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Cangyu Qu

Publications and source records attributed to Cangyu Qu.

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Mechanochemical Nano-Writing of an Atomically Thin Metal

Mechanical energy accelerates many physicochemical processes, including materials syntheses that are hard to produce with thermal energy alone. However, physical understanding connecting applied mechanical forces with internal stresses and ensuing reaction mechanisms is lacking. Here we demonstrate mechanical force-enabled synthesis and nanoscale patterning to metallize a two-dimensional (2D) material, producing an atomically-thin superconducting material. Localized force applied by atomic force microscope tips to van der Waals (vdW) encapsulated stacks of 2D bilayer MoTe2 and adjacent source Pd guides 2D Pd7MoTe2 growth with 50 nm lateral resolution. Force accelerates reaction kinetics exponentially per Eyring's stress-assisted thermal activation model, reducing synthesis temperatures from ~200 {\deg}C to near-room temperature. Finite element simulations, density functional theory, and ab-initio grand canonical Monte Carlo calculations show that tip-induced compression facilitates Pd chemisorption to tensile-strained MoTe2 that converts to uniform Pd7MoTe2. This demonstrates a new, generalizable paradigm for nanoscale synthesis of quantum materials, and high-precision engineering of superconductivity.

cond-mat.mes-hall

Rotational instability in superlubric joints

Surface and interfacial energies play important roles in a number of instability phenomena in liquids and soft matters, but are rare to play a similar role in solids. Here we report a new type of mechanical instabilities that are controlled by surface and interfacial energies and are valid for a large class of materials, in particular two-dimensional layered materials. When sliding a top flake cleaved from a square microscale graphite mesa by using a probe acted on the flake through a point contact, we observed that the flake moved unrotationally for a certain distance before it suddenly transferred to a rotating-moving state. The theoretical analysis that agrees well with the experimental observation reveals that this mechanical instability is an interesting effect of the structural superlubricity (a state of nearly zero friction). Our further analysis shows that this type of instability holds generally for various sliding joints on different scales, as long as the friction is ultralow. Thus, the uncovered mechanism provides useful knowledge for manipulating and controlling all these sliding joints, and can guide design of future structural superlubricity based devices.

cond-mat.mes-hall