Overhauser effect in individual InP/GaInP dots

Sizable nuclear spin polarization is pumped in individual InP/GaInP dots in a wide range of external magnetic fields B_ext=0-5T by circularly polarized optical excitation. We observe nuclear polarization of up to ~40% at Bext=1.5T and corresponding to an Overhauser field of ~1.2T. We find a strong feedback of the nuclear spin on the spin pumping efficiency. This feedback, produced by the Overhauser field, leads to nuclear spin bi-stability at low magnetic fields of Bext=0.5-1.5T. We find that the exciton Zeeman energy increases markedly, when the Overhauser field cancels the external field. This counter-intuitive result is shown to arise from the opposite contribution of the electron and hole Zeeman splittings to the total exciton Zeeman energy

Suppression of nuclear spin diffusion at a GaAs/AlGaAs interface measured with a single quantum dot nano-probe

Nuclear spin polarization dynamics are measured in optically pumped individual GaAs/AlGaAs interface quantum dots by detecting the time-dependence of the Overhauser shift in photoluminescence (PL) spectra. Long nuclear polarization decay times of ~ 1 minute have been found indicating inefficient nuclear spin diffusion from the GaAs dot into the surrounding AlGaAs matrix in externally applied magnetic field. A spin diffusion coefficient two orders lower than that previously found in bulk GaAs is deduced.Comment: 5 pages, 3 figures, submitted to Phys Rev

Overhauser effect in individual InP/GaInP dots

Sizable nuclear spin polarization is pumped in individual InP/GaInP dots in a wide range of external magnetic fields B_ext=0-5T by circularly polarized optical excitation. We observe nuclear polarization of up to ~40% at Bext=1.5T and corresponding to an Overhauser field of ~1.2T. We find a strong feedback of the nuclear spin on the spin pumping efficiency. This feedback, produced by the Overhauser field, leads to nuclear spin bi-stability at low magnetic fields of Bext=0.5-1.5T. We find that the exciton Zeeman energy increases markedly, when the Overhauser field cancels the external field. This counter-intuitive result is shown to arise from the opposite contribution of the electron and hole Zeeman splittings to the total exciton Zeeman energy

Atomic scale study of the impact of the strain and composition of the capping layer on the formation of InAs quantum dots

The impact of the capping material on the structural properties of self-assembled InAs quantum dots (QDs) was studied at the at. scale by cross-sectional scanning tunneling microscopy. Capping with lattice matched layers and with strained layers was analyzed. When the different capping materials are lattice matched to the substrate, the differences in the QD properties can be dominated by chem. effects: InAs/InP QDs capped with InP have a 2 ML smaller height than those capped with InGaAs or InGaAsP due to As/P exchange induced decompn. The height of the dots is found to be much more strongly affected when strained capping layers are used. InAs/GaAs, QDs capped with InGaAs are considerably taller than typical GaAs-capped dots. When GaAsSb is used as the capping layer, the dots are almost full pyramids with a height of 9.5 nm, indicating that dot decompn. is almost completely suppressed. This indicates that the dot/capping layer strain plays a major role in inducing dot decompn. during capping. [on SciFinder (R)

Complexity of gene resources conservation and utilisation of a differently managed multipurpose tree species (Castanea sativa Mill.): What, where and how to conserve

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Study of the microwave vacuum drying process for a granulated product

The objectives of this work were to study and evaluate the process of drying a pharmaceutical granule from 21% to 3 % (d.b.) moisture, also determining the power absorbed by the product, using a microwave assisted vacuum dryer with two absolute pressures: 50 and 75 mbar. A specific objective was to compare the drying kinetics of the microwave assisted vacuum process (MAVP) with two other drying processes, one using hot air convection and the other combining microwaves with hot air convection. The results of such a study showed that the drying kinetics were not affected by the vacuum levels, whereas the absorbed microwave power was higher for smaller vacuum levels. It was also observed that the samples obtained by the microwave assisted vacuum process, when submitted to compression, complied with the required specifications. The drying kinetics of the MAVP showed the shortest drying times when compared to the other drying processes