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Published in Luis Liz-Marzán, Colloidal Synthesis of Plasmonic Nanometals, 2020
There have also been strong advancements in theoretical modeling over the past couple of decades, which have exploited the availability of faster and cheaper computers. Although the standard approaches to light absorption and scattering based on Gustav Mie theory (and modifications thereof)22 are still largely employed, this model is of limited applicability to current systems, such as coupled particles, and fails to properly reproduce the optical response of systems with increasing geometrical comp lexity. Consequently, the development of new models which can be applied in a more general fashion has been demanded. Indeed, theoretical work has been carried out, for instance applying the so-called discrete dipole approximation (DDA),23 in which the particle is divided into small elements interacting with each other through dipole-dipole interactions, and subsequently a global evaluation of absorption and scattering is performed. This approximation was initially devised to model scattering and absorption of electromagnetic waves by targets with arbitrary geometries and complex refractive index but has later been successfully implemented for small particles.24,25
Hierarchical Assembled Structures Based on Nanoparticles: Structure-Property Relations and Advanced Three-Dimensional Characterization
Published in Jeffrey P. Simmons, Lawrence F. Drummy, Charles A. Bouman, Marc De Graef, Statistical Methods for Materials Science, 2019
Dhriti Nepal, Sushil R. Kanel, Lawrence F. Drummy
The breakthrough in understanding light scattering by spherical structures came from the work of Mie in 1908. On the basis of electromagnetic theory, Mie obtained a general rigorous solution for the optical scattering by a homogeneous sphere with arbitrary size in a homogeneous medium. This theory is still valid as long as the distance between particles is large enough so that there are no coherent phase relations among the scattered light from different particles [113, 313]. To accommodate other shaped particles, especially for the spheroids, this theory modified by Richard Gans in 1912. In Gans’ theory, the aspect ratio of the particles is the predominant factor to calculate the absorption. As a result, it is widely used to get the exact solution for gold/silver nanorods (NRs). Discrete dipole approximation (DDA) method is one of the most popular alternatives to model the exact shape of the particles without employing physical approximations. DDA is based on an approximation of the continuum target by a finite array of polarizable points, where the points acquire dipole moments in response to the local electric field.
Extinction characteristics of biological aggregated particles with different porosity in the far infrared band
Published in Khaled Habib, Elfed Lewis, Frontier Research and Innovation in Optoelectronics Technology and Industry, 2018
X. Chen, Y.H. Hu, Y.L. Gu, X.Y. Zhao, X.Y. Wang
Discrete dipole approximation (DDA) is an important theoretical method for studying the extinction characteristics of aggregated particles. This method has the advantage of high iterative efficiency and it can be free from the object structure limitation. Therefore, this paper used the DDA method to calculate the extinction characteristics of the BB0919 biological aggregated particles in the far infrared band. When the spatial structure, radius, and the number of original particle are determined, the DDA method can be used to calculate the scattering parameters such as the extinction efficiency factor Qext, absorption efficiency factor Qabs, scattering efficiency factor Qsca and asymmetry factor g. The mass extinction coefficient of biological aggregated particles αe can be calculated by the extinction efficiency factor Qext: () Cext=Qext·π·reff () αe=CextN·43πr3ρ
Complex refractive index of crystalline quartz particles from UV to thermal infrared
Published in Aerosol Science and Technology, 2023
Hervé Herbin, Lise Deschutter, Alexandre Deguine, Denis Petitprez
To overcome this difficulty, some methods for calculating the scattering by nonspherical particles, such as T-matrix or discrete dipole approximation (DDA) (Drain and Flatau 1994; Mischenko et al. 2002) have been tested (Dubovik et al. 2006; Kalashnikova et al. 2005). These methods offer more flexibility in constructing model particles that are inhomogeneous and irregularly shaped, but they are more computationally demanding and they still involve significant approximations and assumptions. Thus, it is clear that further experimental studies are needed to assess the relevance of these different approaches, but at present it is still very difficult to accurately characterize the shape of the particles. For example, SEM appears to be an interesting tool, but it suffers from a lack of statistical representation of the sample and only gives information about the shape in two dimensions.