OPTICAL PROPERTIES OF GATHERED SlNGLE WALL NANOTUBES

为了了解单壁碳纳米管(SWNTs)的电子和振动性质在孤立管和厚束中的差异，我们通过提纯和掺杂-脱掺杂的方法制备了不同束厚的样品，并测量了其共振拉曼光谱。我们发现，几十nm厚的束状物出现了理论预测的径向呼吸模式频率上移5%。另一方面，在多壁碳纳米管中观察到的呼吸模式频率进一步上移。结果表明，层间相互作用越强，呼吸模式频率越高。改变束厚对纳米管的电子结构没有明显的调制作用，但光学跃迁表现出轻微的展宽和下移。这是分子固体的典型特征。由于原始样品是孤立的管和束的混合体，在上述综合作用下，呼吸模喇曼峰随激发波长的变化而发生振荡。这种振荡假象是多种纳米管处于共振状态。换句话说，我们发现在拉曼光谱中观察到的纳米管种类有限。我们在单壁碳纳米管中进行了富勒烯掺杂。我们发现，当我们将直径分布调整到1.37 nm时，可以高产率地合成包裹富勒烯的单壁碳纳米管。由于产率足够高，这种材料应该被视为一种新的碳的固相，因为理论计算表明，C&lt；60&gt；与纳米管有相当大的杂化，C&lt；60&gt；的LUMO带有较大的下移。电子显微镜、X射线。衍射谱和拉曼光谱表明，我们的样品包覆了填充因子为60-70%的富勒烯。有趣的是，人们发现C_&lt；60&gt；在激光照射或钾掺杂后会自发形成二聚体，并转变为一维聚合物。

To see differences on the electronic and vibrational properties of single-wall carbon nanotubes (SWNTs) between isolated tubes and thick bundles, we prepared variety samples in bundle thickness by purification and doping-dedoping methods, and then measured resonance Raman spectra. We found that several tens nm thick bundles show 5% up-shift of radial breathing mode frequency as predicted by theoretical works. On the other hand, breathing mode frequency observed in multi-wall carbon nanotubes show further up-shifts. It was indicated that the stronger inter-layer interaction leads to higher breathing mode frequency. While no significant modulation was observed in electronic structure of nanotubes by changing bundle thickness, optical transition shows slight broadening and downshifts. This is a typical feature of molecular solids. Since the pristine sample is a mixture of isolated tubes and bundles, breathing mode Raman peak shows oscillation by changing excitation wavelength as results of combined effects mentioned above. This oscillation pretends to be many kinds of nanotubes are on resonance. In other words, we found that sorts of nanotubes are limited observed in Raman spectra.We did fullerene doping inside SWNTs. We found that SWNTs encapsulating fullerenes can be synthesized in high-yield when we tuned the diameter distribution to be centered at 1.37 nm. Since the yield is sufficiently high, this kind of material should be regarded as a new solid phase of carbon, as theoretical calculation indicates considerable hybridization between C_<60> and nanotube and large down shift of LUMO band of C_<60>. Electron microscopy, X ray. diffraction, and Raman scattering reveal that our sample is encapsulating fullerenes with filling factor 60 - 70 %. Interestingly, It wa found that C_<60> spontaneously forms dimers and changes to one-dimensional polymer by laser irradiation or potassium doping.