The optical and structural properties of co-doped HfO2 thin films with rare earth trivalent ions prepared by ultrasonic spray pyrolysis technique, are reported. An arrangement of multi-layer (Si-SiO2-HfO2:Eu3+-HfO2:Tb3+-HfO2:Tm3+-SiO2) were deposited on silicon substrates at temperatures from 400 to 550°C, using acetyl acetonates as precursory reagents. A refractive index value of 2.1 was determined by spectral ellipsometry. The surface morphology was obtained by AFM measurements. For 50 to 550 nm thickness films, an average roughness value of ∼56.8 Å was obtained for different substrate temperatures and grown deposition times. EDS measurements showed the presence of hafnium, and rare earths dopants as elemental composition. XPS measurements demonstrated that hafnium and rare earths oxidation species are formed at hafnium dioxide thin films. Photoluminescence emission spectra of multi-layer structures present characteristic emission peaks associated with Tb+3, Eu3+, and Tm3+ dopants. The results presented above motivate us to consider that these multilayer structures could be appropriate to be used as a rare earth host to improve optical emission.

Nanospace governs the dynamics of physical, chemical, material and biological systems, and the facility to model it with analytical formulae provides an essential tool to address some of the worlds’ key problems such as gas purification, separation and storage. This paper aims to provide some analytical models to exploit building blocks representing various geometric shapes that describe nanostructures. In order to formulate the various building blocks, we use the continuous approximation which assumes a uniform distribution of atoms on their surfaces. We then calculate the potential energy of the van der Waals interaction between an atom and the structure to evaluate the location of the atom where the potential energy is at its minimum. We provide applications of the analytical models for some real structures where more than one type of building block is required.

Dielectric capacitors have been the major enabler for many applications in advanced electronic and electrical power systems because of their capability for ultrafast charging/discharging and ultrahigh power density. The low energy densities of polymer dielectrics used in these capacitors have not been able to meet the ever-increasing demands for compact, reliable, and efficient electrical power systems. Polymer nanocomposites, in which high-dielectric-constant (k) nanofillers are incorporated in the polymer matrix, have been actively pursued. In this article, we begin with two theoretical considerations for concomitantly increasing the dielectric permittivity and breakdown strength of nanocomposites: critical interfacial polarization and local electric-field distribution. In the framework of these considerations, we review recent progress toward polymer nanocomposites with high energy densities based on two approaches: core–shell-structured polymer nanocomposites and dielectric anisotropy. In addition, the potential for the enhanced elastic properties of nanocomposites to improve the dielectric strengths of capacitor films is also discussed.

In the present study, an exact solution for free vibration analysis of piezoelectric nanobeams based on the nonlocal theory is obtained. The Euler beam model for a long and thin beam structure is employed, together with the electric potential satisfying the surface free charge condition for free vibration analysis. The governing equations and the boundary conditions are derived using Hamilton's principle. These equations are solved analytically for the vibration frequencies of beams with various end conditions. The model has been verified with the previously published works and found a good agreement with them. A detailed parametric study is conducted to discuss the influences of the nonlocal parameter, on the vibration characteristics of piezoelectric nanobeams. The exact vibration solutions should serve as benchmark results for verifying numerically obtained solutions based on other beam models and solution techniques.

Rutile nanoparticles have been synthesized by acid hydrolysis of titanium isopropoxide by low-temperature dissolution-reprecipitation process. High-resolution transmission electron micrographs of the rutile colloidal solution show needle-shaped rutile nanoparticles with the dimensions of 10–30 nm in diameter and 100–150 nm in length. X-ray diffraction (XRD) data show the existence of only the rutile polymorph in TiO2 powder with a crystallite size of 11.3 nm. The dielectric constant of rutile nanoparticles has been found to be 57 at 10 MHz AC frequency and DC conductance as 2.3 × 10−6 S/cm. Transmission electron micrographs and XRD data analysis imply that the rutile crystallites are self-organized in a regular fashion to produce multilayer three-dimensional linear clusters. The clusters have been found to be microporous (average porosity 1.4 nm) with high specific surface area (132.2 m2/g). At higher concentration, the clusters aggregate to produce interconnected network of star- or flower-like structures. This organized crystalline microporous metal-oxide semiconductor might find various practical applications.

Engineered nanomaterials (ENMs) strongly interact with biomolecules and cells due to their similar size scales. Consequently, ENMs are beginning to emerge as new medical diagnostic tools, probes in cell biology, and delivery vehicles, compelling us to understand the interactions at the nano-bio interface. Optical spectroscopic tools are excellent probes to characterize ENMs and investigate their interactions with complex biological systems, including biomolecules, cells, and even whole animals alike. Here, we discuss the role of many optical spectroscopic techniques such as fluorescence, Raman, surface plasmon, and infrared spectroscopy in elucidating nano-bio interactions. While these spectroscopic tools have the ability to provide valuable information on ENM distribution in biosystems, ENM interaction with proteins, and the mechanisms by which ENMs elicit an adverse physiological response, there are many challenges that remain to be addressed to improve their scope, resolution, and throughput.

Silver-decorated titanium dioxide (Ag/TiO2) nanotube (NT) arrays were successfully prepared using a two-step synthesis route comprised of an anodic oxidation procedure followed by photochemical reduction using ultraviolet irradiation. The resulting Ag/TiO2 NT arrays were characterized using scanning electron microscopy, transmission electron microscopy, x-ray diffraction, and UV-vis diffusion reflectance spectrometry. The characterization results indicated that the silver decoration significantly enhanced the light absorption capability of the TiO2 NT arrays in the visible spectral range. The visible light photocatalytic activity of the subject NT arrays was investigated. The experimental results showed the photocatalytic activity of silver-decorated titanium dioxide Ag/TiO2 NT arrays to be dependent on the size of the silver particles. The improved visible light absorption can be attributed to plasmonic effects induced by particle size phenomenon. The Ag/TiO2 NT arrays exhibit promising application for photocatalytic degradation of dye solutions and pollutants in water using visible irradiation.

Focused ion beam is a powerful method for cross-sectional transmission electron microscope sample preparation due to being site specific and not limited to certain materials. It has, however, been difficult to apply to many nanostructured materials as they are prone to damage due to extending from the surface. Here we show methods for focused ion beam sample preparation for transmission electron microscopy analysis of such materials, demonstrated on GaAs–GaInP core shell nanowires. We use polymer resin as support and protection and are able to produce cross-sections both perpendicular to and parallel with the substrate surface with minimal damage. Consequently, nanowires grown perpendicular to the substrates could be imaged both in plan and side view, including the nanowire–substrate interface in the latter case. Using the methods presented here we could analyze the faceting and homogeneity of hundreds of adjacent nanowires in a single lamella.

We review the work of the present authors to employ variational calculus to formulate continuous models for the connections between various carbon nanostructures. In formulating such a variational principle, there is some evidence that carbon nanotubes deform as in perfect elasticity, and rather like the elastica, and therefore we seek to minimize the elastic energy. The calculus of variations is utilized to minimize the curvature subject to a length constraint, to obtain an Euler–Lagrange equation, which determines the connection between two carbon nanostructures. Moreover, a numerical solution is proposed to determine the geometric parameters for the connected structures. Throughout this review, we assume that the defects on the nanostructures are axially symmetric and that the into-the-plane curvature is small in comparison to that in the two-dimensional plane, so that the problems can be considered in the two-dimensional plane. Since the curvature can be both positive and negative, depending on the gap between the two nanostructures, two distinct cases are examined, which are subsequently shown to smoothly connect to each other.

Uniform PbS nanostructures with varied morphology have been synthesized by a surfactant-assisted reflux route. ZnS and CdS layers were successfully coated onto PbS nanocrystals by encapsulation or epitaxial growth. The nanocrystals were characterized by x-ray diffraction, (high-resolution) transmission electron microscopy, selected area electron diffraction, and scanning electron microscopy. The truncated cubic nanostructures displayed a symmetric emission band at about 860 nm. Diffuse reflectance infrared (IR) spectroscopy was measured to estimate the band gap. High temperature and high frequency measurements of impedance and permittivity taught that the samples were stable and showed collateral evidence of the existence of epitaxial layers. Measurements illustrate that the luminescent properties of semiconductor PbS nanostructures are closely related to their surface nature, and encapsulation can affect their electrical properties and photoluminescence performance greatly. The study may prove useful in developing high frequency IR sensors and light signal amplification devices.

A spectroscopic protocol is proposed to implement confocal microfluorescence imaging to the analysis of microinhomogeneity in the nanocrystallization of the core of fibers belonging to a new kind of broadband fiber amplifier based on glass with embedded nanocrystals. Nanocrystallization, crucial for achieving an adequate light emission efficiency of transition metal ions in these materials, has to be as homogeneous as possible in the fiber to assure optical amplification. This requirement calls for a sensitive method for monitoring nanostructuring in oxide glasses. Here we show that mapping microfluorescence excited at 633 nm by a He-Ne laser may give a useful tool in this regard, thanks to quasi-resonant excitation of coordination defects typical of germanosilicate materials, such as nonbridging oxygens and charged Ge-O-Ge sites, whose fluorescence are shown to undergo spectral modifications when nanocrystals form into the glass. The method has been positively checked on prototypes of optical fibers—preventively characterized by means of scanning electron microscopy and energy dispersive spectroscopy—fabricated from preforms of Ni-doped Li2O-Na2O-Sb2O3-Ga2O3-GeO2-SiO2 glass in silica cladding and subjected to heat treatment to activate gallium oxide nanocrystal growth. The method indeed enables not only the mapping of the crystallization degree but also the identification of drawing-induced defects in the fiber cladding.

CdTe nanorods and various branched nanostructures with different crystal structures were have successfully prepared via the catalyst-assisted vacuum thermal evaporation (CVTE) technique using various experimental parameters. SEM and XRD studies were carried out on the as-prepared CdTe nanostructures. The results show that the morphologies and crystal structures of the products were strongly influenced by the growth conditions and the mole ratios of Bi and CdTe. In the high mole ratio (0.08:1) of Bi and CdTe, CdTe branched nanostructures of CdTe were obtained, while nanorods of CdTe were formed at a lower mole ratio of 0.05:1. The crystal structure of products is either Zinc blende or a two-phase mixture of zinc blende and wurtzite. The content of the wurtzite phase were found to increase with increasing growth temperature. Our results also reveal that high growth temperature tends to form the wurtzite phase, and stacking faults may exist in materials grown in higher temperatures. These nanostructures grow following the vapor–liquid–solid (VLS) mechanism.

Plasma surface activation and antibacterial properties of nanocomposites of polypropylene/silver nanoparticles (PP/nAg) and nylon-6/silver nanoparticles (Ny6/nAg) were investigated. The nanocomposites were prepared by melt blending assisted by ultrasound, while surface activation was achieved by means of argon plasma. To evaluate the antimicrobial properties of the nanocomposites, pathogen microorganisms such as Pseudomonas aeruginosa and Aspergillus niger were tested. Scanning Electron Microscopy (SEM) analyses showed a uniform dispersion of nanoparticles within the polymer matrix, though the presence of some agglomerates was also appreciated. On the other hand, surface topography by Atomic Force Microscopy (AFM) suggested that ions from the argon plasma generated ion collisions with the surface of the nanocomposites removing or etching polymer from surface and improving silver nanoparticles exposure, increasing their antimicrobial properties as corroborated by antimicrobial analyses. Nanocomposites exposed to argon plasma presented higher antimicrobial properties than the ones not exposed. These results indicated that plasma treatment increased the contact area of the nanoparticles with the microorganisms and enhanced the antimicrobial properties of nanocomposites. The results also showed that PP/nAg nanocomposites presented higher bacterial inhibition than Ny6/nAg nanocomposites, indicating that the chemical structure of the polymer also plays a big role in the final performance of the composite.

We present extensive pseudopotential density functional theory calculations dedicated to analyze the stability, electronic properties, and structural isomerism in Cu6 clusters. We consider structures of different symmetries and charge states. Our total energy calculations reveal a strong competition between two- and three-dimensional atomic arrays, the later being mostly energetically preferred for the anionic structures. The bond lengths and electronic spectra strongly depend on the local atomic environment, a result that is expected to strongly influence the catalytic activity of our clusters. Using the nudged elastic band method we analyze the interconversion processes between different Cu6 isomers. Complex atomic relaxations are obtained when we study the transition between different cluster structures; however relatively small energy barriers of approximately 0.3 eV accompany the atomic displacements. Interestingly, we obtain that by considering positively charged Cu6+ systems we reduce further the energy barriers opposing the interconversion process. The previous results could imply that, under a range of experimental conditions, it should be possible to observe different Cu6cluster structures in varying proportions.

In this work we alternate breaking-symmetry-substrates (BSS) and non-breaking-symmetry-substrates (NBSS) such as SiC and SiO2,following the Silver-Mean (MSMGS) and Period-Doubling (MPDGS) sequences. We implement the Transfer Matrix technique to calculate the transmittance and the linear-regime conductance as a function of the most relevant parameters of the multilayered graphene structures: energy and angle of incidence, widths of BSS and NBSS regions and the generation of the quasi-regular sequence. We analyze the main difference of the transmission and conductance properties between MSMGS and MPDGS.

Using a Sutton and Chen interatomic potential, we study the molecular dynamics of Au-Pd nanoparticles with an initial icosahedral structure at different temperatures and concentrations, where each relative concentration of the 561-atom particles was made by placing atoms of the same species at equivalent sites, in order to identify under which conditions the melting transition temperature appears for each particle. In addition, we compute global order parameters in order to correlate the obtained results with the caloric curves of each particle. As a result, we observe that the melting transition temperature depends on the relative atomic positions of gold and palladium. The melting transition temperature of the Au-Pd alloy particles appears at higher temperature than that of the pure-gold particle. From the analysis of the structure of the particles, we found that the melting temperature increases with the proportion of gold atoms, and for those particles with a higher concentration of palladium on the surface, we observe an early migration of gold atoms before the melting transition temperature appears.

We report the evolution of titanium dioxide nanostructures when Au nanoparticles, supported on single crystal TiO2 substrates, were heated under ∼260 Pa of flowing O2 in an environmental transmission electron microscope. Nanostructures with different morphologies were first observed around 500°C. Our measurements show that temperature, oxygen pressure, and the electron beam control the nanostructure growth. We propose a reaction-controlled growth mechanism where mobile Ti atoms generated by the electron- beam-induced reduction of TiO2 are preferentially reoxidized at the Au-TiO2 interface.

The self-organization of porous nanostructures in anodic metal oxideis considered. A mathematical model which incorporates the chemicalreactions at the metal-oxide and oxide-electrolyte interfaces andelastic stress caused by the electrostrictive effects isdeveloped. It is shown through linear stability analysis, that ashort-wave instability exists in certain parameter regimes which canlead to the formation of hexagonally ordered pores observed inanodized aluminum oxide.