Organic electronics—how to make contact between carbon compounds and metal

Feb 17, 2013
Upon contact between the oxygen atoms protruding from the backbone and the metal, the molecules' internal structure changed in such a way that they lost their semiconducting properties and instead adopted the metallic properties of the surface. Credit: Visualisation: Georg Heimel/HU Berlin

An international team of scientists around Dr. Georg Heimel and Prof. Norbert Koch from the HZB and the Humboldt University Berlin has unraveled the mystery of what metal and carbon compounds have in common. Their discovery enables more focused improvements to contact layers between metal electrodes and active materials in organic electronic devices.

Until now it was practically impossible to accurately predict which molecules performed well on the job. They basically had to be identified by trial-and-error.

"We have been working on this question for a number of years now and could at last come up with a conclusive picture using a combination of several experimental methods and theoretical calculations," Georg Heimel explains. The researchers systematically examined different types of molecules whose backbones consist of the same chain of fused aromatic . They differed in just one little detail: the number of projecting from the backbone. These modified molecules were placed on the typical contact metals gold, silver, and copper.

Using photoelectron spectroscopy (UPS and XPS) at HZB's own BESSY II synchrotron radiation source, the researchers were able to identify that formed between the and the molecules as well as to measure the energy levels of the conduction electrons. Colleagues from Germany's Tübingen University determined the exact distance between the molecules and the metal surfaces using x-ray standing wave measurements taken at the ESRF synchrotron radiation source in Grenoble, France.

These experiments showed that, upon contact between the oxygen atoms protruding from the backbone and several of the metals, the molecules' internal structure changed in such a way that they lost their semiconducting properties and instead adopted the metallic properties of the surface. Despite similar prerequisites, this effect was not observed for the "bare"-backbone molecule. From the observation which molecules underwent these kinds of drastic changes on what metal, the researchers could derive general guidelines. "At this point, we have a pretty good sense of how molecules ought to look like and what their properties should be if they are to be good mediators between active organic materials and contacts, or, as we like to call it, good at forming soft metallic contacts," says Heimel.

Explore further: Carbyne morphs when stretched: Calculations show carbon-atom chain would go metal to semiconductor

Related Stories

Searching for molecular radical's secrets of stability

Oct 30, 2012

For the first time, scientists synthesized and characterized a metal-containing complex long thought to be too unstable to study. This complex piqued the interest of scientists at Pacific Northwest National ...

The origin of organic magnets

Mar 02, 2012

Electrical engineers are starting to consider materials made from organic molecules -- including those made from carbon atoms -- as an intriguing alternative to the silicon and metals used currently in electronic ...

Recommended for you

An anti-glare, anti-reflective display for mobile devices?

Jul 16, 2014

If you've ever tried to watch a video on a tablet on a sunny day, you know you have to tilt it at just the right angle to get rid of glare or invest in a special filter. But now scientists are reporting in the journal ACS Ap ...

New materials for future green tech devices

Jul 15, 2014

From your hot car to your warm laptop, every machine and device in your life wastes a lot of energy through the loss of heat. But thermoelectric devices, which convert heat to electricity and vice versa, ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

River_Lan
3 / 5 (2) Feb 17, 2013
Where is the original paper link?
alfie_null
not rated yet Feb 18, 2013