On surface chemistry lead novel compounds

On surface chemistry can lead to novel compounds

9:15 AM, 17th September 2016
On surface chemistry can lead to novel compounds
Catalyzed by the copper atoms of the surface, the precursor molecule alters its structure and spatial arrangement when heated gradually.

BASEL, SWITZERLAND: On surface chemical reactions can lead to novel chemical compounds not yet synthesised by solution chemistry. The first step, second step and third step products can be analysed in detail using a high-resolution atomic force microscope, as demonstrated in the journal Nature Communications by scientists from the Swiss Nanoscience Institute and the Department of Physics at Basel University and their colleagues from Japan and Finland.

In numerous nanotechnology applications, individual molecules are placed on surfaces to fulfil specific functions – such as conducting an electrical current or emitting a light signal. Ideally, scientists will synthesise these sometimes extremely complex chemical compounds directly on the surface. The on surface chemical reactions can be followed step by step with the aid of ultra-high-resolution atomic force microscopes. The data obtained also enables them to calculate the precise molecular structure and the energetics along the path.

For their experiments, colleagues of professor Ernst Meyer from the University of Basel selected a molecule consisting of three benzene rings joined by a triple bond. When the researchers apply this molecule to a silver surface, the molecules arrange themselves in a consistent pattern – but there is no chemical reaction.

Copper as a catalyst

On a copper surface, however, the molecules react already at a temperature of -123°C. Catalysed by the copper atoms, the precursor molecule incorporates two hydrogen atoms thereby altering its structure and spatial arrangement. When the sample is heated to 200°C, a further reaction step takes place in which two pentagonal rings are formed. A further increase in temperature to 400°C causes a cleaving of hydrogen atoms and forms a further carbon-carbon bond. The final two reaction steps lead to aromatic hydrocarbon compounds, which had previously not been synthesised in solution chemistry.

The researchers conducted these experiments in ultra-high vacuum conditions and were able to monitor the synthesis using a high-resolution atomic force microscope with a carbon monoxide terminated tip. Comparative computer calculations generated the precise molecular structure, which perfectly matched the microscope images.

Tailored nanostructures

Through their experiments, the international research team has shown that on surface chemistry can lead to novel products.

“This extremely pure form of chemistry provides us with tailored on-surface nanostructures that can be used in a variety of ways,” said Meyer, commenting on the work largely performed by Dr Shigeki Kawai.

In the example presented, the copper surface functions as a catalyst; the chemical reaction of the precursor molecules is controlled by adding heat and can be monitored via atomic force microscopy.

© University of Basel News

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