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The removal of oxidation debris from the oxidized carbon nanotube surface with a NaOH treatment is a key step for an effective functionalization and quality improvement of the carbon nanotube samples. In this work, we show via infrared spectroscopy and ultrahigh resolution and accuracy mass spectrometry that oxidation debris obtained from HNO 3 -treated multiwalled carbon nanotubes is a complex mixture of highly condensed aromatic oxygenated carbonaceous fragments. We have also evaluated their cytotoxicity by using BALB/c 3T3 mouse fibroblasts and HaCaT human keratinocytes as models. By knowing the negative aspects of dissolved organic carbon (DOC) to the water quality, we have demonstrated the removal of these carbon nanotube residues from the NaOH solution (wastewater) by using aluminium sulphate, which is a standard coagulant agent used in conventional drinking water purification and wastewater treatment plants. Our results contribute to elucidate the structural and proactive safety aspects of oxidation debris from oxidized carbon nanotubes towards a greener nanotechnology.

The deposition of mesoporous silica (SiO(2)) on carbon nanotubes (CNTs) has opened up a wide range of assembling possibilities by exploiting the sidewall of CNTs and organosilane chemistry. The resulting systems may be suitable for applications in catalysis, energy conversion, environmental chemistry, and nanomedicine. However, to promote the condensation of silicon monomers on the nanotube without producing segregated particles, (OR)(4-x)SiO(x)(x-) units must undergo nucleophilic substitution by groups localized on the CNT sidewall during the transesterification reaction. In order to achieve this preferential attachment, we have deposited silica on oxidized carbon nanotubes (single-walled and multiwalled) in a sol-gel process that also involved the use of a soft template (cetyltrimethylammonium bromide, CTAB). In contrast to the simple approach normally used to describe the attachment of inorganic compounds on CNTs, SiO(2) nucleation on the tube is a result of nucleophilic attack mainly by hydroxyl radicals, localized in a very complex surface chemical environment, where various oxygenated groups are covalently bonded to the sidewall and carboxylated carbonaceous fragments (CCFs) are adsorbed on the tubes. Si-O-C covalent bond formation in the SiO(2)-CNT hybrids was observed even after removal of the CCFs with sodium hydroxide. By adding CTAB, and increasing the temperature, time, and initial amount of the catalyst (NH(4)OH) in the synthesis, the SiO(2) coating morphology could be changed from one of nanoparticles to mesoporous shells. Concomitantly, pore ordering was achieved by increasing the amount of CTAB. Furthermore, preferential attachment on the sidewall results mostly in CNTs with uncapped ends, having sites (carboxylic acids) that can be used for further localized reactions.

Polarized Raman scattering studies and lattice-dynamics calculations were performed at ambient pressure and temperature. These results allowed us to propose the normal-mode symmetries and assignments. High-pressure Raman scattering studies were further performed revealing the onset of two reversible phase transformations near 1.2 and 4.5 GPa with different structural characteristics. The pressure dependence of Raman bands provides strong evidence that the first phase transition involves significant shifts of the potassium atoms associated with small shifts of the niobium atoms whereas the second phase transition is associated mainly with significant shifts of the Nb atoms toward the center of the ${\text{NbO}}_{6}$ octahedra. In the structure stable above 4.5 GPa the Nb atoms are dynamically disordered among symmetry equivalent positions.

In this work we report the synthesis, characterization and application of silver vanadate nanowires decorated with silver nanoparticles as a novel antibacterial agent. These hybrid materials were synthesized by a precipitation reaction of ammonium vanadate and silver nitrate followed by hydrothermal treatment. The silver vanadate nanowires have lengths of the order of microns and diameters around 60 nm. The silver nanoparticles decorating the nanowires present a diameter distribution varying from 1 to 20 nm. The influence of the pH of the reaction medium on the chemical structure and morphology of silver vanadates was studied and we found that synthesis performed at pH 5.5-6.0 led to silver vanadate nanowires with a higher morphological yield. The antimicrobial activity of these materials was evaluated against three strains of Staphylococcus aureus and very promising results were found. The minimum growth inhibiting concentration value against a MRSA strain was found to be ten folds lower than for the antibiotic oxacillin.

Lattice dynamics calculations and high-pressure Raman scattering study of ${\text{Bi}}_{2}{\text{W}}_{2}{\text{O}}_{9}$, which is an $m=2$ member of the cation-deficient bismuth layered Aurivillius family of compounds, are presented. These studies showed the onset of two reversible second-order phase transitions near 2.8 and 4.8 GPa. The pressure dependence of Raman bands provides strong evidence that the first phase transition involves the loss of the ${\text{WO}}_{6}$ tilt mode around pseudotetragonal axis. The second transition is likely related to some shift of the W atoms and/or tilting of the ${\text{WO}}_{6}$ octahedra plus shift of the Bi atoms or the whole ${\text{Bi}}_{2}{\text{O}}_{2}$ layers. In contrast to the $m=1$ cation-deficient bismuth layered compounds, ${\text{Bi}}_{2}{\text{WO}}_{6}$ and ${\text{Bi}}_{2}{\text{MoO}}_{6}$, no soft-mode behavior was observed for ${\text{Bi}}_{2}{\text{W}}_{2}{\text{O}}_{9}$ and the transition at 4.8 GPa leads to symmetry lowering.

The power of Raman spectroscopy for the study of the high-pressure evolution of carbon nanotubes is shown. After an introduction to carbon nanotubes and its resonance Raman scattering signal, we discuss the high-pressure Raman studies on single-wall carbon nanotubes with particular emphasis on the identification of pressure-induced structural and electronic transitions.

Raman spectra of (3C–SiC)8−δ/(3C–SiC0.5Si0.5)δ/(Si)8−δ/(3C–SiC0.5Si0.5)δ superlattices with interfacial transition regions of thickness δ varying from one to three monolayers are calculated. It is shown that severe frequency shifts (up to −86 cm−1) and the flattening of the folded optical phonons dispersion curves are due to the interfacial regions, strongly affecting the Raman spectrum in consequence. With increasing interface thickness, the Raman peaks are enhanced in the middle frequency range. These effects are mainly attributed to localization of atomic displacements at the Si/3C–SiC or the 3C–SiC/Si interfacial transition regions.

The effect of 170 keV Si and 100 keV C ion bombardment on the structure and properties of highly pure, double-wall carbon nanotubes has been investigated using resonance Raman spectroscopy. The implantations were performed at room temperature with ion doses ranging between $1\ifmmode\times\else\texttimes\fi{}{10}^{13}\text{ }\text{ions}/{\text{cm}}^{2}$ and $1\ifmmode\times\else\texttimes\fi{}{10}^{15}\text{ }\text{ions}/{\text{cm}}^{2}$. As expected, the Si irradiation created more disorder than the C irradiation for the same ion fluence. For both species, as the ion-implantation fluence increased, the $D$-band intensity increased, while the $G$-band intensity decreased, indicating increased lattice disorder, in analogous form to other forms of graphite and other nanotube types. The frequency of the $G$ band decreased with increasing dose, reflecting a softening of the phonon mode due to lattice defects. With increasing ion fluence, the radial breathing modes (RBMs) of the outer tubes (either semiconducting or metallic) disappeared before the respective RBM bands from the inner tubes, suggesting that the outer nanotubes are more affected than the inner nanotubes by the ion irradiation. After Si ion bombardment to a dose of $1\ifmmode\times\else\texttimes\fi{}{10}^{15}\text{ }\text{ions}/{\text{cm}}^{2}$, the Raman spectrum resembled that of highly disordered graphite, indicating that the lattice structures of the inner and outer nanotubes were almost completely destroyed. However, laser annealing partially restored the crystalline structure of the nanotubes, as evidenced by the re-emergence of the $G$ and RBM bands and the significant attenuation of the $D$ band in the Raman spectrum.

The growing incidence of microbial infections and the increasing ability of such organisms to acquire resistance to antimicrobial treatment lead the requirement of fast bacteria and fungi identification methods. In this work we explored optical spectroscopic techniques on fungal identification. We show that some fungal infections can be identified by ultraviolet optical excitation of fungi fluorescence followed by the spectral analysis of the emitted light. Moreover, we demonstrate that ultraviolet LED and LASER could be applied in fungal identification and a new device for fungal diagnosis is proposed.

Carbon nanotubes are very stable systems having a considerable chemical inertness due to the strong sp 2 hybridized covalent carbon bonds on their surface. However, various applications of carbon nanotubes require their doping or ­chemical modification through the addition of atoms and/or molecules (covalently or ­noncovalently) in order to alter their physicochemical properties. In this chapter we review the importance of different types of doping in carbon nanotubes (single, double, and multiwalled). Regarding the location of the dopant species within the nanotubes, it is possible to classify the doping process as being exohedral ­(intercalation), endohedral (filling), and in-plane (replacing carbon atoms). The effects of doping on the electronic, vibrational, chemical, magnetic, and mechanical properties are discussed by analyzing the experimental results obtained with different spectroscopic techni­ques such as resonant Raman, X-ray photoelectron (XP), electron energy loss, and others. Applications of doped-carbon nanotubes are also summarized.

Magnetic properties of graphenic carbon nanostructures, which are relevant for future spintronic applications, depend crucially on doping and on the presence of defects. In this paper we study the magnetism of the recently detected substitutional Ni (Nisub) impurities. Nisub defects are nonmagnetic in flat graphene and develop a nonzero-spin moment only in metallic nanotubes. This surprising behavior stems from the peculiar curvature dependence of the electronic structure of Nisub. A similar magnetic-nonmagnetic transition of Nisub can be expected by applying anisotropic strain to a flat graphene layer., E.J.G.S., A.A., and D.S.P. acknowledge support from the Basque Government and UPV/EHU Grant No. IT-366-07, CSIC, the Spanish MEC Grant No. FIS2007-66711-C02-02, and the Basque Government and Diputación Foral de Guipuzcoa through the ETORTEK program. A.G.S.F. acknowledges the support from Brazilian agencies FUNCAP, CAPES/FAPERGS, CNPq Grant No. 306335/2007-7, Rede Nacional de Pesquisa em Nanotubos de Carbono, Rede de Nanobioestruturas, and Instituto do Milenio de Nanotecnologia CNPq/MCT-Brazil.

High-pressure Raman scattering and luminescence studies of ${\mathrm{Bi}}_{2}\mathrm{W}{\mathrm{O}}_{6}:{\mathrm{Eu}}^{3+}$, which is a member of the bismuth layered Aurivillius family of ferroelectrics, are presented. These studies showed the onset of two reversible second order phase transitions near 3.4 and $6.2\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. The pressure dependence of Raman bands provides strong evidence that the first phase transition involves the loss of the $\mathrm{W}{\mathrm{O}}_{6}$ tilt mode around the pseudotetragonal axis. This structural change may be the same as that observed at ambient pressure at $660\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ (from the $Pca{2}_{1}$ to $B2cb$ structure). The second phase transition is associated with the instability of a low wave number mode, which behaves as soft mode. The discovery of the soft mode in ${\mathrm{Bi}}_{2}\mathrm{W}{\mathrm{O}}_{6}$ that corresponds most likely to the ${E}_{u}$ mode responsible for ferroelectricity in Aurivillius family of compounds proves that this transition is of displacive type. Our studies also suggest that the structure above $6.2\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ is orthorhombic and centrosymmetric and, consequently, the phase transition can be classified as a pressure-induced ferroelectric to a paraelectric phase transition.

The structural and electronic properties of $\mathrm{Cr}{\mathrm{O}}_{3}$ interacting with graphene layer are calculated using ab initio methods based on the density functional theory. The $\mathrm{Cr}{\mathrm{O}}_{3}$ acts as an electron acceptor modifying the original electronic and magnetic properties of the graphene surface through an adsorption process. The changes induced in the electronic properties are strongly dependent on the $\mathrm{Cr}{\mathrm{O}}_{3}$ adsorption site, and for some sites, it is possible to open a gap in the electronic band structure. Spin polarization effects are also predicted for some adsorption configurations for which the binding energy is lower and charge transfer is higher.

MCM-41, MCM-48 and FAU molecular sieves were used as template to prepare carbon nitrides (CN). The amine-functionalized CN were characterized by XRD, Raman and infrared (FTIR) spectroscopy, N 2 adsorption isotherms as well as the catalytic activity in a fine chemistry reaction was evaluated. MCM-41 is the best matrix to obtain ordered materials with a graphitic character. Also, sucrose is the best carbon precursor to obtain a pore filling of 32 wt.% compared with naphthalene and carbon tetrachloride. The nanoporous carbons studied are potentially of great importance because of their textural features and high catalytic performance. It must be correlated to the basic active sites that provide active, selective and stable catalysts to the target reaction.

In this work, we performed a detailed study of the Raman spectra of double-wall carbon nanotube (DWNT) bucky paper samples. The effects of ${\mathrm{H}}_{2}\mathrm{S}{\mathrm{O}}_{4}$ doping on the electronic and vibrational properties of the DWNTs are analyzed and compared to the corresponding effects on single-wall carbon nanotubes (SWNTs). Analysis of the radial breathing mode (RBM) Raman spectra indicates that the resonance condition for the outer wall nanotubes and the SWNTs are almost the same, indicating that the effect of the inner-outer wall interaction on the transition energies of the outer walls is weak compared to the width of the resonance window for the RBM peaks. The effect of ${\mathrm{H}}_{2}\mathrm{S}{\mathrm{O}}_{4}$ on the RBM frequencies of the outer wall of the DWNTs is stronger for larger diameter nanotubes. In the case of the inner walls, only the metallic nanotubes were affected by the acid treatment, while the RBM peaks for the inner semiconducting nanotubes remained almost unchanged in both frequency and intensity. The ${G}^{+}$ band was seen to upshift in frequency with ${\mathrm{H}}_{2}\mathrm{S}{\mathrm{O}}_{4}$ doping for both DWNTs and SWNTs. However, the effect of the acid treatment on the ${G}^{\ensuremath{-}}$ band frequency for DWNTs was opposite to that of SWNTs in the $2.05--2.15\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ range, for which the acid treatment causes a ${\ensuremath{\omega}}_{{G}^{\ensuremath{-}}}$ upshift for SWNTs and a downshift for DWNTs. The ${G}^{\ensuremath{'}}$ band line shape of the DWNTs is explained in terms of four contributions from different components which are in resonance with the laser excitation. Two of these peaks are more related to the inner wall nanotube while the other two are more related to the outer wall.

In this work we study the electronic, magnetic and structural properties of cobaltocene molecule (bis‐cyclopentadienyl cobalt) interacting with (13, 0) semiconductor single‐wall carbon nanotubes through ab initio simulations. The calculations are based on the first principles spin‐polarized density functional theory, using numerical atomic orbitals as basis set implemented in the SIESTA code. Our calculations indicated that the cobaltocene molecule inside the SWNT behave as electron donor thus charging the electronic bands of the nanotube and increasing its Fermi energy due to the molecule‐nanotube interaction.

The interaction of 2,3,7,8-tetrachlorinated dibenzo-p-dioxin (dioxin) with carbon nanotubes is analyzed by ab initio methods. The structural and electronic properties of the dioxin interacting with the pristine, defective and B-, N-, and Si-doped SWNTs are considered by studying different geometries. We have found that the dioxin interacts with a pure carbon nanotube although it depends on the geometry of the molecule approximation, increasing if the tube is defective., The authors acknowledge CENAPAD-SP for computer time and financial support from Brazilian agencies CNPq (Grant 307417/2004-2, 51732/2005-9 and 555183/2005-0), FAPERGS (Grants 0511570/05 and 05/2096.2), FAPESP and FUNCAP (Grant PPP-985/03).

Various applications of carbon nanotubes require their chemical modification inorder to tune/control their physicochemical properties. One way for achieving thiscontrol is by carrying out doping processes through which atoms and moleculesinteract (covalently or noncovalently) with the nanotube surfaces. The aim of thischapter is to emphasize the importance of different types of doping in carbonnanotubes (single-, double- and multiwall). There are three main categories ofdoping: exohedral, endohedral and inplane doping. We will review the most efficientways to dope carbon nanotubes and discuss the effects on the electronic, vibrational,chemical, magnetic and mechanical properties. In addition, we will discuss thedifferent ways of characterizing these doped nanotubes using spectroscopictechniques, such as resonant Raman, X-ray photoelectron, electron energy lossspectroscopy and others. It will be demonstrated that doped carbon nanotubes couldbe used in the fabrication of nanodevices (e.g., sensors, protein immobilizers,field emission sources, efficient composite fillers, etc.). We will also presentresults related to the importance of inplane-doped nanotubes for attachingvarious metal clusters and polymers covalently using wet chemical routes.

Article, Physical Review B. 73(23):235413 (2006)

In this paper we report the ion exchange reactions and the thermal decomposition of titanium oxide nanotubes, obtained by hydrothermal treatment of TiO2 and NaOH. Based on these results we propose a new composition for the as-prepared nanotubes as Na2Ti3O7·nH2O. Our results also suggest that nanotube walls have structure similar to those observed in the layer of the bulk Na2Ti3O7. Depending on how the washing process is performed on the nanotubes (water or acid solutions) the Na+ content can be modified via the exchange reaction of Na+ by H+. Thus, a general chemical formula was also proposed: Na2-xHxTi3O7 ·nH2O (0 < x < 2), x being dependent on the washing process. Neste trabalho reportamos reações de troca iônica e decomposição térmica em nanotubos de óxido de titânio, obtidos pelo tratamento hidrotérmico de TiO2 e NaOH. Considerando os resultados obtidos, sugerimos uma nova composição química para os nanotubos: Na2Ti3O7·nH2O. Os resultados também indicam que a estrutura da parede dos nanotubos seria isoestrutural às lamelas observadas para o Na2Ti3O7 bulk. Dependendo da natureza da lavagem (água deionizada ou solução ácida) executada no nanotubo após o tratamento hidrotérmico a concentração de íons Na+ pode ser modificada através de um processo de troca iônica do Na+ por H+. Tais resultados permitem sugerir a seguinte fórmula química geral para os nanotubos obtidos: Na2-xHxTi3O7 ·nH2O (0 < x < 2), sendo x dependente das condições de lavagens.

Recent optical absorption/emission experiments showed that the lower energy optical transitions in carbon nanotubes are excitonic in nature, as predicted by theory. These experiments were based on the symmetry aspects of free electron-hole states and bound excitonic states. The present work shows, however, that group theory does not predict the selection rules needed to explain the two photon experiments. We obtain the symmetries and selection rules for the optical transitions of excitons in single-wall carbon nanotubes within the approach of the group of the wavevector, thus providing important information for the interpretation of theoretical and experimental optical spectra of these materials., 4 pages, 1 figure, 1 table

The structural and electronic properties of FeCl3 interacting with single-wall carbon nanotubes SWNTs were investigated by ab initio methods. By using first-principles spin-polarized calculations, we studied the structural and electronic behavior of FeCl3 adsorbed on both semiconducting and metallic SWNTs. It was found that the FeCl3 molecule behaves as an electron acceptor. The binding energy is very small, thus suggesting that the interaction is through a physisorption regime.

In this Letter, we report the effects of strain on the electronic properties of single-wall carbon nanotubes. When we normalize the electronic transition energies to the corresponding values obtained for unstrained tubes, we obtain that, regardless of the tube diameter, all the data collapse onto universal curves following an n - m = constant family pattern. In the case of metallic tubes, quantum interference effects on the Raman cross section are predicted for strained tubes when the energies of the lower and the upper components have nearly the same values. Experimental evidence for the strain-induced Raman cross section changes is observed in single nanotube spectroscopy.

M\"ossbauer and Raman measurements for ${\mathrm{Li}}_{x}\mathrm{Fe}\mathrm{P}{\mathrm{O}}_{4}$ and ${\mathrm{Li}}_{x}{M}_{0.03}{\mathrm{Fe}}_{0.97}\mathrm{P}{\mathrm{O}}_{4}$ $(M=\mathrm{Cr},\mathrm{Cu},\mathrm{Al},\mathrm{Ti})$ were performed. The results for the ${\mathrm{Li}}_{0.11}\mathrm{Fe}\mathrm{P}{\mathrm{O}}_{4}$ oxide require an unknown additional contribution, besides the high-spin ${\mathrm{Fe}}^{2+}$ doublet and the high-spin ${\mathrm{Fe}}^{3+}$ doublet, for the M\"ossbauer profile to be properly accounted for. The corresponding Raman scattering suggests a two-phase material and an additional disordered structure present in the mixture. The M\"ossbauer-transformed patterns indicate the unknown doublet to be due to a disordered phase also. In addition, the observation of a high amount of ${\mathrm{Fe}}^{2+}$ sites for the low-lithium-content ${\mathrm{Li}}_{x}{M}_{0.03}{\mathrm{Fe}}_{0.97}\mathrm{P}{\mathrm{O}}_{4}$ oxides is analyzed on the basis of the electronic charge configuration of the Li-lacking octahedral units to suffer small changes upon lithium extraction.

We calculate structural and electronic properties of ${\mathrm{CaCu}}_{3}{\mathrm{Ti}}_{4}{\mathrm{O}}_{12}$ from ambient pressure up to 10.0 GPa using total-energy first-principles methods. Analysis of the simulated high-pressure structure suggests a pressure-induced structural phase transition between 3 and 4 GPa with the crystalline structure changing from $\mathrm{Im}\overline{3}$ (cubic) to $R\overline{3}$ (rhombohedral). By analyzing the electronic band structure, we have observed a pressure-induced semiconductor-metallic transition between 6 and 7 GPa.

In this paper we report the effects of strain on the electronic properties of single wall carbon nanotubes and its consequence on the resonant Raman cross section. A quantum interference effect has been predicted for the radial breathing mode spectra for metallic tubes. For metallic tubes, the lower and upper components of Eii resulting from the trigonal warping effect are affected differently and for low chiral angle they cross for some strain value. Near (at) the crossing point, the resonant Raman spectra profile exhibits a maximum (minimum) value due to a quantum interference in the Raman cross section. This Raman cross section interference effect was observed in Raman experiments carried out on isolated SWNTs. The Raman experiment performed on an isolated strained metallic SWNT supports our modeling predictions.

High pressure Raman scattering and x-ray diffraction studies of the molybdate ${\mathrm{Sc}}_{2}({\mathrm{MoO}}_{4}{)}_{3}$ are presented. A sequence of changing symmetry effects is observed through two structural phase transitions ending up with an amorphous state. The observed two structural phase transformations are reversible. The crystal to amorphous transition is irreversible. Our results point out that the amorphization process in ${\mathrm{Sc}}_{2}({\mathrm{MoO}}_{4}{)}_{3}$ may be due to a kinetic hindrance of a phase transition rather than due to chemical decomposition effects as have been proposed to occur for some molybdates and tungstates.

A review is presented of one-dimensional cutting lines that are utilized to obtain the physical properties of carbon nanotubes from the corresponding properties of graphite by the zone-folding scheme. Quantization effects in general low-dimensional systems are briee y discussed, followed by a more detailed consideration of one-dimensional single-wall carbon nanotubes. The geometrical structure of the nanotube is described, from which quantum cone ned states are constructed. These allowed states in the momentum space of graphite are known as cutting lines. Different representations of the cutting lines in momentum space are introduced. Electronic and phonon dispersion relations for nanotubes are derived by using cutting lines and the zone-folding scheme. The relation between cutting lines and singularities in the electronic density of states is considered. The selection rules for carbon nanotubes are shown to be directly connected with the cutting lines. Different experimental techniques are considered that cone rm the validity of cutting lines and the zone-folding approach.

To better understand the very high thermal conductivity to weight ratio of the graphitic foams recently developed at the Oak Ridge National Laboratory, a Raman spectroscopy study was performed. It was also shown that the Raman scattering can be useful for the characterization of the graphitic foam, being able to evaluate the quality of the samples with respect to the density and location of lattice defects.

The optical absorption spectra of \ensuremath{\pi} electrons are calculated for graphite and carbon nanotubes. Particular attention is paid to the processes contributing to the optical absorption as a function of the electron wave vector k and light polarization direction. The optical absorption amplitude around the K point in the Brillouin zone has a node in the two-dimensional Brillouin zone of graphite. The formula for the absorption scattering matrix around the K point is given analytically by expanding the matrix element into a Taylor series. The chirality dependence of the absorption matrix element of a single-wall carbon nanotube is presented.

The one-dimensional structure of carbon nanotubes leads to quantum confinement of the wave vectors for the electronic states, thus making the double resonance Raman process selective, not only of the magnitude, but also of the direction of the phonon wave vectors. This additional selectivity allows us to reconstruct the phonon dispersion relations of 2D graphite, by probing individual single wall carbon nanotubes of different chiralities by resonance Raman spectroscopy, and using different laser excitation energies. In particular, we are able to measure the anisotropy, or the trigonal warping effect, in the phonon dispersion relations around the hexagonal corner of the Brillouin zone of graphite.

In this work, we discuss the resonant Raman process in nanographites and carbon nanotubes, relating the most important Raman features to a first‐order (single resonance) or a second‐order (double resonance) process. We also show that, in the case of 1D systems, the term “resonance” has a more strict meaning and occurs when the energy of the photon does not simply coincide with the energy of a possible electron‐hole pair, but rather matches the separation between van Hove singularities in the valence and conduction bands.

Dispersive features observed in graphite, carbon nanotube bundles and isolated single‐wall carbon nanotubes are discussed. Special attention is given to the effects of the van Hove singularities in 1D nanotubes.

A review is presented on the observation of the resonant Raman spectra from one isolated single wall carbon nanotube, focusing on the important structural information that is provided by single nanotube spectroscopy including the (n, m) determination of the individual tubes. The special sensitivity of the radial breathing mode to the (n, m) determination is emphasized, and the corroboration of this (n, m) assignment by diameter- and chirality-dependent phenomena in other Raman modes, such as the G-band, D-band, and G‘-band features is also discussed. The significance of single nanotube spectroscopy for future nanotube research in general is briefly reviewed.

In this paper we present a Raman-scattering study of the phase transitions in the ${\mathrm{PbZr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}$ systems around the morphotropic phase boundary over a wide temperature range. The boundary between rhombohedral and monoclinic phases was found to be a quasivertical line between $x=0.46$ and $x=0.47.$ We also studied the monoclinic-tetragonal phase boundary and our spectroscopic results agree very well with those reported by using x-ray diffraction.

We report G-band resonance Raman spectra of single-wall carbon nanotubes ~SWNTs! at the singlenanotube level. By measuring 62 different isolated SWNTs resonant with the incident laser, and having diameters dt ranging between 0.95 nm and 2.62 nm, we have conclusively determined the dependence of the two most intense G-band features on the nanotube structure. The higher-frequency peak is not diameter dependent (v G 51591 cm 21 ), while the lower-frequency peak is given by v G 5v G 2C/dt , with C being different for metallic and semiconducting SWNTs (CM.CS). The peak frequencies do not depend on nanotube chiral angle. The intensity ratio between the two most intense features is in the range 0.1 ,I v G /I v G,0.3 for most of the isolated SWNTs (;90%). Unusually high or low Iv G /I v G ratios are observed for a few spectra coming from SWNTs under special resonance conditions, i.e., SWNTs for which the incident photons are in resonance with the E44 interband transition and scattered photons are in resonance with E33 . Since the Eii values depend sensitively on both nanotube diameter and chirality, the ( n,m) SWNTs that should exhibit such a special G-band spectra can be predicted by resonance Raman theory. The agreement between theoretical predictions and experimental observations about these special G-band phenomena gives additional support for the (n,m) assignment from resonance Raman spectroscopy.

The resonant second-order G'-band Raman spectra of isolated single-wall carbon nanotubes (SWNTs) exhibit an interesting resonance phenomenon, whereby the G' band for some special (n,m) isolated SWNTs exhibits a two-peak structure, while for most SWNTs, the G'-band profile is a single Lorentzian peak. The two-peak phenomenon is explained by combining the double-resonance Raman effect, originally introduced for graphite, with the singular electronic structure of SWNTs, which is unique for a given (n,m) pair. Therefore, the G'-band profile is strongly dependent on the joint density of electronic states and provides useful information about the electronic structure and on the (n,m) assignment for the specific SWNT that is in resonance with the laser.

The optical absorption for ? electrons as a function of the electron wavevector k is investigated by first order perturbation theory in graphite and single wall carbon nanotubes (SWNTs). The matrix element connecting two states in the valence and conduction bands is found to be significantly anisotropic in k-space and polarization dependent. In the case of graphite, the absorption shows a node around the equi-energy contour, and in the case of SWNTs we obtain selection rules that allow only transitions between certain pairs of subbands. The strength of the optical absorption is not only diameter dependent but also chirality dependent. The implications of the optical absorption matrix element on the resonant conditions are discussed.

New experimental results on the resonance Raman spectra of isolated single wall carbon nanotubes (SWNTs) are reported and are explained in terms of the one‐dimensional (1D) physics of SWNTs. The lineshape of both the non‐dispersive and dispersive Raman features depend on (n,m) and Elaser. In addition to the structural (n,m) information about isolated SWNTs, the lineshape analysis of the resonance Raman features of isolated SWNTs gives detailed information not otherwise available about the 1D electronic structure of an isolated SWNT.

The possible semiconducting device use of single wall carbon nanotubes (SWNTs) requires a technique for the determination of the exact structure of the nanotubes assembled in the device configuration. Raman spectroscopy has been established as a precise and non-destructive tool for the characterization of graphitic nanostructures. Double resonance theory, which is used to explain the dispersive nature of the Raman bands, has attracted much attention for its potential use for the characterization of the electronic and phonon spectra of these nanostructures. Dispersive features in the Raman spectra of low dimensional graphitic materials, such as carbon nanotubes, can be used to measure directly the anisotropy, or the trigonal warping effect, in the phonon dispersion relations about the hexagonal corner of the Brillouin zone (BZ) of graphite.

We study the electronic properties of a series of coronene-derived graphitic nanoribbons recently synthesized in a pre-programmed, nanotube assisted, chemical route [Talyzin et al. Nano Lett., 2011, 11, 4352 and Fujihara et al. J. Phys. Chem. C, 2012, 116, 15141]. We employ a combination of density functional theory and spin-polarized tight-binding methods to show how details of the molecular building blocks and their assembly uniquely determine the electronic structure of the resulting ribbon. We demonstrate the onset of multiple magnetic states for these systems and a non-trivial dependence of the electronic bandgap with both atomic structure and spin configuration, which make these coronene-based ribbons potential candidates for applications in nanoelectronics.

The Raman spectra of zinc-blende InN/GaN superlattices were calculated assuming the existence of an interface region with thickness \ensuremath{\delta} varying from one to three monolayers. The acoustic branches are weakly affected by interfacing, but the optical branches can present frequency shifts up to $60 {\mathrm{cm}}^{\ensuremath{-}1}.$ A downward shift is observed for the higher frequency and an upward shift for the lower frequency modes. As a consequence, the Raman peaks collapse together in the middle frequency range giving rise to a most prominent structure in the spectrum, for $\ensuremath{\delta}=3.$ These effects are tracked to the localization of atomic displacements at the direct and inverse interface regions. The localization effects are strong in the InN/GaN superlattices because of the wide gap observed in the phonon density of states for both constituent materials.

A resonant Raman study of the anti-Stokes and Stokes spectra for individual isolated single-wall carbon nanotubes is presented. The observed asymmetry between the anti-Stokes and Stokes spectra is analyzed within the framework of resonant Raman scattering theory, thereby providing a method for accurately determining the transition energy between van Hove singularities ${E}_{\mathrm{ii}}$ in the electronic density of states and unambiguously assigning the $(n,m)$ nanotube indices. Furthermore, resonant Raman theory allows us to determine whether the resonance is with the incident or scattered photon, and to estimate the relative magnitudes of the matrix elements for the G-band and the radial breathing mode Raman processes.

The Raman spectra of ${\mathrm{PbZr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}$ ceramics with titanium concentration varying between $x=0.40$ and 0.60 were measured at 7 K. By observing the concentration-frequency dependence of the vibrational modes, we identified the boundaries among the rhombohedral, monoclinic, and tetragonal ferroelectric phases. The analysis of the spectra was made in the view of group theory analysis making possible the assignment of some modes for the monoclinic phase.