In situ formation of 1D nanostructures from ceria nanoparticle dispersions by liquid cell TEM irradiation

Deliberate electron irradiation of cerium oxide nanoparticles in water is used to trigger chemical reactions in a liquid cell transmission electron microscope. Formation of nanorods and nanoneedles is observed starting from predominantly octahedral shape nanoparticles. Detailed morphologies found include free-standing needles, needles connected to specific octahedral ceria facets and star-shaped multi-needle patterns. It is found that rod-axis orientations and crystallographic directions are aligned. It is suggested that high ion and radical concentration of radiolysed water dissolves layers of the original CeO2 particles which re-arrange as needles in the direction of energetically preferred facets

Nanoherding: Plasma-chemical synthesis and electric-charge-driven self organization of SiO2 nanodots

We report on the chemical synthesis of the arrays of silicon oxide nanodots and their self-organization on the surface via physical processes triggered by surface charges. The method based on chemically active oxygen plasma leads to the rearrangement of nanostructures and eventually to the formation of groups of nanodots. This behavior is explained in terms of the effect of electric field on the kinetics of surface processes. The direct measurements of the electric charges on the surface demonstrate that the charge correlates with the density and arrangement of nanodots within the array. Extensive numerical simulations support the proposed mechanism and prove a critical role of the electric charges in the self-organization. This simple and environment-friendly self-guided process could be used in the chemical synthesis of large arrays of nanodots on semiconducting surfaces for a variety of applications in catalysis, energy conversion and storage, photochemistry, environmental and biosensing, and several others

Generation of Charged Nanoparticles During the Synthesis of Silicon Nanowires by Chemical Vapor Deposition

The generation of charged nanoparticles in the gas phase has frequently been reported during the synthesis of thin films and nanostructures, Such as nanowires, using chemical vapor deposition (CVD). In an effort to confirm whether charged silicon nanoparticles were also generated during the synthesis of Si nanowires by CVD, a differential mobility analyzer (DMA) combined with a Faraday cup electrometer (FCE) was connected to an atmospheric-pressure CVD reactor under typical conditions for Si nanowire growth. DMA measurements showed that both positively and negatively charged nanoparticles were abundantly generated in the gas phase during CVD. The process parameters such as reactor temperature, molar ratio of SiCl4/H-2, and hydrogen flow rate affected not only the growth behavior of the Si nanowires but also the size distribution of both positively and negatively charged nanoparticles.close9