Speedy single molecules for switches
UK researchers are playing their part in the long-term quest to incorporate single molecules into electronic circuits for nanoscale high speed devices. This technology would not rely on a material’s bulk properties to perform electronic functions such as switching or logic.
Teams at the Universities of Oxford, Cardiff and Liverpool have synthesised and tested a family of porphyrin molecules – best known as being the basis of haemoglobin – that could one day be used as ‘molecular wires’ in nano-electronics. While porphyrins have been explored previously for molecular wires, this work is said to be novel in the specific combination of molecules used and single-molecule testing regime.
Professor Richard Nichols of Liverpool University’s Department of Chemistry explains that research has revealed that porphyrins have many redox states that can be controlled, meaning they could be used as molecular switches. They conduct charge over ‘long’ distances (in the range of 10nm), which is ideal for nanoscale connectors, and they have ‘synthetic versatility’, so can be modified by a range of ligands and metal cations.
The molecules are also stable up to 400ºC, and so able to handle typical semiconductor manufacturing operations. ‘The temperature stability also means they can withstand more switching cycles,’ Nichols says.
He explains that this combination of properties could give porphyrins the edge over ‘rival’ nanowire materials such as ligoynes and polythiophenes.
Nichols is using scanning tunnelling microscopy to characterise the electronic properties of around 20 porphyrin molecules, which have been synthesised by Professor Harry Anderson’s team at Oxford University, using a technique called non-covalent self assembly.
Nichols is testing the porphyrins under ambient conditions in solution, while the Cardiff team is testing under high vacuum conditions.
‘We can capture a molecule between a pair of electrodes and measure its electrical properties,’ Nichols says. In each case, he carries out repeated tests on a ‘homologous series’ of molecules – which might have structural variations in terms of the number of porphyrin rings, attached ligands or metal cations. The molecules have been tested on their own, and in larger assemblies as might be seen in a ‘realisable, near future device’.
His team used dynamic gap techniques to measure the electrical properties of porphyrin wires up to 10nm long. A key property was low attenuation of the wires – that is, their ability to maintain charge transport along their length. In one experiment, a porphyrin monomer showed a single molecule conductance value of 2.13nS and an attenuation factor of 0.04.
One further potential future area of research, he says, is to incorporate and test better end groups such as C60, which shows a lot of promise as a contact material.
The co-ordinator of the Nanoscale Exploratory Technology Lab at IBM Research in Switzerland, Paul Seidler, said that incorporating single molecules into commercial electronic devices was ‘decades away’, although prototypes have been fabricated.
‘We are interested in high speed devices, which will have to move into the realm of individual molecules,’ he says. ‘If you can have switching between two electronic states, you have a potential successor to the transistor,’ he says. Also, ‘molecular electronics devices would be very low power, as they could rely on quantum mechanical states rather than being charge-based,’ he says.Materials World Magazine, 01 Aug 2010
Teams at the Universities of Oxford, Cardiff and Liverpool have synthesised and tested a family of porphyrin molecules – best known as being the basis of haemoglobin – that could one day be used as ‘molecular wires’ in nano-electronics. While porphyrins have been explored previously for molecular wires, this work is said to be novel in the specific combination of molecules used and single-molecule testing regime.
Professor Richard Nichols of Liverpool University’s Department of Chemistry explains that research has revealed that porphyrins have many redox states that can be controlled, meaning they could be used as molecular switches. They conduct charge over ‘long’ distances (in the range of 10nm), which is ideal for nanoscale connectors, and they have ‘synthetic versatility’, so can be modified by a range of ligands and metal cations.
The molecules are also stable up to 400ºC, and so able to handle typical semiconductor manufacturing operations. ‘The temperature stability also means they can withstand more switching cycles,’ Nichols says.
He explains that this combination of properties could give porphyrins the edge over ‘rival’ nanowire materials such as ligoynes and polythiophenes.
Nichols is using scanning tunnelling microscopy to characterise the electronic properties of around 20 porphyrin molecules, which have been synthesised by Professor Harry Anderson’s team at Oxford University, using a technique called non-covalent self assembly.
Nichols is testing the porphyrins under ambient conditions in solution, while the Cardiff team is testing under high vacuum conditions.
‘We can capture a molecule between a pair of electrodes and measure its electrical properties,’ Nichols says. In each case, he carries out repeated tests on a ‘homologous series’ of molecules – which might have structural variations in terms of the number of porphyrin rings, attached ligands or metal cations. The molecules have been tested on their own, and in larger assemblies as might be seen in a ‘realisable, near future device’.
His team used dynamic gap techniques to measure the electrical properties of porphyrin wires up to 10nm long. A key property was low attenuation of the wires – that is, their ability to maintain charge transport along their length. In one experiment, a porphyrin monomer showed a single molecule conductance value of 2.13nS and an attenuation factor of 0.04.
One further potential future area of research, he says, is to incorporate and test better end groups such as C60, which shows a lot of promise as a contact material.
The co-ordinator of the Nanoscale Exploratory Technology Lab at IBM Research in Switzerland, Paul Seidler, said that incorporating single molecules into commercial electronic devices was ‘decades away’, although prototypes have been fabricated.
‘We are interested in high speed devices, which will have to move into the realm of individual molecules,’ he says. ‘If you can have switching between two electronic states, you have a potential successor to the transistor,’ he says. Also, ‘molecular electronics devices would be very low power, as they could rely on quantum mechanical states rather than being charge-based,’ he says.Materials World Magazine, 01 Aug 2010
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He seems to have his hopes