Characterization of Carbon Nanotube Fiber Compressive Properties Using Tensile Recoil Measurement

The tensile properties of carbon nanotube (CNT) fibers have been widely studied. However, the knowledge of their compressive properties is still lacking. In this work, the compressive properties of both pure CNT fibers and epoxy infiltrated CNT fibers were studied using the tensile recoil measurement. The compressive strengths were obtained as 416 and 573 MPa for pure CNT fibers and CNT–epoxy composite fibers, respectively. In addition, microscopic analysis of the fiber surface morphologies revealed that the principal recoil compressive failure mode of pure CNT fiber was kinking, while the CNT–epoxy composite fibers exhibited a failure mode in bending with combined tensile and compressive failure morphologies. The effect of resin infiltration on CNT fiber compressive properties, including the compressive strength and the deformation mode, is discussed. This work expands the knowledge base of the overall mechanical properties of CNT fibers, which are essential for their application in multifunctional composites

Microbuckling-Enhanced Electromagnetic-Wave-Absorbing Capability of a Stretchable Fe₃O₄/Carbon Nanotube/Poly(dimethylsiloxane) Composite Film

This paper reports enhancement of the electromagnetic (EM)-wave-absorbing capability of stretchable nanocomposites through the introduction of microbuckling. Three-dimentional composites are fabricated by laminating carbon nanotube films decorated with in situ grown Fe₃O₄ nanoparticles using a solvothermal process. The highly wavy morphology enhances the dispersion of EM-wave energy through multiple reflections and gives rise to higher active material content per unit area. The minimum reflection loss of −53.3 dB with a 8.1 GHz bandwidth is achieved for a three-layer buckled Fe₃O₄/carbon nanotube/poly­(dimethylsiloxane) composite, which is superior to the performance of the corresponding unbuckled composite. The fundamental EM-wave absorption mechanism of the composite is discussed. This research has demonstrated microbuckling as a viable approach to fabricating stretchable, broad-bandwidth, and efficient EM-wave-absorbing composites

Semiconductor SERS enhancement enabled by oxygen incorporation

<p>Semiconductor-based surface-enhanced Raman spectroscopy (SERS) substrates represent a new frontier in the field of SERS. However, the application of semiconductor materials as SERS substrates is still seriously impeded by their low SERS enhancement and inferior detection sensitivity, especially for non-metal-oxide semiconductor materials. Herein, we demonstrate a general oxygen-incorporation-assisted strategy to magnify the semiconductor substrate–analyte molecule interaction, leading to significant increase in SERS enhancement for non-metal-oxide semiconductor materials. Oxygen incorporation in MoS₂ even with trace concentrations can not only increase enhancement factors by up to 100,000 folds compared with oxygen-unincorporated samples, but also endow MoS₂ with low limit of detection below 10^-7 M. Intriguingly, combined with the findings in previous studies, our present results indicate that both oxygen incorporation and extraction processes can result in SERS enhancement, probably due to the enhanced charge-transfer resonance as well as exciton resonance arising from the judicious control of oxygen admission in semiconductor substrate.</p

Morphology-Controlled Synthesis of Hybrid Nanocrystals <i>via</i> a Selenium-Mediated Strategy with Ligand Shielding Effect: The Case of Dual Plasmonic Au–Cu_2–<i>x</i>Se

Integrating a plasmonic metal and a semiconductor at the nanoscale is of great importance for exploring their optical coupling properties. However, the synthesis and fine structural control of such nanostructures remain challenging. Herein we report the facile aqueous-phase Se-mediated overgrowth of metal selenides onto Au nanocrystals. Taking plasmonic Cu_2–<i>x</i>Se as an example, the introduction of a Se template allows deposition of large Cu_2–<i>x</i>Se crystalline grains onto Au nanocrystal seeds in various shapes, including spheres, rods, and plates. Moreover, the configuration of Au–Cu_2–<i>x</i>Se hybrids can be tuned from core–shell to heterodimer structure by controlling the growth behavior of the Se template. Se overgrowth depends critically on the absorption strength of stabilizers on Au seeds: a strongly absorbing stabilizer inhibits isotropic overgrowth, which is in agreement with molecular dynamics simulations. The resultant Au–Cu_2–<i>x</i>Se hybrid nanocrystals possess multiple surface plasmon resonance modes. Finally, our synthetic strategy can be extended to prepare other Au–metal selenide hybrids such as Au–Ag₂Se and Au–CdSe with controllable morphologies

Toward self-powered sensing and thermal energy harvesting in high-performance composites via self-folded carbon nanotube honeycomb structures

The development of high-performance self-powered sensors in advanced composites addresses the increasing demands of various fields such as aerospace, wearable electronics, healthcare devices, and the Internet-of-Things. Among different energy sources, the thermoelectric (TE) effect which converts ambient temperature gradients to electric energy is of particular interest. However, challenges remain on how to increase the power output as well as how to harvest thermal energy at the out-of-plane direction in high-performance fiber-reinforced composite laminates, greatly limiting the pace of advance in this evolving field. Herein, we utilize a temperature-induced self-folding process together with continuous carbon nanotube veils to overcome these two challenges simultaneously, achieving a high TE output (21 mV and 812 nW at a temperature difference of 17 °C only) in structural composites with the capability to harvest the thermal energy from out-of-plane direction. Real-time self-powered deformation and damage sensing is achieved in fabricated composite laminates based on a thermal gradient of 17 °C only, without the need of any external power supply, opening up new areas of autonomous self-powered sensing in high-performance applications based on TE materials.</p

Active Manipulation of NIR Plasmonics: the Case of Cu_2–<i>x</i>Se through Electrochemistry

Active control of nanocrystal optical and electrical properties is crucial for many of their applications. By electrochemical (de)­lithiation of Cu_2–<i>x</i>Se, a highly doped semiconductor, dynamic and reversible manipulation of its NIR plasmonics has been achieved. Spectroelectrochemistry results show that NIR plasmon red-shifted and reduced in intensity during lithiation, which can be reversed with perfect on–off switching over 100 cycles. Electrochemical impedance spectroscopy reveals that a Faradaic redox process during Cu_2–<i>x</i>Se (de)­lithiation is responsible for the optical modulation, rather than simple capacitive charging. XPS analysis identifies a reversible change in the redox state of selenide anion but not copper cation, consistent with DFT calculations. Our findings open up new possibilities for dynamical manipulation of vacancy-induced surface plasmon resonances and have important implications for their use in NIR optical switching and functional circuits

Omnidirectionally Stretchable High-Performance Supercapacitor Based on Isotropic Buckled Carbon Nanotube Films

The emergence of stretchable electronic devices has attracted intensive attention. However, most of the existing stretchable electronic devices can generally be stretched only in one specific direction and show limited specific capacitance and energy density. Here, we report a stretchable isotropic buckled carbon nanotube (CNT) film, which is used as electrodes for supercapacitors with low sheet resistance, high omnidirectional stretchability, and electro-mechanical stability under repeated stretching. After acid treatment of the CNT film followed by electrochemical deposition of polyaniline (PANI), the resulting isotropic buckled acid treated CNT@PANI electrode exhibits high specific capacitance of 1147.12 mF cm^–2 at 10 mV s^–1. The supercapacitor possesses high energy density from 31.56 to 50.98 μWh cm^–2 and corresponding power density changing from 2.294 to 28.404 mW cm^–2 at the scan rate from 10 to 200 mV s^–1. Also, the supercapacitor can sustain an omnidirectional strain of 200%, which is twice the maximum strain of biaxially stretchable supercapacitors based on CNT assemblies reported in the literature. Moreover, the capacitive performance is even enhanced to 1160.43–1230.61 mF cm^–2 during uniaxial, biaxial, and omnidirectional elongations

Wrapping Aligned Carbon Nanotube Composite Sheets around Vanadium Nitride Nanowire Arrays for Asymmetric Coaxial Fiber-Shaped Supercapacitors with Ultrahigh Energy Density

The emergence of fiber-shaped supercapacitors (FSSs) has led to a revolution in portable and wearable electronic devices. However, obtaining high energy density FSSs for practical applications is still a key challenge. This article exhibits a facile and effective approach to directly grow well-aligned three-dimensional vanadium nitride (VN) nanowire arrays (NWAs) on carbon nanotube (CNT) fiber with an ultrahigh specific capacitance of 715 mF/cm² in a three-electrode system. Benefiting from their intriguing structural features, we successfully fabricated a prototype asymmetric coaxial FSS (ACFSS) with a maximum operating voltage of 1.8 V. From core to shell, this ACFSS consists of a CNT fiber core coated with VN@C NWAs as the negative electrode, Na₂SO₄ poly­(vinyl alcohol) (PVA) as the solid electrolyte, and MnO₂/conducting polymer/CNT sheets as the positive electrode. The novel coaxial architecture not only fully enables utilization of the effective surface area and decreases the contact resistance between the two electrodes but also, more importantly, provides a short pathway for the ultrafast transport of axial electrons and ions. The electrochemical results show that the optimized ACFSS exhibits a remarkable specific capacitance of 213.5 mF/cm² and an exceptional energy density of 96.07 μWh/cm², the highest areal capacitance and areal energy density yet reported in FSSs. Furthermore, the device possesses excellent flexibility in that its capacitance retention reaches 96.8% after bending 5000 times, which further allows it to be woven into flexible electronic clothes with conventional weaving techniques. Therefore, the asymmetric coaxial architectural design allows new opportunities to fabricate high-performance flexible FSSs for future portable and wearable electronic devices