Super Hardness of Nano-Gold

Many experiments in recent years have shown that plastic flow in metallic materials depends on the volume of material being tested, with smaller sizes being stronger, but the origins of this effect remain elusive, especially in the nanoscale regime below 1 micron (one millionth of a meter). This new collaborative work uses large-scale molecular dynamics methods to simulate crushing of gold nanopyramids up to 40nm x 40nm on the truncated top surface, while performing experiments on real gold nanopyramids as small as 60nm x 60nm. The simulations show that the strength of gold can reach 4-10 GPa, stronger than the strongest steels, and that the strength decreases with increasing contact area in a characteristic manner. The experiments reach strengths of 2-3 GPa, and match the strengths predicted by the parallel modeling effort.

Fig.1. Hardness of Gold nanopyramids as a function of the contact edge length.  Simulations show a characteristic scaling with contact size, reaching hardnesses of 4-10 GPa below 10nm.  Experiments show a similar size scaling, with hardness reaching 2-3 GFig.1. Hardness of Gold nanopyramids as a function of the contact edge length. Simulations show a characteristic scaling with contact size, reaching hardnesses of 4-10 GPa below 10nm. Experiments show a similar size scaling, with hardness reaching 2-3 G

Many experiments in recent years have shown that plastic flow in metallic materials depends on the volume of material being tested, with smaller sizes being stronger, but the origins of this effect remain elusive, especially in the nanoscale regime below 1 micron (one millionth of a meter). This new collaborative work uses large-scale molecular dynamics methods to simulate crushing of gold nanopyramids up to 40nm x 40nm on the truncated top surface, while performing experiments on real gold nanopyramids as small as 60nm x 60nm. The simulations show that the strength of gold can reach 4-10 GPa, stronger than the strongest steels, and that the strength decreases with increasing contact area in a characteristic manner. The experiments reach strengths of 2-3 GPa, and match the strengths predicted by the parallel modeling effort.

  Views of the simulated atomic structure after various depths of compression; a) the first deformation is the injection of dislocations from the contact edges. b,c) injection continues, along with interactions among the dislocations that impedesFigure 2: Views of the simulated atomic structure after various depths of compression; a) the first deformation is the injection of dislocations from the contact edges. b,c) injection continues, along with interactions among the dislocations that impedes