DNAPL dissolution kinetics using high-resolution numerical simulations of DNAPL releases and dissolved phase transport. A percolation model is employed to simulate the distribution of TCE within 10 × 10 × 10 m source zones with spatially heterogeneous aquifer properties following a release event. Distributed aquifer properties and DNAPL saturations are utilized to simulate coupled groundwater flow and long-term dissolved phase transport. Grid-scale dissolution rates are computed based on published bench-scale relationships. Effective field-scale mass transfer coefficients are computed from simulated TCE fluxes at the downstream source zone boundary. Heterogeneity in groundwater velocity and DNAPL distributions leads to field-scale mass transfer coefficients that are much lower than laboratory-scale values. Field-scale mass transfer coefficients are observed to vary in direct proportion to the mean groundwater velocity, in contrast to laboratory studies that indicate proportionality with velocity to a power of ∼0.7. Computed field-scale mass transfer coefficients vary approximately in proportion to relative DNAPL mass raised to an empirical depletion exponent, which is <1 for laterally extensive DNAPL lenses and >1 for more randomly oriented residual DNAPL regions. The former DNAPL geometries exhibit slow reductions in source concentration and contaminant flux with time as mass depletion proceeds. The latter DNAPL geometries exhibit significant and steady declines in source concentration and contaminant flux with time as depletion occurs.
2004. "Electron-Stimulated Production of Molecular Hydrogen at the Interfaces of Amorphous Solid Water Films on Pt(111)." Journal of Chemical Physics 121(8):3736-3744. Abstract The electron-stimulated production of molecular hydrogen (D2, HD and H2) from amorphous solid water (ASW) deposited on Pt(111) is investigated. Experiments with isotopically layered films of H2O and D2O are used to profile the spatial distribution of the electron-stimulated reactions leading to hydrogen within the water films. The molecular hydrogen yield has two components that have distinct reaction kinetics due to reactions that occur at the ASW/Pt interface and the ASW/vacuum interface, but not in the bulk. However, the molecular hydrogen yield as a function of the ASW film thickness in both pure and isotopically layered films indicates that the energy for the reactions is absorbed in the bulk of the films and electronic excitations migrate to the interfaces where they drive the reactions
2004. "Electron-Stimulated Reactions in Thin D2O Films on Pt(111) Mediated by Electron Trapping." Journal of Chemical Physics 121(8):3727-3735. Abstract We have measured the electron-stimulated desorption (ESD) of D2, O2 and D2O, the electron-stimulated dissociation of D2O at the D2O/Pt interface, and the total electron-stimulated sputtering in thin D2O films adsorbed on Pt(111) as a function of the D2O coverage (i.e. film thickness). Qualitatively different behavior is observed above and below a threshold coverage of ~2 monolayers (ML). For coverages less than ~2 ML electron irradiation results in D2O ESD and some D2 ESD, but no detectible reactions at the water/Pt interface and no O2 ESD. For larger coverages, electron-stimulated reactions at the water/Pt interface occur, O2 is produced and the total electron-stimulated sputtering of the film increases. An important step in the electron-stimulated reactions is the reaction between water ions (generated by the incident electrons) and electrons trapped in the water films to form dissociative neutral molecules. However, the electron trapping depends sensitively on the water coverage: For coverages less than ~ 2 ML, the electron trapping probability is low and the electrons trap preferentially at the water/vacuum interface. For larger coverages, the electron trapping increases and the electrons are trapped in the bulk of the film. We propose that the coverage dependence of the trapped electrons is responsible for the observed coverage dependence of the electron-stimulated reactions.
2004. "High Resolution X-ray Photoelectron Spectroscopy of Styrene Oxide Adsorption and Reaction on Ag(111)." Surface Science 571:139-145. Abstract the abstract for this product is not available at this time.
2004. "A Comparative Study of the Structure and Energetics of Elementary Defects in 3C- and 4H-SiC." Journal of Physics. Condensed matter 16(8):1307-1323. Abstract The potential non-equivalent defects in both 3C- and 4H-SiC are classified by a new method that is based on symmetry considerations. In 4H-SiC, their number is considerably higher than in 3C-SiC, since the hexagonal symmetry leads to diversification. The different theoretical methods hitherto used to investigate defects in 3C-SiC are critically reviewed. Classical MD simulations with a recently developed interatomic potential are employed to investigate the stability, structure and energetics of the large number of potential non-equivalent defects that may exist in 4H-SiC. Most of the potential defects in 4H-SiC are found to be stable. The interstitials between hexagonal and trigonal rings, which do not exist in 3C-SiC, are characteristic for 4H-SiC and other hexagonal polytypes. The structure and energetics of some complex and anisotropic dumbbells depend strongly on the polytype. On the other hand, polytypism does not have a significant influence on the properties of the more compact and isotropic defects, such as vacancies, antisites, hexagonal interstitials, and many dumbbells. The results allow conclusions to be drawn about the energy hierarchy of the defects.
2004. "Integrative Analysis of the Mitochondrial Proteome in Yeast." PloS Biology 2(6):0795-0804. Abstract In this study yeast mitochondria were used as a model system to apply, evaluate, and integrate different genomic approaches to define the proteins of an organelle. Liquid chromatography mass spectrometry applied to purified mitochondria identified 546 proteins. By expression analysis and comparison to other proteome studies, we demostrate that the proteomic approach identifies primarily highly abundant proteins. By expanding our evaluation to other types of genomic approaches, including systematic deletion phenotype screening, expression profiling, subcellular localization studies, protein interaction analyses, and computational predictions, we show that an integration of approaches moves beyond the limitations of any single approach. We report the success of each approach by benchmarking it against a reference set of known mitochondrial proteins, and predict approximately 700 proteins associated with the mitochondrial organelle from the integration of 22 datasets. We show that a combination of complementary approaches like deletion phenotype screening and mass spectrometry can identify over 75% of the known mitochondrial proteome. These findings have implications for choosing optimal genome-wide approaches for the study of other cellular systems, including organelles and pathways in various species. Furthermore, our systematic identification of genes involved in mitochondrial function and biogenesis in yeast expands the candidates genes available for mapping Mendelian and complex mitochondrial disorders in humans.
2004. "Room-Temperature Ferromagnetism in Chemically Synthesized Sn₁-xCox O₂ Powders." Applied Physics Letters 85(9):1559-1561. Abstract Room temperature ferromagnetism is observed in chemically synthesized powder samples of Sn₁₋xCox O₂ with x = 0.005 and 0.01. Magnetic hysteresis loops are ovserved at 300K with coercivity Hc ~ 630 Oe, saturation magnetization Ms ~0.133μв and about 31% remenance. Analyses of the magnetization data of paramagnetic samples with x = 0.01 and 0.03, measured as a function of temperature (3-330K) and magnetic field (up to 50kOe), indicated the presence of Co²⁺ ions with spin S = 3/2. Magnetic data obtained from samples prepared at different temperatures indicate that the observed ferromagnetism for x ≤ 0.01 might have been triggered by changes in the oxygen stiochiometry.