Molecular Valves for Controlling Gas Phase Transport Made from Discrete Angstrom-Sized Pores in Graphene

An ability to precisely regulate the quantity and location of molecular flux is of value in applications such as nanoscale 3D printing, catalysis, and sensor design. Barrier materials containing pores with molecular dimensions have previously been used to manipulate molecular compositions in the gas phase, but have so far been unable to offer controlled gas transport through individual pores. Here, we show that gas flux through discrete angstrom-sized pores in monolayer graphene can be detected and then controlled using nanometer-sized gold clusters, which are formed on the surface of the graphene and can migrate and partially block a pore. In samples without gold clusters, we observe stochastic switching of the magnitude of the gas permeance, which we attribute to molecular rearrangements of the pore. Our molecular valves could be used, for example, to develop unique approaches to molecular synthesis that are based on the controllable switching of a molecular gas flux, reminiscent of ion channels in biological cell membranes and solid state nanopores.Comment: to appear in Nature Nanotechnolog

Extraordinary High Microwave Absorption Cross Section of Ultralong Carbon Nanotubes

The microwave-induced heating of nanoparticles has been actively studied in pursuit of more efficient microwave absorbers. Here we systematically investigated the microwave absorption cross section of conductive particles (Al), magnetic particles (Fe3O4), and carbon nanotubes with different lengths. The particles were suspended in silicone oil and irradiated with a microwave at 2.45 GHz using a single-mode microwave reactor. The experimentally measured heating rate was analytically modeled based on the modified Lambert−Beer law to obtain the microwave absorption cross section per mass. The microwave-induced heating rate was primarily dependent on optical absorbance, which is proportional to the mass concentration of suspended particles. Under the similar optical absorbance, longer nanotubes provided greater microwave absorption cross section which could be described by the short dipole antenna theory. The microwave absorption cross section of 5 mm long multiwalled carbon nanotubes was ∼4080 times greater than that of Al particles. One-dimensional ultralong carbon nanotubes provide a unique opportunity as super microwave absorbers which may be useful in chemical, biomedical, and process applications.131411sciescopu

Topological matter: Graphene and superfluid he

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