定向（2,2）碳纳米管的制备及其光学特性研究

发布时间：2018-04-06 21:24

  本文选题：MgAPO-11晶体　切入点：碳纳米管　出处：《深圳大学》2017年博士论文

【摘要】：自首次被发现以来,碳纳米管(carbon nanotubes,CNTs)就因为其独特的物理结构以及所表现出来的各种优异性能成为物理学、化学、材料学和生物医学等领域研究的热点材料之一。单壁碳纳米管(single-walled carbon nanotubes,SWCNTs)的电子结构与其直径和手性密切相关,能否获得均一尺寸和性质的单壁碳纳米管是对其展开基础研究和投入实际应用的关键。传统方法所制备的单壁碳纳米往往含有杂质,而且产物是多种直径碳管的混合体。能否选择性地合成金属型性或者半导体性的单壁碳纳米管是目前迫切需要解决的难题。碳纳米管独特新颖的性质主要源于其纳米尺度的直径,随着碳纳米管直径的减小,量子效应将更加明显,从而表现出很多大直径的碳管所不具备的奇异性能。理论计算预言,能在自由空间稳定存在的最小碳纳米管的直径为0.4 nm。2000年,直径仅为0.4 nm的单壁碳纳米管成功被合成出来,由于直径接近理论极限,这些碳纳米管表现出一维超导特性、一维光学吸收特性和高效率光致发光、选择性吸附、高容量储锂等特殊性能。这些引起了人们对超细直径碳纳米管的极大兴趣,其焦点是:碳纳米管究竟可以小到什么程度?这些碳纳米管又具有什么样的光学和电学性能?可能有什么用途?从2000年到现在,陆续有几个研究小组观察到了0.3 nm单壁碳纳米管的存在,但皆为与其他大直径碳管的混合,而且数量极少,难以对其进行实验上的测试研究。有研究人员利用第一性原理计算了0.3 nm(2,2)单壁碳纳米管的结构稳定性和电学性能,但还有许多问题需要继续深入系统的研究。如何可控合成出尺寸均匀,规整排列并且手性单一的0.3 nm单壁碳纳米管阵列,以便能够操控,并进一步测试其性能,也就成为了全球科学家努力的目标。2008年,直径为0.3 nm的(2,2)碳纳米管阵列在沸石晶体孔道中被合成出来,但是沸石主体的电中性骨架导致所得碳纳米管的密度较低,不利于后续的研究应用。本文主要研究了沸石基高质量(2,2)碳纳米管阵列的制备,并对其进行了拉曼光谱和偏振吸收光谱表征。最后把含有(2,2)碳纳米管的MgAPO-11晶体作为可饱和吸收体引入到掺铥光纤激光器中,得到了稳定的孤子锁模脉冲。本文的主要创新性研究内容如下:1.通过同晶取代往AlPO4-11(AEL)磷酸铝晶体骨架中引入Mg离子,在水热条件下制备MgAPO-11晶体,并且系统研究了合成条件以及凝胶配比对晶体生长的影响。通过优化各种合成参数包括晶化时间,结晶温度,镁铝摩尔比,有机模板剂二丙胺(DPA)含量以及不同镁源等,成功在无氟系统中合成出了高质量、迄今为止尺寸最大的MgAPO-11晶体(25×157×254μm~3),为后续单壁碳纳米管阵列的制备提供了很好的主体模板。X射线粉末衍射(XRD)表明,所合成的MgAPO-11晶体是纯的AEL相。2.利用MgAPO-11晶体作为模板,通过真空高温裂解有机碳前驱物的方法合成出了尺寸均一、排列整齐的单壁碳纳米管阵列。随后测试了所合成的单壁碳纳米管的拉曼光谱,包括室温下的拉曼光谱,偏振拉曼光谱和变温拉曼光谱。拉曼光谱显示所制备的单壁碳纳米管的手性为(2,2)扶手椅型管,且其在沸石孔道中的填充密度比之前所报道的有很大的提高。金属性G-峰和半导体性G-峰的存在说明金属性的(2,2)纳米管和半导体性(2,2)纳米管是共存于MgAPO-11晶体孔道中的,并且半导体性(2,2)纳米管的比例稍高。偏振拉曼光谱表明碳纳米管是按照MgAPO-11晶体孔道方向排列的。随着温度的上升,碳纳米管的各个拉曼模式的频率会发生红移,强度逐渐下降,线宽也随之增大。3.测试了(2,2)碳纳米管阵列的偏振吸收光谱,光谱所表现出来的强烈偏振相关性说明(2,2)碳纳米管在MgAPO-11晶体孔道中是高度定向的,(2,2)扶手椅型管电子态密度中的范霍夫奇点在光谱中得到了清晰的体现,从另一个方面证明了金属性(2,2)纳米管和半导体性(2,2)纳米管共存于MgAPO-11晶体孔道中。对比介电函数的计算结果,我们把位于2.67 eV和2.40 eV处的两个吸收峰归因于金属性的(2,2)碳纳米管,而2.95 eV处的吸收峰则源自半导体性的(2,2)碳纳米管。4.利用(2,2)碳纳米管的可饱和吸收特性,把SWCNTs@MgAPO-11晶体作为可饱和吸收体引入到掺铥光纤激光器中,通过调节激光腔内的偏振态,得到了稳定的孤子锁模运转。当泵浦功率为251 mW时,输出孤子脉冲的中心波长位于1950 nm,光谱宽度为4.2nm。输出脉冲宽度为972 fs,重复频率为21.05 MHz。当泵浦功率达到420 mW时,得到的平均输出功率为2.3 mW.
[Abstract]:Since it was found that carbon nanotubes (carbon nanotubes CNTs) because of its unique physical structure and show excellent performance as physics, chemistry, materials science and biomedical research in the field of the hot material. Single walled carbon nanotubes (single-walled carbon, nanotubes, SWCNTs) of the electronic structure and the diameter and chirality closely related to whether single-walled carbon nanotubes to obtain a uniform size and property is the fundamental research and the key into practical application. The traditional method for single wall carbon nanotube preparation often contain impurities, and the product is a mixture of various diameter carbon nanotubes. Whether single-walled carbon nanotube selective synthesis of metal or the semiconductor is a problem need to be solved urgently at present. The main source of carbon nanotube diameter properties unique to the nanometer scale, with the diameter of carbon nanometer tube The reduced quantum effect will be more obvious, which showed a lot of singular performance of large diameter carbon nanotubes are not available. The theoretical calculation predicts that the minimum carbon nanotubes are stable in the free space of 0.4 nm.2000 in diameter, diameter of only 0.4 nm single wall carbon nanotubes were successfully synthesized, as close to the diameter the theoretical limit, these carbon nanotubes exhibit one-dimensional superconducting properties, one-dimensional optical properties and photoluminescence, selective adsorption, high lithium storage capacity and other special properties. These caused the people of ultrafine diameter carbon nanotubes is of great interest, the focus is: carbon nanotubes can actually small to what extent? These carbon nanotubes and with the optical and electrical properties of what may have what use?? from 2000 to now, have been observed several research groups to 0.3 nm single wall carbon nanotubes, but are instead He large diameter carbon nanotubes are mixed, but the number is very small, it is difficult to test the experiment study on it. The researchers used the first principle calculation of 0.3 nm (2,2) structure stability and electrical properties of single-walled carbon nanotubes, but there are still many problems need to continue in-depth research. How to achieve the controlled synthesis of uniform size the regular arrangement, and a single 0.3 nm chiral single-walled carbon nanotube array, in order to be able to control, and further test its performance, has become the global efforts to the goal of scientists in.2008, diameter of 0.3 nm (2,2) carbon nanotube arrays were synthesized in the zeolite pores, but neutral zeolite skeleton body the result obtained carbon nanotube density is low, is not conducive to the following research. This paper mainly studies the high quality zeolite (2,2) carbon nanotube arrays were prepared, and has carried on the Raman spectrum and partial The vibration absorption spectra. The (2,2) MgAPO-11 crystal containing carbon nanotubes as the saturable absorber into the thulium doped fiber laser, the stable soliton mode-locked pulse. The main innovation of the research contents of this paper are as follows: 1. by isomorphous substitution to AlPO4-11 (AEL) Mg ions introduced aluminum phosphate crystal skeleton. Preparation of MgAPO-11 crystal under hydrothermal conditions, and the effects of synthesis conditions and gel ratio on crystal growth. Through the optimization of various synthesis parameters including crystallization time, crystallization temperature, the molar ratio of Mg to Al, organic template agent two amine (DPA) content and different sources of magnesium, success in the synthesis of fluorine free system high quality, by far the largest size of MgAPO-11 crystal (25 x 157 x 254 m~3), preparing for the subsequent single-walled carbon nanotube arrays were the main template.X ray powder diffraction (XRD) showed good, the MgAPO-11 crystal is the synthesis of pure phase AEL.2. as template using MgAPO-11 crystal by means of vacuum pyrolysis of organic carbon precursor was synthesized with uniform size, arrangement of single walled carbon nanotube array orderly. Raman spectra of single wall carbon nanotubes synthesized by the test then, including the room temperature Raman spectrum, Raman polarization temperature dependent Raman spectroscopy. Spectroscopy and Raman spectra show that the chiral single-walled carbon nanotubes prepared for (2,2) armchair tube, and the zeolite in the filling density than previously reported has been greatly improved. The metal of G- peak and G- peak of semiconductor is that of the metallic (2,2) nanotubes and semiconductor (2,2) nanotubes coexist in MgAPO-11 crystal pores, and semiconducting nanotubes (2,2) slightly higher proportion. Polarized Raman spectroscopy showed that carbon nanotubes are in accordance with the direction of drainage channels of MgAPO-11 crystals Column. With the increase of temperature, the frequency of Raman modes of carbon nanotubes will shift the strength gradually decreased, the linewidth increases.3. test (2,2) polarization arrays of carbon nanotubes show strong absorption spectra, polarization correlation spectra shown in (2,2) carbon nanotubes are highly oriented in the channels of MgAPO-11 crystals in (2,2) armchair tube van Hove singularities in the electronic density of states clearly reflected in the spectrum, from another aspect that metallic and semiconducting nanotubes (2,2) nanotubes (2,2) coexist in the channels of MgAPO-11 crystals. The calculation results of the dielectric function, we put in 2.67 eV and 2.40 eV of the two peaks attributed to metal (2,2) of carbon nanotubes, and the absorption peak at 2.95 eV from semiconducting carbon nanotubes (2,2) using.4. (2,2) carbon nanotube saturable absorber S WCNTs@MgAPO-11 crystal as saturable absorber into the thulium doped fiber laser, the polarization state of the laser cavity has been adjusted, the stable soliton mode-locked operation. When the pump power is 251 mW, the output wavelength of soliton pulses at 1950 nm, the spectral width is 4.2nm. output pulse width is 972 FS, repetition rate of 21.05 MHz. when the pump power reached 420 mW, average output power is 2.3 mW.

【学位授予单位】：深圳大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB383.1;TN248

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