Articles in 2012

A major obstacle to fully understanding the catalytic mechanisms of oxygen reduction reactions and to designing more efficient catalysts is the lack of detailed information about the active site structure. Molecular local chemisorption sites and the long-range supramolecular arrangement of metallophthalocyanine molecules on a metal surface can now be controlled by the fine tuning of the overlayer coverage.

The effect of nanoscale surface roughness on heat transport across solid interfaces has remained contentious. Now, measurements of the pressure dependence of heat transport across polished nanoscale contacts formed between the tip of a scanning thermal microscope and a surface agree with a model that assumes quantum thermal transport across individual contact points.

The origin of the magnetism in manganese-doped gallium arsenide has been the subject of much debate. Now, hard X-ray angle-resolved photoemission has been used to probe the electronic structure of this material and clarify the mechanism through which the magnetism arises.

Phase-change materials show an unusual metal–insulator transition that is induced by disorder in the crystalline state. Numerical computations now show how the transition to the metallic state proceeds from the dissolution of electronic states situated at vacancy clusters to the formation of ordered vacancy layers.

Controlling surface structure at the atomic scale is paramount to developing effective catalysts. The surface structure of MoS₂ is now engineered to preferentially expose edge sites by successfully synthesizing contiguous large-area thin films of a highly ordered double-gyroid MoS₂ bicontinuous network with nanoscale pores.

Solid-state sensors for the detection of heavy-metal cations require for the most part sophisticated chemistry and equipment. It is now shown that toxic cations in environmental samples can be detected with ultrahigh sensitivity and over a broad range of cation concentrations by measuring the tunnelling current across films of nanoparticles decorated with striped monolayers of organic ligands.

Three-dimensional bioactive scaffolds can support tissue growth for studies in cellular biophysics and regenerative medicine. Such scaffolds have now been integrated with semiconductor nanowires to probe their porous interior, allowing for real-time monitoring of signals such as the response of neural and cardiac tissue models to drugs.

Knowledge of the density of optical states is crucial for understanding the function of photonic devices. A method that can map optical states with subwavelength precision, and therefore allow the study and design of optical properties on the nanoscale, is now reported.

Although oxygen vacancy distributions and dynamics control the operation of solid-oxide fuel cells, understanding the atomistic mechanisms involved during operation of the cell has proved difficult. An approach for the direct mapping of oxygen vacancy concentrations based on local lattice parameter measurements by scanning transmission electron microscopy is now proposed.

Although nanoparticulate gold possesses remarkable catalytic activity towards oxidation reactions, catalytic activity usually cannot be observed in particles larger than 5 nm. Atomic insights into dealloyed nanoporous gold catalysts by transmission electron microscopy now demonstrate that surface defects are active sites for the catalytic oxidation of carbon monoxide and that residual silver stabilizes atomic steps.

Innovative solutions for the design of sustainable and efficient systems for the conversion and storage of renewable energy sources are needed, and one promising option is the production of hydrogen through water splitting. A nanoparticulate electrocatalytic material consisting of metallic cobalt coated with a cobalt-oxo/hydroxo-phosphate layer is now found to exhibit active hydrogen evolution, and can also be converted into a cobalt oxide film catalysing oxygen evolution.

Flexible strain-gauge sensors, which could eventually be used in electronic skin, generally require complex device architectures. A simple and highly sensitive resistive sensor for the detection of pressure, shear and torsion with discernible strain-gauge factors has now been fabricated using two interlocked arrays of platinum-coated polymer nanofibres.

Electron transport in semiconducting polymers is usually inferior to hole transport, which is ascribed to charge trapping on defect sites. The observation of an identical electron-trap distribution in a range of materials now points to a common origin of these states that, as calculations suggest, may be related to hydrated oxygen complexes.

Heterointerfaces of organic semiconductors can show high electrical conductivity, but the details of their electronic structure remain largely unexplored. Schottky-gated heterostructures have now been used to probe the interface between single crystals of rubrene and PDIF-CN₂, showing that charge transport is due to electrons whose mobility exhibits band-like behaviour down to ~150 K.

The sustained release of both hydrophilic and hydrophobic immunomodulators for metastatic melanoma by nanoscale liposomal polymeric gels administered intratumorally or systemically is demonstrated. It is also shown that such a co-delivery approach delays tumour growth and increases the survival of tumour-bearing mice, and that its efficacy results from the activation of both innate and adaptative immune responses.

Many nanomaterials can induce cell autophagy, which can be either a concern in most in vivo situations or a benefit when exploited in cancer therapeutics. A family of short synthetic peptides that have a varied affinity to lanthanide oxide and lanthanide-based upconversion nanocrystals are now used to tune the degree of interaction between cells and nanocrystals, and thus the nanocrystals’ autophagy-inducing activity.

The length scale at which phenomena such as ferroelectricity is still present is of fundamental relevance for nanoscale applications. A high-resolution transmission electron microscopy study now shows how ferroelectricity can persist in nanoparticles down to about 5 nm in diameter, pointing the way towards the ultimate size limit for ferroelectric applications.

Electrostatic force microscopy with sub-piconewton resolution can now be used for the label-free identification of single dielectric nanoparticles of similar morphology but distinct low-polarizable materials. The technique can also distinguish between empty and DNA-containing virus capsids, and should be extensible to the characterization of surface and subsurface dielectric properties of nanoscale dielectrics and biological macromolecules in general.

Calcium-rich non-collagenous proteins in the extracellular matrix of bone are believed to be involved in the different steps of bone mineralization. It is now shown that in the absence of these proteins collagen can initiate and orient growing apatite crystals in vitro, and influence both their structural characteristics on the atomic scale and their larger-scale three-dimensional distribution in bone.

Conventional methods for the selection of tumorigenic cells from cancer cell lines rely on stem-cell markers. It is now shown that soft fibrin gels promote the growth of colonies of tumorigenic cells from single cancer cells from mouse or human cancer cell lines, and that as few as ten fibrin-cultured cells can lead to the formation of tumours in mice more efficiently than marker-selected cells.