Tight-binding quantum chemical molecular dynamics simulations of the low friction mechanism of fluorine-terminated diamond-like carbon films
Tight-binding quantum chemical molecular dynamics simulations of the low friction mechanism of fluorine-terminated diamond-like carbon films
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DOI：
10.1039/c4ra04065a
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发表时间：
2014-08
期刊：
影响因子：
3.9
通讯作者：
S. Bai;Hiroki Murabayashi;Y. Kobayashi;Y. Higuchi;N. Ozawa;K. Adachi;J. Martin;M. Kubo
中科院分区：
文献类型：
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作者：
S. Bai;Hiroki Murabayashi;Y. Kobayashi;Y. Higuchi;N. Ozawa;K. Adachi;J. Martin;M. Kubo
利用我们的紧密结合量子分子动力学代码研究了端氟类金刚石（f端DLC）的超低摩擦机理，并与端氢类金刚石（h端DLC）的超低摩擦机理进行了比较。在1 GPa的接触压力下，F端DLC和h端DLC表现出光滑的滑动和低摩擦系数，分别为0.07和0.04。氟离子半径大于氢离子半径，导致末端f的DLC表面粗糙度较大。因此，f端DLC的摩擦系数略大于h端DLC。我们还在3和7 GPa的接触压力下进行了摩擦模拟。在3 GPa的接触压力下，F端DLC和h端DLC的摩擦系数分别为0.09和0.13。f端DLC表现出与1 GPa接触压力下相同的摩擦行为，而h端DLC在3 GPa接触压力下在界面处观察到C-C键形成反应，导致摩擦系数略高于1 GPa接触压力下。因此，在3 GPa的接触压力下，F端和h端DLC表现出不同的摩擦行为。此外，在7 GPa的高接触压力下，在F端和h端DLC的摩擦界面处观察到键的形成和解离。C-C键的形成在h端DLC中比在f端DLC中更频繁，并且C-C键的寿命在h端DLC中更长。在这个较高的压力下，由于摩擦表面有很强的C-C键，h端DLC的摩擦系数为0.42，而f端DLC的摩擦系数为0.08。在高接触压力下，f端DLC的界面处由于氟的大负电荷和离子尺寸而产生的强斥力相互作用保持了DLC膜之间的距离。这阻止了在摩擦表面形成强的C-C键，从而导致f端DLC的低摩擦性能。我们认为F终止可以改善DLC膜在高接触压力下的摩擦性能。
The super-low friction mechanism of fluorine-terminated diamond-like carbon (F-terminated DLC) is investigated by using our tight-binding quantum molecular dynamics code and compared with that of hydrogen-terminated DLC (H-terminated DLC). Under a contact pressure of 1 GPa, F- and H-terminated DLC show smooth sliding and low friction coefficients of 0.07 and 0.04, respectively. The ion radius of fluorine is larger than that of hydrogen, which leads to the larger asperity of the F-terminated DLC surface. Thus, the friction coefficient of F-terminated DLC is slightly larger than that of H-terminated DLC. We also perform friction simulations under contact pressures of 3 and 7 GPa. Under a contact pressure of 3 GPa, the friction coefficients are 0.09 and 0.13 for F- and H-terminated DLC, respectively. F-terminated DLC shows the same friction behavior as seen under a contact pressure of 1 GPa, whereas the C–C bond formation reaction is observed at the interface of H-terminated DLC under a contact pressure of 3 GPa, leading to a slightly higher friction coefficient than when under a contact pressure of 1 GPa. Thus, under a contact pressure of 3 GPa, F- and H-terminated DLC show different friction behaviors. Furthermore, under a high contact pressure of 7 GPa, bond formation and dissociation are observed at the friction interface in F- and H-terminated DLC. C–C bond formation is observed more frequently in H-terminated DLC than in F-terminated DLC, and the lifetime of C–C bonds in H-terminated DLC is much longer. At this higher pressure, H-terminated DLC shows a high friction coefficient of 0.42 due to strong C–C bonds at the friction surface, whereas F-terminated DLC shows a low friction coefficient of 0.08. The strong repulsive interaction at the interface of F-terminated DLC that arises from the large negative charge and ion size of fluorine maintains the distance between DLC films under a high contact pressure. This prevents strong C–C bond formation at the friction surface, which results in the low friction properties of F-terminated DLC. We suggest that the friction properties of DLC films under a high contact pressure are improved by F termination.