Many nanotech applications would be furthered by the development of efficient and flexible methods for forming large areas of nanometer-scale arrays created by molecular assembly. Sturdy structures ordered with nanometer precision have now been formed by combining supramolecular assembly of ordered networks with self-assembled monolayers. From Chemistry World, written by Ruth Tunnell “Nanostructures made easy“:
Scotland-based chemists have invented a new way to build nanoscale arrays of molecules over a large surface area: a technique that may be key to making nanostructures in sophisticated sensors, catalysts, and tiny computer parts.
Their solution-based chemistry works by corralling atoms into tiny dimples, themselves created when molecules self-assemble onto a gold surface.
‘We have shown that it is possible to control the assembly of single molecules,’ says Manfred Buck, who led the group at St Andrews University. ‘The copper atoms in our final structure are less than 5 nanometres apart, which opens up the possibility of studying materials with extremely small dimensions.’
The team’s chemical patterning provides an alternative route to nanostructures created by conventional lithography, which etches away patterns in surfaces, but can struggle to be precise on scales of a few nanometres over large areas.
Buck’s team first created a honeycomb-shaped network on top of a gold surface, by mixing together melamine and a derivative of perylene (perylene-3,4,9,10-tetracarboxylic diimide or PTCDI). These two molecules spontaneously form a supramolecular network over the surface, creating pores which can be filled by other particles.
The chemistry of this spontaneous network-forming is well understood. The allure of forming a template which could subsequently be used to sculpt structures means the system has been investigated many times before. But this type of assembly normally requires high vacuum conditions so that it can be seen with scanning tunnelling microscopy, and there is little chance of using the fragile structure in real applications.
Buck’s network, by contrast, was stable enough to be dunked in different solutions of thiols (molecules with sulfur caps). This allowed monolayer films of thiol molecules to organise into coils inside the pores – as the sulfur atoms preferred to be near the gold than lie on top of the melamine/PTCDI layer. The team finally inserted copper atoms between the gold substrate and thiol molecules, making a nanoscale atomic structure strong enough to be handled under ambient conditions.
The research was published in Nature (abstract).
—Jim
