DE102007041374A1 - Producing quantum structures and/or continuous nano-metal islands on substrate for bipolar plates, by cleaning substrate surface from impurities and/or oxide layers, structuring and then depositing active atomic- and/or molecular clusters - Google Patents

Abstract

The method for producing quantum structures and/or continuous nano-metal islands on substrate for bipolar plates, comprises cleaning a substrate surface from impurities and/or oxide layers, structuring and then simultaneously depositing active atomic- and/or molecular clusters. The in-situ cleaning, structuring and depositing of clusters are simultaneously carried out for creating photovoltaic, photoelectro-chemical and/or electro-catalytic active surfaces from a highly-ionized metal plasma by applying a voltage of larger than 200 V on the substrate. The method for producing quantum structures and/or continuous nano-metal islands on substrate for bipolar plates, comprises cleaning a substrate surface from impurities and/or oxide layers, structuring and then simultaneously depositing active atomic- and/or molecular clusters. The in-situ cleaning, structuring and depositing of clusters are simultaneously carried out for creating photovoltaic, photoelectro-chemical and/or electro-catalytic active surfaces from a highly-ionized metal plasma by applying a voltage of larger than 200 V on the substrate. A high metal ion density of more than 70% of loaded ions presents in the plasma of the metal atoms to be deposited. The metal plasma deposition is carried out by evaporating a metal target by cathodic light-arc or high-performance magnetron sputtering. The application of metal ions from highly-ionized metal plasma under applying defined negative potentials at the substrate, and the atomization of the substrate material are simultaneously carried out. The metal deeply penetrates itself in the surface of 1-10 atomic layers. A discontinuous metal film is formed from the equilibrium of the atomization rate of the substrate material and the deposition of the metals to be deposited, and is formed by an inductively coupled plasma for post-ionized, atomized or evaporated metal atoms. The porosity of the substrate surface is adjustable by highly applied negative voltages at the beginning of the process. A roughness and/or a micro-porous surface are adjustably obtained in the substrate surface by removing the oxide layer over the cleaning. The metal ions are subjected in defined penetration depth by applying a negative bias-voltage on the substrate between 200-1200 V into the surface-near atomic layers locally and uniformly without the formation of barrier layers in the high reproducibility in the first 5-20 atom layers of the substrate surface. A texture of the surface is increased by increasing the pulse lengths of several milliseconds during sputtering in desired manner. An independent claim is included for an electrically-conductive corrosion-resistant surface for bipolar plates.

Description

The The invention relates to a method for coating substrates for the creation of photovoltaic, electrochemical and / or electrocatalytic active surfaces.

For Such active surfaces will be targeted, but not full-surface application and introduction of heavy metal atoms and ions on the surfaces or in the upper atomic layers aimed at the surface.

As prior art is U.S. Patent 7,081,186 which already discloses a coating process with a strong magnetic field sputtering assisted by a pulsed magnetic field and a magnetron. The patent describes the sequential application of two coating processes to provide adhesive layers for tribological applications.

The The invention, on the other hand, has set itself the task of quantized states or so-called discontinuous metal islands on substrates create. Electrochemical or photocatalytic active surfaces this type or anticorrosive surfaces are becoming increasingly popular in many fields of technology. On the one hand, with discontinuous noble metal layers z. B. specifically increase photovoltaic efficiencies on silicon, On the other hand, electrochemical surfaces are in particular for the production of highly active electrodes with low overvoltages for the production of hydrogen or in fuel cells of importance.

After all are electrically conductive, corrosion resistant Surfaces for bipolar plates, be it for electrolysis or for fuel cells also with the inventively proposed Method can be produced in a particularly advantageous manner. precious metal layers nanoscale or subnanoscaled thickness are mentioned with the high efficiencies to cost-effective conditions mass produced.

So far were in the prior art very different ways used from various coating techniques. Galvanic leaves For example, platinum in just a few atomic layers as UPD (under Depositing or leaving potential deposition layer from the precious metal compound by spraying with deposition of subsequent annealing process.

Also by the so-called ALD (atomic layer deposition) method, with the atomic layer via a mostly organometallic precursor chemistry For atomic layer, the desired metal is deposited on the surface However, precious metal compounds could be deposited, however just about the costly detour over the precursor materials and always with poor adhesive properties.

Farther are as already mentioned above PVD coating process has been used, in particular the sputtering process has attained a certain importance. However, targeted metal islands To generate the samples must be at an angle to the sputtering wave can be arranged and the sample is strip coated after structuring. This has a rapidly decreasing efficiency in the prior art result.

A further possibility for the generation of discrete metal clusters near the surface provides ion implantation. With this method, metal ions in high vacuum at Biasspannungen> 10 KV in the surface deeply implanted in some atomic layers.

Alles However, these methods have the disadvantage that the substrates not even in good repeatability can be coated and that in oxide-forming surfaces like silicon and most compound semiconductors, too in corrosion-resistant refractory metal compounds the adhesion to these substrates is inadequate and undefined form electrical transitions to the substrate material. The above-mentioned ion implantation has the further disadvantage that ions be introduced to deep below the surface and thus the chemical-constitutional character of the resulting Surface is not defined adjustable.

According to the invention resolved these disadvantages with the method according to the main claim. In particular by methods such as cathodic arc evaporation or the high-voltage pulse sputtering can be conditionally due to the high ionization of the gas phase Coating material the ratio of coating / implantation Targeted to substrate removal.

If one then applies the metals from highly ionized metal plasmas with the application of defined negative potentials to the substrate so that on the one hand a sputtering of the substrate material takes place and on the other hand the metal can "interfere" in the surface and, if required, subsequently in a closed metal film in is formed in a process step, an "interference" either from the balance of sputtering rate of the substrate material and the deposition of the metal to be deposited or / and by partial implantation into inner atomic layers of the substrate material follows. It has been shown that in particular the cathodic arc evaporation has advantageous aspects.

Similar Good effects are also due to the high-power pulse sputtering or other methods in which high metal plasma densities can be generated, as inductively coupled Plasmas for deionizing atomized or with precursor vaporized metal atoms.

When Working title is here for this highly ionizing process the term plasma ion mixing method is used.

Preferably become the investigations with the cathodic arc evaporation the precious metals performed due to the simplicity of the process. A disadvantage of the method lies in the droplet formation, which is but obviously due to the short surface modification time does not have a particularly negative effect.

In order to leaves the inventive method Compared to the other methods mentioned above, that too a substrate matrix surface to be modified in situ of contamination or interfering passive layers quickly is cleaned, for example, silicon quickly from its oxide layer is released.

Further is the penetration depth of the doping metals and their discontinuous Expansion at the surface by the applied negative Stress predeterminable on the substrate. For voltages in the range between 200 and 1200 volts can be used for most precious metals like platinum, Iridium, gold, ruthenium, rhodium and palladium near the surface in substrates such as silicon or the like uniformly without the training of barrier layers. The same goes for equally for other heavy non-metals like molybdenum, tantalum or tungsten.

Prefers finds this in the first, preferably 5 to 20 atomic layers of the Substrate surface instead, where the physico-chemical Properties gradually by varying the voltage during of the surface modification process still influenced can be, so that z. B. small metal islands with few Nanometer expansion at high voltages up to closed Films grow at lower voltages.

there is the modification of the surface evenly, d. h., both the lateral dimensions and distances as The depth distribution can also be adjusted reproducibly. Also if the penetration depth is to be limited to 10 atomic layers, is this possible. Next is especially at the beginning of the process High porosity due to high applied negative voltages the substrate surface adjustable by over the cleaning by removing the oxide layer also a Roughness or a microporous surface adjustable can be achieved.

In spite of the use of those in other procedures only limited controllable Precious metal ions, this process can be cost-effective also in industrial large-scale production.

Further Features and advantages of the invention will become apparent from the following Description of several preferred embodiments.

[Example 1]

A titanium substrate body is coated with 4 μm (Ti, Nb) O ₂ and then positioned 10 cm in front of an iridium target. The substrate is at a potential of -600 V relative to the ground potential. The iridium is then evaporated by means of a cathodic arc at a current of 60 amps, and after 10 seconds the potential on the substrate body becomes 5 seconds. lowered to -300V. After 15 seconds the process is finished.

1 shows the current-voltage characteristic before doping and in 2 the same is shown after the doping.

The Current / voltage characteristics has essentially not changed with the exception of a significantly increased electricity with increased Hydroxyl radical formation, the in situ aromatic impurities capable of oxidizing in water.

The in Example 1 produced surfaces for targeted production Hydroxyl radicals, hydrogen peroxide and ozone are used when cleaning water. There arises under normal conditions on platinum, gold, palladium and in alkaline media on nickel surfaces For thermodynamic reasons preferably oxygen. The equilibrium electrolysis voltage for generating hydrogen and oxygen is without overvoltage effects at 1.23 V. In water purification systems, however, is the generation of hydrogen peroxide, ozone and especially of hydroxyl radicals he wishes. With these radically reacting oxygen species you can effectively kill bacteria.

A particularly high reactivity have hydroxyl radicals, in addition the stable aromatic compounds with splitting of the Partial oxidation of benzene rings is also possible Pollutants in water purification to harmless degradation products can split. Hydroxyl radicals are formed under standard conditions only at a potential of 2.8 V against NHE.

Without at this point further on the kinetisch mechanistic peculiarities to deal with the method of the invention with certain stable n-doped oxide semiconductor electrodes the prerequisite for generating the desired hydroxyl radicals Therefore be particularly favorable because they high overvoltages against oxygenation and into the CV (current-voltage) Curves only above 2.5 V noticeable formation of oxygen species are recognizable.

Indeed have the oxide semiconductor electrodes such. For example, titanium dioxide, Titanium niobium oxide and other ternary mixed oxides have the disadvantage on that they "passivate" quickly under the high anodic tension. Passivation should mean at this point that they are near the surface Area lose their n-doping by annealing and thus only still very small currents flow. In a comprehensive investigation program For example, the surfaces became discontinuous in different ways modified according to the invention with the precious metals platinum, gold, palladium and iridium. Coating methods were classical chemical reductive processes, like the deposition of metals from organic or inorganic Complexes, the sputtering process and the invention Plasma-ion mixing method (PIM) applied. For one thing was at All procedures found that it is very important a particular Degree of coverage of the surface with the precious metals not to exceed (for example 20 or 30% depending on the application), around the surface not the electrochemical characteristic imprint of the same precious metal. Produced on the surface discontinuous islands e.g. B. Metal clusters in nanometer size with likewise nanometer-sized distances to each other the basic characteristic of the semiconductor electrode with small Preserve displacements in the offset voltage by a few millivolts become.

Naturally additional dependencies on the used precious metals found. Especially with gold range obviously subnanometer large clusters on the surface to set the gold characteristic. Very cheap By the way, iridium and platinum behave.

The Inventive deposition process is hereby characterized by two special parameters complex. All procedures lead in sulfuric acid solution (pH3) to a significant increase in current densities unmodified surfaces. With the plasma ion mixing process On the other hand, it was possible to increase the current density more than 20 times when using iridium and 15 times when using of platinum. The other procedures were initially at a Increase the current densities by 5 to 10 times. After several times Cyclize up to 3 V lost the modified in the standard procedure Samples their activity while the inventively prepared Even after 100 cycles of cyclization, samples dropped less than 5%.

[Example 2]

One n-silicon semiconductor wafer with a thickness of 400 microns at a resistance of 0.8 ohms / cm to 2 ohms / cm is the same positioned in front of a platinum target as in Example 1. In this Case, the silicon is initially at a voltage of 800 V for 5 seconds doping cleaned and in the following step at 600 V, the reaction becomes stronger for deposition by more Steered for 8 seconds and then over for 6 seconds 300 V treated. It should be emphasized that in all voltage increments simultaneously Substrate material is dusted, the ratio from deposited metal to the dusted surface but shifts.

3 shows photo current curves in a Na ₂ SO ₄ solution at pH3 compared to untreated samples.

In order to compare the performance of the PIM process for the production of discontinuous platinum islands on n-silicon with conventional coating methods published in the literature, according to the publication of Nakato et. al ( Journal of Phys. Chem. 92, (8) 1988, 2316 ) n-silicon surfaces with a conductivity of 0.4 to 0.8 ohm / cm by PIM method. In the publication by Nakato, the silicates are, after an etch in 4 molar sodium hydroxide solution, intermittently coated with platinum at an angle of attack of <20 degrees to the target. The authors find in a HBr / Br ₂ solution a photoelectrochemical efficacy of 11.4% at a radiation of 100 Wcm ^-2 , a V _OC of 0.685 V and a short circuit current of 25 mA / cm ² against a platinum electrode.

at the preparation of the coating produced according to the invention In contrast, the samples were placed head-on to the arc targets and under different bias voltages for just a few seconds treated. Surprisingly, all samples were at 600 and 800V treated with platinum were higher surface conductivities than those exposed to platinum ions at 300V.

Obviously will be at the higher voltages - like not to expect differently - from the surface more silicon atoms atomized, as at low voltage without at the same time the deposited platinum atoms atomized again to the same extent (which was not expected).

Particularly for the samples produced at 600 to 800 V, voltages above 0.6 V are found without further chemical etching treatment of the silicon open circuit, and the short-circuit current densities were even above the values of Nakato at 35 mA / cm ^-2 . The solution was adjusted to pH3 with HBr and with 0.1 M Br. ₂

[Example 3]

A stainless steel sheet of steel X5CrNi189 coated with 3 μm (Ti _0.95 Nb _0.05 ) ON is positioned approximately 12 cm in front of an iridium target of a high-power pulse magnetron source as described above. The sheet is polarized in this area from the beginning with -300 V relative to the mass and treated only for 15 seconds with highly ionized iridium. After that, the sheet has a surface resistance of only 5.8 milliohms / cm, even lower than a 3 μm thick gold layer on the same substrate.

A such surface can be used, for example, in fuel cells or electrolysis cells are used. The titanium-niobium oxide nitride layer initially had about 6 atomic percent oxygen and became the Corrosion protection but also for electrical wiring approx. 1 μm thick coated. The surface tends to passivate Loss of conductivity. By the described modification with high-energy iridium ions was a mass loss of 50 Reached nanometers of titanium niobium oxide nitride layer. simultaneously increases the conductivity of the layer with Iridium clusters in the subnanoid order larger values are as an applied 3 micron thick galvanic gold layer. Overall, the iridium is thus at the same time as a removal medium for the light atoms of the matrix layer have been used as well the surface mixed in heterogeneously.

The Thus, in addition to a method for coating substrates also a novel layer whose high electrical conductivity for electrochemical applications special applications offers.

electrochemical Investigations using voltage-current curves not only show the typical iridium characteristic in a sulfuric acid solution adjusted to pH1 but surprisingly, at the same voltage higher current densities with reduced overvoltage by almost 100 mV compared to a closed iridium layer observed.

Obviously, heterogeneous electrolysis takes place in the vicinity of the matrix layer, which improves the kinetics for the formation of desorbed O ₂ molecules compared to homogeneous surfaces.

In 4 the curves are compared to this.

From this According to the invention, there were also new possibilities for the production of electrodes of low temperature and medium temperature fuel cells by using conductive metal oxide powder on carbide, Boride or nitride based on their heterogeneous surface doping with discontinuous noble metal films.

The Invention expressly excludes the replacement of Iridium by other precious metals, in particular from the group platinum, Gold, ruthenium, rhodium and palladium or the metals tungsten and molybdenum.

According to the invention at the same time an in-situ cleaning, structuring and deposition of clusters of dopant atoms to create photovoltaic, photo-electrochemical and / or electrocatalytically active surfaces, the steps the removal and the deposition by a method from the group: pulsed high-power sputtering, cathodic arc discharge evaporation and inductively coupled plasma deposition take place, wherein a high metal ion density of more than 70% charged ions in high vacuum plasma is present.

A Application of metal ions from highly ionized metal plasmas under Application of defined negative potentials on the substrate takes place in such a way that simultaneously a sputtering of the substrate material takes place and the metal is in the surface between 1 and 5 Atomic layers can penetrate deeply. As a result, a closed Metal film formed from the balance of sputtering rate of the substrate material and the deposition of the metal to be deposited or by processes more atomized after deionization or vaporized metal atoms serve. Actually the "doping atoms" even at greater depths the surface of the substrate was found to be fast Atomization of the Substartatome with simultaneous roughening explained the surface.

After this at the beginning of the process by high applied negative voltages adjusts the porosity of the substrate surface has been particularly advantageous over the cleaning by removing the oxide layer also a Roughness or a microporous surface adjustable reach, z. B. a roughness of the surface in the range of 1-50 atomic layers to "sink" ions into the surface to be able to.

Furthermore, metal ions in a defined depth of penetration can be uniformly localized by an applied negative bias voltage on the substrate between 300 and 2000 V in the near-surface atomic layers without the formation of barrier layers in high reproducibility in the first 5-20 atom layers of the substrate surface are embedded, which is interesting for the production of Hydroxlradikale by the surfaces thus formed.

By an enlargement of the pulse lengths in the range several milliseconds in high-power pulse sputtering can according to the invention Texture of the surface in the desired manner enlarged become.

The so possible creation also electrically conductive, corrosion resistant surfaces for Bipolar plates, can then by clusters of at least four Metallio NEN completed in the upper 5-20 atomic layers completed become. Finally, it is proposed a thin Layer of less than 1 micron titanium niobium oxynitride previously was applied and with short-term high-performance sputtering with a duration of only 5-25 s under a bias voltage of 300-1000 V partially again with the inclusion of metal ions deeper in the substrate was removed. Electrodes of low temperature and Medium temperature fuel cells can also be more conductive by creating Carbide, boride or nitride-based metal oxide powders are produced, on their heterogeneous surfaces as described quantized or discontinuous noble metal films are produced.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• US 7081186 [0003]

Cited non-patent literature

• - Journal of Phys Chem 92, (8) 1988, 2316 [0033]

Claims (17)

Process for the production of quantum structures or / and discontinuous nano-metal islands on substrates with the following steps: removal of impurities and / or oxide layers from a substrate surface, and structuring, and simultaneous deposition of active atomic or molecular clusters, characterized in that the in-situ purification, structuring and deposition of clusters to create photovoltaic, photoelectrochemical and / or electrocatalytically active surfaces from a highly ionized metal plasma by applying a voltage greater than 200 V to the substrate occur simultaneously, with a high metal ion density of more than 70% charged ions present in the plasma of the metal atoms to be deposited. Method according to claim 1, characterized in that that the metal plasma by the evaporation of a metal target done by cathodic arc. Method according to claim 1, characterized in that that the metal plasma by the evaporation of a metal target using high power magnetron sputtering. Method according to claim 1, characterized by a Application of metal ions from highly ionized metal plasmas under Creation of defined negative potentials on the substrate, that at the same time a sputtering of the substrate material takes place and the metal is in the surface between 1 and 10 Atomic layers can penetrate deeply. Method according to claim 2, characterized in that that subsequently formed a discontinuous metal film becomes out of balance of sputtering rate of the substrate material and the deposition of the metal to be deposited. Method according to claim 2 or 3, characterized that subsequently formed a discontinuous metal film is by at least one inductively coupled plasmas for deionization atomized or vaporized metal atoms. Method according to one of the preceding claims, characterized in that at the beginning of the process by high applied negative voltages adjust the porosity of the substrate surface, by cleaning over by removing the oxide layer In addition, a roughness or a microporous surface can be achieved adjustable. Method according to one of the preceding claims, characterized in that metal ions in defined Penetration depth by applying a negative bias voltage to the substrate between 200 and 1200 V in the near-surface atomic layers locally even without the formation of barrier layers in high reproducibility in the first 5-20 atomic layers embedded the substrate surface. Method according to one of the preceding claims, characterized in that by enlarging the Pulse lengths in the range of several milliseconds during sputtering a texture of the surface in the desired manner is enlarged. Method according to one of the preceding claims, characterized in that as metal ions iridium ions be used. Method according to one of the preceding claims, characterized in that as metal ions iridium ions be used. Method according to one of the preceding claims, characterized in that as metal ions gold ions be used. Method according to one of the preceding claims, characterized in that as metal ions ruthenium ions be used. Method according to one of the preceding claims, characterized in that as metal ions rhodium ions be used. Method according to one of the preceding claims, characterized in that as metal ions palladium ions be used. Electrically conductive, corrosion-resistant surface for bipolar plates, characterized by a surface structured by a method of claims 1-14 was roughened and with clusters of at least four metal ions embedded in the upper approx. five to ten atomic layers has been. Surface according to claim 14, characterized that a thin layer of less than 1.5 microns Metal metalloid film was applied previously and with a short time Heavy duty sputtering lasting only a few seconds a bias voltage of 300-1000 V partly under again Deduction of metal ions was removed deeper into the substrate.