A Method For The Manufacture Of Patterned Functional Monolayer Structures And Products Thereof

Description

Title: A method for the manufacture of patterned functional monolayer structures and products thereof

CROSS-RELATION TO OTHER APPLICATIONS

[0001] The present invention claims priority from pending German patent application number 102007022251.5.

FIELD OF INVENTION

[0002] The present invention relates to a method for the manufacture of patterned functional monolayer structures and products made thereof.

PRIOR ART

[0003] The manufacture of monolayer nanostructures is known in the literature. For example, international patent publication number WO2008/013959, which is titled "Method and devices for forming nanostructure monolayers and devices including such monolayers' is assigned to NANOSYS Inc. of the USA. The method of the Nanosys patent application for forming or patterning nanostructure arrays discloses the steps of: a) Depositing resist and a monolayer of nanostructures on a first layer, wherein the nanostructures are embedded in the resist, to provide a resist layer, b) exposing a predetermined pattern on the resist layer (e.g. to ionising radiation such as ultraviolet light or an electron beam, to provide exposed resist in at least a first region of the resist layer and an unexposed resist in at least a second region of the resist layer, c) removing the unexposed resist and its embedded nanostructures from the first layer without removing the exposed resist and its embedded nanostructures, whereby at least one nanostructure monolayer array defined by the first region remains on the first layer, and d) after step c), exposing the first layer, the exposed resist and its embedded nanostructures to a temperature of at least about 3000C (e.g. about 7000C or at least 9000C). [0004] United States patent application publication number US 2007/0254169 Al is assigned to Hewlett Packard Company of the USA and is titled "Structures including organic self-assembled monolayers and methods of making the structures". The Hewlett Packard patent application discloses a structure, including a self assembled monolayer comprising a substrate including a nano patterned surface; and a self assembled monolayer of an organic material on the nano patterned surface. The self assembled monolayer is ordered with respect to features of the nano patterned surface. Furthermore the HP patent application describes a filament switching device comprising a lower electrode having a nano patterned surface, a self assembled monolayer of an organic material formed on the nano patterned surface, wherein the self assembled monolayer is ordered with respect to features of the nano patterned surface; and an upper electrode formed on the self assembled monolayer. The HP patent application also discloses a method of making a structure including a self assembled monolayer, which comprises forming a self assembled monolayer on an organic material on a nano patterned surface of a substrate, wherein the self assembled monolayer is ordered with respect to features of the nano patterned surface.

BACKGROUND OF INVENTION

[0005] Chemical surface nanostructures often consist of distinct areas that expose different chemically reactive groups. These distinct areas provide templates for the spatially defined fabrication of a plethora of different functionalities of the chemical groups by allowing the attachment of biomolecules, supramolecular complexes or other organic or inorganic nanoparticles with nanometre precision.

[0006] The manufacture of chemical surface nanostructures is an area of extensive research; (see, for example, Chem. Soc. Rev. 2006, 35, 29 by Garcia et. al. and Phys. Chem. 2007, 9, 207 by Woodson et. al.).

[0007] However, there still remains an inherent need to overcome the challenges associ- ated with the manufacture of chemical surface nanostructures that comprise functional self assembled monolayers with nanometre resolution on large surface areas rapidly and efficiently (see, for example, Angew. Chem. Int. Ed. 1998, 37, 550 by Xi et. al). [0008] Efficient and fast methods for the manufacture of patterned functional monolayer nanostructures that comprise functional self assembled monolayers with nanometre resolution on large surface areas are therefore desirable.

[0009] Nanostructures of functional self assembled monolayers can be based on, for example, alkyltrichlorosilanes, alkylmethoxysilanes and alkylethoxysilanes and/or molecules with thiol, carboxyl or amino end groups having potential applications in the fields of binding metal nanoparticles (gold and silver), biomolecules (such as peptides), (see ,for exam- pie, Langmuir 2003, 19, 4217 by Pavlovic et.al.). Examples of self assembled monolayers include, but are not limited to, 11-bromoundecyltrichlorosilane, aminopropyltrimethoxysi- lane and undecenyltrichlorosilane. Where the binding of materials is required, the self assembled monolayers require a specific surface of nanometre scale precision to facilitate reproducible binding.

[0010] Potential applications of nanostructures of functional self assembled monolayers are seen, for example, in the selective binding of molecules for the manufacture of bio- chips, protein nano-arrays and components for sensor applications.

[0011] It remains a challenge to increase the precision of chemical nanostructure fabrication in the range below 50nm, but also to produce nanostructures with different functional monolayer nanostructures, i.e. with different chemical functional groups on the monolayer. Such a manipulation of the monolayer by altering its functional group allows the monolayer to be tailored to bind with a wide range of chemical substances, especially in the area of bimolecular binding. The binding would enable the optimisation of the interaction between the functional group and consequently tuning the physical-chemical properties of the functional groups allowing for the fabrication of a large diversity of functional monolayer nanostructures.

[0012] These challenges are addressed by means of fabricating a patterned functional monolayer nanostructure utilising a combination of chemical and lithographic techniques that allows for the deposition of a patterned functional monolayer nanostructure that can be further functionalised as required whilst still maintaining nanometre precision across the patterned functionalised monolayer.

SUMMARY OF INVENTION

[0013] The present invention teaches a method for the manufacture of structures on a substrate. The manufacture process starts with depositing an inhibition layer over a patterned mask. The patterned mask is then removed. In this way an inhibition layer is formed which covers those areas of the substrate where the substrate was not covered by the patterned mask. The substrate is exposed to the surface where it is not covered by the inhibition layer. A first self assembled monolayer is deposited on the substrate. The inhibition layer is removed and the substrate is exposed to the surface where it was covered by the inhibition layer before its removal. Upon removal of the inhibition layer a second self assembled monolayer is then deposited.

[0014] The method allows the manufacture of a structure with nanometre precision. The structure can be further functionalised by chemical modification whilst still maintaining the nanometre precision of the patterned functionalised monolayer.

[0015] It has been observed to be not a trivial task to form structures with small structural surface features with dimensions in the nanometre range. The present application discloses several aspects of such nanostructures with small structural surface features.

[0016] In one aspect of the invention a surface charge pattern of different surface charges is created on a surface of the substrate. This surface charge pattern may serve to bind selectively chemical substances of opposite charge with different chemical end groups (functional groups). The surface charge pattern exposes two different chemical end groups at the surface and therefore produces a chemical pattern in an aspect of the present invention. Since, however the electrostatic interactions have a long range, which can extend to several 100 nanometres, the binding of charged substances to one of the surface feature of opposite charge does not necessarily occur with a high spatial resolution. It is therefore possible in this aspect to create chemical micro structures (i.e. surface features with dimensions in the micrometer range) in this way but it is very difficult to create chemical nanostructures. The creation of the chemical nanostructures depends on the strength of the ionic bond of the oppositely charged chemical groups and there is a gradual transition between rather weak purely electrostatic interactions between oppositely charged groups and a strong ionic chemical bond which depends on the exact composition of the oppositely charged end groups.

[0017] A second aspect of the present invention is to form a bifunctional chemical nanos- tructure by functionalisation of a functional self- assembled molecule (SAM) with a chemi- cally reactive end group at selective sites on the functional SAM. The functionalisation of the SAM is achieved by a chemical reaction of the chemically reactive end group of the SAM such that this chemically reactive end group is modified and a different end group is formed which has different chemical properties than the first functional group. One known problem which may occur in this aspect is that the modification reaction of the chemically reactive end group occurs only with a limited yield. The result is that the modification of the chemically reactive end group takes place only at a limited number of the selective sites. The invention comprises several further aspects to perform the modification of the chemically reactive end group at selective sites.

[0018] In a third aspect of the invention, the creation of a bifunctional chemical nanostruc- ture is disclosed. In this aspect, the substrate is covered with an inhibition layer and a first SAM is formed on the exposed substrate. The inhibition layer is removed and a second SAM with a different functional group is formed at the newly exposed substrate. The yield of this self assembly process can be very high. A bifunctional nanostructure is obtained in which the areas of the surface are covered with two different types of silanes which are densely packed with the respective silane molecules.

DESCRIPTION OF DRAWINGS

[0019] Figure 1 depicts a schematic for the manufacture of patterned functional monolayer nanostructures according to the present invention. [0020] Figure 2 illustrates a flow diagram of the method of manufacture of patterned functional monolayer nanostructures according to the present invention.

[0021] Figure 3 illustrates tapping-mode AFM images of the inhibition layer of gold metal produced by nanosphere lithography a) before the deposition of the OTS monolayer on the substrate, b) after the deposition of the self assembled unfunctionalised OTS monolayer, c) grazing angle FTIR spectrum after deposition of the self assembled OTS monolayer on the substrate where the inhibition layer is still present.

[0022] Figure 4 illustrates contact- mode AFM images of the substrate: a) after removal of the inhibition layer and b) representative height profile.

[0023] Figure 5 illustrates contact- mode AFM images: a) height and b) corresponding friction images of the OTS/bromine structure, c) friction image after the conversion of the bromine to thiocyanate and d) to thiol and the line profiles bellow for comparison.

[0024] Figure 6 shows a method of manufacturing a patterned functional monolayer structure with more than two functions.

DETAILED DESCRIPTION OF THE INVENTION

[0025] For a complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the figures.

[0026] It should be appreciated that the aspects of the invention discussed herein are merely illustrative of specific ways to make and use the invention, and do not therefore limit the scope of the invention when taken into consideration with the claims and the following detailed description including the examples of the present invention. In particular it should be noted that the features found in aspects of the present invention can be combined with features for other aspects of the invention.

[0027] The teaching of the prior art cited herein are incorporated by reference. [0028] The patent application teaches three different aspects of the invention to create patterned functional nanostructures 100 on the surface of a substrate 120.

[0029] A first aspect of the invention involves the creation of a surface charge pattern of different surface charges on the surface of the substrate 120. The surface charge pattern may serve to bind selectively chemical substances of the opposite charge with different chemical end group's i.e. different functionalities. The surface charge pattern exposes two different types of chemical groups at the surface of the substrate 120 and is therefore a chemical pattern (in the sense of the application). Since, however the electrostatic interactions have a long range, which can extend to several hundred nanometres, the binding of charged substances to a surface feature of opposite charge does not necessarily occur with a high spatial resolution. As discussed in the introduction, it is therefore possible to create chemical microstructures in this way, but it is very difficult to create chemical nanostruc- tures. The invention includes this possibility of forming self assembled monolayers with a charged end group, such as a negatively charged carboxylate group or a positively charged amino group. Another possibility to create charged nanostructures is by first forming a functional SAM with a chemically reactive end group and to functionalise this SAM according to the second aspect of the invention in two steps at selected sites to form posi- tively or negatively charged end groups.

[0030] In a second aspect of the invention a bifunctional chemical nanostructure is formed by functionalisation of a functional SAM with a chemically reactive end group at selective sites. The functionalisation is achieved by a chemical reaction of the chemically reactive end group of the SAM such that this chemically reactive end group is modified and a different end group is formed which has different chemical properties than the initially chemically reactive end group . The modification reaction may occur with a limited yield, such that the modification takes place only at a limited number of the selective sites. To perform the modification at selective sites the invention describes different possibilities.

[0031] It is possible, for example, to make the SAM of a functional silane with a chemically reactive end group like 11-bromo undecyltrichlorosilane as described below. This SAM may be covered with an inhibition layer (i.e. an inhibition nanostructure). The formation of the inhibition layer on the basis of latex bead projection patterns is carried out as follows. In this case a patterned mask 110 of closely packed latex spheres is not directly deposited on the SAM but the patterened mask 110 is transferred from a different substrate as described in the journal Surface Interface Analysis 2002; 33, p75 - 80, by Fischer et. al. The inhibition layer 130 is then formed from the mask of closely packed latex spheres. The subsequent chemical reaction may serve to replace the bromine end group by a different functional group such as a thiol group. After removal of the inhibition layer 130 a bifunc- tional chemical nanostructure is obtained with two different functional groups, the bromine end group and the thiol end group. It has been found that in such a chemical reaction all the bromine end groups are modified. This occurs only to a certain percentage.

[0032] An alternative is to fabricate a bifunctional chemical nanostructure by chemical modification of the functional SAM in a slightly different way. First the SAM of a func- tional silane with a reactive end group such as 11-bromo undecyltrichlorosilane is made on the substrate 120 which is covered with the inhibition layer 130 (as discussed above). The SAM is only formed at the sites which are not covered by the inhibition layer 130. Then a functionalisation of the SAM is made by a chemical reaction of the bromine end groups such that they are replaced by thiol end groups as discussed below. The inhibition nanos- tructure is removed and a self assembled monolayer of a functional silane with a reactive end group like 11-bromo undecyltrichlorosilane is formed on the newly exposed substrate 120. In this way a bifunctional chemical nanostructure is obtained with two different functional groups, the thiol and bromine group.

[0033] In a third aspect of the invention, a bifunctional chemical nanostructure is created. In this aspect of the invention, the substrate 120 is covered with the inhibition layer 130 and the first SAM is formed on the exposed substrate 120. The inhibition layer 130 is removed and a second SAM with a different functional group is formed at the newly exposed substrate 120. As the yield of the self assembly process can be very high, a bifunctional nanostructure is obtained. The area of the surface is covered with the two different types of silanes and is densely packed with the respective silane molecules. [0034] The invention will now be described in more detail.

[0035] Figure 1 depicts a schematic for the manufacture of patterned functional monolayer nanostructures 100 according to the present invention. Figure 1 should be referred to in conjunction with Figure 2 which illustrates a flow diagram of the method 200 of manufacture of the patterned functional monolayer nanostructures 100 according to the present invention.

[0036] The method 200 for the manufacture of patterned functional monolayer nanostruc- tures 100 commences as in step 205. Step 210 involves creating the patterned mask 110 on the substrate 120. The creation of the patterned mask 110 on the substrate 120 according to the present invention has been previously described in the journal Surface Interface Analysis 2002; 33, p75 - 80, by Fischer et. al.. This patterned mask 110 creation technique combines the advantage that the technique provides patterning of a large surface area by a self organisation phenomenon, with inherently high resolution of patterning by physical vapour deposition. Hereby, the negatively charged latex spheres 105 are transferred to a hydro- philic substrate 120. The negatively charged latex spheres 105 spontaneously self organise into a hexagonal pattern during evaporation of a solvent. After the self organisation of the negatively charged latex spheres 105, the result is an array of resultant patterned apertures between the hexagonally organised latex spheres 105. These apertures exhibit a triangular shape as disclosed by Fischer et. al in Surface Interface Analysis 2002; 33, p75 - 80. This self organisation serves as the patterned mask 110 on the substrate 120, for the subsequent deposition of an inhibition layer 130 by evaporation through the apertures.

[0037] It will be appreciated that the patterned mask creation technique is not restricted to hexagonal or other periodic patterns and that many variations are possible. Examples of the many variations include, but are not limited to statistically distributed circular holes and random structures and are described in Fischer et. al in Surface Interface Analysis 2002; 33, p75 - 80. It will also be appreciate that the invention does not require the "nanosphere lithography" discussed above as a lithographic technique. Any technique which creates the removable patterened mask 110 can be used. [0038] The substrate 120 according to an aspect of the present invention is selected from one of the following materials glass, silica, silicon dioxide, mica, quartz, aluminium oxide, indium, tin oxide, tungsten oxide or titanium oxide. It will be noted that the oxides may have catalytic functions and also that titanium oxide may be used for light energy conver- sion. The substrate 120 may also comprise polymer substrates terminated with -OH groups, such as those created by plasma treatment (e.g. poly(tetrafluoroethylene) described in ref. Bin Zhao (1) ; Brittain W. J. (1) ; Vogler E. A. (1) Macromolecules, 1999, 32, 796- 800 ).

[0039] The use of the latex spheres 105 for the formation of a patterned mask 110 for metal deposition provides a simple and highly efficient means for forming the patterned mask 110. The patterned mask 110 produces apertures reproducibly and in large numbers, with aperture diameters in the range of 10 - lOOOnm.

[0040] The next stage 215 is the deposition of an inhibition layer 130 over the patterned mask 110 onto the substrate 120. It will be appreciated that the inhibition layer 130 can be formed in an alternative aspect of the invention by non-metallic materials suitable for this purpose. During the deposition of the inhibition layer 130 onto the substrate 120, the material of the inhibition layer 130 forms a contact with the substrate 120 only in those areas which were not covered by the patterned mask 110 i.e. the apertures formed by the hexagonal arrangement of the latex spheres 105. The resultant inhibition layer 130 is only formed in the apertures which are resultant of the closely packed latex spheres 105.

[0041] The inhibition layer 130 comprises a material such as gold, silver or aluminium. In the case that a non purely metallic layer is used as the inhibition layer 130, then the material can be selected from one of aluminium oxide or lithium fluoride.

[0042] In a further aspect of the present invention other materials deposited by physical vapour deposition, electron beam bombardment, or ion sputtering can be used as the inhi- bition layer 130. [0043] In a further aspect of the present invention the inhibition layer 130 is deposited on the substrate 120 in an atmosphere that is oxygen rich. The use of an oxygen rich atmosphere in the aspect of the invention where the inhibition layer 130 comprises aluminium ensures that the inhibition layer 130 is deposited with a uniform and fine aluminium parti- cle size. This is due to the fact that the oxygen promotes the formation of aluminium oxide. The aluminium oxide inhibits the growth of aluminium crystals during the aluminium deposition. This leads to fine films of an aluminium inhibition layer 130 with fine grains that promotes better results with regards to reproducibility and allows for the control of particle size of the aluminium inhibition layer 130 on the substrate 120. Alternatively the aluminium oxide can be deposited as an inhibition layer 130 by sputtering techniques.

[0044] The removal step 220 of the patterned mask 110 reveals a patterned projected inhibition layer 130a - 13Oz on the substrate 120 which serves as the inhibition layer 130. The removal 220 of the patterned mask 110 is achieved by applying an organic solvent, such as methylene chloride (CH2Cl2), in combination with ultrasonic treatment of the substrate 120. It will be noted that there are also other methods to remove the patterned mask 110.

[0045] In a further aspect of the present invention the removal 220 of the patterned mask 120 is achieved by dipping the substrate 120 into distilled de-ionised water such that the patterned mask 110 floats on the distilled de-ionised water surface.

[0046] In the next stage 225, a self assembled monolayer 140 is deposited on the substrate 120 and possibly also on the inhibition layer 130 for the case of an oxidic material where a chemical binding of a silane is possible. If the inhibition layer 130 comprises gold, then no silane bond is formed and thus the self-assembled monolayer 140 will only be formed on the exposed areas of the substrate 120. The self assembled monolayer 140 is deposited by a silane self assembly process from solution.

[0047] The self assembled monolayer 140 in an aspect of the present invention comprises w-octadecyltrichlorosilane (OTS). The self assembled monolayer 140 can also comprise

11-undecyltrichlorosilane, aminopropyltrimethoxysilane, undecenyltrichlorosilane, fluoro- alkylsilanes or other alkyltrichlorosilanes or alkylmethylsilanes or alkylethylsilanes. The self assembled monolayer 140 is deposited on areas of the substrate 120 that previously were covered by the patterned mask 110. Atomic force microscopy (AFM) height imaging (see Figure 3) reveals this new structure of the self assembled monolayer 140 on the substrate 120. This suggests the formation of a densely packed self assembled monolayer 140 on the substrate 120. This observation is additionally confirmed by grazing angle FTIR spectroscopy (Figure 3c) with the infrared peak positions of the alkyl CH2 group vibrations of the alkyl chains within the unfunctionalised self aseembled monolayer 140 (in an aspect of the present invention where the inhibition layer 130 is gold) The peak positions of the CH2 vibrations are observed at 2850 cm"1 and 2918 cm"1. These values are in agreement with values reported for a well packed monolayer of an w-octadecyltricholosilane as disclosed by R A MacPhail et al. J Phys Chem 1984, 88, 334.

[0048] The next step 230 involves the removal of the projected metallic layer (inhibition layer) 130a - 13Oz from the substrate 120 to expose a pattern 120a - 120z on the surface of the substrate 120. The projected inhibition layer 130a - 13Oz can be removed from the substrate 120 by mechanical wiping of the substrate 120 with a tissue saturated in an organic solvent, such as acetone.

[0049] In a further aspect of the present invention the projected inhibition layer 130a - 13Oz can be removed from the substrate 120 by spin coating a thin polycarbonate film on the substrate 120. This is followed by the removal of the thin polycarbonate film. The projected inhibition layer 130a- 13Oz is embedded within the removed thin polycarbonate film. In the aspect where the thin polycarbonate film is used, water or another aqueous solution, such as an acidic solution, is used as a solvent and the water penetrates between the thin polycarbonate film with the inhibition layer 130 and the substrate 120, thus functioning as a lever to facilitate the separation of the inhibition layer 130 from the substrate 120. The thin polycarbonate film with the inhibition layer 130 is then floated onto a water surface and the substrate 120, immersed into the water, is removed from the water and dried.

[0050] This removal 230 of the projected inhibition layer 130a - 13Oz from the substrate 120 has been previously reported Fischer et. al in Surface Interface Analysis 2002; 33, p75 80.

[0051] In each case the complete removal of the projected inhibition layer 130a - 13Oz, as in step 120 is achieved and can be confirmed by AFM investigations of the structures of the substrate 120 after the removal step 230. The removal of the inhibition layer 130 results in this aspect of the invention in a hexagonally arranged pitted pattern 120a - 120z. The hexagonally arranged pitted pattern 120a - 120z is a result of the self organisation of the patterned mask 110 as described above.

[0052] The hexagonally arranged pitted pattern 120a - 120z can be observed in contact mode AFM images (see Figure 4). A typical height difference between the self assembled monolayer 140 of w-octadecyltrichlorosilane and the exposed substrate 120 shows a height difference of around 2.8nm (see Figure 4b), which is in good agreement with the estimated thickness of a well ordered monolayer.

[0053] The substrate 120 thus comprises an w-octadecyltrichlorosilane self assembled monolayer 140 formed in the former position of the apertures of the patterned mask 110. The hexagonally arranged pitted pattern 120a - 120z resembles areas of a triangular form, from where the inhibition layer 130 was removed. The triangular form of the hexagonally arranged pitted pattern 120a - 120z is a result of the shape of the apertures formed by the self organised latex spheres 105 of the patterned mask 110.

[0054] The hexagonally arranged pitted pattern 120a - 120z, exposes the substrate 120 such that the pitted pattern 120a - 120z of the substrate 120 can be used for receiving the deposition of a second monolayer i.e. the deposition of a self assembled monolayer 150 as in step 235.

[0055] The next step of the method for the manufacture of patterned functional monolayer nanostructures 100 involves the deposition of a further (second) self assembled monolayer 150 on the pitted pattern 120a - 120z of the substrate 120 in step 235. [0056] In an aspect of the present invention the second self assembled monolayer 150 comprises 11-bromo undecyltrichlorosilane. The second self assembled monolayer 150 can also be selected form a group consisting of w-octadecyltrichlorosilane, aminopropyl- trimethoxysilane, undecenyltrichlorosilane, fluoroalkylsilanes or other alkyltrichlorosilanes or alkylmethylsilanes or alkylethylsilanes. The second self assembled monolayer 150 comprises chemically functionalised groups that can be further functionalised be further chemical conversion reactions. The self assembled monolayer 150 is deposited as in step 235 by immersing the substrate 120 in a solution of the silane molecules 150, for 5 minutes, followed by sonication in an organic solvent.

[0057] The advantage of the nanostructure 100 on the substrate 120 is that the substrate 120 can be used in a number of further chemical reactions to alter the functionality of the functionalised monolayer 150. An advantage of having the patterned second self assembled monolayer 150 is that the functionality of the patterned second self assembled monolayer 150 can be manipulated for further investigations. Such applications are the use of the present invention in the binding of biomolecules to build biochips, protein nano-arrays and components for sensor applications as described above. Such applications require a specific size and spatial arrangement which is achieved by the aspects of the present invention.

[0058] In an aspect of the present invention the conversion of the second self-assembled monolayer 150 of 11-bromo undecyltrichlorosilane into a differently functionalised monolayer is achieved by a two- stage reaction 240a and 240b. This two- stage reaction proceeds exclusively in the areas where the 11-bromo undecyltrichlorosilane (i.e. the second self-assembled 150) is deposited on the substrate 120.

[0059] Such further functionalisation of the second self assembled monolayer 150 proceeds as in step 240a. In an aspect of the present invention the chemical conversion to form different functional groups is investigated by means of friction force microscopy.

[0060] The changes of the surface properties of the substrate 120 cause changes in the friction force images which have been acquired with comparable conditions for all func- tionalisation steps. The friction force analysis of the modification of the bromine terminated patterned functional monolayer nanostructure 100 on the substrate 120 clearly shows that the characteristic shape of patterned functional monolayer nanostructures 100 is completely preserved during the functionalisation process. Therefore a further advantage if the present invention is that despite the harsh reaction conditions, the pattern of the monolayers are not hindered (see Figure 5).

[0061] The bromine terminated end group of the patterned functional monolayer nanostructure 100 can be converted by a chemical reaction to produce a variant of the patterned functional monolayer nanostructure 100 as in step 240a. In an example of the present invention the bromine is substituted by a thiocyanate. In contact mode AFM friction image (see Figure 5c) a higher contrast is observed, as the polarity of the thiocyanate is slightly higher than for the bromine terminated patterned functional monolayer nanostructure.

[0062] In a further aspect of the present invention additional functionalisation of the second self-assembled monolayer 150 can be achieved again in step 240b. In an embodiment of the present invention the thiocyanate can be reduced to a thiol to render a patterned thiol functional monolayer nanostructure 100. In contact mode AFM friction image (see Figure 5c) a higher contrast is observed, as the polarity of the thiol group is slightly higher than for the thiocyanate terminated patterned functional monolayer nanostructure 100.

[0063] Further functionalisation routes of the patterned functional monolayer nanostructure 100, as in step 240a or step 240b, can be carried out depending on the desired functionality of the patterned functional monolayer nanostructure 100.

[0064] It should be noted that the choice of an w-octadecyltrichlorosilane as a self assembled monolayer 140 is one of a number of possible options. Instead of the self assembly of a chemically inactive monolayer i.e. the first self-assembled monolayer 140 such as an n- octadecyltrichlorosilane, also silane molecules bearing a chemically active functional group can be employed. This allows for additional possibilities to tailor the substrate 120 with differently functionalised monolayers. [0065] In a further aspect of the present invention it should be noted that where the inhibition layer 130 comprises gold or silver, the inhibition layer 130 can be removed from the substrate 120 by using an organic solvent. Furthermore, the inhibition layer 130 can be removed from the substrate 120 by spin coating methods as described. However when the inhibition layer 130 comprises aluminium, the aluminium is removed with an acid. It should be realized that these harsh removing techniques of the inhibition layer 130 do not hinder nor affect the patterning of the self assembled monolayer 140 present on the substrate 120. It should also be noted that the inhibition layer 130, and/or the projected inhibition layer 130a - 13Oz are inert with respect to the organic solvent used for the manufacture of the first and second self assembled monolayers 140 and 150. Thus not only the metals are resistant to the chemicals used in the manufacture of patterned chemical nanostruc- tures, an advantage is that they are very easily removed by abrasion and interestingly the first self assembled monolayer 140 is not affected by such abrasive techniques.

EXAMPLES

[0066] Polystyrene latex spheres of around 0.22 μm were obtained from the BASF Company, 11-bromo undecyltrichlorosilane from ABCR, w-octadecyltrichlorosilane from ABCR, potassium thiocyanate from Fluka, lithium aluminium hydride from Sigma Aldrich in tetrahydrofuran from Biosolve, hydrochloric acid from Fluka, DMF from Biosolve, ethanol from Sigma Aldrich, and chloroform from Biosolve were purchased Bicyclohex- ane (BCH) was distilled over sodium before use. Double side polished p-type silicon wafers were obtained from UniversityWafer, Microscope cover glasses were obtained from PLANO. The substrate 120 was sonicated for 30 minutes at 70 0C in a 1% detergent solu- tion prior to use. The substrate 120 with the deposited inhibition layer 130 was treated on both sides in a UV/Ozone chamber before the deposition of a first self assembled monolayer 140.

Example 1

[0067] The w-octadecyltrichlorosilane monolayers 140 were produced by immersion of the glass substrate 120 in a solution of w-octadecyltrichlorosilane (5 μL) in BCH (5mL) for 5 mins followed by sonication in toluene. The substrate 120 comprising the monolayer 140 was dried in air before the procedure repeated twice.

Example 2

[0068] The 11-bromo undecyltrichlorosilane patterned functional monolayer nanostruc- tures 100 was manufactured by immersion of the glass substrate 120 in a solution of 11- bromo undecyltrichlorosilane (5 μL) in BCH (5mL) for 5 mins followed by sonication in hot chloroform. The substrate 120 comprising the patterned functional monolayer nanos- tructures 100 was dried in air before the procedure repeated twice.

Example 3

[0069] The thiocyanate patterned functional monolayer nanostructures 100 were produced by immersion of the bromine patterned functional monolayer nanostructure 100 substrates 120 in a solution of 50 mg potassium thiocyanate in 5 mL DMF at 70 0C for 24 hours. The substrates were then sonicated in DMF followed by sonication in ethanol and subsequently dried in air.

[0070] The reduction to a thiol patterned functional monolayer nanostructure 100 was performed by immersing the thiocyanate-functionalised glass substrate 120 for 24 hours in 2 mL in a 2.3M solution of lithium aluminium hydride in THF at room temperature, followed by hydrolysis in hydrochloric acid. It was sonicated in water and then chloroform before drying in air.

[0071] The thiol terminated glass substrate 120 was placed in a diluted solution of gold nanoparticles (6 +/- 2nm diameter) in water for 24 hours at room temperature. Afterwards the glass substrate 120 sonicated in water and further sonicated in water before drying in a stream of air. This last step illustrates that the self assembly processes and the following chemical modifications were successful because the last modification was the formation of a thiol end group and the gold nanoparticles bind to the thiol groups. There is no direct analytical method to analyse the chemical composition of a surface at a nanoscopic scale. Therefore this indirect method of the binding of gold nanoparticles to the thiol groups was chosen as an indirect method for the detection of the thiol at a nanoscopic scale.

Example 4

[0072] It is also of interest to fabricate patterned functional monolayer nanostructure 100 with more than 2 functions. This can in general be achieved by introducing additional steps in the formation and the removal of the inhibition layer 130. A process of forming a tri functional chemical nanostructure is described in Fig. 6.

[0073] In a first step the aluminium inhibition layer 130 is made by NSL consisting either of periodically arranged triangular protrusions (left) or of statistically distributed circular holes (right). A gold inhibition layer 130 is formed by gold evaporation at an oblique angle or oblique rotary evaporation. A first silane is applied as a first self assembled monolayer 140. The gold barrier (inhibition layer 130) is then removed mechanically and a second silane as the second self assembled monolayers 150 is applied. The aluminium inhibition layer 130 is removed by acid treatment and a third silane is applied as a third self assembled monolayer.

Reference Numerals

nanostructures 100 latex spheres 105 patterned mask 110 substrate 120 pattern 120a- 120z; inhibition layer 130 projected inhibition layer 130a- 13Oz; first self assembled monolayer 140 second self assembled monolayer 150 depositing 215 removal 220 depositing 225 removal 230 depositing 235 functionalisation of the self assembled monolayer 240

Claims

1. A method (200) for the manufacture of structures (100) by lithographic techniques comprising: creating (210) a patterned mask (110) on a substrate (120); depositing (215) an inhibition layer (130) on the patterned mask (110); removal (220) of the patterned mask (110) to provide a projected inhibition layer (130a, 130b, 130c...13Oz); depositing (225) a first self assembled monolayer (140) on the substrate (120) removal (230) of at least part of the projected inhibition layer (130a...103z) from substrate (120) to expose a pattern (120a..120z); depositing (235) a second self assembled monolayer (150) on the substrate not covered by the projected inhibition layer (120a-120z).

2. The method (200) according to claim 1, wherein the patterned mask (110) is created by transferring latex spheres (105) to the substrate (120).

3. The method (200) according to any one of the above claims, wherein the substrate (120) is selected from a group consisting of glass, silica, silicon dioxide, mica, quartz, aluminium oxide, titanium oxide or other metal oxide, indium tin oxide and

-OH terminated polymer substrate.

4. The method (200) according to any one of the above claims, wherein the inhibition layer (130) is deposited by physical vapour deposition.

5. The method (200) according any one of the above claims, wherein the inhibition layer (130) comprises at least one metal selected from a group consisting of gold, silver or aluminium, titanium, indium, tin, copper, tungsten.

6. The method (200) according to any of the above claims, wherein the inhibition layer (130) comprises at least one metal oxide.

7. The method (200) according to any one of the above claims, wherein the inhibition layer (130) is deposited in an oxygen-containing gaseous atmosphere or by sputtering of a metal oxide

8. The method (200) according to any one of the above claims, wherein the removal of the patterned mask (110) is by sonication in a solvent.

9. The method (200) according to any one of the above claims, wherein the removal of the patterned mask (110) on the substrate (120) is achieved by removing with water or an aqueous acidic solution.

10. The method (200) according to any one of the above claims, wherein the first self assembled monolayer (140) is deposited by immersing the substrate (120) in a solution selected from the group consisting of w-octadecyltrichlorosilane, 11- undecyltrichlorosilane, aminopropyltrimethoxysilane, undecenyltrichlorosilane, fluoroalkylsilanes or other alkyltrichlorosilanes or alkylmethylsilanes or alkylethyl- silanes.

11. The method (200) according to any one of the above claims, wherein the projected inhibition layer (130a...13Oz) is removed from the substrate (120) by removing with a solvent.

12. The method (200) according to any one of the above claims, wherein the removal of the projected inhibition layer (130a...13Oz) from the substrate (120) is by spin coating the substrate (120) with a polymer film and removal of the polymer film with the inhibition layer (130) embedded within.

13. The method (200) according to any one of the above claims, wherein the removal of the projected inhibition layer (130a...13Oz) from the substrate (120) is by disso- lution with an acid.

14. The method (200) according to any one of the above claims, wherein the second self assembled monolayer (150) on the pattern (120a..12Oz) is deposited by immersion of the substrate (120) in a solution consisting of a silane with a functional end group.

15. The method (200) according to claim 14, wherein the silane is selected from the group consisting of 11-bromoundecyltrichlorosilane, 11-undecyltrichlorosilane, aminopropyltrimethoxysilane, undecenyltrichlorosilane, fluoroalkylsilanes or other alkyltrichlorosilanes or alkylmethylsilanes or alkylethylsilanes..

16. The method (200) according to any one of the above claims, further comprising treating (240) the second self assembled monolayer with a different functional groups.

17. The method (200) according to claim 16, wherein the different functional groups are selected from a group consisting of a thiocyanate and a thiol.

18. A product manufacture according to any one of claims 1-17.

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