Ultrathin hexagonal hybrid nanosheets synthesized by graphene oxide-assisted exfoliation of ß-Co(OH)2 mesocrystals.

In the present study, we report the synthesis of a high-quality, single-crystal hexagonal ß-Co(OH)2 nanosheet, exhibiting a thickness down to ten atomic layers and an aspect ratio exceeding 900, by using graphene oxide (GO) as an exfoliant of ß-Co(OH)2 nanoflowers. Unlike conventional approaches using ionic precursors in which morphological control is realized by structure-directing molecules, the ß-Co(OH)2 flower-like superstructures were first grown by a nanoparticle-mediated crystallization process, which results in large 3D superstructure consisting of ultrathin nanosheets interspaced by polydimethoxyaniline (PDMA). Thereafter, ß-Co(OH)2 nanoflowers were chemically exfoliated by surface-active GO under hydrothermal conditions into unilamellar single-crystal nanosheets. In this reaction, GO acts as a two-dimensional (2D) amphiphile to facilitate the exfoliation process through tailored interactions between organic and inorganic molecules. Meanwhile, the on-site conjugation of GO and Co(OH)2 promotes the thermodynamic stability of freestanding ultrathin nanosheets and restrains further growth through Oswald ripening. The unique 2D structure combined with functionalities of the hybrid ultrathin Co(OH)2 nanosheets on rGO resulted in a remarkably enhanced lithium-ion storage performance as anode materials, maintaining a reversible capacity of 860 mA h g(-1) for as many as 30 cycles. Since mesocrystals are ubiquitous and rich in morphological diversity, the strategy of the GO-assisted exfoliation of mesocrystals developed here provides an opportunity for the synthesis of new functional nanostructures that could bear importance in clean renewable energy, catalysis, photoelectronics, and photonics.

Dust mobilization in the presence of magnetic fields.

We present a study of surface dust mobilization due to photoelectric charging in the presence of a magnetic field. Dust mobilization is observed to be inhibited in certain regions and is correlated with the orientation of the magnetic field. The recent patched charge model, which describes a mechanism for dust charging and mobilization, is extended to explain the effects of magnetic fields seen in our laboratory results. We propose that ambient electrons collected in photoemitting areas precipitate changes in the emission and reabsorption of photoelectrons inside microcavities between dust grains. This affects the charging, repulsion, and subsequent mobilization of the dust grains surrounding the microcavities. The magnetic field controls the movement of ambient electrons across the dusty surface, resulting in active and inactive regions of dust mobilization. Computer simulations show that regions of ambient electron accumulation as imposed by the magnetic field match the areas of high dust activity.

A large ion beam device for laboratory solar wind studies.

The Colorado Solar Wind Experiment is a new device constructed at the Institute for Modeling Plasma, Atmospheres, and Cosmic Dust at the University of Colorado. A large cross-sectional Kaufman ion source is used to create steady state plasma flow to model the solar wind in an experimental vacuum chamber. The plasma beam has a diameter of 12 cm at the source, ion energies of up to 1 keV, and ion flows of up to 0.1 mA/cm2. Chamber pressure can be reduced to 4 × 10-5 Torr under operating conditions to suppress ion-neutral collisions and create a monoenergetic ion beam. The beam profile has been characterized by a Langmuir probe and an ion energy analyzer mounted on a two-dimensional translation stage. The beam profile meets the requirements for planned experiments that will study solar wind interaction with lunar magnetic anomalies, the charging and dynamics of dust in the solar wind, plasma wakes and refilling, and the wakes of topographic features such as craters or boulders. This article describes the technical details of the device, initial operation and beam characterization, and the planned experiments.