Gas-Phase Synthesis of Nanoparticles ..
21/10/2008 · Vapor-Phase Synthesis of Mesostructured Silica Nanofibers Inside ..
Nanoparticles from the Vapor Phase Synthesis ..
Magnetic nanoparticles from transition metals and metal alloys have also been synthesized by laser ablation. Since magnetic properties are strongly influenced by purity, crystallinity, and particle size of the nanoparticles, advanced laser ablation () is significantly more capable of controlling nanoparticle morphologies. fabricated Ni particles of a select size coated with a NiO shell with the laser ablation method. They also applied the aerosol process, i.e., LPDMA size classification, and gas phase annealing to improve Ni nanoparticle morphology. A Ni/NiO core shell structure was successfully generated by the oxidation of Ni nanoparticles. , investigated the magnetic properties of Ni/NiO nanoparticles generated by this method using a superconducting quantum interference device (SQUID) magnetometer at room temperature. Ferromagnetism was observed with a film comprising nickel particles larger than 6.2 nm in core diameter. In contrast, smaller Ni nanoparticles with core diameters of 3 nm exhibited superparamagnetism. They reported that the formation of an antiferromagnetic NiO shell is effective for controlling the manifestation of superparamagnetism in the nanometer-sized ferromagnetic Ni core.
In 2003 Dr. Markus Winterer was elected to become Professor for Nanoparticle Process Technology at the Institute for Combustion and Gas Dynamics at the University of Duisburg-Essen. He studied chemistry at the Albert-Ludwigs-University of Freiburg and the Westfälische Wilhelms-University of Münster where he received his doctoral degree in natural sciences in 1989 for research in physical chemistry on paramagnetic hyperfine structure of rare earth ions in glasses. He worked then as visiting scholar at the Materials Science Division of the Argonne National Laboratory (USA) on chalcogenide clusters encapsulated in molecular sieves for the catalytic conversion of methane and was supported by a Feodor-Lynen fellowship of the Alexander von Humboldt-foundation. From 1993 to 2003 he was scientific associate at the Institute of Materials Science at Darmstadt University of Technology where he received his habilitation degree in 2001 for research on synthesis and characterization of nanocrystalline ceramics. Current research topics include the development of processes for the controlled synthesis and deposition of nanoparticles from the gas phase and the preparation of functional nanomaterials for a wide range of potential applications.
Characterization of vapor-phase-grown ZnSe nanoparticles
A semiconductor quantum dot is a nanocrystal that exhibits quantum properties such as tunable light emission driven by the quantum confinement effect (Canham, 2000) and single electron transport phenomena (). There are some reports on the synthesis of II– VI and III–V semiconductor quantum dots by laser ablation such as formation of GaAs nanocrystals (Perriere et al., 2001), ZnSe and CdS quantum dots (), CdSe and CdTe nanoparticles () that can be applied to the study of optical imaging therapy (). However, the laser ablation process for composite materials is challenged in controlling the stoichiometry and crystallinity in the process for rebuilding laser-vaporized elements. Group-IV elements such as silicon and germanium and carbon nanoparticles are single element semiconductors. Silicon and carbon are abundant (non-rare metal) elements that exhibit a variety of unique properties when the particle sizes are in the nanometer range. Therefore, we will focus on the synthesis of silicon and carbon nanoparticles in this review.
is a schematic of the nanoparticle formation process by laser ablation. When the laser beam is focused on the surface of a solid target material in the ambient media (gas or liquid), the temperature of the irradiated spot rapidly increases, vaporizing the target material. The collisions between the evaporated species (atom and clusters) and the surrounding molecules result in excitation of the electron state coupled with light emission and generation of electrons and ions, forming a laser-induced plasma plume (). The plasma structures (size of the plume and its emission spectrum) depend on the target material, ambient media (liquid or gas), ambient pressure, and laser conditions. shows typical transmission electron micrographs of nanoparticles generated by laser ablation of various materials. In general, laser ablation in low-pressure background gas is preferable for creating a large plume and works well in generating small particles (). Laser ablation in liquid is employed to confine the plasma plume in a small region to directly disperse nanoparticles in the liquid phase (). In any case, the ambient media must be carefully selected because the laser-generated particles easily react with surrounding molecules to create complexes such as oxides and other undesirable species (). Coagulation is another critical phenomena that must be finely controlled in the later stages of nanoparticle formation. Since laser-generated particles have a very clean surface, agglomerated particles create chemical bonds at the contact point (neck), which significantly compromise the properties of primary particles (, ). The low-pressure gas process is advantageous not only for reducing the size of the primary particles but also for preventing coagulation.
Single-phase synthesis of functionalized gold nanoparticles ..
Various nanoparticle fabrication methods have been developed with the bottom-up approach in the liquid phase (including sol-gel and chemical reduction) as well as vapor phase (such as physical/chemical vapor deposition and flame synthesis). Each fabrication method has advantages and disadvantages. Liquid phase methods are cost-effective and are used for synthesizing various kinds of nanoparticles with well-controlled structures at the laboratory scale. Vapor phase processes are superior at synthesizing high purity nanoparticles by means of the continuous flow reactor. In both of the liquid and gas bottom-up processes, solid nanoparticles are generated from the nucleation of supersaturated species that are prepared by precursor reactions and/or evaporation of solids. Laser ablation is a method that utilizes laser (which is an acronym for light amplification by stimulated emission of radiation) as an energy source for ablating solid target materials. In this process, extremely high energy is concentrated at a specific point on a solid surface to evaporate light-absorbing material. The term ‘ablation’ refers to the removal of surface atoms and involves not only a single photon process (breaking the chemical bonds) but also multiphoton excitation (thermal evaporation). High-purity nanoparticles can be generated by laser ablation because the purity of the particles is basically determined by the purity of the target and ambient media (gas or liquid) without contamination from the reactor. However, it is difficult to control size distribution, agglomeration, and crystal structure in the conventional laser ablation process since nanoparticles are built by random (Brownian) motion of molecules. Therefore, several advanced laser ablation techniques have been developed for fabricating morphology-controlled nanoparticles. In this review, laser ablation-based nanoparticle formation processes and their mechanisms are briefly discussed, followed by a review of recent studies of laser ablation techniques for synthesizing various kinds of nanoparticles. Finally, advanced laser ablation processes for synthesizing functional nanomaterials with highly controlled nanostructures are introduced.
Schematic of nanoparticle synthesis process using laser ablation, which is composed of (a) particle generation, (b) gas phase annealing, (c) particle classifying, and (d) particle measurement.
gas-phase synthesis of metal nanoparticles.
Journal of Nanoscience and Nanotechnology
In the first example, the vapor phase synthesis of Au–Ag, Au–Pd, and Au–Pt nanoparticle alloys are presented.
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Vapor phase synthesis of titania (TiO2) nanoparticles has been extensively investigated since they have photovoltaic and photocatalytic applications (; ). synthesized TiO particles by Nd:YAG laser ablation of a TiO2 target in a background gas (He) with pressure ranging from 2.6 to 13.3 kPa. They observed increases in the mobility diameter due to agglomeration as the pressure increased. High-resolution TEM analysis of the nanostructures of the generated revealed that the metallic (Ti) core was covered with a sub-stoichiometric shell structure with a thickness of several nanometers. also synthesized TiO nanoparticles by laser ablation and investigated the effect of aerosol post-annealing temperatures of up to 900 °C. They reported an increase in the primary particle diameter due to sintering and change in crystallinity from amorphous form to anatase and rutile, which was confirmed by Raman scattering. They also discussed the non-stoichiometric phase of TiO particles such as Ti2O3. More recently, investigated the effect of nucleation (particle formation) temperature on the morphology of TiO2 nanoparticles generated by the laser oven process (laser ablation in a tubular furnace).
JCEJ Outstanding Paper Award Winners - 化学工学会
The benefit of non-equilibrium laser ablation nucleation processes is that it can generate various kinds of crystal phases and allotropes that are not seen in the normal (equilibrium) synthesis processes. shows transmission electron micrographs of nanometer scale carbon allotropes (nanocarbons) such as carbon nanotubes (CNTs, ), onion-like carbon (), and nano-diamonds () synthesized by laser ablation. Since laser ablation is superior at generating high-purity and nanometer-sized metal particles, it is also suitable as a catalyst for the growth of single walled carbon nanotubes (SWCNTs) on the substrate. For example, generated Co/Mo and Co/Pt alloy nanoparticles by laser ablation and investigated the ethanol-CVD growth of the CNT on the substrate. In another development, laser ablation in a high temperature flow reactor (laser oven method) has been widely used to generate high-purity SWCNTs (). References on carbon-related nanomaterial synthesis using gas-phase laser ablation are arranged in . Compared to conventional CVD formation on substrates, the laser oven method has an affinity for generating SWCNTs with low level of defects in a continuous flow-type generator.
Outstanding Paper Award of 2016
Zhang reported PEG coated SPIONs for both MRI and optical imaging. The biocompatible PEG coating bearing amine functional group could serve as a platform to incorporate a variety of targeting, therapeutic or imaging ligands . In this case, chlorotoxin was conjugated to PEG@SPION and Cy5.5 (a near-infrared fluorescent dye). These SPIONs have shown specifically to accumulate in xenograft tumors of a brain tumor mouse model. Furthermore, they did not have any toxicity or negative health effects from the results of histopathology and blood toxicity assays. Huang and coworkers have designed hyaluronic acid (HA) coated SPIONs for targeting activated macrophages . The HA-coated SPIONs had specific biological recognition with the receptor CD44. The cell uptake studies showed a significant uptake of SPIONs by activated macrophage cell line THP-1 and enabled MRI of THP-1 cells. The dual modal probes could be used to track the magnetite core and cargo individually. The magnetite core was only present inside the cells while the cargo fluorescein was found to be delivered to the cell nucleus. This study reveals the fact that the HA-based SPIONs have great potential in nucleus targeting drug delivery.
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