Atomically thin two-dimensional (2D) materials face significant energy barriers for synthesis and processing into functional metastable phases such as Janus structures. Here, the controllable implantation of hyperthermal species from pulsed laser deposition (PLD) plasmas is introduced as a top-down method to compositionally engineer 2D monolayers. The kinetic energies of Se clusters impinging on suspended monolayer WS2 crystals were controlled in the <10 eV/atom range with in situ plasma diagnostics to determine the thresholds for selective top layer replacement of sulfur by selenium for the formation of high quality WSSe Janus monolayers at low (300 °C) temperatures and bottom layer replacement for complete conversion to WSe2. Atomic-resolution electron microscopy and spectroscopy in tilted geometry confirm the WSSe Janus monolayer. Molecular dynamics simulations reveal that Se clusters implant to form disordered metastable alloy regions, which then recrystallize to form highly ordered structures, demonstrating low-energy implantation by PLD for the synthesis of 2D Janus layers and alloys of variable composition.

Mechanical failure of π-conjugated polymer thin films is unavoidable under cyclic loading conditions, due to intrinsic defects and poor resistance to crack propagation. Here, the first tear-resistant and roomtemperature self-healable semiconducting composites is presented, consisting of conjugated polymers and butyl rubber elastomers. This new composite displays both record-low elastic modulus (< 1 MPa) and ultra-high deformability with fracture strain above 800%. More importantly, failure behavior is not sensitive to precut notches under deformation. Autonomous self-healing at room temperature, both mechanical and electronic, is demonstrated through physical contact of two separate films. The composite film also shows device stability in the ambient environment over five months due to muchimproved barrier property to both oxygen and water. Butyl rubber is broadly applicable to various Ptype and N-type semiconducting polymers for fabricating self-healable electronics to provide new resilient electronics that mimic the tear resistance and healable property of human skin.

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