We investigate atomic and molecular nanostructures on metal surfaces by variable low-temperature scanning tunnelling microscopy.
In combination with molecular dynamics calculations we achieve a detailed understanding of the stability of these structures.?Atomic
nanostructures in homoepitaxial metallic systems are thermodynamically only metastable. Two-dimensional islands on Ag(110)
decay above a threshold temperature of Tl=175 K. Caused by the anisotropy of the surface, distinct decay behaviours exist above and below a critical temperature of
Tc=220 K. Calculations based on effective medium potentials of the underlying rate limiting atomic processes allow us to identify
the one-dimensional decay below Tc as well as the two-dimensional decay above Tc.?In contrast to atoms, the intermolecular electrostatic interaction of polar molecules leads to thermodynamically stable
structures. On the reconstructed Au(111) surface, the pseudo-chiral 1-nitronaphthalin forms two-dimensional supermolecular
clusters consisting predominantly of ten molecules. Comparison of images with submolecular resolution to local density calculations
elucidates the thermodynamical stability as well as the internal structure of the decamers.
Received: 25 March 1999 / Accepted: 17 August 1999 / Published online: 6 October 1999 相似文献
In this review, some established concepts from Colloidal Science and their application to graphene and carbon nanotubes dispersions in organic or aqueous media are highlighted to rationalize alternatives for some issues in terms of colloidal properties. Recent applications for carbon-based dispersions are presented, as well as van der Waals interactions in carbon materials and strategies to overcome these interactions, such as increasing electrostatic repulsion between dispersed particles, surface functionalization, or adsorption of passivation agents such as macromolecules, which are the basis of many dispersion and exfoliation procedures. The demonstration of how knowledge and fine control of colloidal interactions have been used to overcome several limitations, such as the preparation of stable and concentrated dispersions of carbon materials and keeping appreciable electrical conductivity, is presented. It is also showed that the same knowledge can help the development of more environmentally friendly carbon-based colloids as well as the improvement of similar systems as dispersions of two-dimensional materials. 相似文献
In an exclusive measurement of the reaction gammad-->K(+)K(-)pn, a narrow peak that can be attributed to an exotic baryon with strangeness S=+1 is seen in the K(+)n invariant mass spectrum. The peak is at 1.542+/-0.005 GeV/c(2) with a measured width of 0.021 GeV/c(2) FWHM, which is largely determined by experimental mass resolution. The statistical significance of the peak is (5.2+/-0.6)sigma. The mass and width of the observed peak are consistent with recent reports of a narrow S=+1 baryon by other experimental groups. 相似文献
In this paper the different loss mechanisms of light in multimode fibres are analysed from the point of view of the extinction of leaky skew rays. First, the intrinsic loss mechanism of leaky rays due to optical tunnel effect is fully investigated by means of a quasi-classical approach and a well approximated form of the relative extinction coefficient is derived. Second, the influence of other loss phenomena, due to imperfections or impurities in the fibre such as core and cladding absorption and scattering, on the relative contribution of leaky rays is analysed. Finally some phenomena of failed excitation of leaky rays are also examined. The phenomena are analysed both qualitatively and quantitatively and a comparative analysis of various effects referring to actual fibres is made.R. Vanucci now is with FACE — Standard S.p.A. — Pomezia. 相似文献
The problem of scattering in optical fibres is approached by means of a ray theory and by considering both the parameters that characterize each ray congruence. Starting from a general transport equation a two-variable diffusion equation is derived and its field of validity is discussed. Preliminary results (steadystate power distribution among ray congruences; steady-state attenuation and steady-state length) are given in some simple but common cases. These results permit interesting comparisons with other theories. 相似文献
The evaluation of power decay along the fibre by means of the backscattering technique may be altered by the presence of unknown irregularities. In the present paper the effects of such imperfections are estimated; it is demonstrated that mainly local inhomogeneities and numerical aperture fluctuations influence backscattered power. Finally an efficient and simple method for the separation of the power decay contribution from the irregularity contribution is proposed. 相似文献
Summary: The synthesis of aqueous dispersions of hybrid acrylic copolymer particles with either a monofunctional or a multifunctional polyhedral oligomeric silsesquioxane methacrylate comonomer has been performed by free radical heterophase polymerization. The miniemulsion process gives stable latexes, whereas the less controlled emulsion route results in colloidal instability of the products. The thermal and mechanical properties of the nanocomposite latex films have been preliminarily investigated.
The nanocomposite latex particles based on hybrid copolyacrylates with highly dispersed POSS cages. 相似文献