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.
Investigation of the GaAs-pyramids overgrowth using MOCVD
Abstract In this work, the epitaxial overgrowth of high and smooth GaAs mesas is presented. GaAs mesas of sidewall slope 35°, 40°, 45°, and 55° were first prepared by wet-chemical etching in H 3 PO 4 , H 2 O 2 , H 2 O based solution. Then the metallorganic chemical vapour deposition was used for the mesas overgrowth. The influence of the growth conditions—temperature, V/III ratio, and growth rate—on the mesa-sidewall morphology was studied using optical microscopy, scanning electron microscopy and atomic force microscopy. We show that the sidewall quality is very high for all mesa slopes for growth rate 0.6 μm/h, V/III ratio 383, and growth temperature 640°C. Grown structures reveal strong tendency for faceting into {1 1 0} crystallographic planes.
Evaluation of antioxidants by a rapid polarographic method
A simple, rapid, precise, and reproducible method and an adaptable apparatus for polarographic measurement of lipid peroxidation and antioxidant activity is described. This method measures antioxidant activity within a few min time as compared to the hours or days needed for several widely used methods. Peroxidation rates were measured for different lipids as a function of amount of lipid, and amount of biocatalyst. The method is applicable to the detection and measurement of the antioxidant effects exhibited by weak antioxidants and has been satisfactorily used for the measurement of the antioxidant activity of different concentrations of powerful antioxidants.