Researchers at the University of Vienna have demonstrated precise control over the shape of nanopores within hexagonal boron nitride at the atomic level. The team reports creating circular pores using electron irradiation in ultra-high vacuum, while the addition of even small amounts of oxygen yields triangular pores, a result building on electron irradiation techniques used to create triangular pores for nearly two decades.
“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, a doctoral student and first author of the study. This ability to tailor pore shapes allows for advancements in filtration, DNA sequencing, and quantum technologies.
Electron Irradiation Creates Defined Pore Shapes in White Graphene
Hexagonal boron nitride membranes exhibiting triangular nanopores have been created by electron irradiation for nearly two decades, a team at the University of Vienna reports. By introducing small amounts of oxygen during electron irradiation, physicists created pores with sharply defined triangular shapes, a departure from the traditionally formed circular pores produced in ultra-high vacuum conditions. This level of control over pore geometry at the atomic scale opens possibilities for tailoring membrane properties for specific applications.
The ability to manipulate pore shape stems from a competition between physical sputtering by the electron beam and chemical etching mediated by oxygen, according to the research published in Nature Communications. In an exceptionally good vacuum, the electron beam removes boron and nitrogen atoms at similar rates, resulting in circular pores; however, the introduction of even trace amounts of oxygen dramatically alters this process.
The team observed that oxygen facilitates the removal of boron atoms at a significantly higher rate leading to the formation of triangular pores with nitrogen-terminated edges. This interplay between physics and chemistry is not merely an observation, it’s a tool for precise fabrication. The researchers demonstrated that by carefully adjusting the atmospheric composition during electron irradiation, they could selectively create either circular or triangular pores.
This control extends beyond simply choosing a shape; it allows for the engineering of pore edges with specific atomic terminations, influencing the membrane’s interaction with passing molecules. This precision is important for applications like filtration, where pore size and surface chemistry determine selectivity, and DNA sequencing, where the interaction between DNA and the pore lining generates a signal. The researchers show that pore shape results from a competition between direct physical removal of atoms by energetic electrons and oxygen-mediated chemical etching.
Hexagonal boron nitride itself provides a porous membrane and is an electrically insulating material, hBN is a protective layer for other two-dimensional materials, like graphene, shielding them from environmental degradation. “At the atomic scale, physics and chemistry unlock a wide range of applications through nanopore engineering,” notes Jani Kotakoski, senior author of the study. The implications extend to fields beyond filtration and sequencing. The small size of these nanopores imparts quantum mechanical properties, making them potentially useful in catalysis and quantum technologies.
The team, working within the Austrian Science Fund (FWF) Cluster of Excellence “Materials for Energy Conversion and Storage,” intends to explore using this method to create new catalytically active structures. “This is extremely exciting,” says 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.” The ability to tailor atomically precise structures, the researchers suggest, could have a significant impact on a range of technologies.
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.
Umair Javed, first author of the study and a doctoral student in the Kotakoski group at the Faculty of
See today’s quantum computing news on Quantum Zeitgeist for the latest breakthroughs in qubits, hardware, algorithms, and industry deals.
