Role of defects in atom probe analysis of sol-gel silica

TL;DR

This study demonstrates that UV and deep UV lasers enhance atom probe tomography of silica by increasing absorption through defects, with density functional theory explaining the defect-related absorption mechanisms.

Contribution

It provides new insights into how defects in silica influence laser absorption and APT analysis, combining experimental results with theoretical modeling.

Findings

UV lasers achieve high chemical resolution in silica APT

Defects increase silica absorption in UV range

Defects may cause deviations in chemical composition

Abstract

Silicon dioxide is a suitable material to encapsulate proteins at room temperature so that they can be analysed at the atomic level using laser-assisted atom probe tomography (La-APT). To achieve this goal, in this study we show that UV and deep UV lasers can achieve a high success rate in La-APT of silica in terms of chemical resolution and three-dimensional image volume, with both lasers providing comparable results. Since the La-APT analyses are driven by photon absorption, in order to understand the mechanisms behind the enhanced absorption of UV light, we performed density functional theory calculations to model the electronic and optical properties of amorphous silica matrices generated using a Monte Carlo approach to structural optimisation. In particular, we have investigated the role of various defects introduced during sample preparation, such as substitutional and interstitial carbon, sodium and gallium ions, and hydrogen. Our results show that the presence of defects increases the absorption of silica in the UV and deep-UV range and thus improves the La-APT capabilities of the material. However, due to the low density of free charge carriers resulting from the absorption of laser energy by defects, deviations from the nominal chemical composition and suboptimal chemical resolution may occur, potentially limiting the optimal acquisition of APT mass spectra.