Shim Moonsub, Ozel Taner, Gaur Anshu, Wang Congjun
Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
J Am Chem Soc. 2006 Jun 14;128(23):7522-30. doi: 10.1021/ja058551i.
Doping of individual single-walled carbon nanotubes via noncovalent adsorption of polyethylenimine which converts p-type semiconducting nanotubes into n-type is examined by micro-Raman studies. Distinctively different responses are observed in metallic and in semiconducting nanotubes. Very little or no changes in the radial breathing and the disorder modes are observed upon polymer adsorption on semiconducting carbon nanotubes indicating noncovalent nature of this process. Tangential G-band spectral downshift of up to approximately 10 cm(-)(1) without line broadening is observed for semiconducting tubes suggesting similar magnitude of electron transfer as commonly observed in electrochemical doping with alkali metals. Strong diameter dependence is also observed and can be explained by thermal ionization of charge carriers with activation barrier that scales as the energy gap of the semiconducting nanotubes. In contrast, metallic nanotubes exhibit very different behavior with significant line broadening of the G-band and concurrent enhancement of the disorder mode. In certain cases, initially symmetric Lorentzian line shapes of the G-band features with narrow line widths similar to semiconducting tubes are converted to a broad, asymmetric Breit-Wigner-Fano line shape. Implications on the effects of electron injection and the local chemical environment on the intrinsic line shape of isolated carbon nanotubes are discussed.
通过微拉曼研究考察了通过聚乙烯亚胺的非共价吸附对单个单壁碳纳米管进行掺杂的情况，该吸附可将p型半导体纳米管转变为n型。在金属纳米管和半导体纳米管中观察到明显不同的响应。在聚合物吸附到半导体碳纳米管上时，径向呼吸模式和无序模式几乎没有变化或没有变化，这表明该过程具有非共价性质。对于半导体管，观察到切向G带光谱下移高达约10 cm⁻¹且没有谱线展宽，这表明电子转移的幅度与在碱金属电化学掺杂中通常观察到的相似。还观察到强烈的直径依赖性，这可以通过具有与半导体纳米管能隙成比例的激活势垒的电荷载流子的热电离来解释。相比之下，金属纳米管表现出非常不同的行为，G带出现明显的谱线展宽，同时无序模式增强。在某些情况下，最初具有类似于半导体管的窄线宽的G带特征的对称洛伦兹线形会转变为宽的、不对称的布赖特 - 维格纳 - 法诺线形。讨论了电子注入和局部化学环境对孤立碳纳米管本征线形的影响。
