One-dimensional nanosized core/shell PN-junctions are formed from N-type SnO 2 nanorods (synthesized via a hydrothermal method; diameter ∼10 nm, length ∼100 nm) uniformly coated with P-type CuO nanoparticles (diameter ∼4 nm). Gas sensors are realized from these PN-junction nanorods, and their resistances greatly decrease upon exposed to H 2 S at room temperature. The sensitivity against 10 ppm H 2 S at 60 °C is up to 9.4 × 10 6 . At the same time, the sensors have very good selectivity against H 2 S. Such good performances are probably attributed to the destruction of PN-junctions and the small size effect of nanostructures. Our results imply that one-dimensional heterostructured nanomaterials are promising candidates for high-performance gas sensors.

We report a novel nanomanufacturing technique that incorporates patterned arrays built entirely from Fe₃O₄ nanoparticles into a flexible and transparent polymer film. First, the nanoparticles are patterned using the enormous magnetic field gradients at the surface of commercial disk drive media, and then the resulting architecture is transferred to the surface of a polymer film by spin-coating and peeling. Since the particles are immobilized by the field gradients during the spin-coating process, the patterned array is preserved after peeling. To demonstrate the potential of this technology, we fabricate a 5 mm diameter all-nanoparticle diffraction grating capable of producing a white-light optical spectrum. We also demonstrate several extensions to this technology, where, by adding an external magnetic field during assembly, we create both periodic variations in topography, as well as a nanocomposite with two vertically and horizontally separated nanoparticle layers. As this technique leverages the nanometer resolution inherent in current magnetic recording technology, strong potential exists for low-cost nanomanufacturing of optical and electronic devices from a variety of nanomaterials with ∼10 nm resolution.

Indium-doped tin oxide (ITO) nanowires are synthesized in mass production via thermal evaporation of In2O3, SnO, and graphite mixture powders. The transverse sizes of these nanowires range from 70 to 150 nm, and the lengths are up to several tens of micrometers. The three elements In, Sn, and O uniformly distribute over the whole nanowire, respectively. The atomic concentration of In is about 5%. The gas sensors realized from these ITO nanowires are very sensitive to ethanol gas, and the sensitivity is about 40 against 200ppm ethanol at the work temperature of 400°C. Both the response and recovery time are shorter than 2s. These results suggest that ITO nanowires are good candidates for fabricating gas sensors.