EP0780871B1 - Structured surface with pointed elements - Google Patents

Description

The present invention relates to a structured surface containing a carrier layer and with this electrically connected tip-shaped elements. The invention relates further the use of this structured surface, and a method for its Manufacturing.

Every component of vacuum electronics, such as a display tube, is required a cathode for emitting electrons into a vacuum. So far, for this purpose predominantly thermal cathodes used, which at temperatures of, for example 1000 ° C and higher are heated so that the electrons on the cathode surface like this get a lot of thermal energy that they have the potential barrier on the cathode surface can overcome. The surfaces of thermal cathodes are chosen so that that to achieve high electron emission, the work function of the electrons becomes as deep as possible by choosing appropriate surface layers.

Another possibility for the production of electron-emitting cathode surfaces consists in applying high electric field strengths to a cold, i.e. not specially heated, Cathode. Such cold electron emitting cathode surfaces are called field emission surfaces To achieve significant field emission flows very high electric field strengths on the cathode surface necessary. To the to the To keep the cathode applied operating voltage at the lowest possible level and still The cathode surfaces achieve locally high electrical field strengths expediently provided with finely structured tips. Such field emission surfaces are used, for example, for field emission screens (FED or field emission display) used.

Those used today, for example, in laptop computers or portable television sets Flat screens usually work as liquid crystal screens (LCD or liquid crystal display). Such LCD screens, however, leave only a small amount with rapidly moving images Switching speed too and the color rendering generally does not meet that of conventional ones Tube screens required high quality.

The field emission display technology (FED) overcomes this Disadvantages that occur with LCD screens.

FED screens usually consist of a conventional but not curved one Phosphor screen with mask. At a distance of 0.2 mm, for example, is a plate-shaped Cathode arranged, which carries a matrix of fine and sharp tips. This Tips can be supplied with high voltage in groups or addressed, whereby they emit electrons due to the field effect, which are then accelerated and so activate the opposite phosphor dot on the phosphor screen.

A picture element of an FED screen expediently consists of three points, the are provided with red, green or blue emitting phosphor. Each of these points are on the cathode side assigned about a thousand microtips, which together form one such high yield of field effect electrons deliver that the FED screen compared to conventional tube screens with the same brightness a much smaller Shows power consumption.

Compared to the LCD screens, the FED screen has the advantage of being inertial Control of every pixel. In addition, the image quality is from the viewing angle independently.

A known method for producing cold-emitting cathode surfaces consists in the microstructuring of the cathode surface by using photolithographic Techniques such as those used for the manufacture of semiconductor components for a long time are known. In a first process step, a Photoresist mask with a field of rectangular or circular openings on the Generated cathode surface. In a second step, this is not protected by the masks Substrate etched so that after the remaining photoresist mask has been removed pyramid or conical emitter tips are created.

Another possibility for producing field emission surfaces is anisotropic Etching a crystalline material, such as Si, with fine tips, which are coated, for example, with an electron-emitting material. In the further can also semiconductor surfaces, such as Si, using photolithographic methods structured and for example subsequently coated with an electron-emitting material become.

US 459 17 17 describes a photoelectric detector based on a field emission surface, containing a photosensitive layer with a plurality of tips electrically conductive material. The manufacture of the tips is done by anodic Oxidation of a substrate surface, wherein pores lying vertically to the substrate surface are created into which metal is deposited in such a way that metal tips are created, which protrude above the oxide layer.

EP 0 351 110 describes a method for producing cold cathode emitter surfaces, after which an alumina surface with a variety of elongated, essentially Pores lying orthogonal to the main surface of the aluminum oxide layer the pores are filled with an electron-emitting material, at least one Part of this aluminum oxide layer is removed, leaving a surface with exposed electron-emitting Peaks and the tips are inclined towards each other.

The field emission surfaces known from the prior art, which by forming a Pore-containing surface layer, the deposition of electron-emitting material on the surface layer and in the pore cavities, and the final removal of the layer containing the pores are always produced with a maximum of as many electron-emitting ones Tips on how to make pores in the surface layer were present.

The object of the present invention is to produce a field emission surface at low cost to create the field emission surfaces known from the prior art has a higher number of electron-emitting peaks per unit area.

According to the invention, this object is achieved in that each point-shaped element a cylindrical or frustoconical trunk area lying against the support layer and at least two, preferably 2 to 4, molded onto the free end of the trunk area, has terminal tips.

The carrier layer surface of the structured surface can be a flat or curved one Surface, for example a plane, the surface of an ellipsoid, especially a sphere, one single or double-shell hyperboloids, a paraboloid or an elliptical, hyperbolic or parabolic cylinder.

The part of the carrier layer lying between the tip-shaped elements is expediently essentially flat, creating a well-defined surface structure point-like elements that clearly stand out from it.

In a preferred embodiment, the tip-shaped elements are according to the invention structured surface evenly distributed over the carrier layer.

The pointed elements of the structured surface preferably have at least in a part projecting from the support layer is orthogonal to the support layer Trunk area on. Point-shaped elements, the whole of which are particularly preferred Trunk area is orthogonal to the surface of the base layer. Are very particularly preferred tip-shaped elements with a trunk area orthogonal to the surface of the carrier layer, whose terminal tips are such that their longitudinal axes coincide with those of their Free ends leading surface normals of the carrier layer, an acute angle, preferably enclose an angle of 5 to 40 ° (based on a full circle of 360 °).

In a preferred embodiment, the tip-shaped elements and / or the Carrier layer made of Ni, Al, Pd, Pt, W, Fe, Ta, Rh, Cd, Cu, Au, Ag, In, Co, Sn, Si, Ge, Te, Se, or a chemical compound containing at least one of these substances, such as Sn or InSn oxide, or an alloy of the aforementioned metals. Preferably exist the tip-shaped elements and the carrier layer made of the same material.

Surfaces structured according to the invention, the surface of which at least are preferred is partially coated with one of the above materials.

In a further preferred embodiment, the carrier layer has between the tip-shaped Elements on a mechanical support layer, which consists of an electrically insulating Material, preferably consists of an oxide and in particular of aluminum oxide. The layer thickness of the mechanical support layer expediently measures less than that Average height of the trunk areas of all tip-shaped areas over the entire structured surface Elements.

Structured surfaces are further preferred, the tip-shaped elements of which have an im have substantially uniform height, being below the height of a lacy Elementes the maximum dimension measured orthogonally to the surface of the carrier layer of the lacy element, i.e. the trunk area and the terminal tips, is understood. The height of each point-shaped element very preferably does not vary by more than ± 5% of the height averaged over all pointed elements.

Further advantageous developments of the invention can be found in the subclaims.

The surfaces of the surfaces structured according to the invention are particularly suitable for Use as field emission surfaces for cold cathode emitter elements, in particular as cold cathode electron emission sources for super flat screens, for electron lithography or for scanning or transmission microscopy. The terminal tips the tip-shaped elements serve as emitter tips. To be a well defined one Reaching the emitter structure is the part lying between the pointed elements the field emission surface preferably substantially flat, i.e. the one between the lacy ones Part of the field emission surface lying in the elements does not contribute to the field emission at. Due to the high number of. Required for the realization of field emission surfaces Emitter tips are also field emission surfaces with curved support layers in between the area lying in the lacy elements is substantially flat.

The tip-shaped elements of the structured surface are further preferably designed such that when an operating voltage of less than 2000 V, suitably less than 1800 V, preferably less than 900 V and in particular less than 100 V is applied, an electric field strength is produced at the terminal tips of more than 10 ⁹ V / m results. The operating voltage here means the voltage applied by an external voltage source to the structured surface, for example its carrier layer.

a) in einem ersten Schritt ein Formkörper (22) mit einer zur gewünschten strukturierten Oberfläche spiegelbildlichen Formkörperoberfläche (23) dadurch geschaffen wird, dass ein Substratkörper (24) aus Aluminium anodisch in einem Aluminiumoxid rücklösenden Elektrolyten oxidiert wird, wobei die Anodisierspannung in einem ersten Anodisierschritt kontinuierlich oder schrittweise von 0 auf einen ersten Wert U₁ erhöht wird, und in einem zweiten Anodisierschritt die Anodisierspannung kontinuierlich oder schrittweise auf einen zweiten, gegenüber U₁ kleineren Wert U₂ reduziert wird.

b) in einem zweiten Schritt die Formkörperoberfläche (23) ganzflächig derart beschichtet wird, dass die in der Oberflächenschicht (23) des Formkörpers (22) vorhandenen Poren-Kavitäten (36) vollständig mit dem Beschichtungsmaterial ausgefüllt werden, und eine die spitzenförmigen Elemente (14) elektrisch verbindende Trägerschicht (12) gebildet wird, und die Trägerschicht (12) eine zusammenhängende, mechanisch tragende Schicht darstellt;

c) und in einem dritten Schritt wenigstens ein Teil des Formkörpers (22) derart entfernt wird, dass die endständigen Spitzen (20) frei liegen.

According to the invention, the object directed to the method is achieved in that

a) in a first step, a shaped body (22) with a shaped body surface (23) that is mirror-image to the desired structured surface is created in that a substrate body (24) made of aluminum is oxidized anodically in an aluminum oxide-redissolving electrolyte, the anodizing voltage being applied in a first anodizing step is increased continuously or step by step from 0 to a first value U ₁ , and in a second anodizing step the anodizing voltage is reduced continuously or step by step to a second value U ₂ which is smaller than U ₁ .

b) in a second step, the entire surface of the molded body (23) is coated in such a way that the pore cavities (36) present in the surface layer (23) of the molded body (22) are completely filled with the coating material, and one is the tip-shaped elements (14 ) electrically connecting carrier layer (12) is formed, and the carrier layer (12) is a coherent, mechanically supporting layer;

c) and in a third step at least part of the shaped body (22) is removed in such a way that the terminal tips (20) are exposed.

The molded article necessary for the production of the structured surface according to the invention with an essentially mirror image of the desired structured surface The molded body surface expediently consists of a substrate body and a Shaped layer, the latter being essentially the desired structured surface contains mirror image surface structure.

The substrate body preferably represents part of a piece good, for example a profile, Bar or other form of pieces, plate, tape, sheet or one Aluminum foil, or an aluminum cover layer of a composite material, in particular as an aluminum cover layer of a composite panel, or relates to any one Material - for example electrolytically - applied aluminum layer, such as a clad aluminum layer. The substrate body more preferably relates to Workpiece made of aluminum, which e.g. through a rolling, extrusion, forging or Extrusion process is made. The substrate body can also be bent, deep drawn, Cold extrusion or the like may be formed.

With the material aluminum in the present text aluminum of all purity levels, as well as all commercially available aluminum alloys. For example, the term includes Aluminum all rolled, kneading, casting, forging and pressing alloys made of aluminum. The substrate body expediently consists of pure aluminum with a degree of purity of equal to or greater than 98.3% by weight or aluminum alloys with at least one of the Elements from the range of Si, Mg, Mn, Cu, Zn or Fe. The substrate body made of pure aluminum can be made, for example, of aluminum with a purity of 98.3% by weight and higher, expediently 99.0% by weight and higher, preferably 99.9% by weight and higher and in particular 99.95 wt .-% and higher, and the rest are commercially available impurities.

In addition to aluminum, the substrate body can also be made from an aluminum alloy consist of containing 0.25% by weight to 5% by weight, in particular 0.5 to 2% by weight, Magnesium or containing 0.2 to 2% by weight of manganese or containing 0.5 to 5% by weight Magnesium and 0.2 to 2% by weight of manganese, in particular e.g. 1% by weight of magnesium and 0.5 % By weight of manganese or containing 0.1 to 12% by weight, preferably 0.1 to 5% by weight, of copper or containing 0.5 to 5% by weight of zinc and 0.5 to 5% by weight of magnesium or containing 0.5 to 5% by weight of zinc, 0.5 to 5% by weight of magnesium and 0.5 to 5% by weight of copper or containing 0.5 to 5% by weight iron and 0.2 to 2% by weight manganese, in particular e.g. 1.5 % By weight iron and 0.4% by weight manganese.

The molded layer preferably consists of aluminum oxide. The production of one for the invention The required molding layer is preferably carried out by anodic oxidation the substrate body surface in an electrolyte under pore-forming conditions. It is essential to the invention that the pores are open towards the free surface. The pore distribution over the surface is advantageously uniform. The layer thickness of the The molding layer is expediently 50 nm to 20 μm and preferably 0.5 to 3 μm.

In their vertical extent, the pores have a trunk area directed against the surface of the molding layer and a branching area directed against the substrate body, i.e. each pore lying essentially vertically to the surface of the molding layer consists of an elongated pore which is open to the free surface of the molding layer and which is divided into at least two, preferably 2 to 4 wells or pore branches in the branching area. The pores in the trunk area expediently have a diameter of 1 to 250 nm, preferably between 10 and 230 nm and in particular between 80 and 230 nm. The number of pores, ie the number of pores in the trunk area, is expediently 10 ⁸ pores / cm ² and higher, preferably 10 ⁸ to 10 ¹² pores / cm ² and in particular 10 ⁹ to 10 ¹¹ pores / cm ² . The average density of the molded layer is preferably 2.1 to 2.7 g / cm ³ . The molded layer more preferably has a dielectric constant between 5 and 7.5.

The molded layer is produced, for example, by anodic oxidation of the Substrate body surface in an electrolyte that redissolves the aluminum oxide. The electrolyte temperature is expediently between - 5 and 85 ° C, preferably between 15 and 80 ° C and especially between 30 and 55 ° C. To carry out the anodic Oxidation can be carried out by the substrate body or at least its surface layer or at least the part of the substrate body surface which is to be provided with a molding layer, placed in a corresponding electrolyte and switched as a positive electrode (anode) become. Another electrode in the same electrolyte serves as the negative electrode (cathode) Electrode made of, for example, stainless steel, lead, aluminum or graphite.

Usually, the substrate body surface is before the inventive method subjected to a pretreatment, for example the substrate body surface first degreased, then rinsed and finally pickled. The pickling is done with a Sodium hydroxide solution with a concentration of 50 to 200 g / l at 40 to 60 ° C during one to ten minutes. The surface can then be rinsed and washed with an acid, such as nitric acid, in particular a concentration of 25 to 35% by weight at room temperature, i.e. typically in the temperature range 20 - 25 ° C, during Neutralized for 20 to 60 s and rinsed again.

The properties of an oxide layer produced by means of anodic oxidation, for example the pore density and the pore diameter largely depend on the anodizing conditions such as electrolyte composition, electrolyte temperature, Current density, anodizing voltage and anodizing time, as well as of the anodized base material from. During the anodic oxidation in acid electrolytes, the A substantially pore-free base or barrier layer and a porous outer layer, which during the anodic oxidation on its free surface partly redissolved chemically by redissolving. This creates in the outer layer Pores that are essentially vertical to the substrate body surface and against the free surface of the oxide layer are open. The thickness of the oxide layer reaches its Maximum value if growth and redissolution balance each other, for example the applied anodizing voltage, the electrolyte composition, the current density, the electrolyte temperature, anodizing time and the anodized base material.

Electrolytes which contain one or more inorganic and / or organic acids are preferably used to carry out the process according to the invention. Anodizing voltages from 10 to 100 V and current densities from 100 to 3000 A / m ² are further preferred. The anodizing time is typically 1 to 300 s.

The anodic oxidation of the substrate body surface preferably takes place in such a way that the anodizing voltage for forming cylindrical or truncated-cone-shaped long pores is set to a first value (U ₁ ), preferably between 12 and 80 V, and subsequently to form at least two pore branches on the opposite the aluminum layer-oriented end of each long pore is set to a second value (U ₂ ), the second value being lower than the first value and preferably being between 10 and 20 V.

The anodizing voltage is applied, for example, by continuous increase the applied voltage up to the respective predetermined, constant value over time. The Current density also increases as a function of the applied anodizing voltage one after reaching the respectively predetermined constant voltage Maximum value and then coincides with a lower value.

The layer thickness of the barrier layer is voltage-dependent and is, for example, in the range 8 to 16 angstroms / V and especially between 10 and 14 angstroms / V. The pore diameter the porous outer layer is also voltage-dependent and is, for example between 8 and 13 angstroms / V and in particular 10 to 12 angstroms / V.

The electrolyte can contain, for example, a strong organic or inorganic acid or a mixture of strong organic and / or inorganic acids. Typical examples of such acids are sulfuric acid (H ₂ SO ₄ ) or phosphoric acid (H ₃ PO ₄ ). Other acids that can be used are, for example, chromic acid, oxalic acid, sulfamic acid, malonic acid, maleic acid or sulfosalycilic acid. Mixtures of the acids mentioned can also be used. For the process according to the invention, for example, sulfuric acid is used in amounts of 40 to 350 g / l and preferably 150 to 200 g / l (sulfuric acid based on 100% acid). Phosphoric acid can also be used as an electrolyte in an amount of 60 to 300 g / l and in particular 80 to 150 g / l, the amount of acid being based on 100% pure acid. Another preferred electrolyte is sulfuric acid in a mixture with oxalic acid, an amount of 150 to 200 g / l sulfuric acid in particular being mixed with, for example, 5 to 25 g / l oxalic acid. Electrolytes containing, for example, 250 to 300 g / l of maleic acid and for example 1 to 10 g / l of sulfuric acid are further preferred. Another electrolyte contains, for example, 130 to 170 g / l sulfosalycilic acid mixed with 6 to 10 g / l sulfuric acid.

After the anodizing process, the surface of the molded layer can be subjected to further treatments, such as. chemical or electrolytic etching, plasma etching, rinsing or impregnation become.

The finished molded layer is coated over the entire surface in such a way that that in the surface layer of the molded body existing pore cavities completely with the coating material be filled in, and an electrically connecting the tip-shaped elements Backing layer is formed, and the backing layer is a coherent, mechanical represents the supporting layer.

Ni, Al, Pd, Pt, W, Fe, Ta, Rh, Cd, Cu, Au, Ag, In, Co, Sn, Si, Ge, Se, Te, or containing a chemical compound at least one of these elements, or an alloy of the metals listed above is used.

The coating of the molded body surface can be, for example, chemical or electrolytic Methods, or by PVD (Physical Vapor Deposition) or CVD (Chemical Vapor Deposition). A chemical and / or electrolytic is preferred Deposition of the coating material, expediently the pore cavities be chemically activated beforehand.

As the last step of the method essential to the invention, the tip-shaped elements, especially their terminal tips, by completely or partially removing the Form layer exposed.

The full exposure of the lacy elements, i.e. separating the structured Surface layer of the molded body, for example, by completely etching away the Shaped body happen. In a preferred embodiment, however, only the molding layer chemically etched away so that the structured surface layer is completely removed from the molded body is separated and is thus in the form of a structured surface.

In a further preferred embodiment, only a part of the molded layer is etched away that on the support layer between the trunk areas of the lacy elements The molding layer remains and forms a mechanical support layer. This happens, for example by chemically etching away the substrate body, the barrier layer and one Part of the porous layer. However, the porous part of the molded layer must be removed in such a way that the terminal tips of the tip-shaped elements are completely exposed.

In a further preferred embodiment of the method according to the invention the exposed tip-shaped elements are subjected to a further etching process, for example by plasma etching, or by wet chemical or electrolytic etching. This allows, for example, the shape of the terminal tips with regard to their use can be optimized as electron emission peaks.

Post-treatment of the surface structured according to the invention is further preferred by deposition of an additional, thin metal layer, which the electron-emitting Properties of the lacy elements improved. This extra thin metal layer consists preferably of a noble metal, in particular of Au, Pt, Rh or Pd, or an alloy containing at least one of these noble metals. The deposition of this additional metal layer can, for example, by chemical or electrolytic methods, through PVD (Physical Vapor Deposition), such as sputtering or electron beam evaporation, or by CVD (Chemical Vapor Deposition).

Exemplary embodiments for the production of the structures structured according to the invention are described below Surface described. All details in parts or percentages relate to the weight unless otherwise stated.

First embodiment

An aluminum sheet made of 99.9% by weight Al with a glossy surface serves as the substrate body. The aluminum sheet is cleaned in a mild alkaline degreasing solution, in Rinsed water, pickled in nitric acid, rinsed in water, briefly immersed in acetone and dried.

A suitable masking varnish is then applied to the back of the sheet and the substrate body pretreated in this way in a phosphoric acid electrolyte with a concentration of 150 g / l H ₃ PO ₄ at an electrolyte temperature of 35 ° C. with direct current with a current density of 100 A / m ² anodized for 3 minutes, continuously increasing the anodizing voltage from 0 to 50 V. Immediately afterwards, the anodizing voltage is reduced in 5 to 6 steps to approx. 15 V, the voltage lowering steps being initially small and gradually increasing. After the anodizing voltage of approx. 15 V has been reached, this is maintained for approx. 40 seconds. The resulting layer thickness of the aluminum oxide layer is typically 1 μm.

The molded layer now has pores, one against the free surface of the aluminum oxide layer protruding, upwardly open trunk area and one against the substrate body have directed branching area.

The molding, in particular the free surface of the molding layer, is then rinsed with water and in an activation bath containing nickel salt (100 g / l NiSO ₄ .7 H ₂ O and 40 g / l boric acid, pH 4.0 to 5.0) with an applied AC voltage of 16 V treated for 5 seconds and then rinsed again with water.

The pores of the shaped layer prepared in this way have nickel particles embedded on the pore base, which preferably serve as nuclei for a further selective nickel deposition. The selective deposition of nickel, ie the further deposition of nickel on the nickel particles already in the pores, is initially carried out chemically in a nickel bath at a temperature of 85 ° C and a pH of 5.0, which contains a sodium hypophosphite solution as a reducing agent . The selective nickel deposition takes 1 hour, a layer of nickel-phosphorus with 10 to 12% by weight of phosphorus and a layer thickness of approximately 10 μm being produced. The nickel-coated mold layer is then rinsed again with water and then the nickel layer is in a commercially available, galvanic nickel bath ("Watt" bath, which for example 300 g / l nickel sulfate, 60 g / l nickel chloride, 40 g / l boric acid and organic Contains additives such as wetting agents) with a current density of 400 A / m ² measured at the cathode for 20 minutes. The electrolyte temperature is 50 to 60 ° C, the electroplated nickel layer reaching a thickness of about 16 microns.

After the nickel-coated molded article has been rinsed again with water, the covering lacquer becomes removed, for example, chemically or by plasma etching. The molded body is now chemically dissolved in sodium hydroxide solution (50 g / l NaOH). At a NaOH bath temperature of At 20 ° C, this process takes several hours, for example 1 to 5 hours.

After the shaped body has been removed, the desired structured nickel foil remains tip-shaped elements, the tip-shaped elements attaching to the Ni carrier layer adjacent trunk area and as a vertical continuation a branching area, containing at least two terminal tips.

The structured nickel foil is rinsed again with water, in 5% citric acid at 20 ° C for 30 minutes, rinsed again with water, placed in ethanol and finally dried.

The tip-shaped elements represent a precise image of the one in the aluminum oxide layer existing pore cavity, since the aluminum oxide layer as a mask for its Ni exposure serves. The structured nickel foil has many tips that are close together 1 µm in length, the largest diameter of which is typically less than 0.2 µm lies.

Second embodiment

An aluminum sheet serving as a substrate body, as described in the first exemplary embodiment, is according to the method described in the first embodiment cleaned and anodized. The shaped body surface thus formed is according to the first Embodiment activated.

The selective nickel deposition now takes place in a chemical nickel bath with a Temperature of 70 ° C and a pH of 6.0, using the nickel bath as a reducing agent Contains dimethylamine borane. The selective nickel deposition takes 1 hour, with one Nickel-boron deposition with a layer thickness of approx. 5 µm and a boron content of less than 1% is formed. According to the first embodiment, the nickel layer grows due to the special activation method initially only on the pore base.

After a rinsing process with water according to the first embodiment, the Masking varnish removed, the molded body dissolved and thus a structured nickel foil exposed.

The tip-shaped elements of the structured nickel foil are then subjected to an electrolytic aftertreatment, the radius of curvature of the terminal tips being reduced, so that a field emission surface with better electron-emitting properties is produced. The electrolyte used for this contains 638 ml / l 96% sulfuric acid and 9 g / l glycerin. The electrolytic aftertreatment is carried out for 5 to 10 seconds at an electrolyte temperature of 20 ° C., with a cathode made of pure lead, a current density of 500 to 1000 A / m ² and an electrolysis voltage of 6 V. Then the structured nickel foil is again rinsed with water and dried.

Third embodiment

A structured nickel foil produced according to the first or second exemplary embodiment is retrofitted for 60 seconds in a commercially available, electroless gold bath gold-plated, the gold bath having a gold concentration of 2 g / l, a bath temperature of 85 ° C and has a pH of 4.2 to 4.8. Here, a charge is exchanged Gold layer of approx. 0.05 µm was formed. The gold-plated nickel foil is then with Rinsed water, treated with ethanol and dried.

Refining the structured nickel foil in this way significantly improves its properties as a field emission surface.

The present invention is further explained by way of example with reference to FIGS. 1 to 4.

Figure 1 shows schematically a cross section through a not yet finished molded body 22, its pores lying vertically to the molded body surface 23 and open at the top only an elongated cavity 32 without pore branches, i.e. the trunk area 32 of the Pores. The molded body shown in FIG. 1 consists on the one hand of the substrate body 24 and on the other hand from the molded layer 26, which in turn consists of a barrier layer 28 and a porous layer 30 is formed.

A body formed according to FIG. 1 is formed, for example, after anodic oxidation with a constant or continuously or gradually increasing anodizing voltage a substrate body 24 made of aluminum in an electrolyte that redissolves the aluminum oxide.

Figure 2 shows schematically a cross section of a usable for the inventive method Shaped body 22. The shaped body 22 is made of the substrate body 24 and the Form layer 26 formed. The cavity 36 of the pores contains a pore stem region 32 and a pore branching area 33, each pore cavity 36 in the branching area 33 has two pore branches 34.

A molded body 22 designed according to FIG. 2 is formed, for example, when - starting of a not yet finished shaped body 22 according to FIG. 1 - the anodic oxidation is continued with a lower anodizing voltage. This can be done using the anodizing voltage be lowered gradually or continuously. Because the during the anodic Oxidation-forming pore diameter, as well as the layer thickness of the barrier layer that forms 28 depend on the size of the anodizing voltage, decreases during one such a second stage of the process, the thickness of the barrier layer 28, the layer thickness of the porous oxide layer 30 continues to grow. Because the formation of oxide layer 28, 30 at the interface between aluminum substrate body 24 and barrier layer 28 takes place, and the The pore diameter is dependent on the anodizing voltage and then forms on the pore trunk area 32 several pore branches 34 with one opposite the trunk area 32 smaller diameters.

Figure 3 shows schematically the cross section of an electron-emitting material coated molded body 22. The molded body 22 consists of a substrate body 24 and a molding layer 26. The molding layer 26 contains pores, the cavity 36 of which is a trunk area 32 and a branching area 33 with at least two pore branches 34 having. The cavity 36 is completely filled with electron-emissive material, and the resulting tip-shaped elements 14 made of electron-emitting material are connected to one another in an electrically conductive manner by a carrier layer 12.

A shaped body designed according to FIG. 3 and coated with electron-emitting material 22 arises, for example, if - starting from a molded body 22 according to FIG. 2 - the molded body surface 23, at least in the pores, is chemically activated, the Pore cavities 36 using chemical and / or electrochemical methods with electron-emitting Material is applied, and on the resulting tip-shaped Elements 14, as well as on the molded body surface lying between the pore cavities 36 23 an electron-emitting layer 12 made of, for example, metal or semimetal is deposited.

FIG. 4 schematically shows the cross section of a surface structured according to the invention. This consists of a carrier layer 12 with tip-shaped elements 14 connected to it in an electrically conductive manner, for example made of metal or semimetal, ie of electron-emitting material. The tip-shaped elements have a trunk area 16 and a branching area 18, the tip-shaped elements 14 in the branching area 18 having two terminal tips 20, the longitudinal axes a ₁ , a _{2 of which form} an acute angle α. The trunk areas 16 of the tip-shaped elements 14 are mechanically supported by a support layer 15 lying between them, a portion of the trunk areas 16 and the terminal tips 20 being exposed.

A structured surface designed according to FIG. 4 arises, for example, if starting from a shaped body 22 coated with electron-emitting material 3 - the substrate body 24 and part of the molded layer 26 chemically etched away becomes.

Claims (15)

1. Structured surface, having a support layer (12) and, connected electrically to it, peak-shaped elements (14),
   characterised in that
   each peak-shaped element (14) exhibits adjacent to the support layer (12) a cylindrical or blunted cone-shaped stem region (16) and at least two, preferably 2 to 4 end peaks (20) at the free end of the stem region (16).
2. Structured surface according to claim 1, characterised in that the peak-shaped elements (14) and/or the substrate layer (12) are of Ni, Al, Pd, Pt, W, Fe, Ta, Rh, Cd, Cu, Au, Ag, In, Co, Sn, Si, Ge, Se, Te or a chemical compound containing at least one of these substances or an alloy of the above mentioned metals.
3. Structured surface according to claim 1 or 2, characterised in that provided on the substrate layer (12) between the peak-shaped elements (14) is a mechanical support layer (15) made of an electrically insulating material, preferably an oxide, in particular aluminium oxide.
4. Structured surface according to one of the claims 1 to 3, characterised in that the longitudinal axes (a₁, a₂) of the end peaks (20) enclose an acute angle α of 10 to 80°, in particular from 20 to 60°, referred to a circle of 360°.
5. Structured surface according to one of the claims 1 to 4, characterised in that the density of end peaks is 10⁸/cm² and greater.
6. Structured surface according to one of the claims 1 to 5, characterised in that the largest cross-sectional diameter of each peak-shaped element (14) is 250 nm or less, preferably 10 to 230 nm, especially 80 to 230 nm.
7. Structured surface according to one of the claims 1 to 6, characterised in that the peak-shaped elements(14) exhibit a height of 50 nm to 20 µm, preferably 0.5 to 3µm.
8. Structured surface according to one of the claims 1 to 7, characterised in that the free ends of the end peaks (20) exhibit a radius of curvature of 200 nm or less, preferably 50 to 100 nm.
9. Use of the structured surface according to one of the claims 1 to 8 as a field emission surface of cold cathode emitter elements, especially as electron emission source for ultra-flat imaging screens, for electron lithography or for scanning or transmission microscopy.
10. Process for manufacturing structured surfaces according to one of the claims 1 to 8, characterised in that,

    a) in a first step a mould body (22) with a surface (23) that is a mirror-image of the desired structured surface is created, whereby a substrate (24) of aluminium is oxidised anodically in an electrolyte that dissolves aluminium oxide, whereby the anodising voltage in a first anodising step is increased continuously or in steps from 0 to a first value U₁, and in a second anodising step the anodising voltage is reduced continuously or in steps to a second value U₂ that is smaller than U₁;

    b) in a second step the surface (23) of the mould body (22) is coated over the whole surface area such that the pore cavities (36) present in the surface layer (23) of the mould body (22) are completely filled with the coating material and, a support layer (12) is formed connecting the peak-shaped elements (14) electrically, and that the support layer (12) represents a continuous, mechanically supporting layer;

    c) and in a third step at least a part of the mould body (22) is removed such that the end peaks (20) are exposed.
11. Process according to claim 10, characterised in that the first value U₁ of the anodising voltage for forming cylindrical, or blunted cone-shaped, long pores lies between 12 and 80 V and, in order to form at least two pore branches at the end of each long pore facing the aluminium layer, the second value U₂ lies between 10 and 20 V.
12. Process according to claim 10 or 11, characterised in that the materials used for coating the mould body surface (23) are preferably Ni, Al, Pd, Pt, W, Fe, Ta, Rh, Cd, Cu, Au, Ag, In, Co, Sn, Si, Ge, Se, Te, or a chemical compound containing at least one of these elements, or an alloy of the above mentioned metals.
13. Process according to one of the claims 10 to 12, characterised in that the coating on the mould body surface (23) is performed by chemical and/or electrolytic methods.
14. Process according to one of the claims 10 to 13, characterised in that the removal of at least part of the mould body (22) is performed by etching away chemically the substrate body (24) and at least a part of the mould layer (26).
15. Process according to one of the claims 10 to 14, characterised in that the peak-shaped elements (14), which are at least partially exposed, are subjected to a chemical or electrolytic etching process.

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