High-Throughput Mechanical Exfoliation for Low-Cost Production of van der Waals Nanosheets.

A method is presented for scaling up the production of flakes of van der Waals materials via mechanical exfoliation. Using a roll-to-roll setup and an automatized, massive parallel exfoliation process, adhesive tapes with a high density of nanosheets of van der Waals materials are produced. The technique allows for obtaining a good trade-off between large lateral size and excellent area scalability, while also maintaining low cost. The potential of the method is demonstrated through the successful fabrication of field effect transistors and flexible photodetectors in large batches. This low-cost method to produce large area films out of mechanically exfoliated flakes is very general, and it can be applied to a variety of substrates and van der Waals materials and, moreover, it can be used to combine different van der Waals materials on top of each other. Therefore, it is believed that this production method opens an interesting avenue for fabrication of low-cost devices while maintaining a good scalability and performance.

Fabrication of a Postfunctionalizable, Biorepellent, Electroactive Polyurethane Interface on a Gold Surface by Surface-Assisted Polymerization.

This study describes surface-assisted (SurfAst) urethane polymerization, providing a modular/postfunctionalizable, biorepellent, electroactive ∼10 to 100 nm-thick polyurethane (PU) interface on a gold surface. SurfAst is a functionalization methodology based on sequential incubation steps of alkane diisocyanates and alkanediol monomers. The gold surface is functionalized by alkane diisocyanates in the first incubation step, and our theoretical calculations reveal that while the isocyanate group atoms (N, C, and O) at one end of the molecule exhibits strong interactions (∼900 meV) with surface atoms, the other end group remains unreacted. After the first incubation step, sequential alkanediol and alkane diisocyanate incubations provide formation of the PU interface. The extensive analysis of the PU interface has been conducted via X-ray photoelectron spectroscopy, and the chemical mapping verifies that the interface is made of PU moieties. The topographical analysis of the surface conducted by the atomic force microscopy shows that the PU interface consists of mostly a nanoporous texture with 150 nm total roughness. The adherence force mapping of the PU interface reveals that the nanoporous matrix exhibits an adhesion force of about 14 nN. The electrostatic force microscopy characterizing long-range electrostatic interactions (40 nm) shows that the PU interface has been attracted by positively charged species as compared to negative objects. Finally, it is demonstrated that the PU interface is readily postfunctionalizable by polyethylene glycol (PEG 1000), serving as a biorepellent interface and preserving electroactivity. We foresee that SurfAst polymerization will have potential for the facile fabrication of a postfunctionalizable and modular biointerface which might be utilized for biosensing and bioelectronic applications.