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Atomically thin circuits have recently been explored for applications in nextgeneration electronics and optoelectronics and have been demonstrated with 2D lateral heterojunctions. In order to form true 2D circuitry from a single material, electronic properties must be spatially tunable. Here, tunable transport behavior is reported which is introduced into single layer tungsten diselenide and tungsten disulfide by focused He+ irradiation. Pseudometallic behavior is induced by irradiating the materials with a dose of ≈1 x 1016 He+ cm-2 to introduce defect states, and subsequent temperaturedependent transport measurements suggest a nearest neighbor hopping mechanism is operative. Scanning transmission electron microscopy and electron energy loss spectroscopy reveal that Se is sputtered preferentially, and extended percolating networks of edge states form within WSe2 at a critical dose of 1 x 1016 He+ cm-2. First-principle calculations confirm the semiconductor- to-metallic transition of WSe2 after pore and edge defects are introduced by He+ irradiation. The hopping conduction is utilized to direct-write resistor loaded logic circuits in WSe2 and WS2 with a voltage gain of greater than 5. Edge contacted thin film transistors are also fabricated with a high on/off ratio (>106), demonstrating potential for the formation of atomically thin circuits. [ABSTRACT FROM AUTHOR]

An in situ study is reported on the structural evolution in nanocluster films under He+ ion irradiation using an advanced helium ion microscope. The films consist of loosely interconnected nanoclusters of magnetite or iron-magnetite (Fe-Fe3O4) core-shells. The nanostructure is observed to undergo dramatic changes under ion-beam irradiation, featuring grain growth, phase transition, particle aggregation, and formation of nanowire-like network and nanopores. Studies based on ion irradiation, thermal annealing and electron irradiation have indicated that the major structural evolution is activated by elastic nuclear collisions, while both electronic and thermal processes can play a significant role once the evolution starts. The electrical resistance of the Fe-Fe3O4 films measured in situ exhibits a super-exponential decay with dose. The behavior suggests that the nanocluster films possess an intrinsic merit for development of an advanced online monitor for fast neutron radiation with both high detection sensitivity and long-term applicability, which can enhance safety measures in many nuclear operations. [ABSTRACT FROM AUTHOR]