Surface Layering in Liquid Gallium: An X-Ray Reflectivity Study

Surface-induced atomic layering in liquid gallium has been observed using x-ray reflectivity, ultrahigh vacuum conditions, and sputtered clean surfaces. Reflectivity data, collected on a supercooled liquid sample to momentum transfers as large as $q_z$ = 3.0 Å$^{-1}$, exhibit a strong maximum near 2.4 Å$^{-1}$ indicating a layer spacing that is comparable to its atomic dimensions. The amplitude of the electron density oscillations decays with a characteristic length of 6 Å. This is unexpectedly twice that of recent results for Hg, and the difference may be related to covalent bonding or supercooling.Engineering and Applied Science

X-Ray Reflectivity Study of the Surface of Liquid Gallium

X-ray reflectivity from the surface of liquid gallium was measured under ultrahigh vacuum conditions using a novel technique for curved surfaces. The small deviations between the measured and theoretical Fresnel reflectivity for an ideally sharp flat interface for wave-vector transfer $\lesssim$0.5 Å$^{-1}$ imply an interfacial width for the electron density profile of $\lesssim$1.3$\pm$0.2 Å. This is consistent with a model of atomic close packing which lacks structure along the surface normal at length scales >10 Å.Engineering and Applied Science

A HIGH RESOLUTION STUDY OF THE CUKα SATELLITE SPECTRUM

The Cukα x-ray satellite spectrum was measured using a silicon monolithic double crystal spectrometer. The intensity relative to that of the Kα1 line was found to be 6.2•10-3 and the width 12.7 eV, both in good agreement with previous measurements and theoretical predictions. The spectrum was resolved into four component lines, which are downshifted by ~1 eV relative to previous measurements but otherwise are in good agreement with them. The uncertainties in the widths positions and relative intensities of the component lines are also discussed

A grazing incidence x-ray diffraction study of the transverse structure function of the liquid-vapor interface of Ga

We report the results of a grazing incidence x-ray diffraction study of the liquid-vapor interface of Ga. It is shown that the transverse structure function in the liquid-vapor interface of Ga is indistinguishable from the structure function of bulk liquid Ga. When compared with the transverse structure functions obtained from calculations of models of the liquid-vapor interface of a similar system [J. Chem. Phys. 86, 1036 (1987)], this result implies that the widely used point local density approximation to the properties of an inhomogeneous liquid is inaccurate and must be replaced by a representation which includes, at least to first order, the effect of the force which generates the density inhomogeneity in the liquid. © 1992 American Institute of Physics.link_to_subscribed_fulltex

X-ray Studies of Atomic Layering at Liquid Metal Surfaces

Surface-induced layering has been observed in liquid gallium and mercury using X-ray reflectivity. The specular reflectivity R($q_z$) has been measured to wavevector transfers as large as $q_z$ = 3.0 Å$^{−1}$. For Ga, the only major deviations from Fresnel theory $R_f$ are near qz = 2.4 Å$^{−1}$, where there is a peak in the ratio $R/R_f$, For Hg, there is a broad peak near 2.15 Å$^{−1}$. The data have been collected on a sputtered clean, ultra-high vacuum Ga surface and on a Hg surface in a reducing atmosphere of hydrogen. The data can be explained with a layered liquid/vapor interface that is roughened by thermally excited capillary waves. The layer spacing is similar to the Ga or Hg atomic dimensions, extending into the bulk with an exponential decay length of 6 Å for Ga and 3 Å for Hg.Engineering and Applied Science

X-ray Reflectivity Studies of the Surface Structure of Liquid Metals

Extensive theoretical predictions of atomic layering at the surfaces of liquid metals have remained unconfirmed due to the limited range of wave vector transfer qz that has been previously measured. We report here on X-ray reflectivity studies from the surfaces of liquid mercury to qz greater-than or equivalent to 2.8 Å−1, and gallium to qz greater-than or equivalent to 3.0 Å−1, that show peaks which clearly demonstrate atomic layering with spacing on the order of the atomic diameter. The exponential decay of layer penetration into the bulk for Ga (6.5 Å) is larger than for Hg (3–3.5 Å). The prominent features of the layering remain unchanged under self-assembled monolayers of thiols. The Ga layering shows an unexpected strong temperature dependence. Differences between the reflectivity from Ga and Hg at small qz indicate fundamental differences in the surface structure for these two liquid metals.Engineering and Applied Science