Interesting optical properties of peroxo-titanium hydrogen peroxide complex against pH changes were studied for the first time using an analytical UV-VIS spectrophotometer. A freshly prepared peroxo titanium complex with pH value of 2.21 exhibited an orange color. This color changed to light orange, cloudy yellow, and then translucent pale-yellow as its pH value increased to 3.9, 5.8 and 6.7 or above. UV-VIS spectra show that the fresh complex had an absorption band rising at wavelength around 400 nm to higher energy, but had no maximum peak. A new absorption peak appears at 245nm for the cloudy yellow samples. This is similar to that of colloidal TiO2, which suggests that TiO2 particles might form upon increasing pH value to or above 5.80. The formation of TiO2 particles was accelerated in the pH value range from 6 to 9, but not in the acidic environment. In H2SO4 acidified environment, the color turned red-orange instead, and a strong absorption at 397nm was observed only at pH =0.99. Based on the experimental observations, a model for the color-forming species and possible applications by using the techniques generated from the present study were proposed.

Nanocomposite heterogeneous semiconductors with suitable energy levels (gaps) are exhibiting excellent photocatalytic properties under visible light irradiation. TiO2/ZnFe2O4 has been selected among different alloys because of (i) its low band gap ∼1.9 eV (ii) the nontoxicity of ZnFe2O4 (iii) visible light absorption characteristics of ZnFe2O4 due to its narrow band gap and (iv) not being susceptible to photoanodic corrosion. A mechanochemical synthesis approach using high energy milling is employed to prepare TiO2/ZnFe2O4 under different experimental parameters and conditions. The effects of ball milling and calcination on the photocatalytic behavior of TiO2 and TiO2/ZnFe2O4 have been determined. The as-milled nanocomposite materials are characterized with PXD, SEM and EDS procedures. The photocatalytic activity of TiO2/ZnFe2O4 nanocomposites for the photodegradation of phenol under visible light irradiation has been studied systematically by UV-Vis spectrometer. It is interesting to note a red shift of 0.25 eV in the absorption edge of the ball-milled TiO2 sample when compared to the non ball milled TiO2 photocatalyst.

ZnO nanowires (NWs) were fabricated on Au coated sapphire (0001) substrates by using a pulsed laser deposition (PLD) system in vacuum furnace with a Q-switched Nd:YAG laser. ZnO NWs have various size and shape with a substrate position inside a furnace, and their morphologic construction is reproducible. Scanning electron microscopy (SEM) images indicate that the diameters of ZnO NWs ranged from 100 to 150 nm and the average length was greater than 3 μm. Room-temperature photoluminescence spectra of the NWs show the near band-edge emissions and the deep-level green light emissions. The formation mechanism of the NWs is discussed.

A synthetic method for the design of heterogeneous catalysts incorporating monodisperse platinum nanoparticles into ordered mesoporous oxide frameworks has been developed. Nanoparticles were synthesized in solution in the presence of surface templating polymer and encapsulated into mesoporous oxide matrices. After polymer removal by calcination, ethylene hydrogenation rates were consistent with previously reported results, while superior activity of low coordination atoms in small crystallites during ethane hydrogenolysis was demonstrated. Changes in reaction selectivity with particle size during the hydrogenation/dehydrogenation of cyclohexene were attributed to a hydrogen coverage effect influencing the hydrogenation pathway and the apparent structure sensitivity of the dehydrogenation pathway.

Magnetostrictive nanobars as sensor platform were induced. Based on the resonance behavior of strips made from thin films, it is identified that the amorphous Fe-B alloy is a good candidate for fabricating high performance sensor platform. The fabrication process of amorphous Fe-B nanobars using electrochemical deposition is reported. The magnetization hysteresis loop of Fe-B nanobars with the diameters of 50, 100 and 200 nm, respectively, was characterized. It is found that, for all nanobars, the coercive field measured along length direction is smaller than the coercive field measured perpendicular to length direction. The physics behind the phenomena is discussed.

In this paper, we report preliminary studies of formation of water from molecular oxygen and hydrogen. Using a series of atomistic simulations carried at finite temperature, we describe the dynamics of water formation at a Pt catalyst using a new reactive ReaxFF potential. By performing a series of studies, we obtain statistically meaningful trajectories to extract rate constants of water formation. This allows an estimate for the activation energy during water formation, which is found to be in reasonable agreement with the activation barrier calculated by restraint driven molecular dynamics simulation of water formation at the Pt surface.

Label-free, real-time, parallel and complementary electrical detection of proteins is demonstrated by p-type and n-type silicon nanowire field-effect transistors in the same arrays. Composed of hundreds of individually electrically addressable nanowire devices with highly sensitive and reproducible performances, these nanowire arrays can be controllably modified by monoclonal antibodies, and show discrete conductance changes characteristic of highly selective binding and unbinding of target proteins, such as prostate specific antigens (PSA), thus providing a general and powerful platform for high-throughput real-time parallel detection and rapid screening of libraries of biomolecules. Studies show that the PSA proteins can be routinely detected at femtomolar concentrations with high selectivity, and simultaneously incorporation of both p-type and n-type silicon nanowire devices enable discrimination against false positive/negative signals. The integrated complementary nanowire sensor arrays open up substantial opportunities for diagnosis and treatment of complex diseases such as cancer, detection of biological threats, and fundamental proteomic and biophysical studies.

Even though most microarrays present good quality, accuracy and reliability, they are made on a planar surface structure, which neither enough increases the accessibility of the targets to the probes nor the loading capacity of the solid support. To achieve a high density of reactive functions, the use of a non-planar structure is investigated to increase the available surface area for grafting of biomolecules. We propose to build up a pseudo-three-dimensional silicon structure, covered with a specific oxide layer, and then functionalized, allowing to introduce covalent and stable bindings of amino-modified oligonucleotides probes on the reactive layer of the support. The performances of these supports after silanisation are investigated by means of hybridization experiments using complementary fluorescent labeled-oligonucleotides targets. Our results indicate that these novel surfaces provide a higher specific surface area for attaching biomolecules and higher accessibility of the targets, which will increase the density of biomolecules and hence, the sensitivity of the fluorescence signal in comparison to the results obtained with a planar surface structure.

In many carbon nanotube synthesis methods, catalyst nanoparticles are formed via pyrolysis of a precursor such as ferrocene. Since the diameter of a carbon nanotube is usually determined by the diameter of the catalyst nanoparticle, it is of great importance to control the size of nanoparticles. To do so, it is necessary to identify the key reaction parameters that influence nanoparticle size. For engineering purposes, a simple analytical model offers a convenient first estimation of particle diameter. It also clarifies the dependence of nanoparticle diameter on each reaction parameter and enhances our understanding of the formation mechanism of nanoparticles. This paper presents a simplified model that can calculate the diameter of particles and the model's analytical solutions.

Gas sensors based on WO3 thin films doped with platinum (Pt) or palladium (Pd) were prepared by KrF excimer pulsed laser deposition method combined with dc sputtering. The films were deposited on silicon, quartz and Al2O3 sensor substrate with Pt interdigital electrodes at various substrate temperatures from 300°C to 500 °C, and oxygen pressures from 100 mTorr to 300 m Torr, respectively during the deposition. The morphology and structure of the films were examined by AFM and XRD. The sensor property of the WO3−x thin films was measured by the two terminal resistance method at operating temperatures of 25 °C to 400 °C. The sensitivity of the WO3 thin film gas sensors with doping (platinum or palladium) was found to be higher than that of undoped WO3 thin films gas sensors. The sensitivity of the pt doped WO3 films to different concentration of NO gas was examined and the sensitivity was found to be increased with increasing NO gas concentration.

We report plasmon excitation in 3-dimensional, ordered, gold nanocrystal(NC) arrays using a prism coupler. The gold NCs are arranged in the silica host matrix in a face-centered cubic lattice with the mono-dispersion gold core size of ∼3 nm. We observed the collective optical behavior of the gold NC array and found a blue shift in the plasmon absorption peak with increasing gold volume fraction (Au loading). Plasmon resonance bands centered at 536, 530 and 520 nm are measured for gold NC arrays with gold loading factors of 0.25, 0.5 and 1.0, respectively. The corresponding angular spectra of the gold NC arrays show resonance angles at 60.3, 63.3 and 66.4 degree.

We examined atomic and electronic structures of Pt supported on graphene, using the first-principles calculations based on the density functional theory (DFT). First, we examined the interaction between graphene and a Pt(111) monolayer. The stable distance between graphene and the Pt-monolayer is 3.48Å and the adhesive energy is 0.09 eV/atom. The density of states (DOS) for the Pt(111)/graphene system is the same with the sum of respective DOS's of the graphene sheet and the Pt monolayer. These results indicate that the interaction between graphene and a Pt(111) monolayer is very weak. Second, we examined the interaction between graphene and a Pt atom. The Pt-C bond length is 2.31Å and the adsorption energy is 2.82 eV/adatom, which means the stronger interaction. Finally, we examined the interaction between graphene and a Pt cluster consisting of ten atoms. The distance between graphene and the bottom layer of the cluster is about 2.7Å, which is shorter than that between graphene and the Pt(111) monolayer. This shows that the interaction between the Pt10 cluster and graphene is stronger than the Pt-monolayer/graphene interaction. The center atom in the hexagonal bottom layer of the Pt cluster has the nearest distance with graphene of about 2.5Å. If there is a defect on graphene, the center atom of the hexagonal bottom layer strongly interacts with that.

We report a successful demonstration of a position control technique for carbon nanotube growth catalyzed by an iron nano-dot array, which was fabricated by using electron beam induced chemical vapor deposition (EB-CVD). Point irradiation of an electron beam with ferrocene source gas produced an amorphous carbon dot containing iron atoms that were uniformly dispersed into each dot, and its position could be precisely controlled. Vacuum annealing of the ferrocene based dots induced segregation of iron nano-particles, whose size was almost proportional to the beam irradiation time. After removing the carbon residue, an ethanol CVD process carried out at 800°C under 40 mmHg of ethanol vapor induced carbon nanotube growth from the dots. Many grown nanotubes were very thin, being 0.7 to 1.8 nm in diameter. These diameters were much less than that of the bottom iron particles.

The structure of Au nano-particles supported on CeO2 was investigated by using an analytical transmission electron microscope (TEM). The shape change of Au particles was observed during TEM observation, such as shrinking down to a mono-atomic layer on the CeO2 substrate. The electron beam irradiation experiment revealed that the shape change of Au particles is concerning with the oxidation state or the density of oxygen vacancies of CeO2 substrate where the rapid desorption and adsorption of oxygen occurs. It was also found that the reduction by strong electron beam irradiation and subsequent oxidation generate the decoration of Au particles by cerium oxide.

Upon extrusion process, first vanadium oxide macroscopic fibers have been obtained. They are associated to longitudinal Young modulus from 15 to 25 GPa and depict strong high scale textural anisotropy as observed through cross-polarized microscopy. TEM observations and SAXS experiments reveal that those macroscopic fibers are made of nanoscopic ribbons associated to preferential orientation parallel to the macroscopic fiber main axis, while XRD and NMR investigations reveal a microstructure close to the V2O5.1.8H2O xerogels. These fibers can detect down to 0.1 ppm of ethanol within 16 seconds at 40°C.

The interpretation of the continuous wave electron paramagnetic resonance (CW-EPR) spectra of Cu2+ exchanged in Faujasite zeolite is not straightforward. Recent literature points to the role of both Cu2+ zeolite sites and Cu2+ relationship to lattice Al in determining the parameters of Cu2+ spin Hamiltonian. Our work shows that at low concentration, Cu2+ EPR signals show negligible spin-spin interactions. At higher Cu (II) concentrations, a third CW-EPR spectrum that has contributions from both the CW-EPR and the spin-spin interactions, appears.

Silicon carbide is a promising wide-bandgap semiconductor intended for use in fabrication of high temperature, high power, and fast switching microelectronics components running without cooling. For hydrogen sensing applications, silicon carbide is generally used in conjunction with either palladium or platinum, both of them being good catalysts for hydrogen. Here we are reporting on the temperature-dependent surface morphology and depth profile modifications of Au, Ti, and W electrical contacts deposited on silicon carbide substrates implanted with 20 keV Pd ions.

Anodized aluminum oxide (AAO) membranes consist of highly uniform and aligned nanopores with pore diameters ranging between 10 and 200 nm. Based on these nanoporous materials, we developed a new AAO nanowell structure that was synthesized through short-term anodization of aluminum foil. The nanowell structure was made of shallow wells that were oriented in a hexagonally closed packed configuration with well diameter around 50 nm and depth less than 100 nm. The chemical composition was amorphous alumina on aluminum substrate. Thin palladium film was then fabricated on the surface of the as-synthesized AAO nanowell to prepare a Pd/AAO nanowell structure. These devices demonstrated unexpectedly high hydrogen sensitivity. The response time ranged from a few hundred milliseconds to a few seconds with hydrogen concentration between 1 and 0.05%. They also showed modest responses at hydrogen concentration as low as 5 ppm.

In this work, we report a success in fabricating highly-ordered and densely-packed array of silicon nano-needles that are vertically aligned, straight and long, meeting many of the requirements for biomolecular sensing and integration with silicon electronics. Yet, we show that they can be fabricated with a relatively simple and non-lithographic method.

In this approach the array of nano-needles of high uniformity in length and diameter are made out of silicon by reactive ion etching (RIE) through either an anodic aluminum oxide (AAO) membrane or an array of metallic nano-dot caps that are evaporated on a silicon wafer using an AAO membrane as mask. The AAO membrane itself is formed non-lithographically via anodization of pure aluminum foil and contains an array of highly-ordered and highly-uniform nano-pores. By using the AAO membrane either directly as an etching mask or as an evaporation mask to deposit metallic nanodots which in turn serve as an etching mask, deep and high aspect-ratio etching is possible to allow the formation of the nanoneedles in a Si substrate.

Ex-situ transmission electron microscopy (TEM) was performed on catalytically-grown multi-wall carbon nanotubes (MWCNTs), leading to the identification of two types of catalyst-nanotube wall interfaces – respectively characterized by a quasi-spherical, low aspect ratio particle closer to the nanotube root and by a tapered, high aspect ratio particle farther away from it. The nanotubes exhibit two distinct types of boundaries between crystalline domains with different orientations – twist and twin boundaries in correspondence with quasi-spherical particles and tilt boundaries in correspondence with the tapered particles. TEM evidence suggests that the domain boundaries maintain a rather steady position coupled to the catalytic particles, while the carbon atoms diffuse along the nanotube axis away from the particles. From these considerations, it is possible to conclude that the relative movement of the carbon atoms with respect to the dislocation lines comprising the nanotube domain boundary located at the catalyst-wall interface is a significant mechanism for nanotube crystal growth mainly driven by surface diffusion. The results are interpreted in light of the concurrence of base- and tip- growth for the catalytic synthesis of nanotubes dominated by surface diffusion.