A simulated microscopy image of hexagonal boron nitride with a circular pore surrounded by triangular ones. Darker circles correspond to individual boron and brighter circles to nitrogen atoms.
Image Credit: © Umair Javed
Scientific Frontline: Extended "At a Glance" Summary: Nanopore Engineering in White Graphene
The Core Concept: A novel technique for precisely controlling the shape of nanopores—holes only a few atoms wide—in hexagonal boron nitride (hBN), a two-dimensional material also known as "white graphene."
Key Distinction/Mechanism: Instead of pore shape being determined solely by electron beam irradiation, it is dictated by the interplay between the electron beam and the surrounding atmosphere. In an ultra-high vacuum, the energetic electrons physically remove boron and nitrogen atoms at similar rates, creating circular pores; however, introducing a small amount of oxygen causes oxygen-mediated chemical etching, which predominantly removes boron atoms and yields triangular pores with nitrogen-terminated edges.
Origin/History: For nearly two decades, scientists believed that electron irradiation of hBN invariably produced triangular pores due to inherent differences in the atomic displacement rates of boron and nitrogen. The University of Vienna team, led by Jani Kotakoski, disproved this in September 2026 by demonstrating the atmospheric influence using a microscope with an exceptionally high vacuum.
Major Frameworks/Components:
- Hexagonal Boron Nitride (hBN): An electrically insulating 2D material acting as the substrate.
- Transmission Electron Microscopy (TEM): Utilized both to image the material down to individual atoms and to supply the energetic electrons that knock atoms out of the lattice.
- Physical Drilling vs. Chemical Etching: The core competing mechanisms where the electron beam provides the physical force and the introduced oxygen, split into reactive species by the beam, provides the chemical attack.
Branch of Science: Materials Science, Nanotechnology, and Quantum Physics.
Future Application: The ability to tailor pore shapes at the atomic scale holds potential for advanced filtration systems, highly precise DNA sequencing, novel catalytic processes, and new quantum technologies.
Why It Matters: The shape and edge-atom composition of a nanopore dictate how it interacts with passing molecules or ions; mastering this atomic-level control unlocks the potential to design membranes and quantum components with specific, tailored functionalities.
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 an ultrahigh 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.
Electrons Can Image and Alter Atomic Structures
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.
Interplay Between Chemistry and Physics
Electron microscopes operate under vacuum, though residual gas molecules typically remain. 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. Under an ultrahigh vacuum, the electron beam removed boron and nitrogen atoms at roughly equal rates, causing circular pores to form. Adding nitrogen had little effect. With even a small amount of oxygen present, however, boron atoms were removed much more readily, and triangular pores with nitrogen-terminated edges emerged. Oxygen alone was not enough: the results indicate that the electron beam splits molecular oxygen into reactive species that can chemically attack the material. The pore shape therefore results from a competition between physics and chemistry: "drilling" with energetic electrons favors circular pores, while oxygen-mediated chemical etching favors triangular ones. By adjusting the atmosphere during electron irradiation, the researchers can control which pore shape forms.
Toward Further Control
"This is extremely exciting," says senior author Jani Kotakoski. "We expect to find similar ways to control pore shapes in other materials, and perhaps also to create different shapes in hexagonal boron nitride." Such control could help tailor atomically precise structures for applications ranging from water filtration to catalysis and quantum technologies.
Funding: The research is part of the Austrian Science Fund (FWF) Cluster of Excellence "Materials for Energy Conversion and Storage," where Kotakoski's group aims to use this method to create new catalytically active structures.
Published in journal: Nature Communications
Title: Origin of circular and triangular pores in electron-irradiated hexagonal boron nitride
Authors: Umair Javed, Manuel Längle, Vladimír Zobač, Alexander Markevich, Barbara Maria Mayer, Clara Kofler, Martin Paul, Darwin Lorber, Nandhini Ravindran, Clemens Mangler, Toma Susi, and Jani Kotakoski
Source/Credit: Universität Wien
Edited by: Scientific Frontline
Reference Number: ms091026_01
