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Chemical doping can be used to control the charge-carrier polarity and concentration in two-dimensional van der Waals materials. However, conventional methods based on substitutional doping or surface functionalization result in the degradation of electrical mobility due to structural disorder, and the maximum doping density is set by the solubility limit of dopants. Here we show that a reversible laser-assisted chlorination process can be used to create high doping concentrations (above 3 × 1013 cm−2) in graphene monolayers with minimal drops in mobility. The approach uses two lasers—with distinct photon energies and geometric configurations—that are designed for chlorination and subsequent chlorine removal, allowing highly doped patterns to be written and erased without damaging the graphene. To illustrate the capabilities of our approach, we use it to create rewritable photoactive junctions for graphene-based photodetectors.more » « less
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Abstract Both amorphous and crystalline silicon are ubiquitous materials for electronics, photonics, and microelectromechanical systems. On‐demand control of Si crystallinity is crucial for device manufacturing and to overcome the limitations of current phase‐change materials (PCM) in active photonics. Fast reversible phase transformation in silicon, however, has never been accomplished due to the notorious challenge of amorphization. It is demonstrated that nanostructured Si can function as a PCM, since it can be reversibly crystallized and amorphized under nanosecond laser irradiation with different pulse energies. Reflection probing on a single nanodisk's phase transformations confirms the distinct mechanisms for crystallization and amorphization. The experimental results show that the relaxation time of undercooled silicon at 950 K is 10 ns. The phase change provides a 20% nonvolatile reflectivity modulation within 100 ns and can be repeated over 400 times. It is shown that such transformations are free of deformation upon solidification. Based on the switchable photonic properties in the visible spectrum, proof‐of‐concept experiments of dielectric color displays and dynamic wavefront control are shown. Therefore, nanostructured silicon is proposed as a chemically stable, deformation free, and complementary metal–oxide‐semiconductor compatible (CMOS) PCM for active photonics at visible wavelengths.
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Abstract Micro‐electromechanical (MEM) switches, with advantages such as quasi‐zero leakage current, emerge as attractive candidates for overcoming the physical limits of complementary metal‐oxide semiconductor (CMOS) devices. To practically integrate MEM switches into CMOS circuits, two major challenges must be addressed: sub 1 V operating voltage to match the voltage levels in current circuit systems and being able to deliver at least millions of operating cycles. However, existing sub 1 V mechanical switches are mostly subject to significant body bias and/or limited lifetimes, thus failing to meet both limitations simultaneously. Here 0.2 V MEM switching devices with ≳106safe operating cycles in ambient air are reported, which achieve the lowest operating voltage in mechanical switches without body bias reported to date. The ultralow operating voltage is mainly enabled by the abrupt phase transition of nanolayered vanadium dioxide (VO2) slightly above room temperature. The phase‐transition MEM switches open possibilities for sub 1 V hybrid integrated devices/circuits/systems, as well as ultralow power consumption sensors for Internet of Things applications.
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Abstract The unique correspondence between mathematical operators and photonic elements in wave optics enables quantitative analysis of light manipulation with individual optical devices. Phase‐transition materials are able to provide real‐time reconfigurability of these devices, which would create new optical functionalities via (re)compilation of photonic operators, as those achieved in other fields such as field‐programmable gate arrays (FPGA). Here, by exploiting the hysteretic phase transition of vanadium dioxide, an all‐solid, rewritable metacanvas on which nearly arbitrary photonic devices can be rapidly and repeatedly written and erased is presented. The writing is performed with a low‐power laser and the entire process stays below 90 °C. Using the metacanvas, dynamic manipulation of optical waves is demonstrated for light propagation, polarization, and reconstruction. The metacanvas supports physical (re)compilation of photonic operators akin to that of FPGA, opening up possibilities where photonic elements can be field programmed to deliver complex, system‐level functionalities.