Enhanced SERS Stability of R6G Molecules with Monolayer Graphene

In this work, we used monolayer graphene, either underneath or on top of the R6G molecules, to enhance the stability and reproducibility of surface enhanced Raman spectroscopy (SERS). The time evolution of characteristic peaks of the organic molecules was monitored using Raman spectroscopy under continuous light irradiation to quantitatively characterize the photostability. Graphene underneath the organic molecules inhibits the substrate-induced fluctuations; and graphene on top of the organic molecules encapsulates and isolates them from ambient oxygen, greatly enhancing the photostability. Our results showed that the average lifespan of R6G molecules with graphene encapsulation can be increased by about 6-fold under high laser power density (3.67 × 10⁶ W/cm²) and is less dependent on the power density of light irradiation

Multifunctional Sensor Based on Porous Carbon Derived from Metal–Organic Frameworks for Real Time Health Monitoring

Flexible and sensitive sensors that can detect external stimuli such as pressure, temperature, and strain are essential components for applications in health diagnosis and artificial intelligence. Multifunctional sensors with the capabilities of sensing pressure and temperature simultaneously are highly desirable for health monitoring. Here, we have successfully fabricated a flexible and simply structured bimodal sensor based on metal–organic frameworks (MOFs) derived porous carbon (PC) and polydimethylsiloxane (PDMS) composite. Attributed to the porous structure of PC/PDMS composite, the fabricated sensor exhibits high sensitivity (15.63 kPa^–1), fast response time (<65 ms), and high durability (∼2000 cycles) for pressure sensing. Additionally, its application in detecting human motions such as subtle wrist pulses in real time has been demonstrated. Furthermore, the as-prepared device based on the PC/PDMS composite exhibits a good sensitivity (>0.11 °C^–1) and fast response time (∼100 ms), indicating its potential application in sensing temperature. All of these capabilities indicate its great potential in the applications of health monitoring and artificial skin for artificial intelligence system

Mass Transport Mechanism of Cu Species at the Metal/Dielectric Interfaces with a Graphene Barrier

The interface between the metal and dielectric is an indispensable part in various electronic devices. The migration of metallic species into the dielectric can adversely affect the reliability of the insulating dielectric and can also form a functional solid-state electrolyte device. In this work, we insert graphene between Cu and SiO₂ as a barrier layer and investigate the mass transport mechanism of Cu species through the graphene barrier using density functional theory calculations, second-ion mass spectroscopy (SIMS), capacitance–voltage measurement, and cyclic voltammetry. Our theoretical calculations suggest that the major migration path for Cu species to penetrate through the multiple-layered graphene is the overlapped defects larger than 0.25 nm². The depth-profile SIMS characterizations indicate that the “critical” thickness of the graphene barrier for completely blocking the Cu migration is 5 times smaller than that of the conventional TaN barrier. Capacitance–voltage and cyclic voltammetry measurement reveal that the electrochemical reactions at the Cu/SiO₂ interface become a rate-limiting factor during the bias-temperature stressing process with the use of a graphene barrier. These studies provide a distinct roadmap for designing controllable mass transport in solid-state electrolyte devices with the use of a graphene barrier

Ultrafast, Self-Driven, and Air-Stable Photodetectors Based on Multilayer PtSe₂/Perovskite Heterojunctions

We report on the large-scale synthesis of polycrystalline multilayer PtSe₂ film with typical semimetallic characteristics. With the availability of the large-area film, we constructed a heterojunction composed of multilayer PtSe₂ and Cs-doped FAPbI₃, which can function as a self-driven photodetector in a broadband wavelength from the ultraviolet to the near-infrared region. Further photoresponse analysis revealed that the heterojunction device showed outstanding photosensitive characteristics with a large <i>I</i>_light/<i>I</i>_dark ratio of 5.7 × 10³, high responsivity of 117.7 mA W^–1, and decent specific detectivity of 2.91 × 10¹² Jones at zero bias. More importantly, the rise/fall times were estimated to be 78/60 ns, rendering our device the fastest device among perovskite-2D photodetectors reported to date. In addition, it was also observed that the PtSe₂/perovskite photodetector can almost retain its photoresponse properties after storage in ambient conditions for 3 weeks. This study suggests the potential of the present PtSe₂/perovskite heterojunction for future air-stable ultrafast photodetecting applications

Uncooled Mid-Infrared Sensing Enabled by Chip-Integrated Low-Temperature-Grown 2D PdTe₂ Dirac Semimetal

Next-generation mid-infrared (MIR) imaging chips demand free-cooling capability and high-level integration. The rising two-dimensional (2D) semimetals with excellent infrared (IR) photoresponses are compliant with these requirements. However, challenges remain in scalable growth and substrate-dependence for on-chip integration. Here, we demonstrate the inch-level 2D palladium ditelluride (PdTe2) Dirac semimetal using a low-temperature self-stitched epitaxy (SSE) approach. The low formation energy between two precursors facilitates low-temperature multiple-point nucleation (∼300 °C), growing up, and merging, resulting in self-stitching of PdTe2 domains into a continuous film, which is highly compatible with back-end-of-line (BEOL) technology. The uncooled on-chip PdTe2/Si Schottky junction-based photodetector exhibits an ultrabroadband photoresponse of up to 10.6 μm with a large specific detectivity. Furthermore, the highly integrated device array demonstrates high-resolution room-temperature imaging capability, and the device can serve as an optical data receiver for IR optical communication. This study paves the way toward low-temperature growth of 2D semimetals for uncooled MIR sensing