Hybrid Approach in Microscale Transport Phenomena: Application to Biodiesel Synthesis in Micro-reactors

A hybrid engineering approach to the study of transport phenomena, based on the synergy among computational, analytical, and experimental methodologies is reviewed. The focus of the chapter is on fundamental analysis and proof of concept developments in the use of nano- and micro-technologies for energy efficiency and heat and mass transfer enhancement applications. The hybrid approach described herein combines improved lumped-differential modeling, hybrid numericalanalytical solution methods, mixed symbolic-numerical computations, and advanced experimental techniques for micro-scale transport phenomena. An application dealing with micro-reactors for continuous synthesis of biodiesel is selected to demonstrate the instrumental role of the hybrid approach in achieving improved design and enhanced performance

Mechanism of lateral ordering of InP dots grown on InGaP layers

The mechanisms leading to the spontaneous formation of a two-dimensional array of InP/InGaP dots grown by chemical-beam epitaxy are discussed. Samples where the InGaP buffer layer was grown at different conditions were characterized by transmission electron microscopy. Our results indicate that a periodic strain field related to lateral two-dimensional compositional modulation in the InGaP buffer layer determines the dot nucleation positions during InP growth. Although the periodic strain field in the InGaP is large enough to align the InP dots, both their shape and optical properties are effectively unaltered. This result shows that compositional modulation can be used as a tool for in situ dot positioning. (c) 2005 American Institute of Physics.87

Self-assembled islands on strained systems: Control of formation, evolution, and spatial distribution

The dynamics of island formation on strained epitaxial films is investigated using the system formed by InAs on InP. Island shape, size, and spatial distribution are determined by surface atom diffusion that is modified by the presence of steps and/or corrugations on the surface. Different step characteristics-type and density-are shown to strongly affect the islanding process. By controlling the morphology of the underlying InP film we were able to achieve InAs/InP structures with periodic spatial distribution in one single step of growth.5719125011250

Three-dimensional mapping of the strain anisotropy in self-assembled quantum-wires by grazing incidence x-ray diffraction

Three-dimensional strain mapping of InAs self-assembled nanowires on an InP substrate using grazing incidence x-ray diffraction is reported. A remarkable anisotropy was observed for the strain components, parallel [-220] and perpendicular [220] to the wire axis. The highest strain relaxation was measured along the [220] direction. The relationship between the interatomic distances along the [-220] and [220] directions, for each z position (height) in the nanostructure, was obtained by angular scans in the vicinity of the (040) reciprocal lattice point. (C) 2004 American Institute of Physics.85163581358

Fractal analysis of Xylella fastidiosa biofilm formation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)We have investigated the growth process of Xylella fastidiosa biofilms inoculated on a glass. The size and the distance between biofilms were analyzed by optical images; a fractal analysis was carried out using scaling concepts and atomic force microscopy images. We observed that different biofilms show similar fractal characteristics, although morphological variations can be identified for different biofilm stages. Two types of structural patterns are suggested from the observed fractal dimensions D(f). In the initial and final stages of biofilm formation, D(f) is 2.73 + 0.06 and 2.68 + 0.06, respectively, while in the maturation stage, D(f) = 2.57 + 0.08. These values suggest that the biofilm growth can be understood as an Eden model in the former case, while diffusion-limited aggregation (DLA) seems to dominate the maturation stage. Changes in the correlation length parallel to the surface were also observed; these results were correlated with the biofilm matrix formation, which can hinder nutrient diffusion and thus create conditions to drive DLA growth. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3173172]1062Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)FAPESP [04/14576-2, 04/09132-8

Light scattering and atomic force microscopy study of InAs island formation on InP

Some aspects of the morphology of InAs island formation on InP have been studied by atomic force microscopy, photoluminescence, photoluminescence excitation spectroscopy, and Raman scattering. The InAs layer is grown by chemical beam epitaxy on top of InP surfaces with sawtooth-like channels. The deposition of a thin InAs layer results in quantum dots strongly aligned along the InP channels. Subsequent annealing in an arsenic atmosphere produces growth and loss of coherency of the islands. Atomic force microscopy shows the changes in size and alignment of the islands. Optical measurements serve to give quantitative estimates of the strain distribution among the top of the InP buffer layer, the wetting layer and the islands for the differently treated samples. (C) 2000 American Institute of Physics. [S0021-8979(00)02003-X].8731165117

Surface morphologies in GaAs homoepitaxy: Mound formation and evolution

Atomic force microscopy has been used to observe surface morphologies during growth of GaAs films on GaAs(001) by chemical beam epitaxy. Mound formation is observed at the beginning of GaAs growth as a function of the surface prior to deposition. GaAs substrates exhibit a large density of pits and cracks after usual thermal treatment employed for oxide desorption. On this kind of surface mounds form and coalesce as film thickness increases; surface planarization is eventually achieved-at this point, morphologies are typically those expected from two-dimensional growth. In this sense we observe that monolayer island size distribution is determined by the kinetic conditions used for the growth; nucleation sites and island spatial distribution, however, are strongly influenced by the topography of the initial surface where the film is deposited even for films thousands of monolayers thick. The final morphologies present wide terraces and few monolayer islands on top of them independent of growth conditions. This picture agrees with theoretical results where negligible step edge barriers are considered.5841947195

Evidence of Be3P2 formation during growth of Be-doped phosphorus-based semiconductor compounds

In this work, we present evidence that Be3P2 microcrystals are formed in Be-doped phosphorus-based semiconductor compounds grown by chemical beam epitaxy. Our results suggest that microcrystal formation occurs when high Be concentrations (> 10(18) cm(-3)) and temperatures higher than 500 degrees C are used for crystal growth. The main consequence of Be3P2 formation is a high phosphorus consumption close to these microcrystals that causes a large density of P vacancies in the semiconductor layer. This results in reduced electrical mobility, lattice parameter reduction, and poor crystalinity of the film in general. (c) 1999 American Institute of Physics. [S0003-6951(99)01624-1].74243669367

Strain relaxation and stress-driven interdiffusion in InAs/InGaAs/InP nanowires

The authors have investigated strain relaxation in InAs/InGaAs/InP nanowires (NW's). Transmission electron microscopy images show an additional stress field attributed to compositional modulation in the ternary layer, which disrupts NW formation and drives Ga interdiffusion into InAs, according to grazing incidence x-Ray diffraction under anomalous scattering conditions. The strain profile along the NW, however, is not significantly affected when interdiffusion is considered. Results show that the InAs NW energetic stability is preserved with the introduction of ternary buffer layer in the structure. (c) 2007 American Institute of Physics.91

On the optical properties of InAs/InP systems: The role of two-dimensional structures and three-dimensional islands

We investigate the effects of the interface morphology on the electronic properties of InAs/In systems using in-air atomic force microscopy and low temperature photoluminescence. Atomic force microscopy results show that the distribution of InAs strained film into three-dimensional islands and the two-dimensional wetting layer-typical of the Stranski-Krastanov growth mode-is strongly affected by the characteristics of the substrate and by the morphology of the InP buffer layer. The differences in the optical data are correlated to the different interface characteristics observed by atomic force microscopy. We discuss the origin of emission peaks taking into account the diffusion process of adsorbed atoms on the different types of surface. (C) 1998 American Institute of Physics.7291015101