Syntheses of Novel Metallofullerene Nano-Peapods

金属富勒烯-peapods（CNT encaging fullerenes）如Gd@C_ peapods的迷人特征之一<82>是，我们可以在富勒烯吸热插入的位置进行“局部带隙工程”。先前的TEM图像和电子能量损失谱表明，在高密度的“peapod”结构中，金属富勒烯可以规则地间隔为1.1 nm，而在低密度的peapod中经常观察到1.1-3 nm的间距。在本研究的Gd@C_<82>peapod样品中，在200多张单壁碳纳米管的图像中，约有10%显示出半导体带隙的局部改变，扫描隧道显微镜和光谱（dI/dY）给出了偏压依赖的碳纳米管形貌图像和费米能级附近的局域态密度（LDS）。在STS图中，可以清楚地看到对应于导带和价带边缘的两个强VHS峰，在较高的偏置电压下有两个较小的VHS峰。Gd@C_ peapods的带隙由原来的0.43 eV减小到0.17 eV，并且<82>表现出双极FET特性，通过简单的静电栅可以很容易地获得n沟道和p沟道。类似的结果，从超过10个独立的设备组成的一小束的Gd@C_<82>peapods。TEM<60>图像和电子能量损失谱表明，在高密度的“peapod”结构中，金属富勒烯的间距可以达到1.1 nm，而在低密度的“peapod”结构中，金属富勒烯的间距通常为1.1-3 nm。在本Gd@C_<82>peapod样品中，超过200个单壁碳纳米管图像中约有10%显示出局部修饰的半导体带隙。

One of the fascinating features of metallofullerene-peapods (CNT encaging fullerenes) such as Gd@C_<82> peapods is that we can perform a 'local band gap engineering' at the site where a fullerene is endothermally inserted. Previous TEM images and electron energy loss spectra suggested that the metallofullerenes can be spaced regularly as close as 1.1 nm in a high-density 'peapod' structure, while 1.1-3 nm spacing was often observed in a low-density peapod. In the present Gd@C_<82> peapod samples, about 10% of over 200 SWNT images showed locally modified semiconducting band gaps.Scanning tunneling microscopy and spectroscopy (dI/dY) give bias-dependent topographic images and local density of states (LDS) on carbon nanotubes near the fermi level. In the STS map, two strong VHS peaks corresponding to conduction and valence band edges are clearly seen with two smaller ones at higher bias voltages. The original band gap of 0.43 eV is narrowed down to 0.17 eV where the fullerene is expected to be located.Furthermore, Gd@C_<82> peapods exhibit ambipolar FET behavior with both n-and p-channels easily accessible by simple electrostatic gates. Similar results were obtained from more than 10 independent devices composed of a small bundle of Gd@C_<82> peapods. Such ambipolar behavior has never been observed for C_<60> peapods.TEM images and electron energy loss spectra suggested that the metallofullerenes can be spaced regularly as close as 1.1 nm in a high-density 'peapod' structure, while 1.1-3 nm spacing was often observed in a low-density peapod. In the present Gd@C_<82> peapod samples, about 10% of over 200 SWNT images showed locally modified semiconducting band gaps.