Strong Charge-Transfer Doping of 1 to 10 Layer Graphene by NO2

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• 作者：Andrew C. Crowther ; Amanda Ghassaei ; Naeyoung Jung ; Louis E. Brus
• 刊名：ACS Nano
• 出版年：2012
• 出版时间：February 28, 2012
• 年：2012
• 卷：6
• 期：2
• 页码：1865-1875
• 全文大小：639K
• 年卷期：v.6,no.2(February 28, 2012)
• ISSN：1936-086X

文摘

We use resonance Raman and optical reflection contrast methods to study charge transfer in 1鈥?0 layer (1L鈥?0L) thick graphene samples on which NO₂ has adsorbed. Electrons transfer from the graphene to NO₂, leaving the graphene layers doped with mobile delocalized holes. Doping follows a Langmuir-type isotherm as a function of NO₂ pressure. Raman and optical contrast spectra provide independent, self-consistent measures of the hole density and distribution as a function of the number of layers (N). At high doping, as the Fermi level shift E_F reaches half the laser photon energy, a resonance in the graphene G mode Raman intensity is observed. We observe a decrease of graphene optical absorption in the near-IR that is due to hole-doping. Highly doped graphene is more optically transparent and much more electrically conductive than intrinsic graphene. In thicker samples, holes are effectively confined near the surface, and in these samples, a small band gap opens near the surface. We discuss the properties and versatility of these highly charge-transfer-doped, few-layer-thick graphene samples as a new class of electronic materials.

Keywords:

graphene; NO₂; nitrogen dioxide; Raman spectroscopy; charge transfer; doping