一、二甲基丙烯基與硫甲醛共價態/雷得堡態的多光子共振游離光譜研究 二、一維奈米材料電傳導特性之研究：碳奈米螺旋與二氧化錫奈米線

I. Investigations of Valence/ Rydberg States of 2-Methylallyl Radical and Thioformaldehyde by Resonant Ionization Multiphoton Spectroscopy. II. Electrical Transport Properties of One Dimensional Nanoscale Materials: SnO2 nanowire and Hydrocarbon helix wire.

吳幸臻(Hsing-Chen Wu)

指導教授 ： 陳逸聰

國立臺灣大學/理學院/化學研究所/博士(2007年)

https://doi.org/10.6342/NTU.2007.00687

摘要

這篇論文主要區分為兩個部分，第一個部分主要是談氣體分子光譜，利用多光子游離共振光譜的技巧研究氣態分子或自由基。第二部份的目的主要在探討一維奈米材料的電性傳導特性，包括載子濃度，遷移率，與傳導機制。
利用熱解方式產生二甲基丙烯基，並用1+1與2+2 REMPI技術研究其位於4.6-5.6 eV的電子-振動激發態。結合ab initio計算，躍遷能量、強度與FCFs都可以得到。在2+2 的光譜中，3s雷得堡態與其振動都被指認出來。另一方面，由MRCI計算結果的七個最低能量躍遷則用來輔助指認1+1光譜。值得注意的一點是在1+1光譜中位於能量較高的兩個較寬的能帶躍遷是與(n,pi*)躍遷強度的借用有關。
另一個研究的則是硫醛家族中最簡單的的分子-硫甲醛，這裡利用了兩色的REMPI去研究其激發態，稱做1+1'+1'REMPI。我們選擇了 C1B2 當作中間態，用雙光子共振方式研究62000-72000 cm-1的能帶。藉由不同的選擇律，比較單光子吸收與1+1'+1'REMPI光譜，指認出屬於硫甲醛新的躍遷能階。
第二部分的重點則是在奈米材料的電傳導特性。首先是研究半徑介於微奈米尺度的碳氫螺旋電性，電性的量測的範圍從室溫到64 mk，這個與溫度相關的電阻特性用Mott-variable range hopping模型分析可以得到一個三維的電子跳躍模式，與拉曼光譜得到的短區域石磨狀晶體排列是互相映證的。
再來我們製造了以二氧化錫為基礎的場效電晶體，從元件導電度對閘極的反應，一些元件參數如：起始電壓、載子密度、遷移率皆可得到。此外我們也證明了從染料分子到半導體的光致電流現象是可以經由場效電晶體的閘極所調控的。
最後是利用奈米碳管為基礎的場效電晶體來作為生物感測器，主要偵測神經傳導物質嗜鉻粒蛋白A的釋放。藉由在奈米碳管上化學修飾抗體，經由分子之間的辨識，可以達到極低的偵測極限 (~100pM) 並可以即時的偵測到由神經釋放出來的嗜鉻粒蛋白A，這是在傳統生物分析檢測上都還未能達到的水準。

關鍵字

雷得堡態 ； ab initio 計算 ； Franck-Condon Factors ； VRH hopping model ； 二氧化錫奈米線場效電晶體 ； 奈米碳管生物檢測器 ； 嗜鉻粒蛋白A

並列摘要

The content of this thesis would be divided into two main parts. First, the molecular spectroscopy was concerned. Gas phase vibronic spectra of radical and small molecule were studied by resonant multiphoton ionization (REMPI) technique. The purpose of second part was to explore the electrical transport characters of one dimensional nanomaterials. The carrier number, mobility, and transport mechanism etc. were included.
To begin with the flash pyrolytic generated 2-methylallyl radical, one- and two-photon excitations were applied at 4.6-5.6 eV. Combining with the ab initio calculations, information of excitation energies, oscillator strengths and Franck Condon factors (FCFs) of electronic states at 4–6 eV making the spectra successfully resolved. In the 2+2 REMPI spectrum, the 3s Rydberg state along with its vibrational progressions were identified. On the other hand, seven lowest-lying electronic states below 6 eV, were assigned by MRCI calculation in the 1+1 spectrum. The other point to notice was the much broader 1+1 bands at higher energy region which were due to an intensity borrowing from the (n,pi*) transition that accidentally near-resonant in energy.
Secondly, another molecule studied was the simplest molecule in the thiocarbonyl family- thioformaldehyde (H2CS). There is fairly general agree that H2CS is unstable as a monomeric species under normal conditions. Here, we use a two-color REMPI scheme to investigate electronic states of H2CS. The vibronic excited states of H2CS were studied by 1+1'+1' double-resonance enhanced three-photon ionization (1+1'+1')REMPI) spectroscopy. The C1B2 state of H2CS was selected as an intermediate for the double resonance to high-lying excited states at 62000-72000 cm-1. According to distinct selection rules between one-photon absorption and two-photon transitions excited from X1A1 and C1B2, respectively, new electronic sates of H2CS can be assigned by 1+1'+1'DRETPI spectroscopy.
The second part of this thesis was focused on the electrical transport prooperities of nano-materials. First, an investigation of hydrocarbon helical wires (HCHWs) with wire diameters ranged from nano- to micro-meter scale was conducted. HRTEM and EELS investigations reveal that the HCHWs comprise graphite-short-range-ordering (GSRO) clusters with sp3 bonds inserted in the discontinuous graphitic layers, suggesting hydrogen termination in the broken boundaries of the GSRO domains. A crystallite size of ~5 nm for the GSRO domains has been determined by micro-Raman spectroscopy. Electric transport in single HCHWs has been measured from ambient temperature to 64 mK. The temperature-dependent resistance was analyzed with the Mott-variable range hopping model, indicating a three-dimensional electron hopping conduction among the GSRO domains inside the HCHWs. The analysis also yields a hopping length of ~5 nm, in excellent consistence with the GSRO domain size determined by micro-Raman spectroscopy.
Second, the SnO2 nanowire (NW) based filed–effect transistor (FET) was fabrecated. It was observed that the conductance could improve three orders of magnitude when the applying gate voltage up to ten volts. From this variation of conductance with gate voltage, the device parameters such as threshold voltage, carrier density and mobility etc. were found. In addition, we have successfully demonstrated that the sensitization of photocurrent by electron transfer from dye molecules to semiconductor, a prevalent mechanism in dye-sensitized solar cells, can also be studied in single-nanowire scale.
Finally, a biosensor based on carbon nanotube was studied. The target molecule was Chromogranin A (CgA), it is a neuron transmittance that released from secretory vesicles when fused with plasma membrane. We have successfully demonstrated that the detection limit of molecular recognition could down to ~100 pM. An in-situ detection of CgA by living neuron cell was also observed.

並列關鍵字

Ab initio ； Franck-Condon Factors ； VRH hopping model ； SnO2 nanowire field effect transistor ； dye-sensitized solar cell ； carbon nanotube FET biosensor ； Chromogranin A.

參考文獻

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