Wu Xiaojun, Zeng Xiao Cheng
Department of Chemistry and Nebraska Center for Materials and Nanoscience, University of NebraskaLincoln, Lincoln, Nebraska 68588, USA.
ACS Nano. 2008 Jul;2(7):1459-65. doi: 10.1021/nn800256d.
Carbon nanobuds (CNBs), a novel carbon nanostructure, have been synthesized recently via covalently bonding C(60) buckyballs to the sidewall of a single-walled carbon nanotube (SWCNT) through cycloaddition reaction [Nasibulin, A. G. et al., Nat. Nanotechnol. 2007, 2, 156]. We perform a first-principles study of structural, electronic, chemical, and field-emission properties of CNBs. It is found that relative stabilities of CNBs depend on the type of carbon-carbon bond dissociated in the cycloaddition reaction. All CNBs are semiconducting regardless of the original SWCNT base being metallic or semiconducting. Chemical attachment of C(60) to SWCNTs can either open up the band gap (e.g., for armchair SWCNT) or introduce impurity states within the band gap, thereby reducing the band gap (for semiconducting SWCNT). In addition, the band gap of CNBs can be modified by changing the density of C(60) attached to the sidewall of the SWCNT. The work function of CNBs can be either slightly higher or lower than that of the parent SWCNT, depending on whether the attached SWCNT is armchair or zigzag. Computed reaction pathway for the formation of CNBs shows that the barriers of both forward and backward reactions are quite high, confirming that CNBs are very stable at room temperature.
碳纳米芽（CNBs）是一种新型碳纳米结构，最近通过环加成反应将C(60)巴基球共价键合到单壁碳纳米管（SWCNT）的侧壁上而合成出来[纳西布林，A.G.等人，《自然·纳米技术》，2007年，第2卷，第156页]。我们对碳纳米芽的结构、电子、化学和场发射特性进行了第一性原理研究。发现碳纳米芽的相对稳定性取决于环加成反应中解离的碳 - 碳键的类型。无论原始的单壁碳纳米管基底是金属性的还是半导体性的，所有碳纳米芽都是半导体。C(60)与单壁碳纳米管的化学连接既可以打开带隙（例如，对于扶手椅型单壁碳纳米管），也可以在带隙内引入杂质态，从而减小带隙（对于半导体性单壁碳纳米管）。此外，通过改变附着在单壁碳纳米管侧壁上的C(60)的密度，可以改变碳纳米芽的带隙。碳纳米芽的功函数可能略高于或低于母体单壁碳纳米管的功函数，这取决于附着的单壁碳纳米管是扶手椅型还是锯齿型。计算得到的碳纳米芽形成反应路径表明，正向和反向反应的势垒都相当高，这证实了碳纳米芽在室温下非常稳定。
