Patent Application: US-2525704-A

Abstract:
the present invention describes a method for producing a large area two - dimensional nanoscale network on the surface of a substrate . the network is formed by depositing a sub - mono - layer of molecule a onto the surface of the substrate followed by a different molecule b . the formation of the network relies on the hetero - molecular hydrogen bonding between molecules a and b to be stronger than the homo - molecular hydrogen bonding . by appropriate choice of molecules a and b , together with the substrate , it is possible to manipulate and control the structure , dimensions and chemical functionality of the network . the pores of the network can act as containment vessels for other molecules and be made sufficiently large to accommodate several large molecules or atomic / molecular clusters or particles .

Description:
molecular entrapment in nanoscale vessels formed by surface supramolecular assembly , the method of self - assembly of a nano - scale network described here is a bimolecular method that requires the two molecules , a and b , to exhibit stronger hetero - molecular hydrogen bonding compared to homo - molecular hydrogen bonding , and also to have a compatible molecular geometry . perylene tetra - carboxylic di - imide ( ptcdi ) 10 , illustrated in fig1 a , and melamine 12 , illustrated in fig1 b , are two such molecules that exhibit these properties . fig1 c illustrates the compatibility of the molecular geometries of melamine 12 and ptcdi 10 which results in three hydrogen bonds 14 per melamine - ptcdi pair . it is understood that melamine 12 and ptcdi 10 are used in the following description to exemplify the invention only and other molecular pairs that exhibit the similar properties of compatible molecular geometry and strong hetero - molecular hydrogen bonding compared to homo - molecular hydrogen bonding may also be used . examples of further molecules that can be used are shown in fig2 . the formation of the nano - scale network is a two stage process where a sub - monolayer of the molecule a is first deposited onto a prepared substrate . molecule b is then deposited on the substrate and the network is formed . methods of deposition that may be used to carry this out include , but are not limited to , ultra - high vacuum deposition and solution based deposition . the melamine - ptcdi network illustrated in fig3 was prepared under ultra - high vacuum conditions ( base pressure ˜ 5 × 10 − 11 torr ). ptcdi 10 and melamine 12 were placed in effusion cells and sublimed through heating to ˜ 360 ° c . and ˜ 100 ° c . respectively , onto a ag / si ( 111 )-{ square root } 3 ×{ square root } 3r30 ° surface held at room temperature . the method of deposition and preparation of such substrates is well - known to those skilled in the art . the first step in the formation of the network 18 was the deposition of 0 . 1 - 0 . 3 mono - layers of ptcdi 10 to form close packed islands and short chains on the surface of the substrate . melamine 12 was then deposited while the sample was annealed at ˜ 100 ° c . the annealing provides sufficient thermal energy for molecules to detach from ptcdi islands and diffuse across the surface . these ptcdi molecules 10 interact with melamine 12 to nucleate the hexagonal network 18 which then grows through further capture of diffusing molecules . stm images of the resulting melamine - ptcdi network 18 are shown in fig3 a . the network has principal axes at 30 ° to those of the ag / si ( 111 )-{ square root } 3 ×{ square root } 3r30 ° surface and a lattice constant 3 { square root } 3a o = 34 . 6 å . the geometry and dimensions of the nano - scale network formed by the bi - molecular pair is determined by geometries and dimensions of the two molecules used in the network &# 39 ; s formation . the hexagonal structure seen with the melamine - ptcdi network 18 is determined by the threefold symmetry of the melamine 12 which forms the vertices of the network while the straight edges correspond to ptcdi 10 . alternative geometries such as rectangles , wires and triangles are achievable through appropriate choice of molecules . the use of bimolecular assembly using long molecules to define the edges of the network results in pores which are much larger than the constituent building blocks of the networks and enables their use as traps , or vessels , which may be used to co - locate several large molecules , clusters or particles . this potential is demonstrated through the sublimation of c 60 20 onto the hexagonal melamine - ptcdi network 18 top form a new fullerene nanophase — the heptamer 22 — in the pores . however , sublimation and other methods may be used to fill the pores with other technologically exciting molecular species or combination of species , clusters or particles . fig4 a shows an stm image acquired following the deposition of 0 . 03 monolayers ( ml ) of c 60 20 . heptameric clusters 22 of c 60 20 , in which molecules are ordered in a compact hexagonal arrangement are seen to have formed within the pores . the clusters 22 formed in different pores are aligned , and are all oriented parallel to the principal axes of the si ( 111 ) surface . the molecular arrangement of the heptamers 22 has been deduced from the stm images of fig4 a and are shown in fig4 b . clusters of fewer molecules are also observed . for example there are clusters of six molecules in fig4 a and clusters of 2 - 5 molecules have also been observed , while many pores remain empty for this coverage of c 60 20 . as the coverage of c 60 20 is increased the fraction of pores capturing adsorbed molecules and stabilising heptameric clusters 22 increases . this is accompanied by the adsorption of c 60 20 directly above the ptcdi 10 and melamine 12 molecules reproducing the underlying hexagonal network 18 . stm images showing second layer c 60 20 , heptamers 22 and the melamine - ptcdi network 18 in close proximity are shown in fig5 a . a further increase in c 60 20 coverage results in a near perfect termination of the second layer as shown in stm images fig5 b . an array of c 60 20 molecules sits directly above the melamine - ptcdi network 18 and the lateral positions within this array correspond exactly to those of a hexagonally close packed layer . however , the elevation of the hexagonal network &# 39 ; s 18 constituent molecules results in an increase in their separation with molecules at the heptamer 22 edge and this arrangement thus constitutes a new surface phase of fullerene which is controlled and templated by the hydrogen bonded network . further deposition of c 60 20 up to a total of 3 ml does not lead to the formation of higher layers of fullerene on the hexagonal network . this observation is attributed to the absence of sites in the termination shown in fig5 which are suitable for the stable nucleation of higher layers . the foregoing description is considered as illustrative only of the principles of the invention . further , since numerous modifications and changes will readily occur to those skilled in the art , it is not desired to limit the invention to the exact construction and process shown as described above . accordingly , all suitable modifications and equivalents which may be resorted to can be considered to fall within the scope of the invention . de wild , m ., berner , s ., suzuki , h ., yanagi , h ., schlettwein , d ., ivan , s ., baratoff , a ., guentherodt h - j . & amp ; 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