“Magic size” effect in the packing of n-alkanes on Au(1 1 1): evidence of lowered sliding force for molecules with specific length

Molecular structure of monolayers formed at the interface between Au(1 1 1) surfaces and solutions containing n-alkanes has been studied by in situ scanning tunneling microscopy at room temperature. Increasing the C_nH_2n+2 length from n=10 up to 50 with even n numbers alternates rectangular and tilted arrangement of alkanes within the self-organized layers. This alternation is related to the dramatically lowered sliding force for molecules with a length close to mT (m-integer), where T is the period of commensurability between the CH₂-CH₂-CH₂ period along alkyl chains and the interatomic distance along Au〈1 1 0〉 direction.     

A study of Si-L and O-K ELNES in plant material: SiO2, Ca- and Zn-silicate in Minuartia

The formation of vacuolar precipitates containing silicon and calcium, as well as the accumulation of metal-silicates in cell walls of Minuartia has been investigated by electron microscopy, energy-dispersive X-ray analysis and electron spectroscopic imaging. The bond state of the elements concerned is examined by analysing energy-loss near-edge structures (ELNES), particularly the Si-L_2,3 and the O-K ELNES. Experimental ELNES results are compared with local densities of unoccupied states calculated by molecular orbital methods and results of XANES calculations.     

STM study of the structure of the sulphur (1×2) overlayer on molybdenum (001) in air: ordered domains,phase boundaries and defects

A (001) surface of molybdenum, covered by one monolayer of sulphur was prepared in UHV and characterized by LEED, Auger and XPS. This surface was found to be stable in air for periods of several days. STM images of the surface, obtained in air in the topographic and local barrier height modes, revealed the atomic arrangement of sulphur atoms in domains with 1×2 and 2×1 periodicities. Boundaries between domains, adsorbate and substrate defect structures and crystallites formed during the initial oxidation of the Mo substrate were observed.