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arXiv 0810.5627cond-mat.mtrl-scicond-mat.stat-mech
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碳纳米管表面超流$^4$ He膜的吸附特性和第三声传播

Adsorption properties and third sound propagation in superfluid $^4$He films on carbon nanotubes

Sonny Vo, Hossein Fard, Anshul Kogar, Gary A. Williams

摘要:

研究了超流$^4$ He膜在碳纳米管上的吸附特性。吸附的一个主要因素是纳米管非常小的直径所产生的表面张力力。计算表明,即使当氦蒸汽增加到饱和压力时,表面张力也使管上的膜厚度保持很薄。由于圆柱形几何形状而减弱的范德华力也对此有贡献。这两种效应都起到降低沿着管的第三声传播的预测速度的作用。在直径约为1 nm的单壁纳米管上,似乎不可能出现超流性,因为即使在饱和时,膜厚度也小于3个原子层。然而,超流性在大直径纳米管束和多壁纳米管上是可能的。我们已经观察到第三个声音信号的平均直径为5纳米的纳米管束被喷涂到有机玻璃表面上,形成网络的管。

英文摘要:

We consider the adsorption properties of superfluid $^4$He films on carbon nanotubes. One major factor in the adsorption is the surface tension force arising from the very small diameter of the nanotubes. Calculations show that surface tension keeps the film thickness on the tubes very thin even when the helium vapor is increased to the saturated pressure. The weakened Van der Waals force due to the cylindrical geometry also contributes to this. Both of these effects act to lower the predicted velocity of third sound propagation along the tubes. It does not appear that superfluidity will be possible on single-walled nanotubes of diameter about one nm, since the film thickness is less than 3 atomic layers even at saturation. Superfluidity is possible on larger-diameter nanotube bundles and multi-walled nanotubes, however. We have observed third sound signals on nanotube bundles of average diameter 5 nm which are sprayed onto a Plexiglass surface, forming a network of tubes.

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