Electromagnetic fields around silver nanoparticles and dimers
Electromagnetic fields around silver nanoparticles and dimers
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DOI：
10.1063/1.1629280
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发表时间：
2004-01-01
影响因子：
4.4
通讯作者：
Schatz, GC
中科院分区：
文献类型：
--
作者：
Hao, E;Schatz, GC
我们利用离散偶极子近似研究了银纳米粒子(包括单体和二聚体)的局域表面等离子体共振光激发产生的电磁场，重点研究了粒子表面附近的尺寸、形状和排列方式导致的最大局部电场(E-场)增强。结果被用来确定什么条件最有利于产生足够大的增强来观察单分子表面增强拉曼光谱。大多数计算都涉及到三棱镜，它表现出明显的偶极和四极共振，可以很容易地通过改变颗粒大小来控制。此外，对于二聚体的计算，我们研究了二聚体的分离和取向的影响，特别是对于相距几纳米的二聚体。我们发现，二聚体的最大E_2值比所考察的所有单体的E_2值大约10倍。对于所有粒子和粒子取向，导致最大电场的等离子体共振是那些具有最长波长偶极激发的等离子体共振。二聚体中粒子的间距起着至关重要的作用，我们发现，对于尺寸小于100 nm的粒子，达到给定的E2所需的间距与纳米粒子的尺寸成正比。粒子形状和曲率不那么重要，头到尾的两个三角形配置提供了可与头到头或圆头到尾相媲美的增强场。对于2 nm或更大的间距，我们计算的最大\E\(2)值类似于10(5)。(C)2004年美国物理研究所。
We use the discrete dipole approximation to investigate the electromagnetic fields induced by optical excitation of localized surface plasmon resonances of silver nanoparticles, including monomers and dimers, with emphasis on what size, shape, and arrangement leads to the largest local electric field (E-field) enhancement near the particle surfaces. The results are used to determine what conditions are most favorable for producing enhancements large enough to observe single molecule surface enhanced Raman spectroscopy. Most of the calculations refer to triangular prisms, which exhibit distinct dipole and quadrupole resonances that can easily be controlled by varying particle size. In addition, for the dimer calculations we study the influence of dimer separation and orientation, especially for dimers that are separated by a few nanometers. We find that the largest \E\(2) values for dimers are about a factor of 10 larger than those for all the monomers examined. For all particles and particle orientations, the plasmon resonances which lead to the largest E-fields are those with the longest wavelength dipolar excitation. The spacing of the particles in the dimer plays a crucial role, and we find that the spacing needed to achieve a given \E\(2) is proportional to nanoparticle size for particles below 100 nm in size. Particle shape and curvature are of lesser importance, with a head to tail configuration of two triangles giving enhanced fields comparable to head to head, or rounded head to tail. The largest \E\(2) values we have calculated for spacings of 2 nm or more is similar to10(5). (C) 2004 American Institute of Physics.