Dye molecules in hybrid nanomaterials are manipulated to behave like diodes

Geoffrey Ashwell and Martial Berry from Cranfield University have used hybrid structures of self-assembled monolayers and Langmuir-Blodgett films (thin films of organic molecules deposited onto a solid) to manipulate the orientation of dye molecules. By doing this, they can recreate the asymmetric current-voltage characteristics typical of a diode.

Molecular diodes, the organic counterpart of the pn junction in semiconductors, are an area of intense investigation. Molecular rectifiers, or rectifying diodes, are structures that make it more difficult for an electric current to go through them in one direction than the other. They have been used since the start of the electronics revolution. Ashwell’s development will affect the design of the molecules used for these components.

The squaraine dyes used contain donor-acceptor-donor units arranged vertically in the monolayer and horizontally in the film. This arrangement makes the molecules’ different energy levels in each part of the hybrid material become mismatched. The material’s resulting current-voltage properties make them behave as rectifiers.

With the electronics industry constantly seeking smaller components to feed the consumer appetite for smaller gadgets, molecular electronics may hold the solution to the miniaturisation conundrum. Speaking about his latest breakthrough, Ashwell says ’the discovery has important implications in the design of component molecules’.

Rebecca Lavender