New nano semiconductor materials show promise

“Our silicon-germanium adamantane… enables the investigation of important chemical and physical properties of silicon-germanium alloys on the molecular model. We also want to use it in the future to produce silicon-germanium alloys with faultless crystal structures.”Benedikt Köstler

Scientists from Goethe University Frankfurt and the University of Bonn have developed new substance classes for nanomaterials with potential applications in nano semiconductors. Nano spheres and diamond slivers made of silicon and germanium were produced that could lead to new nano semiconductors that can convert electricity into light, and vice versa.

With the ongoing reduction in the size of computer chips down to only a few nanometers, this miniaturization is being achieved in tandem with improved energy-efficiency and power. However, the standard etching processes in chip production is reaching its limits, which means the design of new nanostructured semiconductor materials is crucial. In this new study, reported in the Journal of the American Chemistry Society [Bamberg et al. J. Am. Chem. Soc. (2021) DOI: 10.1021/jacs.1c05598], molecular nano “spheres” made of 20 silicon atoms, known as silafulleranes, were successfully synthesised.

The 20 silicon atoms of silafullerane form a dodecahedron, a body composed of regular pentagons, which encapsulates a chloride ion. A hydrogen atom sticks out at each silicon corner of the body. This silafullerane has been long sought after as a progenitor of this new class of substances, especially as the hydrogen atoms can easily be replaced with functional groups, allowing the silafullerane to be provided with different properties. Fullerenes correspond to silafulleranes and can work to improve the efficiency of organic solar cells, as well as making the batteries of electric cars safer, and hold promise in high-temperature superconductivity.

The silicon sphere, synthesised here for the first time, has the potential for new applications in semiconductor technology, while the team also developed another new class of materials of crystal building blocks made of 10 silicon and germanium atoms with a diamond-like structure. The silicon-germanium adamantane represents the building block of a mixed silicon-germanium alloy, while nanodiamonds could also have applications in areas such as pharmaceuticals and catalysis.

Although silicon-germanium alloys have been demonstrated as superior to pure silicon semiconductors in key application areas, the production of such alloys is not straightforward and there are often mixtures of different compositions. Here, the team managed to produce a simple synthesis path. As researcher Benedikt Köstler said: “Our silicon-germanium adamantane… enables the investigation of important chemical and physical properties of silicon-germanium alloys on the molecular model. We also want to use it in the future to produce silicon-germanium alloys with faultless crystal structures.”

In the form of quantum dots, nanostructured silicon and germanium are already used to produce light in all colours of the visible spectrum, something that is being explored for computer and mobile phone displays, and in telecommunications.