Gold-mediated exfoliation of ultralarge optoelectronically perfect monolayers with lateral dimensions up to ≈500 μm is reported. Electrical, optical, and X-ray photo-electron spectroscopy characterization show that the quality of the gold-exfoliated flakes is similar to that of tape-exfoliated flakes. Large-area flakes allow manufacturing of large-area mono-layer transition metal dichalcogenide electronics.

The Kerker preconditioner, based on the dielectric function of homogeneous electron gas, is designed to accelerate the self-consistent field (SCF) iteration in the density functional theory calculations. However, a question still remains regarding its applicability to the inhomogeneous systems. We develop a modified Kerker preconditioning scheme which captures the long-range screening behavior of inhomogeneous systems and thus improves the SCF convergence. The effectiveness and efficiency is shown by the tests on long-z slabs of metals, insulators, and metal-insulator contacts. For situations without a priori knowledge of the system, we design the a posteriori indicator to monitor if the preconditioner has suppressed charge sloshing during the iterations. Based on the a posteriori indicator, we demonstrate two schemes of the self-adaptive configuration for the SCF iteration.

Nanoparticles, often referred to as 'artifi cial atoms', can be arranged into 1D, [ 1 , 2 ] 2D, [3][4][5][6] and 3D assemblies, [ 7 , 8 ] in analogy to the formation of crystals by atoms and molecules in nature. These artifi cial solids exhibit unique collective optical, [ 9 ] electrical, [10][11][12] and magnetic properties, [ 13 ] which stem from the novel electronic properties of the individual nanoparticles and the coupling between neighboring building blocks. [ 14 ] Motivated by fundamental and practical interests, researchers have developed various techniques to assemble 2D nanoparticle arrays and investigated their properties. [ 9 , 12 , 15 ] Freestanding 2D nanoparticle arrays not only offer a new type of ultrathin, robust, and fl exible material, but also enable the study of substrate-free optical and electrical properties. [ 16 ] Thus far, freestanding nanoparticle membranes have been fabricated by embedding them in polymers, [ 17 , 18 ] crosslinking, [ 19 , 20 ] sintering, [ 21 ] layer-by-layer assembly, [ 22 ] and electrophoretic deposition. [ 23 ] These nanoparticle membranes, however, either lack the packing order or lose the intrinsic features of nanoparticle superlattices. Impressive progress has been made by two groups. Jaeger and co-workers self-assembled freestanding, close-packed nanoparticle arrays over prefabricated holes. [ 24 , 25 ] Interactions between ligand molecules rendered the fi lms freestanding without the need for polymer encapsulation or ligand crosslinking. This method is also applicable to binary nanocrystal superlattices. [ 26 ] Luo and co-workers demonstrated another strategy to fabricate freestanding nanoparticle superlattices, using DNA molecules as ligands. [ 27 ] Both groups characterized the mechanical properties of as-prepared freestanding nanoparticle arrays. Despite these advances, measurement of the substrate-free transport properties of freestanding nanoparticle superlattices requires techniques to manipulate them and integrate them into solid-state devices, although it remains a great experimental challenge.Herein, we present a feasible route for the preparation, transfer, and electrical measurements of monolayered freestanding nanoparticle sheets. Under a gas fl ow, freestanding nanoparticle arrays can be transferred from microgrids onto arbitrary solid substrates. We measured the electronic transport properties of nanoparticle sheets suspended over trenches, and found the scaling exponent to be signifi cantly different from that of substrate-supported nanoparticle arrays prepared by the same technique. Our method enables the investigation of the intrinsic transport properties of artifi cial assemblies and paves the way towards device applications of freestanding nanoparticle arrays. Figure 1 a shows a schematic representation of the homemade experimental setup used to prepare monolayered freestanding nanoparticle sheets over a microgrid. For the convenience of transmission electron microscopy (TEM) characterization, we used TEM grids. In our confi guration...

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