Study of the optical and structural properties of multi quantum well structures grown on high-index surfaces
The MOVPE overgrowth of high [01@?1]-oriented ridges confined at sides by facets related to {n11} crystallographic planes is reported. We studied the influence of the side tilt on the thickness of the AlGaAs and GaAs epitaxial layers grown under the condition of the kinetic growth mode. The multi quantum well (MQW) structures were prepared on the sides of ridges tilted at 54.7^o, 45^o and 30^o to (100). The sidewall surface morphologies before and after epitaxial growth were evaluated and compared. We observed no tendency towards planarization towards a neighbouring high-index crystallographic plane, such as (211) and (311). We also showed that the quantum wells of the MQW structure make a smooth transition over the edge between the top surface and the facet as both AlGaAs and GaAs grew at similar rates on the surfaces.
Fabrication of GaAs symmetric pyramidal mesas prepared by wet-chemical etching using AlAs interlayer
We present a wet-chemical-etching method developed for the preparation of GaAs four-sided pyramid-shaped mesas. The method uses a fast lateral etching of AlAs interlayer that influences the cross-sectional profiles of etched structures. We have tested the method using H3PO4:H2O2:H2O etchant for the (100) GaAs patterning. The sidewalls of the prepared pyramidal structures together with the (100) bottom facet formed the cross-sectional angles 25° and 42° for mask edges parallel, resp. perpendicular to {011} cleavage planes. For mask edges turned in 45° according to the cleavage planes, 42° cross-sectional angles were obtained. Using the method, symmetric and more than 10-μm-high GaAs “Egyptian” pyramids with smooth tilted facets were prepared.
Scaffolds Containing Spirulina sp. LEB 18 Biomass: Development, Characterization and Evaluation of In Vitro Biodegradation.
Polymer nanofibers are nanomaterials that can be used as scaffolds in tissue engineering. The objective of this study was to develop, characterize and evaluate the in vitro degradation of a biomaterial consisting of nanofibers produced from biodegradable and biocompatible polymers with potential applications as a scaffold for tissue regeneration and containing Spirulina sp. LEB 18 biomass as the bioactive compound. The polymers used were poly(hydroxybutyrate-co-hydroxyvalerate) and polycaprolactone. The polymeric solutions exhibited sufficiently high viscosity to produce uniform nanofibers with diameters between 335 and 617 nm. The applied conditions were as follows: a voltage of 25 kV, a distance from the capillary to the collector of 120 mm, a capillary diameter of 0.80 mm, and 12% polycaprolactone and a blend of 5% polycaprolactone and 10% poly(hydroxybutyrate-co-hydroxyvalerate). The biomass was incorporated into the nanofibers at a concentration of 3%, and the incorporation was confirmed using confocal microscopy. The nanofibers were characterized using differential scanning calorimetry and thermogravimetric analysis, which showed that the addition of biomass did not alter the thermal properties of the biomaterial. The addition of biomass improved the tensile strength and elongation of the scaffolds compared with those produced with polymers alone. A biodegradation assay showed enzymatic action toward the biomaterial, simulating the behavior of natural tissue. Based on the analysis, it was concluded that the scaffolds that were produced have the potential to be applied in the field of tissue regeneration as biomaterials with pharmacological properties.