Patricia Santiago

Structural analysis and growing mechanisms for long SnO2 nanorods synthesized by spray pyrolysis

Flat-surfaced, rod-like materials were obtained by synthesizing long one-dimensional SnO2 structures using a new spray pyrolysis method. The structure and growing mechanisms were evaluated by using scanning and transmission electron microscopy and atomic force microscopy. Molecular simulation tools and high resolution transmission electron microscopy images allowed the analysis of a dynamic behaviour for energy release which determines how the structures are formed by searching for an axial energy release direction.

Synthesis of macroporous poly(acrylic acid)–carbon nanotube composites by frontal polymerization in deep-eutectic solvents

Deep Eutectic Solvents (DESs) formed between Acrylic Acid (AA) and Choline Chloride (CCl) exhibit certain properties of ionic liquids (e.g. high viscosity) that make them suitable for frontal polymerization (FP). The use of DESs not only as a monomer but also as the solvent prevents the use of additional solvents (i.e. typically of organic nature) and offers a green tool for the synthesis of functional composites. We have recently explored this approach for the preparation of poly(acrylic acid) (PAA) and poly(methacrylic acid). In this work, we have taken advantage of the outstanding capability of DESs to solubilize and/or disperse a number of substances to incorporate – in a homogeneous fashion – carbon nanotubes (in this particular case, N-doped MWCNT – CNxMWCNTs) in the polymerizable DES. Interestingly, CNxMWCNTs also played the role of an inert filler in FP. The resulting PAA–CNxMWCNT composites exhibited some distinct features as compared to previous PAA also obtained via DES-assisted FP. For instance, PAA–CNxMWCNT composites can undergo swelling depending on the pH, as bare PAA. However, the presence of CNxMWCNTs allows the formation of a macroporous structure after submission to a freeze-drying process, the achievement of which was not possible in bare PAA. The combination of structural (e.g. macroporosity) and functional (e.g. stimuli responsive) properties exhibited by these materials besides an eventually high biocompatibility – coming from the green character of the DES-assisted synthesis – should make the resulting macroporous PAA–CNxMWCNT composites excellent candidates for their future application as biomaterials.

Synthesis and Photocatalytic Activity of Yb Doped TiO2 Nanoparticles under Visible Light

Developing new semiconductor materials with improved photocatalytic activity is a promising technology for the remedy of environmental pollution. Here we report on the synthesis of Yb containing TiO2 nanoparticles and their catalytic activity under visible light. Highly monodispersed, spherical TiO2 and TiO2 :Yb nanoparticles of 27- 40 nm size range were prepared through controlled hydrolysis of titanium tetrabutoxide (TTB) and characterized by X-ray diffraction (XRD), energy dispersion spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), high angle annular dark field (HAADF), and ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) techniques. Average size of the nanoparticles was found to decrease with the increase of Yb doping concentration. The photocatalytic activity of Yb doped TiO2 was evaluated by measuring the degradation rates of methylene blue (MB) under UV and visible lights. Doping with ytterbium ions enhanced significantly the photocatalytic activity of TiO2 nanoparticles for MB oxidation under visible light.

Structural Studies of ZnS Nanoparticles by High Resolution Transmission Electron Microscopy

Zinc sulfide (ZnS), a representative of wide band gap semiconductor nanocrystals, has an excitonic Bohr radius (aBZnS ) of 2.5 nm. It makes ZnS nanoparticles (ZnS NP) having such size very interesting as small biomolecular probes for fluorescence and laser scanning microscopy. To date, ZnS NP of diameters larger than aBZnS has been subject of extensive experimental and theoretical studies. However many questions remain open concerning the synthesis of undoped and uncapped ZnS NP of diameters less than 2.5 nm. To further probe into the physical properties of undoped and uncapped ZnS NP, in this work we report on studies of uncapped ZnS nanoparticles synthesized by a wet chemical process at room temperature. Three colloidal suspensions (named A, B and C, respectively) were obtained from 9:1, 1:1 and 1:9 volume mixtures of 1mM ZnSO4 and 0.85mM Na2S aqueous solutions. Qualitative differences in UV-Vis absorption spectra are discussed in the context of Z-contrast scanning transmission electron microscopy (Z-contrast), low and high resolution transmission electron microscopy (TEM) results. Distribution of particle size is dependent on different volumes of source solutions. For the intermediate mixture, it has been found that about 78% of ZnS nanoparticles have a diameter smaller than the excitonic Bohr Radius of 2.5 nm. HRTEM studies have revealed that nanoparticles grow preferentially with hexagonal structure.

Characterization, Imaging and Degradation Studies of Quantum Dots in Aquatic Organisms

There are numerous potential environmental risks of engineered nanoparticles that are not yet well-characterized or understood. Nanoparticles may be introduced into aquatic environments during production processes and also as a result of release following their use in electronic and biological applications. The objectives of these studies were to characterize the behavior of quantum dots (QD) in water, and the accumulation of and toxicity to potential biological receptors in aquatic ecosystems. There are natural differences in environmental factors that may affect the degradation rates of QD’s as well as their toxicity, including temperature, salinity, and pH conditions. To assess the responses under different pH conditions, nonfunctionalized QD’s composed of a Cd/Se core surrounded by a ZnS shell (Evident Technologies) were added to distilled water, at pHs of 4, 6, and 8, and the changes in fluorescent emission spectra over time were determined. Likewise, to determine the effects of salinity on degradation rates, QD’s were added to 0.22 filtered seawater samples of different salinities (10, 20, and 30‰). The accumulation and potential toxicity of QD’s were evaluated using hepatopancreas cells of oysters, Crassostrea virginica. Fluorescent spectroscopy studies with water and cell samples indicated some degradation in low pH and high salinity waters, but did not indicate that there was increased degradation of QD’s accumulated in cells. Fluorescent confocal microscopy verified that QD’s were accumulated into the hepatopancreas cells. Transmission electron microscopy (TEM) studies verified cellular accumulation, and also indicated some limited degradation of the QD’s by the cells over the short time periods (e.g. hours) used in these preliminary studies. Using a lysosomal destabilization assay, there was some evidence of toxicity to hepatopancreatic cells. These kinds of basic studies are essential for characterizing potential cellular toxicity and addressing the potential impacts of nanoengineered particles on aquatic organisms and basic cellular responses.

Material design and evaluation of nanocomposite resist for next generation lithography

A chemically amplified resist, Poly(4-hydroxystyrene-co-tertiarybutylmethacrylate-co-MethacrylphenylPOSS) with different Polyhedral oligosilsesquioxane (POSS) loading has been synthesized by free radical polymerization. The incorporation of POSS units into the resist matrix has been found to affect their RIE resistance in O2 plasma. The thickness of the films were monitored using ellipsometry at various etch intervals to determine the etch rate and selectivity. It was observed that etch rate of these nanocomposite resists were comparable to the standard PHOST and Novolac based resists. HRTEM and HAADF studies showed that the POSS units exhibit a morphology of rectangular crystallites that are responsible for the plasma etch behavior. We have obtained 120 nm (1:1) (Line/Space) feature using 248 nm lithography. The protecting group, tertiary butyl protecting group exhibits acceptable outgassing. Using e-beam lithography, 70nm pattern feature was obtained.

Synthesis and characterization of quantum dot superlattices.

Gold nanoparticles have been synthesized using n-alkylthiol molecules as a passivating agent. By fixing the length of the thiol chain, it is possible to produce nanocrystal arrays, such as 1D chains, 2D arrays of chains and 3D crystals.