Applications and limitations of electron correlation microscopy to study relaxation dynamics in supercooled liquids

Electron correlation microscopy (ECM) is a way to measure structural relaxation times, τ, of liquids with nanometer-scale spatial resolution using coherent electron scattering equivalent of photon correlation spectroscopy. We have applied ECM with a 3.5nm diameter probe to Pt_57.5Cu_14.7Ni_5.3P_22.5 amorphous nanorods and Pd₄₀Ni₄₀P₂₀ bulk metallic glass (BMG) heated inside the STEM into the supercooled liquid region. These data demonstrate that the ECM technique is limited by the characteristics of the time series, which must be at least 40τ to obtain a well-converged correlation function g₂(t), and the time per frame, which must be less than 0.1τ to obtain sufficient sampling. A high-speed direct electron camera enables fast acquisition and affords reliable g₂(t) data even with low signal per frame.