Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
2002-08-13
2004-07-20
Jackson, Monique R. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S420000, C428S457000, C427S496000, C427S498000, C427S504000, C427S506000, C427S508000, C427S512000, C427S520000
Reexamination Certificate
active
06764758
ABSTRACT:
The present invention relates to surface-modified layer systems, a method for the production and use thereof. The present invention relates in particular to surface-modified layer systems that include a substrate and, at least partially disposed thereon, a laterally cross-linked monolayer, composed of low molecular weight aromatic and/or heteroaromatic compounds, that is covalently bonded via anchor groups to at least one surface of the substrate. The laterally cross-linked monolayer of the surface-modified layer systems according to the invention, that is composed of low molecular weight aromatic and/or heteroaromatic compounds, exhibits the characteristics of a cross-linked solid and consequently protects the surfaces of the corresponding substrates, particularly advantageously against damage from friction and corrosion.
According to the current state of the art, surfaces are usually protected against corrosive actions and mechanical stress, due to friction, by physisorbed thin fluid films (e.g., oils, waxes) or polymer coatings applied thereon. These conventional films usually have layer thicknesses in the range of a few micrometers up to millimeters. Their exact layer thickness, however, is difficult to control by process technology.
In the prior art, non-cross-linked monolayers, in particular those based on aliphatic hydrocarbon chains, have low mechanical stability and therefore provide insufficient protective action. Moreover, non-cross-linked monolayers desorb on contact with corrosive agents, since individual molecules at defect sites are displaced from the surface and detachment of the layer progresses from such sites.
Conventional methods for producing such non-cross-linked monolayers of organic molecules on various substrates are described in more detail in, for example, A. Ulman, “
An Introduction to Ultrathin Films,
” Academic Press, Boston 1991, and A. Ulman, Chem. Rev. 96, 1533 (1996).
The aim of the present invention is therefore to provide coating systems in which the coatings have high mechanical and chemical stability and the underlying substrate surfaces should be effectively protected against damage from friction or corrosive agents. The layer thickness for such protective layers should be precisely controllable and range from 0.3 nm to 3 nm. Such systems should be particularly suitable for surface protection of mechanically moving devices with small working clearances in the micrometer or nanometer range, such as hard disk drives for electronic data storage, or for surface protection of micromechanical devices with moving parts of dimensions in the micrometer range and smaller.
This aim is achieved by the embodiments specified in the claims. In particular, a surface-modified layer system is provided that includes a substrate and, at least partially disposed thereon, a laterally cross-linked monolayer, composed of low molecular weight aromatic and/or heteroaromatic compounds, that is covalently bonded via anchor groups to at least one surface of the substrate.
In contrast to coating systems available in the prior art, for example those based on physisorbed thin fluid films or polymer coatings, the protective layers according to the invention can be precisely controlled or, as the case may be, adjusted by virtue of the spatial extent of the molecules that make up the laterally cross-linked monolayer and are covalently bonded to the substrate surface via anchor groups.
The monolayer of the surface-modified layer system according to the invention preferably has a layer thickness in the range from 0.3 nm to 3 nm.
By means of covalent bonding to the substrate surface, the monolayer of the surface-modified layer system according to the invention effectively protects the underlying substrate surface against damage from friction or corrosive agents.
The laterally cross-linked monolayer of the surface-modified layer system according to the invention is preferably composed of aromatic compounds selected from the group consisting of phenyl, biphenyl, terphenyl, naphthalene, and anthracene, and/or composed of heteroaromatic compounds selected from the group consisting of bipyridine, terpyridine, thiophene, bithienyl, terthienyl, and pyrrole.
In one embodiment of the present invention, the monolayer, composed of low molecular weight aromatic compounds and/or heteroaromatic compounds, can have on its surface functional groups selected from halogen atoms, carboxy, trifluoromethyl, amino, nitro, cyano, thiol, hydroxy, or carbonyl groups. The low molecular weight aromatic and/or heteroaromatic molecules or units that comprise the monolayer are then, with the help of an anchor group, coupled chemically to the underlying substrate surface or covalently bonded to the latter.
Cross-linking of the monolayer in the lateral direction can in particular be achieved by treatment with electron beam radiation, plasma radiation, x-ray radiation, &bgr;-radiation, &ggr;-radiation, or UV radiation.
The substrate, which is given high mechanical and chemical stability by the laterally cross-linked monolayer according to the invention and whose surface is therefore effectively protected against damage from friction or corrosive agents, is preferably selected from the group consisting of gold, silver, titanium, zirconium, vanadium, chromium, manganese, tungsten, molybdenum, platinum, aluminum, iron, steel, silicon, germanium, indium phosphide, gallium arsenide, and oxides or alloys or mixtures thereof as well as indium-tin oxide (ITO) and silicate or borate glasses.
If the surface of the substrate material is atomically flat and homogeneous, i.e., if for example it has no edge dislocations or defects, then the protective layer is also atomically flat, homogeneous, and defect-free, and forms a nearly perfectly smooth protective film on the substrate surface to be protected. The protective layer matches the morphology of the substrate almost perfectly. In this way, objects with three-dimensional surface morphologies can also be covered with a cross-linked protective layer of defined thickness.
The monolayers of the surface-modified layer system according to the invention can also exhibit electrical conductivity by means of passage of electrons or holes. This makes it possible to use the monolayers according to the invention in devices in which the passage of charge through the surface can be controlled by means of a stable protective layer, as for example in coated electronic components or electrodes.
The anchor group that chemically anchors the monolayers according to the invention to the substrate material is preferably selected from the group consisting of carboxy, thio, trichlorosilyl, trialkoxysilyl, phosphonate, hydroxamic acid, and phosphate groups, where the anchor groups, with the help of a spacer with length from 1 to 10 methylene groups, can be covalently bonded to the laterally cross-linked monolayer composed of low molecular weight aromatic and/or heteroaromatic compounds.
The nature of the anchor group is tailored to the particular substrate material, in a way known to one skilled in the art. For example, trichlorosilanes or trialkoxysilanes such as trimethyloxysilane, triethoxysilane, etc. are particularly suitable as anchor groups for oxidized silicon surfaces. Alcohol groups can be used for anchoring for hydrogenated silicon surfaces. For gold and silver surfaces, thio groups for example can be used as anchor groups; for oxidized metal surfaces such as iron or chromium, suitable anchor groups are phosphonic acids, carboxylic acids, or hydroxamic acids.
In a particularly preferred embodiment of the present invention, the surface-modified layer system includes a monolayer composed of biphenyl units that is covalently bonded to the corresponding substrate surface, such as for example gold or silver surfaces, via thio groups as anchor groups.
A further object of the present invention is to provide a method for production of surface-modified layer systems, according to the invention, that includes the steps:
(a) preparation of a substrate,
(b) modification of the substrate surface
Eck Wolfgang
Geyer Wolfgang
Gölzhäuser Armin
Grunze Michael
Stadler Volker
Jackson Monique R.
Universitat Heidelberg
Weingarten Schurgin, Gagnebin & Lebovici LLP
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