TW201329285A - Method - Google Patents

Abstract

The present invention relates to a method for applying a zinc oxide coating to a substrate, a zinc oxide coating obtainable by such a method, and an apparatus comprising a substrate and such a zinc oxide coating on the substrate.

Description

method

The present invention relates to a method of applying a zinc oxide coating to a substrate, a zinc oxide coating obtainable by the method, and a device comprising the substrate and the zinc oxide coating on the substrate.

Zinc oxide is a transparent semiconductor having a wurtzite (hexagonal dense) crystal structure and a band gap of about 3.3 eV. The zinc oxide exhibits many desirable properties including ultraviolet light absorption, photoconductivity, photocatalytic, photo-wetability, piezoelectricity, antimicrobial characteristics, and wound healing. These properties were found to be technically applicable to thin film transistors, dye-sensitized solar cells, kinetic energy harvesters, transparent electrodes in liquid crystal displays, sunscreens, fabric protection, and medical dressings. Zinc oxide is often used in the form of thin films produced by RF sputtering, chemical vapor deposition, vapor diffusion catalysis, spray pyrolysis, electrodeposition, sol-gel synthesis or pulsed laser deposition.

The inherent limitations of such methods may include their substrate dependence (e.g., the need for a conductive or physically stable substrate) and (often) stringent process conditions (e.g., high temperature or oxidizing chemical environments). Thus, in terms of generating zinc oxide surfaces, a more versatile approach is strongly desired, especially in view of future applications of the versatility of materials for applications in emerging fields such as fibertronics.

Electroless deposition of zinc oxide is potentially attractive due to its relatively low temperature and low crystalline yield at high temperatures (less than 50 ° C). Izaki, M. et al., J. Electrochem. Soc. , 1997, 144, L3 and Shinagawa, T. et al., Electrochim . Acta, 2007, 53, 1170, which are described in the presence and aqueous conditions of palladium (0) catalyst. The reaction between zinc nitrate and dimethylaminoborane (DMAB) (where dimethylaminoborane reduces nitrate). Palladium (0) effectively catalyzes the oxidation of dimethylaminoborane: (CH ₃ ) ₂ NHBH ₃ +2H ₂ O → HBO ₂ +(CH ₃ ) ₂ NH ₂ ⁺ +5H ⁺ +6e ^-

Thereby a corresponding reduction of the nitrate ions (which causes a local increase in pH) is achieved: NO ₃ ^- + H ₂ O + 2e ^- → NO ₂ ^- + 2OH ^- .

This increase in pH triggers the growth of zinc oxide according to the following acid-base reaction: Zn ²⁺ + 2OH ^- → ZnO + H ₂ O.

It is an object of the present invention to provide a method of applying a zinc oxide coating to a substrate via electroless deposition, which can be implemented to increase the ease and/or efficiency with which the zinc oxide coating can be produced, and can also enhance its performance characteristics.

According to a first aspect of the present invention, there is provided a method of applying a zinc oxide coating to a substrate, the method comprising the steps of: (i) applying a nitrogen-containing aromatic heterocyclic functionalized coating to the substrate; (ii) including a nitrogen-containing aromatic heterocyclic functionalized coating is contacted with an agent comprising palladium (II) and/or platinum (II) to produce a coating comprising mis-palladium (II) and/or platinum (II); Reduction of the mis-palladium (II) and/or platinum (II) in the coating to palladium (0) and/or platinum (0); and (iv) inclusion in the presence of a reducing agent and aqueous conditions The coating of palladium (0) and/or platinum (0) is contacted with a zinc salt to form a zinc oxide coating on the substrate. Floor.

In an embodiment, the reagent comprising palladium (II) and/or platinum (II) is a reagent comprising palladium (II).

Figure 1 shows the reaction scheme of an embodiment of the invention.

Step (i) involves applying a nitrogen-containing aromatic heterocyclic functionalized coating to the substrate.

Step (i) can be a solventless process for functionalizing a solid surface with a nitrogen-containing aromatic heterocyclic group.

In an embodiment, the step (i) of applying a nitrogen-containing aromatic heterocyclic functionalized coating to the substrate is carried out by plasma deposition.

Plasma chemical deposition is an established technique for functionalizing surfaces. The film thickness can be easily controlled, and the process is solvent-free, conformal, and substrate-independent, thereby making it well suited for application to three-dimensional substrates such as textiles.

For example, pulsed plasma chemical deposition, for example, poly(4-vinylpyridine) is a promising way to bind a pyridyl group to a solid surface. This involves adjusting the discharge in the presence of a gaseous precursor containing a polymerizable carbon-carbon double bond. Mechanically, there are two different reaction schemes corresponding to the plasma duty cycle: the on period and the off period (typical time scales are microseconds and milliseconds, respectively). That is, monomer activation and reactive site formation ( via VUV irradiation, ion or electron bombardment) occurs at the surface during each short burst of plasma, followed by conventional carbon in the subsequent extended off time - Carbon double bond polymerization (in the absence of any VUV-, ion- or electron-induced damage to the growth film). A very high degree of retention of the bulk structure can be achieved within the deposited nanolayer, whereby specific functional groups are obtained at the surface. In addition, the surface density of the desired chemical group can be controlled (i.e., adjusted) by a programmed pulsed plasma duty cycle. The functional film obtained is covalently attached to the underlying substrate via the free radical sites generated at the interface during the onset of plasma exposure. Other advantages include the fact that the plasma chemistry method is fast (single step), solvent free, high energy efficiency, and the reactive gaseous properties of the discharge are the entire substrate material and complex geometries (eg, microspheres, fibers, tubes, etc.) The subject provides shape retention. Any surface that depends on a particular functional group due to performance can in principle be effectively produced by the above-described pulsed plasma chemistry. Examples of past designs include: functionalization with anhydrides, carboxylic acids, amines, cyano groups, epoxides, hydroxyl groups, halides, thiols, mercapto groups, perfluoroalkyl groups, perfluoromethylene groups, and trifluoromethyl groups. The surface.

WO 2006/111711 A1 describes a method of applying a coating comprising a reactive nitrogen functional group contained in an aromatic heterocyclic ring structure to a substrate, the method comprising subjecting the substrate to a plasma of a monomer having the heterocyclic nitrogen functional group. Discharge.

In an embodiment, step (i) of the method of the invention uses a pulsed plasma deposition procedure.

In an embodiment, step (i) of the method of the invention uses a substantially continuous wave plasma deposition procedure.

In an embodiment, step (i) of the method of the invention uses a low average power plasma deposition procedure. In an embodiment, the procedure occurs at a power density of up to 10 mW/cm ³ . Low average power plasma polymerization can potentially overcome the limitations of other techniques for producing a surface with a nitrogen-containing aromatic heterocyclic moiety.

However, palladium catalyst attachment does not require many surface sites, which is autocatalyzed by the electroless deposition process, so it is not necessary to perform the deposited plasma. The polymer layer is conventionally used with high structural retention criteria, and the electroless deposition process can also operate at higher average power.

In an embodiment, step (i) comprises subjecting the substrate to a plasma discharge of a monomer having an aromatic heterocyclic nitrogen functional group.

Step (i) of the process of the invention may use a monomer having at least one conventionally polymerizable unsaturated functional group (e.g., selected from the group consisting of acrylates, methacrylates, olefins, styrenes, alkynes, and/or derivatives thereof) The functional group is substantially different from the desired nitrogen-containing aromatic ring structure at the surface of the substrate (e.g., selected from the group consisting of pyridine, pyrrole, quinoline, isoquinoline, indole, pyrimidine, indole, and/or derivatives thereof). Suitable monomers are described in WO 2006/111711 A1. In an embodiment, the nitrogen-containing aromatic ring structure is derived from pyridine. A specific example of a suitable monomer is a vinyl pyridine, for example, 4-vinyl pyridine:

In an embodiment, the nitrogen-containing aromatic heterocyclic group in the nitrogen-containing aromatic heterocyclic functionalized coating is derived from pyridine.

The step (i) of the process of the invention may use a plasma polymerization procedure as set forth in WO 2006/111711 A1.

Step (i) of the process of the invention produces a product which is completely coated with a polymer coating having a nitrogen-containing aromatic heterocyclic functional group. Alternatively, only the nitrogen-containing aromatic heterocyclic functionalized polymer coating is applied to one or more of the selected surface domains of the substrate. The application of the patterned substrates includes areas that consider spatial control, such as surface wettability. a nitrogen-containing aromatic heterocyclic coating on a specific surface domain The limitation can be achieved by the method described in WO 2006/111711 A1.

Instead of using plasma deposition, the step (i) of applying a nitrogen-containing aromatic heterocyclic functionalized coating to the substrate can also be carried out by techniques selected from the group consisting of, for example, spin coating, solvent casting, UV-induced grafting. Polymerization and use of self-assembled monolayers (SAM).

After the nitrogen-containing aromatic heterocyclic functionalized coating is applied to the substrate, the nitrogen-containing aromatic heterocyclic group is further mismatched in step (ii).

Step (ii) involves contacting the nitrogen-containing aromatic heterocyclic functionalized coating with an agent comprising palladium (II) and/or platinum (II) to produce a mis-containing palladium (II) and/or platinum (II) ) coating.

The palladium and/or platinum centers can be coordinated via an electron lone pair interaction to a nitrogen-containing heterocycle such as pyridine. WO 2006/111711 A1 describes a process in which after applying a nitrogen-containing aromatic heterocyclic functionalized coating to the surface as described above, the surface is rendered such that the metal salt is mismatched with the surface heterocyclic group. A solution of a metal salt such as palladium chloride is contacted.

In an embodiment, the reagent comprising palladium (II) and/or platinum (II) in step (ii) comprises a salt of palladium (II) and/or platinum (II). In the examples, the salt of palladium (II) and/or platinum (II) is a salt of palladium (II). In the examples, the salt of palladium (II) is a halide, for example, palladium chloride.

Step (ii) of the process of the invention may be carried out using a procedure for the mismatching of palladium chloride with a nitrogen-containing aromatic heterocyclic functionalized coating as set forth in WO 2006/111711 A1.

Step (iii) involves reducing the mis-palladium (II) and/or platinum (II) in the coating to palladium (0) and/or platinum (0).

In an embodiment, the reduction of the palladium (II) and/or platinum (II) to palladium (0) and/or platinum (0) in step (iii) is in dimethylaminoborane (DMAB). Occurs in existence.

In an embodiment, step (iii) of the process of the invention requires the reduction of the mis-palladium (II) to palladium (0) by a reducing agent (e.g., DMAB).

Step (iv) involves contacting a coating comprising mis-palladium (0) and/or platinum (0) with a zinc salt in the presence of a reducing agent and aqueous conditions to form a zinc oxide coating on the substrate.

In an embodiment, the zinc salt in step (iv) is zinc nitrate.

In an embodiment, the reducing agent in step (iv) is DMAB.

In the examples, steps (iii) and (iv) of the process of the invention require reduction of the mis-palladium (II) center to palladium (0) by DMAB followed by zinc nitrate in the presence of palladium (0) center. DMAB reaction.

In the examples, steps (iii) and (iv) of the process of the invention occur together in a one-pot reaction. In an embodiment, reducing the palladium (II) and/or platinum (II) in the coating to palladium (0) and/or platinum (0) in step (iii) may also be carried out in the step. Used as a reducing agent in (iv).

In the examples, steps (iii) and (iv) of the process of the invention require in situ reduction of the mis-palladium (II) center to palladium (0) by DMAB, followed directly in the presence of the resulting palladium (0) center. The zinc nitrate is reacted with DMAB.

A second aspect of the invention provides a zinc oxide coating that can be obtained by the method of the first aspect or that has been produced using it.

In an embodiment, the zinc oxide coating is an antimicrobial coating.

In an embodiment, a zinc oxide coating is used in UV protection.

A third aspect of the invention provides a device comprising a substrate and a second aspect of a zinc oxide coating.

In an embodiment, the device is a medical dressing.

In an embodiment, the device is a thin film transistor.

In an embodiment, the device is a dye sensitized solar cell.

In an embodiment, the device is a kinetic energy harvester.

In an embodiment, the device is an electrode. In an embodiment, the device is, for example, a transparent electrode in a liquid crystal display.

Throughout the description of the specification and the scope of the patent application, the words "comprise" and "contain" and variations of the words (such as "comprising and comprises") mean "including but not limited to" And does not exclude other parts, additions, components, integers or steps. In addition, the singular encompasses the singular and the singular and the singular and the singular.

Preferred features of each aspect of the invention may be as described in connection with any of the other aspects. Other features of the invention will be apparent from the examples which follow. In general, the invention extends to any novel feature or combination of novel features disclosed in the specification, including any accompanying claims and drawings. Thus, features, integers, characteristics, compounds, chemical moieties or groups that are described in connection with the specific aspects, examples, or examples of the invention are to be construed as being applicable to any other aspects, embodiments or embodiments set forth herein. Examples, unless they are incompatible. In addition, unless otherwise stated, this article Any feature disclosed may be replaced by alternative features for the same or similar purpose.

If the upper and lower limits are used for the nature (such as the concentration or temperature of the component), the range of values defined by any combination of any of the upper and the lower limits may also be implied.

In the present specification, unless otherwise stated, properties (eg, film thickness, contact angle, and the like) refer to under ambient conditions (ie, at atmospheric pressure and at a temperature of from 18 ° C to 25 ° C (eg, about 20 ° C)) The nature of the measurement.

Embodiments of the invention will now be further elucidated with reference to the following non-limiting examples and the accompanying drawings in which: FIG.

experimental method

Film thickness measurements were performed using a spectrophotometer (nkd-6000, Aquila Instruments Co., Ltd.). The transmittance and reflectance curves across the 300-1000 nm wavelength range were fitted to the Cauchy model of the dielectric using the modified Levenberg-Marquardt method. The pulsed plasma poly(4-vinylpyridine) deposition rate was measured to be 15 ± 2 nm min ^-1 .

X-ray photoelectrons were applied to the functionalized substrate using a VG Escalab spectrometer equipped with a non-monochromated Mg-Kα X-ray source (1253.6 eV) and a concentric hemisphere analyzer operating in a constant analyzer energy mode (pass energy = 20 eV) Spectral (XPS) characterization in which photoelectrons were collected at a sweep angle of 12° to the substrate normal. The elemental composition is calculated using a sensitivity factor derived from a chemical standard: C(1s): O(1s): N(1s): Pd(3d): Zn(2p) is equal to 1.00:0.36: 0.57: 0.05: 0.05. All binding energies are based on the C(1s) hydrocarbon peak at 285.0 eV. The core energy level spectrum is fitted to a linear background.

The deposited film was subjected to Fourier transform infrared (FTIR) analysis using a Perkin-Elmer Spectrum One spectrometer equipped with a liquid nitrogen cooled MCT detector. Reflection-Absorption (RAIRS) Measurements The components of the s-polarized light were removed using an angular variable fitting (Specac Co., Ltd.) equipped with a KRS-5 polarizer and set to 66°. All spectra were averaged over 128 scans with a resolution of 4 cm ^-1 .

Depth profiling measurements were performed by a Rutherford backscatter technique using a ⁴ He ⁺ ion beam (5SDH Pelletron Accelerator). Backscatter ⁴ He ⁺ ions were detected at a resolution of 19 keV using a PIPS detector.

A zinc oxide layer (1 μm thick, mounted with electroless deposition) was collected using a powder diffractometer (Bruker d8) equipped with a Cu tube (1.5418 Å wavelength) and a linear position sensitive detector (Lynx Eye with Ni filter) An X-ray diffraction pattern on a (100) substrate. Data from 5° 2θ to 65° 2θ were collected in steps of 0.02°.

The electrolessly deposited zinc oxide layer was imaged using an optical microscope (Olympus BX40) equipped with a x50 magnifying lens.

For photochemical studies, UV light from a low-pressure Hg-Xe arc lamp (Oriel, Model 6136, emitting a strong line spectrum in the 240-600 nm region) operating at 100 W was focused at a focal length of 30 cm. Deposited on the zinc oxide film.

Conductivity measurements were performed using a pair of parallel silver electrodes (length 6 mm and 1 mm apart) sprayed onto a zinc oxide film that had been deposited on a non-conductive On the glass substrate. The conductive features of the zinc oxide film were found to be ohmic (0-200 V range) before and after UV exposure. In the case of the UV response curve, a constant voltage of 10 V was applied and the current was measured using a Keithley 2400 source meter.

Hanging drip contact angle measurements were performed using a video capture device in combination with a 2 μL droplet size electric syringe (VCA2500XE, A.S.T.Products) at ambient temperature. High purity water (Grade 1 B.S. 3978) was used as the probe liquid.

The antibacterial test was carried out according to the modified Japanese Industrial Standard Protocol. A bacterial cell culture (wild type Escherichia coli K-12 laboratory strain W3110) grown to A _{650 nm} of 0.4 was applied to a zinc oxide coated polypropylene nonwoven fabric and uncoated in a low salt buffer. Overlaid on the control. The samples were incubated for 24 h at 37 ° C in a humid dark environment. The excess culture and cloth were transferred to a 2 ml centrifuge tube and centrifuged at 9000 rpm for 2 min to maximize recovery. The recovered culture was vortexed to resuspend the cells; a ten-fold dilution was performed and spotted on LB agar. The plates were incubated overnight at 30 ° C, after which the pure coefficients were counted. To control cell uptake on the sample, the above procedure was repeated on coated and uncoated cloth using bacteria exposed for 1 min.

Instance

Pulsed plasma chemical deposition was carried out in a cylindrical glass reactor (4.5 cm diameter, 500 cm ³ volume, 1 x 10 ^-3 mbar base pressure, and a leak rate better than 1.7 x 10 ^-9 mol s ^-1 ). A copper coil (4 mm diameter, 10 revolutions) wound around the reactor was attached to a 13.56 MHz radio frequency (RF) power source via an LC matching unit. The entire device was enclosed in a Faraday cage. The chamber was evacuated using a 30 L min ^-1 rotary pump attached to a liquid nitrogen cold trap and the system pressure was monitored using a Pirani gauge. A pulse signal generator is used to trigger the RF power generator and an oscilloscope is used to monitor the pulse shape. Prior to deposition, the glass reactor was cleaned by scrubbing with detergent, rinsing in acetone, oven drying and then running 40 W continuous wave air plasma for 30 min. Next, insert 矽100 wafer (Silicon Valley Microelectronics), glass coverslip (VWR International) or polypropylene non-woven fabric (Corovin GmbH) into the chamber and pump the system back to the base pressure . At this stage, the reactor was purged with a 4-vinylpyridine precursor (+95%, Sigma-Aldrich, further purified with three refrigerated pump-thaw cycles) at a pressure of 0.2 mbar for 5 min followed by discharge ignition. For pyridine ring retention, the optimal duty cycle is: on-time = 100 μs and off-time = 4 ms, and peak power = 40 W. After the deposition is complete, the precursor is allowed to continue to flow through the system for an additional 5 minutes to quench any captured reactive sites contained within the deposited film.

The poly(4-vinylpyridine) functionalized surface was then immersed in 2 μM palladium(II) chloride (+99.999%, Alfa Aesar), 3.0 M sodium chloride (+99.5%, Sigma) and 0.5 M. Aqueous sodium citrate (+99%, Aldrich) aqueous solution (which has been adjusted to pH 4.5 with citric acid monohydrate (+99%, Aldrich) for 12 h, and subsequently washed in deionized water.

Next, the surface fixed with palladium chloride (II) was placed at a temperature of 323 K to contain 0.05 M zinc nitrate (+98%, Sigma-Aldrich) and 0.05 M dimethylamino borane (+97). %, Sigma-Aldrich) in an aqueous chemical bath up to 2 h. After the zinc oxide is grown, the surface is rinsed with deionized water.

XPS characterization of the pulsed plasma deposited poly(4-vinylpyridine) layer confirmed the presence of only carbon and nitrogen at the surface, and the Si(2p) signal from the underlying ruthenium substrate was never shown, see Table 1. It has also been found that there is a good correlation between the atomic percentages calculated for the precursor (theoretical) and the pulsed plasma deposited poly(4-vinylpyridine) film, which is consistent with a high degree of structural retention. Immersion into a palladium chloride (II) solution caused the appearance of Pd (3d _5/2 ) and Pd (3d _3/2 ) signals at 338.3 eV and 343.5 eV, respectively, and the Cl (2p) peak at 198.8 eV. This may indicate that PdCl _{2 is} mismatched to the poly(4-vinylpyridine) surface (the O(1s) peak at 532.7 eV is attributed to the water absorption from the aqueous palladium chloride (II) solution), see Figure 1 and Figure 2 .

For 4-vinylpyridine monomers, the following infrared band assignments can be made: vinyl C=C stretching (1634 cm ^-1 ), aromatic sector C=C stretching (1597 cm ^-1 and 1548 cm ^-1 ) , aromatic semicircle C=C and C=N stretching (1495 cm ^-1 and 1409 cm ^{-1 , respectively} ) and =CH ₂ sway (927 cm ^-1 ), see Figure 3. After the pulsed plasma deposition, all of these bands were discernible except for the vinyl carbon-carbon double bond characteristics which disappeared during polymerization. This is consistent with the high degree of structural retention associated with pulsed plasma deposition.

A control sample of poly(4-vinylpyridine) without pulsed plasma deposition of palladium (II) chloride seeded resulted in the absence of electroless zinc oxide growth, which highlights the critical role of immobilized palladium catalyst. In contrast, for a poly(4-vinylpyridine) film which is pulsed plasma deposited by palladium catalyst seeding, the zinc oxide film is clearly visible to the naked eye. Only zinc, oxygen and traces of carbon (due to atmospheric adsorption) can be detected by XPS, see Figure 2 and Table 1. The absence of N(1s) and Pd(3d) signals confirmed that the catalytically seeded poly(4-vinylpyridine) layer was completely covered by zinc oxide. The growth rate of zinc oxide film was determined by ion beam analysis to be 230±20 nmh ^-1 .

The X-ray diffraction characterization shows peaks at 31.9°, 34.5°, 36.3°, 47.6°, 56.6°, and 62.9°, which are consistent with zinc oxide in the wurtzite structure (hexagonal dense), see Figure 4. Rietveld refinement confirmed that the ratio of peak intensities matched the expectations for wurtzite zinc oxide. Thus, the film is polymorphic and randomly oriented. The peak width measured by the powder diffraction pattern indicates that the minimum crystallite size is 25 nm; however, many other parameters, including lattice strain, can also be the influence factor.

Optical microscopy shows roughened surfaces corresponding to different crystal faces, see Figure 5.

During UV irradiation, the zinc oxide film deposited on the flat non-conductive glass flakes exhibits a significant increase in conductivity, which increases from a dark conductivity value of 10 ^-7 mS cm ^-1 to a maximum of 1.5 mS cm after 750 s ^{- 1.} See Figure 6. It was observed that the conductivity slowly decayed after terminating the UV exposure. In the case of storage under ultra-high vacuum (pressure <10 ^-8 mbar), photoconductivity is maintained after a period of several weeks, while UV irradiation under vacuum causes an increase in conductivity.

The flat zinc substrate coated with zinc oxide has a high water contact angle value of 150°, but has a large contact angle hysteresis, see Table 2. The exposure of these surfaces to UV radiation in the air caused a significant drop in the equilibrium water contact angle due to surface hydrophilicity, see Table 2 and Figure 6. Exposure to higher intensity UV light over the same period of time causes the contact angle to drop below 20°. After the UV exposure was terminated, the contact angle slowly recovered to its initial value of 150° over a period of about 3 weeks, Figure 6. However, when the zinc oxide coated tantalum wafers (which have been exposed to UV in air) are stored under ultra-high vacuum conditions (<10 ^-8 mbar), the contact angle does not recover (ie, via 4) The period of the week is kept at 60°). In addition, UV irradiation of the zinc oxide coated sample under ultra-high vacuum conditions or pure O ₂ (instead of air) did not produce a discernable change in contact angle (i.e., maintained at 150°). These control experiments highlight that contact angle decay during UV exposure and subsequent hydrophobic recovery after termination of UV involves reaction with the surface of the air. The XPSC (1s) envelope corresponding to a small amount of adsorbed hydrocarbon material (285.0 eV) did not change, see Figure 7.

Electroless plating of zinc oxide on a pulsed plasma poly(4-vinylpyridine) coated nonwoven polypropylene substrate results in superhydrophobicity (high equilibrium water contact angle, over 150°, combined low contact angle hysteresis), see Table 2. In this case, The water repellency of the zinc oxide surface was not found to be affected by exposure to UV radiation, see Table 2.

The zinc oxide coated polypropylene cloth fragments also showed significant antibacterial activity against Gram negative bacteria (E. coli) (log kills up to 2.9), see Table 3. The control sample of the polypropylene cloth fragments did not exhibit antibacterial activity, however, after exposure to the pulsed plasma poly(4-vinylpyridine) coated cloth, only a decrease in log 0.2 was observed. This small decrease can be attributed to the absorption (rather than killing) of the cells on the hydrophilic layer, as similar results were obtained after 1 min incubation period (compared to 24 h control).

In these experiments, XPS and infrared analysis showed that a well-defined poly(4-vinylpyridine) layer could be used to coat various substrates (with early high-power continuous wave plasma derived from 4-vinylpyridine) The polymer formed a significant contrast). Subsequently, the zinc oxide is seeded with a catalytic palladium center to locally electrolessly grow zinc oxide. Another benefit of this method is that the functional polymer nanolayer can be used to protect the underlying substrate material from subsequent chemical processing steps, such as oxidizing and reducing the reagents contained in the zinc oxide electroless deposition solution.

The semiconducting properties of zinc oxide result from the natural doping (n-type) in the form of separately charged interstitial zinc cations (Zn ⁺ ), which are close to the conduction band and thus can be easily ionized (formed as Zn ²⁺ +) e) thereby supplying electrons to the conductive strip. The above excess electrons leaving the gap Zn ⁺ can be trapped at the surface by adsorbed oxygen (O _{2 (ads)} ) to obtain an O ₂ ^- _(ads) substance. The zinc oxide coated pulsed plasma poly(4-vinylpyridine) film exhibited photoconductivity during UV light exposure, see Figure 6. The contribution to the shape of the photoconductivity curve can be divided into fast reversible (electron excitation from the valence band to the conduction band) and slow irreversibility (surface chemistry of the adsorbed species). In addition, when zinc oxide is exposed to UV photon radiation having an energy greater than or equal to its band gap (3.3 eV), electron excitation from the valence band to the conductive band causes an electron-hole pair to form. The electrons may also be trapped at the surface by physically adsorbed oxygen, thereby forming a self-limiting concentration of chemisorbed O ₂ ^- _(ads) up to O ₂ ^- _(ads) due to electrostatic repulsion between O ₂ ^- _(ads) at the surface. . The O ₂ ^- _(ads) substances are capable of attracting holes from the body, and the holes migrate toward the surface to combine with the O ₂ ^- _(ads) substance, thereby causing surface vacancies and molecular oxygen light desorption: ZnO + hv → ZnO+eh (electron-hole pair)

e+O _2(ads) → O ₂ ^- _(ads)

h+O ₂ ^- _(ads) → O _2(g) ↑+□

After the molecular oxygen is lost from the surface via desorption, other electrons excited by the valence band to the conductive band during UV irradiation can no longer be captured by the adsorbed oxygen, and instead contribute to conductivity. Conversely, for example, re-adsorption of oxygen on the surface after termination of photodesorption results in a decay in conductivity, see Figure 6. Thus, in the case of a zinc oxide film, due to the inherently high surface area of the deposited material, the shift in equilibrium between the oxygen desorption process and the re-adsorption process will dominate the shape of the photoconductivity increase and decay curve. In the case of storage under vacuum, at the end After UV irradiation, the photoconductivity is maintained for a period of several weeks, which is consistent with the conductivity decay mechanism governed by molecular oxygen adsorption.

Reversible wettability was also observed after UV irradiation of a flat substrate coated with zinc oxide. The cleaned zinc oxide surface is hydrophilic (balanced water contact angle <35°, along with many other metal oxides), but in environmental conditions, such clean zinc oxide surfaces are known to attract amphiphilic carbonaceous contamination in the atmosphere. Things. The adsorbents, such as surfactants, act to attract a hydrophilic domain toward the surface of the zinc oxide (via an electron lone pair interaction with an electron depletion layer at the surface of the zinc oxide); thus, a hydrophobic structure of the carbonaceous material The domain is responsible for the hydrophobicity of the zinc oxide surface that is widely observed in environmental conditions. In the literature, two mechanisms are proposed for the UV-induced zinc oxide surface hydrophilic transition: First, UV light induces a photocatalytic reaction at the zinc oxide surface, thereby removing carbon contaminants (as in the case of titanium dioxide self-cleaning surfaces) Or second, UV light causes molecular oxygen to desorb from the surface of the zinc oxide, followed by dissociation of water adsorption. The carbon of the zinc oxide surface: oxygen: zinc XPS element ratio and C (1s) envelope shape did not change before and after UV irradiation, indicating that the first mechanism is impossible to be the main factor, see Table 1 and Figure 7. O _{2 (g)} light desorption from the surface of the zinc oxide causes vacancies that allow water molecules (stored in ambient air) to adsorb. The presence of water is required during UV exposure (as evidenced by controlled experiments where the contact angle is not reduced for UV-irradiated and ultra-high vacuum or zinc oxide surfaces exposed to air, see table 2) Indicate the light-assisted dissociation water adsorption mechanism, see Figure 2. The photogenerated hydroxide group is responsible for the surface transition from hydrophobic to hydrophilic. After a period of several weeks, the contact angle is fully recovered after the disappearance of UV radiation (the exact duration depends on the UV intensity), see Figure 6. Supporting reversible surface wetting characteristics to return to hydrophobic recovery oxygen re-adsorption process when UV is irradiated with zinc oxide in air (on a flat substrate) and then stored in ultra-high vacuum for an extended period of time The verification is achieved by observing the lack of increased contact angle. Thus, in air, water adsorbed at the surface during light irradiation is thermodynamically replaced by oxygen species over a period of time. This substitution (making it again hydrophobic) is slow and it is determined that the hydrophobic recovery time observed for zinc oxide is longer. Due to the much slower oxygen desorption and re-adsorption surface chemistry, this photochemical contact angle decay and subsequent reversal observed for UV exposure in air is not shown to correlate with fast (pure electron) bulk electron photoconductivity processes. Sex, see Figure 8.

During UV irradiation, zinc oxide showed surface chemistry similar to that reported for titanium dioxide (another metal oxide semiconductor having a comparable band gap). It is assumed that molecular oxygen is adsorbed at the surface defect site of titanium dioxide, and then it captures electrons generated by light to become O ₂ ^- _(ads) substances. During UV irradiation, the O ₂ ^- _(ads) materials undergo photodesorption as O _{2 (g)} from the surface of TiO _{2 in a} manner similar to zinc oxide. Thus, for both zinc oxide and titanium dioxide surfaces, the same characteristics are observed with respect to photoconductivity and photo-switchable wetting.

Since zinc oxide is deposited on roughened surfaces (eg, nonwoven polypropylene), the above reversible wettability change is not observed for flat substrates such as tantalum wafers or glass coverslips; water contact angle hysteresis becomes negligible See Table 2. Theoretical studies predict that for an ideal surface where the water droplets are in contact with all surfaces, the water contact angle hysteresis should reach a maximum as the roughness increases, beyond which the liquid does not completely wet the entire surface. In this regard, the surface Wetting follows the Cassie-Baxter relationship where the roughness is so great that air is trapped during liquid-surface contact resulting in incomplete wetting. In this experiment, it was the rough texture of the deposited zinc oxide film (visible to the naked eye) that produced a high equilibrium water contact angle, Figure 5.

In addition, the Cassie-Baxter feature is enhanced by changing the substrate from a two-dimensional structure (flat) to a porous three-dimensional structure (nonwoven), ultimately achieving very low contact angle hysteresis, see Table 2. Although in the case of zinc oxide coated nonwoven polypropylene, the surface energy will be increased during UV exposure (as shown in Figure 8), sufficient Cassie-Baxter characteristics should be maintained for superhydrophobicity. .

The zinc oxide coated polypropylene cloth substrate was also measured to have a significant bactericidal effect. E. coli was tested because it is known for its resistance to the killing of many conventional antibacterial surfaces. The antibacterial activity observed in this study is most likely due to the presence of the oxidized group material on the zinc oxide surface. For example, an oxygen group material can form a molecular precursor such as hydrogen peroxide, which is toxic to bacteria by causing damage to bacterial cell walls, proteins, and nucleic acids. This antibacterial mechanism does not appear to be closely related to UV-induced photoconductivity and photo-wetability mechanisms, such as by continuous killing of bacteria by UV-irradiated zinc oxide surfaces, see Table 3.

Pulsed plasma poly(4-vinylpyridine) nanolayers seeded with palladium catalyst have been used for electroless plating of crystalline zinc oxide films. These crystalline zinc oxide films were found to exhibit photoconductivity, photo-switchable wetting, superhydrophobicity, and antibacterial properties.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a reaction scheme of an embodiment of the present invention, i.e., palladium catalyst seeding of a pulsed plasma deposited poly(4-vinylpyridine) film followed by electroless plating of zinc oxide.

Figure 2 shows the following XPS spectra: (a) pulsed plasma deposited poly(4-vinylpyridine); (b) pulsed plasma deposited poly(4-vinyl) with palladium chloride (II) seeding Pyridine); (c) electroless zinc oxide grown on poly(4-vinylpyridine) deposited by pulsed plasma deposition of palladium chloride (II).

Figure 3 shows the following infrared spectra: (a) 4-vinylpyridine monomer; and (b) pulsed plasma deposited poly(4-vinylpyridine). * indicates the absorbance of the polymerizable olefin bond in the precursor.

Figure 4 shows an X-ray diffraction analysis of a 500 nm thick zinc oxide film electrolessly grown on poly(4-vinylpyridine) pulsed plasma deposited by palladium seeding.

Figure 5 is an optical microscopy image of a zinc oxide film grown electrolessly on poly(4-vinylpyridine) deposited by pulsed plasma deposition of palladium.

Figure 6 shows 500 nm thick zinc oxide grown by electroless deposition onto non-conductive glass: (a) Conductivity and equilibrium water contact angle after UV irradiation in air (closed at 750 s); (b) The equilibrium water contact angle of the zinc oxide film after UV light disappeared at 750 s (offset time = 0 h).

Figure 7 shows the XPS C (1s) envelope of electrolessly deposited zinc oxide on a germanium wafer: (a) without UV exposure and (b) 750 s UV exposure.

Figure 8 shows the mechanism by which the material adsorbed on the zinc oxide surface changes over time during UV irradiation and subsequent oxygen resorption.

Claims (13)

A method of applying a zinc oxide coating to a substrate, comprising the steps of: (i) applying a nitrogen-containing aromatic heterocyclic functionalized coating to the substrate; (ii) functionalizing the nitrogen-containing aromatic heterocyclic compound The layer is contacted with an agent comprising palladium (II) and/or platinum (II) to produce a coating comprising mis-palladium (II) and/or platinum (II); (iii) the coating in the coating Substituting palladium (II) and/or platinum (II) to palladium (0) and/or platinum (0); and (iv) allowing the inclusion of mis-palladium (0) in the presence of a reducing agent and aqueous conditions / or a coating of platinum (0) is contacted with a zinc salt to form a zinc oxide coating on the substrate. The method of claim 1, wherein the step (i) of applying a nitrogen-containing aromatic heterocyclic functionalized coating to the substrate is carried out by plasma deposition. The method of claim 2, wherein the step (i) comprises subjecting the substrate to a plasma discharge of a monomer having an aromatic heterocyclic nitrogen functional group. The method of any one of the preceding claims, wherein the reagent comprising palladium (II) and/or platinum (II) in step (ii) comprises a salt of palladium (II) and/or platinum (II). The method of claim 4, wherein the salt of palladium (II) and/or platinum (II) is a salt of palladium (II). The method of claim 5, wherein the salt of the palladium (II) is palladium chloride. The method of any one of the preceding claims, wherein the reduced palladium (II) and/or platinum (II) to palladium (0) and/or platinum (0) in the step (iii) is in the second Occurs in the presence of methylaminoborane (DMAB). The method of any of the preceding claims, wherein the zinc in step (iv) Salt is zinc nitrate. The method of any of the preceding claims, wherein the reducing agent in step (iv) is dimethylaminoborane (DMAB). A method of applying a zinc oxide coating to a substrate, the method being substantially as set forth and illustrated herein. A zinc oxide coating obtainable by the method of any of the preceding claims. A zinc oxide coating substantially as set forth and illustrated herein. A device comprising a substrate and a zinc oxide coating as claimed in claim 11 or 12 on the substrate.