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http://www.archive.org/details/vortexformations00axe

Effect of Hydrostatic Pressure on the Incommensurate Phase of K\u3csub\u3e2\u3c/sub\u3eSeO\u3csub\u3e4\u3c/sub\u3e

A neutron scattering study of the effect of hydrostatic pressure on the incommensurate phase transformation in K2SeO4 was performed in order to obtain information concerning the nature of the competing forces that give rise to a structural instability at a general wave vector. It was found that an increase in pressure lowers the transition temperature (dTi/dPi = - 6.5 K/kbar) and results in a smaller value of the initial incommensurate wave vector. The pressure dependence of the incommensurate to ferroelectric phase transition was also investigated (dTc/dPc = - 9 K/kbar). The latter transition displays a distinct pressure hysteresis

The Structure of Self-Assembled Monolayers of Alkylsiloxanes on Silicon: A Comparison of Results from Ellipsometry and Low-Angle X-Ray Reflectivity

The thicknesses of C10-C18 alkylsiloxane monolayers on silicon-silicon dioxide substrates have been measured with ellipsometry and low-angle X-ray reflection. Although, for any given sample, thicknesses measured by the two methods agree to within experimental error, ellipsometric measurements are systematically larger by approximately $2 \mathring{A}$. This difference may result from variations in the sensitivity of the two techniques to the structure of the interface between silicon dioxide and the alkylsiloxane monolayer. The X-ray reflectivity measurements provide evidence that these organic monolayers do not build up as island structures and demonstrate that the approximate area projected by each alkyl group in the plane of the monolayer is $~21 \pm 3 \mathring{A}^2$. Preliminary studies indicate that this technique can be used to follow the changes in the structure of a monolayer which result from chemical transformations. The influence of damage that is induced by X-ray radiation on these measurements is discussed.Engineering and Applied Science