In the decades-old quest to build artificial muscles, many materials have been investigated with regard to their suitability for actuator application (the ability of a material to reversibly change dimensions under the influence of various stimuli). Recently, hope in obtaining improved artificial muscles was revitalized by the discovery of the extraordinary mechanical and electrical properties of graphene and its chemical derivatives. A new study shows that electrical heating of graphene oxide nanoribbons mats results in reversible generation of 1.6% stress and maximum work capacity of about 40 J/kg, which is similar to that of natural muscle. Unlike previous studies, the team obtained the graphene material by chemical unzipping of multi-walled carbon nanotubes.
Photonic crystals are used to guide and localize light for all-optical processing of signals/information; to engineer dispersion and slow light; to harvest light (collect and redirect); and thresholdless lasing, that can be engineered by setting spectral ranges where light can be emitted. so far, there have been no demonstrations of full photonic bandgap at visible wavelengths - i.e., that at a certain visible range (between 400 nm to 780 nm) determined by the 3D photonic crystal structure, the light is rejected (reflected) at all angles of incidence. Researchers have now used a 3D nano-sculpturing process to fabricate 3D photonic crystal. The great potential of these 3D photonic crystal lies in the possibility to control light on a sub-wavelength scale.
The commercial realization of carbon nanotube-based electronic devices and their integration into the existing silicon-based processor technologies is still hampered by the inability to scale up the - currently lab-based - fabrication processes to manufacture a large number of devices on a single chip. The fundamental issue of carbon nanotube device fabrication still remains the biggest challenge for effective commercialization of nanotube electronics. In a further step towards large-scale integration of single-walled carbon nanotubes (SWCNTs) into complex functional electronic circuits, researchers have now combined a previously developed dielectrophoretic deposition approach with SWCNT sorting using density gradient ultracentrifugation, ensuring high purity of SWCNTs in suspension and consequently in the assembled devices.
The efficiency of catalyzing the oxygen reduction reaction (ORR) - the process that breaks the bonds of oxygen molecules - to a large degree determines the electrochemical performance of fuel cells. Platinum and platinum-based composites have long been considered as the most efficient ORR catalysts. In their search for practically viable non-precious metal ORR catalysts, researchers have also been investigating vertically-aligned nitrogen-containing carbon nanotubes. Having a strong electron-withdrawing ability, poly(diallyldimethylammonium chloride) (PDDA) was used to create net positive charge for carbon atoms in the nanotube carbon plane via intermolecular charge transfer. The resultant PDDA functionalized/adsorbed carbon nanotubes were demonstrated to act as metal-free catalysts for oxygen reduction reaction in fuel cells with similar performance as platinum catalysts.
In a standard dye sensitized solar cell, an organic molecule adsorbed on the surface of a porous electrode absorbs light and then initiates the charge separation process eventually leading to generation of photocurrent. While the dye appears to have "sensitized" the large bandgap material, it never actually does, because only the dye molecules absorb the light and generate the carriers, the large bandgap material primarily serves the function of a conducting channel to take the electrons out. While wide bandgap materials alone can not absorb the sun light efficiently, it has been predicted that if two large bandgap materials with type-II band alignment form coaxial nanowires, the effective indirect bandgap could be substantially smaller than either of the individual materials. After a few years effort, one research team has now demonstrated a real functional device that exhibits the key feature of the idea: the use of two large bandgap materials to make a solar cell behaving like a small bandgap material.
At the core of research efforts to determine the impact of synthetic nanoparticles on the environment and living systems is a fundamental understanding of the interactions between man-made nanoparticles and natural living systems that have evolved over millions of years. To describe nanoparticles at large, it may be beneficial to acknowledge that 1) biological systems are part of the food chain and therefore an essential component of the ecosystems and 2) collaborations are essential for such interdisciplinary research. Researchers have now presented a biophysical perspective that describes the fate of nanoparticles in both the aqueous phase and in living systems.
Although organic semiconductor materials cannot yet be packed as densely as state-of-the-art silicon chips, they require less power, cost less and do things silicon devices cannot: bend and fold, for example. Once perfected, organic semiconductors will permit the construction of low-cost, spray-on solar cells and even spray-on video displays. Notwithstanding tremendous progress in the area of organic electronics, several major challenges still exist. To address these challenges, researchers have combined organic electronics with nanoelectronics and developed the first 2D crystal of organic semiconductors on the millimeter scale, the thickness of which is only a single molecular layer, but with perfect long-ranged crystalline order.
In order to get a true picture of the processes and events that take place inside unmodified, living cells, probing techniques need to be non-destructive, noninvasive and in real-time. Due to their small dimensions, high-aspect ratio nanomaterials such as nanofibers, nanowires and carbon nanotubes are ideal for cellular applications since they can cross the cell membrane without causing significant damage. In particular, semiconductor nanowires attract a lot of interest because of their uniformity, reproducibility and possibility of fine-tuning their intrinsic properties - physical dimensions, crystal structure, electrical and optical properties, etc. Researchers have now shown, for the first time, the spontaneous and close interface of arrays of vertically aligned indium arsenide nanowires with two relevant cell lines, human embryonic kidney cells and rat embryonic dorsal root ganglion neurons.