The influence of grain boundaries on the vibrational properties of nanoscale phononic crystals is studied with the help of molecular dynamics simulations. The low-frequency vibrational density of states of phononic crystals made from single crystal and polycrystalline silicon are derived from the simulations. The results show that the presence of grain boundaries leads to an increase of the density of states and a change of its peak structure at low frequencies. Calculations of the band structure of the model systems along one direction reveal that the grain boundaries affect the bands differently and in a non-uniform manner.

Stability of functional devices such as light-emitting devices and chemical or biological sensors is an important issue nowadays. Nanostructured silicon made using top-down methodologies is being employed as a material to develop such systems, but surface stability to external ambient conditions is still an open question. One of those important conditions is oxidation. Although there exist models accounting for the role of oxide layers on semiconductor systems, experimental data is still required to provide further useful information. In this paper, we perform oxidation processes to light-emitting nanostructured silicon and study the contribution of quantum dots and quantum wires to photoluminescence as surface oxidation evolves. Cross-correlations with infrared spectroscopy are also included.

Progress in ultrafast terahertz (THz) communications has been limited due to the lack of picosecond switchable modulators with sufficient modulation depth. Gallium arsenide nanowires are ideal candidates for THz modulators as they absorb THz radiation, only when photoexcited – giving the potential for picosecend speed switching and high modulation depth. By embedding the nanowires in a polymer matrix and laminating together several nanowire–polymer films, we increase the areal density of nanowires, resulting in greater modulation of THz radiation. In this paper, we compare PDMS and Parylene C polymers for nanowire encapsulation and show that a high modulation depth is possible using Parylene C due to its thinness and its ability to be laminated. We characterize the modulator behavior and switching speed using optical pump–THz probe spectroscopy, and demonstrate a parylene–nanowire THz modulator with 13.5% modulation depth and 1ps switching speed.

We present the optical characterization of quantum dot cascade laser (QDCL) structures using photoluminescence. In this work, two InAs/AlAs quantum dot structures are investigated with different GaAs QW thicknesses. Low temperature photoluminescence measurements show peaks at 1.03 eV, 1.28 eV, and 1.51 eV for QDCL1, and 1.07 eV, 1.27 eV, and 1.47 eV for sample QDCL2, corresponding to ee-hh transition in both QD and QW. A three dimensional QD-QW model in Nextnano is developed to simulate the energy states, wave functions, and transition rates between conduction and valence bands using a typical QD size obtained from atomic force microscope measurements. The simulation results agree well with the experimental data. This allows us not only to understand the optical characteristics of the QD-QW structure, but also to optimize the QDCL structure design.

We propose a new technique suitable for on-line monitoring of gas phase synthesis of nanoparticles. It is based on aerodynamic focusing of nanoparticles followed by Laser-Induced Breakdown Spectroscopy (LIBS) under vacuum. The laser crosses a beam of particles at low pressure so that the plasma-produced photons to be analyzed are emitted only from the particles. Unlike previous experiments, the background from interaction with the gaseous component is totally eliminated from the collected spectra. Vacuum allows also for easier spectra collection in the UV range. Moreover, as the nanoparticle beam is highly collimated, the optical interface windows are not obstructed by particle deposition and the system can be kept running for hours.

This study reports the development of a one-step method for the production of antimicrobial protective coatings for aluminum surfaces with titania nanoparticles. An aerosol flame synthesis system was used to produce monodisperse, ultra-fine TiO2 nanoparticles, which were directly deposited by thermophoresis onto plates of aluminum alloy by means of a rotating disc. Fuel-lean reactor conditions were used to synthesize pure anatase nanoparticles of 3.5 nm in diameter. Substrates were mounted onto the rotating disc that repetitively passes through the flame. Convection due to the rotational motion cooled the substrates, on which particles were deposited as films by thermophoresis. Such a system allowed to obtain submicron coatings of different thickness, by varying the total time of deposition. The antimicrobial activity of TiO2 coatings was tested against the Gram positive bacterium Staphylococcus aureus. To determine the inhibition of biofilms formation, microbes were plated on TiO2 coatings and a semi-quantitative colorimetric assay was performed using crystal violet. The tests showed that the TiO2 coating obtained with tdes=10 s inhibits up to 70-80% Staphylococcus aureus biofilm formation, and the inhibition of biofilms formation was confirmed by means of Scanning Electron Microscopy observation. Also, the antimicrobial properties of the coatings was enhanced by irradiating the samples in the UV region. The results of the present work are promising for using titania films as protective coatings for applications where an antimicrobial activity is required.

Catalytic chemical vapor deposition enables the synthesis and deposition of carbon nanotubes (CNT) directly on substrates, thereby immobilizing them and potentially preventing them from bundling after synthesis. In this work, we investigate the use of this strategy to prepare ceramic hybrids with unbundled CNTs on aluminum oxide (AO) powder and fabric substrates, which are commonly used in the fabrication of ceramic laminate composites. CNT –AO powder hybrids are produced in 250 g batches with up to about 3 wt% CNT content, which is a sufficient amount for sintering into composite plates for mechanical and ballistic characterization. CNT – AO fabric hybrids are produced and it is found that the polymer coating that comes on the as-purchased fabric aids with CNT deposition. Conformal nickel and nickel oxide films deposited by an atomic layer deposition process are found to be excellent catalysts for CNT deposition. These conformal metal films are being used to create better CNT – ceramic hybrids for processing into better composite materials.

SnO2 doped with Sb and Nb has been investigated for its use as catalyst support materials replacing carbon to enhance PEM fuel cells stability. Nanostructured powders of various doping levels were prepared by flame spray pyrolysis (FSP). The specific requirements of surface area >50 m2g-1 and electronic conductivity >0.01 Scm-1 were obtained, and pore sizes ranging mainly from 10 to 100 nm. Pt particles (9-20 wt.% in loading targeted) of ∼1 nm well dispersed in Sb-doped SnO2 was prepared by a one-step FSP procedure providing microstructures of high interest for further investigations as cathode in PEM fuel cells.

A simulation method is presented which encompasses all relevant mechanisms, which are necessary for the description of the early stages of particle formation in arc discharges. Next to discrete coagulation and nucleation events, a continuous surface growth process is included into the simulation, making thus the description of the evaporation of thermodynamic unstable particles possible. The driving force for the nucleation and growth/evaporation is coupled to the monomer concentration in the gaseous phase and thus subject to change in the further course of the simulation. It is shown, that the simulation results gained by the incorporation of all three of these processes cannot be reproduced, if one of those processes is not simulated.

Lanthanum zirconate (La2Zr2O7) nano-crystalline films with cubic structure have been successfully prepared by a facile synthesis approach called reactive spray deposition technology (RSDT). La2Zr2O7 nanoparticles are produced by combusting a precursor solution of lanthanum acetylacetonate hydrate and zirconium acetylacetonate dissolved in an organic solvent mixture. The nanoparticles formed during the combustion process are directly deposited onto the substrate. The composition and microstructure of the as-deposited films are extensively characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The thermal diffusivities of the films are investigated by the means of laser flash method.