State-selective electron capture for keV He2+ ions on helium collisions studied by recoil momentum spectroscopy

State-selective single electron capture cross sections are measured by recoil ion momentum spectroscopy technique for He2+ on He at 30 keV incident energy. The cross sections for capture into ground and excited states are obtained and compared to classical model calculations as well as to the quantum mechanical calculations. The experimental results are in good agreement with quantum mechanical results.

Properties of alpha-decay to ground and excited states of heavy nuclei

Branching ratios and half-lives of alpha-decay to the ground-state rotational bands as well as the high-lying excited states of even-even nuclei have been calculated in the framework of the generalized liquid drop model (GLDM) and Royer's formula that we improved very recently. The calculation covers the isotopic chains from Ra to No in the mass regions 222 <= A <= 252 and 88 <= Z <= 102. The agreement between the calculated results and the experimental data indicates the reliability of investigating the properties of the unfavored alpha-decay with our method, especially the improved Royer's formula, which is very valuable for the analysis of experimental data. In addition, the dependence of half-lives on excitation energies of daughter nuclei has been investigated. It is shown that the influence on half-lives becomes stronger and stronger with the increase of the excitation energies.

Electronic and magnetic properties of YBa2Fe3O8 from a first-principles study

The electronic and magnetic properties of YBa2Fe3O8 have been systematically investigated within the framework of density-functional theory using the standard generalized gradient approximation (GGA) as well as the GGA plus Hubbard U(GGA + U) method. The GGA results show that the G-type antiferromagnetic (AFM) state is preferred among the considered magnetic configurations. The striking ionic character is shown for Y and Ba atoms while very strong hybridization is found between Fe 3d and O 2p orbitals

Ab initio study on the electronic, magnetic, and mechanical properties of CaCu3V4O12

The electronic, magnetic, and mechanical properties of CaCu3V4O12 are investigated by use of the density functional theory method. The calculated results indicate that CaCu3V4O12 is a half-metallic and ferrimagnetic compound. The magnetic coupling for Cu-V is antiferromagnetic, while those for Cu-Cu and V-V are ferromagnetic. The obtained elastic constants suggest that the compound is mechanically stable. The calculated oxidation states and density of states reveal the existence of a mixed valence for Cu and V. This supports the experimental observation of the mixed valence in Ca2+Cu2+Cu2+(V25+V24+)O-12.

Electronic and mechanical properties of 5d transition metal mononitrides via first principles

The electronic and mechanical properties of 5d transition metal mononitrides from LaN to AuN are systematically investigated by use of the density-functional theory. For each nitride, Six Structures are considered, i.e., rocksalt, zinc blende, CsCl, wurtzite, NiAs and WC structures. Among the considered structures, rocksalt structure is the most stable for LaN, HfN and ALIN, WC structure for TaN, NiAs structure for WN, wurtzite structure for ReN, OsN, IrN and PtN. The most stable Structure for each nitride is mechanically stable. The formation enthalpy increases from LaN to AuN.

Near compensated half-metal in Sr2NiOsO6

The electronic and magnetic properties of tetragonal double perovskite Sr2NiOsO6 were studied by use of the density functional theory and including the spin-orbit coupling. Compensated half-metal is found if the spin-orbit coupling is not considered. Spin-orbit coupling induces orbital moments on both Ni and Os, making Sr2NiOsO6 a near compensated half-metal. Ferromagnetic phase is slightly favored over antiferromagnetic phase (by 4 meV). The small energy difference also suggests that both phases are competitive for the ground state. At ferromagnetic phase, the calculated net magnetic moment is 3.53 mu(B), in good agreement with experimental value of 3.44 mu(B). At antiferromagnetic phase, the net magnetic moment is 0.69 mu(B), in which the contribution from the net spin moment is 0.09 mu(B).

Ab initio study on the electronic and mechanical properties of ReB and ReC

The structural, electronic, and mechanical properties of ReB and ReC have been studied by use of the density functional theory. For each compound, six structures are considered, i.e., hexagonal WC, NiAs, wurtzite, cubic NaCl, CsCl, and zinc-blende type structures. The results indicate that for ReB and ReC, WC type structure is energetically the most stable among the considered structures, followed by NiAs type structure. ReB-WC (i.e., ReB in WC type structure) and ReB-NiAs are both thermodynamically and mechanically stable. ReC-WC and ReC-NiAs are mechanically stable and becomes thermodynamically stable above 35 and 55 GPa, respectively. The estimated hardness from shear modulus is 34 GPa for ReB-WC, 28GPa for ReB-NiAs, 35GPa for ReC-WC and 37GPa for ReC-NiAs, indicating that they are potential candidates to be ultra-incompressible and hard materials.

Structural stability and magnetic coupling in CaCu3Co4O12 from first principles

The structural, electronic and magnetic properties of CaCu3Co4O12 were studied by use of the full-potential linearized augmented plane wave method. The calculated results indicate that CaCu3Co4O12 is stable both thermodynamically and mechanically. Both GGA (generalized gradient approximation) and GGA + U methods predict that CaCu3Co4O12 is metallic. The ferromagnetic configuration is only slightly more stable in energy compared with the non-magnetic configuration (3.7 meV), suggesting that they are competitive for being the ground state. Co is in the low spin state (S = 1/2).

Chemical Bonding and Electronic Structure of 4d-Metal Monosulfides

Bond distances, vibrational frequencies, dissociation energies, electron affinities, ionization potentials and dipole moments of the title molecules in neutral and charged ions were studied by use of density functional method. Ground states for each molecule were assigned. The calculated bond distance decreases with the increasing of atomic number of 4d metals, reaches minimum at RhS, then increases. For cationic molecules, the calculated bond distance decreases to the minimum at MoS+, then increases. The calculated vibrational frequency decreases from YS(YS+) to PdS(PdS+) for both neutral and cationic molecules. The bond ionic character decreases from YS(YS+) to PdS(PdS+) for neutral and cationic molecules. The bonding patterns are discussed and compared with the available studies.

Theoretical investigation of 5D-metal monocarbide

Bond distances, vibrational frequencies, electron affinities, ionization potentials and dissociation energies of the title molecules in neutral, positively and negatively charged ions were studied by use of density functional method. The calculated results were compared with previous theoretical and experimental studies. Ground states for each molecule were assigned. It was found that for some molecules, low-lying state, in which the energy is much close to the ground state, was obtained. In this case, further studies both experimentally and theoretically are necessary in order to find the true global minimum.

Charge ordering induced metal-semiconductor transition in Ag2BiO3: A first-principles study

Accurate ab initio density-functional calculations are performed to investigate the relationship of the ground-state crystal structures and electronic properties of Ag2BiO3 compound. The results indicate that Ag2BiO3 in Pnna phase, in which the bismuth atoms occupy the same Wyckoff positions, exhibits metallic conductivity, while in Pnn2 and Pn phases, Ag2BiO3 exhibits semiconducting character, which is in agreement with the experimental results. Charge ordering is indeed induced by the crystal inversion twin in the Pnn2 phase compared with the Pnna phase. In the low temperature phase Pn, the charge ordering is similar to that of Pnn2 phase although it is more distorted in Pn phase. In addition, the calculation indicates that the charge ordering is caused in the 6s electron rearrangement.

Orbital ordering in Cs2AgF4 from first principles

First-principles calculations using the augmented plane wave plus local orbital method, as implemented in the WIEN2K code, have been used to investigate the structural, electronic, and magnetic properties of the layered perovskite Cs2AgF4. Our calculations indicate that an orthorhombic ground state for Cs2AgF4 is energetically favored over tetragonal. We also find that Cs2AgF4 should be a strong two-dimensional ferromagnet, with very weak antiferromagnetic coupling between the layers, in agreement with the experiment. More importantly, an antiferrodistortive ordering of z(2)-x(2) and z(2)-y(2) orbitals is inferred from the density of states and from a spin density isosurface analysis.

Competition of lamellar orientation in thin films of a symmetric poly(styrene)-b-poly(L-lactide)diblock copolymer in melt state

We have studied the lamellar orientation in thin films of a model diblock copolymer, symmetric poly(styrene)-b-poly(L-lactide) (PS-PLLA), in the melt state on supported silicon wafer surface. In this system, while the PLLA block prefers to wet the polymer/substrate interface, the polymer/air as well as polymer/polymer interface is neutral for both blocks due to the similar surface energies of PS and PLLA in melt state. Our results demonstrate that the interplay of the interfaces during phase separation results in a series of structures before approaching the equilibrium state. Lamellar orientation of thin films with different initial film thicknesses at different annealing stages has been investigated using atomic force microscopy (AFM), transmission electronic microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). It is found that in the early stage (annealing time t < 10 min), the polymer/substrate interface dominates the structure evolution, leading to a parallel lamellar structure with holes or islands formed depending on the initial film thickness. Later on, the neutral air interface becomes important and leads to a transition of lamellar orientation from parallel to perpendicular. It is interesting to see that for films with thickness h > 2L, where L is the bulk lamellar period, the lamellar orientation transition can occur independently in different parallel lamellar domains due to the neutrality of polymer/polymer interface.

Synthesis of PtNPs/AQ/Ru(bpy)(3)(2+) colloid and its application as a sensitive solid-state electrochemiluminescence sensor material

The facile synthesis of the novel platinum nanoparticles/Eastman AQ55D/ruthenium(II) tris( bipyridine) (PtNPs/ AQ/Ru(bpy)(3)(2+)) colloidal material for ultrasensitive ECL solid-state sensors was reported for the first time. The cation ion-exchanger AQ was used not only to immobilize ECL active species Ru(bpy)(3)(2+) but also as the dispersant of PtNPs. Colloidal characterization was accomplished by transmission electron microscopy (TEM), X-ray photoelectron spectrum (XPS), and UV-vis spectroscopy. Directly coating the as-prepared colloid on the surface of a glassy carbon electrode produces an electrochemiluminescence (ECL) sensor. The electronic conductivity and electroactivity of PtNPs in composite film made the sensor exhibit faster electron transfer, higher ECL intensity of Ru(bpy)(3)(2+), and a shorter equilibration time than Ru(bpy)(3)(2+) immobilized in pure AQ film. Furthermore, it was demonstrated that the combination of PtNPs and permselective cation exchanger made the sensor exhibite excellent ECL behavior and stability and a very low limit of detection (1 x 10(-15) M) of tripropylamine with application prospects in bioanalysis. This method was very simple, effective, and low cost.

Influence of Mn-O-Mn bond angle on the magnetic and electronic properties in YBaMn2O5

The influence of the Mn-O-Mn bond angle on the magnetic and electronic properties of YBaMn2O5 was studied by density functional theory, which was implemented in the CASTEP code. In practical calculation, both G- and A-type antiferromagnetic (AFM) orderings were considered. The calculated results indicated that G-type is more stable than A-type, in agreement with both experiment and previous theoretical study. It is also interesting to note that a transition from G-type to A-type at an Mn-O-Mn angle of ca. 170 degrees was found upon increasing Mn-O-Mn angle. Therefore, the calculation suggested that what is essential to stabilize the G-type AFM state is the reduction of the Mn-O-Mn bond angle. For both magnetic orderings, the compound changes from semiconductor to metal with the increase of Mn-O-Mn angle.