This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A research team at the University of Vienna led by physicist Jani Kotakoski demonstrates how the shape of nanopores in hexagonal boron nitride—the electrically insulating counterpart to graphene, also known as "white graphene"—can be precisely controlled at the atomic level. Electron irradiation in ultra-high vacuum creates circular pores, while adding small amounts of oxygen yields triangular pores.
The nanopore engineering presented in the journal Nature Communications thus unlocks new applications in filtration, DNA sequencing, catalysis, and quantum technologies. Two-dimensional hexagonal boron nitride (hBN) is an insulating material that consists of a single layer of atoms. It forms a stable barrier that can also be used to protect other two-dimensional materials, such as graphene, from their environment.
Creating pores only a few atoms across makes this barrier permeable, resulting in a nanoporous membrane through which molecules or ions can pass. Such membranes could be used to filter substances or analyze DNA as it passes through a nanopore. At this scale, the pore's precise shape and the atoms lining its edges influence how it interacts with passing molecules.
At the same time, due to their small size, the pores have quantum mechanical properties that make them useful for catalysis and quantum applications. One way to create such tiny pores is by using the electron beam of a transmission electron microscope: The same electrons used to image two-dimensional materials down to individual atoms can also knock atoms out of the material. With continued irradiation, these defects grow into nanopores.
For nearly two decades, electron irradiation of hBN has been known to produce triangular pores. Their shape was generally attributed to differences in how easily boron and nitrogen atoms are displaced. "We show for the first time that the shape of the pores is not due to the electrons alone, but is influenced by the atmosphere around the sample," says Umair Javed, first author of the study and a doctoral student in the Kotakoski group at the Faculty of Physics at the University of Vienna.
Electron microscopes operate under vacuum, but this normally still contains residual gas molecules. The Vienna team used a microscope with an exceptionally good vacuum and the ability to introduce selected gases into the sample environment. This allowed them to study what happens when the electron beam acts on hBN almost on its own—and what changes when gases are added.
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