Nanotubes and nanowires

Nanotube Structure of AsPS4-xSex (x = 0, 1)

Single-wall nanotubes of isostructural AsPS4-xSex (x = 0, 1) are grown from solid-state reaction of stoichiometric amounts of the elements. The structure of AsPS4 was determined using single-crystal X-ray diffraction and refined in space group P 1 ¯ . The infinite, single-walled AsPS4 nanotubes have an outer diameter of ≈1.1 nm and are built of corner-sharing PS4 tetrahedra and AsS3 trigonal pyramids. Each nanotube is nearly hexagonal, but the ≈3.4 Å distance between S atoms on adjacent nanotubes allows them to easily slide past one another, resulting in the loss of long-range order. Substituting S with Se disrupted the crystallization of the nanotubes, resulting in amorphous products that precluded the determination of the structure for AsPS3Se. 31P solid-state NMR spectroscopy indicated a single unique tetrahedral P environment in AsPS4 and five different P environments all with different degrees of Se substitution in AsPS3Se. Optical absorption spectroscopy revealed an energy band gap of 2.7 to 2.4 eV for AsPS4 and AsPS3Se, respectively. Individual AsPS4 microfibers showed a bulk conductivity of 3.2 × 10-6 S/cm and a negative photoconductivity effect under the illumination of light (3.06 eV) in ambient conditions. Thus, intrinsic conductivity originates from hopping through empty trap states along the length of the AsPS4 nanotubes.

Carbon-Related Materials: Graphene and Carbon Nanotubes in Semiconductor Applications and Design

As the scaling technology in the silicon-based semiconductor industry is approaching physical limits, it is necessary to search for proper materials to be utilized as alternatives for nanoscale devices and technologies. On the other hand, carbon-related nanomaterials have attracted so much attention from a vast variety of research and industry groups due to the outstanding electrical, optical, mechanical and thermal characteristics. Such materials have been used in a variety of devices in microelectronics. In particular, graphene and carbon nanotubes are extraordinarily favorable substances in the literature. Hence, investigation of carbon-related nanomaterials and nanostructures in different ranges of applications in science, technology and engineering is mandatory. This paper reviews the basics, advantages, drawbacks and investigates the recent progress and advances of such materials in micro and nanoelectronics, optoelectronics and biotechnology.

Slot Self-Allocation Based MAC Protocol for Energy Harvesting Nano-Networks

Nano-networks are composed of interconnected nano-nodes and can enable unprecedented applications in various fields. Due to the peculiarities of nano-networks, such as high density, extremely limited energy and computational resources, traditional carrier-sensing based Media Access Control (MAC) protocols are not suitable for nano-networks. In this paper, a Slot Self-Allocation based MAC protocol (SSA-MAC) is proposed for energy harvesting nano-networks. Two transmission schemes for centralized and distributed nano-networks are designed, respectively. In centralized nano-networks, nano-nodes can only send packets to the nano-controller in their Self-Allocation Slots (SASs), while, in distributed nano-networks, nano-nodes can only receive packets from surrounding nano-nodes in their SASs. Extensive simulations were conducted to compare the proposed SSA-MAC with PHysical LAyer aware MAC (PHLAME), Receiver-Initiated Harvesting-aware MAC (RIH-MAC) and Energy Efficient Wireless NanoSensor Network MAC (EEWNSN). From the results, it can be concluded that the proposed SSA-MAC achieves better performance and can reduce the collision probability, while improving the energy efficiency of nano-networks.

Tunable synthetic control of soft polymeric nanoparticle morphology

With a growing variety of nanoparticles available, research probing the influence of particle deformability, morphology, and topology on the behavior of all polymer nanocomposites is also increasing. In particular, the behavior of soft polymeric nanoparticles in polymer nanocomposites has displayed unique behavior, but their precise performance depends intimately on the internal structure and morphology of the nanoparticle. With the goal of providing guidelines to control the structure and morphology of soft polymeric nanoparticles, we have examined monomer starved semi-batch nano-emulsion polymerizations that form organic, soft nanoparticles, to correlate the precise structure of the nanoparticle to the rate of monomer addition and crosslinking density. The synthesis method produces 5-20 nm radii polystyrene nanoparticles with tunable morphologies. We report small angle neutron scattering (SANS) results that correlate synthetic conditions to the structural characteristics of soft polystyrene nanoparticles. These results show that the measured molecular weight of the nanoparticles is controlled by the monomer addition rate, the total nanoparticle radius is controlled by the excess surfactant concentration, and the crosslinking density has a direct effect on the topology of each nanoparticle. These studies thus provide pathways to control these 3 structural characteristics of the nanoparticle. This research, therefore provides a conduit to thoroughly investigate the effect of structural features of soft nanoparticles on their individual properties and those of their polymer nanocomposites.

Gold Nanostructures from Cube-Shaped Crystalline Intermediates

Conventional bottom-up approaches for building nanostructures rely on the ability to synthesize nanoparticles of different shapes and sizes in a controlled manner that are then assembled to produce useful structures. Here, we present an alternate approach for producing nanostructures based on the formation of a crystalline intermediate in which the metal ion can be reduced in a controlled manner. Partial reduction of HAuCl4 by a long-chain amine results in the formation of a cube-shaped crystalline intermediate in which Au is present in a +1 oxidation state. By control of the nucleation of the metal in the intermediate, a variety of nanostructures can be synthesized. Here, we present results on the formation of superlattices, hollow cubes, nanotubes, and extended hollow structures starting from the intermediate. Direct evidence for the formation of metal within the intermediate by in situ electron-beam-induced reduction in the transmission electron microscope is presented.