Fast Surface Dynamics of Metallic Glass Enable Superlatticelike Nanostructure Growth

Contrary to the formation of complicated polycrystals induced by general crystallization, a modulated superlatticelike nanostructure, which grows layer by layer from the surface to the interior of a ${\mathrm{Pd}}_{40}{\mathrm{Ni}}_{10}{\mathrm{Cu}}_{30}{\mathrm{P}}_{20}$ metallic glass, is observed via isothermal annealing below the glass transition temperature. The generation of the modulated nanostructure can be solely controlled by the annealing temperature, and it can be understood based on the fast dynamic and liquidlike behavior of the glass surface. The observations have implications for understanding the glassy surface dynamics and pave a way for the controllable fabrication of a unique and sophisticated nanostructure on a glass surface to realize the properties’ modification.

Figure 1

XRD spectra of ${\mathrm{Pd}}_{40}{\mathrm{Ni}}_{10}{\mathrm{Cu}}_{30}{\mathrm{P}}_{20}$ MG annealed at 546 K ($=T_g-20\mathrm{K}$) for different times. Inset: The surface crystalline layer ($\sim 100\mathrm{nm}$ thick) in MG annealed at 546 K for 200 h can be removed by ion milling.

Figure 2

(a) The cross-sectional Cs STEM view of the sample annealed at 546 K for 200 h. Insets: The SAED patterns of amorphous, amorphous-crystalline interface, and crystalline layer regions (denoted as regions $A$, $B$, $C$), respectively. (b) The magnified image of the selected amorphous-crystalline interface region $B$ in (a). (c) The magnified image of the crystalline nanostructure.

Figure 3

(a)–(d) EDS elemental mapping of Pd, Ni, Cu, and P of region $E$ in Fig. 2. The diffusion directions are labeled by arrows. (e) The atomic percentages of the components with depth varying. The constituents with different depths were quantitatively determined by XPS.

Figure 4

(a) The XRD patterns of the samples annealed at different temperatures for 200 h. (b) The cross-sectional HRTEM image of the sample annealed at 556 K ($=T_g-10\mathrm{K}$) for 200 h. (c) The magnified image of the selected zone in (b); the two grains show a small-angle misorientation of 8°.

Figure 5

The formation schematic of (a) surface superlatticelike nanostructure; (b) polycrystals. The red, pink, and blue balls represent crystalline, mobile, and frozen atoms, respectively.