奈米材料的振動與電子組態性質之第一原理研究;First-Principles Investigations of Vibrational and Electronic properties of selected Nanomaterials

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/77091

Title:	奈米材料的振動與電子組態性質之第一原理研究;First-Principles Investigations of Vibrational and Electronic properties of selected Nanomaterials
Authors:	巴, 特;Sainbileg, Batjargal
Contributors:	物理學系
Keywords:	P3HT;MOFs;DFT;DFPT;Nanomaterials;Raman;First-Principles Investigations;P3HT;MOFs;DFT;DFPT;Nanomaterials
Date:	2018-07-03
Issue Date:	2018-08-31 13:56:52 (UTC+8)
Publisher:	國立中央大學
Abstract:	在本篇論文中，我們使用第一原理的方法－電子密度泛函理論(density functional theory, DFT)來研究奈米材料－聚(3-己烷基噻吩) (Poly(3-hexylthiophene), P3HT)與金屬有機骨架化合物(Metal‒organic frameworks, MOFs)的震動與電子組態性質。本篇論文包含兩個部分：(一)以第一原理的方法研究聚(3-己烷基噻吩)的拉曼光譜與聲子。(二) 以第一原理的方法研究金屬有機骨架化合物的電子組態結構。在第一部分中，聚(3-己烷基噻吩)為半導體聚合物且廣泛應用於光電元件，如有機光伏材料(organic photovoltaics, OPVs)與有機場效電晶體(organic field-effect transistors, OFETs)且價格不高。聚(3-己烷基噻吩)具有高的電子移動率且此電子移動率與其固態的堆疊方式相關。因此，原子層級的了解晶體結構的堆疊方式對於此材料的基礎研究與應用相當重要。然而，精確的確定規則排列的聚(3-己烷基噻吩)之排列方式仍是一項挑戰。使用第一原理的方法與拉曼光譜，我們探討了聚(3-己烷基噻吩)可能的排列方式以及其對應的拉曼光譜與聲子震動模式特徵。我們找到了兩種聚(3-己烷基噻吩)的排列方式，而基於此兩種結構所模擬出的拉曼光譜和聲子震動模式與實驗觀察到的光譜一致。藉由光譜上的對應，我們了解到當聚(3-己烷基噻吩)層的平面性下降時，拉曼光譜中的碳－碳單鍵聲子震動模式的頻率呈現紅位移而碳－碳雙鍵聲子震動模式的頻率則呈現藍位移。此外，當聚(3-己烷基噻吩)主幹上的環為夾角22度時，碳－碳雙鍵的峰分裂成兩個明顯的峰。此研究藉由第一原理計算結合拉曼光譜作為直接且有力的研究方法，為詳細了解聚合晶體的排列方式打開了道路。在第二部分中，金屬有機骨架化合物為包含了無機、有機與溶劑成分的奈米複合結構且被認為具有相當大的潛能來應用於電子元件上。因此，確認其關鍵的電子結構性質，如能隙、能帶結構、能帶形式與狀態密度中的價帶(VBM)與傳導帶(CBM)為了解金屬有機骨架化合物電子特性的重要基礎。在此我們研究了兩個新穎的材料的電子組態性質：鍶化物與銅化物的金屬有機骨架化合物－結合了第一原理中的密度泛函的方法與實驗上的擴散反射光譜(Diffuse Reflectance Spectroscopy, DRS)。我們發現這些金屬有機骨架化合物皆為半導體性質且相較一般的絕緣金屬有機骨架化合物具有較窄的能隙。這是由於這兩個金屬有機骨架化合物具有獨特的金屬節點與高傳導性的連結方式。 ;In this dissertation, the vibrational and electronic properties of selected nanomaterials such as Poly(3-hexylthiophene) (P3HT) and Metal‒organic frameworks (MOFs) were investigated by utilizing first-principles simulation methods which are based on density functional theory (DFT) as well as density functional perturbation theory (DFPT). The dissertation consists of two topics that are first-principles investigations of (1) Raman spectra and phonon modes of the P3HT and (2) the electronic structures of MOF. For topic (1), P3HT is a semiconducting polymer with a wide range of applications in flexible optoelectronic devices, such as organic photovoltaics (OPVs) and organic field-effect transistors (OFETs) with low processing costs. It possesses a high charge mobility that is highly sensitive to its packing configuration in the solid-state phase. Atomistic knowledge of the packing of crystalline structures is therefore of great importance for its fundamental study and practical applications. However, the accurate determination of packing geometry of ordered P3HT still remains challenging. By using first-principles calculation methods together with Raman spectroscopy, we search the possible packing structures of crystalline P3HT characterizing their Raman spectra and phonon modes. We find two packing structures of crystalline P3HT. Raman spectra and phonon modes are simulated based on these structures, and the resulting spectra are consistent with the experimentally observed ones. The spectral correspondences reveal that the frequency of Raman peak with C-C phonon mode shows a red-shift while the peak with C=C phonon mode exhibits a blue-shift as decreasing the layer planarity of P3HT. Furthermore, the C=C peak decomposes in two prominent peaks when backbone rings in the P3HT layer possess a dihedral angle of 22° with respect to each other. This study paves the way that the first-principles calculation combined with Raman spectroscopy can be used as a direct powerful method to specify packing structures of crystalline polymers. For topic (2), MOFs are emerging as a promising class of nanoporous composite structures which consist of inorganic, organic and solvent components, expecting to have great potential for the advanced applications in electronics. In this regard, the determination of key electronic structures—energy bandgap, band structure, band type, density of states as well as features of VBM (HOMO) and CBM (LUMO) at band edges—is of prime importance to understand the fundamental electrical nature of MOFs. We investigated the electronic structures of novel two materials—Strontium and Copper based MOFs—as exemplary studies for electronic properties of Metal−Organic Frameworks by both theoretical first-principles DFT calculations and experimental Diffuse Reflectance Spectroscopy (DRS). We found these MOFs have the semiconducting behavior with relatively narrow bandgap compared with the conventional insulating MOFs due to their unique metal nodes and highly conductive linkers.
Appears in Collections:	[Graduate Institute of Physics] Electronic Thesis & Dissertation

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