Arrays of Ni nanorods were electrodeposited into alumina oxide templates with various lengths (11-50 micro meter) and fixed pore diameter (150 nm). The magnetization behavior of these rods were investigated with ferromagnetic resonance (FMR) techniques; fixed frequency (conventional FMR) and swept frequency (Network Analyzer FMR). Both resonance spectra indicate the presence of strong dipolar interaction between the nanorods. The fundamental magnetic parameters like spontaneous magnetization, gyromagnetic ratio, and magnetic anisotropies of the nanorods were derived from the angular variation of resonance field data. Further, the use of nanorods as a tunable stop-band notch-filter in a coplanar waveguide geometry has been assessed. The stop-band frequency (fr) is observed to be tunable up to 24 GHz with an applied field (H) of up to 6 kOe. The theoretical fitting of fr(H)data to resonance relation yield values of effective field (Heff) and gyromagnetic ratio, which are a little higher than the conventional FMR results.

To observe the axial growth behavior of InAs on GaAs nanowires, InAs was grown for different growth durations on GaAs nanowires using Au nanoparticles. Through transmission electron microscopy, we have observed the following evolution steps for the InAs growth. (1) In the initial stages of the InAs growth, InAs cluster into a wedge shape preferentially at an edge of the Au/GaAs interface by minimizing Au/InAs interfacial area; (2) with further growth of InAs, the Au particles move sidewards and then downwards by preserving an interface with GaAs nanowire sidewalls. The lower interfacial energy of Au/GaAs than that of Au/InAs is attributed to be the reason for such Au movement. This downward movement of Au nanoparticle later terminates when the nanoparticle encounters InAs growing radially on the GaAs nanowire sidewalls, and with further supply of In and As vapor reactants, the Au nanoparticles assist the formation of InAs branches. These observations give some insights of vapor-liquid-solid growth and the kinks formation in nanowire heterostructures.

Herein, we present the capability of creating silicon carbide (SiC) nanowires and branched nanostructures via a released cataltic process. Core-shell structured carbon-encapsulated iron nanoparticles were used as catalysts for SiC nanostructures formations by vapor-solid reaction. Various SiC nanostructures, including SiC nanocones, biaxial SiC-SiC composite nanowires, SiC-Fe-SiC junctions, Y, T branched SiC nanowires, and other complex heterostructures were observed from this process. It was demonstrated that the encapsulated iron could gradually migrate out of the carbon shell, and the released iron nanoparticles catalyzes the SiC nanostructures formation. Their morphologies and microstructures were investigated by different techniques, including scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM), and their formation mechanisms are proposed.

Molecular wires of charge transfer molecules were formed by co-evaporating the 7 7 8 8-Tetracyanoquinodimethane [TCNQ] (acceptor) and Tetrathiafulvalene [TTF] (donor) molecules across prefabricated metal electrodes. Molecular wires of TTF TCNQ were also formed by evaporating single complex of TTF:TCNQ across prefabricated metal electrodes The prefabricated metal electrodes were made using electron beam lithography on SiO2 and glass cover slip substrates. Even though TTF: TCNQ wires grown from both co-evaporation and evaporation techniques show semiconductor like behavior in temperature dependence of resistance they show different activation energies due the difference in stoichiometry of TTF and TCNQ.

Homo-epitaxial growth of Si nanowires on Si (100) substrate was accomplished using a combination of anodic aluminum oxide (AAO) template and Vapor-Liquid-Solid (VLS) growth. We prepared two types of AAO template for epitaxial growth of Si nanowires.

We observed vertically grown epitaxial Si (100) nanowires in the AAO template. In addition, after leaving filled pores, Si nanowires changed their growth direction from [100] to <111>. This result shows that the walls of the pores forced the growth direction of Si nanowires parallel to the direction of the pores, and after complete filling, the growth direction changes to that of the Si nanowires on a bare Si substrate.

Nanowires have great potential as building blocks for nanoscale electrical and optoelectronic devices. The difficulty in achieving functional and hierarchical nanowire structures poses an obstacle to realization of practical applications. While post-growth techniques such as fluidic alignment might be one solution, self-assembled structures during growth such as branches are promising for functional nanowire junction formation. In this study, we report vapor-liquid-solid (VLS) self-branching of GaN nanowires during AuPd-catalyzed chemical vapor deposition (CVD). This is distinct from branches grown by sequential catalyst seeding or vapor-solid (VS) mode. We present evidence for a VLS growth mechanism of GaN nanowires different from the well-established VLS growth of elemental wires. Here, Ga solubility in AuPd catalyst is limitless as suggested by a hypothetical pseudo-binary phase diagram, and the direct reaction between NH3 vapor and Ga in the liquid catalyst induce the nucleation and growth. The self-branching can be explained in the context of the proposed VLS scheme and migration of Ga-enriched AuPd liquid on Ga-stabilized polar surface of mother nanowires. This work is supported by DOE Grant No. DE-FG02-98ER45701.

Metallic nickel nanowires with excellent physical properties have been introduced into polydimethylsiloxane matrix to form polymer nanocomposites. Nanowires were synthesized by template-assisted electrochemical deposition. By utilizing ferromagnetic nickel nanowires, small external magnetic field can be used to control their alignment and distribution during composite synthesis. Unlike dielectrophoresis, optical tweezers, and microfluidic flow control, magnetic manipulation provides a cost-effective, non-contact, and versatile approach to control nanostructured materials in fluids over a large area. Polydimethylsiloxane composites with nanowires arranged in longitudinal, transverse, and random orientations with respect to the applied load direction were studied. Tensile tests showed that the composites with longitudinal arrangement have higher elastic modulus and tensile strength than the other composite samples. Experimentally obtained elastic modulus values were compared with the prediction of classical Halpin-Tsai model. Metallic nickel nanowires with excellent physical properties have been introduced into polydimethylsiloxane matrix to form polymer nanocomposites. Nanowires were synthesized by template-assisted electrochemical deposition. By utilizing ferromagnetic nickel nanowires, small external magnetic field can be used to control their alignment and distribution during composite synthesis. Unlike dielectrophoresis, optical tweezers, and microfluidic flow control, magnetic manipulation provides a cost-effective, non-contact, and versatile approach to control nanostructured materials in fluids over a large area. Polydimethylsiloxane composites with nanowires arranged in longitudinal, transverse, and random orientations with respect to the applied load direction were studied. Tensile tests showed that the composites with longitudinal arrangement have higher elastic modulus and tensile strength than the other composite samples. Experimentally obtained elastic modulus values were compared with the prediction of classical Halpin-Tsai model.

We present the formation of SnO2-In2O3 hetero nanostructures. Kinetically, SnO2 nanowires form prior to the heterostructure. In2O3shell was regularly distributed on the SnO2 nanowire surface, and form sheath subsequently. We theoretically explained the morphological evolution of an anisotropic heterostructure such as core-sheath structure.

Silicon nanowires with high aspect ratio were grown using PPECVD and a gold catalyst on a variety of different substrates. The morphology of the nanowires was investigated for a range of crystalline silicon, glass, metal, ITO coated and amorphous silicon coated glass substrates. Deposition of the nanowires was carried out in a parallel plate PECVD chamber modified for PPECVD using a 1kHz square wave to modulate the 13.56MHz RF signal. Samples were analyzed using either a Phillips XL20 SEM of a ZEISS 1555 VP FESEM. The average diameter of the nanowires was found to be independent of the substrate used. The silicon nanowires would grow on all of the substrates tested, however the density varied greatly. It was found that nanowires grew with higher density on the ITO coated glass substrates rather than the uncoated glass substrates. Aligned nanowire growth was observed on polished copper substrates. Of all the substrates trialed, ITO coated aluminosilicate glass proved to be the most effective substrate for the growth of silicon nanowires.

Noble metal such as Ag normally exists in an fcc crystal structure. However as the size of the material is decreased to nanometer lengthscales, a structural transformation from that of its bulk state can be expected with new atomic arrangements due to competition between internal packing and minimization of surface energy. In many previous studies, it has been shown that silver nanowires (AGNWs) grown inside anodic alumina (AAO) templates by ac or dc electrochemical deposition from silver salts or complexes, adopt fcc structure and below some critical diameter ∼ 20 nm they may acquire hcp structure at low temperature. This is, however, critically dependant on the nature of confinement, as AgNWs grown inside nanotube confinement with subnanometer diameter have been reported to have fcc structure. Hence the question of the crystal structure of metal nanowires under combined influence of confinement, temperature and deposition condition remains open. In this abstract we show that the alternative crystal structures of AGNWs at room temperature can be achieved with electrochemical growth processes under specific conditions determined by the deposition parameters and nature of confinement. We fabricated AgNWs of 4H hexagonal structure with diameters 30 – 80 nm inside polycarbonate (PC) templates with a modified dc electrodeposition technique, where the nanowires were grown at deposition potentials as low as 10 mV in 2 M silver nitrate solution[1]. We call this low-potential electrodeposition (LPED) since the electrodeposition process occurs at potential much less than the standard Nernst potential (770 mV) of silver. Two types of electrodes were used – stainless steel and sputtered thin Pt film, neither of which had any influence on the crystal structure of the nanowires. EDS elemental analysis showed the nanowires to consist only of silver. Although the precise atomic dynamics during the LPED process is unclear at present, we investigated this with HRTEM (high-resolution transmission electron microscopy) characterization of nanowires grown over various deposition times, as well as electrical conductivity measurements. These experiments indicate that nanowire growth does not occur through a three-dimensional diffusion controlled process, as proposed for conventional over-potential deposition, but follow a novel instantaneous linear growth mechanism. Further experiments showed that, (a) conventional electrochemical growth at a small over-potential in a 2 mM AgNO3 solution yields nanowires with expected fcc structure inside the same PC templates, and (2) no nanowire was observed under the LPED conditions inside hard AAO templates, indicating that LPED-growth process, and hcp structure of the corresponding nanowires depend on deposition parameters, as well as nature of confinement.

We demonstrate high temperature glancing deposition (HT-GLAD) of metals on the heated substrate. It has been found that Al, Ag, Au, Fe nano-whiskers grow on the substrate of Si, SiO2, and glass substrates. The robustness in the selection of materials suggests that the HT-GLAD is a universal method to grow nano-whiskers of various metals. We also demonstrate the selective growth of the nano-whiskers on the substrate with micro-trench patterns. The metal nano-whiskers are useful for the nano electromechanical devices and vacuum microelectronics.

High quality InN nanowires have been synthesized in a horizontal quartz-tube furnace through direct reaction between metallic Indium and Ammonia using Nitrogen as the carrier gas. Thin film of Au on SiO2/Si substrate has been used as the catalyst layer, facilitating vapor-liquid-solid growth of the nanostructures. The nanowires were grown at a very fast rate of up to 30 μm/hr. Smooth and horizontal nanowire growth was achieved only with nanoscale catalyst patterns, while large area catalyst coverage resulted in uncontrolled and three-dimensional growth. The InN nanowires, which were usually covered with a thin shell layer of In2O3, grew along [110] direction, with overall diameters 20 - 60 nm and lengths 5 - 15 μm. The synthesized nanowires bent spontaneously or got deflected from other nanowires at multiples of 30 degrees forming nano-networks. The catalyst particles for the NWs were found mostly at the sides of the NW apex which helped them to bend spontaneously or get deflected from other NWs at angles which were multiples of 30 degrees. The NW based FETs with a back-gated configuration have already been investigated. The gate-bias dependent mobility of the NWs ranged from 55 cm2/Vs to 220 cm2/Vs, and their carrier concentration was ∼1018 cm−3.