自支撑石墨烯上吸附物的弹道热泳
Ballistic thermophoresis of adsorbates on free-standing graphene
摘要：
作用于流体中的物体的教科书热泳力与局部温度梯度成比例。这同样适用于物理吸附在固体表面上的扩散团簇或分子的宏观漂移行为。我们在这里探索的问题是，这在2D膜上是否仍然有效，例如短片长度的石墨烯。通过一个非平衡分子动力学研究的测试系统-一个金纳米团簇吸附在独立的石墨烯夹在两个温度之间$ΔT$分开-我们发现一个泳力的亚微米片长度是平行的，但基本上独立的，当地的梯度大小。这确定了一个热泳制度，是弹道，而不是扩散，持续高达和超过一百纳米片的长度。分析表明，泳力是由于弯曲声子，其流动是已知的弹道和距离无关的相对较长的平均自由路径。然而，普通的谐波声子应该只携带晶体动量，当撞击在集群上时，不应该能够留下真正的动量。我们表明，石墨烯，和其他膜状单层，支持特定的非谐连接之间的弯曲声子和纵向声子的快速逃逸留下了一个2D投影的质量密度增加赋予弯曲声子，因为他们移动与他们的群速度，与真正的动量，其中一部分是通过散射传输到吸附物。由此产生的与距离无关的弹道热泳力并非不可能具有实际应用。
英文摘要：
The textbook thermophoretic force which acts on a body in a fluid is proportional to the local temperature gradient. The same is expected to hold for the macroscopic drift behavior of a diffusive cluster or molecule physisorbed on a solid surface. The question we explore here is whether that is still valid on a 2D membrane such as graphene at short sheet length. By means of a non-equilibrium molecular dynamics study of a test system -- a gold nanocluster adsorbed on free-standing graphene clamped between two temperatures $ΔT$ apart -- we find a phoretic force which for submicron sheet lengths is parallel to, but basically independent of, the local gradient magnitude. This identifies a thermophoretic regime that is ballistic rather than diffusive, persisting up to and beyond a hundred nanometer sheet length. Analysis shows that the phoretic force is due to the flexural phonons, whose flow is known to be ballistic and distance-independent up to relatively long mean-free paths. Yet, ordinary harmonic phonons should only carry crystal momentum and, while impinging on the cluster, should not be able to impress real momentum. We show that graphene, and other membrane-like monolayers, support a specific anharmonic connection between the flexural corrugation and longitudinal phonons whose fast escape leaves behind a 2D-projected mass density increase endowing the flexural phonons, as they move with their group velocity, with real momentum, part of which is transmitted to the adsorbate through scattering. The resulting distance-independent ballistic thermophoretic force is not unlikely to possess practical applications.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
