本文選題：高壓 + 飛秒瞬態(tài)吸收　； 參考：《吉林大學(xué)》2016年博士論文

【摘要】：金剛石對(duì)頂砧高壓裝置的發(fā)明使我們可以更方便的研究極端條件下物質(zhì)的結(jié)構(gòu)和性質(zhì),極大地促進(jìn)了高壓科學(xué)研究的發(fā)展。瞬態(tài)吸收光譜可以探測(cè)到光與物質(zhì)相互作用的瞬態(tài)過(guò)程,是研究光物理和光化學(xué)過(guò)程中激發(fā)態(tài)動(dòng)力學(xué)及瞬態(tài)產(chǎn)物的強(qiáng)有力的手段。將金剛石對(duì)頂砧高壓技術(shù)與瞬態(tài)吸收光譜技術(shù)相結(jié)合,可以更好地研究物質(zhì)在極端條件下,在飛秒和皮秒時(shí)間尺度內(nèi)的光物理和光化學(xué)現(xiàn)象,例如電子躍遷、能量轉(zhuǎn)移和新物種的生成及其隨時(shí)間的變化情況等。我們?cè)诮梃b前人工作的基礎(chǔ)上,利用金剛石對(duì)頂砧和瞬態(tài)吸收光譜技術(shù),成功搭建了高壓飛秒瞬態(tài)吸收光譜系統(tǒng),這套系統(tǒng)的特點(diǎn)是采用共軸泵浦-探測(cè)方式來(lái)探測(cè)變壓時(shí)不同能態(tài)上粒子數(shù)布局的變化;樣品前使用顯微物鏡對(duì)泵浦光和探測(cè)光進(jìn)行聚焦,使會(huì)聚后的泵浦光和探測(cè)光的光斑直徑僅有幾個(gè)微米大,保證了高壓原位測(cè)量實(shí)驗(yàn)數(shù)據(jù)的可靠性;利用CCD實(shí)時(shí)觀測(cè)壓機(jī)內(nèi)的情況;通過(guò)變換泵浦光和探測(cè)光之間的相對(duì)延時(shí)來(lái)實(shí)現(xiàn)時(shí)間分辨;利用自主編寫的時(shí)間分辨控制軟件和數(shù)據(jù)采集軟件進(jìn)行數(shù)據(jù)采集和分析。這套系統(tǒng)可以用來(lái)研究物質(zhì)在不同壓力條件下的一些超快光物理過(guò)程,為進(jìn)一步研究極端條件下物質(zhì)的結(jié)構(gòu)和性質(zhì)提供了一個(gè)有效的方法。高壓飛秒瞬態(tài)吸收光譜系統(tǒng)搭建完成以后,我們利用這套系統(tǒng)對(duì)有機(jī)共軛聚合物PDPP-F薄膜和無(wú)機(jī)單、雙層MoS_2這幾種典型的光電功能材料進(jìn)行了不同壓力條件下的超快光物理過(guò)程的研究,從分子水平上揭示了材料的結(jié)構(gòu)和物理特性的關(guān)系,以及高壓極端條件對(duì)材料結(jié)構(gòu)性質(zhì)的影響。利用高壓飛秒瞬態(tài)吸收系統(tǒng)對(duì)PDPP-F共軛聚合物薄膜在不同壓力條件下的光物理特性進(jìn)行了研究,探明了高壓對(duì)PDPP-F共軛聚合物薄膜材料中的激子弛豫動(dòng)力學(xué)的影響。我們發(fā)現(xiàn)常壓時(shí),PDPP-F薄膜中的激子只有一個(gè)較慢的弛豫過(guò)程,相應(yīng)的激子弛豫壽命是172ps,表明常壓時(shí)激子弛豫過(guò)程是自由激子弛豫。而高壓時(shí),PDPP-F薄膜中的激子在初始弛豫過(guò)程有一個(gè)非�？斓某谠ミ^(guò)程,之后跟著一個(gè)比較慢的弛豫過(guò)程,這說(shuō)明高壓時(shí),有多物種參與了弛豫。我們發(fā)現(xiàn)這個(gè)壓力依賴的快的弛豫過(guò)程是激子-激子湮滅過(guò)程,而之后的慢弛豫過(guò)程是自由激子擴(kuò)散過(guò)程。根據(jù)不同壓力下的激子弛豫動(dòng)力學(xué)實(shí)驗(yàn)數(shù)據(jù),我們對(duì)PDPP-F薄膜中的激子離域程度進(jìn)行了定量計(jì)算。發(fā)現(xiàn),隨著壓力的增加,PDPP-F薄膜中的激子的離域程度明顯增加,30萬(wàn)大氣壓時(shí),PDPP-F薄膜中的激子的離域程度是常壓時(shí)的3倍。而且我們發(fā)現(xiàn)隨著壓力的增加,PDPP-F薄膜中不僅激子的擴(kuò)散速率增加了,而且激子的弛豫時(shí)間也增加了,由此我們認(rèn)為激子的擴(kuò)散長(zhǎng)度是隨著壓力的增加而增加的。這個(gè)工作使我們更好的了解了聚合物的光物理特性,有益于聚合物太陽(yáng)能電池效率的提高。利用飛秒瞬態(tài)吸收系統(tǒng)對(duì)單、雙層MoS_2薄膜樣品的結(jié)構(gòu)和層數(shù)依賴的光物理特性及進(jìn)行了對(duì)比性研究。首先我們用化學(xué)氣相沉積方法在石英襯底上生長(zhǎng)單、雙層MoS_2薄膜,并通過(guò)拉曼光譜來(lái)確定了MoS_2樣品的層數(shù)。我們對(duì)單、雙層MoS_2薄膜樣品分別進(jìn)行了拉曼光譜、穩(wěn)態(tài)吸收光譜、穩(wěn)態(tài)熒光光譜和瞬態(tài)吸收光譜的測(cè)量和分析。發(fā)現(xiàn)單、雙層MoS_2樣品都存在A激子和B激子的吸收。雙層MoS_2樣品的兩個(gè)吸收帶較單層樣品發(fā)生了一定程度的紅移,這是由于隨層數(shù)的增加,量子限域效應(yīng)減弱導(dǎo)致的。將單、雙層MoS_2樣品的熒光光譜與吸收光譜進(jìn)行比對(duì),我們發(fā)現(xiàn)單、雙層MoS_2樣品都有的兩個(gè)熒光峰與A、B激子的共振吸收對(duì)應(yīng),因此我們認(rèn)為實(shí)驗(yàn)中測(cè)得的單、雙層MoS_2樣品的兩個(gè)熒光帶屬于直接躍遷發(fā)光。而熒光信號(hào)的強(qiáng)度隨MoS_2樣品層數(shù)的減少而增強(qiáng),這種層數(shù)依賴的熒光特性是源于從雙層MoS_2樣品到單層MoS_2樣品發(fā)生了從間接帶隙半導(dǎo)體向直接帶隙半導(dǎo)體的轉(zhuǎn)變,致使發(fā)光量子效率顯著提高。另外,從單、雙層MoS_2樣品的瞬態(tài)吸收光譜中我們發(fā)現(xiàn)雙層MoS_2樣品的激子弛豫動(dòng)力學(xué)曲線衰退的比單層MoS_2樣品的快,這說(shuō)明雙層MoS_2樣品中激子的復(fù)合更快。我們先從光物理特性差異的角度分析,認(rèn)為這是由于雙層MoS_2具有更快的非輻射躍遷速率。之后我們從半導(dǎo)體特性差異的角度即利用激子模型來(lái)分析,認(rèn)為這是由于雙層MoS_2樣品具有更小的激子結(jié)合能;作為間接帶隙半導(dǎo)體的雙層MoS_2比單層MoS_2多一個(gè)從布里淵區(qū)內(nèi)K點(diǎn)的導(dǎo)帶底到Γ點(diǎn)的價(jià)帶頂?shù)妮椛滠S遷途徑;此外雙層MoS_2具有的層間耦合作用會(huì)使激子的振動(dòng)加強(qiáng),這些因素都會(huì)促進(jìn)激子的快速?gòu)?fù)合,由此我們認(rèn)為層間耦合作用對(duì)激子復(fù)合起到了促進(jìn)的作用。此外,我們對(duì)單層MoS_2薄膜進(jìn)行了高壓下的激發(fā)態(tài)弛豫動(dòng)力學(xué)研究,得到了壓力調(diào)控的單層MoS_2薄膜的能帶結(jié)構(gòu)對(duì)超快光物理特性的影響。我們所研究的層數(shù)依賴的MoS_2的光物理特性和半導(dǎo)體特性可以為制備基于MoS_2的光電器件和半導(dǎo)體器件提供重要的指導(dǎo)和依據(jù),并為其它過(guò)渡金屬硫化物材料的結(jié)構(gòu)及物理性質(zhì)的研究提供重要指導(dǎo)。
[Abstract]:The invention of the high pressure device of the diamond to the anvil makes it more convenient for us to study the structure and properties of the material under extreme conditions, which greatly promotes the development of high pressure scientific research. Transient absorption spectra can detect the transient process of interaction between light and matter. It is a study of the dynamics and transient of excited states in photophysical and photochemical processes. The strong means of the product. The combination of the high pressure technology with the diamond anvil and the transient absorption spectroscopy can better study the photophysical and photochemical phenomena, such as the electron transition, the energy transfer and the generation of new species and their changes in time, in extreme conditions, in the extreme conditions of the femtosecond and picosecond time. On the basis of the predecessors' work, the high pressure femtosecond transient absorption spectrum system has been successfully constructed by using the diamond anvil and transient absorption spectroscopy. The system is characterized by the use of coaxial pump detection to detect the change of the particle number distribution on different states of energy in the variable pressure. The sample is used to pump the pump light and probe before the sample. The focus of the light measurement makes the pump light and the spot diameter of the probe light only a few microns in diameter. It ensures the reliability of the experimental data in the high pressure in situ measurement; the real-time observation of the pressure in the press by CCD is used to realize the time resolution by changing the relative delay between the pump light and the detection light, and the time resolved time resolved control written by ourselves is used. Software and data acquisition software are used for data acquisition and analysis. This system can be used to study some ultra fast light physical processes under different pressure conditions. It provides an effective method to further study the structure and properties of material under extreme conditions. After the completion of the high pressure femtosecond transient absorption spectrum system, we can benefit This system is used to study the ultra fast optical physical processes of organic conjugated polymer PDPP-F film and inorganic single, double layer MoS_2, the typical photoelectric functional materials under different pressure conditions. The relationship between the structure and physical properties of the material is revealed from the molecular level, and the influence of the extreme conditions of the high pressure on the structure and properties of the material is also revealed. The photophysical properties of PDPP-F conjugated polymer film under different pressure conditions were studied by high pressure femtosecond transient absorption system. The effect of high pressure on exciton relaxation kinetics in PDPP-F conjugated polymer film materials was explored. We found that only a slower relaxation process in the exciton in PDPP-F film at atmospheric pressure is corresponding. The exciton relaxation life of the exciton is 172ps, indicating that the exciton relaxation process at atmospheric pressure is free exciton relaxation. At high pressure, the exciton in the PDPP-F film has a very fast relaxation process in the initial relaxation process, followed by a slower relaxation process, which indicates that at high pressure, there are many species involved in relaxation. We find this pressure dependence. The fast relaxation process is the exciton exciton annihilation process, and the slow relaxation process after the exciton diffusion process is a free exciton diffusion process. According to the experimental data of exciton relaxation kinetics under different pressure, we calculate the exciton dissociation degree in the PDPP-F thin film quantitatively. It is found that the exciton dissociation degree in the PDPP-F film increases with the increase of pressure. It is obvious that the exciton in the PDPP-F film is 3 times that of the normal pressure at 300 thousand atmospheric pressure. Moreover, we find that the diffusion rate of the exciton in the PDPP-F film increases with the increase of pressure, and the relaxation time of the exciton increases, thus we think the diffusion length of the exciton increases with the increase of pressure. This work gives us a better understanding of the photophysical properties of the polymer and is beneficial to the improvement of the efficiency of the polymer solar cells. By using the femtosecond transient absorption system, the structure and number dependent photophysical properties of the single and double layer MoS_2 thin film samples are compared. First we use the chemical vapor deposition method in Shi Yingchen. A single, double layer MoS_2 film is grown on the bottom, and the number of MoS_2 samples is determined by Raman spectrum. We have measured and analyzed the Raman spectra, steady absorption spectra, steady-state fluorescence and transient absorption spectra of single and double layer MoS_2 thin films. It was found that the absorption of A exciton and B exciton in the single, double layer MoS_2 samples were both in the double layer M. The two absorption bands of the oS_2 sample have a certain degree of red shift compared with the single layer, which is due to the decrease of the quantum confinement effect as the number of layers increases. The comparison between the fluorescence spectra of the single and double layer MoS_2 samples and the absorption spectra shows that the two fluorescence peaks of the single, double layer MoS_2 samples are corresponding to the resonance absorption of the A and B excitons. Therefore, we think that the two fluorescent bands of the single, double layer MoS_2 samples measured in the experiment are direct transition luminescence. The intensity of the fluorescence signal is enhanced with the decrease of the number of MoS_2 samples. The fluorescence characteristics of this number dependence are derived from the indirect band gap semiconductors to the direct band gap semiconductors from the double layer MoS_2 sample to the single layer MoS_2 sample. In addition, in the transient absorption spectra of single and double MoS_2 samples, we found that the decay of the exciton relaxation kinetics curve of the double layer MoS_2 sample is faster than that of the single MoS_2 sample, which shows that the complex of the exciton in the double layer MoS_2 sample is faster. It is considered that this is due to the faster non radiation transition rate of the double layer MoS_2. Then we use the exciton model to analyze from the point of view of the difference of semiconductor properties, which is attributed to the smaller exciton binding energy of the double layer MoS_2 sample, and the double layer MoS_2 as the indirect band gap semiconductor is more than the single layer MoS_2 from the Brillouin region K point. In addition, the interlayer coupling effect of the double MoS_2 will enhance the vibration of the exciton, and these factors will promote the rapid recombination of the exciton. Therefore, we think the interlayer coupling plays an important role in promoting the exciton recombination. In addition, we have carried out the high pressure of the monolayer MoS_2 film under high pressure. The study of excited state relaxation kinetics has obtained the influence of the band structure of the single layer MoS_2 film controlled by pressure on the ultra fast optical physical properties. The photophysical and semiconductor properties of the MoS_2 based on the number of layers we have studied can provide important guidance and basis for the preparation of MoS_2 based optoelectronic devices and semiconductor devices. The study of the structure and physical properties of transition metal sulfides provides important guidance.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：O469

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