Highly luminescent nanocrystal quantum dots fabricated by lattice-type mismatched epitaxy

Lattice-type mismatched heteroepitaxy is demonstrated as a novel concept for the fabrication of almost ideal, highly luminescent nanocrystal quantum dots that are coherently embedded in a single-crystalline matrix. In this approach, the formation of quantum dots is induced by transformation of a metastable epitaxial 2D quantum well into an array of isolated nanocrystals with-highly symmetric shape. This process is driven by the lattice-type mismatch between the constituent materials and the resulting miscibility gap. The investigated PbTe/CdTe heterosystem has a model character because it combines two compounds with different cubic lattice types but almost identical lattice constants. The obtained epitaxial nanocrystals exhibit outstanding properties such as a well-defined symmetric shape, the absence of strain, intermixing and a wetting layer, which is in contrast to the conventional Stranski–Krastanow quantum dots. The small-rhomboedric-cubo-octahedron PbTe/CdTe nanocrystals on GaAs substrates display intense room temperature mid-infrared luminescence as is crucial for device applications. Ab initio density functional theory is used to clarify the interface structure, indicating that the covalent and ionic bonding character of CdTe and PbTe is maintained across the interface.     

Picosecond proton ejection: an ultrafast pH jump

The rates of proton ejection from 2-naphthol-3,6-disulfonate (pK^* = 0.5 ± 0.1) and 8-hydroxy 1,3,6-pyrene trisulfonate (pK^* = 0.4 ± 0.1) have been found to be 3.1 × 10¹⁰ s^?1 and 3.2 × 10¹⁰ s^?1, respectively. This is in keeping with the scaling of the ejection rate inversely with the excited state pK^*.     

The Fix–Heiberger procedure for solving the generalized Ill-conditioned symmetric eigenvalue problem

We review a formalism introduced by Fix and Heiberger in 1972 for solving the generalized (or nonorthogonal) eigenvalue problem for ill-conditioned symmetric matrices and we discuss its application in quantum chemistry. A few examples dealing with the calculation of high Rydberg orbitals are presented.     

The correlation functions near intermittency in a one-dimensional Piecewise parabolic map

Piecewise parabolic maps constitute a family of maps in the fully developed chaotic state and depending on a parameter that can be smoothly tuned to a weakly intermittent situation. Approximate analytic expressions are derived for the corresponding correlation functions. These expressions produce power-law decay at intermittency and a crossover from power-law decay to exponential decay below intermittency. It is shown that the scaling functions and the exponent of the power law depend on the kind of the correlations.     

ESR identification of the iron double electron trap state in GaP

By Electron Spin Resonance (ESR) it has been found that neutral substitutional iron impurities in gallium phosphide can trap two electrons. The 3d⁷-character of the two-electron trap state of iron in GaP was inferred from the characteristic angular dependence of the Zeeman-splitting of its Γ₈-ground state.