Nanowire structural element

Abstract

A template based process is used for the production of the nanowire structural element, wherein the nanowires are electrochemically depositioned in the nanopores. The irradiation is carried out at different angles, such that a nanowire network is formed. The hollow chamber-like structure in the nanowire network is established through the dissolving of the template foil and removal of the dissolved template material. The interconnecting of the nanowires provides stability to the nanowire structural element and an electrical connection between the nanowires is created thereby.

Claims

1. A process for the production of a nanowire structural element, comprising the steps of: (a) preparing a template, (b) irradiation of the template with energetic radiation at, at least, two different angles to the surface of the template for the purpose of generating an intersecting network of numerous latent tracks permeating the template, wherein the template is irradiated from at least three different directions with high-energy radiation and wherein the three directions do not share a common plane, and wherein the template is irradiated from at least three different directions at predefined angles including a polar angle of 45 degrees and azimuth angles of 0 degrees, 120 degrees and 240 degrees, or from at least three different directions at predefined angles, such that the intersecting nanowires run at an angle of 90 degrees to each other, or from at least four different directions at predefined angles including a polar angle of 45 degrees and azimuth angles of 0 degrees, 90 degrees, 180 degrees, and 270 degrees such that the template is rotated at least three times during irradiation, (c) etching the template in order to etch the radiation induced latent tracks into a network of intersecting, interconnected nanopores, (d) deposition of matter in the nanopores to generate a network of intersecting, interconnected nanowires in the nanopore network such that the nanowire network permeates the template, and such that nanowires intersect at nodes between ends of the nanowires, and (e) dissolving and removal of the template from the nanowire network to result in a freestanding nanowire structural element.

2. A process according to claim 1, wherein prior to the step (d) an electroconductive cathode layer is applied to a first side of the template and in the step (d) the nanowire network develops in the nanopore network by means of electrochemical deposition to the cathode layer.

3. A process according to claim 1, wherein the nanowire network is applied through electrochemical pulsed deposition.

4. A process according to claim 1, wherein the template is irradiated through a mask with one or more openings, such that the latent tracks are only generated in the region(s) of the opening(s).

5. A process according to claim 1, wherein the nanowires run at predefined angles within the network.

6. A process according to claim 1, wherein the element has a stable hollow chamber-like structure.

7. A process according to claim 1, wherein the nanowires are greater than 50 nm in diameter.

8. A process according to claim 1, wherein the freestanding nanowire structural element has a hollow chamber-like and sponge-like structure and is open on at least four sides.

9. A process according to claim 1, wherein at least some of the nanowires have multiple nodes along their lengths.

10. A process according to claim 1, wherein the freestanding nanowire structural element has a geometrically specific surface area A.sub.v, as follows: $A_v=.Math.\frac{\mathrm{nD}}{F\cos }$ wherein D is an average diameter of the nanowires, n/F is a surface density of the nanowires, and is the average angle of the nanowires to a surface plane of the template, and wherein A.sub.v is at least 1 mm.sup.2/(cm.sup.2 m).

Description

SHORT DESCRIPTION OF THE ILLUSTRATIONS

(1) They show:

(2) FIG. 1 An overview of the production of a nanowire structural element with a nanowire network.

(3) FIG. 2 A three-dimensional presentation of the deposition device used for electrochemical deposition.

(4) FIG. 3 A three-dimensional transparent exploded view of the deposition device for the deposition of the cathode layer.

(5) FIG. 4 A three-dimensional transparent exploded view of the deposition device for the deposition of the nanowires and, where applicable, a cover layer.

(6) FIG. 5 An SEM image of a nanowire structural element with a nanowire network.

(7) FIG. 6 An SEM image of the nanowire structural element from FIG. 5, significantly enlarged.

(8) FIG. 7 A schematic overview of the production of a nanowire structural element with a three-dimensional (3-D) nanowire network.

(9) FIG. 8 A TEM image of a nanowire structural element open at two sides and closed at two sides with a nanowire array of platinum nanowires.

(10) FIG. 9 An SEM image of the three-dimensional nanowire network from FIG. 8 slightly enlarged.

(11) FIG. 10 An SEM image of the three-dimensional nanowire network from FIGS. 8 and 9 enlarged to a lesser degree.

(12) FIG. 11 A schematic exploded view of a microreactor with the nanowire structural element for use in flow operations.

(13) FIG. 12 A schematic presentation of a sensor element with two nanowire structural elements.

DETAILED DESCRIPTION OF THE INVENTION

(14) Overview of the Production Process

(15) The production of nanowire structural elements is based on a template based process. The partial steps of the process are schematically presented in FIG. 1 as follows:

(16) (a) Preparation of the template foil,

(17) (b) Irradiation with ions,

(18) (b1) Application of a gold layer,

(19) (b2) Electrochemical reinforcement of the gold layer (optional),

(20) (c) Etching of the ion tracks to form nanopores,

(21) (d) Deposition of the nanowires in the nanopores,

(22) (d1) Removal of the cathode layer (optional),

(23) (e) Dissolving and removal of the template foil.

(24) Ideally, the process steps are carried out in the order shown in FIG. 1, i.e. (a), (b), (b1), (b2), (c), (d), (d1), (e). It is, however, basically possible to use a different sequence, such as, to etch from two sides and subsequently to then first to apply the cathode layer partial step ((c) before (b1) and (b2)) (see, e.g., FIG. 7).

(25) In accordance with FIG. 1(b), first a template foil 12 is bombarded with ions 14, wherein latent ion tracks 16 are generated in the substance of the template foil 12 along the trajectory (b1). The template foil 12 is a polymer foil in this example, specifically, a polycarbonate foil. A special feature of the process described here consists of the fact that the template foil is irradiated with ions from two angles in this example. In this example, the template foil is irradiated once at an angle of +45 to the surface of the template foil, and once at 45, such that the latent tracks and later the intersecting nanopores, or respectively, intersecting nanowires run at an angle of 90 to each other. It is to be understood that other angles may also be used.

(26) For successive irradiation of the template foil 12 at different angles, the template foil 12 is first positioned in an appropriate irradiation tube at a first angle to the direction of the ion beam, for example in the synchrotron of the GSI, and irradiated with a predetermined first ion surface density. Subsequently the template foil 12 is tilted in relation to the beam direction and irradiated with a second predetermined ion surface density. Should it be the case that nanowires are to be generated at different angles, the process is repeated until the angles have been obtained. The density of the ions, or respectively, the surface density necessary for a specific surface density of nanowires is calculated in advance and determined. The irradiation is then carried out with this predetermined ion surface density. To produce a 3-D network as explained below, a template foil 12 positioned at a polar angle to the beam axis is rotated on the beam axis to the azimuth angle.

(27) Subsequently, on the first side 12a of the template foil 12, a thin, conductive metallic layer 22a, e.g. gold, is sputtered onto said (b1), forming a first partial layer. Subsequently, the first partial layer 22a is reinforced electrochemically with a second partial layer 24a thus forming the cathode layer 26a (b2), which later serves as a cathode for nanowire deposition (d). For the electrochemical deposition of the second partial layer 24a, the template foil 12 is mounted in the deposition device 82 shown in FIGS. 2-4.

(28) Subsequently, the template foil 12 coated on one side is then removed from the deposition device 82, and the latent ion tracks 16 are chemically etched, wherein the continuous intersecting channels are created. These channels are referred to as nanopores and due to their different directions in the template foil 12, form intersecting and interconnected nanopores 32. Alternatively, the etching process may also be carried out in the deposition device 82, in that the etching solution is placed in the appropriate cell 88, and the repeated insertions are not necessary. The diameter of the nanopores 32 can be controlled by controlling the etching time period (c).

(29) Following this, the template foil 12 prepared in this manner, permeated with the intersecting network 33 of nanopores 32, is placed again in the deposition device 82, and in a second electrochemical process, the desired metal for the formation of a network 37 of nanowires 34 in the nanopores 32 is electrochemically depositioned (d). In this example, platinum is depositioned in the nanopores, such that the nanowires 34, or respectively, the nanowire network 37, consist(s) of platinum. This platinum nanowire network 37 forms a catalytic active network due to the catalytic active surface of the platinum nanowires 34.

(30) After the deposition of the nanowires, or respectively, the generation of the nanowire network 37 in the template foil 12, the cathode layer 26a may be removed if desired (d1). The removal of the cathode layer 26a is ideally carried out before the template foil is dissolved and removed. The gold cathode layer used in this example can be readily removed from the platinum nanowires. The cathode layer 26a can, however, remain on the template foil 12, and after the dissolving and removal of the template foil, forms a substrate layer 27, on which the nanowire network 37 is positioned and firmly joined (see FIG. 7 in the following).

(31) Finally, the polymer foil 12 is dissolved in an organic solvent suited to this purpose (e). The nanowire structural element 1 produced hereby in accordance with the invention is shown in FIG. 1(e).

(32) The nanowire structural element 1 contains or consists of a nanowire array 35 of intersecting, interconnected nanowires 34, which form an integrally meshed nanowire network 37. The network 37 displays a certain stability due to the meshed structure of the merged together nanowires, even without cover layers, or, in other words, open on all sides, even when cover layers of this typed, e.g. on one side (substrate layer 27) or on both sides to form a sandwich structured are not excluded as a possibility.

(33) The template based method has the advantage that many of the parameters can be specifically manipulated. The length of the nanowires 34 is determined by the thickness of the template 12 used and ideally is 10-200 m, particularly preferred is circa 50 m50%. The surface density of the nanowires 34 is determined by the irradiation. The minimal surface density of the ion irradiation, and thereby the nanopores, should be selected such that a sufficient portion of the nanowires 34 can merge together. In this regard, a preferred surface density for the production of the array is ideally between approx. 110.sup.7 cm.sup.2 and 110.sup.9 cm.sup.2. The diameter D of the nanowires 34 is determined by the time period of the etching and may be from ca. 20 nm to 2000 nm. The aspect ratio may have values of up to 1000.

(34) Possible materials for the nanowires are electroconductive materials, particularly metals or metallic compounds which are suited to electrochemical deposition. Experience has been made with the following metals which have been proven suitable: Cu, Au, Bi, Pt, Ag, Cu, Cu/Co multilayer, Bi.sub.2Te.sub.3.

(35) On the one hand a large number of nanowires 34 with small diameters D is desired, in order to obtain a large active surface area, and on the other hand a good mechanical stability should be obtained. The optimization of this depends on the material used and is adjusted to the needs accordingly.

(36) For nanowire structural elements 1 with platinum nanowires 34, a stable construction is produced with 10.sup.8 wires per cm.sup.2 having a diameter of 250 nm and a length of 30 m. The aspect ratio here is 120. Such nanowire structural elements are suited, for example, for use as catalytic elements due to the catalytic characteristics of, for example platinum of the other elements contained therein.

EXAMPLE 1

(37) For the production of a nanowire structural element 1, a 30 m thick circular shaped (r=1.5 cm) polycarbonate foil 12 (Macrofol) irradiated with heavy ions 14 having an energy of 11.1 MeV/u and at two angles (+45, 45) each having a fluence of 510.sup.8 ions/cm.sup.2 is used. Prior to the application of the conductive metallic layer 22a, each side of the polymer foil 12 is irradiated for one hour with UV light, in order to increase the selectivity of the etching along the tracks 16.

(38) A gold layer 22a is sputtered onto the first side 12a of the polymer foil 12, having a thickness of ca. 30 nm (b1). This is reinforced by a potentiostatic deposition of copper from a CuSO.sub.4 based electrolyte solution (Cupatierbad, Riedel) with a voltage of U=500 mV, wherein a copper rod electrode serves as the anode (partial step 24a) (b2). The deposition is stopped after 30 minutes, at which point the copper layer 24a is approx. 10 m thick. Subsequently, etching is carried out from the untreated side 12b of the template foil 12 at 60 C. with an NaOH solution (6 M) for 25 minutes and thoroughly rinsed with deionized water, to remove residual etching solution. At this point, the nanoporous template foil 12 is mounted in the deposition device 82.

(39) The deposition of nanowires 34 is carried out at 65 C. with alkaline Pt electrolytes (PtOH bath, Metakem). To generate the nanowires 34, the process of the reversed pulse deposition is used in order to compensate for the slow diffusion driven transportation in the nanopores 32, and to obtain uniform development of nanowires 34. Following a deposition pulse of U=1.3 V for 4 seconds, there is an anodic pulse for 1 second at U=+0.4 V. After a few tens of minutes, the deposition is stopped, and the development is checked. At this point, the nanowires 34 have developed sufficiently to merge together in the nanopores.

(40) Finally, the template foil is removed, wherein the entire nanowire structural element 1 with the template foil 12 is placed in a container with 10 ml dichloromethane for several hours. In this example, the cathode layer remains as a substrate 27 on the nanowire array 35 and forms a component of the nanowire structural element 1. The solvent is replaced three times in order to fully remove residual polymers from the interior 38 of the nanowire array 35.

(41) A nanowire structural element 1 produced in this manner may be seen in the scanning electron microscope images (SEM) in FIGS. 5 and 6. The nanowires 34 here have a diameter of approx. 150 nm. Because the irradiation is carried out at two angles it is referred to as 2-dimensional. Such a 2-D nanowire network structure may be seen therefore in FIGS. 5 and 6, which has been produced in a template that has been irradiated twice at different angles (+45, 45). It has formed a network which is relatively stable after removal of the polymer matrix, distributed on the substrate and joined to said.

(42) The enlarged SEM image of a few nanowires 34 in FIG. 6 shows that the nanowires 34 have merged nicely at the nodes 39 and are thereby firmly joined and remain in place due to the predetermined radiation orientation of 90. The nodes 39 where the nanowires 34 have merged together are predetermined by the intersections of the nanopores and are distributed at one or more places over the length of the nanowires 34, or between the ends of the nanowires 34.

EXAMPLE 2

(43) In reference to FIGS. 7-10, a further embodiment is produced. FIG. 7 shows schematically, and partially summarized the following partial steps of the process:

(44) (a) Preparation of the template foil,

(45) (b), (c) Irradiation and etching of the ion tracks to form nanopores,

(46) (b1), (b2), (d) Generation of a cathode layer and deposition of the nanowires in the nanopores,

(47) (e) Dissolving and removal of the template foil.

(48) With reference to FIG. 7, the template foil or polymer membrane 12 is irradiated from more than two different directions. The irradiation is carried out in this example from four different directions, wherein the four irradiation directions are not in the same plane. With reference to perspective view shown in FIG. 7, radiation is applied in each case once from each of the four sides diagonally from above, and this being at a polar angle of 45 to the surface of the substrate and at azimuth angles of 0, 90 180 and 270. The template foil 12 is therefore rotated at least three times during the irradiation.

(49) When the template foil has been irradiated from at least three directions (in this example, four directions) which are not in a common plane, a three-dimensional nanopore network 33(c) and subsequently a three-dimensional nanowire network 37(d) and (e) can be produced. In other words, the irradiation directions and thereby the nanowires 34 lie in numerous (non-parallel) planes, which are at an angle to the template surfaces 12a, 12b. With a three-dimensional nanowire network 37 generated in this manner, the nanowires accordingly run in three non-parallel planes, thus forming a three-dimensional interconnected network structure. Expressed mathematically, the nanowires run along at least three non-parallel axes, which form at least two planes which in turn are not parallel. In this manner, the nanowires are not only connected to other nanowires in the same plane, but nanowires also exist which run at an angle to one of the planes formed by these nanowires. In other words, in the language of vector mathematics, it is possible with the at least three axes, or respectively, nanowire directions, to span a three-dimensional vector space. The, at least three, axes, or respectively, nanowire directions, are independent on a linear level. A three-dimensional interconnected nanowire network of this type is referred to here as a three-dimensional (3-D) nanowire network.

(50) FIG. 8 shows a transmission electron microscope image (TEM) and FIG. 9 shows an SEM image with slight enlargement of a three-dimensional nanowire network 37 of this type, in which it may be seen that a mechanically stable, cohesive system of nanowires running at predefined angles has been formed, which remains erect to a large degree as a result of the predetermined orientation of the polymer matrix after the template has been removed, which can be seen particularly well in the SEM image in FIG. 9. The template 12 of the network 37 displayed here has been produced with 4 irradiations from four different linearly independent directions in each case with 510.sup.8 ions/cm.sup.2. The thickness of the nanowires here is approx. 50 nm.

(51) Aggregation and loss of the active surface area is rarely observed, which means that excellent accessibility and ready catalyzer returns are obtained. The production process allows for a simple controlling of the network parameters by means of adjustment of the diameter of the wires, the integration density and the complexity (number of different nanowire directions) of the network. It is possible to produce very large nanowire networks 37 which are of several millimeters in two dimensions, as can be seen for example in FIG. 10. FIG. 10 shows an SEM image of the approx. 1 cm.sup.2 nanowire structural element from FIG. 9. The entire nanowire structural element 1 is accordingly large on a macroscopic level. At the left edge of the image another somewhat smaller nanowire structural element may be seen. The Pt nanowire networks have a large catalytic active surface area, without a carrier substrate 27 being necessary, although this possibility is not excluded.

(52) The nanowire structural element 1 in accordance with the invention accordingly has nanowires 34 connected to a network 37 wherein the network structure, in particular the 3-D network structures display the possibility for connecting, in a mechanically stable manner, micro- and even macroscopic structures. The stability is so great that they are suited for integration without cover layers on both sides, and as the case may be, even without a carrier substrate. Nearly all nanowires 34 are not only mechanically firmly connected, but also connected to each other in an electroconductive manner, wherein these structures have a large potential for use in electro catalysis.

(53) A Further Example Regarding the Deposition Parameters

(54) In another example, the etching period is set at 18 minutes, resulting in nanowires 34 with a diameter of approx. 250 nm. The surface density (number for each surface) here is 10.sup.8 cm.sup.2. For the electrochemical deposition of the wires, the reversed pulse deposition is used again. A deposition pulse of U.sub.1=1.4 V for 40 ms is followed by a short counter-pulse of U.sub.1=0.1 V for 2 ms and a pulse interval of 100 ms at a voltage of U=0.4 V, corresponding to a surplus voltage of approx. 0 V. This means that during the counter-pulse, the system is in a state of equilibrium.

(55) Construction for the Electrochemical Deposition

(56) With reference to the FIGS. 2-4 the electrochemical deposition of the nanowire array 35 consisting of numerous nanowires 34 is carried out using the deposition device 82, which shown in FIG. 2, in its entirety. It consists of a metal housing 84, in which the metal sled containing one of the two electrolysis cells 86, 88 can be inserted. Due to the good heat transfer properties of metal, it is possible to temper the deposition device by controlled external heating.

(57) The electrolysis cells 86, 88 made of PCTFE have on their two facing sides, in each case, circular openings 87, 89 of the same size and can be pressed together firmly with a hand turned screw. A copper ring 92 between the two electrolysis cells 86, 88 serves as a cathode, or respectively, to establish contact with the first cover layer for the electrochemical deposition.

(58) With reference to FIG. 3, for electrochemical reinforcement of the partial layer 22a, the ion track etched template foil 12 is mounted between the two electrolysis cells 86, 88 such that the partial layer 22a, in this case, the sputtered gold layer 22a, establishes good contact with the ring shaped copper electrode 92. On both sides of the copper ring used as a cathode, electrolytes are injected into the electrolysis cells. The electrochemical reinforcement of the gold layer 22a on the first cover layer 26a is carried out with a first anode 94, which is placed in the electrolysis cell 86 facing the partial layer 22a, and an external power source with a control device.

(59) After removing the template foil 12 and etching the nanopores 32 outside of the deposition device 82, the template foil 12 is placed again in the deposition device 82.

(60) With reference to FIG. 4, the template foil 12 which has been coated on one side and made porous is again placed in the deposition device 82 as in FIG. 3 for electrochemical deposition of the nanowires 34 and, where applicable, the completion of cover layer opposite the cathode layer 26a, such that the cover layer 26a makes contact with the ring electrode 92. At this point, deposition is carried out on the second side 12b of the template foil 12 with a second anode 96 located in the electrolysis cell 88 on the side away from the cathode layer 26a.

(61) Examination of the Influence of the Electrochemical Deposition Conditions to the Development of the Nanowires

(62) With the pulsed deposition procedure for generating nanowires 34, a uniform length of the nanowires can be advantageously obtained at any point in time of the deposition. This can be explained, without claim to completeness and accuracy, in that the diffusion layers are kept relatively short in comparison to direct current deposition. In the intervals (equilibrium or counter-pulse) between the deposition pulses, metal ions in the nanopores 32 can re-diffuse such that on the entire electrode surface a nearly uniform concentration is obtained at the beginning of each deposition pulse, which results in a homogenous development. The diffusion layers barely overlap each other and irregularities in the surface are not enhanced.

(63) Structural Characteristics of the Nanowires

(64) In the framework of the invention the structural characteristics of the nanowires 34 made of different materials are also studied. With electrochemically depositioned material it is possible, for example, to control the size of the crystallite. This affects the mechanical stability, the thermal and electrical transference characteristics as well as the surface area and thereby also the catalytic activity. Many characteristics can thereby be strategically influenced.

(65) In particular, the structure of the nanowires 34 is studied using X-ray diffraction. For this, the texture as a function of the electrochemical deposition is analyzed.

(66) Pt nanowires 34 produced using direct current show a clear <100> texture. The texture coefficient TC.sub.100 is 2.32, wherein the maximum value is 3. The size of the crystallite is determined by the half-width of the platinum signal by means of the Scherrer equation, and is 8 nm. For catalytic application, the smallest possible crystallite is desired. The value given here lies in the range of the nanoparticles otherwise used for catalysis. Based on this it may be assumed that the crystallite size can be reduced even more through modification of the electrochemical deposition conditions.

(67) When studying nanowires 34 which are produced using pulsed deposition, one finds no specific texture. The intensity of the signals corresponds to those of polycrystalline platinum.

(68) Finally, a sample produced using reversed pulse deposition, is studied. This also shows a clear <100> texture, wherein the texture coefficient TC.sub.100 is 4.6. The crystallites display accordingly a preferred orientation, wherein the degree of the alignment is 83%. An alignment of at least 50% in this case is advantageous.

(69) The characterization by means of X-ray diffraction of nanowires 34 produced using different means has shown that the deposition conditions have an effect on the texture. Therefore, the structure of the nanowire can be strategically influenced.

(70) The surface of a nanowire 34 does not correspond to smooth surface of a cylinder, which is the basis for the calculation of the geometrical surface, but rather, it displays numerous recesses and swellings in its contour which significantly increases the surface area. The actual size of the surface area is therefore typically larger than the geometrical surface area, because, among other reasons, the crystallites from which the nanowires 34 are constructed are very small. In order to obtain a more precise idea of the surface area of the nanowire arrays 35, cyclovoltammetric measurements at 60 C. in 0.5 M H.sub.2SO.sub.4 are carried out for a potential range of 0-1,300 mV with a standard hydrogen electrode. From the load in which the adsorption of hydrogen is transmitted, it is possible, taking into account the capacitive currents, to calculate the surface area of the electrodes. The cyclovoltammetric examination of nanowire arrays shows that the actual surface area is greater than the geometrical surface area by a factor ranging from 4-5.

(71) Applications

(72) As a catalyzer it is possible to connect a series of numerous nanowire structural elements 1 according to the invention. Based on measurements, the nanowire structural element 1 is suited individually for application in microstructured systems having three-dimensional structures wherein the internal measurement is less than 1 mm and for the most part lies between ten and a few hundred micrometers.

(73) FIG. 10 shows a schematic illustration of a microcatalyzer 100, in which a nanowire structural element 1 according to the invention is placed between a fluid intake 102 and a fluid discharge 104. It is conceivable that in a microcatalyzer 100 of this sort gas or fluid phase reactions can be carried out. For this purpose, a gas or fluid flow is directed under pressure through the microcatalyzer 100.

(74) The nanowire structural element 1 produced according to the invention furthermore inherently contains an electric contact to all of the nanowires. As a result, a controlled voltage may be applied to the nanowires 34 thereby enabling Electrocatalytic processes. Furthermore, the component may be used as an amperometric sensor.

(75) Production of Microelements using a Radiation Mask

(76) In accordance with the invention, it is possible to create nanowire structural elements or nanowire arrays of very small sizes, in that the template foil 12, a polymer foil in this example, is irradiated with heavy ions through a corresponding mask. The mask, e.g. a perforated mask, which is already applied contains numerous openings or perforations, wherein each opening defines a future microelement 1a. The mask covers the template foil 12 during the irradiation, and latent ion tracks 16 are formed thereby, which are subsequently etched to form nanopores 32 only in the areas which are not covered by the mask, i.e. at the openings of the mask. The layout and the shape of the microelement 1a are determined therefore by the mask.

(77) This process is specifically for the production of many very small nanowire structural elements, as stated, in the form of microelements. The microelements which may be produced in this manner consist of a 2- or 3-dimensional nanowire network 37 which may have a size of less than 500 m, and particularly less than 100 m, and where applicable, even less, to a size of only a few micrometers.

(78) For example, a perforated mask for the ion irradiation with approximately 2,000 perforations is placed on the entire deposition surface of approximately 0.5 cm.sup.2, such that approximately 2,000 microelements with nanowire arrays in islands in the template foil 12 can be created at once. After removal of the cathode layer, the microelements are separated from each other, and when the template foil has been dissolved and removed, are no longer attached to each other. It is, however, also possible to implement further steps, e.g. in order to generate cover layers for each individual microelement.

(79) Because all nanowires 34 have electrical contact at both ends, the microelements with nanowire arrays are suited for production of miniaturized sensors. Due to the large number of wires, not only a high sensitivity but also a defect tolerance should result.

(80) Further Applications

(81) In particular, the microelements are suited for the production of sensor elements, e.g. for measuring gas flow, temperature and for use as movement sensors. In reference to FIG. 12, such a sensor 150 has at least one measuring unit with a first and second nanowire structural element 1a, wherein the nanowire structural element 1a in each case has a cover layer 27 on each side, wherein each of the two nanowire structural elements 1a establishes electrical contact by means of one or both of the cover layers 27, wherein the two nanowire structural elements 1a establish electrical contact separately. A heating element is located between the two nanowire structural elements, e.g. a microwire 152 which can be heated through application of voltage. Modification of the resistance of the sensor element 150 is used as a measure for the gas flow, the temperature or the change in movement.

(82) It is clear to the person skilled in the art that the preceding descriptions of embodiments are to be understood as exemplary, and that the invention is not limited to said, but rather, can be varied in numerous ways, without abandoning the scope of the invention. In particular, the production of a microcatalyzer is only one of many uses for the nanowire structural element of the invention. Furthermore, it is clear that the characteristics are, regardless of whether they are presented in the description, the claims, the illustrations or otherwise, also define significant components of the invention, even if they are described in conjunction with other characteristics.