OPTICAL PROPERTIES OF GATHERED SlNGLE WALL NANOTUBES

为了了解单壁碳纳米管（SWNTs）在单管和粗束之间的电子和振动性质的差异，采用提纯和掺杂-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，几十纳米厚的束显示出5%的径向呼吸模式的频率上移的理论工作预测。另一方面，在多壁碳纳米管中观察到的呼吸模式频率显示出进一步的上移。结果表明，层间相互作用越强，呼吸模态频率越高。虽然没有观察到显着的调制通过改变束的厚度在纳米管的电子结构，光学跃迁显示轻微的加宽和下移。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物，呼吸模式拉曼峰显示出作为上述组合效应的结果的通过改变激发波长的振荡。这种振荡假装是多种纳米管的共振。也就是说，我们发现在拉曼光谱中观察到的碳纳米管种类是有限的。我们发现，单壁碳纳米管封装富勒烯可以在高产率合成时，我们调整的直径分布集中在1.37 nm。由于产率足够高，理论计算表明C_2与纳米管之间存在着相当程度的杂化，且C_2的LUMO带明显下移，因此这种材料应被视为一种新的碳固相。<60><60>电子显微镜，X射线。衍射和拉曼散射显示我们的样品包封了填充因子为60 - 70%的富勒烯。有趣的是，我们发现C_2在激光照射或钾离子掺杂下自发地形成二聚体并转变为一维聚合物。<60>

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.