Nano

Scanning Tunneling Microscopy and Spectroscopy have been used in an attempt to elucidate the electronic structure of nanotube systems containing two constituent shells. Evidence for modified electronic structure due to the inter-layer interaction in double-walled carbon nanotubes is provided by the experimental tunneling spectra and the contribution of the inner tube to the local density of states of the "composite" double-walled system is identified in agreement with previous theoretical calculations. An explicit correlation between the chirality of the two constituent tubes, the inter-wall interaction and the overall electronic structure for double-walled carbon nanotubes, is demonstrated by our experiments, showing that the effect the inner tube has on the overall electronic structure of double-walled nanotubes cannot be neglected, and is key to the opto-electronic properties of the system. We postulate that previous analysis of the opto-electronic properties on multiple-walled carbon nanotubes based purely on the outer layer chirality of the tube needs significant modification based on new understanding brought forth with our analysis.

Site-specific single polyaniline nanowires were fabricated through electrophoresis growth with acetone wetting. After growing the nanowires, the post-process of acetone wetting of the nanowires improved morphology, topology, and electrical conductivity with coagulation and substitution in polyaniline. They showed resistance changes of 39.57 ± 11.57% and presented 2.38 × 10^-4 ± 3 × 10^-5 Ω · cm, 133.77 ± 13.82 nm thickness, and 133.17 ± 13.01 nm width in 1 μm to 5.5 μm length. The new combined growth process of electrophoresis and acetone wetting significantly improved reproducibility, reliability, and controllability in the fabrication of single polymer nanowires.

We review the progress in observation of electrically induced conformational changes of a range of single molecules and molecular assemblies using scanning tunneling microscopy (STM). Recent results using species with optical active functional groups and supramolecular structures confirmed the previously observed effects that the cholesterol molecules with soft linkers have the conformational bistability when switching the bias polarity, while no discernable changes were observed for the mesogen molecules, containing rigid linking units. In addition, it was also observed that the linker units could have appreciable impacts on the assembling characteristics.

Hydrocarbons such as methane, ethylene, and CO with high purity (> 99.9%) have been widely used to synthesize single-walled carbon nanotubes (SWCNTs). Here, liquefied petroleum gas (LPG) was used to synthesize SWCNTs by catalytic chemical vapor deposition. The LPG converted into CNTs and other stable hydrocarbons. The BET specific surface area of SWCNT was about 583 m²/g. The as-grown SWCNT showed good graphitization. The graphitization can be further modulated by the growth temperature. Certain amount of sulfur in LPG was a promoter for SWCNT growth. Compared SWCNTs obtained from methane, more semiconductive SWCNTs were synthesized from LPG as carbon source. The LPG is in low price, thus, a methodology to lower the production cost of SWCNTs with hydrocarbon mixtures is realized.

We measured the content of single-walled carbon nanotubes (SWCNTs) in SWCNT soot within 3.7% error using UV-VIS-NIR absorption spectroscopy. We also propose a better overall evaluation method by combining thermogravimetic analysis with UV-VIS-NIR absorption spectroscopy to analyze the purity of SWCNT providing the accurate assessment of the amounts of noncarbonaceous impurity, carbonaceous impurity, and SWCNT each with respect to a highly purified reference.

A series of cadmium telluride (CdTe) nanocrystals were synthesized by a modified organometallic synthesis method at various reaction temperatures ranging from 130 to 250°C. In this method, octadecylamine (ODA) was introduced as an additional coordinating component to the mixture of trioctylphosphine oxide (TOPO) and trioctylphosphine (TOP). CdO was used as a precursor. The prepared CdTe nanocrystals were studied by the absorption and emission spectra as well as the powder X-ray diffraction (XRD) patterns. The result shows that besides the traditional continuous-growth mode observed frequently at relatively high reaction temperature, a discontinuous-growth mode was confirmed at the initial growth stage of CdTe nanocrystals, arising from the change of the absorption spectra of CdTe nanocrystals with the reaction time at relatively low reaction temperature. The structures of CdTe nanocrystals, e.g., the cubic zinc blende structure at 160°C and the hexagonal wurtzite structure at 250°C, were characterized by XRD.