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The excellent intrinsic properties of aligned nanofibers, such as carbon nanotubes (CNTs), and their ability to be easily formed into multifunctional 3D architectures motivate their use for a variety of commercial applications, such as batteries, chemical sensors for environmental monitoring, and energy harvesting devices. While controlling nanofiber adhesion to the growth substrate is essential for bulk-scale manufacturing and device performance, experimental approaches and models to date have not addressed tuning the CNT array–substrate adhesion strength with thermal processing conditions. In this work, facile “one-pot” thermal postgrowth processing (at temperatures Tp= 700–950 °C) is used to study CNT–substrate pull-off strength for millimeter-tall aligned CNT arrays. CNT array pull-off from the flat growth substrate (Fe/Al2O3/SiO2/Si wafers) via tensile testing shows that the array fails progressively, similar to the response of brittle microfiber bundles in tension. The pull-off strength evolves nonmonotonically with Tpin three regimes, first increasing by 10 times through Tp= 800 °C due to graphitization of disordered carbon at the CNT–catalyst interface, and then decreasing back to a weak interface through Tp= 950 °C due to diffusion of the Fe catalyst into the substrate, Al2O3crystallization, and substrate cracking. Failure is observed to occur at the CNT–catalyst interface below 750 °C, and the CNTs themselves break during pull-off after higher Tpprocessing, leaving residual CNTs on the substrate. Morphological and chemical analyses indicate that the Fe catalyst remains on the substrate after pull-off in all regimes. This work provides new insights into the interfacial interactions responsible for nanofiber–substrate adhesion and allows tuning to increase or decrease array strength for applications such as advanced sensors, energy devices, and nanoelectromechanical systems (NEMS).

Boron nitride nanotubes (BNNTs) possess a broad range of applications because of several engineering-relevant properties, including high specific strength and stiffness, thermal stability, and transparency to visible light. The morphology of these nanoscale fibers must be controlled to maximize such properties, which can be achieved by synthesizing long aligned arrays of crystalline hexagonal boron nitride (hBN) nanotubes. Herein, we synthesize high-quality millimeter length, vertically aligned (VA-) BNNTs using free-standing carbon nanotube (CNT) arrays as scaffolds. In addition to high optical transparency of the VA-BNNTs, we also demonstrate several micro- and macrostructures of BNNTs via patterning and/or postprocessing of the arrays, including engineering of either disconnected or interconnected tubes in VA-, horizontally aligned (HA-), or coherently buckled BNNTs. The internanotube spacings and interconnections between aligned BNNT can thus be tailored to create BN macrostructures with complex shapes and advantaged morphologies for hierarchical materials and devices.

Performance challenges as electronics continue to scale down motivate searches for new interconnect materials. In a recent report in Matter, Lipatov and coworkers demonstrate that MXene may be a candidate for interconnects by measuring conductivity and breakdown current density of Ti3C2Tx.

The chemical inertness of carbon nanotubes (CNT) requires some degree of “defect engineering” for controlled deposition of metal oxides through atomic layer deposition (ALD). The type, quantity, and distribution of such defects rules the deposition rate and defines the growth behavior. In this work, we employed ALD to grow titanium oxide (TiO2) on vertically aligned carbon nanotubes (VACNT). The effects of nitrogen doping and oxygen plasma pretreatment of the CNT on the morphology and total amount of TiO2were systematically studied using transmission electron microscopy, Raman spectroscopy, and thermogravimetric analysis. The induced chemical changes for each functionalization route were identified by X-ray photoelectron and Raman spectroscopies. The TiO2mass fraction deposited with the same number of cycles for the pristine CNT, nitrogen-doped CNT, and plasma-treated CNT were 8, 47, and 80%, respectively. We demonstrate that TiO2nucleation is dependent mainly on surface incorporation of heteroatoms and their distribution rather than structural defects that govern the growth behavior. Therefore, selecting the best way to functionalize CNT will allow us to tailor TiO2distribution and hence fabricate complex heterostructures.

Mesoporous silica nanoparticles (MCM-41) with different surface chemistry were used as carrier system to study its influence on drug delivery and anticancer activity of curcumin (CUR). CUR was encapsulated in pristine MCM-41 (hydrophilic and negatively charged), amino functionalized MCM-41 (MCM-41-NH2which is hydrophilic and positively charged), and methyl functionalized MCM-41 (MCM-41-CH3which is hydrophobic and negatively charged) and evaluated for in vitrorelease and cell cytotoxicity in human squamous cell carcinoma cell line (SCC25). Various techniques were employed to evaluate the performance of these materials on cellular uptake and anticancer activity in the SCC25 cell line. Both positively and negatively charged surfaces demonstrated enhanced drug release and anticancer activity compared to pure CUR. Positively charged nanoparticles showed higher cell uptake compared to negatively charged nanoparticles owing to its electrostatic interaction with cells. However, hydrophobic surface modified nanoparticles (MCM-41-CH3) showed no improvement in drug release and anticancer activity due to its poor wetting effect. Cell cycle analysis and cell apoptosis studies revealed different pathway mechanisms followed by the positively and negatively charged nanoparticles but exhibiting similar anticancer activity in SCC25 cells.

Heterogeneous materials possess unique combinations of strength, toughness, and multifunctionality, which are derived from the interplay between the different material constituents. The performance of such materials can be further improved via hierarchical architecting, including down to the nanoscale. Here, a novel hierarchical nanoengineered layered architecture is created by harnessing the coherent buckling of vertically aligned carbon nanotube (CNT) arrays followed by their integration with existing aerospace-grade carbon microfiber polymer-matrix advanced composites. In-plane tensile and interlaminar shear strengths are improved beyond the aerospace composite by ∼30% and 10%, respectively, and also beyond another CNT hierarchical architecture. Multiscale reinforcement mechanisms responsible for the strength enhancement, including nanofiber pullout, bridging, and suppression of delamination, are revealed by scanning electron microscopy and 3D X-ray computed tomography. The ability to design and create scalable, hierarchical materials with characteristic dimensions spanning from the nanoscale to the macroscale opens up a wide new avenue of next-generation advanced materials with enhanced mechanical and multifunctional properties.