Screened Hybrid Exact Exchange Correction Scheme for Adsorption Energies on Perovskite Oxides

The bond formation between an oxide surface and oxygen, which is of importance for numerous surface reactions including catalytic reactions, is investigated within the framework of hybrid density functional theory that includes nonlocal Fock exchange. We show that there exists a linear correlation between the adsorption energies of oxygen on LaMO3 (M = Sc–Cu) surfaces obtained using a hybrid functional (e.g., Heyd–Scuseria–Ernzerhof) and those obtained using a semilocal density functional (e.g., Perdew–Burke–Ernzerhof) through the magnetic properties of the bulk phase as determined with a hybrid functional. The energetics of the spin-polarized surfaces follows the same trend as corresponding bulk systems, which can be treated at a much lower computational cost. The difference in adsorption energy due to magnetism is linearly correlated to the magnetization energy of bulk, that is, the energy difference between the spin-polarized and the non-spin-polarized solutions. Hence, one can estimate the correction ...

Microwave Plasma Assisted ALD Development for the Deposition of Gate Oxides & ALD of High-k Dielectrics

The semiconductor industry's urge towards faster, smaller and cheaper integrated circuits has lead the industry to smaller node devices. The integrated circuits that are now under volume production belong to 22 nm and 14 nm technology nodes. In 2007 the 45 nm technology came with the revolutionary high- /metal gate structure. 22 nm technology utilizes fully depleted tri-gate transistor structure. The 14 nm technology is a continuation of the 22 nm technology. Intel is using second generation tri-gate technology in 14 nm devices. After 14 nm, the semiconductor industry is expected to continue the scaling with 10 nm devices followed by 7 nm. Recently, IBM has announced successful production of 7 nm node test chips. This is the fashion how nanoelectronics industry is proceeding with its scaling trend. For the present node of technologies selective deposition and selective removal of the materials are required. Atomic layer deposition and the atomic layer etching are the respective techniques used for selective deposition and selective removal. Atomic layer deposition still remains as a futuristic manufacturing approach that deposits materials and lms in exact places. In addition to the nano/microelectronics industry, ALD is also widening its application areas and acceptance. The usage of ALD equipments in industry exhibits a diversi cation trend. With this trend, large area, batch processing, particle ALD and plasma enhanced like ALD equipments are becoming prominent in industrial applications. In this work, the development of an atomic layer deposition tool with microwave plasma capability is described, which is a ordable even for lightly funded research labs.

Geochemical analysis at ODP Site 207-1261 from the Demerara Rise in the western equatorial Atlantic

A high-resolution geochemical record of a 120 cm black shale interval deposited during the Coniacian-Santonian Oceanic Anoxic Event 3 (ODP Leg 207, Site 1261, Demerara Rise) has been constructed to provide detailed insight into rapid changes in deep ocean and sediment paleo-redox conditions. High contents of organic matter, sulfur and redox-sensitive trace metals (Cd, Mo, V, Zn), as well as continuous lamination, point to deposition under consistently oxygen-free and largely sulfidic bottom water conditions. However, rapid and cyclic changes in deep ocean redox are documented by short-term (~15-20 ka) intervals with decreased total organic carbon (TOC), S and redox-sensitive trace metal contents, and in particular pronounced phosphorus peaks (up to 2.5 wt% P) associated with elevated Fe oxide contents. Sequential iron and phosphate extractions confirm that P is dominantly bound to iron oxides and incorporated into authigenic apatite. Preservation of this Fe-P coupling in an otherwise sulfidic depositional environment (as indicated by Fe speciation and high amounts of sulfurized organic matter) may be unexpected, and provides evidence for temporarily non-sulfidic bottom waters. However, there is no evidence for deposition under oxic conditions. Instead, sulfidic conditions were punctuated by periods of anoxic, non-sulfidic bottom waters. During these periods, phosphate was effectively scavenged during precipitation of iron (oxyhydr)oxides in the upper water column, and was subsequently deposited and largely preserved at the sea floor. After ~15-25 ka, sulfidic bottom water conditions were re-established, leading to the initial precipitation of CdS, ZnS and pyrite. Subsequently, increasing concentrations of H2S in the water column led to extensive formation of sulfurized organic matter, which effectively scavenged particle-reactive Mo complexes (thiomolybdates). At Site 1261, sulfidic bottom waters lasted for ?90-100 ka, followed by another period of anoxic, non-sulfidic conditions lasting for ~15-20 ka. The observed cyclicity at the lower end of the redox scale may have been triggered by repeated incursions of more oxygenated surface- to mid-waters from the South Atlantic resulting in a lowering of the oxic-anoxic chemocline in the water column. Alternatively, sea water sulfate might have been stripped by long-lasting high rates of sulfate reduction, removing the ultimate source for HS**- production.

Study of Co-based hydrotalcite-derived mixed metal oxides partially modified with silver as potential catalysts for N2O decomposition

Co-Al-Ox mixed metal oxides partially modified with Cu or Mg, as well as Ag were successfully prepared, characterized and evaluated as potential catalysts for the N2O decomposition. The materials were characterized by the following techniques: X-Ray Diffraction, Thermogravimetric Analysis (TGA), N2 Physisorption, Hydrogen Temperature-Programmed Reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). Ag-modified HT-derived mixed oxides showed enhanced activity compared to the undoped materials, the optimum composition was found for (1 wt.% Ag)CHT-Co3Al. The catalyst characterization studies suggested that the improved catalytic activity of Ag-promoted catalysts were mainly because of the altered redox properties of the materials.

Engineering thin films of magnetic alloys and semiconductor oxides at the nanoscale

The thesis aims to exploit properties of thin films for applications such as spintronics, UV detection and gas sensing. Nanoscale thin films devices have myriad advantages and compatibility with Si-based integrated circuits processes. Two distinct classes of material systems are investigated, namely ferromagnetic thin films and semiconductor oxides. To aid the designing of devices, the surface properties of the thin films were investigated by using electron and photon characterization techniques including Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), grazing incidence X-ray diffraction (GIXRD), and energy-dispersive X-ray spectroscopy (EDS). These are complemented by nanometer resolved local proximal probes such as atomic force microscopy (AFM), magnetic force microscopy (MFM), electric force microscopy (EFM), and scanning tunneling microscopy to elucidate the interplay between stoichiometry, morphology, chemical states, crystallization, magnetism, optical transparency, and electronic properties. Specifically, I studied the effect of annealing on the surface stoichiometry of the CoFeB/Cu system by in-situ AES and discovered that magnetic nanoparticles with controllable areal density can be produced. This is a good alternative for producing nanoparticles using a maskless process. Additionally, I studied the behavior of magnetic domain walls of the low coercivity alloy CoFeB patterned nanowires. MFM measurement with the in-plane magnetic field showed that, compared to their permalloy counterparts, CoFeB nanowires require a much smaller magnetization switching field , making them promising for low-power-consumption domain wall motion based devices. With oxides, I studied CuO nanoparticles on SnO2 based UV photodetectors (PDs), and discovered that they promote the responsivity by facilitating charge transfer with the formed nanoheterojunctions. I also demonstrated UV PDs with spectrally tunable photoresponse with the bandgap engineered ZnMgO. The bandgap of the alloyed ZnMgO thin films was tailored by varying the Mg contents and AES was demonstrated as a surface scientific approach to assess the alloying of ZnMgO. With gas sensors, I discovered the rf-sputtered anatase-TiO2 thin films for a selective and sensitive NO2 detection at room temperature, under UV illumination. The implementation of UV enhances the responsivity, response and recovery rate of the TiO2 sensor towards NO2 significantly. Evident from the high resolution XPS and AFM studies, the surface contamination and morphology of the thin films degrade the gas sensing response. I also demonstrated that surface additive metal nanoparticles on thin films can improve the response and the selectivity of oxide based sensors. I employed nanometer-scale scanning probe microscopy to study a novel gas senor scheme consisting of gallium nitride (GaN) nanowires with functionalizing oxides layer. The results suggested that AFM together with EFM is capable of discriminating low-conductive materials at the nanoscale, providing a nondestructive method to quantitatively relate sensing response to the surface morphology.

Opportunities for ceria-based mixed oxides versus commercial platinum-based catalysts in the soot combustion reaction. Mechanistic implications

The aim of this paper is to study the activities of ceria–zirconia and copper/ceria–zirconia catalysts, comparing with a commercial platinum/alumina catalyst, for soot combustion reaction under different gas atmospheres and loose contact mode (simulating diesel exhaust conditions), in order to analyse the kinetics and to deduce mechanistic implications. Activity tests were performed under isothermal and TPR conditions. The NO oxidation to NO2 was studied as well. It was checked that mass transfer limitations were not influencing the rate measurements. Global activation energies for the catalysed and non-catalysed soot combustion were calculated and properly discussed. The results reveal that ceria-based catalysts greatly enhance their activities under NOx/O2 between 425 °C and 450 °C, due to the “active oxygen”-assisted soot combustion. Remarkably, copper/ceria–zirconia shows a slightly higher soot combustion rate than the Pt-based catalyst (under NOx/O2, at 450 °C).

Mesoporous mixed Nb2O5-ZrO2 catalysts for dehydration of glucose into 5-hydroxymethylfurfural

Biomass is the world’s most important renewable carbon source, whose major component, carbohydrates, can be valorized by transformation into biofuels and high value-added chemicals. Among the latter, 5-hydroxymethylfurfural (HMF), obtained by C6 carbohydrates dehydration, is a versatile and key intermediate for the production of a large spectrum of biobased chemicals. Different catalytic systems have been evaluated for HMF production, mostly based on heterogeneous catalysis as alternative to the use of conventional mineral acids [1]. Moreover, niobium oxide has shown interesting properties as acid catalyst for dehydration of sugars [2-3]. On the other hand, the high surface area and large pore size of mesoporous solids make them suitable for many catalytic processes. In the present work, the dehydration of glucose to HMF has been evaluated by using different mesoporous mixed Nb2O5-ZrO2 in a biphasic water–Methyl Isobutyl Ketone (MIBK) solvent system to avoid the HMF degradation. Different experimental parameters, such as reaction temperature and time, as well as the addition of CaCl2 have been studied in order to maximize the HMF yield.N2 adsorption-desorption isotherms have corroborated the mesostructured character of catalysts, being all isotherms of Type IV according to the IUPAC classification. BET surface area decreases for catalysts with higher Zr content (Table 1). Likewise, pore volume and average pore diameter values diminish after Zr incorporation. Concerning the acid properties, a clear correlation between Nb and acidity can be observed, in such a way that total acidity, as deduced from NH3-TPD, decreases when the Zr content rises, and consequently the amount of Nb is reduced.These mesoporous Nb-Zr catalysts have been tested in the dehydration of glucose to HMF at 175 ºC under batch operation in aqueous solution, using MIBK as co-solvent. It can be observed that both glucose conversion and HMF yield increase with the Nb content, being maximum (90% and 36%, respectively) after 90 minutes for Nb2O5. This trend changes when CaCl2 is added to the reaction medium, improving the catalytic performance of mixed oxides and ZrO2, but Nb2O5 maintains similar results than without salt addition. This could be justified by the interaction between CaCl2 and Lewis acid sites, since zirconium oxide possesses a higher amount of this acid sites type.

Effects of zirconium and strontium on the biocorrosion of Mg-Zr-Sr alloys for biodegradable implant applications

The successful applications of magnesium (Mg) alloys as biodegradable orthopedic implants are mainly restricted due to their rapid degradation rate in the physiological environment, leading to a loss of mechanical integrity. This study systematically investigated the degradation behaviors of novel Mg-Zr-Sr alloys using electrochemical techniques, hydrogen evolution, and weight loss in simulated body fluid (SBF). The microstructure and degradation behaviors of the alloys were characterized using optical microscopy, XRD, SEM, and EDX. The results indicate that Zr and Sr concentrations in Mg alloys strongly affected the degradation rate of the alloys in SBF. A high concentration of 5 wt% Zr led to acceleration of anodic dissolution, which significantly decreased the biocorrosion resistance of the alloys and their biocompatibility. A high volume fraction of Mg17Sr2 phases due to the addition of excessive Sr (over 5 wt%) resulted in enhanced galvanic effects between the Mg matrix and Mg17Sr2 phases, which reduced the biocorrosion resistance. The average Sr release rate is approximately 0.15 mg L^-1 day^-1, which is much lower than the body burden and proves its good biocompatibility. A new biocorrosion model has been established to illustrate the degradation of alloys and the formation of degradation products on the surface of the alloys. It can be concluded that the optimal concentration of Zr and Sr is less than 2 wt% for as-cast Mg-Zr-Sr alloys used as biodegradable orthopedic implants.

The influence of titania-zirconia-zirconium titanate nanotube characteristics on osteoblast cell adhesion

Studies of biomaterial surfaces and their influence on cell behavior provide insights concerning the design of surface physicochemical and topography properties of implant materials. Fabrication of biocompatible metal oxide nanotubes on metallic biomaterials, especially titanium alloys such as Ti50Zr via anodization, alters the surface chemistry as well as surface topography of the alloy. In this study, four groups of TiO2-ZrO2-ZrTiO4 nanotubes that exhibit diverse nanoscale dimensional characteristics (i.e. inner diameter Di, outer diameter Do and wall thicknesses Wt) were fabricated via anodization. The nanotubes were annealed and characterized using scanning electron microscopy and 3-D profilometry. The potential applied during anodization influenced the oxidation rate of titanium and zirconium, thereby resulting in different nanoscale characteristics for the nanotubes. The different oxidation and dissolution rates both led to changes in the surface roughness parameters. The in vitro cell response to the nanotubes with different nanoscale dimensional characteristics was assessed using osteoblast cells (SaOS2). The results of the MTS assay indicated that the nanotubes with inner diameter (Di)≈40nm exhibited the highest percentage of cell adhesion of 41.0%. This result can be compared to (i) 25.9% cell adhesion at Di≈59nm, (ii) 33.1% at Di≈64nm, and (iii) 33.5% at Di≈82nm. The nanotubes with Di≈59nm exhibited the greatest roughness parameter of Sa (mean roughness), leading to the lowest ability to interlock with SaOS2 cells.

Development of a 1-D Catalyzed Diesel Particulate Filter Model for Simulation of the Performance and the Oxidation of Particulate Matter and Nitrogen Oxides Using Passive Oxidation and Active Regeneration Engine Experimental Data

Back-pressure on a diesel engine equipped with an aftertreatment system is a function of the pressure drop across the individual components of the aftertreatment system, typically, a diesel oxidation catalyst (DOC), catalyzed particulate filter (CPF) and selective catalytic reduction (SCR) catalyst. Pressure drop across the CPF is a function of the mass flow rate and the temperature of the exhaust flowing through it as well as the mass of particulate matter (PM) retained in the substrate wall and the cake layer that forms on the substrate wall. Therefore, in order to control the back-pressure on the engine at low levels and to minimize the fuel consumption, it is important to control the PM mass retained in the CPF. Chemical reactions involving the oxidation of PM under passive oxidation and active regeneration conditions can be utilized with computer numerical models in the engine control unit (ECU) to control the pressure drop across the CPF. Hence, understanding and predicting the filtration and oxidation of PM in the CPF and the effect of these processes on the pressure drop across the CPF are necessary for developing control strategies for the aftertreatment system to reduce back-pressure on the engine and in turn fuel consumption particularly from active regeneration. Numerical modeling of CPF's has been proven to reduce development time and the cost of aftertreatment systems used in production as well as to facilitate understanding of the internal processes occurring during different operating conditions that the particulate filter is subjected to. A numerical model of the CPF was developed in this research work which was calibrated to data from passive oxidation and active regeneration experiments in order to determine the kinetic parameters for oxidation of PM and nitrogen oxides along with the model filtration parameters. The research results include the comparison between the model and the experimental data for pressure drop, PM mass retained, filtration efficiencies, CPF outlet gas temperatures and species (NO2) concentrations out of the CPF. Comparisons of PM oxidation reaction rates obtained from the model calibration to the data from the experiments for ULSD, 10 and 20% biodiesel-blended fuels are presented.

Patterning optically clear films: co-planar transparent and color-contrasted thin films from interdiffused electrodeposited and solution-processed metal oxides

Transparent thin films can now be site-selectively patterned and positioned on surface using mask-defined electrodeposition of one oxide and overcoating with a different solution-processed oxide, followed by thermal annealing. Annealing allows an interdiffusion process to create a new oxide that is entirely transparent. A primary electrodeposited oxide can be patterned and the secondary oxide coated over the entire substrate to form high color contrast coplanar thin film tertiary oxide. The authors also detail the phase formation and chemical state of the oxide and how the nature of the electrodeposited layer and the overlayer influence the optical clearing of the patterned oxide film.

Opening lids: modulation of lipase immobilization by graphene oxides

Lipases, which can be immobilized and reused for many reaction cycles, are important enzymes with many industrial applications. A key challenge in lipase immobilization for catalysis is to open the lipase lid and maintain it in an open conformation in order to expose its active site. Here we have designed "tailor-made" graphene-based nanosupports for effective lipase (QLM) immobilization through molecular engineering, which is in general a grand challenge to control biophysicochemical interactions at the nano-bio interface. It was observed that increasing hydrophobic surface increased lipase activity due to opening of the helical lid present on lipase. The molecular mechanism of lid opening revealed in molecular dynamics simulations highlights the role of hydrophobic interactions at the interface. We demonstrated that the open and active form of lipase can be achieved and tuned with an optimized activity through chemical reduction of graphene oxide. This research is a major step toward designing nanomaterials as a platform for enhancing enzyme immobilization/activity.

Enzyme architectonics on graphene oxides.

The thesis focuses on use of carbon nanoparticles, namely graphene oxides for studying the effect of hydrophobicity on enzyme structure and how they it influences the enzyme activity at molecular level. It was observed that controlling the hydrophobicity of the nanoparticle is a key towards modulating enzyme activity.

Nitrogen oxides and CO2 from an Oxisol cultivated with corn in succession to cover crops.

2016