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Ballistic molecular transport through two- dimensional channels

机译：通过二维通道的弹道分子传输

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摘要

Gas permeation through nanoscale pores is ubiquitous in nature and has an important role in many technologies(1,2). Because the pore size is typically smaller than the mean free path of gas molecules, the flow of the gas molecules is conventionally described by Knudsen theory, which assumes diffuse reflection (random-angle scattering) at confining walls(3,7). This assumption holds surprisingly well in experiments, with only a few cases of partially specular (mirror-like) reflection known(5,8-11). Here we report gas transport through angstrom-scale channels with atomically flat walls(12,13) and show that surface scattering can be either diffuse or specular, depending on the fine details of the atomic landscape of the surface, and that quantum effects contribute to the specularity at room temperature. The channels, made from graphene or boron nitride, allow helium gas flow that is orders of magnitude faster than expected from theory. This is explained by specular surface scattering, which leads to ballistic transport and frictionless gas flow. Similar channels, but with molybdenum disulfide walls, exhibit much slower permeation that remains well described by Knudsen diffusion. We attribute the difference to the larger atomic corrugations at molybdenum disulfide surfaces, which are similar in height to the size of the atoms being transported and their de Broglie wavelength. The importance of this matter-wave contribution is corroborated by the observation of a reversed isotope effect, whereby the mass flow of hydrogen is notably higher than that of deuterium, in contrast to the relation expected for classical flows. Our results provide insights into the atomistic details of molecular permeation, which previously could be accessed only in simulations(10,14), and demonstrate the possibility of studying gas transport under controlled confinement comparable in size to the quantum-mechanical size of atoms.
机译：气体通过纳米级孔隙的渗透本质上是普遍存在的，并且在许多技术中具有重要作用（1,2）。由于孔径通常小于气体分子的平均自由程，因此通常使用Knudsen理论描述气体分子的流动，该理论假设在限制壁处会发生漫反射（随机角度散射）（3,7）。这个假设在实验中非常令人惊讶，只有少数情况是部分镜面（镜面）反射（5,8-11）。在这里，我们报告了通过原子级平坦壁的埃级通道的气体传输（12,13），并表明表面散射可以是扩散的或镜面的，这取决于表面原子景观的精细细节，并且量子效应有助于室温下的镜面反射率。由石墨烯或氮化硼制成的通道允许氦气的流动比理论上预期的快几个数量级。这可以通过镜面表面散射来解释，这会导致弹道运输和无摩擦气流。相似的通道，但具有二硫化钼壁，显示出的渗透速度要慢得多，这仍然可以通过Knudsen扩散很好地描述。我们将差异归因于二硫化钼表面较大的原子波纹，其高度与所传输原子的大小及其de Broglie波长相似。这种物质波贡献的重要性通过观察到反向同位素效应得到了证实，与传统的流态相比，氢的质量流明显高于氘的质量流。我们的结果提供了对分子渗透的原子学细节的见解，以前只能在模拟中才能访问（10,14），并证明了研究在与分子的量子力学尺寸相当的受控约束下进行气体传输的可能性。

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  • 来源
    《Nature》 |2018年第7710期|420-424|共5页
  • 作者

    Keerthi A.; Geim A. K.; Janardanan A.; Rooney A. P.; Esfandiar A.; Hu S.; Dar S. A.; Grigorieva I. V.; Haigh S. J.; Wang F. C.; Radha B.;

  • 作者单位

    Univ Manchester, Sch Phys & Astron, Manchester, Lancs, England;

    Univ Manchester, Sch Phys & Astron, Manchester, Lancs, England;

    Univ Manchester, Sch Phys & Astron, Manchester, Lancs, England;

    Univ Manchester, Sch Mat, Manchester, Lancs, England;

    Univ Manchester, Natl Graphene Inst, Manchester, Lancs, England;

    Univ Manchester, Natl Graphene Inst, Manchester, Lancs, England;

    Univ Manchester, Sch Phys & Astron, Manchester, Lancs, England;

    Univ Manchester, Sch Phys & Astron, Manchester, Lancs, England;

    Univ Manchester, Sch Mat, Manchester, Lancs, England;

    Univ Manchester, Sch Phys & Astron, Manchester, Lancs, England;

    Univ Manchester, Sch Phys & Astron, Manchester, Lancs, England;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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