Chemists synthesise molecular diode

University of Chicago chemists have successfully created a molecular diode that could prove crucial in the continuing push to miniaturise electronic devices.

University of Chicago chemists have reportedly synthesised an electronic component the size of a single molecule, a development that could prove crucial in the continuing push to miniaturise electronic devices.

The component, called a molecular diode, restricts current flow to one direction. In the semiconductor industry these components, called p-n junctions, form half of a transistor.

Other researchers have synthesised other types of molecular components, but the Chicago chemists, Man-Kit Ng and Luping Yu, are believed to be the first to synthesise a p-n junction.

‘Professor Yu has developed diblock copolymer-based molecular diodes. Essentially, he has shown that the important electronic properties of this circuit element can be engineered into a single polymer molecule,’ Penner added.

Synthesising the molecular diode, which measures 2.5 nanometers in diameter, required a multi-step process that involved creating two different compounds that display opposite electronic properties, then chemically bonding them together (the diblock copolymer).

The compounds, which are made mostly of hydrogen and carbon, are embedded in a monolayer, a sheet measuring only one molecule thick. The sheets are then transferred to a gold platform, where a scanning tunnelling microscope (STS) measures the properties of the diodes.

STS encompasses many methods: taking ‘topographic’ (constant-current) images using different bias voltages and comparing them; taking current (constant-height) images at different heights; and ramping the bias voltage with the tip positioned over a feature of interest while recording the tunnelling current. The last example results in current vs. voltage (I-V) curves characteristic of the electronic structure at a specific x, y location on the sample surface.

It took Ng and Yu more than six months to develop the synthesis process, but now they can mass-produce molecular diodes with relative ease. Yu is confident that he can now synthesise a molecular transistor, but a more difficult hurdle remains, namely how to connect molecular components to make a working computer.

‘If you can solve that issue, that’s the ultimate computer you can have as far as component size is concerned,’ concluded Yu.