Nucleation of Dislocations in 3.9 nm Nanocrystals at High Pressure

As circuitry approaches single nanometer length scales, it has become important to predict the stability of single nanometer-sized metals. The behavior of metals at larger scales can be predicted based on the behavior of dislocations, but it is unclear if dislocations can form and be sustained at single nanometer dimensions. Here, we report the formation of dislocations within individual 3.9 nm Au nanocrystals under nonhydrostatic pressure in a diamond anvil cell. We used a combination of x-ray diffraction, optical absorbance spectroscopy, and molecular dynamics simulation to characterize the defects that are formed, which were found to be surface-nucleated partial dislocations. These results indicate that dislocations are still active at single nanometer length scales and can lead to permanent plasticity.

Figure 1

TEM images of nanocrystals. (a) Monodisperse 3.9 nm Au nanocrystals. Scale bar is 10 nm. High-resolution images of (b) icosahedral and (c) decahedral nanocrystals. Scale bar is 4 nm.

Figure 2

Experimental high-pressure XRD patterns. (a) All diffraction peaks and (b) magnified view of (111) and (200) peaks. Change in diffraction peak (c) position and (d) width (each division is 0.1°), upon loading (solid line) and unloading (dashed line).

Figure 3

MD simulation of a 3.9 nm icosahedral nanocrystal. (a) Schematic of nanocrystal geometry and slip planes for stacking fault type 1 and type 2. (b) Atomic configurations during loading and unloading process. Top row shows the surface atoms and the loading direction (red arrows). In the next two rows, outermost atoms are omitted to visualize the formation of defects. Images in middle row have green atoms for FCC, white atoms for unclassified crystal structure (typically near the core of a partial dislocation or at the surface), and red atoms for HCP. Images in bottom row are colored according to nonaffine squared displacement, in which the slip plane swept by a perfect dislocation is identified.

Figure 4

Simulated high-pressure XRD patterns from MD simulations. (a) All diffraction peaks and (b) magnified view of (111) and (200) peaks. Change in diffraction peak (c) position and (d) width (each division is 0.1°), upon loading (solid line) and unloading (dashed line).