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1.
Carbon films with a diamondlike structure that are chemically bonded to surfaces have been deposited by means of low-energy C(+) ion beams. When mass-selected C(+) beams at energies in the range from 20 to 200 electron volts impinge on atomically clean surfaces, the first carbon monolayer grows as a carbide structure that is chemically bonded to the surface. As deposition continues, the structure evolves over the next several atomic layers into a diamondlike structure. These pure carbon films are strongly adhered to the surface through the carbide bonds, which also provide for an intimate interface. There are significant applications for such films, particularly as insulators and doped semiconductors. 相似文献
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It is shown that it is possible to use soil microorganisms for utilizing organic poultry farming wastes with the production of ecologically clean fertilizer that increases the yield and quality of agricultural products. The results obtained are the basis for developing highly effective technologies for environmental rehabilitation. 相似文献
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Nanometer-thick films at interfaces and surfaces exist in various materials and can substantially influence their properties. Whether these films are an equilibrium or transient state is debated. To address this question, we equilibrated 1.2-nanometer-thick films at gold-sapphire interfaces in the presence of anorthite glass and measured the solid-solid interface energy. The equilibrated film significantly reduced the interfacial energy and could be described by the Gibbs adsorption isotherm expanded to include structure in addition to chemical excess. Unlike artificially made conventional thin films, these films do not break up during equilibration and offer an alternative design criterion for thin-film technology. These results demonstrate that nanometer-thick films at interfaces and surfaces can be an equilibrium state and included in phase diagrams with dedicated tie-lines. 相似文献
4.
用田间采样及室内培养的方法,研究短期和长期中水和清水灌溉下3种常见绿地植物根系层土壤微生物的数量变化。结果表明:金叶假连翘和黄金榕的根际土壤细菌、真菌和放线菌数量均随土层深度的增加而减少,但真菌在短期清水灌溉下20~40cm土层中数量分布最多;台湾草的根际土壤细菌、真菌在各土层间的数量分布与金叶假连翘和黄金榕相似,放线菌在20—40cm土层数量分布最多;与清水灌溉相比,3种植物在短期中水灌溉下,其根际土壤细菌、真菌和放线菌数量在O-20cm土层差异显著,20—4J0、40—60cm土层中的数量分布因植物种类不同而有所差异。 相似文献
5.
An experimental technique is described for simultaneously measuring the static and dynamic interactions of very thin liquid films between two surfaces as they are moved normally or laterally relative to each other. Film thickness can be measured and controlled to 1 angstrom. Initial results are presented of the transition in the physical properties of liquid films only one molecular layer thick to thicker films whose properties are practically indistinguishable from the bulk. In particular, the results show that two molecularly smooth surfaces, when close together in simple liquids, slide (shear) past each other while separated by a discrete number of molecular layers, and that the frictional force is "quantized" with the number of layers. 相似文献
6.
Eom CB Marshall AF Laderman SS Jacowitz RD Geballe TH 《Science (New York, N.Y.)》1990,249(4976):1549-1552
YBa(2)Cu(3)O(7) films have been grown epitaxially on SrTiO(3) (100) and LaAlO(3) (100) substrates with nearly pure a-axis orientation and with transition temperature T(c) (R = 0) of 85 K. A unique feature of these films is their smooth surface. These smooth surfaces enable the growth of short-period superlattices with well-defined modulations. The films are untwinned and the grains grow with their c-axis along one of two perpendicular directions on the substrate ([100] or [010]). The fabrication of sandwich-type Josephson junctions with good characteristics may now be possible because unlike c-axis-oriented films, the superconducting coherence length of these smooth films is appreciably large perpendicular to their surfaces. 相似文献
7.
Thin gold films placed in contact on compliant elastomeric poly(dimethylsiloxane) supports weld together. This ;;cold welding' is remarkable both for the low loads required and for the fact that it occurs under ambient laboratory conditions, conditions in which the gold surfaces are covered with films of weakly adsorbed organic impurities. These impurities are probably displaced laterally during the welding. Welding can be prevented by the presence of a self-assembled gold(I) alkylthiolate monolayer on the gold surfaces. The welded contacts have low electrical resistivity and can be made thin enough to transmit light. This system is a promising one with which to study interaction between interfaces. 相似文献
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Biomimetic Pathways for Assembling Inorganic Thin Films 总被引:3,自引:0,他引:3
IA Aksay M Trau S Manne I Honma N Yao L Zhou P Fenter PM Eisenberger SM Gruner 《Science (New York, N.Y.)》1996,273(5277):892-898
Living organisms construct various forms of laminated nanocomposites through directed nucleation and growth of inorganics at self-assembled organic templates at temperatures below 100°C and in aqueous solutions. Recent research has focused on the use of functionalized organic surfaces to form continuous thin films of single-phase ceramics. Continuous thin films of mesostructured silicates have also been formed on hydrophobic and hydrophilic surfaces through a two-step mechanism. First, under acidic conditions, surfactant micellar structures are self-assembled at the solid/liquid interface, and second, inorganic precursors condense to form an inorganic-organic nanocomposite. Epitaxial coordination of adsorbed surfactant tubules is observed on mica and graphite substrates, whereas a random arrangement is observed on amorphous silica. The ability to process ceramic-organic nanocomposite films by these methods provides new technological opportunities. 相似文献
10.
The interaction in water of neutral hydrocarbon and fluorocarbon surfaces, prepared by Langmuir-Blodgett deposition of surfactant monolayers, has been investigated. The attraction between these hydrophobic surfaces can be measured at separations of 70 to 90 nanometers and thus is of considerably greater range than previously found. Spontaneous cavitation occurred as soon as the fluorocarbon surfaces were brought into contact but occurred between the hydrocarbon surfaces only after separation from contact. The very long range forces measured are a consequence of the metastability of water films between macroscopic hydrophobic surfaces. Thus the hydrophobic interaction between macroscopic surfaces may not be related to water structure in the same way that the hydrophobic effect between nonpolar molecules is related to water structure. 相似文献
11.
Supramolecular Materials: Self-Organized Nanostructures 总被引:1,自引:0,他引:1
SI Stupp V LeBonheur K Walker LS Li KE Huggins M Keser A Amstutz 《Science (New York, N.Y.)》1997,276(5311):384-389
Miniaturized triblock copolymers have been found to self-assemble into nanostructures that are highly regular in size and shape. Mushroom-shaped supramolecular structures of about 200 kilodaltons form by crystallization of the chemically identical blocks and self-organize into films containing 100 or more layers stacked in a polar arrangement. The polar supramolecular material exhibits spontaneous second-harmonic generation from infrared to green photons and has an adhesive tape-like character with nonadhesive-hydrophobic and hydrophilic-sticky opposite surfaces. The films also have reasonable shear strength and adhere tenaciously to glass surfaces on one side only. The regular and finite size of the supramolecular units is believed to be mediated by repulsive forces among some of the segments in the triblock molecules. A large diversity of multifunctional materials could be formed from regular supramolecular units weighing hundreds of kilodaltons. 相似文献
12.
Biofilms are formed by the aggregation of microorganisms into multicellular structures that adhere to surfaces. Here we show that bakers' yeast Saccharomyces cerevisiae can initiate biofilm formation. When grown in low-glucose medium, the yeast cells adhered avidly to a number of plastic surfaces. On semi-solid (0.3% agar) medium they formed "mats": complex multicellular structures composed of yeast-form cells. Both attachment to plastic and mat formation require Flo11p, a member of a large family of fungal cell surface glycoproteins involved in adherence. The ability to study biofilm formation in a tractable genetic system may facilitate the identification of new targets for antifungal therapy. 相似文献
13.
Two marine and one terrestrial wood-boring isopod species and one wood-inhabiting amphipod species maintain a digestive tract free of microorganisms. Digestive tracts examined in toto with the scanning electron microscope were devoid of microorganisms. In contrast, the outer exoskeleton surfaces of these crustaceans support a dense bacterialflora. Observations of the hindgut of termites revealed a diverse gut microflora as expected. 相似文献
14.
Eng PJ Trainor TP Brown GE Waychunas GA Newville M Sutton SR Rivers ML 《Science (New York, N.Y.)》2000,288(5468):1029-1033
The physical and chemical properties of the hydrated alpha-Al(2)O(3) (0001) surface are important for understanding the reactivity of natural and synthetic aluminum-containing oxides. The structure of this surface was determined in the presence of water vapor at 300 kelvin by crystal truncation rod diffraction at a third-generation synchrotron x-ray source. The fully hydrated surface is oxygen terminated, with a 53% contracted double Al layer directly below. The structure is an intermediate between alpha-Al(2)O(3) and gamma-Al(OH)(3), a fully hydroxylated form of alumina. A semiordered oxygen layer about 2.3 angstroms above the terminal oxygen layer is interpreted as adsorbed water. The clean alpha-Al(2)O(3) (0001) surface, in contrast, is Al terminated and significantly relaxed relative to the bulk structure. These differences explain the different reactivities of the clean and hydroxylated surfaces. 相似文献
15.
The surface microstructure of c-axis (Ca,Sr)CuO(2) thin films, grown by laser molecular beam epitaxy on SrTiO(3)(001) substrates, was studied by ultrahigh-vacuum scanning tunneling microscopy (STM). Images were obtained for codeposited Ca1-xSrxCuO(2) thin films, which show a layered-type growth mode. The surfaces consist of atomically flat terraces separated by steps that are one unit cell high. A pronounced dependence of the growth mechanism on the Sr/Ca ratio of the films was observed. Atomic resolution STM images of the CuO(2) sheets in the ab plane show a square lattice with an in-plane spacing of 4 angstroms; the lattice contains different concentrations of point defects, depending on the polarity of the sample-tip bias. 相似文献
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Macrae AU 《Science (New York, N.Y.)》1963,139(3553):379-388
This discussion of a few preliminary experiments with nickel points out some of the potential uses of low energy electron diffraction in improving our understanding of many types of surface phenomena. The first, and probably the most basic use, is in the study of clean surfaces. As illustrated in this article, the physical properties of the surface layer of atoms may be totally unlike those in the bulk of the crystal. It is necessary to understand such phenomena before a thorough understanding of chemical effects on surfaces can be achieved. The adsorption of gases, oxidation and corrosion, and the formation of epitaxial layers can all be studied in great detail by low energy electron diffraction. 相似文献
18.
Scanning electron microscopy and energy dispersive x-ray analyses of desert varnish reveal that microorganisms concentrate ambient manganese that becomes greatly enhanced in brown to black varnish. Specific characteristics of desert varnish and of varnish bacteria support a microbial origin for manganese-rich films. Varnish microbes can be cultured and produce laboratory manganese films. Accordingly, natural desert varnish and also manganese-rich rock varnishes in nondesert environments appear to be a product of microbial activity. 相似文献
19.
Wear limits the life-span of many mechanical devices with moving parts. To reduce wear, lubricants are frequently enriched with additives, such as zinc phosphates, that form protective films on rubbing surfaces. Using first-principles molecular dynamics simulations of films derived from commercial additives, we unraveled the molecular origin of how antiwear films can form, function, and dissipate energy. These effects originate from pressure-induced changes in the coordination number of atoms acting as cross-linking agents to form chemically connected networks. The proposed mechanism explains a diverse body of experiments and promises to prove useful in the rational design of antiwear additives that operate on a wider range of surface materials, with reduced environmental side effects. 相似文献
20.
Colson JW Woll AR Mukherjee A Levendorf MP Spitler EL Shields VB Spencer MG Park J Dichtel WR 《Science (New York, N.Y.)》2011,332(6026):228-231
Covalent organic frameworks (COFs), in which molecular building blocks form robust microporous networks, are usually synthesized as insoluble and unprocessable powders. We have grown two-dimensional (2D) COF films on single-layer graphene (SLG) under operationally simple solvothermal conditions. The layered films stack normal to the SLG surface and show improved crystallinity compared with COF powders. We used SLG surfaces supported on copper, silicon carbide, and transparent fused silica (SiO(2)) substrates, enabling optical spectroscopy of COFs in transmission mode. Three chemically distinct COF films grown on SLG exhibit similar vertical alignment and long-range order, and two of these are of interest for organic electronic devices for which thin-film formation is a prerequisite for characterizing their optoelectronic properties. 相似文献