Nano Focus: Shrinkage leads to nanoscale resolution in 3D geometries and with a variety of materials
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US Shrinkage leads to nanoscale resolution in 3D geometries and with a variety of materials
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ptical metamaterials are structures that interact with light to challenge the laws of physics. They can exhibit a negative refractive index to be used in electromagnetic cloaks, for super-high resolution imaging, and for unusual color effects. To interact with electromagnetic waves, however, these materials have to possess dimensions comparable to the wavelengths, namely 100 nm and smaller. Such precision is enabled in state-of-the art two-dimensional (2D) nanofabrication but remains challenging in three-dimensional (3D) geometries. The research team of Edward S. Boyden at the Massachusetts Institute of Technology has developed a unique approach to fabricate 3D patterns with nanoresolution. The process, called ImpFab for “implosion fabrication,” was reported in a recent issue of Science (doi:10.1126/science.aau5119) and relies on the following principle. A porous hydrogel, typically a polyacrylate or a polyacrylamide, is swollen in an aqueous solution containing ions or organic molecules that readily diffuse through the pores and deposit at the surface of polymeric chains. Chemical reactions can occur, such as the growth of metallic nanoparticles from
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Department of Energy. The improved ORR catalytic activity was attributed to the synergistic catalysis between the PtCo nanoparticles and the Co, N-containing carbon support. Specifically, in addition to directly reducing O2 to water over the PtCo nanoparticles, the N-coordinated cobalt (Co-Nx-Cy) sites on the substrate can also reduce O2 to water and H2O2. The generated H2O2 then diffuses to the surface of nearby Pt-Co nanoparticles where it is eventually reduced to water. Bao Yu Xia of Huazhong University of Science & Technology, China, says that the key deliverables of this work, “developing cost-effective and scalable approaches for some of the most
ionic suspension, directly within the hydrogel. After this internal coating, the composite is shrunk down, and then further solidified by sintering to create metallic structures. Since hydrogels can be 3D-printed at the microscale, this principle can be easily coupled with 3D printing. Using hydrogels with controllable cross-linking density, the homogeneous shrinkage occurring after dehydration results in retention of the shape, but a decrease in dimensions. As a result, 3D patterns with complex shapes and resolutions of 50 nm could be fabricated in silver. These were found to exhibit an electrical conductivity only about 10 times less than that of bulk silver despite the high porosity (see Figure). Shweta Agarwala, a researcher at the Singapore Centre for 3D Printing and leading innovator in additive manufacturing for electronics and biotechnology, says that “currently, direct-writing of nanostructures is possible using noncontact methods like inkjet and aerosol jet, but the resolution is limited to 10 µm. Moreover, these techniques are able to print in 2D plane only. This research of using sacrificial scaffolds to patt
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