Covalent Bonding and Atomic-Level Plasticity Increase Adhesion in Silicon-Diamond Nanocontacts
Covalent Bonding and Atomic-Level Plasticity Increase Adhesion in Silicon-Diamond Nanocontacts
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DOI：
10.1021/acsami.9b08695
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发表时间：
2019-10-30
影响因子：
9.5
通讯作者：
Carpick, Robert W.
中科院分区：
文献类型：
--
作者：
Milne, Zachary B.;Schall, J. David;Carpick, Robert W.
利用透射电子显微镜（TEM）原位进行了单晶硅原子力显微镜探针在真空中与金刚石基体接触的纳米压痕和滑动实验。滑动后，实验测得的粘附功显着大于纯货车范德华（vdW，）相互作用的估计值。此外，在滑动过程中，粘附功随着法向应力和速度的增加而增加，表明施加的应力在界面的反应性中起着核心作用。互补分子动力学（MD）模拟被用来深入了解在这些实验中发生的原子级过程。模拟使用不同程度的粗糙度和金刚石衬底与不同数量的氢终止的晶体硅提示证明了两个相关的现象。首先，共价键形成的整个接口，其中形成的键的数量受到影响的氢终止的基板，尖端粗糙度，施加的应力，和随机性质的键形成。第二，对于最初粗糙的尖端，滑动运动和相关的剪切应力的应用产生了不可逆的原子尺度塑性的增加，倾向于平滑尖端的表面，这导致了伴随的粘附力的增加。相反，对于最初光滑的尖端，滑动使其中一些尖端变粗糙。在低施加的应力的限制，实验确定的工程相匹配的内在（货车德瓦尔斯）工作的粘附从MD模拟获得的原子级光滑的硅金刚石界面的粘附。结果提供了滑动引起的变化和界面粘附力的机械解释，并可能有助于通知涉及粘合剂界面的应用程序，受到施加的剪切力和位移。
Nanoindentation and sliding experiments using single-crystal silicon atomic force microscope probes in contact with diamond substrates in vacuum were carried out in situ with a transmission electron microscope (TEM). After sliding, the experimentally measured works of adhesion were significantly larger than values estimated for pure van der Waals (vdW,) interactions. Furthermore, the works of adhesion increased with both the normal stress and speed during the sliding, indicating that applied stress played a central role in the reactivity of the interface. Complementary molecular dynamics (MD) simulations were used to lend insight into the atomic-level processes that occur during these experiments. Simulations using crystalline silicon tips with varying degrees of roughness and diamond substrates with different amounts of hydrogen termination demonstrated two relevant phenomena. First, covalent bonds formed across the interface, where the number of bonds formed was affected by the hydrogen termination of the substrate, the tip roughness, the applied stress, and the stochastic nature of bond formation. Second, for initially rough tips, the sliding motion and the associated application of shear stress produced an increase in irreversible atomic-scale plasticity that tended to smoothen the tips' surfaces, which resulted in a concomitant increase in adhesion. In contrast, for initially smooth tips, sliding roughened some of these tips. In the limit of low applied stress, the experimentally determined works of adhesion match the intrinsic (van der Waals) work of adhesion for an atomically smooth silicon diamond interface obtained from MD simulations. The results provide mechanistic interpretations of sliding-induced changes and interfacial adhesion and may help inform applications involving adhesive interfaces that are subject to applied shear forces and displacements.