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Scientists Propose a New Method for Direct Fabrication of Sub-10 nm Nanopores
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Chinese scientists have lately proposed a new method for direct fabrication of sub-10 nm nanopores in WO3 nanosheets using swift heavy ions. The results have been published in Nano Letters.  
The study was conducted by the scientists at the Materials Research Center of the Institute of Modern Physics (IMP), Chinese Academy of Sciences (CAS) and their collaborator at the Joint Institute for Nuclear Research, Russia.
Fabrication of high-quality solid-state nanopores is of great importance to the applications of single molecule detection, nanofluidic devices and nanofiltration membranes. The most popular way to fabricate nanopores in inorganic films, such as SiN,  SiO2 and Al2O3, is to use focused ion or electron beam. However, the feedback system or direct imaging is required using this poring method, and only one single nanopore can be fabricated at a time, which limits mass production. Therefore, it is very significant to explore a new poring method which could create size- and density-controllable nanopores without any feedback system.
Based on the Heavy Ion Research Facility in Lanzhou (HIRFL), the scientists have successfully demonstrated a direct poring method in WOnanosheets using swift heavy ions irradiation. 
In addition, the researchers applied molecular dynamics simulations to explain the underlying mechanism. It was found that the viscosity and surface tension of the transient molten phase caused by swift heavy ions are the key factors for the formation of nanopores.
By selecting ions of different electronic energy losses, the researchers created nanopores with sizes from 1.8 to 7.4 nm in WO3 nanosheets. And they can control the density of nanopores by applying different ion fluences. This new poring method, involving no chemical etching process, has certain potential for wide use.
This method paves a way to fabricate solid-state nanopores in materials with a low viscosity and surface tension using swift heavy ions. It also provides an insight into the latent ion track formation in solid materials.
This work was supported by the National Key Research and Development Program of China, National Natural Science Foundation of China and the Youth Innovation Promotion Association of CAS.
Figure. The sub-10 nm nanopores in the WO3 nanosheets created using single swift heavy ions. (Image by XU Lijun and ZHAI Pengfei)


LIU Fang

Institute of Modern Physics


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