Eletronic and mechanical properties of ordered carbon nanotube networks are studied using molecular dynamics simulations and tight-binding calculations. These networks are formed by single walled carbon nanotubes (SWNT) regularly connected by junctions. The use of different types of junctions (“Y”-, “X”-like junctions, for example) allows the construction of networks with different symmetries. These networks can be very flexible and the elastic deformation was associated with two main deformation mechanisms (bending and stretching ) of the constituents SWNTs. Rolling up the networks, “super” carbon nanotubes can be constructed. These super-tubes share some of the main electronic features of the SWNT which form them but important changes are predicted (e.g. reduction of bandgap value). Simulations of their deformations under tensile stress have revealed that the super-tubes are softer than the corresponding SWNT and that their rupture occur in higher strain values.

Monocrystalline nanowires of cubic silicon carbide were synthesized using a combined sol-gel and carbothermal reduction process in which tetraethoxysilane was used as primary sili-con and sucrose as carbon source. The diameters of the as-grown nanowires varied depending on process parameters from several tens to several hundreds nanometers, whereas the length of the wires was located in the millimetre region. By precisely controlling the atomic ratio of Si / C, silicon carbide nano wires were synthesized exclusively and pure without the presence of resid-ual carbon or unwanted silica, thus leads to semi-insulating behaviour. Supported by their consis-tence the silicon carbide micro or nano wires can be processed to textile or felt structures and are therefore usable for many applications such as for fireproof clothing, high temperature or chemi-cal filters and composite materials. Additionally during sol-gel synthesis the silicon carbide mi-cro / nano wires were easily doped to achieve p- or n-conduction, guiding to new applications in the field of wide bandgap semiconductors. The structure of 3C-SiC micro and nano wires was determined using scanning electron microscopy, X-ray diffraction, nuclear magnetic resonance and fourier transform infrared spectroscopy. The electronic properties were studied using elec-tron paramagnetic resonance spectroscopy, Hall effect and current-voltage measurements.

Polycrystalline SiC nanowires and composite Si nanowire-SiC nanograin structures have been synthesized using a combined catalytic chemical vapor deposition and carburization method. Si nanowires are grown at low temperature (550-650 C) and subsequently carburized at 1100-1200 C in a methane/hydrogen or propane/hydrogen environment. Thermochemical calculations showed that the Si carburization is thermodynamically favorable over a wide tempareture range, whereas our studies showed that the Si nanowire carburization is kinetically limited below ∼1100 °C. Partially carburized nanowires contained distinct SiC nanosized grains on the Si nanowire surface, whereas fully carburized nanowires were polycrystalline 3C SiC with grain sizes of ∼ 50-100 nm.

Boron (B) doped silicon nanowires (SiNWs) were synthesized by laser ablation. Local vibrational modes of B in SiNWs were observed by micro-Raman scattering measurements at room temperature. Broadening due to a coupling between the discrete optical phonon and a continuum of interband hole excitations was also observed in the Si optical phonon peak. This is called Fano broadening. These results prove that B atoms were doped in substitutional sites of crystalline Si core of SiNWs during laser ablation.

Carbon nanotubes (CNTs) have been grown on silicon nanowires (SiNWs) by chemical vapor deposition using Co catalyst nanoparticles. Single-walled CNTs have been grown mainly when a thin Co film (0.1 nm thick) was deposited on SiNWs, while both SWNTs and MWNTs have been grown on SiNWs on which Co 0.5 nm thick was deposited. The correlation between the diameter of catalyst nanoparticles and that of CNTs has been investigated by transmission electron microscopy. The average diameter of CNTs is smaller than that of catalyst nanoparticles.

We use the ReaxFF reactive force field to model extreme tensile deformation of a (10,10) armchair carbon nanotube. The ReaxFF force field has been developed based on DFT quantum mechanical calculations without any empirical parameters (Duin et al., 2001). We report an analysis of the stress-strain relationship for the elastic and plastic regime, including a description of the microscopic fracture mechanisms. We find Young's modulus to be around 1 TPa, close to experimental values. Our modeling yields a fracture tensile strain of approximately 30%, with a maximum tensile stress of approximately 300 GPa. Fracture of the CNT originates from formation of 5-7 Stone-Wales-like defects, leading to formation of micro-cracks. We also report preliminary results of straining hybrid CNTs embedding a nickel nanowire.

A fuel cell (FC) generates electricity by chemical reactions. The catalyst dispersion in membrane electrode assembly (MEA) of FC is a crucial factor to affect the performance of the cell. A novel grafting method is adopted in this study to grow secondary carbon nano-tubes (CNTs) on a substrate comprised of primary CNTs, in order to form branchy CNTs with higher specific surface area (SSA). The as-obtained branchy CNTs are then used as catalyst, Pt, carriers in the MEA of direct methanol fuel cell (DMFC). A self-assembled DMFC of air-breathing type with active MEA area of 2 × 2 cm2 is used in this study as the standard FC for the electrical performance test. The peak power of DMFC comprised of an MEA with sole primary CNTs is 0.002 watts at 0.15 V. Such peak power can be increased up to 0.01 watts at 0.4 V for the replaced MEA with new branchy CNTs. The open circuit voltages (OCVs) are 0.4 V and 0.6 V for DMFCs with MEAs of sole primary CNTs and branchy CNTs, respectively. Furthermore, the patterns of CNTs was designed to provide micro-channels of fuel. The pattern growth of CNTs have been fabricated by selective area growth method in this research.

Magnetic polymers are multi-functional composites emerging as a new category of smart materials. This work focuses on fabrication and characterization of magnetic polymer nanocomposites based on polydimethylsiloxane (PDMS) elastomer matrix. The magnetic fillers are commercially available Ni nanoparticles and respectively in-house fabricated Ni nanowires. Synthesis of Ni nanowires is achieved by electroless deposition inside nanoporous anodic alumina templates. After template removal, the nanowires are coated with 1-Octodecanethiol surfactant and mixed with PDMS using a FlackTek SpeedMixer™. In parallel, nanoparticles are mixed with PDMS, without undergoing surfactant coating. Both composites are evaluated by scanning electron microscope (SEM) to determine dispersion uniformity. Mechanical properties are resolved by tensile tests performed by an instron. Preliminary results suggest that surfactant addition enhances dispersion, while mechanical properties of the composites for up to 5 vol. % of added nickel remain close to that of the polymer matrix without filler.

Single-walled carbon nanotubes have been integrated on top of an individual CMOS device using lithography, chemical vapor deposition and chemical mechanical planarization. Hybrid integration of silicon and nanotube transistors is demonstrated for the first time by making an inverter with a p-type CNTFET placed on top of an n-type MOSFET. A polysilicon gate is positioned between the silicon device channel and carbon nanotube for dense integration of opposite-polarity devices. Such a configuration offers many advantages for high-density electronics and ultra-sensitive detection.