  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 SiO$_2$ membranes,
fabricated using the scalable track etch technique. Pores are fabricated by
irradiation of 1 $\mu$m thick SiO$_2$ windows with 2.2 GeV $^{197}$Au ions and
subsequent chemical etching. Structural characterisation is performed using
atomic force microscopy (AFM), scanning electron microscopy (SEM), small angle
X-ray scattering (SAXS), ellipsometry, and surface profiling. Conductometric
characterisation 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 $\pm$ 0.1) nm, a half-cone angle of (12.6
$\pm$ 0.1)$^{\circ}$, and a length of (710 $\pm$ 5) nm. The $pK_a$, $pK_b$, and
$pI$ are determined to 7.6 $\pm$ 0.1, 1.5 $\pm$ 0.2, and 4.5 $\pm$ 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
challenges that contemporary nanopore systems face, and offers a platform to
improve the performance of existing applications.
