scholarly journals Simulated Optical Properties of Gold Nanocubes and Nanobars by Discrete Dipole Approximation

2012 ◽  
Vol 2012 ◽  
pp. 1-9 ◽  
Author(s):  
Mohammed Alsawafta ◽  
Mamoun Wahbeh ◽  
Vo-Van Truong
Keyword(s):  
Absorption Spectrum ◽  
Cross Section ◽  
Longitudinal Mode ◽  
Transverse Mode ◽  
Dipole Approximation ◽  
Discrete Dipole Approximation ◽  
Absorption Cross ◽  
Extinction Cross Section ◽  
Band Position ◽  
Mode Tm

The absorption spectra for a gold nanocube and for a gold nanobar are calculated by using the Discrete Dipole Approximation (DDA). The results show the excitation of a single albeit broad surface plasmon (SP) band of the gold nanocube. The extinction cross section of the gold nanocube is dominated by the absorption cross section that gains importance as the width increases. Further increasing the nanocube size beyond 80 nm will result in an optical response mainly characterized by scattering properties. The absorption spectrum of the nanobar shows the excitation of both the longitudinal mode (LM) and the transverse mode (TM). The nanobar is also compared to a cylinder, a spherically capped cylinder, and a spheroid of the same aspect ratio. The band position of the TM of the nanobar is red-shifted as compared to the ones calculated for other morphologies, while the LM is either blue-shifted or red-shifted depending on the morphologies considered.

scholarly journals Using the DDA (Discrete Dipole Approximation) Method in Determining the Extinction Cross Section of Black Carbon

2015 ◽  
Vol 22 (1) ◽  
pp. 153-164 ◽  
Author(s):  
Krzysztof Skorupski
Keyword(s):  
Refractive Index ◽  
Black Carbon ◽  
Cross Section ◽  
Main Parameter ◽  
Complex Refractive Index ◽  
Dipole Approximation ◽  
Discrete Dipole Approximation ◽  
Extinction Cross Section ◽  
Quality Of Results

AbstractBC (Black Carbon), which can be found in the atmosphere, is characterized by a large value of the imaginary part of the complex refractive index and, therefore, might have an impact on the global warming effect. To study the interaction of BC with light often computer simulations are used. One of the methods, which are capable of performing light scattering simulations by any shape, is DDA (Discrete Dipole Approximation). In this work its accuracy was estimated in respect to BC structures using the latest stable version of the ADDA (vr. 1.2) algorithm. As the reference algorithm the GMM (Generalized Multiparticle Mie-Solution) code was used. The study shows that the number of volume elements (dipoles) is the main parameter that defines the quality of results. However, they can be improved by a proper polarizability expression. The most accurate, and least time consuming, simulations were observed for IGT_SO. When an aggregate consists of particles composed of ca. 750 volume elements (dipoles), the averaged relative extinction error should not exceed ca. 4.5%.

scholarly journals Plasmonic Modes and Optical Properties of Gold and Silver Ellipsoidal Nanoparticles by the Discrete Dipole Approximation

2012 ◽  
Vol 2012 ◽  
pp. 1-10 ◽  
Author(s):  
Mohammed Alsawafta ◽  
Mamoun Wahbeh ◽  
Vo-Van Truong
Keyword(s):  
Principal Axis ◽  
Length Distribution ◽  
Longitudinal Mode ◽  
Specific Rotation ◽  
Dipole Approximation ◽  
Absorption Efficiency ◽  
Discrete Dipole Approximation ◽  
Band Position ◽  
Principal Axes ◽  
Axis Length

The discrete dipole approximation (DDA) is used to model the absorption efficiency of isolated gold (Au) and silver (Ag) ellipsoidal nanoparticles. The characteristics of the plasmonic bands of those nanostructures depend strongly on the size and orientation of the particles in both the lab and target frames. At specific rotation and incident angles, the desired plasmonic mode can be excited. The result of the simulation shows the possibility of excitation of three plasmonic modes—one longitudinal mode (LM) and two transverse modes (TM)—corresponding to the redistribution of the polarization charges along each principal axis. At oblique incidence of the incoming light, both the Au LM and a hybrid Au TM are observed whereas three more distinct plasmonic modes can be found in the case of the Ag particle. The effect of length distribution on the characteristics of the plasmonic bands is also examined for the three principal axes. The band position of the plasmonic bands associated with the electronic oscillation along each principal axis is found to vary linearly with the axis length. The linear variation of the band position of the LM is steeper as compared with the one found for the other modes.

scholarly journals Aggregation affects optical properties and photothermal heating of gold nanospheres

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yiru Wang ◽  
Zhe Gao ◽  
Zonghu Han ◽  
Yilin Liu ◽  
Huan Yang ◽  
...  
Keyword(s):  
Optical Properties ◽  
Cross Section ◽  
Laser Heating ◽  
Dipole Approximation ◽  
Gold Nanospheres ◽  
Extinction Cross Section ◽  
Heating Efficiency ◽  
Photothermal Heating ◽  
New Framework ◽  
Laser Calorimetry

AbstractLaser heating of gold nanospheres (GNS) is increasingly prevalent in biomedical applications due to tunable optical properties that determine heating efficiency. Although many geometric parameters (i.e. size, morphology) can affect optical properties of individual GNS and their heating, no specific studies of how GNS aggregation affects heating have been carried out. We posit here that aggregation, which can occur within some biological systems, will significantly impact the optical and therefore heating properties of GNS. To address this, we employed discrete dipole approximation (DDA) simulations, Ultraviolet–Visible spectroscopy (UV–Vis) and laser calorimetry on GNS primary particles with diameters (5, 16, 30 nm) and their aggregates that contain 2 to 30 GNS particles. DDA shows that aggregation can reduce the extinction cross-section on a per particle basis by 17–28%. Experimental measurement by UV–Vis and laser calorimetry on aggregates also show up to a 25% reduction in extinction coefficient and significantly lower heating (~ 10%) compared to dispersed GNS. In addition, comparison of select aggregates shows even larger extinction cross section drops in sparse vs. dense aggregates. This work shows that GNS aggregation can change optical properties and reduce heating and provides a new framework for exploring this effect during laser heating of nanomaterial solutions.

Longitudinal Vibrational Absorption Modes of Hydrogenated Amorphous Silicon Nitride Thin Films

1998 ◽  
Vol 507 ◽  
Author(s):  
Tong Li ◽  
Jerzy Kanicki
Keyword(s):  
Thin Films ◽  
Absorption Spectrum ◽  
Silicon Nitride ◽  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Longitudinal Mode ◽  
Transverse Mode ◽  
Amorphous Silicon Nitride ◽  
Vibrational Absorption ◽  
Hydrogenated Amorphous

ABSTRACTWe have identified longitudinal and transverse optical modes of Si-N bond in vibrational absorption spectrum of hydrogenated amorphous silicon nitride thin films. The locations of longitudinal optical resonances coincide with transverse mode of Si-O and closely neighbor bending modes of N-H, Si-H2 bond. Furthermore, the conventionally assigned asymmetric and symmetric stretching modes of Si-N bond are merely transverse modes of Si-N bond. Features of pure longitudinal vibrational modes can be revealed by subtracting appropriately scaled transverse mode components from the vibrational absorption spectrum. Analysis of the longitudinal spectrum indicates that, in addition to their association with Si-N bond, the density of the peak located at about 1215 cm−1 is also well correlated to hydrogen and nitride content in the film, while the density of the peak located at about 880 cm−1 is closed related to silicon density in the film. Peak located at about 1040 cm−1 is the longitudinal mode associated with Si-N bond.

Structure in the Hgi absorption spectrum from 20 to 120 Å associated with the excitation of the 4f and 5s subshells

1973 ◽  
Vol 335 (1600) ◽  
pp. 87-96 ◽  
Keyword(s):  
Absorption Spectrum ◽  
Cross Section ◽  
Absorption Cross Section ◽  
Background Radiation ◽  
Absorption Cross ◽  
Continuous Absorption ◽  
Theoretical Predictions ◽  
The University

Observation of a broad transmission maximum, centred at about 80 Å, in the continuous absorption cross-section of Hgi is reported. The experiments were performed with a windowless system, using the background radiation of the 2.5 GeV synchrotron of the University of Bonn. The existence of such a transmission maximum is discussed in relation to theoretical predictions. New features are also reported and identified as due to excitation from the 4f and 5s subshells.

The spectrum of Cr I between 179.8 and 200 nm wavelengths, absorption cross sections, and oscillator strengths

1975 ◽  
Vol 342 (1630) ◽  
pp. 431-438 ◽  
Keyword(s):  
Absorption Spectrum ◽  
Ionization Potential ◽  
Cross Section ◽  
Cross Sections ◽  
Ground State ◽  
Absorption Cross Section ◽  
Column Density ◽  
Oscillator Strengths ◽  
Absorption Cross ◽  
Ionization Limit

The absorption spectrum of furnace-heated Cr vapour at wavelengths below 200 nm was recorded photoelectrically and by photography. By use of the hook method, the column density of neutral Cr atoms in the ground state was determined with the aid of the accurately known oscillator strengths of the resonance lines near 427 nm. The absorption cross section of the autoionized lines that dominate the ionization continuum could thus be obtained on an absolute scale. We also measured the wavelengths of many hitherto unreported lines near the ionization limit and derived a new value for the ionization potential, namely 54575.6 ± 0.3 cm -1 . Oscillator strengths for some of these lines are also given.

scholarly journals Поглощение электромагнитного излучения аморфным углеродом, модифицированным металлами

2021 ◽  
Vol 47 (2) ◽  
pp. 18
Author(s):  
С.Г. Ястребов ◽  
И.Е. Истомин ◽  
M. Singh
Keyword(s):  
Electromagnetic Wave ◽  
Radio Frequency ◽  
Electromagnetic Radiation ◽  
Amorphous Carbon ◽  
Cross Sections ◽  
Theoretical Study ◽  
Dipole Approximation ◽  
Discrete Dipole Approximation ◽  
Structural Studies ◽  
Absorption Cross

This article presents a theoretical study of the scattering and absorption of an electromagnetic wave from the gigahertz to the red range for a model of amorphous carbon modified by metals. On the basis of structural studies of this material, a cylindrical anisotropic nanoparticle - a nanotube responsible for its absorbing and antireflection properties - was selected as a candidate. A model of such a particle was developed and the scattering and absorption cross sections of an electromagnetic wave were calculated within the framework of the theory of the discrete dipole approximation. A pair of nanotubes allowed us to explain the contribution of the interaction of immediate neighbors to scattering and absorption. The constructed model explains the effect of absorption of radio-frequency electromagnetic radiation, observed experimentally in amorphous carbon modified with metals.

Growth and Absorption Spectrum of Tm,Ho:BaY2F8 Crystal

2011 ◽  
Vol 335-336 ◽  
pp. 1025-1028 ◽  
Author(s):  
Fan Ming Zeng ◽  
Guang Tian Zou ◽  
Jing He Liu
Keyword(s):  
Absorption Spectrum ◽  
Single Crystal ◽  
Cross Section ◽  
Absorption Cross Section ◽  
Room Temperature ◽  
Laser Crystal ◽  
Rotation Speed ◽  
Absorption Cross ◽  
Technical Parameters ◽  
Cell Parameters

The Tm,Ho:BaY2F8 single crystal was successfully grown by the Cz method. The optimal technical parameters obtained are as follows: the pulling rate is 0.5—0.6mm/h; the rotation speed is 5—7rpm; the cooling rate is 10°C/h. The result of XRD curve shows that as-grown Tm,Ho:BaY2F8 laser crystal belongs to the monoclynicsystem and space group I41/a, the cell parameters calculated are: a = 0.69829 nm, b = 1.0519 nm, c = 0.42644 nm, β=99.676°, Z=2. Absorption spectra of Tm,Ho:BaY2F8 laser crystal at room temperature were measured and analysed, the absorption cross-section at 781nm calculated are 7.66×10-21cm-2.

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