2 research outputs found
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 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.Comment: 27 pages, 5 figures in main text, plus supporting informatio
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Emergence of reconfigurable wires and spinners via dynamic self-assembly
Dissipative colloidal materials use energy to generate and maintain structural complexity. The energy injection rate, and properties of the environment are important control parameters that influence the outcome of dynamic self-assembly. Here we demonstrate that dispersions of magnetic microparticles confined at the air-liquid interface, and energized by a uniaxial in-plane alternating magnetic field, self-assemble into a variety of structures that range from pulsating clusters and single-particle-thick wires to dynamic arrays of spinners (self-assembled short chains) rotating in either direction. The spinners emerge via spontaneous breaking of the uniaxial symmetry of the energizing magnetic field. Demonstration of the formation and disaggregation of particle assemblies suggests strategies to form new meso-scale structures with the potential to perform functions such as mixing and sensing