Old silicon discovers new tricks: Silicon pyramids with peculiar magnetic properties are atomically constructed

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Arrays of atomically flat, iron-coated silicon pyramids with peculiar magnetic properties have been made by researchers at the Nara Institute of Science and Technology.

Cell phones, home appliances, cars and other everyday devices have been revolutionized by ultra-small integrated circuits.

Circuits must be accurately produced in three dimensions to further miniaturize electronics and allow advanced functions.

It is difficult to achieve ultra-fine 3D shape control by silicon etching, since even atomic-scale damage reduces the performance of the system. In a new study published in Crystal Growth and Design, researchers at the Nara Institute of Science and Technology (NAIST) report on silicon etched to take the form of atomically smooth pyramids.

Coating these silicon pyramids with a thin layer of iron only potentially gives them previously established magnetic properties.

Ken Hattori, NAIST researcher and lead author of the study, has published widely in the atomically controlled nanotechnology field. One focus of Hattori’s research is on enhancing the functionality of technology based on silicon.

“Silicon is the workhorse of modern electronics because it can act as a semiconductor or an insulator and is an abundant element. However, future technological advances require atomically smooth device fabrication in three dimensions,” Hattori says.

To make arrays of pyramid-shaped silicon nanostructures, a combination of standard dry etching and chemical etching is required. Until now, generating atomically smooth surfaces has been extremely difficult.

Our ordered series of silicon pyramids of isosceles were all the same size and had planes of flat facets.

Low-energy electron diffraction patterns and electron microscopy have confirmed these findings, explains the lead author of the study, Aydar Irmikimov.

The silicon was deposited with an ultra-thin layer of iron – 30 nanometers thin – which gave the pyramids unusual magnetic properties.

At the atomic level, the orientation of the pyramids determined the orientation – and thus the properties – of the overlying iron.

The anisotropic form of the nanofilm was made possible by the epitaxial growth of iron.

The curve for magnetization was rectangular in form as a function of the magnetic field, but with breaks caused by the asymmetric motion of the magnetic vortex bound at the tip of the pyramid, Hattori explains.

The researchers observed that the curve had no break points in analogous experiments conducted on planar iron-coated silicon. The anomalous curve for pyramid shapes has been theoretically predicted by other researchers, but the NAIST researchers are the first to demonstrate it in a real nanostructure.

“Our technology will enable the fabrication of a circular magnetic array simply by tuning the shape of the substrate,” Irmikimov says.

The versatility of 3D electronics will be greatly accelerated by integration with advanced technologies such as spintronics – which encodes information by spin rather than electrical charging of an electron.

Reference: Aydar Irmikimov, Liliany N. Pamasi, Azusa N. Hattori, Takaaki Higashi, Shunta Takahashi, Emilia E. Hashamova, Xiaoqian Shi, Fangzhun Guo, Nobuyoshi Hosoito, Ai I. Osaka, Hidekazu Tanaka, and Ken Hattori, January 5, 2021, Crystal Growth and Design, “Atomically architected silicon pyramid single-crystalline structure supporting epitaxial material growth and characteristic magnetism”

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