Abstract:
An arrangement ( 90 ) has a support ( 10 ) and nanoparticles ( 40, 70 ) that are located thereupon. At least two nanoparticles ( 40, 70 ), both of which are made of a metal material (M 1 , M 2 ) and are different regarding the metal material, are disposed at a distance from one another on a surface ( 130 ) of the support ( 10 ). The two metal materials have a different degree of preciousness.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Stage Application of International Application No. PCT/EP2007/057464 filed Jul. 19, 2007, which designates the United States of America, and claims priority to German Application No. 10 2006 033 866.9 filed Jul. 21, 2006, the contents of which are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to an arrangement comprising nanoparticles. 
       BACKGROUND 
       [0003]    In this context, the term “nanoparticles” refers to particles which have a particle size of less than one micron—in at least one spatial dimension. As is known, nanoparticles can be used in various fields of technology. For example, the international publication WO 03/095111 A1 describes that nanoparticles can be arranged in array structures. 
       SUMMARY 
       [0004]    According to various embodiments, an arrangement can be provided which has not only nanoparticle character but also further properties and thus qualifies for still further possible uses. 
         [0005]    According to an embodiment, an arrangement may comprise a support and nanoparticles present thereon, wherein at least two nanoparticles which each comprise a metal material and differ in respect of the metal material are arranged at a distance from one another on a support surface of the support, and wherein the two metal materials are noble to a different extent. 
         [0006]    According to a further embodiment, the distance between the two nanoparticles can be set so that the two nanoparticles form an electrochemical cell in an electrolyte. According to a further embodiment, the distance between the two nanoparticles may be from 5 μm to 10 μm. According to a further embodiment, the support may consist of an electrically nonconductive material or a material which has poor electrical conductivity. According to a further embodiment, the less noble metal material may be silver or comprises silver. According to a further embodiment, the more noble metal material may consist at least of one of palladium, platinum, rhodium and ruthenium or may comprise one of these metals. According to a further embodiment, a plurality of nanoparticles can be arranged in the manner of a chessboard so that each nanoparticle of one type is surrounded by four nanoparticles of the other type. 
         [0007]    According to another embodiment, a process for producing an arrangement may comprise nanoparticles, wherein at least two nanoparticles which each comprise a metal material and differ in respect of the metal material are arranged at a distance from one another on a support surface of the support, and wherein the two metal materials are noble to a different extent. 
         [0008]    According to a further embodiment, the distance between the two nanoparticles can be set so that the two nanoparticles form an electrochemical cell in an electrolyte. According to a further embodiment, the distance between the two nanoparticles may be from 5 μm to 10 μm. According to a further embodiment, an electrically nonconductive material or a material which has poor electrical conductivity may be selected for the support. According to a further embodiment, the less noble metal material can be silver or comprises silver. According to a further embodiment, the more noble metal material may consist of at least one of palladium, platinum, rhodium and ruthenium or may comprise one of these metals. According to a further embodiment, a plurality of nanoparticles which include at least two types of nanoparticles comprising metal materials which are noble to a different extent can be applied to the support surface. According to a further embodiment, each nanoparticle may have at least one nanoparticle of the other type arranged directly adjacent to it. According to a further embodiment, the distance between each nanoparticle of the one type and the directly adjacent nanoparticle of the other type can be in the range from 5 μm to 10 μm. According to a further embodiment, a first perforated mask having a predetermined first arrangement of holes can be applied to the support surface of the support, nanoparticles of a first metal material can be affixed to the support surface in the positions determined by the arrangement of holes, a second perforated mask having a predetermined second arrangement of holes can be applied to the support surface, and nanoparticles of a second metal material can be affixed to the support surface in the positions determined by the arrangement of holes in the second perforated mask. According to a further embodiment, the nanoparticles of the first metal material can be formed in the holes of the first perforated mask by the first metal material being deposited on the support surface in the region of the holes, and/or the nanoparticles of the second metal material may be formed in the holes of the second perforated mask by the second metal material being deposited on the support surface in the region of the holes. According to a further embodiment, finished nanoparticles of the first metal material can be introduced into the holes of the first perforated mask and affixed to the support surface and/or finished nanoparticles of the second metal material can be introduced into the holes of the second perforated mask and affixed to the support surface. According to a further embodiment, an auxiliary layer which provides chemical coupling positions for each of the two types of nanoparticles, to which the nanoparticles can couple chemically, can be applied to the support surface, with the coupling positions being located at a distance from one another, and a mixture of finished nanoparticles of at least two metal materials which are noble to a different extent can be applied to the support surface provided with the auxiliary layer and a nanoparticle distribution determined by the arrangement of the coupling positions on the auxiliary layer is achieved on the support. According to a further embodiment, the auxiliary layer may be formed by applying a polymer layer having a molecular structure which provides at least one coupling position for each of the two types of nanoparticles to the support surface. According to a further embodiment, the auxiliary layer can be formed by applying a crosslinking material comprising self-assembling molecules which each provide at least one coupling position to the support surface. According to a further embodiment, the plurality of nanoparticles can be arranged in the manner of a chessboard so that each nanoparticle of one type is surrounded by four nanoparticles of the other type. According to a further embodiment, a mixture of finished nanoparticles of at least two metal materials which are noble to a different extent can be applied to a support provided with a perforated mask. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention is illustrated below with the aid of various examples; here, by way of example, 
           [0010]      FIGS. 1-6  show a first example of a process according to an embodiment for producing an example of an arrangement or structure according to an embodiment, in which two perforated masks are used, 
           [0011]      FIGS. 7-11  show a second example of a process according to an embodiment for producing an example of an arrangement or structure according to an embodiment, in which only one perforated mask is used, 
           [0012]      FIG. 12  shows a third example of a process according to an embodiment for producing an example of an arrangement or structure according to an embodiment, in which an auxiliary layer is used, and 
           [0013]      FIG. 13  shows a fourth example of a process according to an embodiment for producing an example of an arrangement or structure according to an embodiment, in which a type of auxiliary layer different from that in  FIG. 12  is used. 
       
    
    
       [0014]    In  FIGS. 1 to 13 , identical reference signs are used in the interests of clarity for identical or comparable components. 
       DETAILED DESCRIPTION 
       [0015]    The various embodiments accordingly provide for at least two nanoparticles which each comprise a metal material and are different in respect of the metal material to be arranged at a distance from one another on a support surface of a support, where the two metal materials are noble to a different extent or have different redox potentials. 
         [0016]    A significant advantage of the arrangement according to various embodiments is that the nanoparticles can, as a result of the different nobility or the different redox potentials of the metal materials, have further chemical properties: for example, they can form an electrochemical cell as soon as they are brought into contact with an electrolyte. The ability to form an electrochemical cell enables the arrangement to be utilized, for example, in various technical fields, for example in the medical sector. For example, the arrangement can display an antibacterial action when its interaction with an electrolyte results in flow of electric current between the nanoparticles. Apart from use in the medical sector, the arrangement is also, owing to its electrochemical properties, suitable for other applications, for example for the internal coating of condenser tubes, heat exchangers or the like. A lotus flower effect or catalytic effects can also be displayed by the arrangement when suitable materials are selected. 
         [0017]    As already mentioned, the distance between the two nanoparticles is preferably set so that the two nanoparticles can form an electrochemical cell in an electrolyte. A distance between the two nanoparticles of from 5 μm to 10 μm is considered to be preferred. 
         [0018]    With regard to simple production of the arrangement, it is considered to be advantageous for the support surface to be planar or flat, at least on sections; in this case, the nanoparticles can lie in the same plane, at least approximately spatially in the same plane. 
         [0019]    The two metallic materials are preferably formed by pure materials such as chemical elements or metal alloys. 
         [0020]    To avoid an electric short circuit between the nanoparticles, it is considered to be advantageous for the support to consist of an electrically nonconductive material or a material which has poor electrical conductivity. 
         [0021]    If the arrangement is used in the human or animal body for the purposes of medical procedures, it is considered to be advantageous for the release of metal ions to be minimized since liberated metal ions in the human or animal body can, if the concentration is too high, sometimes cause damage. A release of ions can be reduced, or at least significantly slowed, when the difference between the redox potentials of the materials of the two nanoparticles is very small. The two metallic materials are preferably selected so that the difference between the redox potentials is less than 200 mV. The difference between the redox potentials corresponds to the thermodynamic driving force for the release of ions. The release of ions is, however, also determined by the kinetic properties of the surface, which influence the chemical behavior of the nanoparticles. 
         [0022]    For use of the arrangement as antibacterial “active compound” in the human or animal body, it is considered to be advantageous for the less noble metallic material of the two nanoparticles to be formed by silver since silver has an antibacterial action, in particular when together with chloride ions of an electrolyte it forms a silver chloride layer on the particle comprising silver. 
         [0023]    To avoid release of silver ions into the human body, the other metallic material should preferably not be much more noble than silver. A suitable partner material for silver is, for example, palladium which has a redox potential of 0.92 V. Since silver has a redox potential of 0.8 V, the difference between the two redox potentials is about 120 mV and therefore relatively low, so that release of silver ions from the silver particle occurs very slowly and/or is prevented for at least some period of time when a silver chloride layer can be formed on the silver particle. 
         [0024]    With a view to a very compact construction of the arrangement, it is considered to be advantageous for a plurality of nanoparticles to be arranged in the manner of a chessboard, for example on a flat or planar support surface, in such a way that each nanoparticle of one type is surrounded by four nanoparticles of the other type. In the case of such a positioning of the nanoparticles, a very low density of electrochemical cells per unit area of the support surface can be achieved. 
         [0025]    Further embodiments provide a process for producing an arrangement comprising nanoparticles. 
         [0026]    In this respect, it is provided according to various embodiments that at least two nanoparticles which each comprise a metal material and differ in respect of the metal material are applied at a distance from one another to a support surface of a support, where the two metal materials are noble to a different extent. 
         [0027]    As regards the advantages of the process resulting from the different nobility of the two metal materials, reference may be made to what has been said above in connection with the arrangement according to various embodiments. 
         [0028]    As already mentioned, the distance between the two nanoparticles is preferably set so that the two nanoparticles can form an electrochemical cell in an electrolyte. For example, the distance between the two nanoparticles is in the range from 5 μm to 10 μm. 
         [0029]    To avoid a situation where the support prevents formation of electrochemical cells between the nanoparticles or makes this difficult, it is considered to be advantageous for an electrically nonconductive material or a material which has poor electrical conductivity to be used as support material. 
         [0030]    As already mentioned, preference is given to using silver or a silver-containing material as the less noble metal material. As the more noble metal material, preference is given to using palladium, platinum, rhodium and/or ruthenium or a material which contains this metal or a plurality of these metals. 
         [0031]    Particular preference is given to applying a plurality of nanoparticles, namely at least two types of nanoparticles which comprise metal materials which are noble to a different extent, to the support surface. Each nanoparticle preferably has at least one nanoparticle of the other type arranged directly adjacent to it. 
         [0032]    As regards the formation of electrochemical cells, it is considered to be advantageous for the distance between each nanoparticle of the one type and the directly adjacent nanoparticle of the other type to be from 5 μm to 10 μm. 
         [0033]    In a particularly preferred variant, it is considered to be advantageous for a first perforated mask having a predetermined first arrangement of holes to be applied to the support surface of the support, for nanoparticles of a first metal material to be affixed to the support surface in the positions determined by the arrangement of holes, for a second perforated mask having a predetermined second arrangement of holes to be applied to the support surface and for nanoparticles of a second metal material to be affixed to the support surface in the positions determined by the second perforated mask. 
         [0034]    For example, the nanoparticles of the first metal material are formed in the holes of the first perforated mask by the first metal material being deposited on the support surface, in particular grown onto the support surface, in the region of the holes, and/or the nanoparticles of the second metal material are formed in the holes of the second perforated mask by the second metal material being deposited on the support surface, in particular grown onto the support surface, in the region of the holes. Growing on can be effected, for example, electrochemically in an electrochemical bath. 
         [0035]    As an alternative, finished nanoparticles of the first metal material can be introduced into the holes of the first perforated mask and affixed to the support surface, and/or finished nanoparticles of the second metal material can be introduced into the holes of the second perforated mask and affixed to the support surface. 
         [0036]    In another preferred variant, it is considered to be advantageous for an auxiliary layer which provides chemical coupling positions for each of the at least two types of nanoparticles, to which the nanoparticles can be chemically coupled, to be applied to the support surface, with the coupling positions being located at a distance from one another, for a mixture of finished nanoparticles of at least two metal materials which are noble to a different extent to be applied to the support surface provided with the auxiliary layer and for a nanoparticle distribution predetermined by the arrangement of the coupling positions on the auxiliary layer to be achieved on the support. 
         [0037]    For example, the auxiliary layer is formed by applying a polymer layer having a molecular structure which provides at least one coupling position for each of the two types of nanoparticles to the support surface. 
         [0038]    As an alternative, the auxiliary layer can be formed by applying a crosslinking material having self-assembling molecules which each provide at least one coupling position to the support surface. 
         [0039]    With a view to a maximum density of electrochemical cells per unit area, it is considered to be advantageous for the plurality of nanoparticles to be arranged in the manner of a chessboard so that each nanoparticle of one type is surrounded by four nanoparticles of the other type. 
         [0040]    In another preferred variant, it is considered to be advantageous for a mixture of finished nanoparticles of at least two metal materials which are noble to a different extent to be applied to a support provided with a perforated mask, and for a nanoparticle distribution which is predetermined by the stoichiometry, or is random or stochastic to be achieved on the support. 
         [0041]    In conjunction with  FIGS. 1 to 6 , a first example of a process for producing an arrangement comprising nanoparticles will now be described. 
         [0042]    In  FIG. 1 , it is possible to see a support  10  on which a first photomask  20  has been applied. The photomask  20  is structured and has holes  30 ; the photomask  20  thus forms a perforated mask. The structuring of the photomask  20  can be carried out in a customary way, for example by electron beam structuring, laser structuring or another optical structuring method. 
         [0043]    Nanoparticles  40  are then grown onto the support  10  which has been coated in this way, by applying a first metal material M 1  to the support  10 . The growing-on of the nanoparticles  40  can be effected in any way, for example in a vapor deposition step (e.g. CVD step) or a sputtering step. In addition, the deposition of the metal material M 1  can be aided magnetically or electrostatically. Deposition of the metal material M 1  by an electrochemical route, for example in an electroplating bath in the form of an “electroforming” step, is also possible. 
         [0044]    The structure provided with the nanoparticles  40  is shown in  FIG. 2 ; the first photomask  20  is still present. 
         [0045]    After deposition of the nanoparticles  40 , the first photomask  20  is removed completely and a second photomask  50  is subsequently applied. The second photomask  50  is likewise structured so that holes  60  are formed. During the application of the second photomask or perforated mask  50 , the nanoparticles  40  which have been deposited in the preceding step are embedded in the second photomask  50 ; this is shown schematically in  FIG. 3 . 
         [0046]    In a second deposition step, nanoparticles  70  of a second metal material M 2  are then deposited; these nanoparticles  70  therefore form a different type of nanoparticles. The growing-on of the second metal material M 2  is carried out in a manner comparable to the growing-on of the first metal material M 1 , i.e., for example, as has been described in relation to  FIG. 2 . The resulting structure is shown in  FIG. 4 . 
         [0047]    After detachment of the second perforated mask  50 , there remains a finished arrangement  90  in which nanoparticles  40  of a first metal material M 1  and nanoparticles  70  of a second metal material M 2  have been applied to the support  10 . The distance between nanoparticles of different metal materials is denoted by the reference sign A in  FIG. 5 . The spacing A is preferably from about 5 to 10 μm. 
         [0048]    The two materials M 1  and M 2  are selected so that the redox potentials of the two materials M 1  and M 2  are different. In the following, it is assumed by way of example that the first material M 1  of the nanoparticles  40  is a metal which is less noble, or a metal alloy which is less noble, than the second material M 2  of the nanoparticles  70 . 
         [0049]    The property of a metal of being noble or not noble is indicated by the respective redox potential or the electrochemical potential series; the following list, which is illustrative and not intended to be conclusive, of metals suitable for nanoparticles is ordered from not noble to noble or in order of increasing redox potentials (redox potential versus standard hydrogen electrode at 25° C.): 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 lithium 
                   −3 V 
               
               
                   
                 magnesium 
                 −2.4 V 
               
               
                   
                 aluminum 
                 −1.7 V 
               
               
                   
                 zinc 
                 −0.8 V 
               
               
                   
                 silver 
                 +0.8 V 
               
               
                   
                 palladium 
                 +0.9 V 
               
               
                   
                   
               
             
          
         
       
     
         [0050]    A material which is very suitable, in particular with a view to medical applications, is, for example, silver since silver or silver ions has/have an antibacterial action. Accordingly, it is assumed below by way of example that silver is used as first not noble material M 1  since the less noble material can release ions in an electrolyte in an electrochemical cell. 
         [0051]    The second material M 2  of the nanoparticles  70  is accordingly a more noble metal, for example gold or palladium. Palladium has a redox potential of 0.92 V, which is relatively similar to that of silver so that the difference D between the redox potentials of the two materials M 1  (silver) and M 2  (palladium) is only D=120 mV. 
         [0052]    If the structure  90  as shown in  FIG. 5  is brought into contact with an electrolyte by, for example, introducing it into the human body, the silver material M 1  will react with chloride ions, which are always present in body fluids or cell fluids of the human body, of the electrolyte so that a highly chemically stable silver chloride layer will form on the nanoparticles  40 . This silver chloride layer will separate the surface of the nanoparticles  40  from the electrolyte, so that direct release of silver ions from the nanoparticles  40  into the electrolyte is prevented or at least greatly slowed. The formation of the silver chloride layer on the surface of the nanoparticles  40  thus ensures that no unacceptably high release of silver ions into the human body can occur. Nevertheless, an antibacterial effect is achieved since the silver chloride layer itself acts as a bactericide. 
         [0053]    Instead of the silver/palladium materials combination described, it is also possible to use other materials combinations, in particular ones based on silver, in order to display an antibacterial action: other suitable materials combinations are, for example, silver-platinum, silver-ruthenium and silver-rhodium. 
         [0054]    In the selection of the materials, it should preferably be ensured that, when silver is used, the not noble material of the two materials M 1  and M 2  is formed by the silver so that it can generate ions and/or form the silver chloride layer described. In addition, the difference between the redox potentials should not be too great. Potential differences which are too great increase the reactivity of the electrochemical cell, so that excessively rapid release of silver ions which may be too high for human or animal bodies could occur. The potential difference is preferably less than 500 mV. 
         [0055]      FIG. 6  shows the resulting structure  90  from above. It can be seen that the nanoparticles  40  and the nanoparticles  70  are arranged in the manner of a chessboard so that each nanoparticle of one type is surrounded by four adjacent partner nanoparticles of the other type. 
         [0056]    In conjunction with  FIGS. 7 to 11 , a second example of the production of an arrangement comprising nanoparticles will now be described. 
         [0057]    In  FIG. 7 , it is possible to see a support  10  to which a perforated mask  100  has been applied. The perforated mask  100  can again be formed by an appropriately structured photomask. 
         [0058]    A mixture of finished nanoparticles  110  is then applied to the support  10  provided with the perforated mask  100 . The mixture  110  comprises nanoparticles  40  of a first metal material M 1  and nanoparticles  70  of a second metal material M 2 . The mixture has such a composition that the number of nanoparticles of the first metal material M 1  corresponds approximately to the proportion of nanoparticles of the second metal material M 2 . 
         [0059]    The mixture  110  is then applied to the support  10  provided with the perforated mask  100  so that the openings or holes  120  of the perforated mask  100  are filled with the nanoparticles  40  or  70 . The distribution of the nanoparticles  40  or  70  in the openings  120  is random and depends essentially on the composition of the mixture  110 . The resulting structure after application of the mixture  110  is shown schematically in  FIG. 9 . 
         [0060]      FIG. 10  shows the arrangement comprising the support  10  and the nanoparticles  40  and  70  after the perforated mask  100  has been removed. To affix the nanoparticles  40  or  70  to the support surface  130  of the support  10 , the nanoparticles can be affixed by means of an additional fixing material. Such a fixing material is not shown further in  FIG. 10  for reasons of clarity. 
         [0061]      FIG. 11  shows, in plan view, the distribution of the nanoparticles  40  and  70  on the support surface  130  of the support  10 . It can be seen that, in contrast to the first example shown in  FIGS. 1 to 6 , the nanoparticles are not distributed in the manner of a chessboard but are distributed randomly. The distribution of the nanoparticles on the support surface  130  is determined by the random distribution or composition of the mixture  110  of the nanoparticles  40  and  70 . 
         [0062]    In conjunction with  FIG. 12 , a third example of a process for producing an arrangement comprising a support and nanoparticles will now be described. A support  10  to which an auxiliary layer  200  has been applied can be seen in  FIG. 12 . The auxiliary layer  200  is, for example, a polymer layer which comprises chain-like molecules  210 . The chain-like molecules  210  are aligned along or parallel to the support surface  130  of the support  10 . As can be seen in  FIG. 12 , the chain-like molecules  210  are provided with a plurality of coupling positions  220  and  230  to which nanoparticles can couple. 
         [0063]    In the example shown in  FIG. 12 , it is assumed by way of example that the coupling positions  220  are suitable or designed for coupling to silver nanoparticles  240  and that the coupling positions  230  are suitable or designed for coupling to palladium nanoparticles  250 . The corresponding coupling possibilities are shown schematically in  FIG. 12  by the shape of the coupling positions  220  and  230  or by the shape of the corresponding countercoupling positions of the palladium nanoparticles  250  and the silver nanoparticles  240 . 
         [0064]    In the third example as shown in  FIG. 12 , it is assumed that the auxiliary layer  200  is specifically suitable for coupling of palladium nanoparticles  250  and silver nanoparticles  240 ; of course, it can be ensured by means of an appropriate configuration of the molecular structure of the chain-like molecules  210  that other types of nanoparticles can be attached in a corresponding way. 
         [0065]    A suitable material for the auxiliary layer  200  is, for example, cetyltrialkylammonium bromide. 
         [0066]    After the support  10  has been provided with the auxiliary layer  200  described, a mixture of finished nanoparticles  240  and  250  is applied to the auxiliary layer  200 . Owing to the coupling points  220  and  230  provided by the auxiliary layer  200 , the nanoparticles  240  and  250  are correspondingly coupled to the auxiliary layer  200 , so that they become attached in a predetermined manner to the support  10 . The arrangement  90  comprising the support  10  and the nanoparticles  240  and  250  is then finished. 
         [0067]    In conjunction with  FIG. 13 , a fourth example of a process for producing an arrangement  90  comprising a support  10  and nanoparticles will now be described. In this example, an auxiliary layer  400  formed by a crosslinking base material  410  with self-assembling molecules  420  present therein is applied to the support surface  130  of the support  10 . The auxiliary layer  400  thus itself forms a self-assembling layer. 
         [0068]    The self-assembling molecules  420  are configured so that they couple by a molecule end  430  to the support surface  130  of the support  10 . By means of another molecule end  440 , they form a coupling position to which the nanoparticles having an appropriate countercoupling position can couple. The left-hand molecule  420 ′ in  FIG. 13  forms, for example, a coupling position  220  for the silver nanoparticles  240  and the middle molecule  420 ″ in  FIG. 13  forms, for example, a coupling position  230  for the palladium nanoparticles  250 . 
         [0069]    The molecules  420  also have functional groups f which fix the distance A between the molecules  420 . The distance A between the molecules  420  thus at the same time defines the spacing A which the nanoparticles  240  and  250  will have on the support  10 . 
         [0070]    After coupling of the nanoparticles  240  or  250  to the molecules  420  and thus to the support  10 , the base material  410  can be removed so that only the molecules  420  and the nanoparticles  240  and  250  are now present on the support  10 . 
         [0071]    A suitable material for the auxiliary layer  400  is, for example, material having oligomeric chains comprising polythiophene derivatives.