Figure 2. In-situ characterization of the T_c of nanorods with varying diameters.

(a–e) Individual nanorods were heated inside the TEM at a constant ramping rate of 0.67 °C s⁻¹ and their crystallization kinetics were monitored in real time. SAED and TEM imaging are used to identify the crystallization kinetics and T_c. For thicker nanorods (diameter >∼35 nm), T_c was determined by identifying the onset of the first SAED spot. For smaller nanorods (diameter <∼35 nm), T_c was determined by identifying the TEM image contrast change in BF and DF modes. (a,b) Snapshot SAED to compare the crystallization kinetics of nanorods of 150 and 38 nm diameters, respectively. The red circles indicate the onset of the first diffraction spot, reflecting the onset of crystallization. (c) Snapshot BF TEM images to compare the crystallization kinetics of nanorods of diameters <25 nm. The dotted yellow lines indicate crystalline grains, which form at a lower temperature for the thicker nanorod. (d) Snapshot DF TEM images to show the crystallization kinetics of a tapered nanorod, revealing that the formation of crystalline grains (bright contrast) initiates on the thicker region. (e) Snapshot DF TEM images to show the crystallization kinetics of an extremely thin, ∼6-nm-diameter nanorod, showing that crystalline grains form at ∼340 °C, which is over 50 °C higher than the T_c of bulk MGs. (f) Quantification of T_c's for nanorods of various diameters based on the intensity change of TEM image contrasts. The abrupt increase of the relative intensity in each trace (denoted by red arrows) reflects the advent of first crystalline grains, which is defined as T_c (see Methods). The decrease of the intensity after T_c is attributed to the dynamic motion of grains under heating, so initial diffraction spots do not last.