溴分子在石墨烯上的物理吸附和电荷转移。

Physical adsorption and charge transfer of molecular Br2 on graphene.

机构信息

Department of Chemistry, ‡Department of Applied Physics and Applied Mathematics, §Department of Mechanical Engineering, and ⊥Department of Electrical Engineering, Columbia University , New York, New York 10027, United States.

出版信息

ACS Nano. 2014 Mar 25;8(3):2943-50. doi: 10.1021/nn500265f. Epub 2014 Feb 17.

DOI:10.1021/nn500265f

PMID:24528378

Abstract

We present a detailed study of gaseous Br2 adsorption and charge transfer on graphene, combining in situ Raman spectroscopy and density functional theory (DFT). When graphene is encapsulated by hexagonal boron nitride (h-BN) layers on both sides, in a h-BN/graphene/h-BN sandwich structure, it is protected from doping by strongly oxidizing Br2. Graphene supported on only one side by h-BN shows strong hole doping by adsorbed Br2. Using Raman spectroscopy, we determine the graphene charge density as a function of pressure. DFT calculations reveal the variation in charge transfer per adsorbed molecule as a function of coverage. The molecular adsorption isotherm (coverage versus pressure) is obtained by combining Raman spectra with DFT calculations. The Fowler-Guggenheim isotherm fits better than the Langmuir isotherm. The fitting yields the adsorption equilibrium constant (∼0.31 Torr(-1)) and repulsive lateral interaction (∼20 meV) between adsorbed Br2 molecules. The Br2 molecule binding energy is ∼0.35 eV. We estimate that at monolayer coverage each Br2 molecule accepts 0.09 e- from single-layer graphene. If graphene is supported on SiO2 instead of h-BN, a threshold pressure is observed for diffusion of Br2 along the (somewhat rough) SiO2/graphene interface. At high pressure, graphene supported on SiO2 is doped by adsorbed Br2 on both sides.

摘要

我们结合原位拉曼光谱和密度泛函理论（DFT），对气态 Br2 在石墨烯上的吸附和电荷转移进行了详细研究。当石墨烯被两侧的六方氮化硼（h-BN）层包裹在 h-BN/石墨烯/h-BN 夹层结构中时，它就不会被强氧化性的 Br2 掺杂。仅由 h-BN 支撑在一侧的石墨烯显示出吸附 Br2 引起的强烈空穴掺杂。我们使用拉曼光谱来确定石墨烯的电荷密度随压力的变化。DFT 计算揭示了每个吸附分子的电荷转移随覆盖率的变化。通过将拉曼光谱与 DFT 计算相结合，获得了分子吸附等温线（覆盖率与压力的关系）。Fowler-Guggenheim 等温线比 Langmuir 等温线拟合得更好。拟合得出吸附平衡常数（∼0.31 Torr(-1))和吸附 Br2 分子之间的排斥横向相互作用（∼20 meV）。Br2 分子的结合能约为 0.35 eV。我们估计，在单层覆盖时，每个 Br2 分子从单层石墨烯中接受 0.09 e-。如果石墨烯不是支撑在 h-BN 上，而是支撑在 SiO2 上，那么 Br2 就会沿着（有些粗糙的）SiO2/石墨烯界面扩散。在高压下，支撑在 SiO2 上的石墨烯在两侧都被吸附的 Br2 掺杂。