奈米與光電材料特殊光學性質之第一原理研究

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Title:	奈米與光電材料特殊光學性質之第一原理研究
Other Titles:	First-Principles Study on Optical Response of Optoelectronic and Nanomaterials
Authors:	薛宏中
Contributors:	淡江大學物理學系
Keywords:	激發態;Bethe-Salpeter方程式;GW近似法;電子電洞交互作用;激子效應;少層奈米層結構;壓力效應;激子傳輸;Excited-states;Bethe-Salpeter equation;GW approximation;electron-hole correlation;excitonic effect;few-layers nanosheets;pressure effect;exciton propagation
Date:	2012-08
Issue Date:	2015-04-29 15:14:24 (UTC+8)
Abstract:	凝態科學中絕大多數有趣且重要的現象，都與材料中具備多電子交互作用的豐富電子結構有非常大的關聯。為了探究此一複雜的電子結構，光學光譜技術是一項非常有效的研究利器；這是因為光譜技術藉由外部光子，激發材料内部電子結構由基態提升為激發態，因此透過光譜分析，可清楚了解各種材料（包括原子、分子、奈米材料以及塊材材料）的電子激發態特性。其中最奇特的是，材料中以相關聯之電子電洞交互作用而形成的激子，對於材料的光譜結構與特性具有決定性的影響，而此激子效應在奈米尺度更為明顯。近年來，有關第一原理激發態計算的發展，非常快速；其中發展最成功的GW+BSE計算方法（以GW近似為基礎來求解Bethe-Salpeter方程式），可以正確的描述電子激發態的性質，讓我們可以窺探外部光子所引發之激子效應。在此三年計晝中，我們將透過GW+BSE計算，研究光電材料與低維度奈米材料(例如單層、雙層及少層奈米層材料)之新奇電子結構與光學特性。此外，通常外加壓力會造成各向異性材料的光學性質的劇烈改變，因此本計晝也將探討外加壓力對於材料光譜與激子效應的影響。最後，本計晝包含一項具有挑戰性的工作：發展新的第一原理量子力學方法，來計算強束缚激子的動態傳輸性質；此工作不僅理論上具有創新的意涵，在應用層面，也能透過分析強束缚激子在塊材或奈米材料上的傳輸行為，為設計未來光電元件，提供更多的研發方向。我們可以預期這項工作的成果，將會對於新興發展的非彈性X光散射實驗產生非常重要的影響，也為我們與相關實驗科學專家，帶來新的合作契機。本計晝將包括以下三個重要的研究課題： 1)平面及皺褶的單層，以及少層奈米層材料的光學特性（包含光譜與激子效應）研究 2)壓力對於材料光學特性的影響 3)強束缚激子之動態傳輸性質研究 Most exciting phenomena in condensed matter science are related to a wealth of electronic properties of interacting many-electron systems. To probe such intrinsic highly complex electronic structures, the optical spectroscopy based on the interaction of external photons exciting the materials to excited-states is a powerful technique and always provides interesting and vital information for the behavior of systems ranging from atoms, molecules, nano-scale, and meso-scale structures to bulk materials. Interestingly, the existence of the excitons as a result from the significant electron-hole correlation dominates the optical properties of materials, especial in nano scales. Beyond ground-state approaches, recently considerably developed first-principles excited-state calculations, highly accurate Bethe-Salpeter equation (BSE) based on the so-called GW approximation, all us to tackle the excited-state electronic structure of a system and its excitonic properties responded to external optical probes. In this three-year proposal, we will perform GW+BSE method to investigate the novel electronic structures and optical properties of optoelectronic semiconductors and advanced reduced-dimensional nanomaterials (such as mono-, bi-, and few- layers nanosheets). Pressure effects changing the optical spectra and electronic properties quite dramatically in highly anisotropic systems will be analyzed in this proposal as well. Meanwhile, the most ambitious task in this proposal is to develop a new first-principles method to investigate the exciton propagation of strongly bound electron-hole pairs in bulk and nano systems. A significant impact to advanced inelastic X-ray scattering experiments is expected from this theoretical framework of exciton dynamics. In this proposal, three interesting and promising research projects are thus proposed and listed below. 1) Optical response in planar, distorted monolayer, and few-layer nanomaterials 2) Optical excitation response to external compression 3) Dynamical properties of strongly bound excitons
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