The controlled synthesis of single-walled carbon nanotubes (SWCNTs), which generally requires a nanoscale catalyst metal, is crucial for their application to nanotechnology. In the chemical vapor deposition (CVD) of SWCNTs, the known effective catalyst species are the iron-family elements iron, cobalt, and nickel, with which a high SWCNT yield can be obtained. However, gold, silver, and copper have never been reported to produce SWCNTs. It is well known that iron, cobalt, and nickel have the catalytic function of graphite formation but that gold does not. The difference between the iron-family metals and gold is that the binding energy of carbon is much larger for the iron-family metals. Carbon atoms cannot stay on gold long enough to form a graphitic network. Thus, it is rather natural for iron, cobalt, and nickel to generate SWCNTs, but it is totally unexpected that gold would produce them too. The same picture is applicable to silver and copper. Nevertheless, researchers in Japan succeeded in developing a nanoparticle activation method that shows that even gold, silver, and copper act as efficient catalysts for SWCNT synthesis. These non-magnetic catalysts could provide new routes for controlling the growth of SWCNTs.
Artificial opals are gemstones that are of considerable scientific and technological interest as photonic crystals, as components of light sources, solar cells, and chemical sensors. They are conveniently made from periodic stackings of nanospheres. It would be exciting if one could fabricate optical cavities in these photonic crystals by removing, or adding high dielectric material to a single unit cell in the structure. These optical cavities would localize light that potentially enables the fabrication of high-resolution miniature on-chip sensors, or even qubits for quantum computers. Previously, such controlled modification of the nanostructure of a single colloid in an opal has not been achieved. Now, researchers in The Netherlands developed a method for realizing both single and arrays of material cavities, or defects, in individual colloids on the surface of silicon dioxide artificial opals by a focused ion beam milling technique. This research could ultimately lead to the fabrication of a photon-on-demand light source.
While the first reported fullerenes and nanotube structures were composed of carbon, it was soon recognized that a plethora of comparable inorganic candidates should also exist. A rich assortment of IF (inorganic fullerene-like structures, or IF for short) nanostructures have been synthesized, and are finding practical uses in tribology, photonics, batteries, and catalysis. On such inorganic molecule that can achieve fullerene-like nanostructures, cesium oxide, is particularly useful for a multitude of applications in photoemissive systems. Unfortunately, it is extremely reactive in the ambient atmosphere, so its production and handling require high vacuum and very pure inert conditions; which translates into problematic and expensive manufacturing and handling, which in turn limits its technological scope and device lifetime. In their quest for a relatively uncomplicated high-yield synthesis method for chemically stable cesium oxide IFs, scientists succeeded in exploiting highly concentrated solar radiation (ultrabright incoherent light) toward that end. This resulted in a simple, inexpensive, and reproducible photothermal procedure for synthesizing IF nanoparticles.
Zinc oxide (ZnO) is considered a workhorse of technological development exhibiting excellent electrical, optical, and chemical properties with a broad range of applications as semiconductors, in optical devices, piezoelectric devices, surface acoustic wave devices, sensors, transparent electrodes, solar cells, antibacterial activity etc. Thin films or nanoscale coating of ZnO nanoparticles on suitable substrates are viewed with great interest for their potential applications as substrates for functional coating, printing, UV inks, e-print, optical communication (security-papers), protection, barriers, portable energy, sensors, photocatalytic wallpaper with antibacterial activity etc. Various methods like chemical, thermal, spin coating, spray pyrolysis, pulsed laser deposition have been used for thin film formation but they are limited to solid supports such as metal, metal oxides, glass or other thermally stable substrates. Coating of ZnO nanoparticles on thermolabile surfaces is scarce and coating on paper was yet to be reported. Paper as a substrate is an economic alternative for technological applications having desired portability and flexibility. Researchers from the National Tsing Hua University in Taiwan found a way of coating paper with ZnO nanoparticles using ultrasound.
Synthetic nanopores are promising biosensors, possibly as a robust and versatile replacement for their biological counterparts in characterizing DNA, RNA, and polypeptides. In the past few years since their first introduction, synthetic nanopores have been found in a wide range of biological and nonbiological applications, including characterization of double-stranded DNA length and folding, detection of immune complexes, profiling of optical traps, and basic studies of nanoscale ion transport mechanisms. Given the broad technological importance of synthetic nanopores, it is highly desirable to develop a reliable technique for fabricating these devices using low-cost materials. Researchers at Brown University now report a systematic study of nanopore formation in a plastics system. They also developed a lithography-free technique for fabricating nanopores with biomolecular sensing capabilities.
Back in March Nanowerk Spotlight reported on work by Sandia researchers who developed a range of novel platinum nanostructures with potential applications in fuel and solar cells (see: Novel platinum nanostructures). Through the use of liposomal templating and a photocatalytic seeding strategy the Sandia team produced a variety of novel dendritic platinum nanostructures such as flat dendritic nanosheets and various foam nanostructures (nanospheres and monoliths). In an intriguing follow-up report on the growth of hollow platinum nanocages, they now show for the first time a one-to-one correspondence between the porphyrin photocatalyst molecules and the seed particles that go on to grow the dendrites. This indicates that the whole process might be used for nanotagging biological molecules and other structures that have been labeled with a photocatalytic porphyrin.
Nanoshells are a novel class of optically tunable nanoparticles that consist of alternating dielectric and metal layers. They have been shown to have tunable absorption frequencies that are dependent on the ratio of their inner and outer radii. Therefore nanoshells can potentially be used as contrast agents for multi-label molecular imaging, provided that the shell thicknesses are tuned to specific ratios. When used as contrast agents, nanoshells of small dimensions offer advantages in terms of delivery to target sites in living tissues, bioconjugation, steric hindrance, and binding kinetics. Besides their improved tissue penetration, smaller nanoshells generate a strong surface plasmon resonance and may exhibit absorption peaks in the visible?near-infrared spectrum. Sub-100 nm nanoshells also provide large surface areas to volume ratios for chemical functionalization that can be used to link multiple diagnostic (e.g. radioisotopic or magnetic) and therapeutic (e.g. anticancer) agents. Researchers at Northwestern University have come up with a relatively easy way to synthesize sub-100 nm nanoparticles that give rise to tunable peaks.
The interest in research on magnetic nanocapsules has increased considerably since it was found that their intermediate states between bulk and atomic materials may present different magnetic behaviors from their correspondent bulk counterparts. This difference offers an opportunity for researchers to develop many important technical applications such as magnetic refrigerators, magnetic recording, or magnetic fluids. As the principal contributor of the novel properties, various magnetic cores of nanocapsules, including rare earths and their carbides, have been researched extensively over the past two decades. In addition, cores of magnetic rare-earth intermetallic compounds are becoming a major research focus. However, there have been considerable difficulties in preventing oxidation of the particles of rare-earth elements and compounds. Researchers in PR China have now succeeded in synthesizing a new type of intermetallic nanocapsule that can be applied in cyrogenic magnetic refrigerator devices.