The amorphization and crystallization of the molybdenum (Mo) nanocontacts (NCs) via pulsed voltage application were observed in situ at the atomic resolution by transmission electron microscopy. Simultaneously, the variation in conductance of NCs during structural transformation was measured. The structural transformation could be controlled by the height of applied pulse waves. The amorphization was accelerated when NCs have longer constriction regions, which has not been found in NCs comprised of other metallic elements. The amorphized states of NCs were maintained during the observation at room temperature. The conductance ratio of amorphous Mo NCs to crystal Mo NCs was 0.62, which is lower than the ratio of liquid to solid Mo and is the lowest among those of other metallic NCs, leading to applications to advanced switching and memory functions.
The amorphization of a pure metal nanocontacts (NCs) via pulse voltage energization was verified in pure hafnium (Hf) NCs with a hexagonal close-packed structure. The structural dynamics during amorphization was examined via in situ lattice imaging of transmission electron microscopy with simultaneous conductance measurements. The similarities and difference in the phase transition dynamics and conductance between Hf NCs and pure metal NCs having body-centered cubic structures were demonstrated. In Hf NCs, step-by-step crystallization from amorphous phases could be coordinated by the adjustment of the energization manner of nanosecond pulse voltages, i.e., the pulse height and the energization number. This led to gradual conductance control of the NCs; the conductance could be decreased down to 0.72 of the conductance of the crystalline phase.
Nanosecond pulse waves were applied to molybdenum nanocontacts under tensile forces, resulting in the fabrication of single-atom-sharpened tips. The process was observed in situ by lattice-imaging of transmission electron microscopy. The single-atom-sharpened molybdenum tips have nanometer-grained polycrystalline textures, leading to the emergence of the inherent properties of their distorted atomic configuration.
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