Radial Breathing Mode Research Articles

The use of 1D carbon nanotube interacting with caffeine molecules for applications in solar cells: structure optimisation, Raman analysis and optoelectronic properties

This study proposes a promising candidate for organic solar cells through the creation of a novel nano-hybrid system composed of caffeine molecules encapsulated within a semiconducting single-walled carbon nanotube known as NT14 (14,0). The stability and optoelectronic properties of this hybrid system, designated as CA@NT14, were thoroughly investigated. We determined the optimal diameter for the NT14 nanotube using molecular mechanics, Density Functional Theory, spectral moment’s method, and bond polarizability model, finding it to be approximately 1.18 nm. The encapsulation’s impact on the Raman-active modes, specifically the radial breathing mode and tangential mode, was analyzed through Raman spectra calculations, revealing structural stability and charge transfer from CA to NT14. Notably, the NT14’s Fermi level position increased upon encapsulation, indicating charge transfer and a type-II band alignment. The study further examined the bandgap characteristics of the hybrid system, finding that the encapsulation of CA within semiconducting NT14 nanotubes minimally impacts the nanotube’s bandgap, thus retaining its excellent visible light absorption properties. Conversely, encapsulating CA within metallic nanotubes significantly reduces their bandgap, limiting their light absorption range. The nonresonant Raman responses of NT14 pre- and post-encapsulation corroborated the charge transfer between CA and NT14. Future research will focus on computing the electronic transport characteristics, transmission spectra, I-V characteristics, and yield of CA@NT14 using DFT and Non-Equilibrium Green’s Function ( formalism. An experimental study will be conducted to validate these theoretical findings. These results indicate the potential of CA@NT14 hybrids as effective active layers in organic solar cells, highlighting their significance in advancing optoelectronic applications.

Coherent Phonon Dynamics in Plasmonic Gold Tetrahedral Nanoparticle Ensembles.

Coherent phonon modes supported by plasmonic nanoparticles offer prospective applications in chemical and biological sensing. Whereas the characterization of these phonon modes often requires single-particle measurements, synthetic routes to narrow size distributions of nanoparticles permit ensemble investigations. Recently, the synthesis of highly monodisperse gold tetrahedral nanoparticles with tunable edge lengths and corner sharpnesses has been developed. Herein, we characterize a size series of these nanoparticles in colloidal dispersion via transient absorption spectroscopy to examine their mechanical and plasmonic responses upon photoexcitation. Oscillations of transient absorption signals are observed in the plasmon resonance and correspond to the lowest-order radial breathing modes of the nanoparticles, the frequencies of which are affected by the edge length and truncation of the corners. Homogeneous quality factor values ranging from 24 to 34 are observed for the oscillations that convey potential utility in mass-sensing and plasmon-exciton-coupling photonics schemes. Finite-difference time domain and finite element analysis calculations establish specific optically relevant phonon modes.

Extended Kataura plot of single-walled carbon nanotubes and on-demand fabrication of mixed-dimensional heterostructures

We present a comprehensive optical spectroscopic study on air-suspended single-walled carbon nanotubes (SWNTs) with diameters ranging from 1.7 nm to 3.4 nm and at higher-order optical transitions, a previously inaccessible regime. We establish an atlas of resonant radial breathing modes (RBMs) for more than 100 new SWNTs in this unknown regime, thus significantly extending the RBM dataset in Kataura plot and enhancing our knowledge of SWNTs. Additionally, we develop an innovative transfer technique for manipulating individual SWNTs of known chiralities (determined by optical spectroscopies) by integrating a polarization imaging technique with the conventional van der Waals (vdW) dry transfer. The unprecedented spatial and structural control of this technique enables a deterministic fabrication and integration of a variety of novel mixed-dimensional vdW heterostructures that were considered unachievable before. Our work significantly extends RBM dataset of SWNT Kataura plot and represents a huge advancement towards controlled fabrication and integration of mixed-dimensional vdW heterostructures encompassing one-dimensional vdW materials.

(Invited) Collective Radial Breathing Modes in Homogeneous Nanotube Bundles

Carbon nanotubes (CNTs) exist in many atomic structures typically grow as mixtures of of many chiralities with a vast variety of properties. Identical CNTs that are arranged into two-dimensional hexagonal lattices, their vibrational properties have been predicted to change with additional low-frequency modes appearing in the Raman spectrum. [1] Up to now, the experimental study of collective vibrations has been limited by a lack of pure homogeneous chirality bundles. We overcome this challenge by employing a self-coil mechanism of a very long CNT that loop into itself during the growth process resulting in a tightly packed hexagonal stack [2]. This lattice is perfectly homogeneous in terms of diameter, chiral twist, and even handedness of the tube. By characterizing and comparing the physical properties of the coil with respect to its tails, the bundling effects are clearly visible. We report on two breathing-like modes for quasi-infinite bundles, compared to the single radial breathing mode characteristic for isolated tubes. The exciton-phonon coupling in these modes is probed with resonant Raman spectroscopy, revealing the same resonance energy for both breathing-like peaks. Additionally, we study the dependence of vibrational coupling on the tube diameter by analysing different tube’s diameter coils and other bundling geometries. Our experimental findings align well with previously reported theoretical studies, demonstrating a 1/d scaling for all modes, as well as confirming the relative shift of the modes dependent on intertube interaction. These vibrations provide insight into the role of intertube lattice dynamics in two-dimensional THz-range phononic crystals.[1] Popov, V. N.; Henrard, L. Evidence for the existence of two breathinglike phonon modes in infinite bundles of single-walled carbon nanotubes. Phys. Rev. B 2001, 63, 233407[2] Nakar, D.; Gordeev, G.; Machado, L. D.; Popovitz-Biro, R.; Rechav, K.; Oliveira, E. F.; Kusch, P.; Jorio, A.; Galvao, D. S.; Reich, S.; others Few-wall Carbon Nanotube Coils. Nano Letters 2019, 20, 953–962.

Ultralow-Frequency Tip-Enhanced Raman Scattering Discovers Nanoscale Radial Breathing Mode on Strained 2D Semiconductors.

Collective excitations including plasmons, magnons, and layer-breathing vibration modes emerge at an ultralow frequency (<1 THz) and are crucial for understanding van der Waals materials. Strain at the nanoscale can drastically change the property of van der Waals materials and create localized states like quantum emitters. However, it remains unclear how nanoscale strain changes collective excitations. Herein, ultralow-frequency tip-enhanced Raman spectroscopy (TERS) with sub-10nm resolution under ambient conditions is developed to explore the localized collective excitation on monolayer semiconductors with nanoscale strains. A new vibrational mode is discovered at around 12 cm-1 (0.36 THz) on monolayer MoSe2 nanobubbles and it is identified as the radial breathing mode (RBM) of the curved monolayer. The correlation is determined between the RBM frequency and the strain by simultaneously performing deterministic nanoindentation and TERS measurement on monolayer MoSe2. The generality of the RBM in nanoscale curved monolayer WSe2 and bilayer MoSe2 is demonstrated. Using the RBM frequency, the strain of the monolayer MoSe2 on the nanoscale can be mapped. Such an ultralow-frequency vibration from curved van der Waals materials provides a new approach to study nanoscale strains and points to more localized collective excitations to be discovered at the nanoscale.

Environmental damping and vibrational coupling of confined fluids within isolated carbon nanotubes

Because of their large surface areas, nanotubes and nanowires demonstrate exquisite mechanical coupling to their surroundings, promising advanced sensors and nanomechanical devices. However, this environmental sensitivity has resulted in several ambiguous observations of vibrational coupling across various experiments. Herein, we demonstrate a temperature-dependent Radial Breathing Mode (RBM) frequency in free-standing, electron-diffraction-assigned Double-Walled Carbon Nanotubes (DWNTs) that shows an unexpected and thermally reversible frequency downshift of 10 to 15%, for systems isolated in vacuum. An analysis based on a harmonic oscillator model assigns the distinctive frequency cusp, produced over 93 scans of 3 distinct DWNTs, along with the hyperbolic trajectory, to a reversible increase in damping from graphitic ribbons on the exterior surface. Strain-dependent coupling from self-tensioned, suspended DWNTs maintains the ratio of spring-to-damping frequencies, producing a stable saturation of RBM in the low-tension limit. In contrast, when the interior of DWNTs is subjected to a water-filling process, the RBM thermal trajectory is altered to that of a Langmuir isobar and elliptical trajectories, allowing measurement of the enthalpy of confined fluid phase change. These mechanisms and quantitative theory provide new insights into the environmental coupling of nanomechanical systems and the implications for devices and nanofluidic conduits.

Collective radial breathing modes in homogeneous nanotube bundles

We present a Raman study of the collective vibrations arising from the homogeneous bundling of single-walled carbon nanotubes and analyze the dependence of their vibrational coupling on the tube diameter using two systems, single-walled carbon nanotube coils and a monochiral carbon nanotube film. We report on two breathing-like modes for quasi-infinite bundles, compared to the single radial breathing mode characteristic for isolated tubes. The exciton-phonon coupling in these modes is probed with resonant Raman spectroscopy, revealing the same resonance energy for both breathing-like peaks. Our experimental findings align well with previously reported theoretical studies, demonstrating a 1/d scaling for all modes, as well as confirming the relative shift of the modes dependent on intertube interaction. These vibrations provide insight into the role of intertube lattice dynamics in two-dimensional THz-range phononic crystals.

Voltage-controlled non-axisymmetric vibrations of soft electro-active tubes with strain-stiffening effect

Material properties of soft electro-active (SEA) structures are significantly sensitive to external electro-mechanical biasing fields (such as pre-stretch and electric stimuli), which generate remarkable knock-on effects on their dynamic characteristics. In this work, we analyze the electrostatically tunable non-axisymmetric vibrations of an incompressible SEA cylindrical tube under the combination of a radially applied electric voltage and an axial pre-stretch. Following the theory of nonlinear electro-elasticity and the associated linearized theory for superimposed perturbations, we derive the nonlinear static response of the SEA tube to the inhomogeneous biasing fields for the Gent ideal dielectric model. Using the State Space Method, we efficiently obtain the frequency equations for voltage-controlled small-amplitude three-dimensional non-axisymmetric vibrations, covering a wide range of behaviors, from the purely radial breathing mode to torsional modes, axisymmetric longitudinal modes, and prismatic diffuse modes. We also perform an exhaustive numerical analysis to validate the proposed approach compared with the conventional displacement method, as well as to elucidate the influences of the applied voltage, axial pre-stretch, and strain-stiffening effect on the nonlinear static response and vibration behaviors of the SEA tube. The present study clearly indicates that manipulating electro-mechanical biasing fields is a feasible way to tune the small-amplitude vibration characteristics of an SEA tube. The results should benefit experimental work on, and design of, voltage-controlled resonant devices made of SEA tubes.

Observing Axial Chirality of Chiral Single-Wall Carbon Nanotubes by Helicity-Dependent Raman Spectra.

Helicity-dependent Raman spectra of an isolated, chiral, single-wall carbon nanotube (SWNT) are reported using circularly polarized light. A polar plot of polarized Raman intensity for the radial breathing mode (RBM), which is excited by left-handed or right-handed circularly polarized light, shows asymmetric angle dependence relative to the nanotube axis direction, which reflects the axial chirality of a SWNT. The asymmetry in the polar plot of the RBM can be analyzed by a complex Raman tensor. The complex phase of each component of the Raman tensor has a maximum at chiral angle θ = 15° of a SWNT which is between two achiral SWNTs, that is, zigzag (θ = 0°) and armchair (θ = 30°) SWNTs. Considering the interaction between the chiral SWNT and the circularly polarized light, we discuss the origin of the complex phases excited by the opposite helicity of the circularly polarized light.

(Invited) Efficient Inner-to-Outer Wall Energy Transfer in Highly Pure Double-Wall Carbon Nanotubes Revealed by Detailed Spectroscopy

The coaxial stacking of two single-wall carbon nanotubes (SWCNTs) into a double-wall carbon nanotube (DWCNT), forming a so-called one-dimensional van der Waals structure, leads to synergetic effects that dramatically affect the optical and electronic properties of both layers [1]. In this work, we explore these effects in purified DWCNT samples by combining absorption, wavelength-dependent infrared fluorescence−excitation (PLE), and wavelength-dependent resonant Raman scattering (RRS) spectroscopy. Purified DWCNTs are obtained by careful solubilization that strictly avoids ultrasonication [2] or by electronic-type sorting [3], both followed by a density gradient ultracentrifugation to remove unwanted SWCNTs that could obscure the DWCNT characterization [2]. Chirality-dependent shifts of the radial breathing mode vibrational frequencies and transition energies of the inner and outer DWCNT walls with respect to their SWCNT analogues are determined by advanced two-dimensional fitting of RRS and PLE data of DWCNT and their reference SWCNT samples. This exhaustive data set verifies that fluorescence from the inner DWCNT walls of well-purified samples is severely quenched, as previously evidenced in single-tube experiments [4]. Moreover, we find that this quenching occurs through efficient energy transfer from the inner to the outer DWCNT walls [5]. Combined analysis of the PLE and RRS results further reveals that this transfer is dependent on the inner and outer wall chirality, and we identify the specific combinations dominant in our DWCNT samples. These obtained results demonstrate the necessity and value of a combined structural characterization approach including PLE and RRS spectroscopy for bulk DWCNT samples.[1] S. Cambré et al, Small 2021, 17, 2102585[2] M. Erkens et al, Carbon 2021, 185, 113[3] H. Li et al, Nature Nanotechnol. 2017, 12, 1176[4] D. Levshov et al, Phys. Rev. B 2017, 96, 195410[5] M. Erkens et al, ACS Nano 2022, 16, 16038

Structural and Dynamical Properties of H2O and D2O under Confinement.

Water (H2O) is of great societal importance, and there has been a significant amount of research on its fundamental properties and related physical phenomena. Deuterium dioxide (D2O), known as heavy water, also draws much interest as an important medium for medical imaging, nuclear reactors, etc. Although many experimental studies on the fundamental properties of H2O and D2O have been conducted, they have been primarily limited to understanding the differences between H2O and D2O in the bulk state. In this paper, using path integral molecular dynamics simulations, the structural and dynamical properties of H2O and D2O in bulk and under nanoscale confinement in a (14,0) carbon nanotube are studied. We find that in bulk, structural properties such as bond angle and bond length of D2O are slightly smaller than those of H2O while D2O is slightly more structured than H2O. The dipole moment of D2O tends to be 4% higher than that of H2O, and the hydrogen bonding of D2O is also stronger than that of H2O. Under nanoscale confinement in a (14,0) carbon nanotube, H2O and D2O exhibit a smaller bond length and bond angle. The hydrogen bond number decreases, which demonstrates a weakened hydrogen bond interaction. Moreover, confinement results in a lower libration frequency and a higher OH(OD) bond stretching frequency with an almost unchanged HOH(DOD) bending frequency. The D2O-filled (14,0) carbon nanotube is found to have a smaller radial breathing mode than the H2O-filled (14,0) carbon nanotube.

Radial-tangential mode of single-wall carbon nanotubes manifested by Landau regulation: reinterpretation of low- and intermediate-frequency Raman signals

The low-frequency Raman signals of single-wall carbon nanotubes (SWNTs), appearing in the range of 100–300 cm−1, have been interpreted as radial-breathing mode (RBM) comprising pure radial Eigenvectors. Here, we report that most of the low-frequency and intermediate-frequency signals of SWNTs are radial-tangential modes (RTMs) coexisting radial and tangential Eigenvectors, while only the first peak at the low-frequency side is the RBM. Density functional theory simulation for SWNTs of ~ 2 nm in diameter shows that dozens of RTMs exhibit following the RBM (~ 150 cm−1) up to G-mode (~ 1592 cm−1) in order with Landau regulation. We specify the RBM and the RTM on Raman spectra obtained from SWNTs, where both appear as prominent peaks between 149 and 170 cm−1 and ripple-like peaks between 166 and 1440 cm−1, respectively. We report that the RTMs have been regarded as RBM (~ 300 cm−1) and ambiguously named as intermediate-frequency mode (300–1300 cm−1) without assignment. The RTMs gradually interlink the RBM and the G-mode resulting in the symmetric Raman spectra in intensity. We reveal high-resolution transmission microscope evidence for a helical structure of SWNTs, informing the typical diameter of commercial SWNTs to be 1.4–2 nm.

Formation of Amorphous Carbon Multi‐Walled Nanotubes from Random Initial Configurations

Amorphous carbon nanotubes (a-CNT) with up to four walls and sizes ranging from 200 to 3200 atoms have been simulated, starting from initial random configurations and using the Gaussian Approximation Potential [Phys. Rev. B 95, 094203 (2017)]. The important variables (like density, height, and diameter) required to successfully simulate a-CNTs, were predicted with a machine learning random forest technique. The models were validated $\textit{ex post facto}$ using density functional codes. The a-CNT models ranged from 0.55 nm - 2 nm wide with an average inter-wall spacing of 0.31 nm. The topological defects in a-CNTs were discussed and new defect configurations were observed. The electronic density of states and localization in these phases were discussed and delocalized electrons in the $\pi$ subspace were identified as an important factor for inter-layer cohesion. Spatial projection of the electronic conductivity favors axial transport along connecting hexagons, while non-hexagonal parts of the network either hinder or bifurcate the electronic transport. A vibrational density of states was calculated and is potentially an experimentally testable fingerprint of the material and the appearance of a low-frequency radial breathing mode was discussed. The thermal conductivity at 300 K was calculated using the Green-Kubo formula.

Level Attraction due to Dissipative Phonon–Phonon Coupling in an Opto-Mechano-Fluidic Resonator

Dissipative couplings between solid-cavity optomechanical oscillators provide an underlying mechanism for many physical phenomena, such as level attraction, non-Hermitian parity-time-symmetric, and topological energy transfer with exceptional points (EPs). Until now, cavity optomechanical mode couplings on different phases of material have not been demonstrated. Here, we report the experimental demonstration of optomechanical mode dissipative coupling, mediated by high-quality-factor photon whispering-gallery modes, between a solid surface wave mode (SWM) and a liquid radial breathing mode (RBM), both of which coexist in an optofluidic microbubble resonator consisting of silica layer and liquid metal core. The resonant frequencies of solid-SWM and liquid-RBM depend mainly on the physical parameters of the silica and liquid metal, respectively. These physical parameters are all related to the microcavity temperature, which can be electrically controlled by wiring the liquid metal to a circuit. The dissipative level attraction between the solid-SWM and liquid-RBM is achieved by changing the current applied to the liquid metal. Our results open new avenues toward exploring topological energy transfer between solid and liquid materials or ultrasensitive biological sensing around EPs.

Formation of Amorphous Carbon Multi‐Walled Nanotubes from Random Initial Configurations

Amorphous carbon nanotubes (a‐CNT) with up to four walls and sizes ranging from 200 to 3200 atoms have been simulated, starting from initial random configurations and using the Gaussian Approximation Potential. The important variables (like density, height, and diameter) required to successfully simulate a‐CNTs were predicted with the machine learning random forest technique. The width of the a‐CNT models ranged between 0.55–2 nm with an average inter‐wall spacing of 0.31 nm. The topological defects in a‐CNTs were analyzed and new defect configurations were observed. The electronic density of states and localization in these phases were discussed and delocalized electrons in the π subspace were identified as an important factor for inter‐layer cohesion. Spatial projection of the electronic conductivity favors axial transport along connecting hexagons, while non‐hexagonal parts of the network either hinder or bifurcate the electronic transport. A vibrational density of states was calculated and is potentially an experimentally comparable fingerprint of the material. The appearance of a low‐frequency radial breathing mode was discussed and the thermal conductivity at 300 K was estimated using the Green‐Kubo formula.

1D van der Waals heterostructures based on single-walled carbon nanotubes encapsulating linear carbon chains: Stability and charge transfer evidence from Raman spectroscopy

The emerging one-dimensional van der Waals heterostructures (1D vdWHTs) are raising a lot of enthusiasm due to the possibilities for creating novel physical properties. In this paper, we focus on single-walled carbon nanotubes (SWCNTs) encapsulating a series of hydrogen-terminated linear carbon chains (LCCs) of lengths ranging from 4 up to 40 carbon atoms as a template for 1D vdWHTs (LCCs@SWCNTs). We explored the structural properties and stability of the LCCs@SWCNTs systems. The optimal SWCNT diameter for which the resulting 1D vdWHTs are stable is determined using Lennard-Jones (LJ) potential. SWCNTs with diameters of around 0.75 nm are found most convenient to accommodate LCCs. Combining the molecular dynamics (MD), the density functional theory (DFT), bond polarizability model (BPM), and the spectral moment’s method (SMM), we computed the Raman spectra of the free LCCs and LCCs@(6,5) 1D vdWHTs. The stability and charge transfer in the LCCs@(6,5) systems are evinced by analyzing the Raman active modes of the LCCs, as well as the radial breathing mode (RBM) and G-band of the (6,5) SWCNT before and after filling. These findings provide benchmark theoretical data to understand both the Raman data of the LCCs and the confinement effect on those of the SWCNTs encasing LCCs which have not been clearly addressed before.

Intermolecular vibrational energy transfer between SWCNTs with different chiralities

Ultrafast spectroscopy was performed for two kinds of SWCNT samples; a sample purified to have a single chirality (purified) and one containing variety of chiralities (non-purified). There are three relaxation processes with corresponding rates which were estimated as 10ps-1,2ps-1,and0.5ps-1. The fastest rate is attributed to intraband relaxation in the electronic excited state, and the other two are for parallel relaxation process of interband relaxation to the electronic ground state. Vibrational frequency of radial breathing mode was found to show up-shift only in the non-purified sample (not in the purified one), which indicates intermolecular vibrational energy transfer between SWCNTs with different chiralities from each other.

Computational and theoretical study of B-doped achiral single-walled carbon nanotubes: A nonresonant polarized Raman analysis

Tailoring the unique properties of carbon nanotubes should be studied. However, chemical doping by incorporation of boron atoms into carbon nanotubes (CNTs) has been examined as a powerful tool which provides various advantages. In this paper, we review several recent researches by which to dope carbon nanotubes by boron atoms into the sp2 carbon lattice, the properties induced by boron doping, and promising applications of this type of doping nanomaterials. We envisage that intrinsic boron doping will accelerate both scientific and industrial developments in the area of CNTs and nanotechnology in a later researches. Furthermore, the calculations of the polarized Raman active modes in boron-doped achiral single-walled carbon nanotubes are performed in the framework of the force constants model. Moreover, The spectral moment’s method was used in order to calculate the nonresonant Raman spectra for systems contain several atoms, it is shown that a powerful tool. The variations of the Raman spectra as a function of the rate doping of boron atoms are identified and the relative intensity ratio between Raman active modes of D and G bands has been analyzed. Raman spectroscopy analysis reveals mathematical expressions, it was derived to describe the dependence of the Radial Breathing Modes (RBM) with the diameter and the B-doping rate. It is shown that the diameter scale in Kataura’s plot must be converted into in order to directly compare to the experimental Raman spectra. Such conversion must be performed by using the relation ωRBM=218−1,2τD. Once this adjustment is done, one is ready to associate each pair (ωRBM,τ) to a specific (n, m) if the ωRBM values are well known. For example the RBM modes at 165 cm−1 and 133 cm−1 are assigned to the single walled carbon nanotube (10,10) and BC3 nanotube (5,5) respectively. The results of this work provide the (n, m) dependence of the RBM of SBCNTs, it gives good benchmark for performing (n,m) assignment of doped SWCNTs.

Efficient Inner-to-Outer Wall Energy Transfer in Highly Pure Double-Wall Carbon Nanotubes Revealed by Detailed Spectroscopy.

The coaxial stacking of two single-wall carbon nanotubes (SWCNTs) into a double-wall carbon nanotube (DWCNT), forming a so-called one-dimensional van der Waals structure, leads to synergetic effects that dramatically affect the optical and electronic properties of both layers. In this work, we explore these effects in purified DWCNT samples by combining absorption, wavelength-dependent infrared fluorescence-excitation (PLE), and wavelength-dependent resonant Raman scattering (RRS) spectroscopy. Purified DWCNTs are obtained by careful solubilization that strictly avoids ultrasonication or by electronic-type sorting, both followed by a density gradient ultracentrifugation to remove unwanted SWCNTs that could obscure the DWCNT characterization. Chirality-dependent shifts of the radial breathing mode vibrational frequencies and transition energies of the inner and outer DWCNT walls with respect to their SWCNT analogues are determined by advanced two-dimensional fitting of RRS and PLE data of DWCNT and their reference SWCNT samples. This exhaustive data set verifies that fluorescence from the inner DWCNT walls of well-purified samples is severely quenched through efficient energy transfer from the inner to the outer DWCNT walls. Combined analysis of the PLE and RRS results further reveals that this transfer is dependent on the inner and outer wall chirality, and we identify the specific combinations dominant in our DWCNT samples. These obtained results demonstrate the necessity and value of a combined structural characterization approach including PLE and RRS spectroscopy for bulk DWCNT samples.

Spectroscopic distinction of carbon nanobelts and nanohoops

Among nanocarbon materials prepared via organic synthesis, carbon nanobelts (NBs), such as cyclacenes and cyclophenacenes, and carbon nanohoops (NHs), such as cycloparaphenylenes, are starting materials for preparing carbon nanotubes with controlled structures. Herein, X-ray photoelectron spectroscopy (XPS) and Raman spectra of zigzag NBs (ZNBs), armchair NBs (ANBs) and NHs were simulated using a computational method and calibrated against the experimental spectra of NHs with 6 and 12 benzenes. The XPS results showed that the C1s peak positions for the ZNBs were at binding energies (BEs) at least 0.5 eV higher than those for the ANBs and NHs. As the diameter increased, the peak position was shifted to higher BEs for the ZNBs but to lower BEs for the ANBs and NHs, because of the change of highest occupied molecular orbital and lowest unoccupied molecular orbital energies. The Raman spectroscopic analysis revealed that there were distinct characteristic modes for each type of structure, i.e., the C–H vibrational band for the ZNBs, the G band for the ANBs, and the D band for the NHs. As the diameter increased, the positions of these characteristic bands and the radial breathing modes were shifted. These results indicate that NBs and NHs can be distinguished using XPS and Raman spectroscopy.