The nanoindentation of a copper substrate by single-walled carbon nanocone tips: a molecular dynamics study

This study dealt with deep nanoindentation of a copper substrate with single-walled carbon nanocones (SWCNCs) as the proximal probe tip, using molecular dynamics (MD) simulations. As an important feature, during the indentation the end part of the SWCNC tip will suffer a narrowing effect due to the radial component of resistant compression from the substrate and then forms into a somewhat flat arrowhead-like shape. The effective cross-sectional area of the SWCNC tip inside the substrate that the resistant force is acting on therefore is reduced to lower the normal resistant force on the tip. The narrowing effect is more significant for longer SWCNC tips. Two categories of SWCNCs are therefore classified according to whether the SWCNC tip buckles at its part inside or outside the substrate. SWCNCs of the first category defined in this paper are found able to indent into the substrate up to a desired depth. Further analyses demonstrate that a longer SWCNC tip of the first category will encounter smaller repulsive force during the indentation and thus require less net work to accomplish the indentation process. Raising temperatures will weaken the narrowing effect, so an SWCNC tip of the first category also encounters greater repulsive force and larger net work in the indentation process performed at a higher temperature. Notably, a permanent hollow hole with high aspect ratio will be produced on the copper substrate, while copper atoms in close proximity to the hole are only slightly disordered, especially when the indentation is manipulated at a lower temperature by using a longer SWCNC tip.