  Physically vitrifying single-element metallic glass requires ultrahigh
cooling rates, which are still unachievable for most of the closest-packed
metals. Here, we report a facile synthetic strategy for creating mono-atomic
palladium metallic glass nanoparticles with a purity of 99.35 +/- 0.23 at% from
palladium-silicon liquid droplets using a cooling rate below 1000 K/s. In-situ
environmental transmission electron microscopy directly detected the leaching
of silicon. Further hydrogen absorption experiment showed that this palladium
metallic glass expanded little upon hydrogen uptake, exhibiting a great
potential application for hydrogen separation. Our results provide insight into
the formation of mono-atomic metallic glass at nanoscale.
