Articles you may be interested inEnhanced photoluminescence of InAs self-assembled quantum dots grown by molecular-beam epitaxy using a "nucleation-augmented" method Photoluminescence properties of self-assembled InAs quantum dots grown on InP substrates by solid source molecular beam epitaxy
Self-assembled monolayers (SAMs) grown on surfaces of ferromagnetic metals have attracted increasing attention as they can act as corrosion inhibitors on easily oxidizable transition metals and are potentially relevant for application in spintronics. We have performed a model study of aromatic thiol SAMs grown on atomically flat Ni(111) by means of synchrotron-based X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and density functional theory. Our analysis demonstrates that well-defined bonding through the sulfur headgroup of the molecules (thiolate bonding) can be established at 200 K. However, the bonding configuration is metastable: breaking of the C−S bond and subsequent chemisorption of both fragments on the Ni surface decreases the total energy. The low activation barrier for C−S dissociation hampers the formation of room-temperature-stable monolayers. In addition, we show that end groups with a strong affinity to the nickel substrate can severely modify the global pattern of interaction of the thiol molecules with the surface upon adsorption.
Midinfrared electroluminescence from a cascade of coupled AlInAs quantum dots and GaAs quantum wells at low temperature (80 K) is demonstrated. At low injection currents, the spectra show a clear peak at 158 meV with a luminescence width of 15 meV which is associated with transitions from the s shells of a resonant subensemble of quantum dots. A Stark shift to 143 meV and spectral broadening is observed at higher injection currents which is associated with luminescence from the inhomogeneously broadened quantum-dot ensemble. The reported design is a possible solution to obtain population inversion in unipolar quantum-dot-cascade structures.
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