X-ray scattering studies of metal surfaces
X-ray-scattering studies of the phase behavior of the clean Au(111), Pt(111), and Au(113) surfaces are described. It is found that the Au(111) surface reconstructs between at least 300 K and 0.93T{sub m}. The surface structure below 0.64T{sub m} consists of an equilibrium density of kinks between rotationally equivalent domains, each of which is composed of a series of discommensurations. the discommensurations incorporate an excess density of surface atoms and separate surface regions with ideal face-centered-cubic (fcc) ABC stacking from regions with faulted ABA stacking. Above 0.66T{sub m}, the arrangement of discommensurations and kinks in disordered, resulting in isotropic compression of the reconstructed layer. A first-order phase transition separates the two structures. The Pt(111) surface structure was studied between 300 K and 0.92T{sub m}. The surface is unreconstructed for temperatures to form a layer isotropically compressed and incommensurate with the underlying bulk (111) planes. A disordered arrangement of discommensurations separates regions with ideal fcc ABC stacking from regions with faulted ABA stacking. With increasing temperature, both the compression of the surface layer and the orientational order of the discommensurations increase. Remarkably, this phase and the high-temperature phase of the Au(111) surface are similar. These results support a simple idea that underlies much of our understanding of metal surface reconstruction. Namely, the equilibrium surface structure is determined by the balance of two competing interactions: the tendency to contract in the plane of the surface due to the larger effective coordination number of surface atoms, and the registry imposed by the underlying bulk. The Au(113) surface structure was studied between 300 and 800 K. From 300 to 732 K, we observe diffraction peaks corresponding to a reconstruction perpendicular to the parallel close-packed rows which compose the ideal surface.
- Research Organization:
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
- OSTI ID:
- 114804
- Resource Relation:
- Other Information: DN: MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307; TH: Thesis (Ph.D.); PBD: 1992
- Country of Publication:
- United States
- Language:
- English
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