WO2006034739A2

WO2006034739A2 - Method for vacuum-coating with a photo-semiconducting layer and use of said method

Info

Publication number: WO2006034739A2
Application number: PCT/EP2005/006238
Authority: WO
Inventors: Peter Frach; Daniel Gloess; Klaus Goedicke; Sigrun Klinkenberg; Christian Gottfried; Volker Kirchhoff
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2004-09-24
Filing date: 2005-06-10
Publication date: 2006-04-06
Also published as: EP1791987A2; DE102004046390A1; WO2006034739A3

Abstract

The invention relates to a method for vacuum-coating an object with a photo-semiconducting layer. Said method is characterized by the following steps: adjusting the temperature of the surface-near area of the object to a value in the range of from -40 °C to +250 °C prior to coating; operating a reactive pulsed magnetron sputter process with at least one electrically conducting target containing titanium as the main component in a working gas containing at least one inert gas and oxygen; controlling the process in accordance with the purpose of application of the coated object in such a manner as to ensure formation of mainly titanium oxide in a defined ratio of the atomic composition of the layer of titanium to oxygen such as 1: (2+x), whereby x ranges from -0.5 to +0.3; adjusting such a ratio of the rates of ionized and neutral particles during layer formation that a portion of at least 5 percent of titanium oxide is formed as a crystalline modification thereof and that the parameters of the sputter process are selected in such a manner that the surface temperature of the object does not exceed a maximum temperature of 300 °C.

Description

Method for vacuum coating with a photo-semiconductive layer and application of the method

Introduction The photo-induced hydrophilic and photocatalytic behavior of TiO ₂ layers of the crystalline anatase phase allows the fabrication of products with new properties such as easy-to-clean surfaces, self-cleaning windows, anti-fog glass, self-sterilizing and anti-tarnish bacterial tiles or air and water cleaning devices. State of the art for preparing crystalline TiO ₂ layers by vacuum coating method is the use of elevated temperatures of decision 300 ⁰ C during film deposition or during the thermal post-crystallization after Ab¬. Often, the post-annealing is carried out at temperatures of up to 550 ⁰ C.

Many applications require high rate coating techniques such as sputtering and scaling up to inexpensively coat large surfaces. It was therefore an object to utilize reactive medium-frequency pulse magnetron sputtering methods for the deposition of crystalline TiO ₂ layers at a high coating rate. It is known that pulse mode has a significant impact on particle bombardment during the growth of a layer on a substrate. This opens the way for the deposition of crystalline TiO ₂ layers at low temperatures. Here, the comparison of the photocatalytic effects of amorphously deposited post-crystallized TiO ₂ layers and in situ crystalline deposited TiO ₂ layers is presented. Another task was the deposition of thin TiO ₂ layers (<50 nm) at low substrate temperatures with sufficient photocatalytic properties.

The object is achieved by a method for vacuum coating at least a part of the surface of an object with a photo-semiconducting layer, wherein

the temperature of the near-surface region of the object is adjusted before coating to a predetermined value in the range from -40 ⁰ C to +250 ⁰ C,

a reactive pulse magnetron sputtering process with at least one electrically conductive target, which contains titanium as its main constituent, in at least one Operated inert gas and oxygen-containing working gas,

by the process control depending on the application of the coated object, the formation of predominantly titanium oxide in a fixed ratio of the atomic composition of the layer of titanium to oxygen as

1: (2 + x) where x is in the range of -0.5 to +0.3,

such a ratio of the rates of ionized and neutral particles is set during the film formation that a proportion of at least 5 percent titanium oxide is formed in crystalline modification

and that the parameters of the pulse magnetron sputtering process are selected such that the surface temperature of the object does not exceed a predetermined maximum temperature of 300 ^° C.

In further embodiments of the invention will

the pulse magnetron sputtering process with at least one magnetron source, energy supply in the unipolar pulse mode and a duty cycle of less than 0.6 performed;

or the pulse magnetron sputtering process with at least two magnetron sources, energy supply in the bipolar pulse mode or energy supply in the pulse packet mode a duty cycle of less than 0.5 carried out;

or the pulse magnetron sputtering process with at least one magnetron source, which is connected as a cathode, a counterelectrode, which is connected as an anode, and a magnetic field in the region of the anode, which has an amount of at least 1 kA / m, and power supply in unipolar, bipolar or pulse packet mode;

or the temperature of the near-surface region of the object before the coating in the range 30 ⁰ C ... 80 ⁰ C set; or at least one target additionally using at least one doping element for the photo-semiconducting layer from the group Fe, Ni, W, Co, Zn, Y, C, Sn, Bi, Pt, Nb, V, Mo, Rh, Si, N contains;

or a working gas used which additionally contains at least one further reactive gas which contains at least one of the elements H, N, C;

or to ensure a defined ratio of the atomic composition of the layer and a constant layer composition, the supply of the working gas or its reactive components as a function of the instantaneous atomization rate,

or at least one magnetron source having an unbalanced magnetic field,

or the ratio of the rates of ionized and neutral particles during Schicht¬ education by adjusting or regulating the electrical discharge power and / or the duty cycle set;

or the ratio of the rates of ionized and neutral particles during the film formation is set by the adjustment or regulation of the reactive working point of the pulse magnetron sputtering process,

or the ratio of the rates of ionized and neutral particles during the Schicht¬ education using an additional external ionisierungsquelle, such as capacitive or inductively coupled high-frequency energy set,

or the ratio of the rates of ionized and neutral particles during the Schicht¬ education set by the additional application of a pulsed or high-frequency bias voltage to the object,

or the parameters of the pulse magnetron sputtering process pressure, duty cycle, type of energy supply, discharge power, reactive operating point, time profile of the coating set so that the temperature in the near-surface region of the object has a value of 130 ^° C., but preferably 80 ⁰ C, does not exceed; or a working gas used, which additionally contains at least one effective as a precursor of a chemical vapor deposition process inorganic or metall¬ organic compound such as Ti tetrachloride TiCl ₄ or Ti tetraisopropoxide Ti (OCH (CH ₃ ) ₂ ) ₄ ;

or a working gas used, which additionally contains at least one inorganic or organometallic compound active as precursor of a chemical vapor deposition process, which leads to the formation of a doping of the photo-semiconducting layer,

or a working gas used, which additionally contains a silicon-containing inorganic or organic compound as a precursor of a chemical vapor deposition process;

or before depositing the photo-semiconducting layer, an electrically insulating layer from the group of the compounds SiO ₂ , Al ₂ O ₃ , ZrO ₂ , AlN, Si ₃ N ₄ is deposited by a reactive powder magnetron sputtering process.

The method according to the invention can be used

for depositing a photo-semiconductive layer on at least part of the surface of an object which consists wholly or partly of a temperature-sensitive material, preferably a polymer;

for producing a superhydrophilic surface of the object for products such as e.g. Anti-fog mirrors, easy-to-clean glass panes, wall and ceiling panels;

to produce an active self-cleaning article such as e.g. Tiles or bricks in the outdoor area;

for the production of a product having antibacterial and / or virucidal activity and / or inactivating effects on microorganisms, eg of medical devices or furniture surfaces; for the production of a product capable of decomposing a chemical bond, for example for denitrification or desulfurization of a gas or for splitting hydrocarbons;

for the production of a layer which is part of a photovoltaic multi-layer coating system, e.g. for use in a Grätzel cell;

for producing a layer which is part of an optically active multilayer coating system.

Experimental

The pulse magnetron sputtering or PMS system used for the reactive sputter deposition of the TiO ₂ layers allows the pulse parameters to be changed: pulse mode (unipolar = UP, bipolar = BP or pulse packet = PP) and duty Cycle (Tast¬ ratio). This system was developed and built at the Fraunhofer Institute for Electron Beam and Plasma Technology (FEP). It consists of two flange magnetrons, a switching unit (UBS-C2) to generate the pulse power, a gas control unit and a process management computer for fully automatic process control.

Tab. 1 Coating parameters for the PMS deposition of TiO ₂ layers presented in this study; UP: unipolar, BP: bipolar; PP: pulse packet.

In the unipolar pulse mode, both targets are operated as cathodes of separate discharges, with a hidden anode of the magnetrons acting as counterelectrode. In the bi-polar pulse mode, each target of the two magnetrons operates alternately as the cathode and anode of a discharge. A further development of the bipolar pulse mode is the so-called pulse packet mode. Each packet consists of a certain number of unidirectional pulses. The next packet again consists of a certain number of unidirectional pulses of opposite polarity. This pulse-packet mode ensures greater process stability, especially in the case of ares occurring.

The duty cycle, i. the ratio of on-time to total time of one pulse cycle can be adjusted for each target. Since the pulse power supply can be changed without further restriction, the PMS system allows a direct investigation of the effects of these coating parameters on the process characteristics such as deposition rate and layer properties. The layers are coated during transit through an in-line coating system (moving substrates). The coating parameters are summarized in Tab. The maximum coating temperatures given are the average of the maximum temperatures measured with temperature gauges on the front and back of the samples.

For the deposition of amorphous TiO ₂ layers, the unipolar pulse mode was selected (as in the deposition of sample 1). These layers were post-crystallized at different temperatures (250 ⁰ C: Sample 1 A 350 ⁰ C: Probei B, 500 C ^0: Sample 1 C) On the one hand deposited temperature in situ crystalline deposited layers at elevated substrate. This resulted in maximum coating temperatures of about 235 ⁰ C. The pulse mode was varied (unipolar: sample 2, bipolar: sample 3, pulse packet: sample 4). By stabilizing the sputtering process in the transition mode between the metallic and the reactive sputtering mode, a very high deposition rate of over 45 nm * m / min was achieved (corresponding to a rate of over 160 nm / min in a stationary sputtering system). The layer thickness for the samples 1 to 4 was 500 nm.

On the other hand, investigations have been carried out to deposit thin in situ crystalline deposited TiO ₂ layers at lower coating temperatures. By choosing a more reactive operating point of the discharge was a lower deposition rate set (about 8 nm * m / min, corresponding to the rate of

30 nm / min in a stationary coating system). The layer thickness was 45 nm

(Sample 5), 85 nm (Sample 6) and 170 nm (Sample 7), respectively.

The layer structure was determined by X-ray diffraction with grazing incidence (Seifert FPM, RD 7, Cu K _α radiation, angle of incidence: 1 °). The photo-induced hydrophilicity of the layers was determined by measuring the water contact angle (G-23E from Krüss GmbH) after irradiation with ultraviolet light (PU _V - _A = 1 mW / cm ² ). Photocatalytic degradation, ie the ability to break chemical bonds, has been studied by the decolorization reaction of methylene blue (MB) at Pu _V - _A = I mW / cm ² . The reduction in optical absorption of the methylene blue solution at the wavelength of 660 nm was determined with a PerkinElmer Lambda 900 spectrometer. Without a photocatalytically active layer, we did not observe any decolorization even after 40 hours of UV-A irradiation.

Results and discussion

1) Comparison of amorphously deposited recrystallized TiO ₂ layers and in situ crystalline deposited TiO ₂ layers

Amorphously deposited recrystallized layers showed many cracks in the TiO ₂ layer when examined by light microscopy as a result of shrinkage during crystallization. In contrast, crystalline deposited layers showed no cracks and were excellent with very little visible roughness that was detectable only with DIC mode (Differential Interference Contrast) of the light microscope.

The surface roughness (RMS) was determined by AFM investigations and is 1, 1 1 nm for amorphously deposited recrystallized (sample 1 B: recrystallized at 350 ⁰ C) and 10.6 nm for in situ crystalline deposited TiO ₂ layers (Sample 4: PP mode). In addition, the measurements of the highest crystallites could be estimated by these measurements. This was in the range of 50 to 100 nm for post-crystallized layers (Sample 1B) and 100 to 300 nm for crystalline deposited layers (Sample 4). From this observation, it was concluded that crystallization by post-crystallization produces very fine crystallites and only slightly increases the layer roughness. In contrast, the crystalline deposited layers showed large crystallites and high roughness, since crystal growth occurred during the layer deposition, The X-ray diffraction analysis revealed the crystalline anatase phase for amorphously deposited, post-crystallized layers (Sample 1B, FIG. Crystalline deposited layers in situ showed a mixture of anatase and rutile. The intensity of the X-ray reflections was significantly higher for the layers deposited in the pulse-packet mode (Sample 4, Figure 1 b) and in the bipolar pulse mode (Sample 3, not shown here) than in the unipolar pulse mode deposited layers (Sample 2, not shown here). Due to the high defect density, the reflections of the crystalline deposited layers are significantly wider, although the crystal size is larger than that of the post-crystallized layers.

Figure 2 shows the decrease in the water contact angle of amorphously deposited, amorphously deposited, recrystallized and crystalline deposited TiO ₂ layers during UV-A irradiation. Amorphous TiO ₂ layers and post-crystallized TiO ₂ layers at 250 ⁰ C showed no significant photo-induced hydrophilic behavior. Amorphous ab¬ divorced layers, recrystallized at temperatures of at least 350 ⁰ C showed the super-hydrophilic effect (water contact angle <10 °) after an irradiation time of 5 hours. There was no difference for the nachkristallisierten at 350 ⁰ C or 500 ⁰ C layers are found.

Among the in-situ crystalline deposited TiO ₂ layers, layers deposited in bipolar and pulse-packet mode exhibited the highest activity and reached the super-hydrophilic state after an irradiation time of only 30 minutes. In contrast, the layers deposited in crystalline form in the unipolar pulse mode show a lower activity. The super-hydrophilic state was not reached even after 6 hours irradiation time. The photocatalytic degradation of methylene blue is shown graphically in FIG. Again, the layers deposited in bipolar and pulse-packet mode showed the highest activity. The test solution of methylene blue was almost completely decolorized after 40 hours irradiation time.

The low photocatalytic activity of crystals deposited in unipolar pulse mode corresponds to the significantly lower reflectances of anatase and rutile in the X-ray diffraction study. Although the post-crystallized layers consist of pure anatase, their activity was considerably lower. 2) Photocatalytic activity of thin, at low temperatures abgeschie¬ which TiO ₂ layers

It has been observed that crystal growth and photocatalytic activity decrease sharply as the film thickness falls below 200 nm. This is especially true when the deposition temperature is below about 350 ⁰ C. In order to optimize the photocatalytic properties for thin layers at low temperatures, smaller deposition rates were selected. The low deposition rate permits crystalline growth with thin layer thicknesses and low substrate temperatures (see Table 1, Samples 5 to 7).

FIG. 4 shows the decrease of the water contact angle during the UV-A irradiation of the thin layers as well as the comparison curve for 500 nm thick TiO ₂ layers. All layers show super hydrophilic behavior after a maximum irradiation time of 5 hours. Among the thin layers, the highest activity was observed for the layers of 170 nm layer thickness (Sample 7). The activity was comparable to the activity of the 500 nm thick reference layer (sample 4).

The comparison of the photocatalytic activity of thin and thick crystalline separated abge TiO ₂ layers is shown in Fig. 5. Again, the 170 nm thick layers showed a similar high activity as the 500 nm thick reference layers. Depending on the photocatalytic activity required and on the substrate material, the appropriate layer thickness can be selected.

Claims

claims

A method for vacuum coating at least a part of the surface of an object with a photo-semiconductive layer, characterized in that

the temperature of the near-surface region of the subject in front of the coating to a predetermined value in the range from -40 ⁰ C to +250 ⁰ C is set,

a reactive pulse-magnetron sputtering process is carried out with at least one electrically conductive target, which contains titanium as the main constituent, in a working gas containing at least one inert gas and oxygen,

the process guidance, depending on the intended use of the coated object, ensures the formation of predominantly titanium oxide in a fixed ratio of the atomic composition of the layer from titanium to oxygen, such as 1: (2 + x), where x is in the range of -0.5 to +0.3,

- Such a ratio of the rates of ionized and neutral particles is set during the stratification that a proportion of at least 5 percent

Titanium oxide is formed in crystalline modification

2. The method according to claim 1, characterized in that the pulse magnetron sputtering process is performed with at least one magnetron source, energy supply in the unipolar pulse mode and a duty cycle of less than 0.6.

3. The method according to at least one of the preceding claims, characterized ge indicates that the pulse magnetron sputtering process with at least two magnetron sources, energy supply in the bipolar pulse mode or Energieeinspei¬ solution in the pulse packet mode a duty cycle less than 0.5.

4. The method according to at least one of the preceding claims, characterized ge indicates that the pulse magnetron sputtering process with at least one magnetron source, which is connected as a cathode, a counter electrode, which is connected as the anode, and a magnetic field in the range the anode, which has an amount of at least 1 kA / m, as well as energy input in unipolar, bipolar or

Pulse packet mode is performed.

5. The method according to at least one of the preceding claims, characterized ge indicates that the temperature of the near-surface region of the object is set before the coating in the range 30 ⁰ C to 80 ⁰ C.

6. The method according to at least one of the preceding claims, characterized ge indicates that at least one target additionally at least one doping element for the photo-semiconducting layer from the group Fe, Ni, W, Co, Zn, Y, C, Sn, Bi, Pt, Nb, V, Mo, Rh, Si, N.

7. The method according to at least one of the preceding claims, characterized ge indicates that the working gas additionally contains at least one further reactive gas containing at least one of the elements H, N, C.

8. The method according to at least one of the preceding claims, characterized ge indicates that to ensure a defined ratio of the atomic composition of the layer and a constant layer composition, the supply of the working gas or its reactive components is controlled in dependence on the instantaneous sputtering rate.

9. The method according to at least one of the preceding claims, characterized ge indicates that at least one magnetron source has an unbalanced Magnet¬ field.

10. The method according to at least one of the preceding claims, characterized ge indicates that the ratio of the rates of ionized and neutral particles during the film formation by adjusting or regulating the electrical discharge power and / or the duty cycle is set.

11. The method according to at least one of the preceding claims, characterized ge indicates that the ratio of the rates of ionized and neutral particles during Schichtbiidung is set by adjusting or regulating the reactive operating point of the pulse magnetron sputtering process.

12. The method according to at least one of the preceding claims, characterized ge indicates that the ratio of the rates of ionized and neutral particles during the film formation using an additional external ionisierungs- source as capacitive or inductively coupled high-frequency energy is set.

13. The method according to at least one of the preceding claims, characterized ge indicates that the ratio of the rates of ionized and neutral particles during the film formation by the additional application of a pulsed or high-frequency bias voltage is set on the object.

14. The method according to at least one of the preceding claims, characterized ge indicates that the parameters of the pulse magnetron sputtering process pressure, duty cycle, type of energy supply, discharge power, reactive operating point, time scheme of the coating are set so that the Temperature in the near-surface region of the object a value of 130 ⁰ C, but preferably of 80 ⁰ C, does not exceed.

15. The method according to at least one of the preceding claims, character- ized in that the working gas additionally effective as a precursor of a chemical vapor deposition process inorganic or • organometallic compound such as Ti-tetrachloride TiCl ₄ or Ti-tetraisopropoxide Ti (OCH ( CH ₃ ) ₂ ) ₄ .

16. The method according to at least one of the preceding claims, characterized ge indicates that the working gas additionally contains at least one effective as a precursor of a chemical vapor deposition process inorganic or organometallic compound, which leads to the formation of a doping of the photovoltaic semiconducting layer.

17. The method according to at least one of the preceding claims, characterized ge indicates that the working gas additionally contains a silicon-containing inorganic or organic compound as a precursor of a chemical vapor deposition process.

18. The method according to at least one of the preceding claims, characterized ge indicates that before depositing the photo-semiconductive layer, an electrically insulating layer from the group of compounds SiO ₂ , Al ₂ O ₃ , ZrO ₂ , AlN, Si ₃ N ₄ by a reactive pulse magnetron sputtering process is deposited.

19. Application of the method according to at least one of claims 1 to 18 for depositing a photo-semiconducting layer on at least a part of the Ober¬ surface of an object which consists wholly or partly of a temperature-sensitive material, preferably a polymer.

Application of the method according to at least one of claims 1 to 18 for producing a superhydrophilic surface of the object for products, such as e.g. Anti-fog mirror, easy to clean glass panels, wall and ceiling panels.

21. Application of the method according to at least one of claims 1 to 18 for producing an active self-cleaning commodity such. Tiles or bricks in the outdoor area.

22. Application of the process according to at least one of claims 1 to 18 for the preparation of a product having antibacterial and / or virucidal activity and / or inactivating effects on microorganisms, e.g. of medical devices or furniture surfaces.

23. Application of the method according to at least one of claims 1 to 18 for the preparation of a product with the ability to split a chemical

Binding, for example for denitrification or desulfurization of a gas or for cleavage of hydrocarbons.

24. Application of the method according to at least one of claims 1 to 18 for the production of a layer which is part of a photovoltaic multi-layer coating system, e.g. for use in a Grätzel cell.

25. Application of the method according to at least one of the claims 1 to 18 for the production of a layer which is part of an optically active multilayer coating system.