Aperiodic incommensurate phase of a C60 monolayer on Ag(100) -: art. no. 245414

被引:50
作者
Hsu, CL [1 ]
Pai, WW [1 ]
机构
[1] Natl Taiwan Univ, Ctr Condensed Matter Sci, Taipei 10764, Taiwan
关键词
D O I
10.1103/PhysRevB.68.245414
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
Detailed combined scanning tunneling microscopy and low-energy electron diffraction measurements reveal that the structure of a C-60 monolayer on Ag(100) is not the previously accepted commensurate c(6x4) phase but rather an incommensurate (111) close-packed phase. The film exhibits a characteristic molecular contrast pattern with merely short-range order, and room-temperature fluctuations of the contrast show that a thermal equilibrium state is reached. The nature of this controversial bright-dim C-60 contrast is clarified as a topographic feature due to C-60-induced reconstruction underneath the dim C-60 molecules. Due to interactions between the incommensurate C-60 adlayer and the reconstructed substrate, the (111) phase is distorted laterally, forming a novel "tetramer" configuration of specific contrast order. The spatial distribution of these tetramers is aperiodic; this has crucial implications for the peculiar short-range contrast order observed experimentally. A lattice gas model with anisotropic nearest-neighbor interactions and a configuration energy of the tetramer is developed. Quantitative agreements between observation and modeling are achieved with reasonable phenomenological parameters derived within experimental constraints.
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页数:12
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