New crystalline form of silicon could potentially be used to create next-generation electronic and energy devices – ScienceDaily
A team led by Thomas Shiell and Timothy Strobel of Carnegie has developed a new method to synthesize a new crystalline form of silicon with a hexagonal structure that could potentially be used to create next-generation electronic and energy devices with enhanced properties that exceed those of the “normal” cubic form of silicon used today.
Their work is published in Physical examination letters.
Silicon plays an inordinate role in human life. It is the second most abundant element in the earth’s crust. When mixed with other elements, it is essential for many construction and infrastructure projects. And in pure elemental form, it’s crucial enough for computing that America’s longtime tech hub – California’s Silicon Valley – has been dubbed in its honor.
Like all elements, silicon can take different crystal forms, called allotropes, in the same way that soft graphite and super hard diamond are both forms of carbon. The most common form of silicon used in electronic devices, including computers and solar panels, has the same structure as diamond. Despite its ubiquity, this form of silicon is actually not fully optimized for next-generation applications, including high-performance transistors and some photovoltaic devices.
While many different silicon allotropes with improved physical properties are theoretically possible, only a handful exist in practice given the lack of known synthetic pathways that are currently accessible.
Strobel’s lab had previously developed a revolutionary new form of silicon, called Si24, which has an open frame made up of a series of one-dimensional channels. In this new work, Shiell and Strobel led a team that used Si24 as the starting point for a multistep synthetic pathway that resulted in highly oriented crystals in a form called 4H silicon, named after its four layers. repetitive in a hexagonal structure.
“Interest in hexagonal silicon dates back to the 1960s, due to the possibility of tunable electronic properties, which could improve performance beyond the cubic form,” Strobel explained.
Hexagonal forms of silicon have been synthesized before, but only by depositing thin layers or in the form of nanocrystals that coexist with a disordered material. The newly demonstrated Si24 pathway produces the first high quality bulk crystals which will serve as the basis for future research activities.
Using the advanced computer tool called PALLAS, which was previously developed by team members to predict structural transition pathways – like how water turns to vapor when heated or to ice when ‘it is frozen – the group was able to understand the transition mechanism from Si24 to 4H -Si, and the structural relationship that allows the conservation of highly oriented product crystals.
“In addition to extending our fundamental control over the synthesis of new structures, the discovery of bulk 4H silicon crystals opens the door to exciting future research perspectives to tune optical and electronic properties through stress engineering and to elemental substitution, ”said Shiell. “We could potentially use this method to seed crystals to grow large volumes of the 4H structure with properties that potentially exceed those of silicon diamond.”
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