Statistics of chaotic tunneling

The distribution of tunneling rates in the presence of classical chaos is derived. We use classical information about tunneling trajectories plus random matrix theory arguments about wave function overlaps. The distribution depends on the stability of a specific tunneling orbit and is not universal, though it does reduce to the universal Porter-Thomas form when the orbit is very unstable. For some situations there may be systematic deviations due to scarring of real periodic orbits. The theory is tested in a model problem and possible experimental realizations are discussed.     

Characterization of silicon nanowires grown on silicon, stainless steel and indium tin oxide substrates

Silicon nanowires (SiNWs) have been grown on crystalline silicon (Si), indium tin oxide (ITO) and stainless steel (SS) substrates using a gold catalyst coating with a thickness of 200 nm via pulsed plasma-enhanced chemical vapor deposition (PPECVD). Their morphological, mineralogical and surface characteristics have been investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman analysis. SiNWs growth is accompanied by oxidation, thus yielding partially (SiO _x ) and fully oxidized (SiO₂) Si sheaths. The mean diameters of these SiNWs range from 140 to 185 nm. Si with (111) and (220) planes exists in SiNWs grown on all three substrates while Si with a (311) plane is detected only for Si and ITO substrates. Computational simulation using density functional theory (DFT) has also been conducted to supplement the experimental Raman analyses for crystalline Si and SiO₂. XPS results reveal that ca. 30 % of the SiNWs have been oxidized for all substrates. The results presented in this paper can be used to aid selection of appropriate substrates for SiNW growth, depending on specific applications.     

Temperature dependence of NMR spectrum of powdered cobalt

NMR spectra of powdered cobalt were obtained from 290 to 580 K. The hcp phase of powdered, and coarse grained bulk samples give different results, indicating effects due to magnetoelastic interactions of the domain walls with lattice defects.     

Quantum zeta function for perturbed cat maps

The behavior of semiclassical approximations to the spectra of perturbed quantum cat maps is examined as the perturbation parameter brings the corresponding classical system into the nonhyperbolic regime. The approximations are initially accurate but large errors are found to appear in the traces and in the coefficients of the characteristic polynomial after nonhyperbolic structures appear. Nevertheless, the eigenvalues obtained from them remain accurate up to large perturbations. (c) 1995 American Institute of Physics.     

Semiclassical description of large multipole-deformed metal clusters

We use the semiclassical periodic orbit theory to describe large metal clusters with axial quadrupole, octupole, or hexadecapole deformations. The clusters are regarded as cavities with ideally reflecting walls. We start from the case of spherical symmetry and then apply a perturbative approach for calculating the oscillating part of the level density in the deformed case. The advantage of this approach is that one only has to know the periodic orbits of the spherical cavity, which makes the calculation very simple. This perturbative method is a priori restricted to small deformations. However, the results agree quite well with those of quantum-mechanical calculations for deformations that are not too large, such as typically occur for the ground states of metal clusters. We also calculate shell-correction energies. With this, it becomes possible to predict at least qualitatively the deformation energy of metal clusters.     

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The characterization of artefacts of cultural heritage significance using physical techniques

All societies attempt to preserve their cultural heritage because it is this that gives them their identity. How artefacts are identified as being of significance to society, and how to preserve these for posterity, depend on the sophistication of those societies, their wealth, and the determination of members of the societies to preserve their past. If conservation or restoration measures are being undertaken complex analytical experiments must be undertaken beforehand to ensure that the work is being undertaken in an appropriate manner. These investigations may employ electromagnetic (IR, VIS, UV, X-ray, γ-ray) or particulate (electron, proton, neutron, and ion beams) radiation. The use of many of these techniques is described in this paper in experiments on Australian Aboriginal bark paintings, a suit of armour belonging to a famous Australian outlaw, and the degradation of colour motion picture film.     

The Ag M5N45N45 Auger photoelectron coincidence spectra of disordered Ag0.5Pd0.5 alloy

An effect of disorder broadening (DB) on the Ag M₅N₄₅N₄₅ Auger spectra in the random substituted Ag_0.5Pd_0.5 has been investigated by Auger photoelectron coincidence spectroscopy (APECS). Data were collected for the Ag M₅N₄₅N₄₅ Auger line coincident with the Ag 3d_5/2 photoelectron line (and its higher and lower binding energy sides). It is shown that the broadening of the Ag M₅N₄₅N₄₅ line is directly associated with the presence of disorder broadening of the Ag 3d_5/2 photoelectron line. The APECS experiment is used to demonstrate the broadening in a novel way.