Additional SEM and TEM images. from Revisiting behaviour of monometallic catalysts in chemical vapour deposition synthesis of single-walled carbon nanotubes

Figure S1 Original SEM image of SWNTs grown from Co catalyst on TEM grid; Figure S2 Original TEM images of Ni catalyst before and after growth; Figure S3 Original SEM image of SWNTs grown from Fe catalyst on suspended SiO2; Figure S4 Original TEM image of SWNTs grown from Fe catalyst on suspended SiO2; Figure S5 Original TEM images of Cu catalyst after SWNT growth; Figure S6 Original TEM images of Pd catalyst after reduction

Tunable Electrical and Thermal Transport in Ice-Templated Multilayer Graphene Nanocomposites through Freezing Rate Control

We demonstrate tunable electrical and thermal conductivities through freezing rate control in solution-based nanocomposites. For a prototypical suspension of 1 vol % multilayer graphene suspended in hexadecane, the solid–liquid electrical conductivity contrast ratio can be tuned from 1 to 4.5 orders of magnitude for freezing rates between 10² and 10^–3 °C/min. We hypothesize that this dramatic variation stems from ice-templating, whereby crystal growth drives nanoparticles into concentrated intercrystal regions, increasing the percolation pathways and reducing the internanoparticle electrical resistance. Optical microscopy supports the ice-templating hypothesis, as these dramatic property changes coincide with changing crystal size. Under the same range of freezing rates, the nanocomposite solid–liquid thermal conductivity contrast ratio varies between 2.3 and 3.0, while pure hexadecane’s varies between 2.1 and 2.6. The nanocomposite’s thermal conductivity contrast ratios and solid phase enhancements are greater than effective medium theory predictions. We suggest this is due to ice-templating, consistent with our electrical measurements, as well as nanoparticle-induced molecular alignment of alkanes

Reversible Diameter Modulation of Single-Walled Carbon Nanotubes by Acetonitrile-Containing Feedstock

Changing the carbon feedstock from pure ethanol to a 5 vol % mixture of acetonitrile in ethanol during the growth of vertically aligned single-walled carbon nanotubes (SWNTs) reduces the mean diameter of the emerging SWNTs from approximately 2 to 1 nm. We show this feedstock-dependent change is reversible and repeatable, as demonstrated by multilayered vertically aligned SWNT structures. The reversibility of this process and lack of necessity for catalyst modification provides insight into the role of nitrogen in reducing the SWNT diameter

Photocurrent Quantum Yield of Semiconducting Carbon Nanotubes: Dependence on Excitation Energy and Exciton Binding Energy

We address the dependence of the relative photocurrent quantum yield (QY) on the excitation energy and the exciton binding energy of semiconducting single-walled carbon nanotubes (s-SWNTs) having well-defined chiral indexes, by analyzing both the optical absorption and the photocurrent spectra. First, we examine the QY of a sample consisting of one sort of nanotube (such as (7,5)), which allows revealing that QY depends on the excitation energy and hence on the nature of the electronic transition. In particular, we demonstrate that the QY of the second excitonic transition (<i>E</i>₂₂) is relatively higher than that of the first excitonic transition (<i>E</i>₁₁). Then, we extend the analysis to a sample consisting of five kinds of nanotubes (namely, (7,5), (7,6), (8,6), (8,7), (9,7)), which permits demonstrating for the first time that QY increases with increasing the nanotube’s diameter and with decreasing the exciton binding energy, according to two categories known as type 1 and type 2 nanotubes. Finally, we discuss these results in the framework of the electric-field-assisted exciton dissociation model in order to gain further insight into the photocarrier generation mechanism in s-SWNTs

On-Chip Sorting of Long Semiconducting Carbon Nanotubes for Multiple Transistors along an Identical Array

Ballistic transport and sub-10 nm channel lengths have been achieved in transistors containing one single-walled carbon nanotube (SWNT). To fill the gap between single-tube transistors and high-performance logic circuits for the replacement of silicon, large-area, high-density, and purely semiconducting (s-) SWNT arrays are highly desired. Here we demonstrate the fabrication of multiple transistors along a purely semiconducting SWNT array <i>via</i> an on-chip purification method. Water- and polymer-assisted burning from site-controlled nanogaps is developed for the reliable full-length removal of metallic SWNTs with the damage to s-SWNTs minimized even in high-density arrays. All the transistors with various channel lengths show large on-state current and excellent switching behavior in the off-state. Since our method potentially provides pure s-SWNT arrays over a large area with negligible damage, numerous transistors with arbitrary dimensions could be fabricated using a conventional semiconductor process, leading to SWNT-based logic, high-speed communication, and other next-generation electronic devices

Highly Stable and Tunable n‑Type Graphene Field-Effect Transistors with Poly(vinyl alcohol) Films

The intrinsic p-type behavior of graphene field-effect transistors (FETs) under ambient conditions poses a fundamental challenge for the assembly of complex electronic devices, such as integrated circuits. In this work, we present a protocol for tunable n-type doping of graphene FETs via poly­(vinyl alcohol) (PVA) coating. Using graphene grown by alcohol catalytic chemical vapor deposition, functionalization of the surface by this hydroxyl anion-rich polymer results in an evolution of the FETs from p-type to ambipolar or n-type even under ambient air conditions. The doping level of graphene is strongly related to the PVA film coating parameters, such as solution concentration, hardening temperature, and hardening time. This PVA coating proves to be a simple and stable approach to tuning the Dirac point and doping level of graphene, which is highly desirable and of great significance for the future of graphene-based electronic devices

Effect of Gas Pressure on the Density of Horizontally Aligned Single-Walled Carbon Nanotubes Grown on Quartz Substrates

We investigate the influence of gas pressure on the growth of horizontally aligned single-walled carbon nanotubes (SWCNTs) on R-cut and r-cut crystal quartz substrates by alcohol catalytic chemical vapor deposition (CVD). The density of horizontally aligned SWCNTs was found to depend highly on gas pressure. A study of the SWCNT growth as a function of CVD time revealed that the density of horizontally aligned SWCNTs continued to increase for 10 min at reduced pressure, whereas the density saturated rapidly at higher pressure even though catalysts were not deactivated. We argue that variation of incubation time for low-pressure CVD is key for independent growth of horizontally aligned SWCNTs and hence higher density growth

Growth Analysis of Single-Walled Carbon Nanotubes Based on Interatomic Potentials by Molecular Dynamics Simulation

Molecular dynamics simulation was performed to understand the growth mechanism of single-walled carbon nanotubes (SWNTs) by using the Brenner–Tersoff potential as the interaction among carbon atoms (C–C) and the Tersoff-type potential as the interaction between carbon and metal (C–M) and between metal and metal atoms (M–M). The potential functions for C–M and M–M bonds were established from the results of ab initio calculations. The growth of high-quality SWNTs was simulated at a suitable temperature and supply ratio of carbon atoms. The potential energy of carbon atoms was strongly dependent on the number of C–C and C–M bonds. The dependence explains the growth process, including cap formation, its lift-off, and the continuous SWNT growth

Diameter Modulation of Vertically Aligned Single-Walled Carbon Nanotubes

We demonstrate wide-range diameter modulation of vertically aligned single-walled carbon nanotubes (SWNTs) using a wet chemistry prepared catalyst. In order to ensure compatibility to electronic applications, the current minimum mean diameter of 2 nm for vertically aligned SWNTs is challenged. The mean diameter is decreased to about 1.4 nm by reducing Co catalyst concentrations to 1/100 or by increasing Mo catalyst concentrations by five times. We also propose a novel spectral analysis method that allows one to distinguish absorbance contributions from the upper, middle, and lower parts of a nanotube array. We use this method to quantitatively characterize the slight diameter change observed along the array height. On the basis of further investigation of the array and catalyst particles, we conclude that catalyst aggregationrather than Ostwald ripeningdominates the growth of metal particles

van der Waals SWCNT@BN Heterostructures Synthesized from Solution-Processed Chirality-Pure Single-Wall Carbon Nanotubes

Single-wall carbon nanotubes in boron nitride (SWCNT@BN) are one-dimensional van der Waals heterostructures that exhibit intriguing physical and chemical properties. As with their carbon nanotube counterparts, these heterostructures can form from different combinations of chiralities, providing rich structures but also posing a significant synthetic challenge to controlling their structure. Enabled by advances in nanotube chirality sorting, clean removal of the surfactant used for solution processing, and a simple method to fabricate free-standing submonolayer films of chirality pure SWCNTs as templates for the BN growth, we show it is possible to directly grow BN on chirality enriched SWCNTs from solution processing to form van der Waals heterostructures. We further report factors affecting the heterostructure formation, including an accelerated growth rate in the presence of H2, and significantly improved crystallization of the grown BN, with the BN thickness controlled down to one single BN layer, through the presence of a Cu foil in the reactor. Transmission electron microscopy and electron energy-loss spectroscopic mapping confirm the synthesis of SWCNT@BN from the solution purified nanotubes. The photoluminescence peaks of both (7,5)- and (8,4)-SWCNT@BN heterostructures are found to redshift (by ∼10 nm) relative to the bare SWCNTs. Raman scattering suggests that the grown BN shells pose a confinement effect on the SWCNT core