Low temperature synthesis of magnetite and maghemite nanoparticles

We report on the synthesis of iron oxide nanoparticles below 100 degrees C by a simple chemical protocol. The uniqueness of the method lies in the use of Ferrous ammonium sulphate (in conjugation with FeCl3) which helps maintain the stability of Fe2+ state in the reaction sequence thereby controlling the phase formation. Hexamine was added as the stabilizer. The nanoparticles synthesized at three different temperatures viz, 5 degrees, 27 degrees, and 95 degrees C are characterized by several techniques. Generally, when a mixture of Fe3+ and Fe2+ is added to sodium hydroxide, alpha-Fe2O3 (the anti-ferromagnetic phase) is formed after the dehydration process of the hydroxide. In our case however, the phases formed at all the three temperatures were found to be ferro (ferri) magnetic, implying modification of the formation chemistry due to the specifics of our method. The nanoparticles synthesized at the lowest temperature exhibit magnetite phase, while increase in growth temperature to 95 degrees C leads to the maghemite phase.     

Magnetite/CdTe magnetic-fluorescent composite nanosystem for magnetic separation and bio-imaging

A new synthesis protocol is described to obtain a CdTe decorated magnetite bifunctional nanosystem via dodecylamine (DDA) as cross linker. High resolution transmission electron microscopy (HRTEM), energy-dispersive x-ray spectroscopy (EDAX), vibrating sample magnetometry (VSM), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS) and fluorescence microscopy are used to characterize the constitution, size, composition and physical properties of these superparamagnetic-fluorescent nanoparticles. These CdTe decorated magnetite nanoparticles were then functionalized with anti-epidermal growth factor receptor (EGFR) antibody to specifically target cells expressing this receptor. The EGFR is a transmembrane glycoprotein and is expressed on tumor cells from different tissue origins including human leukemic cell line Molt-4 cells. The magnetite-CdTe composite nanosystem is shown to perform excellently for specific selection, magnetic separation and fluorescent detection of EGFR positive Molt-4 cells from a mixed population. Flow cytometry and confocal laser scanning microscopy results show that this composite nanosystem has great potential in antibody functionalized magnetic separation and imaging of cells using cell surface receptor antibody.     

Scandium ion doped yttrium oxide transparent ceramic from nitrate alanine microwave combustion synthesized nanopowders

One atomic percent Neodymium ion doped Yttrium oxide, with 25 at% scandium ion (Nd_0.02Sc_0.5Y_1.48O₃), was synthesized by nitrate alanine microwave gel combustion followed by calcinations at 1000 °C for 2 h. Phase purity of nanopowder was characterized by X-Ray Diffraction (XRD). Neodymium and scandium ion doping was confirmed by cell parameter calculation and Scanning Electron Microscope-Electron Dispersive X-ray (SEM-EDX) analysis. Particles with size range 25–35 nm with close to spherical shape were obtained as observed by Transmission Electron Microscopy (TEM). Powder on compaction followed by vacuum sintering at 1765 °C for 40 min led to the formation of ceramic with 76% transmission at 2500 nm compared to translucent ceramic obtained without scandium ion doping. This indicates formation of highly sinterable neodymium doped yttrium oxide nanopowders by nitrate alanine microwave gel combustion route with scandium ion additive. Further the absorption and emission bands of Nd_0.02Sc_0.5Y_1.48O₃ are inhomogeneously broadened and fluorescence lifetime is longer than Nd_0.02Y_1.98O₃.     

Carbon nanotubes: Amino functionalization and its application in the fabrication of Al-matrix composites

Al-matrix composites reinforced with amino-functionalized multiwalled carbon nanotubes (fCNTs) have been fabricated using the powder metallurgy process. Using this method fCNTs (1.5 wt.%) were dispersed in Al powder by high energy ball milling. Al–fCNTs composites (1.5 wt.%) were fabricated by the consolidation of powders at 550 MPa followed by sintering at 620 °C under a vacuum of 10^? 2 Torr for 2 h. Functionalization of the nanotubes was carried out by ball milling multi-walled carbon nanotubes (MWCNTs) in the presence of ammonium bicarbonate. It was observed that the dispersion of fCNTs in Al-matrix was much higher than those of non-functionalized MWCNTs. Microhardness measurements showed that a microhardness value of about 400 kg/mm² could be obtained for Al-matrix composites loaded with 1.5 wt.% fCNTs. Microstructure observations using scanning electron microscopy (SEM) and high-resolution electron microscopy (HRTEM) confirmed that the sintered composites had a good dispersion of fCNTs in Al matrix and they do not agglomerate with each other. Further, the HRTEM characterization of these composites revealed the formation of a thin transition layer of Al₄C₃ between fCNTs and Al matrix, which is believed to be responsible for load transfer from Al matrix to fCNTs. A thorough characterization of MWCNTs and fCNTs synthesized in the present work was carried out using XRD, SEM, TGA, HRTEM, FTIR, SIMS and Raman spectroscopy.     

Ledge-flow-controlled catalyst interface dynamics during Si nanowire growth

Self-assembled nanowires offer the prospect of accurate and scalable device engineering at an atomistic scale for applications in electronics, photonics and biology. However, deterministic nanowire growth and the control of dopant profiles and heterostructures are limited by an incomplete understanding of the role of commonly used catalysts and specifically of their interface dynamics. Although catalytic chemical vapour deposition of nanowires below the eutectic temperature has been demonstrated in many semiconductor-catalyst systems, growth from solid catalysts is still disputed and the overall mechanism is largely unresolved. Here, we present a video-rate environmental transmission electron microscopy study of Si nanowire formation from Pd silicide crystals under disilane exposure. A Si crystal nucleus forms by phase separation, as observed for the liquid Au-Si system, which we use as a comparative benchmark. The dominant coherent Pd silicide/Si growth interface subsequently advances by lateral propagation of ledges, driven by catalytic dissociation of disilane and coupled Pd and Si diffusion. Our results establish an atomistic framework for nanowire assembly from solid catalysts, relevant also to their contact formation.     

Thermally assisted semiconductor-like to insulator transition in gold-poly(methyl methacrylate) nanocomposites

Gold-polymethylmethacrylate (PMMA) nanocomposites were fabricated by mixing gold nanoparticles capped with oleylamine in polymethylmethacrylate. The samples were analysed using UV-vis absorption spectroscopy, transmission electron microscopy, small angle x-ray scattering, Fourier transform infrared spectrometry (FTIR) and x-ray photoelectron spectroscopy (XPS). Electrical resistivity of nanocomposite samples was measured by a four-probe technique in the 70-300?K range. The nanocomposites showed a transition with an onset at ～160-165?K. They exhibited a semiconductor-like conductivity at higher temperatures and nearly temperature independent conductivity at lower temperatures. The interfacial interaction of Au nanoparticles and PMMA polymer is investigated using FTIR and XPS. A ligand-exchange process occurs when capped gold nanoparticles are incorporated in PMMA polymer.