Highly Rectifying Conical Nanopores in Amorphous SiO2 Membranes for Nanofluidic Osmotic Power Generation and Electroosmotic Pumps

Nanopore membranes are a versatile platform for a wide range of applications ranging from medical sensing to filtration and clean energy generation. To attain high-flux rectifying ionic flow, it is required to produce short channels exhibiting asymmetric surface charge distributions. This work reports on a system of track etched conical nanopores in amorphous SiO2 membranes, fabricated using the scalable track etch technique. Pores are fabricated by irradiation of 920 ± 5 nm thick SiO2 windows with 2.2 GeV 197Au ions and subsequent chemical etching. Structural characterization is performed using atomic force microscopy, scanning electron microscopy, small-angle X-ray scattering, ellipsometry, and surface profiling. Conductometric characterization of the pore surface is performed using a membrane containing 16 pores, including an in-depth analysis of ionic transport characteristics. The pores have a tip radius of 5.7 ± 0.1 nm, a half-cone angle of 12.6 ± 0.1°, and a length of 710 ± 5 nm. The pKa, pKb, and pI are determined to 7.6 ± 0.1, 1.5 ± 0.2, and 4.5 ± 0.1, respectively, enabling the fine-tuning of the surface charge density between +100 and −300 mC m–2 and allowing to achieve an ionic current rectification ratio of up to 10. This highly versatile technology addresses some of the challenges that contemporary nanopore systems face and offers a platform to improve the performance of existing applications, including nanofluidic osmotic power generation and electroosmotic pumps.