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Printed electronics are gaining significant interest due to their design flexibility, low fabrication cost, and rapid design-to-manufacturing turnaround. Conventional substrates for printed electronics are often based on nonbiodegradable polymers such as polyimide that pose high environmental challenges by creating massive e-waste and pollution. As the demand for printed electronics and sensors increases, the ability to print such devices on biodegradable substrates can provide a solution to such environmental problems. However, current printing technologies are based on liquids and inks that are incompatible with biodegradable substrates, such as paper. Here, we present a dry-printing process, namely, a dry additive nanomanufacturing (Dry-ANM) technique, for printing conductive silver lines and patterns on biodegradable papers for flexible hybrid papertronics. Pure and dry nanoparticles are generated by pulsed laser ablation of a silver target that is then transported through a nozzle and directed onto paper substrates, where they are deposited and laser-sintered in real time to form the desired pattern without damaging the paper. The effects of different printing parameters on the paper-burning threshold are investigated, and the electrical properties of the lines are characterized by using different line thicknesses and sintering laser power densities. In addition, the mechanical and electrical properties of the printed lines and patterns are evaluated by bending and twisting tests. Furthermore, the feasibility of printing silver on different paper types is demonstrated. This research can potentially lead to biodegradable and environmentally friendly printed electronics and sensors. 

Phonons are important lattice vibrations that affect the thermal, electronic, and optical properties of materials. In this work, we studied infrared phonon resonance in a prototype van der Waals (vdW) material—hexagonal boron nitride (hBN)—with the thickness ranging from monolayers to bulk, especially on ultra-thin crystals with atomic layers smaller than 20. Our combined experimental and modeling results show a systematic increase in the intensity of in-plane phonon resonance at the increasing number of layers in hBN, with a sensitivity down to one atomic layer. While the thickness-dependence of the phonon resonance reveals the antenna nature of our nanoscope, the linear thickness-scaling of the phonon polariton wavelength indicates the preservation of electromagnetic hyperbolicity in ultra-thin hBN layers. Our conclusions should be generic for fundamental resonances in vdW materials and heterostructures where the number of constituent layers can be conveniently controlled. The thickness-dependent phonon resonance and phonon polaritons revealed in our work also suggest vdW engineering opportunities for desired thermal and nanophotonic functionalities.