PHOTOCATALYTIC LAYER ARRANGEMENT AND METHOD FOR PRODUCING SUCH A LAYER ARRANGEMENT

Abstract

A photocatalytic layer arrangement includes a carrier substrate on which a chromium layer with a defined nitrogen content is deposited. A titanium oxide layer having the formula TiO.sub.x (x=2-4) is grown on the chromium layer, and the anatase phase of the titanium oxide layer with respect to the rutile phase of the titanium oxide layer has a percentage in the range of 30%-90%.

Claims

1-15. (canceled)

16. A photocatalytic layer arrangement, comprising: a carrier substrate; a chromium layer having a defined nitrogen content arranged on the carrier substrate; and a titanium oxide layer having the formula TiO.sub.x(x=2-4) arranged on the chromium layer; wherein an anatase phase of the titanium oxide layer with respect to a rutile phase of the titanium oxide layer has a percentage between 30% and 90%.

17. The photocatalytic layer arrangement according to claim 16, wherein the chromium layer is arranged as a deposited layer on the carrier substrate.

18. The photocatalytic layer arrangement according to claim 16, wherein the titanium oxide layer is arranged as a grown layer on the chromium layer.

19. The photocatalytic layer arrangement according to claim 16, wherein the anatase phase of the titanium oxide layer with respect to the rutile phase of the titanium oxide layer has a percentage between 50% and 80%.

20. The photocatalytic layer arrangement according to claim 16, wherein a layer thickness of the titanium oxide layer is between 30 nm and 300 nm.

21. The photocatalytic layer arrangement according to claim 16, wherein the titanium oxide layer has a granular surface structure with anatase crystallites in a size between 20 nm and 120 nm.

22. The photocatalytic layer arrangement according to claim 21, wherein the anatase crystallites in the titanium oxide layer have a substructure.

23. The photocatalytic layer arrangement according to claim 16, wherein a layer thickness of the chromium layer is between 30 nm and 150 nm.

24. The photocatalytic layer arrangement according to claim 16, wherein the nitrogen contents of the chromium layer is between 15 at % and 25 at %.

25. The photocatalytic layer arrangement according to claim 16, wherein the nitrogen content of the chromium layer is between 15 at % and 25 at % at least to a depth of 10 nm.

26. The photocatalytic layer arrangement according to claim 16, wherein the carrier substrate includes glass.

27. The photocatalytic layer arrangement according to claim 16, wherein the photocatalytic layer arrangement is arranged in an optical sensor adapted to examine samples that include biological molecules.

28. The photocatalytic layer arrangement according to claim 16, wherein the carrier substrate includes borosilicate glass and/or quartz glass.

29. The photocatalytic layer arrangement according to claim 16, wherein the carrier substrate includes a glass ceramic, zinc selenide, and/or potassium bromide.

30. A method for producing a photocatalytic layer arrangement, comprising: applying a chromium layer having a defined nitrogen content to a carrier substrate using a reactive sputtering method; and depositing a titanium oxide layer having the formula TiO.sub.x (x=2-4) on the chromium layer using a low-temperature sputtering method; wherein a titanium oxide layer grows during the deposition, an anatase phase of the titanium oxide layer respect to an rutile phase of the titanium oxide layer has a percentage between 30% and 90%.

31. The method according to claim 30, wherein the nitrogen content of the chromium layer is between 15 at % and 25 at %, and the nitrogen is contained near a surface of the chromium layer at least to a depth of 10 nm.

32. The method according to claim 30, wherein the chromium layer is applied using the reactive sputtering method with an argon-nitrogen flow ratio that satisfies the following condition:Ar (sccm)/N.sub.2 (sccm)=1.0 to 2.0.

33. The method according to claim 30, wherein a layer thickness of the chromium layer is between 30 nm and 150 nm.

34. The method according to claim 30, wherein a layer thickness of the titanium oxide layer is between 30 nm and 300 nm.

35. The method according to claim 30, wherein a granular surface structure of the titanium oxide layer includes anatase crystallites having a size between 20 nm and 120 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a cross-sectional view of a layer arrangement according to an example embodiment of the present invention.

[0023] FIG. 2 illustrates the measurement curve of an X-ray diffractometry examination of the layer arrangement, with the marked main peaks for the anatase and rutile phase of the titanium dioxide layer.

[0024] FIGS. 3a-3c are scanning electron microscope images of the surface of a titanium oxide layer with different proportions of the crystalline anatase phase.

DETAILED DESCRIPTION

[0025] FIG. 1 is a cross-sectional sectional view of a photocatalytic layer arrangement according to an example embodiment of the present invention. The layer arrangement includes a carrier substrate 1 on which a chromium layer 2 with a defined nitrogen content is deposited. On top of the chromium layer 2 is a grown, photocatalytically active titanium oxide layer 3 having the formula TiO.sub.x, in which wherein x=2-4. The following description provides further details of the chromium layer 2 and the titanium oxide layer 3.

[0026] Such a layer arrangement can be used, for example, in optical sensors for examining material samples including or consisting of biological moleculeshereinafter referred to as biomolecules. For this purpose, the properties of the photocatalytically active titanium oxide layer 3 are decisive.

[0027] This layer has a high thermal, mechanical, and chemical stability and is also biocompatible. This makes the titanium oxide layer 3 particularly suitable for the accumulationin the form of non-specific non-covalent (physical) bondsof biomolecules, since titanium oxide provides for good electrostatic interaction. In addition, irradiation of the photocatalytically active titanium oxide layer 3 with a suitable UV source in the wavelength range of 200 nm-400 nm can be used to clean the surface of the layer and/or to activate the surface. Photocatalysis results in bond-destroying effects, whereby organic compounds, such as carbon compounds CC, CH, etc., are broken down and a partial oxidation of the surface residues takes place with the formation of carbon oxides C.sub.ox. The granular or rough structure of the surface of the titanium oxide layer 3, which structure will be described in more detail below, additionally results in a significant increase in the active surface area. This provides for improved accumulation of biomolecules and enhances the photocatalytic properties.

[0028] In addition, the layer arrangement that includes the titanium oxide layer 3 and the reflective chromium layer 2 can be used to generate a localized field superelevation in the region of the surface of the titanium oxide layer 3 with fluorescence excitation at a suitable wavelength. This increases the signal yield, for example, with fluorescence detection of biomolecules accumulated on the surface being provided in a corresponding optical sensor. To maximize the detection effect, the layer thickness of the titanium oxide layer 3 and the excitation wavelength used can be matched to each other.

[0029] To produce the photocatalytic layer arrangement described herein, a chromium layer 2 having a defined nitrogen content is first deposited on the carrier substrate 1. The nitrogen-enriched chromium layer 2 serves as an intermediate layer for the titanium oxide layer 3 that grows subsequently.

[0030] The material for the carrier substrate 1 is, for example, glass, e.g., glass types D263 or BF33 or quartz glass are suitable. Alternatively, the use of glass ceramics such as Zerodur are also possible. Similarly, suitable optically transparent crystals such as zinc selenide (ZnSe) or potassium bromide (KBr) could be used as material for the carrier substrate 1, which would have to be provided in a suitable plate-like or planar form. For example, the corresponding carrier substrate material has the lowest possible autofluorescence.

[0031] The nitrogen-enriched chromium layer 2 is deposited using a reactive sputtering method with an argon-nitrogen flow ratio of Ar (sccm)/N.sub.2 (sccm)=1.0-2.0, e.g., an argon-nitrogen flow ratio of Ar (sccm)/N.sub.2 (sccm)=1.2-1.7. Suitable layer thicknesses for the chromium layer 2 are in the range of 30 nm-150 nm.

[0032] A certain nitrogen content in the chromium layer 2 is provided for the subsequent growth of the particularly strongly photocatalytically active anatase-rich phase of the titanium oxide layer 3. The chromium layer 2 thus induces titanium oxide growth with a defined phase mixture of the anatase phase and the rutile phase of the titanium oxide. This phase mixture can have improved photocatalytic properties compared to a pure anatase phase due to charge carrier processes. The nitrogen content in the chromium layer 2 should be in the range of, for example, 15 at %-25 at %, in which the nitrogen content is decisive above all near the surface in relation to the boundary surface to the titanium oxide layer 3, e.g., to a depth of at least 10 nm in the chromium layer 2. The chromium layer 2 enriched with nitrogen in this manner acts as a growth enhancer for the anatase phase of the titanium oxide layer 3 growing thereabove with its good photocatalytic properties.

[0033] For example, the chromium layer 2 promotes the growth of the anatase phase of the titanium oxide layer 3.

[0034] Using a low-temperature sputtering process, the titanium oxide layer 3 is deposited on a chromium layer 2 formed in this manner, in which the following applies with regard to the composition of the titanium oxide layer 3: x=2-4 for TiO.sub.x.

[0035] Typical layer thicknesses for the chromium layer 3 are in the range of 30 nm-300 nm.

[0036] The anatase phase of the titanium oxide layer 3, for example, grows during deposition without the need for further processing steps such as tempering, etc. The titanium oxide shows stem growth perpendicular to the chromium layer 2, which is typical for sputtering processes. The anatase phase of the titanium oxide layer 3 with respect to the rutile phase of the titanium oxide layer 3 as determined by X-ray diffractometry has a percentage in the range of 30%-90% in a region close to the surface, typically less than 100 nm, e.g., a percentage in the region of 50%-80%. The amorphous titanium oxide content in the titanium oxide layer 3 is not taken into account in this regard.

[0037] FIG. 2 illustrates an exemplary measurement curve for regions near the surface of such titanium oxide layers by X-ray diffraction at a constant angle of incidence Omega=0.3?, which typically corresponds to a penetration depth of less than 100 nm. The significantly high percentage of the anatase phase (first peak on the left) with respect to the rutile phase (second peak on the left) in the titanium oxide layer is discernable.

[0038] The titanium oxide layer grown in this manner also has a granular or rough surface structure, which shows a plurality of crystallites forming. The higher the proportion of the anatase phase in the titanium oxide layer, the greater the degree of coverage of the surface of the titanium oxide layer with such crystallites. This can be seen from the comparison of the two images from the scanning electron microscope in FIGS. 3a and 3b, which are images of corresponding surfaces of titanium oxide layers 3. In FIG. 3a, the corresponding titanium oxide layer 3 has an anatase content of approximately 45%, and, in FIG. 3b, the corresponding titanium oxide layer 3 has an anatase content of approximately 75%.

[0039] The image from the scanning electron microscope shown in FIG. 3c is a further enlarged partial view of the layer surface shown in FIG. 3b, which illustrates that the crystallites of the anatase phase forming in the titanium oxide layer 3 have a substructure in the form of a disk structure. For titanium oxide layers with a sufficiently large anatase content, the anatase crystallites have sizes in the range of 20 nm-120 nm, e.g., 30 nm-100 nm. In FIG. 3c, a plurality of crystallites are characterized by corresponding straight line segments, which have a size of 50 nm (white segments) or 100 nm (black segments). Such rough surfaces of the titanium oxide layer 3 are considered to be advantageous, since the active surface area thereabove is significantly enlarged, resulting in improved accumulation of biomolecules and improved photocatalytic properties.