Characterization of ion track etched conical nanopores in thermal and PECVD SiO$_{2}$ using small angle X-ray scattering

TL;DR

This study uses small-angle X-ray scattering to analyze and compare the morphology and size distribution of ion track etched conical nanopores in thermal and PECVD SiO$_{2}$, revealing material-dependent differences crucial for nanofluidic applications.

Contribution

It introduces a novel SAXS analysis method for anisotropic nanopores and provides detailed characterization of pore geometry and size distribution in different SiO$_{2}$ materials.

Findings

Thermal SiO$_{2}$ has a narrow size distribution (~2-4%).

PECVD SiO$_{2}$ shows a broader size variation (~8-18%).

Ion energy has negligible effect on pore size in PECVD SiO$_{2}$.

Abstract

Conical nanopores in amorphous SiO$_{2}$ thin films fabricated using the ion track etching technique show promising potential for filtration, sensing and nanofluidic applications. The characterization of the pore morphology and size distribution, along with its dependence on the material properties and fabrication parameters, is crucial to designing nanopore systems for specific applications. Here, we present a comprehensive study of track-etched nanopores in thermal and plasma-enhanced chemical vapor deposited (PECVD) SiO$_{2}$ using synchrotron-based small-angle X-ray scattering (SAXS). We present a new approach for analyzing the complex highly anisotropic 2-dimensional SAXS patterns of the pores by reducing the analysis to two orthogonal 1-dimensional slices of the data. The simultaneous fit of the data enables an accurate determination of the pore geometry and size distribution. The analysis reveals substantial differences between the nanopores in thermal and PECVD SiO$_{2}$. The track-to-bulk etching rate ratio is significantly different for the two materials, producing nanopores with cone angles that differ by almost a factor of 2. Furthermore, thermal SiO$_2$ exhibits an exceptionally narrow size distribution of only ~2-4%, while PECVD SiO$_2$ shows a higher variation ranging from ~8-18%. The impact of ion energy between 89 MeV and 1.6 GeV on the size of the nanopores was also investigated for pores in PECVD SiO$_{2}$ and shows only negligible influence. These findings provide crucial insights for the controlled fabrication of conical nanopores in different materials, which is essential for optimizing membrane performance in applications that require precise pore geometry.