Epitaxial misfit van der Waals heterostructures unlock new family of materials
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l misfit van der Waals heterostructures unlock new family of materials
T
he engineering of materials with “properties-by-design” has spurred the creation of van der Waals (vdW) heterostructures that are based on the stacking of two-dimensional (2D) materials of varying compositions. These
combination of extraordinary absorption with other properties of metals can open up tremendous opportunities, such as photocatalysis, sensing, and desalination.” These plasmonic absorbers were tested for use in solar steam generation and demonstrated over 90% conversion efficiency at a solar irradiation of 4kW/m2. Shanhui Fan from Stanford University says, “This is innovative work demonstrating an important application in
energy technology of nanophotonic concepts. I look forward to seeing this scaled up into a practical system.” The researchers believe that with more advancements in design and fabrication of different templates along with low-cost plasmonic materials like aluminum, largescale manufacturing of complex nanoscale architectures will be possible for a diverse set of potential application fields. Rachana Acharya
layered structures, held together by weak vdW forces, often show optoelectronic properties that are radically different from their individual building blocks. Typical synthesis of vdW heterostructures relies on large-scale chemical vapor deposition (CVD) or mechanical stacking of single 2D flakes. Recently reported in Science Advances (doi:10.1126/sciadv.1501882), Kai Xiao, a staff scientist at Oak Ridge
National Laboratory (ORNL), and postdoctoral researcher Xufan Li, along with other co-workers from ORNL, Vanderbilt University, and Beijing Computational Science Research Center, presented the first known attempt to grow a misfit layer heterostructure containing GaSe and MoSe2 through a two-step CVD synthesis. The 2D heterostructures were fabricated by first reacting Se vapor with MoO3 to form monolayer MoSe 2 crystals on SiO 2 /Si or fused quartz substrates. Once deposited, the as-synthesized MoSe2 (n-type) was then used to template the controlled growth of p-type GaSe to form a vertical misfit bilayer with no interfacial contamination. Despite considerable success, “current CVD methods to directly grow 2D material heterostructures are limited to materials with similar lattice constants and/or crystal structures,” says Xiao of the Center for Nanophase Materials Sciences at ORNL. “It is a big challenge to put together two 2D materials with a large lattice-constant mismatch, but we are able to overcome this limitation with vdW epitaxial growth to create novel vdW heterostructures based on lattice-mismatched materials. This opens the door to new families of functional 2D materials for applications in photovoltaics, LEDs, transistors, and memory devices.” The atomic structure of the bilayer heterostructures was characterized by scanning transmission electron microscopy, and the images exhibited repeating Moiré patterns, which hinted at longrange superlattice order. Investigation
Light drives the migration of c
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