MXenes, a new family of 2D materials, combine hydrophilic surfaces with metallic conductivity. Delamination of MXene produces single-layer nanosheets with thickness of about a nanometer and lateral size of the order of micrometers. The high aspect ratio of delaminated MXene renders it promising nanofiller in multifunctional polymer nanocomposites. Herein, Ti 3 C 2 T x MXene was mixed with either a charged polydiallyldimethylammonium chloride (PDDA) or an electrically neutral polyvinyl alcohol (PVA) to produce Ti 3 C 2 T x / polymer composites. The as-fabricated composites are flexible and have electrical conductivities as high as 2.2 × 10 4 S/m in the case of the Ti 3 C 2 T x /PVA composite film and 2.4 × 10 5 S/m for pure Ti 3 C 2 T x films. The tensile strength of the Ti 3 C 2 T x /PVA composites was significantly enhanced compared with pure Ti 3 C 2 T x or PVA films. The intercalation and confinement of the polymer between the MXene flakes not only increased flexibility but also enhanced cationic intercalation, offering an impressive volumetric capacitance of ∼530 F/cm 3 for MXene/PVA-KOH composite film at 2 mV/s. To our knowledge, this study is a first, but crucial, step in exploring the potential of using MXenes in polymer-based multifunctional nanocomposites for a host of applications, such as structural components, energy storage devices, wearable electronics, electrochemical actuators, and radiofrequency shielding, to name a few.he history of exfoliated, or delaminated, nanosheets (2D materials) dates back to the 1950s (1); however, few of the produced nanosheets are conductive. In recent years, 2D materials have been receiving increased attention, with graphene as the star material owing to its excellent electric, mechanical, and other properties (2-5). In 2011, our group reported on a new family of 2D early transition metal carbides, which combined metallic conductivity and hydrophilic surfaces (6). This novel 2D family was labeled MXenes to denote that they are produced by etching out the A layers from the layered M n+1 AX n phases (6-8) and their similarity to graphene (7).In the M n+1 AX n , or MAX, phases, "M" is an early transition metal, "A" is a group A (mainly groups 13-16) element, "X" is carbon and/or nitrogen, and n = 1, 2, or 3 (9). So far, the MXene family includes Ti 3 C 2 , Ti 2 C, (Ti 0.5, Nb 0.5 ) 2 C, (V 0.5 ,Cr 0.5 ) 3 C 2 , Ti 3 CN, Ta 4 C 3 (10), Nb 2 C, V 2 C (8), and Nb 4 C 3 (11). Because there are over 70 known MAX phases (9), many more MXenes can be expected. It is important to note here that MXene surfaces are terminated by O, OH, and/or F groups from the etching process. Henceforth, these terminated MXenes will be referred to as M n+1 X n T x , where T represents terminating groups (O, OH, and/or F) and x is the number of terminating groups.If they are not delaminated, MXenes are multilayered structures resembling those of exfoliated graphite, which have shown promising performance as electrodes in both lithium ion batteries and supercapacitors, as well as adsorbents for hea...
In this article, we review our recent work on mid-infrared (mid-IR) photonic materials and devices fabricated on silicon for on-chip sensing applications. Pedestal waveguides based on silicon are demonstrated as broadband mid-IR sensors. Our low-loss mid-IR directional couplers demonstrated in SiNx waveguides are useful in differential sensing applications. Photonic crystal cavities and microdisk resonators based on chalcogenide glasses for high sensitivity are also demonstrated as effective mid-IR sensors. Polymer-based functionalization layers, to enhance the sensitivity and selectivity of our sensor devices, are also presented. We discuss the design of mid-IR chalcogenide waveguides integrated with polycrystalline PbTe detectors on a monolithic silicon platform for optical sensing, wherein the use of a low-index spacer layer enables the evanescent coupling of mid-IR light from the waveguides to the detector. Finally, we show the successful fabrication processing of our first prototype mid-IR waveguide-integrated detectors.
Polymer multilayered nanocoating capable of concentrating various chemical substances at IR-ATR waveguide surfaces is described. The coating affinity to an analyte played a pivotal role in sensitivity enhancement of the IR-ATR measurements, since the unmodified waveguide did not show any analyte detection.
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