金屬奈米顆粒光學性質之理論研究

Theoretical Studies of the Optical Properties of Metal Nanoparticles

駱冠宇(Guan-Yu Luo)

指導教授 ： 郭光宇

國立臺灣大學/理學院/物理研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.01732

摘要

長期以來金屬奈米顆粒的光學性質在物理及化學領域一直都是十分感興趣的話題，其中最早可追朔至十八世紀中葉Michael Faraday對金膠體溶液的研究。而金屬奈米顆粒會逐漸受大家重視的主要原因為其具有局域性表面電漿共振(Surface Plasmon resonance, LSPR)的特殊光學性質；何為局域性表面電漿共振，意即導體電子隨著入射的電磁波作集體性的共振現象。在本論文中我們利用Mie理論對單顆金球及銀球作半徑30~100nm以及銀球殼做吸收、散射以及消散光譜的模擬，並利用離散偶極子近似模擬計算出金屬顆粒的近場強度分佈。在光譜圖的計算結果中可以看出局域性表面電漿共振波長發生在可見光範圍，其共振波長會隨著球半徑的增加而紅移，此外，球殼因為共振膜態會互相偶和之故使得與同大小的單球相比球殼的共振形態會多於單球。
　　在能源議題逐漸受到重視的今日，太陽能電池的發展則為眾多替代能源中重要的一項，其已被證實由於金屬奈米顆粒的局域性表面電漿共振效應能有效的增加其對入射光的吸收效率。在此，我們利用由Mie理論推廣至多顆球的多重散射理論來模擬金與銀的奈米球及圓柱以週期性排列之方式擺上在固定厚度的矽基板上與單只有矽基板對入射光吸收效率做比較，並證實金屬顆粒確實能增加對光的吸收效率，而吸收率則取決於奈米粒子的大小及其排列情形。

關鍵字

奈米金屬顆粒

並列摘要

The optical properties of metal nanoparticles have long been of interest in physical
chemistry, starting with Faraday's researched of colloidal gold in the middles 1800s. It
has received increasing attention for their peculiar optical properties to produce local
surface plasmon resonance (LSPR), which is a collective oscillation of conduction electron when interacting with incident electromagnetic wave. In this thesis, we simulated the optical absorption, scattering, and extinction spectra of gold and silver nanosphere with the radius ranging from 30 to 100nm, and silver nanoshell by using Mie theory and the field enhancement of the near-field by discrete dipole approximation(DDA). An increasing number of LSPR peaks appear in the optical spectra, and their positions will be red-shifted at the same time when the radius increases. In addition, the nanoshell quadruple resonance is manifested more than that for nanosphere quadruple resonance when the nanoparticle size becomes smaller.
The issue of energy resource has became a serious concern, the development of solar cell is one of the alternative source of energy. It has been know that solar cell can have its efficiency increased by scattering from metal nanoparticles due to LSPR. We simulated 2-D periodic nanospheres and nanodiscs placed on a silicon substrate and we have considered both goal and silver nanoparticles by using electromagnetic multiple scattering theory which is extended from Mie theory. For uniform distribution of nanoparticles on the plane, metal nanoparticles with larger radius have better absorption than that of smaller particles, and gold performs better than silver for the absorption of photons.

並列關鍵字

Metal Nanoparticles

參考文獻

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