Letters in 2009

Arrays of quantum dots are produced in carbon nanotubes as a result of the interaction between the nanotubes and a substrate, and show quantized energy-level splittings.

The optical-gradient force between two nanophotonic waveguides can be tuned from attractive to repulsive by controlling the relative phase of the optical fields injected into the waveguides.

It is possible to sequence individual guanine bases in long-chain DNA molecules using a scanning tunnelling microscope by exploiting a distinct electronic state in the base molecule.

Electrochemical measurements show that the quantum capacitance of graphene is influenced by scattering from charged impurities, and also suggest that a longstanding puzzle about the interfacial capacitance in carbon-based electrodes has a quantum origin.

The flexibility of biomolecules at the microsecond timescale can be monitored under physiologically relevant conditions and with high spatial resolution using a technique based on atomic force microscopy.

Gold nanorods added to a laboratory-constructed estuarine mesocosm can accumulate in sediments, biofilms and various organisms such as fish, snails and shrimp. Most of the nanorods ended up in biofilms and clams, indicating that these nanoparticles could readily pass from the water column into the marine food web.

Excitons are created when a carbon nanotube absorbs photons. However, the triplet exciton is usually optically inactive, preventing its direct observation, lowering photocurrent efficiency and making optical injection of spin-polarized carriers impossible. Optical excitation of the triplet exciton has now been achieved.

Shape-memory alloys undergo reversible transformations between two distinct phases. Now researchers have shown that nanoscale pillars made of shape-memory alloys have a figure of merit for mechanical damping — substantially higher than the figures previously reported for bulk materials — making these nanopillars attractive for use in future microscale and smaller devices.

Aqueous droplets connected by single lipid bilayers have been used to examine the properties of protein channels and pores, and networks of droplets can form microscale batteries and detect light. Now, by inserting an engineered pore with diode-like properties into the interface bilayers, droplet networks that mimic simple electronic devices have been produced.

Many strongly correlated electron systems have a domain structure that obscures the fundamental properties of the homogeneous material. Experiments on single-domain nanobeams made of vanadium dioxide have revealed several new aspects of the metal–insulator transition in this material.

Multifunctional nanostructures have been created from DNA-based anisotropic, branched and crosslinkable building blocks — ABC monomers. Using these monomers, a target-driven polymerization process is demonstrated where polymers are generated only in the presence of a specific DNA molecule, leading to highly sensitive pathogen detection. The nanoarchitectures can also be used to deliver drugs to cells.

The electronic properties of graphene samples containing three layers of carbon atoms are significantly different from those of single-layer and bilayer graphene. Trilayer graphene is a semimetal and, unlike other materials, the overlap between the conduction and valence bands can be electrostatically controlled.

Porous membranes are widely used as filters for the production of clean drinking water. A new type of filtration membrane made of crosslinked proteins can cope with water fluxes that are three orders of magnitude higher than those that can be handled by commercial filtration membranes with similar rejection properties.

A new chip-based optical method has been used to actuate and detect the motion of nanocantilevers. This non-interferometric approach does not require a coherent light source. Multiplexed read-out of up to ten nanocantilevers is demonstrated in a silicon photonic chip.

The ability to create controlled patterns on carbon nanotubes could lead to nanoelectronic applications in which multiple transistors are fabricated on individual nanotubes. It has now been shown that carbon nanotubes can be decorated with alternating patterns of block copolymers and that gold nanoparticles can, in turn, be periodically attached to the tubes.

The conductivity of a self-assembled layer of cobalt phthalocyanine molecules is measured as a function of thickness. At low thickness, the molecules lie flat on the substrate and serve only to reduce the conductivity of the substrate. At high thickness, the molecules stand up to form stacks similar to their bulk form, and conduction occurs primarily through them.

A method for the assembly of nanoparticles into granular solids that can be continuously tuned from two dimensions to one dimension is reported. The energy barriers to electron transport in such solids increase in the one-dimensional limit, and an unexpected dependence of the electronic properties on temperature is also observed.

DNA nanotubes can potentially act as stiff interconnects, tracks for molecular motors and nanoscale drug carriers. Researchers have now reported a modular approach to DNA nanotube synthesis that can create geometrically well-defined triangular and square tubes. The method allows parameters such as geometry, stiffness and single- or double-stranded character to be tuned, and could provide access to designer nanotubes for a range of applications.

It is known that cancerous cells have different mechanical and adhesion properties from normal cells, but the reasons for this remain unclear. Atomic force microscopy studies show that the brush layers on the surface of cancerous and normal cervical cells are different, which suggest new considerations when detecting and studying cancerous cells by mechanical methods.

Chemical forces on surfaces have a central role in catalysis, thin-film growth and tribology. Many applications require knowledge of the strength of these forces as a function of position in three dimensions, but until now such information has only been available from theory. An approach based on atomic force microscopy has now been used to experimentally obtain this data, imaging the three-dimensional surface force field of graphite.