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1、2023年中英文摘要 中英文摘要 作者姓名：段小洁 论文题目：单壁碳纳米管的AFM操纵、形变及相关拉曼光谱研究 作者简介：段小洁，女，1980年2月出生，2023年9月师从于北京大学刘忠范教授，于2023年7月获博士学位。 中文摘要 对形变碳纳米管（CNTs）的研究，包括研究其在应力存在下的结构演化、应力对其各种光电性质及电子能带结构的影响等，不仅对CNTs在复合材料、纳电子和纳机电器件、以及应力传感器等中的应用具有重要意义，还对相关理论的发展有巨大推动作用。本论文发展了对表面上单壁碳纳米管（SWNTs）的原子力显微术（AFM）可控操纵方法，基于此AFM可控操纵，研究了CNTs在弯曲形变下的屈
2、曲行为，以及SWNTs在扭转和拉伸两种形变下的共振Raman光谱特征。主要成果包括： 1.发展了对表面上SWNT的AFM可控操纵方法； 通过对操纵过程中针尖运动路径的合理设置、SWNT上操纵位置和针尖下压距离的选择，可以向SWNT中引入各种类型的应力。SWNT中产生的应力由其和基底间的相互作用力保持。发展了基于Si的AFM氧化的SWNT纳米焊接术，以增加AFM操纵的可控性。当对表面有SWNT的基底Si进行AFM氧化时，新生成的SiOx会对SWNT进行包覆，从而可以将SWNT在氧化点有 效的固定到基底表面。而且SWNT的存在会对Si基底的AFM氧化有明显的增强作用，相同条件下，表面有SWNT的S
3、i氧化后产生的SiOx，比没有SWNT时更多，这种增强作用有利于对 SWNT的焊接固定。焊接的强度可以通过改变氧化偏压、针尖运动速率（氧化时间）等进行调节，提高氧化偏压、降低针尖移动速率有利于增强纳米焊接的强度。空气中热氧化实验和拉曼光谱的表征均证明，此焊接过程对SWNT的化学结构无明显影响。在某些点对SWNT进行焊接固定后，AFM操纵引入的形变的大小和分布可以被有效地控制，从而大大增加AFM操纵的可控性。 采用更强的AFM氧化条件，可以实现SWNT和Si的同时氧化，从而可以在任意位点对SWNT进行切割。结合AFM纳米切割、焊接和操纵等操作，可以构筑各种复杂形状的SWNTs，体现 了AFM作为
4、纳米工具箱的作用。 2.研究了CNTs在弯曲形变下的屈曲行为； 通过选择合适的操纵位点、被操纵的CNT片段长度、操纵路径并优化针尖下压距离，可以严格控制弯曲CNT的角度，这样通过AFM操纵对同一CNT的可控弯曲，获得了一系列弯曲角度逐渐增大的CNT。CNT被操纵以后，与基底相互作用力会有明显减小，这使得CNT的有效弯曲区域，位于与基底只有vdW相互作用的被操纵部分，在AFM表征下表现为固定部分和被操纵部分的交点。有效弯曲部分与基底间仅有vdW相互作用，其长度在整个弯曲过程中几乎保持不变。 通过记录弯曲“点”在弯曲角度逐渐增大过程中的高度变化，研究了CNTs在弯曲形变下的结构演化和屈曲行为。发现
5、不同CNTs在弯曲过程中，表现出“突变”和“渐变”两种屈曲模式，分别对应于弯曲“点”高度的突跃、均匀弯曲向屈曲结构的直接转化，和弯曲“点”高度的逐渐增大、均匀弯曲向屈曲结构的逐渐转化。“渐变”屈曲导致一系列屈曲过渡态的出现。“突变”多发生于小直径管，而“渐变”更常见于大直径管。通过对CNTs的层数和厚度等的估算，发现一般情况下，“渐变”屈曲模式的CNTs比“突变”模式的CNTs具有更大的厚度直径比。对“突变”屈曲模式的CNTs，临界屈曲角度随CNTs直径的增大而减小。 分子动力学模拟发现，（1）所研究的CNTs中，SWNTs均为“突变”屈曲模式，而双壁和三壁管均采取“渐变”屈曲模式；（2）“渐
6、变”屈曲过程对应弯曲角度逐渐增大时，多壁管从最外层到最内层的逐渐屈曲，和各管层屈曲程度的逐渐增加，这是由其多层结构导致的各层壁屈曲行为的不同步，和管壁间vdW相互作用对屈曲的阻碍造成的，这说明MWNTs的多层结构是导致其“渐变”屈曲的主要原因；（3）基底的vdW相互作用对CNTs的屈曲行为没有明显影响。从导致两种屈曲模式的机理考虑，除直径外，CNTs的层数对其屈曲行为也有重要影响，这预示了在CNTs的力学性质中，存在不同于传统尺寸效应的双尺寸效应，即直径和层数共同决定CNTs力学行为。 本工作利用AFM可控操纵，在实验上几乎全程观察了CNTs在弯曲过程中的结构演化和屈曲形成过程，其所揭示的两种
7、屈曲模式的形成规律，不仅对大量存在的CNTs形变的理论工作提供了支持和参考，一定程度上填补了实验上的空白，还对CNTs在复合材料、纳电子和纳机电器件、以及应力传感器等中的应用具有重要意义， 3.研究了扭转和拉伸形变下单根SWNTs的共振Raman光谱行为； AFM操纵可以向超长SWNT中同时引入扭转和拉伸应力，由于拉伸形变比扭转形变的传输距离更远，在操纵点附近扭转和拉伸两种形变同时存在，距离操纵点较远的区域，只有纯拉 伸形变存在。扭转形变的产生证明了SWNT在AFM操纵下滚动的发生。 扭转和拉伸形变都会导致SWNTs拉曼模振动频率的变化。研究发现：（1）扭转形变下，wRBM变大，位于1600
8、cm-1的G+(E2(g)模振动频率发生较大的红移，而其他在1590 cm-11560 cm-1范围内的大部分G模会发生轻微的蓝移，振动频率发生红移的G模的位移量，一般远远大于发生蓝移的G模的位移量；（2）拉伸形变下，RBM和G+(E2(g)模振动频率不变，而在1590 cm-1 1560 cm-1范围内的大部分G模会发生明显的红移。（3）不同Raman活性模对形变的敏感度不同，扭转形变下，RBM、位于1600 cm-1的G+( E2(g)模比其他G模更敏感，而在拉伸形变下， 其他G模却具有更高的敏感度。这与形变导致的发生变化的C-C键是否与各模的原子位移模式相关联有关；（4）通过对SWNTs
9、中形变量大小和Raman频率对形变变化率dw/de地计算，发现RBM振动频率对扭转形变的变化率dw(RBM)/det，随SWNTs手性角的增大几乎线性增大。 某些SWNTs中，扭转形变导致的对称性破缺还会导致Raman模的分裂或新模的出现。按照预测，这种分裂或新模的出现最可能发生在锯齿形和椅形SWNTs中。扭转和拉伸形变都会导致SWNTs共振拉曼振动模强度的变化，这体现了形变对SWNTs电子跃迁能Eii的影响。根据 共振拉曼理论和RBM峰的IAS/IS，可以计算扭转和拉伸形变对Eii影响的方向和大小。 应力对SWNTs共振Raman光谱的影响一直是人们关注的重要问题，本工作首次在实验上研究了扭
10、转形变下SWNTs共振Raman振动频率和强度的变化。利用AFM操纵在单根SWNTs水平上的研究，可以排除不同直径和手性带来的平均效应，从而有利于揭示SWNTs的本征性质。对拉伸和扭转形变在同根SWNT中的比较，也为理解不同应力对SWNTs拉曼影响的不同提供了有利条件。 4.AFM操纵引入的应力沿SWNT管轴分布的分析和调控，及SWNTs相关力学性质的比较；分析了超长SWNT中，AFM操纵引入的应力的传输和分布，由于SWNT与基底间摩擦力的存在和AFM操纵后应力的部分驰豫，扭转和拉伸应力沿SWNT管轴都呈“L”形分布，应力分布的各特征量，如应力的最远传输距离、最大应力点的位置和最大应力值、应力
11、线性分布的斜率等，决定于AFM针尖施加到SWNT的力的大小、SWNT的剪切模量或弹性模量、以及SWNT与基底间摩擦力的大小；通过控制AFM操纵和采用图案化基底，对SWNT中应力的大小及分布进行了调控；通过比较不同SWNTs的应力分布特征量，在单根SWNT水平上，研究比较了它们的各力学参量，如剪切模量、杨氏模量，以及与基底间摩擦力的相对大小。各力学参量对SWNTs的直径无单调关系，说明了SWNTs手性对力学性质的影响。 关键词：单壁碳纳米管，AFM操纵与加工，形变，屈曲，共振拉曼光谱 AFM Manipulation, Deformation and Related Raman Spectros
12、copy of Single-Wall Carbon Nanotubes Duan Xiaojie ABSTRACT The study on deformed carbon nanotubes (CNTs), including the study of their structure evolution and properties change under strain, is important not only for the application of CNTs in composite materials, strain sensors, nanoelectronic and
13、nanoelectromechanical devices, but also for the development of related theory.In this thesis, we have developed controlled atomic force microscopy (AFM) manipulation techniques for single-wall carbon nanotubes (SWNTs) on surfaces.Using this controlled AFM manipulation, the buckling behavior of CNTs
14、under bending, and resonance Raman spectroscopy of SWNTs under torsional and uniaxial strains, have been studied.The main results are listed as followings: 1.Controlled AFM manipulation techniques for SWNTs on surfaces have been developed By defining proper tip path, manipulation position on SWNT, a
15、nd choosing optimal tip preing distance, different kinds of deformation can be induced into SWNT.The deformation is stabilized by the interaction between SWNTs and substrate. To get controlled AFM manipulation, a new kind of nanofabrication-nano-welding has been invented based on the AFM oxidation o
16、f Si substrate.When the Si substrate with SWNT on top of it is oxidized by the AFM tip, the newly formed SiOx will grow around the tube, effectively fixing that site of SWNT onto the Si substrate.The existence of SWNT can enhance the oxidation of Si.With same oxidation condition, more SiOx can be pr
17、oduced with the presence of SWNT than the case where there is no SWNT.This is helpful for the fixing.The intensity of the welding can be modulated by changing the oxidation voltage and the tip moving speed.With higher voltage and slower tip moving, stronger welding can be obtained.From the thermal o
18、xidation of SWNTs in air and the Raman characterization, it was found that this nano-welding has no obvious influence on the chemical structure of SWNTs.Together with this nano-welding, the magnitude and distribution of strain induced into SWNT by AFM manipulation can be well controlled. Both SWNT a
19、nd Si can be oxidized when using stronger oxidation condition (much higher voltage and lower tip moving speed), thus the SWNT can be cut at well defined position.Combining this AFM cutting, nano-welding and manipulation, complex SWNT-based structures can be constructed, proved the function of AFM as
20、 a nano-toolbox. 2.The buckling behavior of CNTs under bending has been studied By choosing proper manipulation site on SWNT, the length of the fragment which is being manipulated, manipulation path, and optimal tip preing distance, the angle can be well controlled when SWNT is bent by AFM manipulat
21、ion.Based on this controlled bent of CNT by AFM manipulation, A CNT with a series of different bending angles has been obtained.The interaction between manipulated SWNT fragment and substrate is largely decreased after the manipulation.And the effective bending region is located at the fragment wher
22、e Only vdW interaction exists between it and the substrate.It appears as the cro point between the fixed SWNT part and manipulated SWNT part in the AFM image.Only vdW force exists between the effective bending region and substrate, and its length keeps constant when changing the bending angle. Throu
23、gh recording the height change at the effective bending region when changing the bending angle gradually, The structural evolution and buckling behavior has been investigated under the bending.Two distinct abrupt and gradual buckling modes have been revealed in different CNTs.For the abrupt buckling
24、 mode, the height of the bending point has a sudden increase, and an abrupt transition from the uniform bending to buckling happens.While the gradual mode corresponds to a gradual increase of the height at the bending point, with a gradual transition from uniform bending to buckling.The gradual buck
25、ling results in a series of buckling intermediate formation.Abrupt buckling mode is mostly found for small diameter CNTs, while for large diameter CNTs, the gradual mode is more common.Through the estimation of the wall numbers and thickne of CNTs, it was found that the CNTs with abrupt buckling mod
26、e has smaller thickne diameter ratio than the CNTs with gradual buckling mode.The critical buckling angle decreases with the increase of CNT diameter for the abrupt buckling mode. The buckling behavior has also been investigated by molecular dynamics (MD) simulations.It was found: (1) for all the CN
27、Ts studied, the SWNTs have “abrupt” buckling mode, and double and three walled CNTs take “gradual” buckling modes; (2)the “gradual” buckling corresponded to the proce that different tube walls of MWNTs buckled at different bending stages, and the buckling degree of individual tube walls gradually in
28、creased along with the bending strain increase.This is caused by the unsynchronization of the buckling for different walls caused by the multi-shell character, and the retarding of buckling by the inter-wall vdW force.The study on the formation of the two buckling modes found that the multi-shell st
29、ructure of MWNTs accounts for the “gradual” buckling modes; (3) The MD studies also proved that the vdW interaction with substrate has no remarkable effect on CNTs buckling behavior.The study on the buckling mechanism suggests that except for the diameter, the wall number also determines the bucklin
30、g behavior.This means for the mechanical properties of CNTs, a special “dual-size” effect may exists, that is, both the size and the thickne determine the CNTs mechanical behavior. By using controlled AFM manipulation, the work here observed the structural evolution and buckling formation almost in
31、the whole bending proce.The founding about the two buckling modes, not only provides support and reference for the relevant theoretical study, fills the gap between theory and experiment, but also is important for the application of CNTs in composite materials, nanoelectronics and NEMs, and strain s
32、ensors. 3.The resonance Raman spectroscopy of individual SWNTs under torsional and uniaxial strain has been investigated The AFM manipulation can induce both torsional and uniaxial strains into the ultra-long straight SWNTs.Because the longer propagation distance of uniaxial strain than the torsiona
33、l strain, only pure uniaxial strain exists at region far from the manipulation point.While at region close to the manipulation sites, both the two strains happen.The formation of torsional strain suggested the rolling of SWNT under the present AFM manipulation. Both uniaxial and torsional strain can
34、 change the Raman vibrational frequency.It was found that: (1) the RBM and G-band spectra responded differently to the two types of strains.Under torsional strain, RBM frequency wRBM was found to upshift and one of the modes aigned to E2 symmetry in the G+ band, which occurs at 1600 cm-1( G+(E2(g),
35、downshifted significantly, whereas the rest G modes located in the range of 1590 cm-11560 cm-1 are slightly upshifted.The redshift of the (G+(E2(g), ismuch larger that the buleshift of other G modes; (2) Under uniaxial strain, wRBM and wG+(E2(g) do not have noticeable response and the rest of the G
36、modes in the range of 1590 cm-11560 cm-1 are downshifted.(3) Different Raman modes have different sensitivity to both strains.RBM and G+(E2(g) is more sensitive to torsion than other G modes.Whereas under uniaxial strain, other G modes have larger sensitivity than RBM and G+(E2(g).This is related to
37、 the correlation between the C-C bond change and the atom vibrational displacement of different modes; (4) The calculation on the strain magnitude and frequency shift of Raman modes per strains dw/de found that, under torsional strain, dw(RBM)/det nearly linearly increased along with the increase of
38、 the tube chirality angle. G-band was found to split into multiple sub-bands in some cases, presumably due to broken symmetry induced by torsion.This splitting is most likely found in zig-zag and armchair SWNTs.Both the uniaxial and torsional strains can change the intensity of resonant Raman peaks.
39、This is originated from the influence of strains on electronic tranision energy Eii.From this change, the modulation direction and magnitude of strains on the electronic transition energy of SWNTs can be calculated. The influence of strain on the resonant Raman spectra of SWNTs has drawn much attent
40、ion recently.The work here firstly experimentally studied the torsional strain effect on resonant Raman spectra of SWNTs.And the study in the single SWNT scale by AFM manipulation can exclude the average effect originated from different diameter and chiraligy.This helps to reveal the intrinsic prope
41、rty of SWNts.The comparison of uniaxial and torsional strain for same SWNT, also benefit the understanding of the influence of different strains on SWNTs. 4.The analysis and modulation of strain distribution along SWNTs axis, and the comparison of related mechanical parameters of different SWNTs It
42、was found that after AFM manipulation, both the torsional and uniaxial strain would have a “L” shaped distribution along the SWNT axis, due to the friction between SWNTs and the substrate, and the partial relaxation of strain.The characteristics of the distribution, including the propagation distanc
43、e of strain, the maximum strain and its position, and the slope of the strain distribution, are determined by the force exerted on SWNT by AFM tip, the elasticity modulus E and the shear modulus G, and the friction between SWNT and surface.By controlling the AFM manipulation and using patterned subs
44、trate with different components, the magnitude and distribution of strain in SWNT has been modulated.With the comparison of strain distribution in different SWNTs, their mechanical properties, such as E and G, and the friction with the substrate have been compared, on the single SWNTs scale.It was f
45、ound that there is no monomial relationship between these parameters and the SWNTs diameter, this suggests that the chirality of SWNTs also has important effect on SWNTs mechanical properties. Key words:Single-Walled Carbon Nanotubes (SWNTs), AFM manipulation and fabrication, deformation (strain), buckling, resonance Raman spectroscopy 中英文摘要 中英文摘要 高线中英文摘要 论文中英文摘要 论文中英文摘要 论文中英文摘要格式 中英文摘要的编写要求 如何写中英文摘要 中英文摘要撰写规范（版） 顶岗实习论文摘要中英文