Letters in 2008

Manipulating the properties of semiconducting nanostructures through magnetic doping can lead to interesting fundamental phenomena, as well as potential spintronics or memory devices. The demonstration that the magnetic properties of Mn-doped ZnSe dots can be tuned by adjusting the thickness of a CdSe shell represents a fundamental advance in the field.

Bridging the gap between theoretical and experimental work to understand the effect of plasticity on the crumpling of thin sheets into a small volume has proved difficult. A realistic numerical model now makes a distinction between elastic and elasto-plastic behaviour.

Understanding the short- and medium-range structure of metallic glasses remains a difficult challenge. The observation that the medium-range order has the characteristics of a fractal network may have broader implications in the understanding of the relation between structure and mechanical properties in metallic glasses.

Nanostructured high-surface-area materials capable of converting energy into mechanical work are promising for use as actuation devices. Surface-chemistry-induced changes of the surface stress in nanoporous gold are now observed on alternate exposure to ozone and carbon monoxide.

The growth kinetics and crystallization behaviour of DNA-directed colloidal systems are not well understood. Now, using experiments and simulations, a single nucleotide mismatch in DNA strands attached to two microsphere species enables the kinetics of crystal growth and segregation as a result of crystallization to be investigated.

A long-standing problem with molecular wires is their poor transport properties. Highly conductive and very long wires have now been synthesized by incorporating metal centres into rigid molecular backbones, which shows promise for their use in electronic devices.

A new polymer is investigated as a drug-delivery vehicle for the treatment of inflammatory diseases, such as cardiac dysfunction. The biocompatibility, neutral degradation products and controlled-release properties of the polyketal microparticles indicate the material’s promising future in inflammation inhibition.

Increasing the carrier density of a material to the limit at which superconductivity can be induced has been a long-standing challenge. This is now realized in an insulator by using an electric-double-layer gate in an organic electrolyte.

The trapping of electrons by grain boundaries in semiconducting and insulating materials is important for a wide range of devices such as sensors, and solar and fuel cells. First-principles calculations on MgO, LiF and NaCl reveal a novel type of electron trapping at grain boundaries associated with the negative electron affinity of these materials.

A new, asymmetric glassy state is identified in soft colloidal mixtures composed of large and small star polymers. The results will enable the design, control and tuning of the rheological properties of other soft composite materials.

The structure of C₆₀ is well-known: a perfectly symmetrical sphere of 12 isolated pentagons. But this is only one of 1,812 possible isomers, and the only one to obey the isolated-pentagon rule. So far it has been the only form observed. But now two isomers without isolated pentagons have been made.

Pores in thin films tend to lie in the plane of the substrate, which makes it impractical for applications where diffusion into the pores is necessary. Nanometre-scale epitaxy on a patterned substrate is now used to form vertically oriented pores in honeycomb-structured films.

We are used to thinking that a macroscopic phenomenon can be described in terms of either classical physics or quantum mechanics. But sometimes it can be both. For example, it is shown that the linear magnetoresistance in InSb can be achieved by a classical or quantum route.

Smart windows and switchable displays require electrochomic materials that change their optical properties on electron transfer. Organic polymers offer further benefits including high contrast, greater colour variety and flexible substrates, but their use has remained challenging. Now, a donor–acceptor approach has yielded the first neutral black polymeric electrochrome.

Ammonia is an important compound for producing pharmaceuticals, fertilisers and explosives. It is known to form hydrogen-bonded solids at high pressure, but ionic solids of ammonium amide are now predicted at even higher pressure.

Nanowire lasers have so far consisted of homogeneous semiconductor structures. The achievement of lasing from a multi-quantum-well heterostructure deposited on a nanowire demonstrates a new complexity in nanophotonic devices.

Developing novel strategies to drive or manipulate the migration of particles in solutions is important for lab-on-a-chip technologies, especially in the context of biological and chemical analysis. A strongly amplified and tunable migration of large particles using a passive transport phenomenon is now reported.

Geometric information on lithium diffusion is crucial to understanding electrode reactions for lithium ion battery applications. Combining high-temperature powder neutron diffraction and the maximum entropy method, experimental evidence for a curved one-dimensional chain for lithium motion in Li_xFePO₄ is now provided.

Stimuli-responsive hydrogels show potential as smart materials for drug delivery, however, the triggers used must be applicable in vivo. Now, a hydrogel has been synthesized that contains protein–protein interactions that respond to a specific pharmaceutical drug and enable the hydrogel to controllably release its load of a human growth factor, which increases cell proliferation.

Precise control over the geometry of nanoscale one-dimensional structures is challenging. Cylindrical polymer brushes have now been used to synthesize organo-silica hybrid nanowires that are not only soluble in water but also in many organic solvents.