Self-aligned arrays of long multi-walled carbon nanotubes (MWCNT) were grown by chemical vapor deposition (CVD) from a gas mixture of C2H4-H2-Ar-H2O at 750°C. A catalytically active alumina surfaces coated with a thin layer of iron and supported by a Si/SiO2 substrate were prepared using pulsed laser deposition method. Combinatorial approach has been used for optimization of catalytic properties of the multilayered system Si/SiO2/Al2O3/Fe. Sixteen different combinations of catalytic surfaces having thicknesses of Fe (0, 1, 2, and 3 nm), alumina (0, 10, 20 and 30 nm) per sample were deposited on two Si/SiO2 substrates with silica thickness 150 and 500 nm. To study the effect of alumina phase on efficiency of catalytic surfaces two substrate temperatures 200 and 700°C were used to produce amorphous and γ-alumina phases correspondingly. This approach allowed the optimal structure of catalytic surface to be determined from 64 different substrates on 4 samples in a single MWCNT growth experiment, for a given set of processing conditions. It was found that most efficient growth of MWCNT arrays on amorphous alumina occurred at Fe nanolayer thickness of 2 nm while catalyst having γ-alumina layer has tendency to be more efficient at higher thickness of Fe. Catalytic substrate containing amorphous alumina has less sensitivity to thickness of iron while γ-alumina based catalyst has significant variation in catalytic activity with change of iron content.

Gas sensors based on optical absorption changes in thin films are of interest for detection of various gases such as CO, NO, H2. Optical gas sensors have several advantages over conventional electronic gas sensors, including the potential for higher sensitivity, reduced signal noise, and compatibility with combustible gases. Pulsed laser deposition (PLD) is an excellent method to prepare thin films with controllable thickness, composition and microstructures. Recently, our group reported that films of cobalt oxide prepared by PLD exhibit remarkably high sensitivity), showing an absorbance change in CO gas 70 times greater than those prepared by sputtering methods). Here we examine the effect of film microstructure and composition on CO gas sensing properties in order to identify the origin of the high sensitivity. Cobalt oxide films were prepared by PLD from a CoO target in an inert argon gas at various pressures. Films prepared near vacuum were smooth and continuous while the porosity and grain size increased linearly with pressure. In addition the pressure affected the composition and the thickness of the films. Data on the detection of CO gas suggests a direct relationship between sensitivity to CO gas and the effective surface area of films. We will discuss how the ablation plume can be used to tune the surface area for optimal sensitivity, and will demonstrate origin of the high detection sensitivity based on the structural changes with detecting gas.

Carbon nanotube (CNT) is a promising material which has potential for applications to various nanotechnology devices owing to its unique features like high electrical conductivity, mechanical strength and large specific surface area. Recently, gas sensors using CNTs or carbon nano-fiber, which have extremely high sensitivity at a room temperature with fast response, have been reported. Being exposed to oxidizing gas like NO, NO2 or O3, the conductance of the single-walled carbon nanotubes (SWNTs) changes due to charge transfer between the SWNT surface and gas molecules adsorbed. Therefore CNTs will be applicable to O2 and O3 gas sensors in various fields.

CNTs thin film sensor was prepared and its performance was investigated. CNTs thin film was prepared on a SiN substrate using PLD/CVD method. To prepare a sensor device an Al2O3 substrate with Pt interdigital electrodes (sensor substrate) was used. In this method, Fe catalytic thin film was deposited by pulsed laser deposition (PLD) method using KrF excimer laser of wavelength 248 nm, repetition rate 10 Hz, energy fluence 3 J/cm2. During PLD process the substrate temperature and the ambient gas pressure were kept at room temperature of 25 °C and 3.5×10−5 Torr, respectively. The thickness and roughness of the films were modified by changing a number of ablation laser pulses from 300 to 3,000. A small number of laser pulses deposited Fe nano-particles of less than 10 nm in diameter on the substrate. We used 1000 pulses for a catalytic Fe film preparation as small-sized catalyst is necessary to grow SWNTs. CNTs were grown from Fe thin film on Si or sensor substrates by thermal CVD method. Ethylene gas was used as carbon source. The substrate was set in the quartz reaction tube heated to 1000 °C in an electric furnace. CNTs were grown for 20 ∼ 40 minutes. In our previous studies, it was found that SWNTs can grow under this process. The prepared CNTs were characterized using SEM, TEM and Raman spectroscopy. From SEM observation, randomly oriented CNTs were found on both the Si substrate and the sensor substrate. A diameter of CNTs was found 20 ∼ 50 nm which tended to be proportional to the size of catalyst particle.

The Sensitivity of CNT gas sensor was evaluated by measuring the electrical characteristic of the sensor. The sensor was exposed to NO gas of different concentration in a chamber. Resistance of the sensor was measured by two-terminal method, while the sensor was heated from room temperature to a high temperature on a block heater. The Sensitivity of CNT gas sensors, response time and reproducibility was measured. Initial resistance of the film was about 450 and it decreases with temperature increase. This shows that a prepared CNTs sensor film has semiconductor characteristics. Measured maximum sensitivity of CNTs gas sensor was 6.9 % at sensor temperature 290 deg. Detail studies and the latest data will be presented at the symposium.

Selective synthesis of silica nanowires on silicon wafers catalyzed by Pd ion implantation is reported.Nanoclusters of palladium silicide acts as seeds for nucleation of wires following a Vapor-Liquid-Solid (VLS) growth model. The consumption of silicide towards nanowire growth is confirmed through Rutherford Backscattering Spectrometry (RBS).The influence of growth time, implantation dose and heating temperature on the structure and morphology of the wires is investigated. Optimization of the these tunable parameters would be needed to facilitate controlled and directed bottom-up growth of silica nanowires.Such selective synthesis may enable a large number of applications in wide areas of future technologies such as localization of light, low dimensional waveguides for functional microphotonics, scanning near field optical microscopy (SNOM), optical interconnects, sacrificial templates, optical transmission antennae and biosensors.

Molybdenum oxide/ Poly (ethylene oxide) composite nanofibers were prepared by combining the sol-gel process and electrspinning technique. An ethanol solution of Poly(ethylene oxide) (PEO) was mixed with molybdenum isopropoxide to form a precursor solution. Composite nanofibers were obtained by electrspinning this viscous solution. By calcination of the composite fibers, pure molybdenum oxide nanofibers and nano-rods were obtained with diameters of 100-nanometer scale. Morphology of the fibers has been characterized by scanning electric microscopy. Components and structures of the final products have been identified by EDAX and grazing incidence XRD. Calcination process has been studied by DSC and TG analysis. The real time dynamics of the structural evolution from composite fibers to nanocrystalline metal oxide fibers has been investigated by synchrotron-based in-situ x-ray diffraction.

We describe a fabrication method to prepare highly ordered Si nanopore arrays. A nanoporous alumina template of thickness ∼1μm is prepared by means of anodization of an aluminum film. The template has a highly ordered hexagonal array of pores of diameter ∼50nm. The template is detached from the aluminum layer and placed on a Si substrate. The nanoporous pattern is transferred onto silicon substrate by means of a dry plasma etch process. This produces an array of nanopores in silicon with a diameter of ∼50nm and depth of ∼300nm. We have used such an array to prepare Fe nanopillars inside the pores by means of thermal evaporation. Magnetization versus applied magnetic field measurements for the Fe nanoarrays, demonstrate large perpendicular anisotropy typical of high aspect ratio magnetic nanopillars. The value of coercivity is about 500Oe in the perpendicular direction and 40Oe in the parallel direction.

The focus of this study is on the adsorption properties of the nanocrystalline materials and SnO2 has been chosen as the appropriate example. Therefore model structures consisting on SnO2 grains with a rutile lattice and a size comparable with the experimental ones have been considered and the adsorbed system is generated by depositing a CO molecule above a tin or oxygen atom on the grain surface. The calculations, based on semi-empirical Hartree-Fock and scattering theories, illustrate the dependence of the binding and adsorption energies of grains on their size and shape and show the effects of these energies on the grain conductance.

Thiol-passivated gold nanoparticles were adsorbed on several kinds of support materials such as titania-coated silica aerogels and xerogels etc., and then the thiol was removed by heat treatment. The catalytic activity of the prepared composites for CO oxidation reaction was measured, and the effects of the support on the catalytic activity were investigated. Density of the supports, namely, whether aerogel supports or xerogel ones, hardly affected the catalytic activity. It was found that the catalysts having high catalytic activity could be obtained by this preparation method, even using the xerogels as the support. Calcination of the supports before adsorption of the gold nanoparticles affected the activity. The difference of the catalytic activity was observed between the composites with same gold nanoparticle size, so it was considered that the surface condition of the support materials affects the state of gold nanoparticles in composite.

The investigation of photoconductive properties of chemical bath deposited (CBD) cadmium sulphide (CdS) layers was the main objective of this work. For completeness, the CdS layers were characterized using X-ray diffraction, scanning electron microscopy, optical absorption, DC electrical conductivity, photoconductivity measurements. It has been found that the CdS layers grown are hexagonal with (002) preferential orientation. The n-type CdS materials show 100–200 nm clusters consisting of 10–20 nm size crystallites. The optical band gap is 2.42-2.52 eV, which shows a red-shift to 2.34 eV upon heat treatment. The effect of Cu doping and co-deposition of CdS with PbS were also investigated. Dark conductivity was increased after heat treatment of pure CdS layers, and decreased in case of Cu doped samples. Photoconductive response time of Cu doped CdS and Cd(Pb)S samples were smaller than the response time of pure CdS samples.

Carbon nanotubes (CNTs) were grown using a dc arc discharge process and relevant process parameters were investigated. Unlike the usual process in which a carbon anode is filled with metal catalyst powder, CNTs were prepared using a carbon cathode on which the metal catalyst had been deposited using an electroplating system. Various transition metals, Ni, Co and Ti, were used as a catalyst. The results show that multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs) can both be synthesized using this technique. And yield and morphology of the prepared CNTs varied depending on the experimental condition and catalyst. While MWNTs were produced in the deposit and soot sample, SWNTs with diameters near 1nm were only detected in the soot collects. When Ni film was used as a catalyst, the yield of SWNTs was higher than in case of using Co or Ti film as a catalyst. From these results, the optimized preparing condition of CNTs and the properties of a good catalyst are discussed.

Novel ZnO nanostructures such as hollow nanospheres, nano-cages, nanoneedles, tetra-pods, nanowires, aligned nanorods and nanotubes are synthesized via thermal evaporation of ZnO and graphite powder mixtures in reduced oxygen atmosphere in the presence of argon and nitrogen flows. The ZnO nanostructures, especially nanospheres, have a unique shape and are hollow inside with walls densely decorated with aligned nanowires. Photoluminescence of synthesized ZnO structures measured at 300 K exhibits a strong near band edge peak at ∼380 nm and deep level green band centered at ∼550 nm. Fabricated ZnO structures can be studied for various applications in optoelectronics and sensors.

We investigate the electronic structures of extended helical silver single-wall nanotubes (AgSWNTs). Because these helical nanotubes are essentially comprised of n-atom strands winding about the nanotube's axis, we systematically examine, strand by strand, the electronic properties and the number of conduction channels associated with these structures. Herein, we study a special case of high-symmetry nanotubes. Nanotubes with sufficiently large radii were also calculated with a silver atomic chain inserted along the nanotube's axis. The analysis is carried out within a first-principles, all-electron self-consistent local density functional approach (LDF) adapted for helical symmetry. Modeling helical silver (or gold) single-wall nanotubes entails rolling up a sheet of atoms and mapping the atoms onto the surface of a cylinder, comparable to rolling up a graphite sheet for a carbon nanotube. It is well known that controlling the size and shape of silver and gold nanostructures results in the ability to tailor the optical and catalytic properties of these materials. In this preliminary study, we consider changes in the electronic structures of these materials as each nanotube is built strand by strand.

We demonstrate that single walled carbon nanotube field effect transistors (swCN-FET) decorated with single stranded DNA (ss-DNA) form a new, versatile, and highly sensitive class of nanoscale chemical sensors. These sensors are based on ss-DNA as the chemical recognition site and swCN-FET as the electronic read-out component. The ss-DNA decorated swCN-FETs are sensitive to chemical species (odors) that do not cause a detectable response in bare, as-fabricated swCN-FETs. Furthermore, odor responses ss-DNA decorated FETs differ in sign and magnitude for different odors, and the response characteristics depend on the base sequence of the ss-DNA used to decorate the swCN. The sensor surface is self-regenerating: samples maintain a constant response with no need for sensor refreshing through at least several dozens gas exposure cycles. These remarkable attributes suggest that DNA-decorated swCN-FET sensors could be created with sensitivity to a large variety of compounds, as required for “electronic-nose” and “electronic tongue” applications in medicine and homeland security.

Colloidal metal nanoparticles have a high surface-to-volume ratio which makes them potentially attractive catalysts. Furthermore, atoms located at different facets, edges, or corners could show different catalytic activity. For this reason, different shapes could have different catalytic activities. In addition, surface atoms are so active that there could be significant changes in their shape and size during the course of nanocatalysis. As a result, a thorough examination on the effect of the catalytic process on the shape and size of colloidal metal nanoparticles after catalysis is necessary to fully evaluate their use in catalytic processes.

In this paper, we briefly review our recent work on examining the shape dependence of nanocatalysis as well as the stability of platinum and palladium nanoparticles during the course of two reactions: the electron transfer reaction and the Suzuki reaction. It is found that nanocatalysis is indeed shape-dependent during the early stages of the electron transfer reaction. During the full course of the reaction, there are changes in the nanoparticle shape as well as changes in the activation energy that takes place. In the case of a relatively harsh reaction such as the Suzuki reaction, spherical palladium nanoparticles grow in size due to Ostwald ripening processes. Tetrahedral platinum nanoparticles catalyzing the Suzuki reaction transform into spherical shape and grow larger in size. We also conducted studies on the effect of individual reactants on the nanoparticle size and shape. In addition, the surface catalytic mechanisms of the reactions have been confirmed using spectroscopic tools such as FTIR and Raman spectroscopy. These kinds of studies will be very useful in the process of designing better nanocatalysts in the future.

This paper reports findings of an investigation of the synthesis of monolayer-capped iron oxide and core (iron oxide)-shell (gold) nanocomposite and their assembly towards thin films as sensing materials. Pre-synthesized and size-defined iron oxide nanoparticles were used as seeding materials for the reduction of gold precursors, which was shown to be effective for coating the iron oxide cores with gold shells (Fe oxide@Au). The unique aspect of our synthesis is the formation of Fe oxide@Au core-shell nanoparticles with controllable surface properties. By controlling the reaction temperatures and manipulating the capping agent properties and solution compositions, the size, shape, composition, and monodispersity can be tailored. The core-shell nanoparticles were shown to form molecularly-mediated thin film assemblies using molecular mediators. The sensing properties of the nanostructures on piezoelectric devices were examined for the detection of volatile organic compounds. The preliminary results have provided important insights into the design of core-shell nanocomposites as sensing materials.

This paper presents a novel approach to create silicon nanostructures with controlled sidewall profiles. The nanostructures are fabricated by alternating the reactive ion etching process and the exposure process to the atmosphere with moisture. The air exposure is believed attributed to the sidewall passivation by facilitating the fast formation of a thin SiO2/SiOxFy layer. Using this approach, three types of representative nanostructures are demonstrated, namely: nanopillars with vertical sidewall, nanopillars with narrowed necks, and suspending nanocantilevers. Without requiring expensive facilities and extensive expertise, this work is expected to provide an alternative for developing nanostructures with a variety of geometric profiles for mechanical sensing applications.

The deposition of La0.9Sr0.1Cr0.9Co0.1O3 thin films by RF magnetron sputtering and annealing leads to the formation of a conducting perovskite film for the protection of metallic interconnects in SOFCs. The nanoporous structure, formed by a two-step phase transition, may also be a promising candidate for catalytic applications.

Mn-Co-Ni-O spinel, owing to its large temperature dependant resistivity, is an attractive ternary system for negative temperature coefficient (NTC) thermistor applications, particularly in oxygen rich environments. This research explores the potential of plasma spray as a method for the fabrication of thick film Mn-Co-Ni-O thermistors. Nanostructured Mn-Co-Ni-O spinel powders were synthesized by gel combustion method and were air-plasma-sprayed on to alumina substrates. The as-sprayed deposit formed a rocksalt structure rather than a cubic spinel structure. Annealing in air at 600°C for 3 hours resulted in transformation to the spinel structure while higher temperature annealing resulted in phase separation of rocksalt phase at 1250°C and recombination into spinel monophase at 1350°C. Temperature dependent measurement of resistivity showed -4 to -1% temperature coefficient of resistivity (TCR) from room temperature to 250oC with high reproducibility, making the low temperature annealed coating suitable in thermistor applications.

We report the synthesis of water soluble, monodisperse Fe/Au bimetallic nanoparticles with an average diameter of 7nm. Synthesis involves simultaneous reduction of Fe3+ and Au3+ in water to yield bimetallic nanoparticles. The elemental content of Fe is 1.5%. Nanoparticles exhibit ferromagnetic behavior as measured by SQUID. These particles can be easily conjugated to thiolated DNA, as evidenced by mobility shifts in agarose gel electrophoresis. Nanoparticles heat in solution to temperatures above 40°C, indicating suitability for hyperthermia.

Covalent conjugation of nanoparticles to proteins is challenging as proteins have numerous residues to which the nanoparticle can non-specifically adsorb. This is problematic as non-specific adsorption is known to denature the protein, altering its structure and thus compromising protein activity. We study site specific gold nanoparticle labeling of two enzymes, Ribonuclease S and Cytochrome c, with the goal of understanding conditions that minimize non-specific adsorption and optimize protein structure and activity. Ribonuclease S is a two-piece protein made of S-peptide and S-protein. 3nm gold nanoparticle is attached to a mutated cysteine residue on the S-peptide. The altered enzymatic activity of gold labeled Ribonuclease S is determined using RNA substrate with a fluorophore-quencher couple. Cytochrome c is linked to 1.5nm nanoparticles with ligands having neutral, negatively, or positively charged endgroups, through covalent attachment of gold with a specific surface cysteine residue. The labeled protein is characterized by circular dichroism spectroscopy and UV-visible absorption. For both proteins, agarose gel electrophoresis was used to determine optimal reaction stoichiometry and also probe non-specific adsorption between the nanoparticle and protein.