Volume 11 Issue 12, December 2012

The field of photonic crystals has become one of the most influential and wide-ranging realms of contemporary electromagnetics and optics, with numerous more opportunities on the horizon.

Twenty five years since the birth of the field of photonic crystals, Eli Yablonovitch talks to Nature Materials about his pioneering contributions to the field and his vision for nanophotonics.

The surface properties of topological insulators are protected by time-reversal symmetry. Now, the finding of a topological crystalline insulator with metallic boundary states protected by lattice symmetries promises novel functionality.

Friction classically decreases with decreasing load. Nanoscale measurements on chemically modified graphite now show an opposite trend related to local deformation, which could serve as a probe for determining the exfoliation energy of layered materials.

Stacked bilayers can exhibit columnar alignment of phase-separated domains that propagates across hundreds of layers. The serial coupling of functionality that may result from such a long-range arrangement should lead to new applications in photonics and sensing.

A magnetic on/off switch for cell-death signalling in cancer cells is developed using antibodies conjugated to magnetic nanoparticles. The control of cell death in in vivo systems is demonstrated by a tell-tale morphological change within the zebrafish.

The release and self-assembly of peptides from metal–organic frameworks creates surface tension differences that can fuel the cruising motion of the framework, and a microscale 'boat' wrapped around a framework particle, at the air/liquid interface.

The assembly of hundreds of thousands of semiconductor nanorods into nearly spherical or needle-like colloidal superparticles made of highly ordered supercrystalline domains can be explained by simple thermodynamic and kinetic principles.

Quasicrystals are known for their lack of long-range periodic order. The observation in quasicrystals of quantum critical phenomena that are not seen in their crystalline approximants now demonstrates that the quasicrystals also have unique electronic states.

There are a number of approaches to coupling light with thin-film devices such as solar cells. The demonstration now that multiple scattering processes in two-dimensional random media enable efficient light trapping suggests new possibilities for photon management with the benefit of broad spectral and angular operation.

Topological crystalline insulators are a novel state of matter in which the topological features of the electronic structure have been predicted to originate from crystal symmetries. Now an experimental realization of a topological crystalline insulator is reported, in the form of Pb_1−xSn_xSe.

The dynamical processes associated with the magnetization of a material can be drastically altered by the application of a spin current. This study now demonstrates the feasibility of selectively exciting coherent auto-oscillation modes in magnetic nanostructures.

Classically, friction is known to increase with increasing normal load. Scanning probe experiments now show that reversible local delamination of chemically modified graphite can lead to an enhancement in friction as the applied load decreases, resulting in an effectively negative friction coefficient.

On application of a focused magnetic field, zinc-doped iron oxide nanoparticles with targeting antibodies attached are shown to activate cell death signalling in a spatially controlled manner. This triggering of apoptosis signalling, via the magnetically activated aggregation of receptors, is observed in both in vitro and in vivo systems.

It is now shown that, unlike most semiconductors, plasmonic metal nanostructures constructively couple the energy of photons and thermal energy, with the reaction rate positively responding to both stimuli. These unique characteristics suggest that these photocatalysts could prove useful for heterogeneous catalytic processes that cannot be activated using conventional thermal processes on metals or photocatalytic processes on semiconductors.

Some of the most challenging issues in energy conversion are the insufficient activity of the catalysts for the oxygen-reduction reaction, catalyst degradation and carbon-support corrosion. A class of mesostructured carbon-free metallic catalysts based on thin films and with tunable near-surface composition, morphology and structure that lead to an improved affinity for the electrochemical reduction of oxygen are now reported.

Although the search for new zeolites has traditionally been based on trial-and-error approaches, more rational methods are now available. Using the principle of inverse sigma transformation, the reactivity of framework germanium atoms in strong mineral acid has now been exploited to selectively remove germanium from a germanosilicate zeolite.

Implantable neural microelectrodes are critical to neuroscience research and emerging clinical applications including brain-controlled prostheses. A composite electrode consisting of a carbon fibre core, an insulating polymer coating and a polythiophene-based recording pad has now been developed that shows reduced chronic reactive tissue response in rats compared with existing architectures, owing to its smaller size and improved mechanical compliance with brain tissue.

Stacked lipid bilayers usually display smectic order. It is now found that multicomponent stacked bilayers can also exhibit columnar order, which arises from the coupling of interlayer smectic order and intralayer phase-separated domains, and propagates across hundreds of layers.

Various artificial cells that can store molecules in cages are designed to generate mechanical motion by dissipating energy through chemical reactions or through the reorganization of molecules. A hybrid biomimetic motor system consisting of a metal–organic framework and diphenylanaline peptides is now designed to release guest molecules in the isotropic direction via a bond-breaking framework.

This year marks a quarter of a century since the birth of the field of photonic crystals. Largely stimulated by the early works of Eli Yablonovitch and Sajeev John, it has become a principal area at the interface of photonics and condensed-matter physics. This Nature Materialsfocus issue explores the early history of the field, the challenges that had to be overcome before it gained broader acceptance, the wider scientific and technological impact it has had, as well as the new directions it is now moving in.