The relation between magnetic properties and microscopic structure for a metal/semiconductor system is described. Cobalt films on a CoSi interface possess an in-plane easy axis of magnetization as the result of magnetocrystalline anisotropy of the Co∕CoSi interface. On a Si(111)-7×7 surface, direct evidence for the formation of CoSi2 compounds at the interface was found by the appearance of doubled spot defects in scanning tunneling microscopic images. The interfacial effects cause the easy axis of magnetization of a Co∕Si interface to be canted out of plane.
On many hillsides of Taiwan there is a unique pattern of weed exclusion byPhyllostachys edulis (bamboo) andCryptomeria japonica (conifer) in which the density, diversity, and dominance of understory species are very different. Although the physical conditions of light, soil moisture, and soil nutrients strongly favor the growth of understory in a bamboo community, the biomass of its undergrowth is significantly low, indicating that physical competition among the understory species in the bamboo and conifer communities does not cause the observed differences. However, the biochemical inhibition revealed by these two plants appeared to be an important factor. The growth ofPellionia scabra seedlings, transplanted from the study site into greenhouse pots, was evidently suppressed by the aqueous leachate of bamboo leaves but was stimulated by that of conifer leaves. The radicle growth of lettuce, rye grass, and rice plants was also clearly inhibited by the leachate and aqueous extracts of bamboo leaves but not by those of conifer leaves. Six phytotoxins,o-hydroxyphenylacetic,p-hydroxybenzoic,p-coumaric, vanillic, ferulic, and syringic acids were found in the aqueous leachate and extracts of leaves and alcoholic soil extracts ofP. edulis, while the first three compounds were absent in the extracts ofC. japonica. The phytotoxicities of extracts were correlated with the phytotoxins present in both leaves and soils. The understory species might be variously tolerant to the allelopathic compounds produced by the two plants, resulting in a differential selection of species underneath. Therefore, comparative allelopathic effects ofPhyllostachys edulis andCryptomeria japonica may play significant roles in regulating the populations of the understories.
The orientation of the magnetization and the occurrence of interfacial ferromagnetic dead layers for ultrathin Co films on Si(111) and CoSi2 surfaces have been systematically studied using in situ surface magnetic-optic Kerr effect. We have experimentally demonstrated that an in-plane magnetization can be obtained by using CoSi2 as a buffer layer for ultrathin Co films between 2.8 and 10.5 monolayers (MLs) deposited on Si(111) at 300 K. The ferromagnetic dead layers at the interface are most likely due to the formation of a Co–Si alloy. This region can be reduced from 2.1 to 1.4 ML by lowering the substrate temperature from 300 to 120 K. From a dynamic study of the silicide formation in Co/Si(111), a two-step diffusion mechanism is suggested with two different diffusion activation energies of the Co atoms resulting from different chemical environments.
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