They don’t call this the Silicon Age for nothing – the element is vital to all of the electronics that our modern world is built on. Now, research led by the Carnegie Institution for Science has developed a way to create a new form of silicon with a unique hexagonal structure.
Elements can take on different crystalline forms called allotropes, based on the arrangement of their atoms. These can have quite different properties – carbon, for example, can exist in two-dimensional sheets as graphene, stacks of these sheets as graphite, or cubic lattices as diamond, among others.
The most commonly used form of silicon has the same structure as diamond, but other structures could potentially have other useful electronic properties. In 2014, a team from Carnegie developed a new silicon allotrope called Si24, which was made up of sheets of silicon arranged in rings of five, six and eight atoms. The gaps in the middle of these rings could form one-dimensional channels for other atoms to move through, which the team said could unlock applications in energy storage or filtering.
In the new study, the researchers developed a method to convert Si24 into yet another new allotrope. Heating the Si24 crystals caused the thin sheets to align in hexagonal shapes over four repeating layers, earning the new structure the name 4H-silicon. The team says it’s the first time that stable, bulk crystals of this kind of material have been created.
“In addition to expanding our fundamental control over the synthesis of novel structures, the discovery of bulk 4H-silicon crystals opens the door to exciting future research prospects for tuning the optical and electronic properties through strain engineering and elemental substitution,” says Thomas Shiell, an author of the study. “We could potentially use this method to create seed crystals to grow large volumes of the 4H structure with properties that potentially exceed those of diamond silicon.”
It remains to be seen exactly what kinds of applications the new silicon structure could open up, but the team says that it could lead to improvements in components like transistors – a foundation for electronic devices – or photovoltaic energy systems.
The research was published in the journal Physical Review Letters.
Source: Carnegie Institution of Science
