Terminating surface electromigration at the source

Based on an extensive search across the periodic table utilizing first-principles density functional theory, we discover phosphorus to be an optimal surface electromigration inhibitor on the technologically important Cu(111) surface--the dominant diffusion pathway in modern nanoelectronics interconnects. Unrecognized thus far, such an inhibitor is characterized by energetically favoring (and binding strongly at) the kink sites of step edges. These properties are determined to generally reside in elements that form strong covalent bonds with substrate metal atoms. This finding sheds new light on the possibility of halting surface electromigration via kink blocking impurities.     

Fixed point theorems of upper semicontinuous multivalued mappings with applications in hyperconvex metric spaces

In the present paper, we establish two fixed point theorems for upper semicontinuous multivalued mappings in hyperconvex metric spaces and apply these to study coincidence point problems and minimax problems.     

Suppression of superconductivity in ruthenium alloys

Existing data on the depression of the superconducting transition temperature of Ru by Co, Ni, Ft, Pd, Rh and Ir impurities are analysed using Kaiser's model, which considers resonant scattering from non-magnetic impurity states. Numerical values for various parameters characterising this resonant d-state are thus derived; in particular estimates of the intra-impurity Coulomb repulsion are obtained from which the presence (or absence) of localised spin fluctuations in these alloy systems is inferred.     

Sub-Doppler excited molecule energy transfer spectroscopy

A sub-Doppler spectroscopic technique involving the detection of vibrational energy transfer in excited molecules with selected velocity components at a microphone diaphragm is demonstrated. The technique is applied to the investigation of thev ₃ R(16) transition in HCN and the results compared with a previously derived theoretical model.     

Ionicity in disordered GeSe2: a comparison of first-principles and atomistic potential models

The structural properties of liquid GeSe(2), generated using two distinct computational methodologies, are compared. The results of molecular dynamics simulations, utilizing both first-principles density functional and a potential model which account for aspects of many-body interactions, are considered. The potential model favors ionic character in the bonding, resulting in a structure with very little chemical disorder and no homopolar bonds, in contrast to experimental observation. The use of a relatively simple potential model is shown to be useful in order to understand differences between the observed experimental structure and those obtained from the first-principles approach, the latter being affected by insufficient account of ionic character in the bonding. Both computational schemes are able to predict the appearance of the first sharp diffraction peak in the total neutron structure factor and in some of the partial structure factors as well as the concomitant presence of corner- and edge-sharing tetrahedral connections. For the potential model, this holds true provided the system temperatures are set to values high enough to allow for diffusion properties typical of a liquid. Structural properties obtained for the two sets of configurations are in closer agreement when the potential model is applied at very high temperatures.     

Closure-based density functional theory applied to interfacial colloidal fluids

The behavior of dense colloidal fluids near surfaces can now be probed in great detail with experimental techniques like confocal microscopy. In fact, we are approaching a point where quantitative comparisons of experiment with particle-level theory, such as classical density functional theory (DFT), are appropriate. In a forward sense, we may use a known surface potential to predict a particle density distribution function from DFT; in an inverse sense, we may use an experimentally measured particle density distribution function to predict the underlying surface potential from DFT. In this paper, we tested the ability of the closure-based DFT of Zhou and Ruckenstein (J. Chem. Phys. 2000, 112, 8079-8082) to perform forward and inverse calculations on potential models commonly employed for colloidal particles and surfaces. To reduce sources of uncertainty in this initial study, Monte Carlo simulation results played the role of experimental data. The combination of Rogers-Young and modified-Verlet closures consistently performed well across the different potential models. For a reasonable range of choices of the density, temperature, and potential parameters, the inversion procedure yielded particle-surface potentials to an accuracy on the order of 0.1kT.     

Gd3N@C2n (n = 40, 42, and 44): remarkably low HOMO-LUMO gap and unusual electrochemical reversibility of Gd3N@C88

High-performance liquid chromatography was used to isolate two new trimetallic nitride endohedral fullerenes, Gd3N@C2n (n = 42 and 44), and they were characterized by MALDI-TOF mass spectrometry, UV-vis-NIR, and cyclic voltammetry. It was found that their electronic HOMO-LUMO gaps depend pronouncedly on the size of the cage, from a large band gap for Gd3N@C80 (2.02 V) to a small band gap for Gd3N@C88 (1.49 V). The electrochemical properties also change dramatically with the size of the cage, going from irreversible for the C80 cage to reversible for Gd3N@C88. The latter is the largest trimetallic cluster inside C88 isolated and characterized to date. Gd3N@C88 has one of the lowest electrochemical energy gaps for a nonderivatized metallofullerene.     

Is a Griffiths phase a prerequisite for colossal magnetoresistance?

Detailed measurements of the magnetic and transport behavior of the two La(1-x)Ca(x)MnO(3) single crystals exhibiting colossal magnetoresistance are summarized. The x=0.21 sample exhibits unusual exponents (delta = 20+/-1, gamma = 1.71+/-0.1, beta = 0.09+/-0.01, T(C) = 182+/-1 K) and, more importantly, a Griffiths phase characterized by an exponent lambda = 0.70+/-0.2. By contrast, the x=0.20 specimen displays Heisenberg model behavior with no evidence of such a phase. Thus while a Griffiths phase accounts for the behavior of La(1-x)Ca(x)MnO(3) near optimal doping, it does not appear to be a prerequisite for colossal magnetoresistance in this system.