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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. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, the nonlinear vibrations and energy exchange of single-walled carbon nanotubes (SWNTs) are analysed. The Sanders-Koiter shell theory is used to model the nonlinear dynamics of the system in the case of finite amplitude of vibration. The SWNT deformation is described in terms of longitudinal, circumferential and radial displacement fields. Simply supported, clamped and free boundary conditions are applied. The resonant interaction between radial breathing (axisymmetric) modes (RBMs) is analysed. An energy method, based on the Lagrange equations, is considered in order to reduce the nonlinear partial differential equations of motion to a set of nonlinear ordinary differential equations, which is then solved applying the implicit Runge-Kutta numerical method. The present model is validated in linear field comparing the RBM natural frequencies numerically predicted with data reported in the literature from experiments and molecular dynamics simulations. The nonlinear energy exchange between the two halves along the SWNT axis in the time is studied for different amplitudes of initial excitation applied to the two lowest frequency resonant RBMs. The influence of the SWNT aspect ratio on the numerical value of the nonlinear energy beating period under different boundary conditions is analysed. [ABSTRACT FROM AUTHOR]

Using first-principles calculations, we have investigated the structural stabilities, electronic and vibrational properties of the (4, 2) single-walled coinage metal nanotubes, especially the Raman-active radial breathing modes (RBMs). It is found that (1) the tip-suspended (4, 2) single-walled coinage metal nanotubes may also be grown in future, because of the appearance of local minimums in the string tensions and binding energies variation with the lengths of unit cell. (2) The different coinage metal (4, 2) nanotubes have different characteristic RBMs, whose frequencies correspond exactly to their maximal frequencies. In addition, the vibrational density of states depends on both of their elements and the structural symmetries. (3) The calculated stiffness coefficients of the coinage metal (4, 2) tubes further indicate that their bond strengths are different from each other, for which the Cu Cu bond is harder than both of the Au Au and Ag Ag bonds. (4) The available resonant Raman spectra of their RBMs are sensitive to the species of nanotubes, which may be useful for identifying them in possible experiments. [ABSTRACT FROM AUTHOR]

Bimetallic Ag/Cu nanoparticles have been obtained by green synthesis using Opuntia ficus- indica plant extract. Two synthesis methods were applied to obtain nanoparticles with core-shell and Janus morphologies by reversing the order of precursors. Transmission electronic microscopy revealed size of 10 nm and 20 nm for the core-shell and Janus nanoparticles, respectively. Other small particles with size of up to 2 nm were also observed. Absorption bands attributed to surface plasmon resonance were detected at 440 nm and 500 nm for the core-shell and Janus nanoparticles, respectively. Density functional theory predicted a breathing mode type (BMT) located at low wavenumber due to small, low-energy clusters of (AgCu) with n = 2 to 9, showing a certain correlation with the experimental one (at 220 cm). The dependence of the BMT on the number of atoms constituting the cluster is also studied. [ABSTRACT FROM AUTHOR]

This study reports the synthesis and characterization of gold nanoparticles through an ecological method to obtain nanostructures from the extract of the plant Opuntia ficus-indica . Colloidal nanoparticles show sizes that vary between 10–20 nm, and present various geometric morphologies. The samples were characterized through optical absorption, Raman Spectroscopy and Transmission Electron Microscopy (TEM). Additionally, low energy metallic clusters of Au n ( n =2–20 atoms) were modeled by computational quantum chemistry. The theoretical results were obtained with Density Functional Theory (DFT). The predicted results of Au clusters show a tendency and are correlated with the experimental results concerning the optical absorption bands and Raman spectroscopy in gold nanoparticles. [ABSTRACT FROM AUTHOR]

Silver selenide (Ag 2 Se) quantum dots obtained in synthetic zeolite F9 through ion exchange are reported in this work. A hydrothermal reaction was conducted between the zeolite–Ag + system with Na 2 SeSO 3 . Quantum dots smaller than 10 nm were measured by Transmission Electron Microscopy (TEM). The particles have a cubic structure with a phase lm-m (229). A shoulder centered at 150 cm −1 was experimentally detected after the synthesis of quantum dots by Raman Spectroscopy. The Density Functional Theory (DFT) was employed to determine a possible allocation to the Raman band detected. The LSDA (Local Spin Density Approximation) approximation levels and B3LYP (Becke's three-parameter Exchange functional and the gradient corrected functional of Lee, Yang and Puar) were employed in combination with the basis set LANL2DZ (Los Alamos National Laboratory 2-double-ζ) to study the structural and vibrational properties in minimum energy clusters (AgSe) n . Radial Breathing Modes were detected between 150 and 252 cm −1 for these levels of approximation. [ABSTRACT FROM AUTHOR]

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 s p 2 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 ω R B M = 218 − 1 , 2 τ D . Once this adjustment is done, one is ready to associate each pair ( ω R B M , τ) to a specific (n, m) if the ω R B M values are well known. For example the R B M modes at 165 cm − 1 and 133 cm − 1 are assigned to the single walled carbon nanotube (10,10) and B C 3 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. • Vibrational properties of B-doped Single Walled Carbon NanoTubes (Bdoped-SWCNTs) was investigated for different rate doping. • The frequency of RBM as a function of the nanotube diameter, and Bdoping level have been analyzed. Mathematical expression was derived ω RBM = 218 − 1 , 2 τ D . • The RBM frequencies at 165 cm − 1 and 133 cm − 1 are assigned to the single walled carbon nanotube (10,10) and BC 3 nanotube (5,5). • The intensity ratio (I D / I G) is useful to estimate the defects and degree of disorder of SBCNTs. • Calculations provide benchmark theoretical data for the assignment of experimental one. [ABSTRACT FROM AUTHOR]

The vibrational modes, especially the radial breathing modes (RBMs), of the single-walled silver nanotubes (SWSNTs) have been calculated by the first principles calculations. It is found that (1) the tip-suspended Ag (4,2) and Ag (6,3) tubes can also be potentially realized in future experiments, due to existence of a local minimum in the cohesive energies and string tension variation with their unit cell lengths. (2) The maximal frequencies of the SWSNTs are comparable to those of bulk silver, but its vibrational density of states is quite different. (3) Although the RBM frequencies of the SWSNTs depend on both of their tube diameters and chiral symmetries, they still approximately follow a linear variation law with the inverse tube diameters. (4) By investigating the stiffness coefficient of Ag (4,4) and Au (4,4) tubes, we have found that the Ag–Ag bond is stronger than the Au–Au ones. (5) The calculated first-order resonant Raman spectra are found to be sensitive to the chiral indices of SWSNTs, which may be useful in future experiment. [ABSTRACT FROM AUTHOR]

Cadmium colloidal crystalline nanoparticles were obtained by a simple green synthesis method employing the plant extract of Opuntia ficus-indica. The plant extract reduces the ions and stabilizes the size of cadmium colloidal particles at the nanometric level. The size and morphology of agglomerates of nanoparticles of about 100 nm were analyzed by field-emission scanning electron microscopy (FESEM). The size, shape and crystalline structure of the nanoparticles were determined from TEM analysis. The results show that nanoparticles with hexagonal crystalline structure and average size 2-3 nm were obtained by this green synthesis method. The optical absorption spectrum of the colloidal solution containing the cadmium nanoparticles displays an optical absorption band centered at 236 nm, which was attributed to the plasmon resonance of the colloidal nanoparticles. Mie theory for colloidal systems was applied to reproduce theoretically the plasmon resonance absorption data of the colloidal nanoparticles. Furthermore, the Raman spectrum of powder from dried samples after reduction of cadmium ions, displays a low wavenumber vibration mode centered at 114 cm-1, assigned to the nanoparticles. Density functional theory (DFT) calculations at local spin density approximation (LSDA) level were performed to determine the structure and vibrational properties of small clusters of cadmium consisting of 3-10 atoms. Radial breathing modes with frequencies between 90 cm-1 and 120 cm-1 were found to be the most active Raman modes of the low-energy n clusters. Cadmium nanoparticles were obtained by green synthesis employing the plant extract of Opuntia ficus-indica. The size, shape, and crystalline structure of the Cd nanoparticles were determined from TEM analysis. The Cd nanoparticles with hexagonal crystalline structure and average size 2-3 nm were obtained. The optical absorption spectrum of the colloidal solution containing the cadmium nanoparticles displays an optical absorption band centered at 236 nm. The Raman spectrum of powder samples displays a low wavenumber vibration mode centered at 114 cm−1, assigned to the vibrational modes in small Cd nanoparticles. Radial breathing modes with frequencies between 90 and 120cm−1 were found to be the most active Raman modes of the low-energy Cd n clusters by Density Functional Theory. [ABSTRACT FROM AUTHOR]

This work presents the synthesis of metallic nanoparticles of titanium. The extract from the nopal ( Opuntia ficus-indica) plant was used as the redactor agent. The results of transmission electronic microscopy (TEM) show that nanoparticles have a sphere-like shape with an approximate diameter of 1-4 nm. The presence of in these particles was corroborated by energy dispersive X-ray spectroscopy (EDS). Optical properties were detected with the presence of absorption bands centered in 295 nm and 355 nm, similar to those reported in the literature. Two Raman bands centered at 359 cm-1 and 404 cm-1 were observed after the synthesis of titanium nanoparticles. Afterwards, structural and vibrational parameters of small clusters of (n, n = 3-13) were analyzed by the density functional theory (DFT) at the B3LYP level of approximation combined with the basis set LANL2DZ. Radial breathing modes (RBMs) were detected in the vibrational spectrum of each cluster, placed around 298-387 cm-1. Ti colloidal nanoparticles were obtained in the extract of the Opuntia ficus-indica plant. Optical properties were detected in these particles, showing two bands of about 295 and 355 nm in the UV/Vis spectrum. Two Raman bands centered at 359 and 404 cm−1 were observed after the synthesis of titanium nanoparticles. Calculations by the Density Functional Theory at the B3LYP approximation level suggested that the Raman band detected experimentally at 359 cm−1, could be assigned to Radial Breathing Modes (RBM) in very small Ti nanoparticles. [ABSTRACT FROM AUTHOR]

The first report on lithium nanoparticles synthesized experimentally is presented. The nanoparticles were obtained using the extract of Opuntia ficus-indica through “green synthesis”. The optical, structural and vibrational properties were studied through optical absorption, TEM microscopy and Raman spectroscopy. The particles show a size of approximately 5 nm. The absorption bands were found at 315 and 415 nm in the samples after the synthesis of the nanoparticles. One Raman band was detected at around 280 cm −1 . Several levels of approximation of the density functional theory and the Hartree–Fock method on the structural and vibrational study of the lithium clusters (Li n , n = 2–18) are incorporated. A radial breathing mode (RMB) type Raman mode was found for the case Li n ( n > 3) in the predicted Raman spectrum. This mode shows the highest relative intensity for each case, and a shift to lower wavenumbers when the amount of atoms in the cluster increases. [ABSTRACT FROM AUTHOR]

In this paper the effects of temperature on the radial breathing modes (RBMs) and radial wave propagation in multiwall carbon nanotubes (MWCNTs) are investigated using a continuum model of multiple elastic isotropic shells. The van der Waals forces between tubes are simulated as a nonlinear function of interlayer spacing of MWCNTs. The governing equations are solved using a finite element method. A wide range of innermost radius-to-thickness ratio of MWCNTs is considered to enhance the investigation. The presented solution is verified by comparing the results with those reported in the literature. The effects of temperature on the van der Waals interaction coefficient between layers of MWCNTs are examined. It is found that the variation of the van der Waals interaction coefficient at high temperature is sensible. Subsequently, variations of RBM frequencies and radial wave propagation in MWCNTs with temperatures up to 1 600 K are illustrated. It is shown that the thick MWCNTs are more sensible to temperature than the thin ones. [ABSTRACT FROM AUTHOR]

Based on molecular force fields, a new finite element model is constructed for multi-walled carbon nanotubes where the interlayer interactions and C-C bonds are simulated by the elements of piece-wise linear spring and rectangular cross section beam, respectively. For high computation efficiency and atomic reification, the radial breathing modes of multi-walled carbon nanotubes are studied systemically using this model. The results show the correspondence between carbon nanotube structures and vibrational modes, which provide unequivocal data for the experimental characterization of carbon nanotubes. An empirical relationship of radial breathing modes frequencies with the nanotube radius are also obtained for two-layer carbon nanotubes. [ABSTRACT FROM AUTHOR]

Abstract: The analysis in the paper is based on a multiple-elastic shell model which assumes that each of the concentric tubes of multiwall carbon nanotubes is an individual elastic shell and coupled with adjacent tubes through van der Waals interaction. The effects of the matrix on the frequencies of radial breathing modes and vibration modes of multiwall carbon nanotubes embedded in the matrix is considered by a spring coefficient defined by the Winkler model. Results carried out show that the frequencies of the first mode increase monotonically as the stiffness of the matrix increase. Matrix surrounding multiwall carbon nanotubes not only change the value of amplitude ratios between tube walls of multiwall carbon nanotubes embedded in matrix, but also change the vibration modes between tube walls of multiwall carbon nanotubes from coaxial vibration to non-coaxial vibration. In the absence of the matrix, the frequencies of radial breathing modes and vibration modes of an individual multiwall carbon nanotubes predicted by the present shell model are found to agree very well with the available experimental and molecular dynamic simulation results. [Copyright &y& Elsevier]