Needle-Like Multifunctional Biphasic Microfiber for Minimally Invasive Implantable Bioelectronics.

Implantable bioelectronics has attracted significant attention in electroceuticals and clinical medicine for precise diagnosis and efficient treatment of target diseases. However, conventional rigid implantable devices face challenges such as poor tissue-device interface and unavoidable tissue damage during surgical implantation. Despite continuous efforts to utilize various soft materials to address such issues, their practical applications remain limited. Here, a needle-like stretchable microfiber composed of a phase-convertible liquid metal (LM) core and a multifunctional nanocomposite shell for minimally invasive soft bioelectronics is reported. The sharp tapered microfiber can be stiffened by freezing akin to a conventional needle to penetrate soft tissue with minimal incision. Once implanted in vivo where the LM melts, unlike conventional stiff needles, it regains soft mechanical properties, which facilitate a seamless tissue-device interface. The nanocomposite incorporating with functional nanomaterials exhibits both low impedance and the ability to detect physiological pH, providing biosensing and stimulation capabilities. The fluidic LM embedded in the nanocomposite shell enables high stretchability and strain-insensitive electrical properties. This multifunctional biphasic microfiber conforms to the surfaces of the stomach, muscle, and heart, offering a promising approach for electrophysiological recording, pH sensing, electrical stimulation, and radiofrequency ablation in vivo.

Van der Waals Epitaxially Grown Molecular Crystal Dielectric Sb2O3 for 2D Electronics.

Two-dimensional (2D) semiconducting materials have attracted significant interest as promising candidates for channel materials owing to their high mobility and gate tunability at atomic-layer thickness. However, the development of 2D electronics is impeded due to the difficulty in formation of high-quality dielectrics with a clean and nondestructive interface. Here, we report the direct van der Waals epitaxial growth of a molecular crystal dielectric, Sb2O3, on 2D materials by physical vapor deposition. The grown Sb2O3 nanosheets showed epitaxial relations of 0 and 180° with the 2D template, maintaining high crystallinity and an ultrasharp vdW interface with the 2D materials. As a result, the Sb2O3 nanosheets exhibited a high breakdown field of 18.6 MV/cm for 2L Sb2O3 with a thickness of 1.3 nm and a very low leakage current of 2.47 × 10-7 A/cm2 for 3L Sb2O3 with a thickness of 1.96 nm. We also observed two types of grain boundaries (GBs) with misorientation angles of 0 and 60°. The 0°-GB with a well-stitched boundary showed higher electrical and thermal stabilities than those of the 60°-GB with a disordered boundary. Our work demonstrates a method to epitaxially grow molecular crystal dielectrics on 2D materials without causing any damage, a requirement for high-performance 2D electronics.

Electrically Confined Electroluminescence of Neutral Excitons in WSe2 Light-Emitting Transistors.

Monolayer transition metal dichalcogenides (TMDs) have drawn significant attention for their potential in optoelectronic applications due to their direct band gap and exceptional quantum yield. However, TMD-based light-emitting devices have shown low external quantum efficiencies as imbalanced free carrier injection often leads to the formation of non-radiative charged excitons, limiting practical applications. Here, electrically confined electroluminescence (EL) of neutral excitons in tungsten diselenide (WSe2) light-emitting transistors (LETs) based on the van der Waals heterostructure is demonstrated. The WSe2 channel is locally doped to simultaneously inject electrons and holes to the 1D region by a local graphene gate. At balanced concentrations of injected electrons and holes, the WSe2 LETs exhibit strong EL with a high external quantum efficiency (EQE) of ≈8.2 % at room temperature. These experimental and theoretical results consistently show that the enhanced EQE could be attributed to dominant exciton emission confined at the 1D region while expelling charged excitons from the active area by precise control of external electric fields. This work shows a promising approach to enhancing the EQE of 2D light-emitting transistors and modulating the recombination of exciton complexes for excitonic devices.