Abstract: Hydrogen incorporation in diluted nitride semiconductors dramatically modifies the electronic and structural properties of the crystal through the creation of nitrogen-hydrogen complexes. We report a convergent beam electron-diffraction characterization of diluted nitride semiconductor-heterostructures patterned at a sub-micron scale and selectively exposed to hydrogen. We present a method to determine separately perpendicular mismatch and static disorder in pristine and hydrogenated heterostructures. The roles of chemical composition and strain on static disorder have been separately assessed. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4752464]

Abstract: With the aim of an improved understanding of the metal-complexation properties of alicyclic β-amino acid stereoisomers, and their peptides, the complex equilibria and modes of coordination with copper(II) of l-phenylalanine (F) derivatives of cis/trans-2-aminocyclohexanecarboxylic acid (c/tACHC), i.e. the dipeptides F-c/tACHC and c/tACHC-F, were investigated by a combination of CW and pulsed EPR methods. For the interpretation of the experimental data, DFT quantum-chemical calculations were carried out. Simulation of a pH-dependent series of room-temperature CW-EPR spectra revealed the presence of EPR-active complexes ([Cu(aqua)]2+, [CuL]+, [CuLH1], [CuLH2]−, and [CuL2H1]−), and an EPR-inactive species ([Cu2L2H3]−) in aqueous solutions for all studied cases. [CuLH]2+ was included in the equilibrium model for the c/tACHC-Fcopper(II) systems, and [CuL2], together with two coordination isomers of [CuL2H1]−, were also identified in the F-tACHCcopper(II) system. Comparison of the complexation properties of the diastereomeric ligand pair F-(1S,2R)-ACHC and F-(1R,2S)-ACHC did not reveal significant differences. Considerably lower formation constants were obtained for the trans than for the cis isomers for both the F-c/tACHC and the c/tACHC-F pairs in the case of [CuLH1] involving tridentate coordination by the amino, the deprotonated peptide, and the carboxylate groups. A detailed structural analysis by pulsed EPR methods and DFT calculations indicated that there was no significant destabilization for the complexes of the trans isomers. The lower stability of their complexes was explained by the limitation that only the conformer with donor groups in equatorialequatorial ring positions can bind to copper(II), whereas both equatorial-axial conformers of the cis isomers are capable of binding. From a consideration of the proton couplings obtained with X-band 1H HYSCORE, 2H exchange experiments, and DFT, the thermodynamically most stable cyclohexane ring conformer was assigned for all four [CuLH1] complexes. For the F-cACHC case, the conformer did not match the most stable conformer of the free ligand.

Abstract: We investigate the ground and excited states of a bipolar artificial molecule composed of two vertically coupled quantum dots containing different type of carriers-electrons and holes-in equilibrium. The approach based on exact diagonalization is used and reveals an intricate pattern of ground-state angular momentum switching and a rearrangement of approximate single-particle levels as a function of the interdot coupling strength.

Abstract: We have investigated epitaxially grown single-crystalline Ca-doped LaMnO3 thin films using the pulsed laser deposition technique in a case study aimed to explore the possibilities buried in epitaxial stress tailoring in order to control the transport properties of CMR materials beyond the limits set by equilibrium thermodynamics. Depending on the film thickness there is an abrupt transition from pseudomorphic to epitaxial granular growth observable which is related to the epitaxial strain of the films. This is associated with microscopic stress relaxation and leads to well controllable modifications of the atomic arrangements of the Mn-O sublattice in the films. Due to the interrelation of double exchange, spin-, charge- and orbital ordering and the Jahn-Teller effect mediated coupling of the electronic system to the crystal lattice, the magnetotransport properties of the firms can be modified in a controllable way.

Abstract: http://dx.doi.org/doi:10.1103/PhysRevLett.70.2146

Abstract: The Sr3RFe4O10.5 (R=Y, Ho, Dy) anion-deficient perovskites were prepared using a solid-state reaction in evacuated sealed silica tubes. Transmission electron microscopy and 57Fe Mössbauer spectroscopy evidenced a complete A-cations and oxygen vacancies ordering. The structure model was further refined by ab initio structure relaxation, based on density functional theory calculations. The compounds crystallize in a tetragonal a≈2√2ap≈11.3 Å, с≈4сp≈16 Å unit cell (ap: parameter of the perovskite subcell) with the P42/mnm space group. Oxygen vacancies reside in the (FeO5/4□3/4) layers, comprising corner-sharing FeO4 tetrahedra and FeO5 tetragonal pyramids, which are sandwiched between the layers of the FeO6 octahedra. Smaller R atoms occupy the 9-fold coordinated position, whereas the 10-fold coordinated positions are occupied by larger Sr atoms. The Fe sublattice is ordered aniferromagnetically up to at least 500 K, while the rare-earth sublattice remains disordered down to 2 K.