【作者】 高影；

【导师】 莫育俊；

【作者基本信息】 河南大学 ， 光学， 2003， 硕士

【摘要】 富勒烯是继金刚石、石墨之后碳的第三种同素异型体。它的发现引起了人们的广泛关注。自从在石墨烟灰中发现富勒烯C60 和 C70，尤其是Kr?tschmer等人制得宏观量的C60 / C70混合物的粉末之后，人们利用各种研究手段来研究富勒烯。大量的富勒烯的理论和实验工作开展起来。富勒烯是一种奇特的物质。它具有中空的封闭碳笼状结构。C60、C70是富勒稀中最具代表性的分子。C70在富勒烯家族中的蕴藏量和稳定性仅次于C60分子。由25个六边形和12个五边形构成，分子呈橄榄球状。表面增强拉曼光谱具有很高的灵敏度，是提供物质分子结构信息的有利工具。本文首次报道了C70分子吸附在银表面上的增强拉曼光谱温度效应研究。在实验中，测量了C70在常温下的正常拉曼光谱，以及在93K～298K之间的SERS变温拉曼光谱。实验中所使用的高纯度样品 (纯度高于95%)，是我们实验数据来源准确度的保证。另外，由于SERS活性衬底的高灵敏性，以及所采用的低温测量技术，使我们获得了更完整准确的有关C70拉曼谱峰的信息。本文采用波长为632.8nm的He-Ne激光器作为激发光源。C70的可见-紫外吸收光谱表明，在可见光激发的拉曼光谱中存在弱共振或者预共振拉曼效应。常温下正常拉曼光谱和银衬底的SERS谱的相似性表明，C70分子和银衬底之间的相互作用较弱，银衬底对其的增强主要是电磁增强机制在起作用。它们之间不存在电荷转移。此外，在SERS测量中，出现了一些新峰。依据已有关于C70的理论计算结果，对这些新峰逐个进行了归属，它们中大部分和理论计算结果相吻合。当然由于SERS中C70分子和衬底之间的相互作用，使得一些非拉曼活性的振动模式出现在结果中，我们对这些峰也同样进行了指认。在低温测量的过程中，C70的SERS谱特征峰强度发生了可逆的变化。与常温相比，低温下的谱峰明显增强，但是它们的中心位置却保持不变。这种谱峰强度<WP=5>的增强起源于C70分子共振条件随温度的改变。根据V. K. Dolganov等人报道的研究结果，物质的电子能级在流体静压力的作用下会向低能级方向移动。那么温度的改变对电子能级的影响便可以估计出来。考虑到C70在472nm附近存在一较宽的吸收峰，并一直延伸到670nm处。我们经过分析得出结论：低温时能级的移动使预共振拉曼效应加强，从而使低温SERS谱特征峰强度显著增加。另外，本文针对其它的一些有趣的实验现象，比如：273K附近温度的“反常”变化，以及在测量最低温度93K时非常突出的“双峰”现象，进行了合理的分析，并得到了初步的结论。最后，在论文的第四章中，我们探讨了吸附于粗糙铜表面的C70分子SERS谱。研究发现：C70分子在铜和银表面不同的谱峰相对强度，是由于C70分子不同的吸附状态所引起的。这对于SERS实验中如何选择合适的增强衬底，以及C70分子在金属表面吸附状态的研究都具有重要的参考价值。更多还原

【Abstract】 Fullerene is the third form of pure carbon, and the other two well-known are diamond and graphite. Since fullerenes C60 and C70 were discovered in the soot of carbon, in particular appreciable amount of fullerenes was obtained by Kr?tschmer et al., a lot of theoretical and experimental work has been done. Fullerene is a special material, which has a close hollow carbon-cage structure. C70 is the second stable and abundant molecule next to C60 in the fullerenes family. Consisting of 25 hexagons and 12 pentagons, the molecule C70 has a rugby-shaped structure. This thesis for the first time reports the temperature dependence of C70 molecules adsorbed on silver film by the surface enhanced Raman scattering (SERS). Both SERS spectra of C70 molecules on the surface of silver mirror at different temperatures and the normal Raman spectrum of C70 powder at the room temperature were measured. More complete and accurate vibration modes of C70 were expected, considering the high sensitivity of the SERS active substrate (silver mirror) and the high purity of the C70 sample (better than 95%) used in our experiment. The He-Ne laser with the wavelength 632.8nm was used as the excitation line. Judged by the UV-VIS spectrum of C70, a preresonant or weak resonant effect existed in the Raman spectra in our measurement. SERS spectrum was very similar with the normal Raman spectrum at the room temperature 298K. This means there was only weak interaction between C70 molecules and the silver substrate. Therefore, the remarkable enhancement of the signal in SERS spectra dominantly originated from the physical mechanism. In addition, several new spectral features appeared in the SERS spectra. According to the theoretical computation, some of these new features were assigned to the predicted vibration<WP=7>modes. The results of cryogenic investigation showed the intensities of most features in SERS increased greatly at the low temperature, but not accompanied with the shifts of center positions. This kind of increment of intensity originated from the change of resonant condition in the low temperature. According to the experiment reported by V. K. Dolganov, the electronic gap can shift to the low energies under hydrostatic pressure. Then the temperature influence of electronic gap can be estimated. Considering there is a wide absorption band at about 472nm with a wavelength shoulder tailing to about 670nm, the Raman preresonant or weak resonant effect may be enhanced at the low temperature. This induced the great enhancement of the Raman signal at the low temperature and the reversible temperature dependent change in the measurement. Furthermore, there were some interesting phenomena in our experiment, such as the "abnormal" change of intensity in the range of 273K to 298K and the prominent "double peak" phenomenon at the lowest temperature 93K.Finally, in the fourth chapter, we primarily discussed the SERS effect of C70 molecules adsorbed on the surface of copper. The difference of relative intensity between the SERS spectra of C70 adsorbed on the silver surface and the copper surface originated from the different adsorption state of the C70 molecules on them. This investigation is valuable for the selection of the active substrate for C70 molecules in SERS measurement and the research of the adsorption state of C70 molecules on the surfaces of metals更多还原