Atomic Structure Modulations in Ion-Exchanged Hydroxyapatite Investigated by HRTEM and Single Image Denoising

Hydroxyapatite (HAP) is widely utilized in various applications, where its properties are strongly regulated by ionic substitution. However, the atomic-scale structural origins of such modulation remain poorly understood. Although high-resolution transmission electron microscopy (HRTEM) enables direct structural characterization, achieving atomic-scale resolution in HAP is challenging due to its beam sensitivity. Low-dose imaging mitigates beam-induced damage but often suffers insufficient contrast for local structural analysis. Herein, we developed an HRTEM imaging approach aided with single-image deep-learning denoising to investigate the structural effects of Na⁺ substitution in HAP. The denoising effectively removes noise from low-dose TEM images, facilitating both qualitative and quantitative analysis of atomic arrangements in HAP particles. We show that Na⁺ incorporation induces disordered surface layers, providing direct insight into ion-induced property modulation in HAP. Our low-dose imaging approach combined with single-image denoising offers a framework for atomic-scale structural characterization of beam-sensitive materials that are otherwise obscured by beam damage.