568 research outputs found
Effects of Magnetic System Unbalance on Magnetron Sputtering Characteristics
Deposition rate and ion current density distribution profiles at DC magnetron sputtering of Al, Ti and Cutargets were studied as functions of the process parameters and level of magnetron unbalance. Based onthe experimental data the distributions of the ion-to-atom ratio on the condensing surface under variousdeposition modes were calculated. It was established that in the case of DC magnetron sputtering the ionto-atom ratio on the condensing surface increased if the sputtering yield of the target’s material droppeddown. The minimal energy impact on the growing film and the most uniform distribution profile of theion-to-atom ratio were achieved by applying the I-type unbalanced magnetron system
Band Crossing and Novel Low-Energy Behaviour in a Mean Field Theory of a Three-Band Model on a Cu--O lattice
We study correlation effects in a three-band extended Hubbard model of Cu --
O planes within the 1/N mean field approach, in the infinite U limit. We
investigate the emerging phase diagram and discuss the low energy scales
associated with each region. With increasing direct overlap between oxygen
orbitals, , the solution displays a band crossing which, for an
extended range of parameters, lies close to the Fermi level. In turn this leads
to the nearly nested character of the Fermi surface and the resulting linear
temperature dependence of the quasi-particle relaxation rate for sufficiently
large T. We also discuss the effect of band crossing on the optical
conductivity and comment on the possible experimental relevance of our
findings.Comment: 12 pages, Latex-Revtex, 6 PostScript figures. Submitted to Phys. Rev.
A Dynamic Theory of Resource Wars
We develop a dynamic theory of resource wars and study the conditions under which such wars can be prevented. Our focus is on the interaction between the scarcity of resources and the incentives for war in the presence of limited commitment. We show that a key parameter determining the incentives for war is the elasticity of demand. Our first result identifies a novel externality that can precipitate war: price-taking firms fail to internalize the impact of their extraction on military action. In the case of inelastic resource demand, war incentives increase over time and war may become inevitable. Our second result shows that in some situations, regulation of prices and quantities by the resource-rich country can prevent war, and when this is the case, there will also be slower resource extraction than the Hotelling benchmark (with inelastic demand). Our third result is that because of limited commitment and its implications for armament incentives, regulation of prices and quantities might actually precipitate war even in some circumstances where wars would not have arisen under competitive markets
Electron-Doped Manganese Perovskites: The Polaronic State
Using the Lanczos method in linear chains we study the ground state of the
double exchange model including an antiferromagnetic super-exchange in the low
concentration limit. We find that this ground state is always inhomogeneous,
containig ferromagnetic polarons. The extention of the polaron spin distortion,
the dispersion relation and their trapping by impurities, are studied for
diferent values of the super exchange interaction and magnetic field. We also
find repulsive polaron polaron interaction.Comment: 4 pages, 6 embedded figure
Boundary Energies and the Geometry of Phase Separation in Double--Exchange Magnets
We calculate the energy of a boundary between ferro- and antiferromagnetic
regions in a phase separated double-exchange magnet in two and three
dimensions. The orientation dependence of this energy can significantly affect
the geometry of the phase-separated state in two dimensions, changing the
droplet shape and possibly stabilizing a striped arrangement within a certain
range of the model parameters. A similar effect, albeit weaker, is also present
in three dimensions. As a result, a phase-separated system near the percolation
threshold is expected to possess intrinsic hysteretic transport properties,
relevant in the context of recent experimental findings.Comment: 6 pages, including 4 figures; expanded versio
A novel spin wave expansion, finite temperature corrections and order from disorder effects in the double exchange model
The magnetic excitations of the double exchange (DE) model are usually
discussed in terms of an equivalent ferromagnetic Heisenberg model. We argue
that this equivalence is valid only at a quasi--classical level -- both quantum
and thermal corrections to the magnetic properties of DE model differ from any
effective Heisenberg model because its spin excitations interact only
indirectly, through the exchange of charge fluctuations. To demonstrate this,
we perform a novel large S expansion for the coupled spin and charge degrees of
freedom of the DE model, aimed at projecting out all electrons not locally
aligned with core spins. We generalized the Holstein--Primakoff transformation
to the case when the length of the spin is by itself an operator, and
explicitly constructed new fermionic and bosonic operators to fourth order in
1/\sqrt{S}. This procedure removes all spin variables from the Hund coupling
term, and yields an effective Hamiltonian with an overall scale of electron
hopping, for which we evaluate corrections to the magnetic and electronic
properties in 1/S expansion to order O(1/S^2). We also consider the effect of a
direct superexchange antiferromagnetic interaction between core spins. We find
that the competition between ferromagnetic double exchange and an
antiferromagnetic superexchange provides a new example of an "order from
disorder" phenomenon -- when the two interactions are of comparable strength,
an intermediate spin configuration (either a canted or a spiral state) is
selected by quantum and/or thermal fluctuations.Comment: 21 pages revtex, 11 eps figure
Proposal for the determination of nuclear masses by high-precision spectroscopy of Rydberg states
The theoretical treatment of Rydberg states in one-electron ions is
facilitated by the virtual absence of the nuclear-size correction, and
fundamental constants like the Rydberg constant may be in the reach of planned
high-precision spectroscopic experiments. The dominant nuclear effect that
shifts transition energies among Rydberg states therefore is due to the nuclear
mass. As a consequence, spectroscopic measurements of Rydberg transitions can
be used in order to precisely deduce nuclear masses. A possible application of
this approach to the hydrogen and deuterium, and hydrogen-like lithium and
carbon is explored in detail. In order to complete the analysis, numerical and
analytic calculations of the quantum electrodynamic (QED) self-energy remainder
function for states with principal quantum number n=5,...,8 and with angular
momentum L=n-1 and L=n-2 are described (j = L +/- 1/2).Comment: 21 pages; LaTe
Transmittance optical characteristics of columnar nanoscale niobia arrays formed via anodizing of Al/Nb layers on glass
Anisotropic columnar nanoscale niobia arrays formed via anodizing Al/Nb bilayers on glass showed the sensitivity of transmittance characteristics to the light polarization, which can serve as a basis for applications in photonics and integrated optics
Optical and Tribological Properties of PVD/CVD Diamond-like Carbon Films
The optical and tribological properties of diamond-like carbon (DLC) films deposited by the combination of magnetron sputtering of graphite and plasmochemical dissociation of methane were studied. It was established that at methane concentration in the gas mixture Ar/CH4 at about 5–10 % the formation of DLC films with refraction index n 2.0, microhardness larger than 1000 HK and friction coefficient of 0.06–0.08 becomes possible
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