Magnetic-Field Directed Vapor-Phase Assembly of Low Fractal Dimension Metal Nanostructures: Experiment and Theory.

While gas-phase synthesis techniques offer a scalable approach to production of metal nanoparticles, directed assembly is challenging due to fast particle diffusion rates that lead to random Brownian aggregation. This work explores an electromagnetic-levitation technique to generate metal nanoparticle aggregates with fractal dimension () below that of diffusion limited assembly. We demonstrate that in addition to levitation and induction heating, the external magnetic field is sufficient to compete with random Brownian forces, which enables the formation of altered fractals.

Modelling and simulation of field directed linear assembly of aerosol particles.

Unlike liquid phase colloidal assembly, significantly changing the structure of fractal aggregates in the aerosol phase, is considered impractical. In this study, we discuss the possibility of applying external magnetic and electric fields, to tune the structure and fractal dimension (D) of aggregates grown in the aerosol phase. We show that external fields can be used to induce dipole moments in primary nanoparticles.

Calculating the rotational friction coefficient of fractal aerosol particles in the transition regime using extended Kirkwood-Riseman theory.

We apply our extended Kirkwood-Riseman theory to compute the translation, rotation, and coupling friction tensors and the scalar rotational friction coefficient for an aerosol fractal aggregate in the transition flow regime. The method can be used for particles consisting of spheres in contact. Our approach considers only the linear velocity of the primary spheres in a rotating aggregate and ignores rotational and coupling interactions between spheres.

Friction factor for aerosol fractal aggregates over the entire Knudsen range.

We develop an approach for computing the hydrodynamic friction tensor and scalar friction coefficient for an aerosol fractal aggregate in the transition regime. Our approach involves solving the Bhatnagar-Gross-Krook equation for the velocity field around a sphere and using the velocity field to calculate the force on each primary sphere in the aggregate due to the presence of the other spheres. It is essentially an extension of Kirkwood-Riseman theory from the continuum flow regime to the entire Knudsen range (Knudsen number from 0.

Understanding the mobility of nonspherical particles in the free molecular regime.

An approach to obtain the mobility of nonspherical particles is proposed by averaging the drag force orientationally, and two other widely used approaches in the literature, the averaged-collision-integral and averaged-drift-velocity methods, are summarized and extended. The concept of orientationally averaged collision integrals based on Chapman-Enskog theory for small gas-phase ions is re-examined for macromolecular ions whose surface cannot be treated as specular, but with inelastic interactions. A well accepted collision model considering inelastic collisions is Epstein's theory, which has been extended to include long-range potential forces by Li and Wang [Phys.

Photoacoustic spectrometer with a calculable cell constant for measurements of gases and aerosols.

We benchmark the performance of a photoacoustic spectrometer with a calculable cell constant in applications related to climate change measurements. As presently implemented, this spectrometer has a detection limit of 3.1 × 10(-9) W cm(-1) Hz(-1/2) for absorption by a gas and 1.

Measurement of 100 nm and 60 nm Particle Standards by Differential Mobility Analysis.

The peak particle size and expanded uncertainties (95 % confidence interval) for two new particle calibration standards are measured as 101.8 nm ± 1.1 nm and 60.

Use of laser-induced ionization to detect soot inception in premixed flames.

Experimental measurements of laser-induced ionization were performed for ethene-air premixed flames operated near the soot inception point. Soot was ionized with a pulsed laser operated at 532 nm. The ionization signal was collected with a tungsten electrode located in the postflame region.

Slip Correction Measurements of Certified PSL Nanoparticles Using a Nanometer Differential Mobility Analyzer (Nano-DMA) for Knudsen Number From 0.5 to 83.

The slip correction factor has been investigated at reduced pressures and high Knudsen number using polystyrene latex (PSL) particles. Nano-differential mobility analyzers (NDMA) were used in determining the slip correction factor by measuring the electrical mobility of 100.7 nm, 269 nm, and 19.

Polarized light scattering by dielectric and metallic spheres on oxidized silicon surfaces.

The polarization and intensity of light scattered by polystyrene latex and copper spheres with diameters of approximately 100 nm deposited onto silicon substrates containing various thicknesses of oxide films were measured with 532-nm light. The results are compared with a theory for scattering by a sphere on a surface, originally developed by others [Physica A 137, 209 (1986)] and extended to include coatings on the substrate. Nonlinear least-squares fits of the theory to the observations yield results that were consistent with differential mobility measurements of the particle diameter.

Polarized light scattering by dielectric and metallic spheres on silicon wafers.

The polarization and intensity of light scattered by monodisperse polystyrene latex and copper spheres, with diameters ranging from 92 to 218 nm, deposited on silicon substrates were measured with 442-, 532-, and 633-nm light. The results are compared with a theory for scattering by a sphere on a surface, originally developed by others [PhysicaA 137,209 (1986)], and extended to include coatings on the sphere and the substrate. The results show that accurate calculation of the scattering of light by a metal sphere requires that the near-field interaction between the sphere and its image be included in acomplete manner.

On Two Numerical Techniques for Light Scattering by Dielectric Agglomerated Structures.

Smoke agglomerates are made of many soot sphcres, and their light scattering response is of interest in fire research. The numerical techniques chiefly used for theoretical scattering studies are the method of moments and the coupled dipole moment. The two methods have been obtained in this tutorial paper directly from the monochromatic Maxwell curl equations and shown to be equivalent.

Size and Refractive Index Determination of Single Polystyrene Spheres.

The intensity of the light scattered from individual dielectric spheres was measured as a function of the scattering angle, for light polarized parallel and perpendicular to the scattering plane. These sets of data were used to determine the radius and refractive index of the spheres by fitting the data to the scattering function obtained from Mie theory. The light was produced by a He-Cd laser (=441.