ABSTRACT
The A(n+1)B(n)O(3n+1) Ruddlesden-Popper homologous series offers a wide variety of functionalities including dielectric, ferroelectric, magnetic and catalytic properties. Unfortunately, the synthesis of such layered oxides has been a major challenge owing to the occurrence of growth defects that result in poor materials behaviour in the higher-order members. To understand the fundamental physics of layered oxide growth, we have developed an oxide molecular beam epitaxy system with in situ synchrotron X-ray scattering capability. We present results demonstrating that layered oxide films can dynamically rearrange during growth, leading to structures that are highly unexpected on the basis of the intended layer sequencing. Theoretical calculations indicate that rearrangement can occur in many layered oxide systems and suggest a general approach that may be essential for the construction of metastable Ruddlesden-Popper phases. We demonstrate the utility of the new-found growth strategy by performing the first atomically controlled synthesis of single-crystalline La3Ni2O7.
ABSTRACT
Results of dynamical simulations of collision-induced formation and properties of bimetallic nanoparticles are presented and analyzed. The analysis includes the effects of the collision energy and the impact parameter. For nonzero impact parameters, the formed (in many cases Janus-type) nanoparticles are rotating. The energy of the rotating nanoparticles is decomposed into the rotational and vibrational components, and the structural effects of these components are analyzed. Comparison is made with the case of the corresponding homoatomic systems, formed by collision of nanoparticles with the same elemental composition.
Subject(s)
Alloys/chemistry , Metal Nanoparticles/chemistry , Molecular Dynamics Simulation , Alloys/chemical synthesis , RotationABSTRACT
Computed electron removal energies for Cu(N) (-) clusters, N=9-20, are presented for the three lowest-energy isomers obtained from extensive, unbiased searches for the minimum energy structure at each size. The density functional theory (DFT) computations make use of a scheme introduced by Jellinek and Acioli (JA) [J. Chem. Phys. 118, 7783 (2003)] that obtains electron removal energies from DFT orbital energies using corrections based on DFT total energies. The computed removal energies are compared with the measured photoelectron spectra (PES) for Cu(N) (-). The patterns of computed removal energies are shown to be isomer specific for clusters in this size range. By matching the computed removal energies to the observed PES, the isomers responsible for the PES are identified. The results of the JA scheme are compared to those obtained using other DFT-based methods.
Subject(s)
Copper/chemistry , Electrons , Isomerism , Models, Molecular , Molecular Structure , Photoelectron Spectroscopy , Quantum TheoryABSTRACT
The atomic-level response of Na(N) clusters, N = 2-20, to a small static external electric field is studied using a method that decomposes the total cluster dipole moment and polarizability into contributions from nonoverlapping atomic volumes. The atomic dipole moments and polarizabilities are, in turn, partitioned into the so-called dipole and charge-transfer components. The former characterizes a dielectric type of a response, whereas the latter represents a metallic type of a response. Analysis of the atomic polarizabilities points to their strong dependence on the site, or location, of the atoms within the structure of the clusters. Surface atoms have larger polarizabilities than the interior ones. Overall, the fraction of the charge-transfer component of the averaged atomic polarizabilities is an increasing function of the cluster size. The charge-transfer component is also responsible for the structure/shape driven variations in the atomic polarizabilities. The anisotropy of the total polarizabilities correlates with the shape anisotropy of the clusters.
Subject(s)
Sodium/chemistry , Electricity , Electrons , Models, Molecular , Molecular ConformationABSTRACT
Low-energy isomers of Ag(N) clusters are studied within gradient-corrected density functional theory over the size range of N = 9-20. The candidate conformations are drawn from an extensive structural database created in a recent exploration of Cu(N) clusters [M. Yang et al., J. Chem. Phys. 124, 24308 (2006)]. Layered configurations dominate the list of the lowest-energy isomers of Ag(N) for N < 16. The most stable structures for N > 16 are compact with quasispherical shapes. The size-driven shape evolution is similar to that found earlier for Na(N) and Cu(N). The shape change has a pronounced effect on the cluster cohesive energies, ionization potentials, and polarizabilities. The properties computed for the most stable isomers of Ag(N) are in good agreement with the available experimental data.
ABSTRACT
The role played by the bosonic or fermionic character of He atoms surrounding a Br2(X) molecule is analyzed through vibrotational Raman spectra simulations. Quantum chemistry-type calculations reveal the spin multiplicity to be chiefly responsible for the drastic difference observed by Grebenev et al. [Science 279, 2083 (1998)]] in the rotational structure of molecules embedded in helium droplets.
ABSTRACT
The aim of this paper is to elucidate the role played by the bosonic/fermionic character of N He atoms solvating a Br2(X) molecule. To this end, an adiabatic model in the molecular stretching coordinate is assumed and the ground energy levels of the complexes are searched by means of Hartree (or Hartree-Fock) Quantum Chemistry calculations for 4He (or 3He) solvent atoms. Simulations of vib-rotational Raman spectra point at the spin multiplicity as the main feature responsible for the drastic difference in the rotational structures of molecules embedded in boson or fermion helium drops as already observed by the experiments of Grebenev et al. [S. Grebenev, J. P. Toennies, and A. F. Vilesov, Science 279 (1998) 2083].