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In this work, we explain the origin and the mechanism responsible for the strong enhancement of the Raman signal of sulfur chains encapsulated by single-wall carbon nanotubes by running resonance Raman measurements in a wide range of excitation energies for two nanotube samples with different diameter distributions. The Raman signal associated with the vibrational modes of the sulfur chain is observed when it is confined by small-diameter metallic nanotubes. Moreover, a strong enhancement of the Raman signal is observed for excitation energies corresponding to the formation of excited nanotube-chain-hybrid electronic states. Our hypothesis was further tested by high pressure Raman measurements and confirmed by density functional theory calculations of the electronic density of states of hybrid systems formed by sulfur chains encapsulated by different types of single-wall carbon nanotubes.

Filling carbon nanotubes with molecules is a route for the development of electronically modified one-dimensional hybrid structures for which the interplay between the electronic structure of molecules and nanotubes is a key factor. Tuning these energy levels with external parameters is an interesting strategy for the engineering of new devices and materials. Here we show that the hybrid system composed by quaterthiophene (4T) molecules confined in single-walled carbon nanotubes, presents a piezo-Raman-resonance of the molecule vibrational pattern. This behavior manifests as a rapid pressure induced enhancement of the 4T Raman mode intensities compared to the tubes G-band Raman modes. Density functional theory calculations allow to explain the spectral behaviour through the pressure-enhanced quaterthiophene resonance evolution. By increasing pressure, the tube cross-section deformation leads to a reduction of the intermolecular distance, to the splitting of the molecular levels and then to an increase of resonance channels. Calculations and experiments converge to the 4T piezo-resonance scenario associated with the pressure-induced nanotube radial collapse observed at about 0.8 GPa. Our findings offer possibilities for the development of pressure transducers based on molecule-filled carbon nanotubes.

Cellulose nanocrystals (CNCs) have emerged as a sustainable nanomaterial for several environmental applications, including the development of novel antimicrobial agents. Although previous studies h...

A new approach to improve the electrical and thermal contacts between multi-walled carbon nanotubes and metallic electrodes was developed by using spatially localized laser heating coupled with a micro Raman equipment. After the deposition by dielectrophoresis, the nanotubes were heated in ambient atmosphere by a focused laser beam in order to improve the electrical contacts of the nanostructures with different electrodes (W, Ti and Au) and also to excite the Raman signal of the nanotubes. The changes in the vibrational frequencies of the Raman bands of the nanotubes provides a real time feedback of the treatment conditions allowing to estimate the local temperature, which is used for adjusting the parameters of treatment. Laser treatment tests were performed in a single step (single exposition of the sample to laser) or gradually (successive expositions of the sample to laser, with gradual increase of the used laser power density) and better results were obtained for the gradual treatment tests. Laser treatment of contacts carried out after the calibration of the treatment parameters, showed a reduction of up to three orders of magnitude in the electrical resistance of the devices. The main advantage of this method, when compared with traditional and rapid thermal annealing, is that the thermal treatment is localized in a small region, thus allowing the processing of circuits composed of different materials, whereby each process can be individually controlled.

This article aims to discuss time in two Claricean novels: Perto do coracao selvagem (1944) and Agua viva (1973). The discussion about time in Clarice will not be guided by the dichotomy between psychological time and chronological time, but by the treatment given to time in these two novels separated by an interval of twenty-nine years: time as god, as character, and as theme. The discussion is divided into three main characteristics of time in both novels: time of the time itself, the attempt to seize time, and the relationship between creation and the instant-now.

The search for targeted modifications of graphene to tune its electronic properties has stimulated the proposal of several new allotropic variations of carbon with s p and s p 2 hybridizations. In this study, a class of 2-dimensional carbon nanostructures with mixed s p 2 − s p 3 hybridization is theoretically investigated. These structures contain hexagonal and tetragonal cycles and are shown to exhibit metallic or semiconducting behaviors depending on structural parameters. The key for the manipulation of the physical properties is the extent of the system’s graphene-like section. Remarkable properties emerge, such as Dirac cones, which are allowed by the coupling between different sectors of the system as mediated by tetrahedrally-coordinated carbon atoms. In addition to fundamental properties, we also point aspects suggesting the experimental feasibility of these systems.

Magnetic carbonaceous nanocomposites (MCN) were prepared by hydrothermal carbonization (HTC) of a carbohydrate in the presence of Fe3+, followed by thermal treatment with KOH for simultaneous activation and magnetization. The precursor formed (IOCN) in the HTC process contained iron oxide nanoparticles encapsulated in the hydrochar matrix. The thermochemical parameters of the activation (temperature and IOCN/KOH mass-ratio) were varied to achieve an increase of the specific surface area along with formation of magnetic phases in MCN compared to IOCN. Activation temperature was found to be responsible for the structural and morphological properties of the MCNs whereas the IOCN/KOH mass-ratio controlled the porosity. The magnetic properties of the MCNs originated from the formation of Fe3O4 and Fe0 phases, which are encapsulated in the carbonaceous material. The MCNs were tested for adsorption of methylene blue (MB) dye, followed by magnetic separation. The MCN, produced in the optimized conditions, showed a specific surface area of 766 m2 g−1, magnetization of 8 emu g−1 and a MB adsorption capacity of 570 mg g−1. Detailed kinetic and isotherm studies of MB adsorption were also performed. The methodology of simultaneous activation and magnetization to generate MCNs, presented here, could be extended to obtain new multifunctional carbon-based nanocomposite adsorbent starting from different biomasses.

Doping tungsten oxide with other metals is a promising approach for obtaining improved properties as compared with its undoped counterpart. Here, the effect of molybdenum doping on the morphology, crystalline structure, and adsorption properties of nanostructured WO3 was investigated. Undoped and Mo-doped hexagonal WO3 (h-WO3) nanowire bundles were synthesized by hydrothermal method. The samples were characterized by X-ray powder diffraction, transmission electron microscopy, scanning transmission electron microscopy, selected-area electron diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Raman spectroscopy. The surface areas of the samples were evaluated by N2 adsorption–desorption isotherm, and their adsorption properties were evaluated based on their ability to adsorb cationic dye methylene blue (MB) in aqueous solution. Upon the addition of molybdenum, the morphology of the h-WO3 nanowire changes from large bundles to narrow bundles with a higher number of isolated thin nanowires. Mo doping also has changed the crystalline structure, porosity, and surface area of the bundled h-WO3 nanowires. Interestingly, Mo-doped h-WO3 nanowire bundles exhibit an enhanced and faster MB uptake, thus implying that Mo-doping WO3 can be an effective strategy to improve the adsorption properties, thereby adding value in developing alternative adsorption-based methods for wastewater treatment.

Silver nanoparticles (AgNPs) have a large number of applications in technology and physical and biological sciences. These nanomaterials can be synthesized by chemical and biological methods. The biological synthesis using fungi represents a green approach for nanomaterial production that has the advantage of biocompatibility. This work studies silver nanoparticles (AgNPs) produced by fungi Rhodotorula glutinis and Rhodotorula mucilaginosa found in ordinary soil of the Universidade Federal do Ceará campus (Brazil). The biosynthesized AgNPs have a protein-capping layer involving a metallic Ag core. The focus of this paper is to investigate the size and structure of the capping layer, how it interacts with the Ag core, and how sensitive the system (core + protein) is to visible light illumination. For this, we employed SEM, AFM, photoluminescence spectroscopy, SERS, and dark-field spectroscopy. The AgNPs were isolated, and SEM measurements showed the average size diameter between 58 nm for R. glutinis and 30 nm for R. mucilaginosa. These values are in agreement with the AFM measurements, which also provided the average size diameter of 85 nm for R. glutinis and 56 nm for R. mucilaginosa as well as additional information about the average size of the protein-capping layers, whose found values were 24 and 21 nm for R. mucilaginosa and R. glutinis nanoparticles, respectively. The protein-capping layer structure seemed to be easily disturbed, and the SERS spectra were unstable. It was possible to identify Raman peaks that might be related to α-helix, β-sheet, and protein mixed structures. Finally, dark-field microscopy showed that the silver cores are very stable, but some are affected by the laser energy due to heating or melting.

The knowledge of the phonon coherence length is of great importance for two-dimensional-based materials since phonons can limit the lifetime of charge carriers and heat dissipation. Here we use tip-enhanced Raman spectroscopy (TERS) to measure the spatial correlation length Lc of the A1g1 and A1g2 phonons of monolayer and few-layer gallium sulfide (GaS). The differences in Lc values are responsible for different enhancements of the A1g modes, with A1g1 always enhancing more than the A1g2, independently of the number of GaS layers. For five layers, the results show an Lc of 64 and 47 nm for A1g1 and A1g2, respectively, and the coherence lengths decrease when decreasing the number of layers, indicating that scattering with the surface roughness plays an important role.

2D fullerene-based carbon nanostructures have been recently proposed theoretically. They are conceptually formed by the arrangement of fragments resulting from the unzipping of C 60 molecules. Depending on the details of the assembly, these layer materials exhibit either semiconducting or metallic behavior. Here, we investigate the structural and electronic properties of achiral nanotubes by means of first-principles calculations. We show that this new class of nanotubes are not only energetically stable, but also share many properties similar to those of their 2D counterparts. In addition, the semiconducting cases can exhibit either direct or indirect band gaps. We further show that the electronic properties can be modulated by the presence of a transverse electric field due to an electrostatic potential symmetry breaking. We find that the electric field promotes a radial deformation that grows linearly with the strength of the electric field. In addition, the semiconducting tubes can undergo a semiconducting-metallic transition for a sufficiently large electric field. The study shows that these structures have potential for applications in the area of new nanodevices owing to their tunable band gap.

The radial stability and the irreversible transformation of triple-wall carbon nanotubes (TWCNTs) bundles are investigated at high pressure conditions both experimentally and theoretically (exp. up 72 GPa). The tubes having a mean internal diameter of 0.83 nm and graphite-like intertube distance, show an onset of the radial collapse evidenced by the evolution of optical phonons. The nanotube collapse onset is observed at ∼ 22 GPa completes for the two external tubes at ∼ 29 GPa, however the innermost tube remains stable up to ∼ 37 GPa. Molecular dynamic calculations performed on smaller diameter TWCNTs bundles, as a model system, confirmed the multiple-stage pressure-induced collapse process. An analytical expression for the collapse pressure of carbon nanotubes having an arbitrary number of walls is proposed. Our experiments and modelling show that for pressures beyond ∼ 60 GPa an irreversible structural transformation of TWCNTs takes place. Ex situ transmission electron microscopy characterization on the recovered sample from 72 GPa revealed the mechanical failure of carbon nanotubes which evolve towards ribbon-like structures as corroborated by Raman spectroscopy. Modelling the tubes evolution at high pressure and high temperature showed the formation of new structures ranging from ribbon-like to graphite-like with either different degrees of amorphization or s p 3 interlinking.

Silver nanoparticle (AgNPs) toxicity is related to nanoparticle interaction with the cell wall of microorganisms and plants. This interaction alters cell wall conformation with increased reactive oxygen species (ROS) in the cell. With the increase of ROS in the cell, the dissolution of zero silver (Ag0) to ionic silver (Ag+) occurs, which is a strong oxidant agent to the cellular wall. AgNP interaction was evaluated by transmission electron microscopy (TEM) on Lactuca sativa roots, and the mechanism of passage through the outer cell wall (OCW) was also proposed. The results suggest that Ag+ binds to the hydroxyls (OH) present in the cellulose structure, thus causing the breakdown of the hydrogen bonds. Changes in cell wall structure facilitate the passage of AgNPs, reaching the plasma membrane. According to the literature, silver nanoparticles with an average diameter of 15 nm are transported across the membrane into the cells by caveolines. This work describes the interaction between AgNPs and the cell wall and proposes a transport model through the outer cell wall.

Group-III post-transition-metal monochalcogenides like gallium sulfide (GaS) are layered semiconductors with weakly interacting adjacent layers, which allow them to be reduced to the two-dimensional nanometric thickness level by different exfoliation approaches, similar to graphene. Here, we investigate the intensity polarization dependence of the Raman modes for a different number of GaS layers and use symmetry analysis and density-functional perturbation theory to provide further information on these structures. The Raman polarization-dependent behaviors of the bulk relative modes ${\mathrm{A}}_{1g}$ and ${\mathrm{E}}_{2g}$ were found to be independent of the number of layers, being proportional to ${cos}^{2}(\ensuremath{\theta})$ for ${\mathrm{A}}_{1g}$ modes and constant for ${\mathrm{E}}_{2g}$ modes. The computational calculations for two and three layers show Raman active modes emerging at Raman shifts near the bulk Raman modes, with ${\mathrm{A}}_{1g}$ (${\mathrm{A}}_{1}^{\ensuremath{'}}$) and ${\mathrm{E}}_{g}$ (${\mathrm{E}}^{\ensuremath{'}}$) symmetries for an even (odd) number of layers, some of them being observed as ``shoulders'' in the experimental Raman spectra. These phonon modes present Raman tensors with components similar to those observed in bulk, thus explaining the same polar dependencies for different GaS thicknesses. The Raman intensity calculations were made by implementing the specific experimental geometry used here, thus resulting in good qualitative agreement. These results are fundamental for the understanding of the structural and vibrational changes when GaS is reduced to the few-layer limit, layer-number differentiation, and for further symmetry-lowering studies by strain manipulation or substrate interaction, which are routine issues in both fundamental research and device fabrication.

Tripentaphenes are 2D nanocarbon lattices conceptually obtained from the assembly of acepentalene units. In this work, density functional theory is used to investigate their structural, electronic, and vibrational properties. Their bonding configuration is rationalized with a resonance mechanism, which is unique to each of the 2D assemblies. Their formation energies are found to lie within the range of other previously synthesized carbon nanostructures and phonon calculations indicate their dynamical stability. In addition, all studied tripentaphenes are metallic and display different features (e.g., Dirac cone) depending on the details of the atomic structure. The resonance structure also plays an important role in determining the electronic properties as it leads to delocalized electronic states, further highlighting the potential of the structures in nanoelectronics.

Phonons play a fundamental role in the electronic and thermal transport of 2D materials which is crucial for device applications. In this work, we investigate the temperature-dependence of A[Formula: see text] and A[Formula: see text] Raman modes of suspended and supported mechanically exfoliated few-layer gallium sulfide (GaS), accessing their relevant thermodynamic Gruneisen parameters and anharmonicity. The Raman frequencies of these two phonons soften with increasing temperature with different [Formula: see text] temperature coefficients. The first-order temperature coefficients θ of A[Formula: see text] mode is ∼ -0.016 cm-1/K, independent of the number of layers and the support. In contrast, the θ of A[Formula: see text] mode is smaller for two-layer GaS and constant for thicker samples (∼ -0.006 2 cm-1 K-1). Furthermore, for two-layer GaS, the θ value is ∼ -0.004 4 cm-1 K-1 for the supported sample, while it is even smaller for the suspended one (∼ -0.002 9 cm-1 K-1). The higher θ value for supported and thicker samples was attributed to the increase in phonon anharmonicity induced by the substrate surface roughness and Umklapp phonon scattering. Our results shed new light on the influence of the substrate and number of layers on the thermal properties of few-layer GaS, which are fundamental for developing atomically-thin GaS electronic devices.

This paper reports the study of the metastable hexagonal molybdenum oxide (h-MoO3) rods by looking at the vibrational, structural and morphological properties. The MoO3 as-synthesized rods were prepared by the precipitation method and characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy, revealing a hexagonal phase and submicrometric size of the MoO3. The vibrational modes of the h-MoO3 were calculated by density-functional perturbation theory (DFPT) and used by first time to do the signature of the experimentally observed Raman modes, filling a gap in this field. Experimental temperature-dependent Raman spectroscopy study was carried out on h-MoO3 rods and pointed out to a phase transition in the 675-690 K temperature range. This phase transition was confirmed by scanning electron microscopy that was used to analyze the morphological changes in the MoO3 samples during the heating cycle. Temperature-dependent Raman data analysis combined with DFT calculations allowed us to confirm the mechanism that underlies the stability loss of the hexagonal phase at the critical temperature and to correlate the wavenumber difference of two specific Raman bands with the real temperature of the sample.

Laser-induced thermal effects on the hexagonal MoO3 nanorods at different power density levels were studied using Raman spectroscopy and scanning electron microscopy techniques. The structural features of the nanorods were accompanied by varying the incident laser power from 8.0 to 600 mW by using a gradual increasing rate and a sudden increasing incident laser power. It was shown that the photoeffects observed on the MoO3 nanorods critically depends on the exposure rate. By gradually increasing the incident laser power up to 600 mW, morphology of the nanorods were completely preserved, and the observed thermal behavior was discussed on the basis of thermal contact at nanoscale. However, when the irradiation intensity was suddenly increased, it was observed that overheating of h-MoO3 nanorods at relatively lower laser powers (80 mW) sublimate the nanorods around the laser spot region. The MoO3 molecules on vapor-phase at high temperatures condense and crystallize next to the laser spot on the orthorhombic (α-MoO3) and monoclinic (β-MoO3) phases. Furthermore, the nanorods closest to the laser spot region undergo a structural phase (and morphological) transition from h-MoO3 phase to α-MoO3 phase.

Spin-polarized transport through a rhombic graphene quantum dot (rGQD) attached to armchair graphene nanoribbon (AGNR) electrodes is investigated by means of the Green’s function technique combined with single-band tight-binding (TB) approach including a Hubbard-like term. The Hubbard repulsion was included within the mean-field approximation. Compared to anti-ferromagnetic (AFM), we show that the ferromagnetic (FM) ordering of the rGQD corresponds to a smaller bandgap, thus resulting in an efficient spin injector. As a consequence, the electron transport spectrum reveals a spin valve effect, which is controlled by doping with B/N atoms creating a p-n-type junction. The calculations point out that such systems can be used as spin-filter devices with efficiency close to a 100 % .

MoO3 nanoribbons were studied under different pressure conditions ranging from 0 to 21GPa at room temperature. The effect of the applied pressure on the spectroscopic and morphologic properties of the MoO3 nanoribbons was investigated by means of Raman spectroscopy and scanning electron microscopy techniques. The pressure dependent Raman spectra of the MoO3 nanoribbons indicate that a structural phase transition occurs at 5GPa from the orthorhombic α-MoO3 phase (Pbnm) to the monoclinic MoO3-II phase (P21/m), which remains stable up to 21GPa. Such phase transformation occurs at considerably lower pressure than the critical pressure for α-MoO3 microcrystals (12GPa). We suggested that the applanate morphology combined with the presence of crystalline defects in the sample play an important role in the phase transition of the MoO3 nanoribbons. Frequencies and linewidths of the Raman bands as a function of pressure also suggest a pressure-induced morphological change and the decreasing of the nanocrystal size. The observed spectroscopic changes are supported by electron microscopy images, which clearly show a pressure-induced morphologic change in MoO3 nanoribbons.

The study of the mechanical properties of nanostructured systems has gained importance in theoretical and experimental research in recent years. Carbon nanotubes (CNTs) are one of the strongest nanomaterials found in nature, with Young’s Modulus (EY) in the order 1.25 TPa. One interesting question is about the possibility of generating new nanostructures with 1D symmetry and with similar and/or superior CNT properties. In this work, we present a study on the dynamical, structural, mechanical properties, fracture patterns and EY values for one class of these structures, the so-called pentagraphene nanotubes (PGNTs). These tubes are formed rolling up pentagraphene membranes (which are quasi-bidimensional structures formed by densely compacted pentagons of carbon atoms in sp3 and sp2 hybridized states) in the same form that CNTs are formed from rolling up graphene membranes. We carried out fully atomistic molecular dynamics simulations using the ReaxFF force field. We have considered zigzag-like and armchair-like PGNTs of different diameters. Our results show that PGNTs present EY ∼ 800 GPa with distinct elastic behavior in relation to CNTs, mainly associated with mechanical failure, chirality dependent fracture patterns and extensive structural reconstructions.

The structural and electronic properties of double-walled α -graphyne nanotubes ( α -DWGNTs) are investigated using a combination of computation and theoretical methods, including density functional theory. DWGNTs differ from conventional double-walled carbon nanotubes by the presence of carbon atoms featuring both sp and sp 2 hybridizations, endowing DWGNTs with a set of desirable properties that could lead to a number of applications. Classical molecular dynamics (MD) and Born–Oppenheimer molecular dynamics (BOMD) simulations were performed to reveal the structural stability of these nanotubes at room temperature. Their dynamical stability was confirmed using tight-binding based phonons calculations. The high flexibility of the graphyne sheet and van der Waals interactions between the shells lead to strong deformations of the outer tube. Consequently, the electronic structure of the component single-walled tubes undergoes significant changes once cast into the double-walled geometries due to the coupling of electronic states from the inner wall with the outer tube. Such strong inter-wall hybridization can not only modulate the electronic band gap of semiconducting tubes, in comparison to their isolated single-walled counterparts, but can also affect the electronic properties of the double-walled systems. These behaviors open up possibilities of using such nanostructures in the design of electronic device applications.

In this work, industrial grade multi-walled carbon nanotubes (MWCNT) were coated with humic acid (HA) for the first time by means of a milling process, which can be considered an eco-friendly mechanochemical method to prepare materials and composites. The HA-MWCNT hybrid material was characterized by atomic force microscopy (AFM), scanning electron microscopies (SEM and STEM), X-ray photoelectron spectroscopy (XPS), termogravimetric analysis (TGA), and Raman spectroscopy. STEM and AFM images demonstrated that the MWCNTs were efficiently coated by the humic acid, thus leading to an increase of 20% in the oxygen content at the nanotube surface as observed by the XPS data. After the milling process, the carbon nanotubes were shortened as unveiled by SEM images and the values of ID/IG intensity ratio increased due to shortening of the nanotubes and increasing in the number defects at the graphitic structure of carbon nanotubes walls. The analysis of TGA data showed that the quantity of the organic matter of HA on the nanotube surface was 25%. The HA coating was responsible to favor the dispersion of MWCNTs in ultrapure water (i.e. -42mV, zeta-potential value) and to improve their capacity for copper removal. HA-MWCNTs hybrid material adsorbed 2.5 times more Cu(II) ions than oxidized MWCNTs with HNO3, thus evidencing that it is a very efficient adsorbent material for removing copper ions from reconstituted water. The HA-MWCNTs hybrid material did not show acute ecotoxicity to the tested aquatic model organisms (Hydra attenuata, Daphnia magna, and Danio rerio embryos) up to the highest concentration evaluated (10mgL-1). The results allowed concluding that the mechanochemical method is effective to coat carbon nanotubes with humic acid, thus generating a functional hybrid material with low aquatic toxicity and great potential to be applied in environmental nanotechnologies such as the removal of heavy metal ions from water.

The effect of pressure – by definition a 3-dimensional concept – on 2-dimensional systems brings a number of fundamental questions, which have been partly answered through newly engineered samples and experimental setups. In this review of the high-pressure Raman studies of graphene, we will in particular underline the importance of the presence of a supporting substrate and its role for the production of biaxial strain conditions in high pressure experiments. Raman shifts observed during these experiments may be related to the strain induced by the substrate rather than by the applied pressure, graphene stress, and hydrostatic pressure not being straightforwardly equivalent in this case of a composite 2D-on-3D material. We will also consider the effects of the nature of the substrate surface, the nature of the pressure transmittingmedia, aswell as the effect of the number of layers on the high-pressure response of the 2D–system, by using the phonon behavior as strain probe as pressure is applied. The effects of adhesion and of strain transfer from the substrate to the 2D–system will be at the heart of our discussion.

We synthesized sub-100 nm “biogenic” protein-capped silver nanoparticles (bio-AgNPs) from a yeast extract (Rhodotorula glutinis) and assessed the chemical stability of their coatings formed on various silane-modified substrates up to the millimeter length scale. Large-field (LF) X-ray imaging was used for scanning AgNPs-coated substrates (5 × 5 mm) after they were immersed in physiological PBS for hours. Striking differences were found in the amount and the structural organization of bio-AgNPs in the coatings depending on the type of surface silanization. The relative amount of bio-AgNPs in the coatings increases due to the assembly of enlarged (8–30 μm2 in area) and chemically stable agglomerates of bio-AgNPs formed on a multilayered aminosilane film (average 230 nm thickness), which was generated with the use of 3-aminopropyltrimethoxysilane (APTMS). In contrast, substantially less bio-AgNPs was found on the hydrophobic silane film generated with the use of trimethoxyphenylsilane (TMPS) and on the films...

In this paper we present a Raman spectroscopy study of Na

Graphyne nanotubes (GNTs) are nanostructures obtained from rolled up graphyne sheets, in the same way carbon nanotubes (CNTs) are obtained from graphene ones. Graphynes are 2 D carbon-allotropes composed of atoms in sp and sp 2 hybridized states. Similarly to conventional CNTs, GNTs can present different chiralities and electronic properties. Because of the acetylenic groups (triple bonds), GNTs exhibit large sidewall pores that influence their mechanical properties. In this work, we studied the mechanical response of GNTs under tensile stress using fully atomistic molecular dynamics simulations and density functional theory (DFT) calculations. Our results show that GNTs mechanical failure (fracture) occurs at larger strain values in comparison to corresponding CNTs, but paradoxically with smaller ultimate strength and Young’s modulus values. This is a consequence of the combined effects of the existence of triple bonds and increased porosity/flexibility due to the presence of acetylenic groups.

What aspects are relevant to understand and predict the outstanding properties and uses of nanomaterials? From the combination of the compositional characteristics of atoms (e.g., atomic number, size, electronegativity), the way they organize in space (e.g., symmetry, crystallinity, energy levels), along with their shape (i.e., morphology), it is commonly possible to understand the properties manifested by nanomaterials. This composition-structure-morphology-property correlation was highly refined by 20th century physics and chemistry knowledge. The rational understanding of this correlation enables scientists and engineers to predict and produce nanomaterials that will efficiently remove water contaminants, detect pollutants, or convert sunlight into electricity. In this context, nanomaterials properties of environmental interest will be discussed in this chapter, and representative examples will be provided as an introduction to this multidisciplinary field. In addition, the high-end technics and tools currently used to access and reveal the composition, structure, and morphology of nanomaterials will result in identifying their environmentally significant properties.

Recently, a new two-dimensional carbon allotrope called Penta-graphene membrane was proposed. The Penta-graphene membrane exhibits interesting mechanical and electronic properties, including typical band gap values of semiconducting materials. Penta-graphene has a Cairo-tiling-like 2D lattice of non coplanar pentagons and its mechanical properties still have not been fully investigated. In this work, we combined reactive molecular dynamics (MD) simulations and density functional theory (DFT) calculations to investigate the mechanical properties and fracture patterns of Penta-graphene membranes under tensile stress. We show that Penta-graphene membranes can hold up to 20% of strain and that fracture occurs only after substantial dynamical bond breaking and the formation of 7, 8 and 11 carbon rings, as well as carbon chains. The stress-strain behavior was observed to follow two regimes, one exhibiting linear elasticity followed by a plastic one, involving carbon atom re-hybridization with the formation of carbon rings and chains.

In this study we report the temperature- and laser power-dependence of the out-of-plane A1g Raman mode of mechanically exfoliated few-layered WSe2 suspended on Si3N4 holes. The A1g phonon frequency is red-shifted for a temperature in the range 77–548 K, with first-order temperature coefficients estimated to be −0.0083 and −0.0079 cm−1/K for suspended four- and six-layer WSe2, respectively. The laser power-dependence of suspended four-layer WSe2 sample is estimated to be −0.0079 cm−1/μW and no shift is observed for six-layer WSe2. By using the laser power-dependence of the suspended four layers WSe2 and the 1D Balandin's approach, we calculate the in-plane thermal conductivity of WSe2 at room temperature to be ∼57.7 W/m K.

Nitrogen-containing porous carbonaceous materials based on chitosan were successfully prepared by hydrothermal carbonization (HTC) followed by thermal treatments at different temperatures. A detailed characterization of structure, porosity, and chemical composition of these carbonaceous materials was done by X-ray diffraction, scanning electron microscope, thermogravimetric analysis, Raman and infrared spectroscopies, nitrogen adsorption-desorption isotherms, and CHN elemental analysis techniques. Low structural order like amorphous carbons, low porosity, and various functional groups were observed for the precursor hydrochar (obtained from hydrothermal carbonization of chitosan). When this precursor was thermally treated from 200 to 800 °C it was possible to understand its structural transformations due to the changes in the vibrational properties. These results indicate that an increase in the temperature of the thermal treatment promotes an increase in the graphitization degree of the carbonaceous materials. However, it leads to the formation of a defective graphitic-type structure. Furthermore, it was observed an increase in the meso- and micropores up to 600 °C, affecting considerably the porosity and, consequently, the specific surface area of these materials. However, this porous structure can collapse when the treatment temperature increases to 700 and 800 °C. Also, the prepared carbonaceous materials showed high nitrogen content for all temperature interval, and the morphology of the particles was not strongly affected. Our results suggest that thermal treatments of hydrochars are suitable to prepare carbonaceous materials with controlled compositional, structural and textural properties and containing a high nitrogen content.

This paper reports the temperature-dependent study of β-Ag 2 MoO 4 micro-crystals using Raman spectroscopy. The micro-crystals were prepared by the hydrothermal method, and lattice dynamic calculations based on the density-functional theory (DFT) were used to assign the Raman modes observed in the spectrum and to support the understanding of the mechanism driving the vibrational changes undergone by β-Ag 2 MoO 4 . The effect of the temperature on the vibrational properties of the β-Ag 2 MoO 4 has been investigated in the temperature range from 300 to 850 K. The Raman data indicated that the crystal exhibits two temperature-induced phase transformations. One of them was assigned to a first-order phase transition (from cubic to unknown symmetry) occurring at about 541 K, connected with some disorder in the MoO 4 tetrahedron, therefore, leading to tiltings and/or rotations of the MoO 4 units, as revealed by changes in the Raman spectra. The second phase transition was observed at about 700 K, thus leading the crystal to change its symmetry from the unknown phase to the same cubic room temperature symmetry (reentrant phase transition).

This article reviews recent advances on the use of Raman spectroscopy to study and characterize carbon nanostructures. It starts with a brief survey of Raman spectroscopy of graphene and carbon nanotubes, followed by recent developments in the field. Various novel topics, including Stokes–anti-Stokes correlation, tip-enhanced Raman spectroscopy in two dimensions, phonon coherence, and high-pressure and shielding effects, are presented. Some consequences for other fields—quantum optics, near-field electromagnetism, archeology, materials and soil sciences—are discussed. The review ends with a discussion of new perspectives on Raman spectroscopy of carbon nanostructures, including how this technique can contribute to the development of biotechnological applications and nanotoxicology.

Fabrication of graphene nanostructures it is important for both investigating their intrinsic physical properties and applying them into various functional devices. In this work we present a study on atomic layer deposition (ALD) of Al2O3 to produce patterned graphene through area-selective chemical vapor deposition (CVD) growth. A systematic parametric study was conducted to determine how the number of cycles and the purging time affect the morphology and the electrical properties of both graphene and Al2O3 layers.

In this work, we report results of high-pressure Raman experiments (P

Silver nanoparticles (AgNPs) have a large number of technological applications, such as photonic devices, molecular diagnostics, antimicrobial coating and biomedical devices. These nanomaterials can be synthesized using common fungi, which represents a green approach with the additional advantage of biocompatibility. Here we applied Tip-Enhanced Raman Spectroscopy (TERS) to obtain optical characterization with resolution beyond the diffraction limit of AgNPs produced by Rhodotorula glutinis and Rhodotorula mucilaginosa fungi. Those fungi are conventional found in ordinary soil of north part of Brazil, which biosynthesize core-shell AgNPs with protein-capping layer. With TERS we were able to investigate with lateral resolution of few nanometers the size and structure of the protein capping layer, how it interacts with the Ag core, and how sensitive the system (core + protein) is to visible light illumination. Despite the complex data generated which depends on the orientation of the protein, which is highly, it was possible to detect the stretching of the S - S sulfur bridge in amino acids. This stretch band is induced by a trans C α - S conformation acid on Rm-AgNPs, thus showing the potential of characterization of TERS in nanobiosystems.