金属特性碳纳米管(8,8)的筛选分离及其超快光物理特性研究

Single-walled carbon nanotubes (SWNTs) are rolled graphite sheets along a certain vector defined by the chiral indices (n,m). The electronic structure and optical properties of individual SWNT are uniquely dependent on the chiral indices which separates the tubes into metallic and semiconducting forms. In the as-prepared sample, tubes are generally grown as a mixture of metallic and semiconducting ones, which hampers their widespread application. Selective enrichment and individualization of SWNTs play a vital role in the realization of the true potential of SWNTs in applications. Among the one third metallic species of SWNTs, the armchair SWNTs are of special interest, which is considered as "most metallic tube". .π-Conjugated polymers represent an interesting class of material which can interact with SWNTs through π-π interaction. The interaction is driven by chemical or topological affinity and turns out to be selective in chirality. According to our previous studies, poly[(m-phenyleneethynylene)(PmPV) derivatives show selective interaction with SWNTs of 1.30 nm, e.g., metallic tube (12,6) with the diameter of ~1.25 nm. Along with the conformation-assisted selective wrapping, PmPV showed larger affinity to metallic tubes. After a sequence of sonication-centrifugation process, the content of metallic tubes in the supernatant increases significantly ( from ~33% to ~60%)..Recently, we succeed utilizing the poly[(m-phenyleneethynylene)-alt- (p-phenyleneethynylene)](PmPE) to achieve dispersion of the HiPCO SWNTs, along with its strong affinity toward the armchair (8,8) SWNTs (M-tube (8,8)), which is considered as the most metallic SWNTs. Combining density gradient ultracentrifugation(DGU) with PmPE solution extraction by a sequence of sonication-centrifugation process, M-tube (8,8) will be significantly enriched..The dynamics of exctions, carriers, and phonons is in the heart of electric and optical properties of SWNTs. In S-SWNTs, the lowest-lying photoexcitations are described as bound electron-hole pairs with binding energy of serval hundreds of meV. M-SWNTs, on the other side, support low energy elementary excitations, dubbed Dirac fermions that have been most typically inverstigated in graphene.Strong electron-phonon coupling is know to occur for optical phonons near Γand Κ point in the Brillouin zone, which is determinant for the optical and electric properties of SWNTs. Phonon-phonon interaction plays also a crucial role in the thermal transport and electrical transport of SWNTs. Therefore the dynamics of exctions, carriers, and phonons is considered as one of the most impartant highlights in the area of both fundamental and application of SWNTs. The photoexited dynamics of M-tube (8,8), such as transport and cooling of hot carries, will be studied by using femotsecond time resolution pump-probe technique. The phonon dynamics including electron-phonon coupling, phonon-phonon coupling will be studied?by using TR-CARS.

不同手性的组分彼此混杂且紧紧捆束在一起，极大妨碍单壁碳管（SWNTs）在光电子领域的应用，因此有必要对不同手性的SWNTs进行筛选分离。我们发现共轭聚合物PPE-PPV对M-tube(8,8)具有较强筛选分离作用，可以结合密度梯度超速离心工艺和PPE-PPV溶液超声-离心萃取工艺，制备富含M-tube(8,8)的SWNTs。在此基础上通过飞秒时间分辨的瞬态吸收、相干反斯托克斯拉曼散射(TR-CARS)等方法研究M-tube（8,8）的超快光物理机制，揭示M-tube(8,8)电子-声子耦合、声子-声子耦合的动力学过程，并研究PPE-PPV与M-tube(8,8)之间的pi电子相互作用。通过研究激子、载流子、声子动力学过程，一方面能揭示PPE-PPV对M-tube(8,8)筛选分离的物理机制，另一方面为研究PPE-PPV/SWNTs薄膜光学和电学性能、探索其在纳电子器件方面的应用奠定基础。

不同手性的组分彼此混杂且紧紧捆束在一起，极大妨碍单壁碳管（SWNTs）在光电子领域的应用，因此有必要对不同手性的SWNTs进行筛选分离。本项目通过使用密度梯度超速离心法、凝胶管柱层析法以及聚合物超声-离心萃取法，对金属和半导体特性碳纳米管进行筛选分离，得到M-tube(8,8)高度富含的碳纳米管，在此基础上通过稳态光谱和超快光谱对其光物理过程进行研究。.通过稳态和瞬态光谱系统研究了多种共轭聚合物，如聚苯醚-聚对苯撑乙炔(PPE-PPV)、9,9-二辛基芴-噻吩共聚物(P8FO-TH)、聚3十二烷基基噻吩-2,5-二对氨基偶氮苯（PDTAABQ）等，与金属碳纳米管之间的π电子相互作用，证实二者之间存在超快光致能量传递过程。对比PDTAABQ-SWCNT和纯PDTAAB的皮秒时间分辨荧光光谱，可以发现，聚合物PDTAABQ-SWCNT在最初几十皮秒内的荧光弛豫过程加快，但是数百皮秒的荧光弛豫过程反而变慢。前者是因为PDTAABQ和SWCNT之间的光致能量转移，后者则是因为PDTAABQ分子链扭曲以及偶氮苯被强制发生trans-cis异构，导致激子迁移率降低。.由于在对碳纳米管和石墨烯样品进行向光光学测试时发现其具有较强的光限幅特性，因此我们对其光限幅特性进行了比较系统的研究，发现SWNTs分散液的损伤阈值较高高，而石墨烯分散液具有较低的限幅输出。我们还发现分散在不同容溶剂中的石墨烯光限幅性能如下：G-CB > G-TOL > G-DMF > G-NMP > C60-TOL。G-CB分散液的光限幅性能好主要是由重原子效应引起。实验结果表明：单层石墨烯分散在普通溶剂中的光限幅机制主要是非线性散射，而分散在重原子溶液中，其光限幅机制主要来源于非线性吸收。.此外，我们发现SWNTs的局域光热效应能够大幅度促进抗肿瘤药物如二甲双胍等药效提高，从而能够大幅度降低二甲双胍的使用剂量，使其达到人体安全使用的范畴。其中金属特性碳纳米管具有更加优良的光热特性，与二甲双胍联用，能实现更好的抗肿瘤疗效。