Tag Archives: Li Yuan

Make your carbon atoms stand taller to improve electronic devices

Scientists from Ireland ((Tyndall National Institute at University College Cork [UCC]) and Singapore (National University of Singapore [NUS]) have jointly published a paper about how they achieved a ten-fold increase in the switching efficiency of electronic devices by changing one carbon atom. From the Jan. 21, 2013 news item on ScienceDaily,

These devices could provide new ways to combat overheating in mobile phones and laptops, and could also aid in electrical stimulation of tissue repair for wound healing.

The breakthrough creation of molecular devices with highly controllable electrical properties will appear in the February [2013] issue of Nature Nanotechnology. Dr. Damien Thompson at the Tyndall National Institute, UCC and a team of researchers at the National University of Singapore led by Prof. Chris Nijhuis designed and created the devices, which are based on molecules acting as electrical valves, or diode rectifiers.

Dr. Thompson explains, “These molecules are very useful because they allow current to flow through them when switched ON and block current flow when switched OFF. The results of the study show that simply adding one extra carbon is sufficient to improve the device performance by more than a factor of ten. We are following up lots of new ideas based on these results, and we hope ultimately to create a range of new components for electronic devices.” Dr. Thompson’s atom-level computer simulations showed how molecules with an odd number of carbon atoms stand straighter than molecules with an even number of carbon atoms. This allows them to pack together more closely. Tightly-packed assemblies of these molecules were formed on metal electrode surfaces by the Nijhuis group in Singapore and were found to be remarkably free of defects. These high quality devices can suppress leakage currents and so operate efficiently and reliably. The device can be cleanly switched on and off purely on the basis of the charge and shape of the molecules, just like in the biological nanomachines that regulate photosynthesis, cell division and tissue growth.

The Jan. ??, 2013 University College Cork news release, which originated the news item, provides more details,

The combined experiments and simulations show for the first time that minute improvements in molecule orientation and packing trigger changes in van der Waals forces that are sufficiently large to dramatically improve the performance of electronic devices. Dr. Thompson explains: “These van der Waals forces are the weakest of all intermolecular forces and only become significant when summed over large areas. Hence, up until now, the majority of research into ultra-small devices has used stronger “pi-pi” interactions to stick molecules together, and has ignored the much weaker, but ubiquitous, van der Waals interactions. The present study shows how van der Waals effects, which are present in every conceivable molecular scale device, can be tuned to optimise the performance of the device.”

The devices are based on molecules that act as diodes by allowing current to pass through them when operated at forward bias and blocking current when the bias is reversed. Molecular rectifiers were first proposed back in 1974, and advances in scientific computing have allowed molecularā€level design to be used over the past decade to develop new organic materials that provide better electrical responses. However, the relative importance of the interactions between the molecules, the nature of the molecule-metal contact and the influence of environmental effects have been questioned. This new research demonstrates that dramatic improvements in device performance may be achieved by controlling the van der Waals forces that pack the molecules together. Simply changing the number of carbon atoms by one provides significantly more stable and more reproducible devices that exhibit an order of magnitude improvement in ON/OFF ratio. The research findings demonstrate the feasibility of boosting device performances by creating tighter seals between molecules.

Here a citation and a link to the paper,

The role of van der Waals forces in the performance of molecular diodes by Nisachol Nerngchamnong, Li Yuan, Dong-Chen Qi, Jiang Li, Damien Thompson, & Christian A. Nijhuis. Nature Nanotechnology (2013) doi:10.1038/nnano.2012.238 Advance online publication: Jan. 6, 2013.

This paper is behind a paywall.