Ternary metal-oxy-chalcogenides are emerging as next-generation layered semiconductors beyond binary metal-chalcogenides (i.e., MoS 2 ). Among ternary metal-oxy-chalcogenides, especially Bi 2 O 2 Se has been demonstrated in field-effect transistors and photodetectors, exhibiting ultrahigh performance with robust air stability. The growth method for Bi 2 O 2 Se that has been reported so far is a powder sublimation based chemical vapor deposition. The first step for pursuing the practical application of Bi 2 O 2 Se as a semiconductor material is developing a gas-phase growth process. Here, we report a cracking metal−organic chemical vapor deposition (c-MOCVD) for the gas-phase growth of Bi 2 O 2 Se. The resulting Bi 2 O 2 Se films at very low growth temperature (∼300 °C) show single-crystalline quality. By taking advantage of the gas-phase growth, the precise phase control was demonstrated by modulating the partial pressure of each precursor. In addition, c-MOCVD-grown Bi 2 O 2 Se exhibits outstanding electrical and optoelectronic performance at room temperature without passivation, including maximum electron mobility of 127 cm 2 /(V•s) and photoresponsivity of 45134 A/W.

Flexible microneedles are important tools that allow access to the inside of biological tissue from the outside without surgery. However, it had been hard to realize microneedle sensor arrays on flexible substrates because of the difficulty of attaining a needle with a high Young's modulus for a selected area on a thin or soft substrate. In this work, we developed a microneedle sensor on a hybrid substrate based on high Young's modulus epoxy siloxane for the microneedles and low Young's modulus polydimethylsiloxane for the conformable substrate. Polyaniline was deposited on the microneedle for pH sensing. The mechanical durability of the device was assessed by insertion into pig skin 1000 times. Last, the flexible microneedle pH sensors showed their utility for monitoring pH distribution in rats in a peripheral artery diseases model.

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Reports have recently been published on ultrathin biofluid barriers, which enable the long‐term measurement of biological signals and exhibit conformability on nonlinear surfaces such as skin and organs. However, inorganic‐ and organic‐based barriers have process incompatibility and high water permeability, respectively. Siloxane‐ (inorganic) based fluorinated epoxy (organic) hybrid materials (FEH) are demonstrated for bio‐fluidic barrier and the biocompatibility and barrier performance for flexible electronic systems as solution‐processed oxide thin‐film transistors (TFTs) on 1.2 µm thick polyimide (PI) thin film substrate is confirmed. FEH thin film can be patterned as small as 10 µm through conventional photolithography. The fabricated solution‐processed indium oxide TFTs with FEH barriers exhibit durable performance over 16 h with no dramatic change of transfer characteristics in phosphate‐buffered saline (PBS) environment. Furthermore, to realize FEH barriers for flexible systems, the solution‐processed indium oxide TFTs with FEH barriers on ultrathin PI substrate are demonstrated subjected to compression test and successfully measure the electrical properties with no irreversible degradation during 1000 cycles of mechanical testing in PBS.

Recent developments in wearable and embeddable electronic devices in physiological condition, such as neuroprobe and electroceuticals, have brought forth the need for a reliable passivation layer against water permeation into the devices. On top of the excellent waterproof barrier performance, the passivation layers must also be equipped with stretchability and dermatoid softness for the reliable operation of the devices without failure in the wet environment. Here, this work demonstrates a stretchable, superhydrophobic coating with excellent water barrier performance. The stretchable water barrier coating is formed by depositing alternating layers of a highly stretchable, superhydrophobic copolymer and a crosslinked organosiloxane polymer via initiated chemical vapor deposition. During the deposition, the organosiloxane polymer penetrates into the free volume of superhydrophobic copolymer to form a highly mixed network at the interface. Accordingly, a five‐layered coating shows excellent water and molecular barrier performance with no sign of degradation even at 60% of tensile strain. Moreover, this barrier film formed by vapor deposition is uniformly deposited on the substrate surface regardless of the type and morphology of the substrate. The highly stretchable water barrier coating developed in this study will serve as a promising candidate material for the passivation of various stretchable device applications.