Volume 12 Issue 10, October 2013

For the case of water on supported graphene, about 30% of the van der Waals interactions between the water and the substrate are transmitted through the one-atom-thick layer.

Advances in materials science and layout design have enabled the realization of flexible and multifunctional electronic devices. Two demonstrations of electronic skins, which combine temperature and pressure sensing with integrated thermal actuators and organic displays, unveil the potential of these devices for robotics and clinical applications.

Pristine graphitic surfaces seem to be more hydrophilic than previously assumed because of the unexpected influence of the quick adsorption of hydrocarbons from air.

A study on the subtle interplay between electronic structure and structural defects now explains why the suppression of conduction in the insulating state of bilayer graphene is not as strong as might be expected. It also reveals the possibility of creating graphene-based nanoscale systems with unique electronic properties.

The critical temperature of most superconductors varies with the density of charge carriers, which in turn is most easily tuned by chemical doping. The observation that a specially fabricated two-dimensional superconductor maintains the same critical temperature regardless of doping raises some important questions.

The emergence of superconductivity of insulating oxide interfaces has raised a number of intriguing theoretical challenges. Now, the critical temperature of strontium-doped lanthanum cuprate bilayer samples is shown to remain unchanged over a wide doping range, implying that changes in the carrier density cannot be the origin of the enhanced critical temperatures seen with respect to single-phase samples.

The insulator-to-metal transition occurring in magnetite is known as the Verwey transition, and its precise mechanism has recently come under renewed attention. Using pump–probe X-ray diffraction and optical reflectivity techniques, the dynamics of excitations known as trimerons are now examined, revealing the switching limits of this ubiquitous oxide material.

As indicated by direct band-structure measurements and calculations, tiny native imperfections in bilayer graphene are sufficient to cause the generation of coexisting massive and massless Dirac fermions. The massless spectrum is robust against strong electric fields and has a closed-arc topology consisting of a unique chiral pseudospin texture.

Hard biological materials such as diatoms and sea sponges can inspire the design of structural materials that are mechanically robust yet lightweight. Hollow titanium nitride lattices have now been fabricated that mimic the length scales (from 10 nm to 100 μm) and hierarchy of biological materials. These lattices attain tensile strengths of 1.75 GPa without failing (even after multiple deformation cycles) because of the low probability of pre-existing flaws.

Flexible devices mimicking the sensitivity of human skin typically turn pressure stimuli into electronic signals, which must be further processed to be interpreted by the user. By integrating an active matrix of organic light-emitting diodes in these foldable sensors, pressure can now control the brightness of each coloured pixel, enabling the direct visualization and quantification of the applied stimulus.

Although quantitative understanding of nanocrystal phase transformations is important for efficient energy conversion and catalysis, difficulties in directly monitoring nanoscale systems in reactive environments remain. Direct quantification of hydriding transformations in palladium nanocrystals now clearly reveals that the transformation rates are governed by nanocrystal dimensions.

Heat is a form of energy that is transported from a hot to a cold region, but it is not a notion that is associated with the microscopic measurement of electronic properties. It is now shown that local thermoelectric measurements can be used for imaging structural disorder in graphene, with high sensitivity, on the atomic and nanometre scales, uncovering soliton-like domain-wall line-patterns separating different graphene regions.

The catalytic activity of highly dispersed platinum nanoparticles is not yet well understood. Now, a unique approach that allows precise control of both the size and coverage of platinum nanoclusters reveals that particle proximity influences the oxygen reduction rate of these size-selected clusters, especially in terms of mass normalized activity.

Contact-angle and spectroscopy experiments on clean supported graphene and graphite show that these surfaces become more hydrophobic as they adsorb airborne hydrocarbons. Furthermore, the water contact angle on these graphitic surfaces decreases if these contaminants are partially removed by both thermal annealing and controlled ultraviolet–ozone treatments, suggesting that graphitic surfaces are more hydrophilic than previously believed.

Polyampholyte hydrogels synthesized from the random polymerization of oppositely charged ionic monomers are shown to be mechanically tough and highly viscoelastic. Strong ionic bonds within the gel act as permanent crosslinks and weaker ionic bonds reversibly break and re-form, enhancing the fracture resistance, shock absorbance and self-healing properties of the materials.

A strategy for assessing blood microcirculation and tissue hydration relies on monitoring the temperature and thermal conductivity of skin, respectively. It is now shown that arrays of micrometre-sized sensors and heaters can be integrated on stretchable substrates that conformably adhere to the skin; these devices allow spatially resolved heating and real-time temperature mapping in patients without limiting their motion.

The intrinsic hydrophobicity of graphitic surfaces and the recent claim of wetting transparency of supported graphene are being questioned. In this focus issue we highlight the latest developments aimed at increasing our understanding of how graphene and graphitic surfaces interact with water.