Formation Of Nanoparticle Structures Research Articles

A model flow reactor design for the study of nanoparticle structure formation under well-defined conditions.

Structure formation models describe the change of the particle structure, e.g., by sintering or coating, as a function of the residence time and temperature. For the validation of these models, precise experimental data are required. The precise determination of the required data is difficult due to simultaneously acting mechanisms leading to particle structure formation as well as their dependency on various particle properties and process conditions in the reactor. In this work, a model flow reactor (MFR) is designed and optimized, supported by a validated computational fluid dynamic simulation, to determine the structure formation of nanoparticles under well-defined conditions. Online instrumentation is used to measure the particle mass and different equivalent diameter to detect changes of the particle shape and to calculate the particle structure, defined by the primary particle size, the number of primary particles per agglomerate, coating thickness, effective density, and fractal dimension, by means of structural models. High precision is achieved by examining size-selected particles in a low number concentration and a laminar flow field. Coagulation can be neglected due to the low particle number concentration. Structure formation is restricted to a defined region by direct particle trajectories from the water-cooled aerosol inlet to the water-cooled outlet. A preheated sheath gas is used to concentrate the aerosol on the centerline. The simulated particle trajectories exhibit a well-defined and narrow temperature residence time distribution. Residence times of at least 1 s in the temperature range from 500 K to 1400 K are achieved. The operation of the MFR is demonstrated by the sintering of size-selected FexOy agglomerates with measurements of the particle size and mass distribution as a function of the temperature. An increase of the effective density, resulting from the decreasing particle size at constant particle mass, is observed.

Self-Assembly of Nanoparticles Controlled by Resonant Laser Light

The paper presents theoretical justification for the possibility of formation of nanoparticle structures with the predefined configuration. The process of formation is the self-organized aggregation of nanoparticles under the action of external resonant laser field. The formation of various nanostructures that contain metallic and semiconducting nanoparticles with resonances in the visible spectrum is considered in the dipole-dipole approximation.

Enhanced near-infrared emission from holmium-ytterbium co-doped phosphate glasses containing silver nanoparticles.

The fabrication and spectroscopic characterization of Ho(3+) and Yb(3+) co-doped phosphate glasses, also containing silver nanoparticles (SNPs), is reported. The nucleation and formation of nanoparticle structures in the samples are confirmed using transmission electron microscopy analyses. It is found that the Ho(3+)-Yb(3+)-SNP phosphate glasses exhibit an enhancement of both the resonant-absorption and the fluorescence properties when the SNP concentration is increased.

Formation of Nano-Particle Structures Induced by Ultraviolet Laser Irradiations in KNbO3-TeO2 Glass

We report on a novel technique for formation of nano-particle structures in KNbO3-TeO2 glasses induced by ultraviolet (UV) XeCl excimer laser irradiations operating at 308 nm wavelength. The glasses with a composition of 0.5Er2O3-15K2O-15Nb2O5-70TeO2 (mol%), which are known to exhibit a nano-crystallization behavior by heat treatments, have been used in this experiment. It has been found that the morphological properties of nano-particles, such as diameter, height, and distribution density of nano-particles, can be tailored by the pulsed UV laser conditions. The nature of these nano-structures on glass surface induced by laser processing has been clarified that laser-induced nano-particles are consisting of the same composition as that in glass substrate.

Formation of nano-particle structure on TeO2-based glass by heat-assisted UV laser irradiation

Formation of nano-particle structure on TeO2-based glass by heat-assisted UV laser irradiation