Artem Baskin

Self-assembly of magnetite nanocubes into helical superstructures

Tuning the twisting in helical nanowires Assembly of inorganic nanoparticles into complex structures often requires a template. Researchers can now assemble helical nanowires out of cubic magnetite nanocrystals by tuning interactions that bind or separate them. Singh et al. floated the nanocrystals on a liquid and aligned them with a magnetic field. After the liquid evaporated, different twisted nanowires remained. The helices varied according to the concentration of nanocrystals, their shape, and the strength of the magnetic field. Competition between weak forces drives this self-assembly and can lead to arrays with the same twist direction. Science, this issue p. 1149 The presence of a magnetic field helps control the balance among different assembly forces. Organizing inorganic nanocrystals into complex architectures is challenging and typically relies on preexisting templates, such as properly folded DNA or polypeptide chains. We found that under carefully controlled conditions, cubic nanocrystals of magnetite self-assemble into arrays of helical superstructures in a template-free manner with >99% yield. Computer simulations revealed that the formation of helices is determined by the interplay of van der Waals and magnetic dipole-dipole interactions, Zeeman coupling, and entropic forces and can be attributed to spontaneous formation of chiral nanocube clusters. Neighboring helices within their densely packed ensembles tended to adopt the same handedness in order to maximize packing, thus revealing a novel mechanism of symmetry breaking and chirality amplification.

Chemical sensing with switchable transport channels in graphene grain boundaries

Grain boundaries can markedly affect the electronic, thermal, mechanical and optical properties of a polycrystalline graphene. While in many applications the presence of grain boundaries in graphene is undesired, here we show that they have an ideal structure for the detection of chemical analytes. We observe that an isolated graphene grain boundary has ~300 times higher sensitivity to the adsorbed gas molecules than a single-crystalline graphene grain. Our electronic structure and transport modelling reveal that the ultra-sensitivity in grain boundaries is caused by a synergetic combination of gas molecules accumulation at the grain boundary, together with the existence of a sharp onset energy in the transmission spectrum of its conduction channels. The discovered sensing platform opens up new pathways for the design of nanometre-scale highly sensitive chemical detectors.

Electronic structures of porous nanocarbons

We use large scale ab-initio calculations to describe electronic structures of graphene, graphene nanoribbons, and carbon nanotubes periodically perforated with nanopores. We disclose common features of these systems and develop a unified picture that permits us to analytically predict and systematically characterize metal-semiconductor transitions in nanocarbons with superlattices of nanopores of different sizes and types. These novel materials with highly tunable band structures have numerous potential applications in electronics, light detection, and molecular sensing.

Magnetic field-induced self-assembly of iron oxide nanocubes

Self-assembly of inorganic nanoparticles has been studied extensively for particles having different sizes and compositions. However, relatively little attention has been devoted to how the shape and surface chemistry of magnetic nanoparticles affects their self-assembly properties. Here, we undertook a combined experiment-theory study aimed at better understanding of the self-assembly of cubic magnetite (Fe3O4) particles. We demonstrated that, depending on the experimental parameters, such as the direction of the magnetic field and nanoparticle density, a variety of superstructures can be obtained, including one-dimensional filaments and helices, as well as C-shaped assemblies described here for the first time. Furthermore, we functionalized the surfaces of the magnetic nanocubes with light-sensitive ligands. Using these modified nanoparticles, we were able to achieve orthogonal control of self-assembly using a magnetic field and light.

Clusters and Lattices of Particles Stabilized by Dipolar Coupling

We model stabilization of clusters and lattices of spherical particles with dominant electric and magnetic dipolar coupling, and weak van der Waals coupling. Our analytical results demonstrate that dipolar coupling can stabilize nanoparticle clusters with planar, tubular, Möbius, and other arrangements. We also explain for which parameters the nanoparticles can form lattices with fcc, hcp, sh, sc, and other types of packing. Although these results are valid at different scales, we illustrate that realistic magnetic and semiconducting nanoparticles need to have certain minimum sizes to stabilize at room temperature into nanostructures controlled by dipolar coupling.

Correlated Diskoid-like Electronic States

We study highly excited diskoid-like electronic states formed in the vicinity of charged and strongly polarizable diskotic nanostructures, such as circular graphene flakes. First, we study the nature of such extended states in a simple two-electron model. The two electrons are attached to a point-like nucleus with a charge 2+, where the material electron is forced to move within a 2D disk area centered at the nucleus, while the extended electron is free to move in 3D. Pronounced and complex correlations are revealed in the diskoid-like states. We also develop semiclassical one-electron models of such diskotic systems and explain how the one-electron and many-electron solutions are related.