High-quality cobalt-filled carbon nanotubes (CNTs) were prepared in situ in the decomposition of benzene over Co/silica-gel nano-scale catalysts. Unlike the previous reports, the catalysts needn't be pre-reduced prior to the forming of Co-filled CNTs, thus the advantage of this method is that Co-filled CNTs can be produced in one step, at a relatively low cost. Transmission electron microscopy (TEM) investigation showed that the products contained abundance of CNTs and most of them were filled with metallic nanoparticles or nanorods. High-resolution TEM (HRTEM), selected area electron diffraction (SAED) patterns and energy dispersive X-ray spectroscopy (EDS) confirmed the presence of Co inside the nanotubes. The encapsulated Co was further identified always as high temperature alpha-Co phase with fcc structure, which frequently consists of twinned boundaries and stacking faults. Based on the experimental results, a possible growth mechanism of the Co-filled CNTs was proposed.

We present the fabrication of micron-sized patterns of FePt thin films from Pt@Fe2O3 coreshell nanoparticles. In a typical procedure, Pt@Fe2O3 core-shell nanoparticles were spread and formed a Langmuir film using water as the subphase. This film was lifted onto polydimethylsiloxane (PDMS) stamps with micron-sized patterns of lines, dots and wells, and transferred onto silicon wafers using microcontact printing (ν-CP). The patterns of Pt@Fe2O3 core-shell nanoparticles were converted into face-centered tetragonal phase FePt alloy at enhanced temperatures in the presence of 5% hydrogen. Scanning electron microscopy (SEM), atomic force microscopy (AFM), powder X-ray diffraction (PXRD) and superconducting quantum interference device (SQUID) magnetometer were used to characterize the patterns and the properties of the final FePt alloy films.

We have prepared the diluted assemblies of La1-xSrxMnO3 (x = 0, 0.05, 0.15 and 0.175) nanocrystals (ø ∼ 2∼3 nm) embedded in amorphous SiO2 to clarify the nano-magnetism of both the antiferromagnetic and ferromagnetic La1-xSrxMnO3. All the samples of x = 0, 0.05, 0.15, and 0.175 exhibited superparamagnetism with the blocking temperature of ∼40 K. Except the hump at ∼40 K, the antiferromagnetic x = 0 and 0.05 samples showed simply paramagnetic-like characteristics in both the temperature dependent dc and ac susceptibilities. The ferromagnetic x = 0.15 and 0.175 samples demonstrated complicated characteristics in the temperature dependent susceptibilities. The samples indicated antiferromagnetic and ferromagnetic behavior above ∼50 K and ∼100 K, respectively. The field dependent magnetization is consistent with the predictions of systems having randomly oriented and noninteracting fine particles (ø ∼2∼3 nm). For the ferromagnetic La1-xSrxMnO3 nanocrystals, the antiferromagnetism at crystal surfaces suppressed largely the ferromagnetism in bulk.

We successfully synthesized helical core-shell crystalline SiC/SiO2 nanowires, core-shell crystalline SiC/C nano-crosses and well-aligned core-shell crystalline SiC/C fibers by using a chemical vapor deposition technique. For the helical crystalline SiC/SiO2 nanowires, the SiC core typically has diameters of 10-40 nm with a helical periodicity of 40-80 nm and is covered by a uniform layer of 30-60 nm thick amorphous SiO2. Detailed structural characterizations suggested that the growth of this novel structure was induced by screw dislocations on the nanometer scale. For the core-shell nanocrosses, the crystalline SiC core typically has diameters of 10 to 40 nm and is covered by a uniform layer of 80-110 nm graphitic carbon. The wellaligned SiC/C fibers were shown to be formed by two sequential steps: catalytic SiC growth and graphitic carbon nano-sheets coating. The helical nanowires and core-shell nanocrosses may have potential applications in nano-electronics. The formation mechanism of the carbon fibers suggested that fabrication of field emission filament carbon nano-fibers may be realized by using the aligned crystalline nanowires as templates.

We present one-step synthetic method of magnetic alloy nanocluster wires. This process is simple, less expensive, and saves time. The gas is vaporized in a vacuum chamber from a solution of dicobalt octacarbonyl (Co2(CO)8) and iron pentacarbonyl (Fe(CO)5) mixture, and thermally decomposed by using a nichrome wire. The silicon substrate is placed in a homogeneous magnetic field which is produced by two permanent magnets (4000 gauss), so that the nanowires easily grow in the direction of the magnetic flux. From X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM), we confirmed that these have a body-centered-cubic (BCC) structure with the magnetization easy axis of [110] direction, and a diameter in the range of 4 to 6 nm with a few micrometers in length. Also, we investigated that the squareness of the hysteresis loop is 61% for magnetic fields parallel to the wires and the coercivity along the easy axis is 670 oersteds by using vibrating scanning magnetometer (VSM).

Single-crystalline needle-shaped CdO nanostructures were synthesized using a chemical vapor deposition method and characterized using a variety of techniques. Devices consisting of individual CdO nanoneedles were fabricated and high conductance as well as high carrier concentrations was observed. The temperature dependence of the conductance revealed thermal excitation as the dominating transport mechanism. Our devices exhibited good sensitivity to both infrared light and diluted NO2 gas, indicating potential applications as infrared photo-detectors and toxic gas sensors.

We report our work on the fabrication of nanotube-based field effect transistors (NTFET). Nanotubes were grown by chemical vapor deposition using various approaches, including a new formulation of nanotube growth catalysts that were directly patterned using UV lithography. We also report NTFETs based on randomly oriented nanotube networks that have a modulation of one. Finally, we report that a systematical and statistical characterization of millions of devices has led to the development of a robust process that may be useful in large scale production of reproducible, nanotube-based FETs, which, in turn, can be used as a generic platform for chemical sensors.

Holographic Bragg transmission gratings formed via the anisotropic phase separation of nanosized LC droplets (H-PDLC) were fabricated using thiol-ene photopolymerization. Using coherent UV laser light and a single prism, electrically switchable transmission gratings in the Bragg regime were written. The performance of the thiol-ene-based gratings were compared with those of multifunctional acrylate-based gratings written under similar conditions. Optical and electro-optical measurements suggest that thiol-ene polymers offer promise as hosts for improved H-PDLC performance. Interesting differences in the diffraction efficiencies for s– and p-probe beams are noted for the two matrices. Morphology studies by TEM and SEM exhibit striking differences in droplet shape and uniformity. These differences are speculated to be due to differences in polymer MW growth due to the step-growth propagation mechanism for thiol-enes as compared to the chain-growth propagation mechanism in multifunctional acrylates. The response times of the thiol-ene gratings were ten times slower than those of acrylates.

In a small magnetic tunnel junction (MTJ) whose charging energy is larger than a thermal energy, the tunnel magnetoresistance (TMR) is enhanced by the Coulomb blockade. Transport properties in a double MTJ were theoretically studied by using the Monte Carlo method. The temperature dependence of current-voltage and TMR characteristics indicated that a small junction with 5 nm electrodes exhibited the Coulomb blockade at 300 K. It was also found that the background charge changed the threshold voltage of the Coulomb blockade. In asymmetric double tunnel junctions, the current-voltage characteristic exhibited a Coulomb staircase and the voltage dependence of the TMR ratio oscillated.

We have demonstrated a variety of solution-phase approaches for the synthesis of 1- dimensional nanostructures from chalcogens such as Se and Te. These nanostructures include uniform, single crystalline nanowires and nanorods (lateral dimensions from 10 to 1000 nm, and lengths ranging from 2 to >100 νm). These nanostructures grew via a solid-solution-solid transformation mechanism, in which Se and Te atoms were transported from the less stable source (amorphous colloids) into the more stable product (trigonal phase nanocrystallites). The nanocrystallites (or seeds) were formed either through temperature driven homogeneous nucleation or by sonochemical cavitation. As directed by the highly anisotropic crystal structure, the growth could be confined to one particular direction. These nanowires could be prepared both as dispersions in various solvents or as networked arrays on solid supports.

Energy, in the form of an electronic excitation, can be directed within an inorganicorganic composite of semiconductor quantum dots and organic oligomers by manipulating the structural conformations of the organic component or the size of the inorganic component. Continuous-wave and time-resolved photoluminescence studies indicate that weak electromagnetic resonant coupling between discrete intra-chain and inter-chain excitations of the oligomer and quantum dot excitations can be used to produce a potentially useful optical display material. Thin film blends demonstrate a thermally-induced luminescence-detected chainmelting phenomenon that has the potential for writable optical memory.

A method is suggested for improving the switching characteristics of the metal-hydride mirror by enhancing hydrogen transport in the active film. Nano-pillars of palladium, which has a high diffusion coefficient for hydrogen, are introduced into the active layer and should serve as a “highway” for the rapid introduction of hydrogen. A palladium nano-pillar array is made by electrodeposition in the pores of a polycarbonate membrane. The membrane is dissolved and the active layer (an yttrium-magnesium alloy) is evaporated on the palladium nanostructures. Improved kinetics has not been shown conclusively and is still the subject of research.

We use a two-photon laser-scanning microscope to fabricate two-dimensional (2D) photonic crystal structures in commercially available SU-8 polymer films, and successfully demonstrate making nanostructures beyond the diffraction limit with high aspect ratios. By varying the laser beam power, scanning speed, focal depth, line spacing and scanning angles, we obtain 2D photonic crystals with circular, elliptical, rectangular, or diamond-shape unit cells in a hexagonal or square lattice. An aspect ratio as high as 6.9 with 250 nm line width was achieved. In addition, we can controllably place defects of specific patterns, e.g. lines, dots, and Y-splitters, in the otherwise perfect photonic crystal. We also combine two-photon nanolithography with conventional UV photolithography to make 2D photonic crystals between waveguides. The combination of these two lithography methods was done on a single polymer film, suggesting potential for easy fabrication of complex photonic devices.

Strong influence of the applied or self-induced (i.e. self-biasing) electric field on the alignment, orientation and structures was found in the carbon nano-structure deposition process. This study applied microwave-plasma electron-cyclotron-resonance CVD (ECR-CVD) technique for carbon nano-structure deposition. The deposited structures and properties were characterized with SEM and field emission I–V measurements. The result shows that a negative dc bias applied on the substrate is a necessary condition. In this condition, all carbon nanostructures were well aligned and perpendicular to the substrate surfaces and independent to the plasma/gas flowing directions. Interestingly, when applied an additional electric field near the substrate surface by a guiding metal plate, the CNT growth direction could be manipulated from perpendicular to nearly parallel to the substrate surface. Moreover, a rattan-like CNT would form when prolonging the deposition time or increasing the plasma carbon concentration. These novel nanostructures are expected to have high potential in energy storage, field emission display, nanoelectronics and gas sensing applications accordingly.

We present a methodology based on Dip-Pen Nanolithography 1 to fabricate nanoscale surface patterns composed of polyelectrolytes. Two widely used polymers Poly(diallyldimethylammonium chloride) (PDDA) and Poly(sodium 4-styrenesulfonate) PSS were chosen as the DPN “inks”. Patterns were created and evaluated on silicon oxide surfaces using an Atomic Force Microscope (AFM). To compare the polymer packing and the height of the nanopatterns, additional fabrication was performed using microcontact printing. We were able to generate structures with better polymer packing using DPN and control the height of the polymer structures more reproducibly compared to microcontact printing.

Conducting polymers are interesting materials due to their wide range of applications in electronics, sensing, photonics and display applications. The present paper delineates the synthesis and characterization of the three functionalized poly (p-phenylene)s (PPP) (A-C) and solution properties of the polymers. The self-assembly of the polymers were investigated on various substrates and the optical/morphological properties of thin films of these polymers were also studied. The spontaneous self assembly of the modified PPP's lead to the formation of thin films on both hydrophilic and modified surfaces.

Field emission characteristics were investigated for zinc oxide nanostructures which were grown on NiO catalyzed silicon (100) substrate by chemical vapor deposition method. The asgrown zinc oxide showed needle-shaped nanostructures with tip diameters of 20∼40 nm and length of 3∼5 νm. The turn-on field was found to be about 6 V/νm at a current density of 1 νA/cm2. After several field emission measurements, the turn-on field was increased up to 8.5 V/νm and the magnitude of field enhancement factor was decreased from 1190 to 940. According to SEM, the tip diameter increase of the zinc oxide to 60 nm was observed after several emission measurements. Therefore, degradation of the field emission characteristic after measurements is attributed to this deformation of the tip shape.

Ordered surface adlayers of diacetylene-containing molecules were formed using amide hydrogen-bonding interactions with a pre-formed self-assembled monolayer on gold. Photopolymerization of the diacetylene molecules in the adlayer results in enhanced solvent and processing stability of the adlayer. Patterning of the base monolayer using soft lithography techniques allows patterning of the adlayer as well, and may lead to methods for templating soluble two-dimensional monolayer sheets.

Single crystalline In2O3 nanowires were synthesized and then utilized to construct field effect transistors (FETs) consisting of individual nanowires. Chemical sensors based on these In2O3 nanowire FETs have been demonstrated. Upon exposure to gaseous molecules such as NO2 and NH3, the electrical conductance of the In2O3 nanowire FETs are found to dramatically decrease rapidly, accompanied by substantial shifts in threshold gate voltage. Our In2O3 nanowire sensors exhibit significantly improved sensitivity, as well as shortened response times compared to most existing solid-state gas sensors. In addition, ultraviolet (UV) light is found to be able to greatly enhance the surface molecular desorption kinetics and serve as a “gas cleanser” for the In2O3 nanowire chemical sensors. It has been demonstrated that the recovery time of our devices can be shortened to ∼30 s by illuminating the devices with UV light in vacuum.

Single crystal ZnO nanowires were grown by chemical vapor deposition using monodisperse 5 nm or 20 nm diameter gold nanoparticle catalysts to control the nanowire diameter and location. The nanowires reach several microns in length and grow only from the gold nanoparticles. The nanowires have narrowly dispersed diameters, albeit significantly larger than the diameter of the gold particles used for catalyzing the growth. The nanowires grow in the [ 0 1 10 ] or [ 1 1 10 ] directions normal to the lowest energy planes in ZnO. ZnO nanowires emit in the near ultraviolet region of the electromagnetic spectrum upon excitation with highenergy photons or electrons. Electron diffraction and absence of luminescence associated with oxygen vacancies indicate high quality crystalline ZnO nanowires. Cathodoluminescence e mission along the entire length of the wire is consistent with a lack of non-radiative recombination sites associated with defects, lending further support for the high quality of these nanowires.