Finite-temperature perturbation theory for quasi-one-dimensional spin-1/2 Heisenberg antiferromagnets

We develop a finite-temperature perturbation theory for quasi-one-dimensional quantum spin systems, in the manner suggested by H.J. Schulz (1996) and use this formalism to study their dynamical response. The corrections to the random-phase approximation formula for the dynamical magnetic susceptibility obtained with this method involve multi-point correlation functions of the one-dimensional theory on which the random-phase approximation expansion is built. This ``anisotropic'' perturbation theory takes the form of a systematic high-temperature expansion. This formalism is first applied to the estimation of the N\'eel temperature of S=1/2 cubic lattice Heisenberg antiferromagnets. It is then applied to the compound Cs$_2$CuCl$_4$, a frustrated S=1/2 antiferromagnet with a Dzyaloshinskii-Moriya anisotropy. Using the next leading order to the random-phase approximation, we determine the improved values for the critical temperature and incommensurability. Despite the non-universal character of these quantities, the calculated values are different by less than a few percent from the experimental values for both compounds.Comment: 11 pages, 6 figure

The characterization of interface roughness and other defects in multilayers by x-ray scattering

In this paper we present some theoretical and experimental results on the characterization of roughness in thin films and multilayers by scattering techniques. Particular attention is focused on the difference between specular and diffuse scattering and on correlated roughness between interfaces. 5 refs., 3 figs

X-ray scattering studies of multilayer interfaces

The results of specular and diffuse x-ray scattering studies of multilayers are discussed. We show here that such studies can yield detailed statistical information about the interfacial roughness and morphology. Results on a GaAs/AlAs multilayer are presented and the data is analyzed within the Born approximation

The 3a accessory protein of SARS coronavirus specifically interacts with the 5′UTR of its genomic RNA, using a unique 75 amino acid interaction domain

10.1021/bi062057pBiochemistry46226488-6499BICH

Neutron scattering experiments on well-staged graphite - FeCl/sub 3/

This paper reports results of a neutron diffraction study on both the magnetic and the lattice dynamic structure of graphite-FeCl/sub 3/. The FeCl/sub 3/ system was selected for this study because of the interesting magnetic properties previously reported for this system. Of particular interest is the low temperature magnetic phase transition, which has been shown to be stage dependent. Special emphasis was given to the study of the low temperature magnetic state of the Fe/sup 3 +/ spins and to the longitudinal phonon modes for k/sub z/ axis acoustic branches. All experiments reported here were carried out on a stage 2 sample of graphite-FeCl/sub 3/. The sample was prepared by a two-zone vapor growth technique and was characterized by (00l) x-ray and neutron diffraction patterns to be > 95% stage 2, with only minor inclusions of other stages

Self-Organization of Polymer Brush Layers in a Poor Solvent

Synthesis of densely grafted polymer brushes from good solvent polymer solutions is difficult when the surface interaction is only weakly attractive because of the strong steric repulsion between the polymer chains. To circumvent this difficulty we graft polymer layers in a poor solvent to exploit attractive polymer-polymer interactions which largely nullify the repulsive steric interactions. This simple strategy gives rise to densely grafted and homogeneous polymer brush layers. Model end-grafted polystyrene chains ($M_w = 105,000$) are prepared in the poor solvent cyclohexane (9.5 °C) where the chains are chemically attached to the surface utilizing a trichlorosilane end-group. Polished silicon wafers were then exposed to the reactive polymer solutions for a series of “induction times” $\tau_{\rm I}$ and the evolving layer was characterized by X-ray reflectivity and atomic force microscopy. Distinct morphologies were found depending on $\tau_{\rm I}$. For short $\tau_{\rm I}$, corresponding to a grafting density less than 5 mg/m$^2$, the grafted layer forms an inhomogeneous island-like structure. At intermediate $\tau_{\rm I}$, where the coverage becomes percolating, a surface pattern develops which appears similar to spinodal decomposition in bulk solution. Finally, after sufficiently long $\tau_{\rm I}$, a dense and nearly homogeneous layer with a sharp interface is formed which does not exhibit surface pattern formation. The stages of brush growth are discussed qualitatively in terms of a random deposition model