Multilayer interference mirrors for the XUV range around 100 eV photon energy

For the first time successful results have been obtained demonstrating interference effects in the reflectance of multilayer films at high photon energies where n = 1 and k is large. Films with 3.5 to 4.5 periods of Au/C and Cu/C were investigated for angles of incidence α = 15° to α = 60° in the wavelength interval 80 to 300A?. The highest near-normal incidence reflectance found was R = 2.7% for Au/C and R = 1.2% for Cu/C at λ ～ 190A?and α = 15°. These values were by a factor of 7 higher than those for a single layered opaque Au film (respectively a factor of 6 for Cu) evaporated under the same conditions. Further improvements appear to be possible. Calculations were performed to guide the investigations and to help the interpretation of the results.     

Surface orbital magnetism

We compute the surface correction to the density of states of a particle in a convex box subjected to a magnetic field. Applying these results to orbital magnetism, we find that at high temperatures or weak magnetic fields the surface magnetization is always paramagnetic, but oscillations appear at low temperatures. In two dimensions they can give very large paramagnetic contributions near integer values of the filling factor. Explicit formulas are given for the zero-field susceptibility and for samples with a cylindrical shape in arbitrary magnetic field.     

Dark energy versus modified gravity

There is now strong observational evidence that the expansion of the Universe is accelerating. The standard explanation invokes an unknown "dark energy" component. But such scenarios are faced with serious theoretical problems, which has led to increased interest in models where instead general relativity is modified in a way that leads to the observed accelerated expansion. The question then arises whether the two scenarios can be distinguished. Here we show that this may not be so easy, demonstrating explicitly that a generalized dark energy model can match the growth rate of the Dvali-Gabadadze-Porrati model and reproduce the 3+1 dimensional metric perturbations. Cosmological observations are then unable to distinguish the two cases.     

A one-site polarizable model for liquid chloroform: COS/C

A one-site polarizable liquid chloroform model based on the charge-on-spring method is presented. It consists of five van der Waals sites and point charges, with one polarizable center on the carbon atom. The partial charges were adjusted to fit the gas-phase dipole moment of chloroform, and the Lennard–Jones parameters were varied to reproduce the density and the heat of vapourization of liquid chloroform. In this way, a simple polarizable model for liquid chloroform was obtained that correctly describes a variety of its thermodynamic, dynamic and dielectric properties, while the computational costs are only a factor of 2 higher than for a similar non-polarizable chloroform model. The model is simpler than two previously developed polarizable chloroform models, with four or five polarizable sites. The developed COS/C model is expected to show realistic behaviour of chloroform molecules in response to changes in electric field strength or the dielectric environment and should be applicable in simulations of biomolecules in conjunction with the GROMOS biomolecular force field.     

Synthesis and Characterization of Ligand-Linked Pt Nanoparticles: Tunable,Three-Dimensional,Porous Networks for Catalytic Hydrogen Sensing

Porous networks of Pt nanoparticles interlinked by bifunctional organic ligands have shown high potential as catalysts in micro-machined hydrogen gas sensors. By varying the ligand among p-phenylenediamine, benzidine, 4,4‘‘-diamino-p-terphenyl, 1,5-diaminonaphthalene, and trans-1,4-diaminocyclohexane, new variants of such networks were synthesized. Inter-particle distances within the networks, determined via transmission electron microscopy tomography, varied from 0.8 to 1.4 nm in accordance with the nominal length of the respective ligand. While stable structures with intact and coordinatively bonded diamines were formed with all ligands, aromatic diamines showed superior thermal stability. The networks exhibited mesoporous structures depending on ligand and synthesis strategy and performed well as catalysts in hydrogen gas microsensors. They demonstrate the possibility of deliberately tuning micro- and mesoporosity and thereby transport properties and steric demands by choice of the right ligand also for other applications in heterogeneous catalysis.