Energy-selective charging of type-II GaSb/GaAs quantum dots

The hole confinement in type-II self-organized GaSb/GaAs quantum dots (QDs) was investigated by combining optical excitation and time-resolved capacitance spectroscopy. The experimental results indicate energy-selective charging even for type-II QDs. With increasing excitation energy the apparent hole activation energy decreases, which is attributed to light absorption in sub-ensembles of QDs with decreasing hole localization. The large localization energy of about 450 meV and the possibility of optical-multiplexing makes type-II GaSb/GaAs QDs a potential material system for QD memory concepts.     

Absolute fluorescence quantum yields for vapour-phase benzene and naphthalene,and comments on the non-radiative processes

Optic—acoustic measurements have been employed in the determination of absolute quantum yields for benzene and naphthalene. Heat yields are measured by a method using oxygen quenching of both triplet and singlet states. For vibrationally relaxed excited singlet states the fluorescence quantum yields, φ^B_f, are 0.16 ± 0.02 and 0.79 ± 0.02 for benzene and naphthalene respectively. For 0.07 torr naphthalene at room temperature with 248 nm excitation, φ_f = 0.35 ± 0.03 and the quantum yield of internal conversion is less than 0.05. The decay of the highly vibrationally excited triplet state is dominated by vibrational relaxation for 0.07 torr naphthalene, but for benzene, even at high pressures, strong competition comes from an indirect coupling process to the ground state.     

The cathodic stripping voltammetry of certain thiols in acetate medium

The cathodic stripping voltammetry of six thiols by deposition at a hanging mercury drop electrode (+0.05 V vs. SCE) from acetate-buffered solution (pH 4.76) and scanning to —0.8 V is described. Peak potentials are reported. The peak height—concentration relationships are reasonably linear in the range 0.4–1.2 μM. The compounds tested are 2-mercaptopyridine, 2-mercapto-3-pyridinol, 2-mercaptopyridine-N-oxide, mercaptosuccinic acid, 2-mercaptopyrimidine and cysteine hydrochloride.     

Thermostaten

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Absorption und Adsorption

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