Eine Plattform für die Wissenschaft: Bauingenieurwesen, Architektur und Urbanistik
Eine Plattform für die Wissenschaft: Bauingenieurwesen, Architektur und Urbanistik
Surface Reconstruction Phase Transformations
Abstract Clean single-crystal (metal) surfaces usually possess well-defined two-dimensional (2D) periodicities closely resembling the atomic ordering in the bulk. In some instances, however, the surfacelattice reconstructs into a phase with new symmetry. This can occur spontaneously with temperature, or it can be induced by small coverages of adsorbed atoms or molecules. The phase transformation may be reversible or irreversible. For example, Au (110) exhibits an irreversible reconstruction into a (2×1) superstructure once the clean surface has been prepared. This surface then undergoes a reversible order-disorder phase transition when the temperature is raised above a critical value, Tc = 700 [K]. Similarly, a carefully cleaned W (100) surface reconstructs into a (√2 × √2) lattice1 which also disorders reversibly at Tc = 300 [K]. A small quantity of chemisorbed hydrogen switches the symmetry of the atomic displacements from domains with p2mg space group symmetry to domains with c2mm symmetry, while maintaining a (√2 × √2) translational periodicity [2]. Increasing the amount of hydrogen produces a commensurate to incommensurate phase transformation which is reversible with coverage [3]. Clean Mo(100) reconstructs into a surface lattice which is incommensurate with the bulk substrate structure over a wide temperature range below 300 [K] [4]. Si (111) forms a (2×1) reconstructed lattice which transforms upon heating irreversibly into a (7×7) superlattice [5]. Surprisingly, the (7×7) structure exhibits a reversible order-disorder phase transition.
Surface Reconstruction Phase Transformations
Abstract Clean single-crystal (metal) surfaces usually possess well-defined two-dimensional (2D) periodicities closely resembling the atomic ordering in the bulk. In some instances, however, the surfacelattice reconstructs into a phase with new symmetry. This can occur spontaneously with temperature, or it can be induced by small coverages of adsorbed atoms or molecules. The phase transformation may be reversible or irreversible. For example, Au (110) exhibits an irreversible reconstruction into a (2×1) superstructure once the clean surface has been prepared. This surface then undergoes a reversible order-disorder phase transition when the temperature is raised above a critical value, Tc = 700 [K]. Similarly, a carefully cleaned W (100) surface reconstructs into a (√2 × √2) lattice1 which also disorders reversibly at Tc = 300 [K]. A small quantity of chemisorbed hydrogen switches the symmetry of the atomic displacements from domains with p2mg space group symmetry to domains with c2mm symmetry, while maintaining a (√2 × √2) translational periodicity [2]. Increasing the amount of hydrogen produces a commensurate to incommensurate phase transformation which is reversible with coverage [3]. Clean Mo(100) reconstructs into a surface lattice which is incommensurate with the bulk substrate structure over a wide temperature range below 300 [K] [4]. Si (111) forms a (2×1) reconstructed lattice which transforms upon heating irreversibly into a (7×7) superlattice [5]. Surprisingly, the (7×7) structure exhibits a reversible order-disorder phase transition.
Surface Reconstruction Phase Transformations
Willis, Roy F. (Autor:in)
01.01.1985
22 pages
Aufsatz/Kapitel (Buch)
Elektronische Ressource
Englisch
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