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1. Aligned 2D carbon nanotube liquid crystals for wafer-scale electronics

   https://doi.org/10.1126/sciadv.abh0640  

   Jinkins, Katherine R.; Foradori, Sean M.; Saraswat, Vivek; Jacobberger, Robert M.; Dwyer, Jonathan H.; Gopalan, Padma; Berson, Arganthaël; Arnold, Michael S. (September 2021, Science Advances)

   Semiconducting carbon nanotubes promise faster performance and lower power consumption than Si in field-effect transistors (FETs) if they can be aligned in dense arrays. Here, we demonstrate that nanotubes collected at a liquid/liquid interface self-organize to form two-dimensional (2D) nematic liquid crystals that globally align with flow. The 2D liquid crystals are transferred onto substrates in a continuous process generating dense arrays of nanotubes aligned within ±6°, ideal for electronics. Nanotube ordering improves with increasing concentration and decreasing temperature due to the underlying liquid crystal phenomena. The excellent alignment and uniformity of the transferred assemblies enable FETs with exceptional on-state current density averaging 520 μA μm −1 at only −0.6 V, and variation of only 19%. FETs with ion gel top gates demonstrate subthreshold swing as low as 60 mV decade −1 . Deposition across a 10-cm substrate is achieved, evidencing the promise of 2D nanotube liquid crystals for commercial semiconductor electronics. 

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2. Chemical and topographical patterns combined with solution shear for selective-area deposition of highly-aligned semiconducting carbon nanotubes

   https://doi.org/10.1039/d1na00033k  

   Dwyer, Jonathan H.; Suresh, Anjali; Jinkins, Katherine R.; Zheng, Xiaoqi; Arnold, Michael S.; Berson, Arganthaël; Gopalan, Padma (March 2021, Nanoscale Advances)

   null (Ed.)

   Selective deposition of semiconducting carbon nanotubes (s-CNTs) into densely packed, aligned arrays of individualized s-CNTs is necessary to realize their potential in semiconductor electronics. We report the combination of chemical contrast patterns, topography, and pre-alignment of s-CNTs via shear to achieve selective-area deposition of aligned arrays of s-CNTs. Alternate stripes of surfaces favorable and unfavorable to s-CNT adsorption were patterned with widths varying from 2000 nm down to 100 nm. Addition of topography to the chemical contrast patterns combined with shear enabled the selective-area deposition of arrays of quasi-aligned s-CNTs (∼14°) even in patterns that are wider than the length of individual nanotubes (>500 nm). When the width of the chemical and topographical contrast patterns is less than the length of individual nanotubes (<500 nm), confinement effects become dominant enabling the selective-area deposition of much more tightly aligned s-CNTs (∼7°). At a trench width of 100 nm, we demonstrate the lowest standard deviation in alignment degree of 7.6 ± 0.3° at a deposition shear rate of 4600 s −1 , while maintaining an individualized s-CNT density greater than 30 CNTs μm −1 . Chemical contrast alone enables selective-area deposition, but chemical contrast in addition to topography enables more effective selective-area deposition and stronger confinement effects, with the advantage of removal of nanotubes deposited in spurious areas via selective lift-off of the topographical features. These findings provide a methodology that is inherently scalable, and a means to deposit spatially selective, aligned s-CNT arrays for next-generation semiconducting devices. 

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3. Vertically aligned carbon nanotubes from premade binary metal oxide nanoparticles on bare SiO2

   https://doi.org/10.1016/j.carbon.2025.120086  

   Hoque, Abdul; Nawarathne, Chaminda P; Alvarez, Noe T (March 2025, Carbon)

   Liu, Chang (Ed.)

   The synthesis of carbon nanotubes (CNTs) requires well-defined catalyst nanoparticles that can influence both diameter and chirality. Herein, catalyst nanoparticles containing both the catalyst and catalyst support material were developed. Bimetallic aluminum oxide–iron oxide (AlOx–Fe2O3) nanorice was synthesized from a mixture containing both aluminum and iron oleate precursors in the solution phase. The nanoparticles were assembled as a monolayer film on a silicon oxide (SiO2) substrate via organic linker molecules to synthesize vertically aligned carbon nanotubes (VA-CNTs). Microscopic and spectroscopic characterization of the premade catalyst nanoparticles and monolayer film assembly revealed the quality of the nanoscale assembly, which facilitated the successful growth of VA-CNTs. The length of the CNTs synthesized using these AlOx–Fe2O3 nanorice catalyst nanoparticles surpassed that of previously reported CNTs grown on bare SiO2 surfaces without oxide buffer layers. In addition, the CNTs appeared to be directly bonded/connected to the SiO2 substrate, suggesting CNT formation via the tip-growth mechanism. The effects of growth temperature and catalyst reduction time were evaluated to obtain high-yield VA-CNTs. 

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4. Modeling Solution Drying by Moving a Liquid-Vapor Interface: Method and Applications

   https://doi.org/10.3390/polym14193996  

   Tang, Yanfei; McLaughlan, John E.; Grest, Gary S.; Cheng, Shengfeng (October 2022, Polymers)

   A method of simulating the drying process of a soft matter solution with an implicit solvent model by moving the liquid-vapor interface is applied to various solution films and droplets. For a solution of a polymer and nanoparticles, we observe “polymer-on-top” stratification, similar to that found previously with an explicit solvent model. Furthermore, “polymer-on-top” is found even when the nanoparticle size is smaller than the radius of gyration of the polymer chains. For a suspension droplet of a bidisperse mixture of nanoparticles, we show that core-shell clusters of nanoparticles can be obtained via the “small-on-outside” stratification mechanism at fast evaporation rates. “Large-on-outside” stratification and uniform particle distribution are also observed when the evaporation rate is reduced. Polymeric particles with various morphologies, including Janus spheres, core-shell particles, and patchy particles, are produced from drying droplets of polymer solutions by combining fast evaporation with a controlled interaction between the polymers and the liquid-vapor interface. Our results validate the applicability of the moving interface method to a wide range of drying systems. The limitations of the method are pointed out and cautions are provided to potential practitioners on cases where the method might fail. 

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5. Premade Nanoparticle Films for the Synthesis of Vertically Aligned Carbon Nanotubes

   https://doi.org/10.3390/c7040079  

   Hoque, Abdul; Ullah, Ahamed; Guiton, Beth S.; Alvarez, Noe T. (December 2021, C)

   Carbon nanotubes (CNTs) offer unique properties that have the potential to address multiple issues in industry and material sciences. Although many synthesis methods have been developed, it remains difficult to control CNT characteristics. Here, with the goal of achieving such control, we report a bottom-up process for CNT synthesis in which monolayers of premade aluminum oxide (Al2O3) and iron oxide (Fe3O4) nanoparticles were anchored on a flat silicon oxide (SiO2) substrate. The nanoparticle dispersion and monolayer assembly of the oleic-acid-stabilized Al2O3 nanoparticles were achieved using 11-phosphonoundecanoic acid as a bifunctional linker, with the phosphonate group binding to the SiO2 substrate and the terminal carboxylate group binding to the nanoparticles. Subsequently, an Fe3O4 monolayer was formed over the Al2O3 layer using the same approach. The assembled Al2O3 and Fe3O4 nanoparticle monolayers acted as a catalyst support and catalyst, respectively, for the growth of vertically aligned CNTs. The CNTs were successfully synthesized using a conventional atmospheric pressure-chemical vapor deposition method with acetylene as the carbon precursor. Thus, these nanoparticle films provide a facile and inexpensive approach for producing homogenous CNTs. 

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