RESUMEN
The intrinsically anisotropic crystallinity of two-dimensional (2D) transition metal dichalcogenide (2D TMD) layers enables a variety of intriguing material properties which strongly depend on the physical orientation of constituent 2D layers. For instance, 2D TMDs with vertically-aligned layers exhibit numerous dangling bonds on their 2D layer edge sites predominantly exposed on the surface, projecting significantly improved physical and/or chemical adsorption capability compared to their horizontally-oriented 2D layer counterparts. Such property advantages can be further promoted as far as the material can be integrated onto unconventional substrates of tailored geometry/functionality, offering vast opportunities for a wide range of applications which demand enhanced surface area/reactivity and mechanical flexibility. Herein, we report a new form of 2D TMDs, i.e., three-dimensionally ordered 2D molybdenum disulfide (2D MoS2) with vertically-aligned layers integrated on elastomeric substrates and explore their tunable multi-functionalities and technological promise. We grew large-scale (>2 cm2) vertically-aligned 2D MoS2 layers using a three-dimensionally patterned silicon dioxide (SiO2) template and directly transferred/integrated them onto flexible polydimethylsiloxane (PDMS) substrates by taking advantage of the distinguishable water-wettability of 2D MoS2vs. SiO2. The excellent structural integrity of the integrated vertical 2D MoS2 layers was confirmed by extensive spectroscopy/microscopy characterization. In addition, the stretch-driven unique tunability of their optical and surface properties was also examined. Moreover, we applied this material for flexible humidity sensing and identified significantly improved (>10 times) sensitivity over conventionally-designed horizontal 2D MoS2 layers, further confirming their high potential for unconventional flexible technologies.
RESUMEN
In this study, a two-step surface treatment was developed to restrain the rapid primary degradation of a biodegradable Mg alloy and to improve their biocompatibility. Micro arc oxidation (MAO) coating was performed in alkaline electrolytes such as 1.0 M NaOH with 0.1 M glycerol and 0.1 M Na3PO4. Hydrothermal treatment was performed in 0.1 M Ca-EDTA (C10H12CaN2Na2O8) and 0.5 M NaOH solution at 90 °C for different times (6, 12, 24, and 48 h). The film morphology and chemical properties were evaluated by XRD and FE-SEM. The electrochemical and corrosion behaviors were examined in the simulated body fluid, and cytotoxicity was assessed using MC3T3-E1 cells. After MAO coating, an oxide layer containing [Formula: see text] formed on the surface. During the hydrothermal treatment in Ca-EDTA solution, calcium phosphate and Mg(OH)2 were produced via a reaction between [Formula: see text] on the surface and Ca2+ in solution. The layer with ceramics and oxides was grown on the surface with increasing hydrothermal treatment time, and improved the surface corrosion resistance. The 24 h hydrothermal-treated group showed the lowest immersion corrosion rate and high cell viability. Therefore, this treatment was the most favorable surface modification for improving the initial corrosion resistance and bioactivity of the biodegradable Mg alloy.