Photoluminescence from Single-Walled MoS$_2$ Nanotubes Coaxially Grown on Boron Nitride Nanotubes
Ming Liu, Kaoru Hisama, Yongjia Zheng, Mina Maruyama, Seungju Seo, Anton Anisimov, Taiki Inoue, Esko I. Kauppinen, Susumu Okada, Shohei Chiashi, Rong Xiang, Shigeo Maruyama
Single- and multi-walled molybdenum disulfide (MoS$_2$) nanotubes have been coaxially grown on small diameter boron nitride nanotubes (BNNTs) which were synthesized from heteronanotubes by removing single-walled carbon nanotubes (SWCNTs), and systematically investigated by optical spectroscopy. The strong photoluminescence (PL) from single-walled MoS$_2$ nanotubes supported by core BNNTs is observed in this work, which evidences a direct band gap structure for single-walled MoS$_2$ nanotubes with around 6 - 7 nm in diameter. The observation is consistent with our DFT results that the single-walled MoS$_2$ nanotube changes from an indirect-gap to a direct-gap semiconductor when the diameter of a nanotube is more than around 5 nm. On the other hand, when there are SWCNTs inside the heteronanotubes of BNNTs and MoS$_2$ nanotubes, the PL signal is considerably quenched. The charge transfer and energy transfer between SWCNTs and single-walled MoS$_2$ nanotubes were examined through characterizations by PL, XPS, and Raman spectroscopy. Unlike the single-walled MoS$_2$ nanotubes, multi-walled MoS$_2$ nanotubes do not emit light. Single- and multi-walled MoS$_2$ nanotubes exhibit different Raman features in both resonant and non-resonant Raman spectra. The method of assembling heteronanotubes using BNNTs as templates provides an efficient approach for exploring the electronic and optical properties of other transition metal dichalcogenide nanotubes.
Using density functional theory, the electronic structures of single walled molybdenum disulfide nanotubes (MoS$_2$ NTs) were investigated as a function of diameter. Our calculations show that the electronic structure near the band gap is sensitive to the NT diameter: armchair MoS$_2$ NTs act as indirect gap semiconductors for diameters up to approximately 5.0 nm, while armchair MoS$_2$ NTs with larger diameters act as direct gap semiconductors with band edges located in the vicinity of $k = 2π/3$. This finding implies that MoS$_2$ NTs with large diameters should exhibit similar photoluminesce…
We study the phonon modes in single-walled MoS$_{2}$ nanotubes via the lattice dynamics calculation and molecular dynamics simulation. The phonon spectra for tubes of arbitrary chiralities are calculated from the dynamical matrix constructed by the combination of an empirical potential with the conserved helical quantum numbers $(κ, n)$. In particular, we show that the frequency ($ω$) of the radial breathing mode is inversely proportional to the tube diameter ($d$) as $ω=665.3/d$ {cm$^{-1}$}. The eigen vectors of the first twenty lowest-frequency phonon modes are illustrated. Based on these ei…
Carbon nanotubes have been observed to emit ultraviolet, visible, and infrared radiation when exposed to microwave fields. We have performed experiments in which both single-walled (~1 nm diameters) and multi-walled carbon nanotubes (>50 nm diameters) were exposed to 2.45 GHz microwaves during several irradiation and cooling cycles at a pressure of ~10-6 torr. A comparison of the spectra of the radiation emitted by the nanotubes indicates that the intensity of radiation with wavelengths ranging from 700 to 1000 nm increased substantially during the course of five irradiation and cooling cycles…
The elasticity and piezoelectricity of zinc oxide (ZnO) crystals and single layers are investigated from the first-principles calculations. It is found that a ZnO thin film less than three Zn-O layers prefers a planar graphite-like structure to the wurtzite structure. ZnO single layers are much more flexible than graphite single layers in the elasticity and stronger than boron nitride single layers in the piezoelectricity. Single-walled ZnO nanotubes (SWZONTs) can exist in principle because of their negative binding energy. The piezoelectricity of SWZONTs depends on their chirality. For most Z…
We show that single walled carbon nanotubes with different isotope compositions exhibit distinct Raman Gband peaks and can be used for multiplexed multi-color Raman imaging of biological systems. Cancer cells with specific receptors are selectively labeled with 3 differently colored SWNTs conjugated with various targeting ligands including Herceptin, anti-Her2, Erbitux, anti-Her1, and RGD peptide, allowing for multi-color Raman imaging of cells in a multiplexed manner. SWNT Raman signals are highly robust against photo-bleaching, allowing long term imaging and tracking. With narrow peak featur…
Membranes of carbon allotropes comprised solely of densely packed pentagonal rings, known as pentagraphene, exhibit negative Poisson's ratio (auxetic behavior) and a bandgap of $3.2$ eV. In this work, we investigated the structural stability, mechanical and fracture properties of nanotubes formed by rolling up pentagraphene membranes, the so-called pentagraphene nanotubes (PGNTs). Single-walled PGNT of three distinct configurations: zigzag, $α$-armchair, and $β$-armchair were studied combining first-principles calculations and reactive molecular dynamics simulations. Our results showed Young's…
How carbon nanotubes behave in an external electric field? What will be the relation between the intensity of the electric field and the tube's deformation? What are the geometry effects on the response of carbon nanotubes to electric fields? To answer these questions, we have developed a new combined computational technique to study electrostatic field induced deformations of carbon nanotubes. In this work, we find that the deflection angle of cantilevered semiconducting single-walled carbon nanotubes is proportional to the square of the electric field strength, and the tubes can be most bent…
We compare the behavior of bond lengths, cross sectional shape and bulk modulus in equilibrium structure at ambient conditions and under hydrostatic pressure of all the three kinds of uncapped single walled carbon nanotubes. Results of our numerical calculations show that two bond lengths completely describe the structure of achiral SWNT whereas only one bond length is required to determine structure of chiral SWNT. In armchair tubes, one bond length is found to be larger than that of graphitic value while in zigzag tubes one bond length has a constant value. These bond lengths are very sensit…
Fullerence encapsulation has been proven to be a powerful approach to enhance mechanical and electronic properties of the single-walled carbon nanotubes (SWCNTs). However, some discrepancies emerge in recent studies of the fullerence encapsulation effect on the thermal conductivity of SWCNTs. More specifically, most previous theoretical works predicted slightly enhancement of the thermal conductivity, but the recent experiment by Kodama et al. (Nat. Mat. 16, 892 (2017)) observed clear reduction of the thermal conductivity in SWCNTs by fullerence encapsulation. We perform molecular dynamics sim…
Wavelength-dependent pump-probe spectroscopy of micelle-suspended single-walled carbon nanotubes reveals two-component dynamics. The slow component (5-20 ps), which has not been observed previously, is resonantly enhanced whenever the pump photon energy coincides with an absorption peak and we attribute it to interband carrier recombination, whereas we interpret the always-present fast component (0.3-1.2 ps) as intraband carrier relaxation in non-resonantly excited nanotubes. The slow component decreases drastically with decreasing pH (or increasing H$^+$ doping), especially in large-diameter …
Heat conduction in 1-dimensional anharmonic systems is anomalous in the sense that the conductivity κscales with a positive power of the system size, κ~ L^α. In two dimensions, previous simulations and theoretical arguments gave a logarithmic divergence. For rectangular systems of size L_\| x L_\perp there should be a cross-over from the 2-d to the 1-d behaviour as the aspect ratio r = L_\| / L_\perp increases from r=1 to r >> 1. When taking periodic boundary conditions in the transverse direction, this should be of direct relevance for the heat conduction in single-walled carbon nanotubes. In…
Single-walled carbon nanotubes (SWCNT) can be assembled into various macroscopic architectures, most notably continuous fibers and films, produced currently on a kilometer per day scale by floating catalyst chemical vapor depositionand spinning from an aerogel of CNTs. An attractive challenge is to produce continuous fibers with controlled molecular structure with respect to the diameter, chiral angle and ultimately(n,m)indices of the constituent SWCNT molecules. This work presents an extensive Raman spectroscopy and high resolution transmission electron microscopy study of SWCNT aerogels prod…
The results from mass spectrometry of clusters sputtered from Cs+ irradiated single-walled carbon nano-tubes (SWCNTs) as a function of energy and dose identify the nature of the resulting damage in the form of multiple vacancy generation. For pristine SWCNTs at all Cs+ energies, C2 is the most dominant species, followed by C3, C4 and C1. The experiments were performed in three stages: in the first stage, Cs+ energy E(Cs+) was varied. During the second stage, the nanotubes were irradiated continuously at E(Cs+) = 5 keV for 1,800 s. Afterwards, the entire sequence of irradiation energies was rep…
A boost in the development of flexible and wearable electronics facilitates the design of new materials to be applied as transparent conducting films (TCFs). Although single-walled carbon nanotube (SWCNT) films are the most promising candidates for flexible TCFs, they still do not meet optoelectronic requirements demanded their successful industrial integration. In this study, we proposed and thoroughly investigated a new approach that comprises simultaneous bilateral (outer and inner surfaces) SWCNT doping after their opening by thermal treatment at 400 C under an ambient air atmosphere. Dopi…
Synergistic Effect of Multi-Walled Carbon Nanotubes and Ladder-Type Conjugated Polymers on the Performance of N-Type Organic Electrochemical Transistors
Linear carbon chains (LCCs) have been shown to grow inside double-walled carbon nanotubes (DWCNTs) but isolating them from this hosting material represents one of the most challenging tasks towards applications. Herein we report the extraction and separation of LCCs inside single-wall carbon nanotubes (LCCs@SWCNTs) extracted from a double walled host LCCs@DWCNTs by applying a combined tip-ultrasonic and density gradient ultracentrifugation (DGU) process. High-resolution transmission electron microscopy (HRTEM), optical absorption, and Raman spectroscopy show that not only short LCCs but clearl…
Single-walled carbon nanotubes show promise as nanoscale transistors, for nanocomputing applications. This use will require appropriate methods for creating electrical connections between distinct nanotubes, analogous to welding of metallic wires at larger length scales, but methods for performing nanoscale chemical welding are not yet sufficiently understood. This study examined the effect of Ar bombardment on the junction of two crossed single-walled carbon nanotubes, to understand the value and limitations of this method for generating connections between nanotubes. A geometric criterion wa…
This review covers recent achievements in the studies of quantum properties of the novel carbon materials (fullerite C60 and bundles of single-walled nanotubes (SWNT)) saturated with such light-mass species as helium isotopes, the homonuclear molecular hydrogens, and neon. It is shown that even some heavy dopants demon-strate kinetic phenomena, in which coherent effects play an essential role. Two theoretical concepts are surveyed which have been suggested for the explanation of the anomalous phenomena in saturation kinetics and linear thermal expansion of doped C60. Most unusual effects have …
Constituting a part of odd electrons that are excluded from the covalent bonding, effectively unpaired electrons are posed by the singlet instability of the single-determinant broken spin-symmetry unrestricted Hartree-Fock (UBS HF) SCF solution. A correct determination of the total number of effectively unpaired electrons ND and its fraction on each atom NDA is well provided by the UBS HF solution. The NDA value is offered to be a quantifier of atomic chemical susceptibility (or equivalently, reactivity) thus highlighting targets that are the most favorable for addition reactions of any type. …
Detection of biomolecules is important in proteomics and clinical diagnosis and treatment of diseases. Here, we apply functionalized, macromolecular, single walled carbon nanotubes SWNTs as multi-color Raman labels to protein arrays for highly sensitive, multiplexed protein detection. Raman detection utilizes the sharp peaks of SWNTs with minimal background interference, affording a high signal to noise ratio needed for ultra-sensitive detection. Surface-enhanced Raman scattering SERS combined with the strong resonance Raman intensity of SWNTs, affords detection sensitivity down to 1 fM, a thr…
