Fabrication of High-Aspect Ratio Nanogratings for Phase-Based X-Ray Imaging

Diffractive optical elements such as periodic gratings are fundamental devices in X-ray imaging – a technique that medical, material science, and security scans rely upon. Fabrication of such structures with high aspect ratios at the nanoscale creates opportunities to further advance such applications, especially in terms of relaxing X-ray source coherence requirements. This is because typical grating-based X-ray phase imaging techniques (e.g., Talbot self-imaging) require a coherence length of at least one grating period and ideally longer. In this paper, the fabrication challenges in achieving high-aspect ratio nanogratings filled with gold are addressed by a combination of laser interference and nanoimprint lithography, physical vapor deposition, metal assisted chemical etching (MACE), and electroplating. This relatively simple and cost-efficient approach is unlocked by an innovative post-MACE drying step with hexamethyldisilazane, which effectively minimizes the stiction of the nanostructures. The theoretical limits of the approach are discussed and, experimentally, X-ray nanogratings with aspect ratios >40 are demonstrated. Finally, their excellent diffractive abilities are shown when exposed to a hard (12.2 keV) monochromatic X-ray beam at a synchrotron facility, and thus potential applicability in phase-based X-ray imaging.     

Ultra-Fine Nano-Mg(OH)2 Electrodeposited in Flexible Confined Space and its Enhancement of the Performance of LiFePO4 Lithium-Ion Batteries

To improve the Li-ion diffusion and extreme-environment performance of LiFePO₄ (LFP) lithium-ion batteries, a composite cathode material is fabricated using ultra-fine nano-Mg(OH)₂ (MH). First, a flexible confined space is designed in the local area of the cathode surface, through the transition of charged xanthan gum polymer molecules under electric field force and the self-assembly of the xanthan gum network. Then, the 20 nm nano-Mg(OH)₂ is prepared through cathodic electrodeposition within the local flexible confined space, and subsequent in situ surface modification as it traverses the xanthan gum network under gravity. LFP-MH significantly changes the density and homogeneity of the cathode electrolyte interphase film and improves the electrolyte affinity. The Li||LFP-MH half-cell demonstrates excellent rate capability (110 mAh g⁻¹ at 5 C) and long-term cycle performance (116.6 mAh g⁻¹ at 1 C after 1000 cycles), and maintains over 100 mAh g⁻¹ after 150 cycles at 60 °C, as well as no structural collapse of the cathode material after 400 cycles at 5 V high cut-off voltage. The cell also shows an obvious decrease in inner resistance after 100 cycles (99.53/133.12 Ω). This work provides a significant advancement toward LiFePO₄ lithium-ion batteries with excellent electrochemical performance and tolerance to extreme-environment.