This work demonstrates the properties of InGaN nanorod arrays with various In mole fractions by modified HVPE using In metal at the low growth temperature. The nanorods grown on (0001) sapphire substrates are preferentially oriented in the c-axis direction. We found that the In mole fractions in the nanorods were linearly increased at x ≤ 0.1. However, In mole fractions were slightly increased at x > 0.1 and then were gradually saturated at x = 0.2. CL spectra show strong blue emissions from 428 nm (x = 0.1, 2.89 eV) to 470 nm (x = 0.2, 2.64 eV) at room temperature. From this result, we found the fact that increasing In mole fraction in the InGaN nanorod shift the peak position of CL spectrum emitted from InGaN nanorod to the low energy region.

Various GaP nanostructures such as nanowires, nanobelts, nanocables, and nanocapsules were synthesized by sublimation of ball-milled powders. They have a single-crystalline zinc blende structure with [111] growth direction. The morphology and structure were controlled by reactant gas, growth time, flow rate, and growth temperature. The size, morphology and properties of the nanostructures were examined by scanning electron microscopy, transmission electron microscopy, electron energy-loss spectroscopy (EELS), electron diffraction, energy dispersive x-ray spectroscopy, powder x-ray diffraction, and Raman spectroscopy using a 514.5 nm argon ion laser. The photoluminescence was carried out using the 458 nm line of an argon ion laser as the excitation source. The GaP nanowires are straight, cylindrical, and smooth in surface, with mean diameter of 40 nm and length up to 300 mm. The nitrogen-doped nanobelts and nanowires were synthesized by ammonia ambient gas. EELS data reveals that the nitrogen doping occurs mainly in the surface region. The PL spectrum shows the typical isoelectronic bound exciton peaks in the range of 2.11∼2.25 e V, suggesting a concentration of (1018 cm-3 nitrogen atoms. We also synthesized two types of GaP nanocables; GaP nanowire sheathed with the amorphous silicon oxide layers and with the graphite layers. The core-shell diameter is under 30 nm and the outerlayer can be removed by acid treatment to produce the 10 nm diameter GaP nanowires. The GaP encapsulated with BCN nanotubes were synthesized under the ammonia flow using the ball-milled carbon-containing boron oxide powders. The number of BCN layers is typically 10∼20.

Platinum nanoparticles were deposited onto Highly Oriented Pyrolitic Graphite (HOPG) substrate by laser ablating a Pt target at room temperature into a vacuum chamber. By varying the helium background pressure (from 10-5 to 0.5 Torr) and the target-to-substrate distance (from 3 to 6 cm), we were able to explore a large range of kinetic energies (i.e., from ∼4 to ∼130 eV/atom) of the Pt ablated neutrals species impinging on the HOPG substrates. Thus, the effect of the kinetic energy on the size and the surface density of Pt nanoparticles has been investigated ex-situ by means of scanning tunneling microscopy (STM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The pulsed laser deposition technique is shown to produce Pt nanoparticles (of which diameter in the 1 – 4 nm range) with a relatively narrow size distribution. While the size of the PLD Pt nanoparticles is shown to be mainly influenced by the number of laser pulses, their shape is found to be more sensitive to kinetic energy of the Pt ablated species.

We present results obtained using low temperature near-field scanning optical microscopy for the measurements of Zeeman splitting and the diamagnetic shift of single self-organized InAs/AlAs, InAs/GaAs and InP/GaInP quantum dots. The measurements allow us to relate the bimodal size distribution of InAs dots with variations in In content. For single InP QDs we observed a strong circular polarization at zero magnetic field accompanied with a negative energy shift, suggesting that strong internal magnetic fields exist in these QDs.

A fundamental quantum theory of conductivity of spatially inhomogeneous systems in weak electro-magnetic fields has been derived using a two-time Green function (TTGF)-based technique that generalizes the original method due to Zubarev and Tserkovnikov (ZT). Quantum current and charge density evolution equations are derived in a linear approximation with regard to the field potentials. Explicit expressions for the longitudinal and transverse conductivity, and dielectric and magnetic susceptibilities have been derived in terms of charge density - charge density and microcurrent - microcurrent TTGFs. The obtained theoretical description and formulae are applicable to any inhomogeneous system, such as artificial molecules, atomic and molecular clusters, thin films, interfacial systems, etc. In particular, the theory is designed to predict charge transport properties of small semiconductor quantum dots (QDs) and wells (QWs), and is a significant step toward realization of a concept of virtual (i.e., theory-based, computational) synthesis of electronic nanomaterials of prescribed electronic properties.

Computer simulations are applied to understand the influence of network geometry on the electron transport dynamics in random nanoparticle networks, and the predicted results are compared with those measured in one class of random nanoparticle networks: dye-sensitized nanocrystalline TiO2 solar cells. The model is applicable to all classes of random nanoparticle networks, such as highly disordered quantum dot arrays. The random nanoparticle networks are simulated by the step-wise condensation of a diffusion-limited aggregate. The fractal dimension of the nanoparticle films was estimated from the simulations to be 2.28, which is in quantitative agreement with gas-sorption measurements of TiO2 nanoparticle films. Electron transport on the computer-generated networks is simulated by random walk. The experimental measurements and random-walk simulations are found to be in quantitative agreement. For both a power-law dependence of the electron diffusion coefficient D on the film porosity P is found as described by the relation: D ∝ | P -Pc |μ. This power-law relation can also be derived from percolation theory, although only qualitatively. The critical porosity Pc (percolation threshold) and the conductivity exponent μ are found to be 0.76 ± 0.01 and 0.82 ± 0.05, respectively. It is estimated that during their respective transit through 50 and 75% porous 10-μm thick films as employed in the dye-cell, the average number of particles visited by electrons increases by 10-fold, from 106 to 107.

We have designed a series of organic oligo- and polyethylene glycol (PEG) based surface capping ligands that allow for QD manipulation in aqueous media. We utilized readily available thioctic acid and various oligo- and polyethylene glycols in simple esterification schemes, followed by reduction of the dithiolane to produce multi-gram quantities of capping substrates. Cap exchange of the native trioctyl-phosphine and -phosphine oxide based ligands with the PEG-terminated dithiol-alkyl cap readily resulted in aqueous dispersions of QDs that were homogeneous and stable in various pH ranges over an extended period of time. Mixed surface capping strategies utilizing ratios of dihydrolipoic acid to the pegylated dihydrolipoic acid were also prepared. We anticipate that such systems should allow one to covalently attach amine containing biomolecules to nanoparticle systems bearing carboxylates, employing known coupling agents, such as (dimethylamino) propyl-3-ethyl-carbodiimide (EDC). This design and conjugation strategy may facilitate the development of a new generation of QD-bioconjugates, which can be directly utilized in bio-related applications such as sensing and cellular imaging.

Nerve cells communicate by passing electrical signals through extensions from their cell bodies. Micron-scale devices such as microelectrode arrays and field effect transistors have already been used to externally manipulate these signals. However, these devices are almost as large as the cell body of the neuron. In order to make functional electrical connections to nerve extensions or their component ion channels that propagate signals, it will be necessary to utilize increasingly smaller components. We propose the use of semiconductor quantum dots, which can be optically activated, as a potential means of perturbing the nerve membrane potentials. As a first step, we have created qdot-neuron interfaces with cadmium sulfide quantum dots. The qdots may be attached to cells either non-specifically or through selected interactions exploiting biorecognition molecules attached to the qdot particle surface. We have investigated the effect of altered synthesis conditions including pH, concentration, reactant ratio, ligand length, ligand R group, and ligand concentration on the nature and quality of qdot-cell binding. We discuss the effect of these altered synthesis conditions on particle fluorescence intensity and color. Additionally, we studied the interaction of these particles with cells and determined that larger particles are more likely to bind non-specifically than smaller particles produced with the same amount of passivating ligand. It is possible this results from reduced surface area coverage of passivating chemical. Finally, we have produced particles passivated with the biorecognition peptide CGGGRGDS in the absence of other chemical stabilizers and characterized their surfaces using NMR and IR.

We fabricated the multi-color electroluminescent (EL) device using hydrofluoric (HF) acid solution treated and oxidized silicon (Si) nanoparticles. Strong red luminescence was obtained from the HF treated Si nanoparticles based EL device under a low forward bias of 4.0 V. On the other hand, green and blue luminescence, which could be seen with naked eye under room illumination, was observed for the oxidized Si nanoparitcles based EL device at the forward bias below 9.5 V, because of reduction of size due to oxidation onto the Si nanoparticle surface. Furthermore, the red/green/blue lights showed good stability for aging of a long period of time in air by the formation of oxidized layer on the surface. These results indicate that the EL devices developed in this study can realize as application to future flat panel display.

Gallium oxide (Ga2O3) and indium oxide (In2O3) nanostructures were synthesized by chemical vapor deposition (CVD). Ga2O3 nanowires were synthesized using Ga/Ga2O3 mixture and O2. The diameter of the nanowires is 30–80 nm with an average value of 50 nm. They are consisted of single-crystalline monoclinic crystal. While the nanowires grown without catalyst exhibit a significant planar defect, the nanowires grown with nickel catalytic nanoparticles are almost defect-free. The growth direction of the nanowires grown without the catalyst is uniformly [010]. In contrast, the nanowires grown with the catalyst have random growth direction. X-ray diffraction, Raman spectroscopy, and photoluminescence are well correlated with the structural characteristics of the nanowires. The result provides an evidence for the catalyst effect in controlling the structure of nanowires. In2O3 nanostructures were also synthesized in a controlled manner by selecting the catalyst. The reactants were In and In/In2O3 mixture. The nanowires were produced using catalytic Au nanoparticles and Ga. But the unique bifurcated-structure nanobelts were instead grown without Ga. The nanowires have uniform [100] growth direction with rectangular cross-section. We converted the In2O3 nanowires to In2O3-Ga2O3 nanostructures.

The photoluminescent (PL) properties and zeta potential of green-emitting CdTe nanocrystals (diameter: 3 nm) capped with a stabilizing surfactant, thioglycolic acid (TGA), have been investigated as a function of pH of the aqueous solution. The green PL intensity reached the maximum at pH5.1 and was somewhat lower in the pH range of 6–10, which was similar to the previously reported result. However, when the pH was at and below 4, the green PL intensity decreased drastically. The relative ratio of the dissociation form of the carboxyl group of TGA showed a large diminution at and below pH5 accompanied by a significant decrease of the absolute value of zeta potential. Since the absolute value of zeta potential reflects the stability of nanocrystals, the results obtained shows that the TGA-capped CdTe nanocrystals are stable only in basic to neutral regions and that the agglomeration of the nanocrystals in acidic range reflects the transition from the dissociated (charged) form to the non-dissociated (non-charged) form of a carboxyl group in TGA. Encapsulation of nanocrystals in glass is a promising way to further improve the long-term photostability of nanocrystals. Therefore, we chose an alkoxide having an amino group for a matrix for the encapsulation. The amino group has a good affinity to TGA as well as promotes the sol-gel reaction. As the result, the CdTe nanocrystals have been dispersed finely in the glass matrix without a deterioration of PL intensity.

We have synthesized CoFe2O4 nanoparticles with length scales ranging from 3.5 nm to 14.2 nm. We have characterized the magnetic properties of these samples using both DC and AC magnetization, and find some slightly anomalous behavior in two of the samples. We tentatively attribute these features to interactions between the magnetic nanoparticles.

There is a great deal of interest in understanding the physical basis for the magnetic properties of nanoparticles in order to facilitate their incorporation into a wide range of commercial applications. By studying the magnetic characteristics of CoFe2O4 nanoparticles using bulk measurement techniques, we are able to probe the properties of both the individual nanoparticles and interactions in these systems. In this report, we discuss our magnetic characterization of a series of CoFe2O4 nanoparticles grown using an aqueous co-precipitation technique. In addition to DC magnetization at fixed fields and temperatures, we also investigated the magnetic properties using AC susceptibility measurements. The long term goal of this research is to understand interparticle interactions in magnetic nanoparticles.

We have produced nitrogen doped, stable, and environmentally benign TiO2-xNx photocatalysts whose optical response can be tuned across the entire visible region using a nanoscale exclusive synthesis route, performed in seconds at room temperature. This synthesis, which can be simultaneously accompanied by metal atom seeding, that can be accomplished through the direct nitration of anatase TiO2 nanostructures with alkyl ammonium salts. Tunability throughout the visible spectrum depends on the degree of TiO2 nano- particle agglomeration and the influence of metal seeding. The introduction of a small quantity of palladium, in the form of the chloride or nitrate, promotes further nitrogen uptake, appears to lead to a partial phase transformation, displays a counter ion effect with the acetate, and produces a material absorbing well into the near infrared. The nitridation process also induces the formation of oxygen hole centers. Silver introduced as the nitrate into a TiO2 or TiO2-xNx nanostructure framework, forms seeded AgxO - TiO2 or TiO2-xNx nanostructure mixtures which can be induced to self-assemble and to agglomerate into nano-needle and planar arrays using select metal probes. Surprisingly, no organics are incorporated into the final TiO2-xNx products. These visible light absorbing photocatalysts readily photodegrade methylene blue and when used to create photocatalytic sites on a surface based microreactor induce ethylene oxidation with visible light. They can be transformed from liquids to gels and placed on the surfaces of sensor and microreactor based configurations to 1) facilitate a photocatalytically induced solar pumped sensor response, and 2) provide a possible means for the catalytically induced disinfection of airborne pathogens. In contrast to a process which is facile at the nanoscale, we find little or no direct nitridation of micrometer sized anatase or rutile TiO2 powders at room temperature. Thus, we demonstrate an example of how a traversal to the nanoscale can vastly improve the efficiency for producing important submicron materials.

Photoinduced conductivity changes and effects of thermal annealing in carbon nanotube transistors have been examined. Low-intensity ultraviolet light significantly reduces the p-channel conductance while simultaneously increasing the n-channel conductance. A combination of optical absorption and electron transport measurements reveals that these changes occur without variations in dopant concentrations. Measurements with different metals reveal that UV induces oxygen desorption from the electrodes rather than from nanotubes. In Ti-nanotube contact where the Schottky barrier plays an important role, photodesorption of oxygen mainly occurs from the native oxide of Ti electrodes. Decrease in the p-channel conductance arises from the metal work function change which causes larger hole Schottky barrier. Non-Schottky Pd-contacted nanotube transistors do not show photodesorption effects with low intensity UV. Thermal annealing of nanotube transistors with Ti/Au electrodes also leads to the disappearance of the photodesorption effects. However, a noticeable p-doping is observed to upon air exposure after thermal annealing.

Lasing from CdSe/ZnS quantum rods and quantum dots both in solution and in a film is studied by utilizing a high Q cylindrical microcavity, showing Whispering Gallery Mode (WGM) lasing. CdSe/ZnS quantum rods, in comparison to quantum dots, exhibited remarkably reduced lasing thresholds. In addition, polarization measurements revealed that quantum rods have a linear polarized lasing, in contrast to quantum dots that show no preferable lasing polarization. Furthermore, an efficient and reproducible method is employed for preparation of nanocrystal films inside capillaries by laser irradiation for achieving robust lasing. Further irradiation of the film resulted in a room temperature stable lasing over hundreds of pump pulses, lasing thresholds as low as 0.02mJ and lasing intensities that are three orders of magnitude larger than the saturated fluorescence intensity. This was successfully applied to CdSe/ZnS quantum rod samples of varied dimensions and was also demonstrated for quantum dot samples.

In this study, a novel thick film nanocrystalline phosphor is synthesized by using postdispersion treatment at low temperature. The post-dispersion treatment is to prevent the agglomeration between the precursors by mixing the organic dispersing agent with them before heat-treatment. The mean size of the particle heat-treated at 500°C is 4nm. Also, europium is uniformly distributed in the yttrium oxide with deviation below 0.5%. The nanocrystalline phosphor is principally composed of cubic structure having preferred orientation of <222>, <440>, and <400>. The photoluminescence properties of the nanocrystalline phosphor characterized with monochrometric systems reveals that the main PL peak is detected at 611 nm, and thick film nanocrystalline phosphor with 15wt% europium exhibits better properties.

The effect of doping on the electron transport dynamics and recombination kinetics in dye-sensitized solar cells was investigated. A simple electrochemical method was developed to dope TiO2 nanoparticle films with Li. Increasing the doping levels is found to slow electron diffusion. The electron diffusion time exhibits a light intensity dependence at all doping levels consistent with a multiple electron-trapping model involving native and doping-induced traps. Importantly, the diffusion time and recombination lifetime of photocarriers are observed to increase in unison with increased doping. This is the first observation that electron diffusion limits recombination with the redox electrolyte under normal working conditions of the dye cell. A model is presented that accounts for the observation. The implications of this mechanism on cell performance are also discussed.

Nanoscaled particles showing a superparamagnetic behavior have been intensively studied these past years for biomedical applications and water-based ferrofluids turned out to be promising candidates for various in vivo as well as in vitro applications. Nevertheless, the lack of well-defined particles remains an important problem. One of the major challenges is still the large-scale synthesis of particles with a narrow size distribution. In this work iron oxide nanoparticles are obtained by classical co-precipitation in a water-based medium and are subsequently coated with polyvinyl alcohol. The thus obtained ferrofluids are studied and a focus is made on their colloidal stability.

Various shaped single-crystalline gallium nitride (GaN) nanostructures were produced by chemical vapor deposition method in the temperature range of 900–1200 °C. Scanning electron microscopy, transmission electron microscopy, electron diffraction, x-ray diffraction, electron energy loss spectroscopy, Raman spectroscopy, and photoluminescence were used to investigate the structural and optical properties of the GaN nanostructures. We controlled the GaN nanostructures by the catalyst and temperature. The cylindrical and triangular shaped nanowires were synthesized using iron and gold nanoparticles as catalysts, respectively, in the temperature range of 900 – 1000 °C. We synthesized the nanobelts, nanosaws, and porous nanowires using gallium source/ boron oxide mixture. When the temperature of source was 1100 °C, the nanobelts having a triangle tip were grown. At the temperature higher up to 1200 °C the nanosaws and porous nanowires were formed with a large scale. The cylindrical nanowires have random growth direction, while the triangular nanowires have uniform growth direction [010]. The growth direction of the nanobelts is perpendicular to the [010]. Interestingly, the nanosaws and porous nanowires exhibit the same growth direction [011]. The shift of Raman, XRD, and PL bands from those of bulk was correlated with the strains of the GaN nanostructures.

ABSTRACT: One of the major shortcomings of silicon (Si) as a semiconductor material is its inability to yield efficient light emission. There has been a continued interest in adding rare earth ion impurities such as erbium (Er) to the Si lattice to act as light emitting centers. The low band gap of Si however has complicated this practice by quenching and absorbing this possible emission. Increasing the band gap of the host has been successfully tried in the case of gallium nitride (GaN) [1] and Si-rich oxide (SRO) [2] alloys. A similar approach has been tried here, where Er oxide (ErOx) nanocrystals have been formed in a yttria stabilized zirconia (YSZ) host deposited on a Si (100) substrate. The YSZ is deposited as a heteroepitaxial, insulating layer on the Si substrate by a reactive sputtering technique. The Er is also incorporated by a sputtering process from a metallic target and its placement in the YSZ host can be easily controlled. The device structure formed is a simple metal contact/insulator/phosphor sandwich. The device has been found to emit visible green light at low bias voltages. The advantage of this material is that it is much more structured than SiO2 which can theoretically lead to higher emission intensity.