Nano Focus: Multishell nanoparticles created within a solid matrix
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Trapping water monolayers with graphene allows AFM imaging
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ayers of water molecules are present on all hydrophilic surfaces, yet studying these dynamic structures at room temperature is problematic. Imaging them with scanning probe microscopy is usually hindered by the formation of a capillary meniscus between the tip and sample. K. Xu of Harvard University and P. Cao and J.R. Heath at the California Institute of Technology have managed to overcome this difficulty by trapping water adlayers on mica beneath a monolayer of graphene. As reported in the September 3rd issue of Science (DOI: 10.1126/ science.1192907; p. 1188), Xu and coworkers deposit a layer of graphene onto mica through mechanical exfoliation, and identify monolayer regions using spatially resolved Raman spectroscopy. Imaging the surface with an atomic force microscope (AFM) under
Nano Focus Multishell nanoparticles created within a solid matrix
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article inclusion in solid matrices is a common strategy used to tailor the properties of structural metallic alloys, such as strength or aging at elevated temperatures; however, it is a complicated story. Requirements for these particles that affect their interaction with dislocations and coarsening resistance are an often contradictory mix of stiffness, shearability, lattice parameter mismatch, diffusivities, and interfacial energies among other considerations. Earlier studies of solidstate precipitation within metallic alloys have focused on chemically homogenous nanoparticles. The ability to generate and tune more complex, chemically heterogeneous nanoparticle structures could lead to increased control over the macroscopic properties of important structural alloys. In a communication recently published
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MRS BULLETIN
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VOLUME 35 • NOVEMBER 2010
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ambient conditions reveals raised regions of graphene thought to be the result of water monolayers trapped beneath it. The height of these islands (corresponding to a layer of ice), and the strong influence of the humidity conditions on the trapped layers point to their identity as water molecules. The monolayer islands form polygonal shapes, with geometries which suggest
The atomic force micrograph shows monolayer islands of water trapped beneath a graphene sheet. More liquid-like water droplets are indicated by the higher peaks.
in the August 16th issue of Small (DOI: 10.1002/ smll.20100325; p. 1728) C. Monachon, D.C. Dunand, and D.N. Seidman of Northwestern University (Monachon now at EPFL, Switzerland) report a solid-state synthesis of nanoparticles with a core and two concentric shells within an aluminumbased alloy matrix. While this nanoparticle architecture has been achieved in solution-based syntheses, this work represents the first demonstration of multishell nanoparticles created within a solid matrix. Their nanoparticles are created using a twostep aging protocol on an aluminum-based alloy
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an ice-like structure formed epitaxially on the mica. Imaging at varying relative humidity sheds further light on the mechanism
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