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Herein, a ternary system of TeO2–ZnO–Na2O (TZN) with competitive roles of covalent Zn–O and ionic Na–O bonds in tellurite glassy network is examined for high‐temperature in situ X‐ray diffraction (XRD) and Raman spectroscopy. TZN glasses are doped with Nd2O3 and the effects of Nd doping on the crystallization of glasses are also written. In situ high‐temperature XRD permits the assignment of each of the differential scanning calorimetry (DSC) crystallization peaks (the first crystallization peak (Tc1) is related to sodium‐based crystalline phases, while the second crystallization peak (Tc2) is correlated with tellurium‐/zinc‐based crystalline phases). The study of in situ high‐temperature Raman spectroscopy shows that Tc1 shows γ‐TeO2 crystallized phase‐like peaks while Tc2 crystallization has more α‐TeO2‐crystallized phase‐like peaks. Comparison at the same temperature (430 °C) permits a first understanding of the structural changes of the glasses in terms of the evolution first to α‐TeO2, ZnO, ZnTeO3, and Zn2Te3O8 crystalline phases compared with Na10Zn4O9 phase. The ZnTeO3 and Zn2Te3O8 crystallization evolution is also compared between the Nd‐doped and nondoped glasses, which gives more insight into the tellurite glass structures. [ABSTRACT FROM AUTHOR]

The present paper is devoted to the influence of the growth temperature of multi‐walled carbon nanotubes (MWCNTs) on their defective structure. The MWCNTs obtained within the range of 610–750 °C have been studied using two methods: Raman spectroscopy and the analysis of the temperature dependence of conductivity. This approach allows us to obtain independent data on the concentration of the defects within the MWCNTs via the intensity ratio of 2D and D bands, on one hand, and charge carrier concentration, on the other hand. The results obtained using Raman spectroscopy and the analysis of the conductivity have provided asymptotic and volcano‐like curves, respectively, of defect concentration within the temperature range studied. This can be attributed to the difference in the probing depth of each method (∼50 nm for Raman spectroscopy, and ∼2–3 nm for conductivity measurements) providing different sensitivity to surface impurities or defects. The secondary factors (the size of the active component, the amount of the lateral carbon deposits) have been shown to mask the influence of the growth temperature. Nevertheless, as these secondary factors and the synthesis temperature independently affect the effective nanotube defectiveness, we have shown the defect concentration to fall with increasing MWCNT growth temperature. [ABSTRACT FROM AUTHOR]

In this paper, we report on the diameter distribution of boron-doped single-walled carbon nanotubes grown from triethyl borate with high vacuum chemical vapor deposition, using multi-frequency Raman resonance spectroscopy. The nanotube yield is higher than in previously reported material produced with the same method. Our results suggest that the amount of as-grown material and the range of diameters are directly correlated with feedstock used in the synthesis. The ID/ IG ratio shows that the morphology of the samples is critically affected by the temperature. The population of diameters in the optimal conditions shows a Poisson distribution with a mean value at ∼1.15 nm. [ABSTRACT FROM AUTHOR]

Curved graphene fragments can be considered as building blocks of carbon nanotubes. Thus, the size of graphene fragments may be considered as one of the most important characteristics of their structural disorder. In this paper, we have performed a comparative Raman study of CVD multi-walled carbon nanotubes (MWCNTs) and graphene flakes deposited on MWCNTs. Raman data have been considered in combination with HRTEM characterization of nanotubes. The basic attention has been paid to the behavior of D (disorder-induced), G (tangential mode), and 2D (two-phonon scattering) bands in Raman spectra in order to use them for MWCNT characterization. A ratio of intensities of 2D and D bands ( I2D/ ID) demonstrates almost a linear dependence on the mean diameter of MWCNTs produced with two different types of catalysts (see abstract figure). It should be mentioned that each type of catalyst provides the linear dependence with its own specific slope. The graphene fragments have been proposed to form a mosaic structure of nanotube walls. I2D/ ID ratio depends on the amount of graphene flakes deposited on nanotube surface via ethylene decomposition. A dependence of intensity ratio I2D/ ID on the diameter of nanotubes produced with different types of catalysts. [ABSTRACT FROM AUTHOR]

This paper reports the analysis of the intensity of diamond line in the Raman spectra of laser modified layers with different thickness on a diamond surface. Since the diamond line passing from substrate through the absorbing layer of moderate thickness can be registered, the thickness of local area is estimated from its micro‐Raman spectra. The comparison between Raman scattering and direct observation of the graphitized layer by transmission electron microscopy shows that Raman spectroscopy can be used as an alternative non‐destructive method for measuring a moderate thickness of graphitized layers. [ABSTRACT FROM AUTHOR]

The structural transformations induced in Gd2O3 and Eu2O3 irradiated with high-energy ions (94-MeV Pb and 1042-MeV Xe), where ionization processes (electronic stopping) dominate the ion slowing-down, have been studied via the combination of XRD and Raman experiments. Irradiation induces a cubic-to-monoclinic phase transformation; the radiation-induced monoclinic phase shows strong preferential orientation. This structural modification is accompanied by changes in the photoluminescence properties of sesquioxides. The results show that swift heavy ion irradiation is a powerful tool to control the properties of oxides at the nanoscale. [ABSTRACT FROM AUTHOR]

In this paper, we have performed the filling of single‐walled carbon nanotubes (SWCNTs) with mean diameters of 1.4 and 1.9 nm synthesized by the arc‐discharge and chemical vapor deposition (CVD) methods, respectively, with silver chloride. The doping effect of the encapsulated compound on SWCNTs is studied by Raman spectroscopy and X‐ray photoelectron spectroscopy. It is shown that the filling of nanotubes with silver chloride leads to p‐doping of SWCNTs accompanied by charge transfer from the SWCNTs to the salt and downshift of their Fermi level. It is found that the filling of SWCNTs synthesized by different methods results in different doping levels of nanotubes. The arc‐discharge 1.4 nm‐diameter SWCNTs have larger doping level than CVD 1.9 nm‐diameter nanotubes. The obtained information about the influence of the filler on the electronic properties of SWCNTs synthesized by different methods is elemental for applications of nanotubes in nanoelectronic devices. Kharlamova et al. perform the filling of single‐walled carbon nanotubes (SWCNTs) synthesized by the arc‐discharge and chemical vapor deposition methods with silver chloride. The electronic properties of the filled nanotubes are characterized by Raman spectroscopy and X‐ray photoelectron spectoscopy. The authors reveal different doping levels of SWCNTs synthesized by the different methods. [ABSTRACT FROM AUTHOR]

Lithium‐ion batteries (LIBs) waste is classified as a dangerous one. Hopefully, LIBs can be recycled, and they are already a valuable source of metals. This work is focused on the properties of the spent LIBs powder, which is a postproduct of the proposed organic leaching process and is presented as a source of nanocarbons with a unique structure. Furthermore, attention is paid to revealing the properties of the carbon component that can find a second life in other applications like photocatalysis or sorbents. Raman spectroscopy is used for the characterization of graphitic carbon. Scanning electron microscopy images are numerically quantitatively analyzed to provide additional parameters (for instance, the total length of edges) about the structure of materials, and X‐ray diffraction (XRD) and energy‐dispersive X‐ray spectroscopy (EDS) further check their composition. [ABSTRACT FROM AUTHOR]

One‐dimensional (1D) atomically thin crystals have attracted considerable interests due to their unique properties and potential applications. For example, reducing graphene physical size down to nanoscale to nanoribbons opens up band gaps, which makes graphene useful in electronic devices. Here, a facile approach to produce single‐ and bi‐layered MoS2 nanobelts by PMMA assisted decoupling of MoO2@MoS2 core–shell nanorods is reported by the authors. Atomic force microscopy (AFM), Raman and photoluminescence (PL) results show that the decoupled monolayer staple‐like MoS2‐shells can fold into bilayer nanobelts during the PMMA removal process. Raman, high‐resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) results reveal that the left MoO2 nanorods exhibit high crystal‐quality. These findings provide a method to produce 1D MoS2 nanobelts, which have potential applications in electronics and catalysis. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO2) powder in anatase phase is thermally evaporated by physical vapor deposition (PVD) on glass substrates. Different‐thickness TiO2 thin films are deposited on glass slides. The samples are then optically and structurally investigated using optical absorption (ABS) and Raman scattering (RS). Optical absorption spectroscopy shows that Urbach energy (EU) related to the width of the long‐wavelength tail decreased from 212 to 176 meV as the film thickness increased from 143 to 221 nm, respectively. The grain size, which depends on thickness of the film, a00nd the grain size distribution are evaluated by fitting the absorption coefficient α experimental data to a model of α as a function of energy E. Absorption edge energy (ER) is also calculated, it decreases by 165 meV as the film thickness increases from 143 to 221 nm. The energies of band gap transitions are also determined from the observed data of absorption. There are two types of transitions, i.e., direct and indirect transitions, in the TiO2 compound. The phonon confinement model is used to interpret the size effect in Raman scattering. Relative to the Raman active Eg mode of bulk TiO2 crystal, a size‐dependent blue shift is noticed in the Raman bands for the first and second Eg modes ( E g ( 1 ) : ≈144 cm−1 and E g ( 2 ): 197 cm−1, respectively). In this study, the results of Raman scattering and optical absorption are combined together in order to investigate the grain size effect, structural disorder, and thickness‐dependent strain. In ABS spectroscopy, it is noticed that (at certain wavelength) the intensity of the transmitted light for the thinner sample is higher than that for the thicker one, which is compatible with the relation I = I0e−αt, where α is the absorption coefficient and t is the thickness. [ABSTRACT FROM AUTHOR]

Here we present a detailed study of the chemical vapor deposition (CVD) method used in a real‐time regime for graphene film fabrication on nickel foils. Thin films with a wide range of thicknesses (from 3 up to 53 layers and more) have been obtained. A home‐made cold‐wall chamber for CVD realization is demonstrated in this work. It is supplied with tools for in situ monitoring the temperature‐dependent electrical resistance of nickel substrate to obtain a desired number of graphene layers in the sample synthesized. An area of 1 × 1 cm2 appeared to be covered by graphene. Raman spectroscopy and optical absorption spectroscopy are used to estimate the quality of graphene films fabricated and the graphene layer number. [ABSTRACT FROM AUTHOR]

The formation of active component of Fe–Mo and Co–Mo catalysts for carbon nanotube growth with variable Mo content is studied with in situ XRD, XPS, and STEM&EDX. The activation of bimetallic Fe–Mo catalysts under the growth conditions leads to the formation of Fe–Mo alloy particles in contrast to Co‐containing catalysts in which active alloy incorporates only a small portion of Mo (<2–3 at.%). The stable carbide formation for these systems is not detected. The effect of Mo content in Fe–Mo and Co–Mo catalysts on the properties of MWCNTs is additionally investigated using the Raman spectroscopy in combination with measurements of the temperature dependence of conductivity. It is shown that MWCNT defectiveness depends on the active component composition for both Fe–Mo and Co–Mo catalysts. The current carrier concentration for the MWCNTs grown on Fe–Mo catalysts slightly increases with the Mo content. The opposite effect is observed for the tubes grown on Co–Mo catalysts, showing a decrease in the current carrier concentration with the increase of Mo concentration. [ABSTRACT FROM AUTHOR]

The structure and electronic properties of the N‐doped bamboo‐like carbon nanotubes with different nitrogen content (N‐CNTs) are studied by the use of transmission electron microscopy, electron energy loss spectroscopy, Raman spectroscopy, and X‐ray photoelectron spectroscopy supplemented by measurements of the temperature dependence of conductivity. XPS data are used to estimate the content of nitrogen represented by pyridinic, pyrrolic, graphitic, and oxidized N species and encapsulated molecular nitrogen. The graphene blocks surrounded by borders containing hole defects and N‐species are considered as building blocks of N‐CNT walls. The intensity ratio of D, G, and 2D bands in Raman spectra and XPS data on the concentration of N‐species are used to analyze the size of defect‐free graphene blocks in N‐CNTs. The size of such blocks depends on the N‐defect content and is estimated to be 1–2 nm. The increase of N‐species content resulting in a decrease of graphene block size correlates with the decrease of current carrier concentration (nES) estimated within the Efros–Shklovskii model. [ABSTRACT FROM AUTHOR]

Structural modifications of tetrahedral amorphous carbon (ta‐C) films, caused by single‐pulse laser irradiation, were investigated. Graphitization of the films, content and size of sp2 carbon clusters were analyzed by means of Raman spectroscopy. It has been shown that pulse duration, as well as laser fluence and wavelength of irradiation, strongly influence the processes of graphitization and ablation of the ta‐C films. In particular, heating of the films by the laser beam leads to formation of sp2 carbon clusters and their enlargement up to the size of several nanometers. Material transformation to graphitized fraction is much more efficient in case of ns pulse duration. In case of fs pulse duration, such factors as multiphoton absorption and evaporation of over‐heated material from the surface at high laser fluence, shorter time of irradiation, and heat transfer to the inner layers of the film lead to relatively weak graphitization characterized by the maximum size of the sp2 carbon clusters of about 1 nm. [ABSTRACT FROM AUTHOR]

The growth of single-walled carbon nanotubes (SWCNT) inside host SWCNTs remains a compelling alternative to the conventional catalyst-induced growth processes. It not only provides a catalyst free process but also the ability to control the constituents of the inner tube if appropriate starting molecules are used. We report herein the growth of inner SWCNTs from 13C-enriched benzene or toluene and C60 fullerene with a natural isotopic distribution. The latter molecule is essentially a stopper which acts to retain the smaller toluene inside the tubes. The Raman spectrum of the inner nanotubes is anomalous as it contains a highly isotope shifted 'tail,' which cannot be explained by assuming a homogeneous distribution of the isotopes. Semi-empirical calculations of the Raman modes indicate that this unusual effect is explicable if small arrays of 13C are assumed. This indicates the absence of carbon diffusion during the inner tube growth. [ABSTRACT FROM AUTHOR]

We present experimental measurements of the features of G band in individual index-identified free-standing double-walled carbon nanotubes. We examine Raman spectra of different electronic configurations of DWNTs, namely: SC@SC, SC@M, M@SC, M@M, and clearly establish that, as in SWNTs, the profile of LO G-mode of each layer is broad (narrow) when the layer is metallic (semiconducting). The dependence of G-modes on the diameter and inter-layer distance in several SC@SC, SC@M, M@SC, M@M index-identified DWNTs is reported. We find, that, independently of the metallic or semiconducting nature of the layers, the frequencies of LO and TO G-mode of the inner and outer layers shift significantly with respect to the frequencies of the same modes in the constituent SWNTs. [ABSTRACT FROM AUTHOR]

Phase transitions in carbon:nickel nanocomposite templates during diameter-selective CVD synthesis of SWCNTs were studied. While almost conserving their pre-defined diameter distribution, as-deposited Ni3C nanoparticles transform into fcc-NiO during activation in low-pressure air atmosphere, and are reduced to a mixture of fcc-Ni and Ni3C under nanotube growth conditions. The first phase transition leads to a substitutional replacement of the protective carbon matrix by a protective oxide layer. The second one reflects competing reduction processes of NiO. A mechanism for the complementary roles of carbon matrix and Ni species in the three-step CVD synthesis is proposed that includes nanoparticle immobilization, carbon delivery and catalysis of nanotube growth. [ABSTRACT FROM AUTHOR]

The effect of the amount of sp3 defects in graphene on the graphene enhanced Raman scattering (GERS) is studied using gradual fluorination of chemical vapour deposition grown graphene covering the Rhodamine 6G molecules. While upon a mild fluorination the GERS effect is preserved, the GERS enhancement disappears in case of a strong fluorination. After partial removal of the fluorine from the strongly fluorinated graphene by water vapor treatment, the GERS effect is restored. [ABSTRACT FROM AUTHOR]

Surface-sensitive UV Raman spectroscopy is used to analyze the crystallinity of silicon films less than 20 nm thick directly on silicon wafers. The 325-nm excitation has a Raman detection thickness of only 13 nm within the silicon film, thus eliminating signal from the substrate. We demonstrate measured crystallinities of microcrystalline silicon thin films that are consistent with the microstructure observed in transmission electron microscopy. Comparison is also made to ellipsometry, which is less able to accurately determine crystallinity than UV Raman spectroscopy. The UV Raman approach is particularly useful for layers grown on substrates of the same material but with different microstructure, and can be extended to non-silicon materials. [ABSTRACT FROM AUTHOR]

A series of experiments was carried out to explore the conditions under which ZnSnN2 would form by vapor-liquid-solid synthesis from a Zn-Sn melt exposed to a nitrogen plasma. ZnSnN2 precipitated at melt temperatures between 455 and 560 °C for melt compositions between 1.5 and 15 at.% Zn. Sn3N4 formed for temperatures between 440 and 560 °C for melt compositions below 1 at.% Zn. Zn3N2 apparently grew only in the vapor phase, and only at melt temperatures between 409 and 463 °C. Each of the materials was identified by its characteristic Raman spectrum and by Auger chemical analysis. The composition profiles of the melts were modeled as a function of time using the measured temperature profiles. The results were compared with post-growth measurements of the melt compositions. These comparisons support the visual observation that exposure of the melt to the nitrogen plasma suppressed Zn evaporation substantially even prior to the formation of a solid crust of precipitate. This work helps define the range of growth conditions available for synthesis of ZnSnN2 by this vapor-liquid-solid method. Material yielded as a function of synthesis temperature and the composition of the melt, measured post-synthesis by EDS. The two ZnSnN2 samples labeled with asterisks were grown with a plasma power of 60 W. All others were grown using a plasma power of 240 W. [ABSTRACT FROM AUTHOR]

Single phase nickel-cobalt-titanate thin films with a formula A1+2 xTi1− xO3, where A is Ni2+,Co2+, and −0.25 < x < 1, were grown by pulsed laser deposition on sapphire substrates. There is a large window in which Ni/Co ratio and x can be chosen independently, allowing a control of properties by the synthesis. In the prototype ilmenite and corundum structures one third of the octahedra are vacant. The reported structure is obtained by filling vacant octahedra ( x > 0) or emptying filled octahedra ( x < 0). Films with x = 1 have all octahedra filled. X-ray photoelectron spectroscopy, X-ray diffraction measurements and Raman scattering techniques were applied to address the structure as a function of x. Data collected on samples with x ≈ 1 are interpreted in terms of hexagonal P63/ mmc space group. The hexagonal structure was obtained when films contained both Ni and Co: pure cobalt oxide thin films possessed the spinel structure. Two factors controlling the magnetism and crystal distortion are identified: a direct overlap between the adjacent cation d-orbitals resulting in a bond formation and magnetic interactions, and x controlling the cation shift toward the vacant octahedron. The displacement decreases and the symmetry increases with increasing x. When x ≈ 1 the cations prefer octahedron center positions. [ABSTRACT FROM AUTHOR]

CuInS2-Cu2ZnSnS4 crystals were synthesized by the pressure-less sintering method using CuInS2 and Cu2ZnSnS4 powders grown from each melt. The x values in Cu2(2In) x(ZnSn)(1.00− x)S4 were evaluated by energy dispersive spectroscopy. Lattice constants were derived from powder X-ray diffraction analysis by Rietveld method. Lattice constants of CuInS2 phase changed linearly at x ≥ 0.49. On the other hand, lattice constants of Cu2ZnSnS4 phase changed almost linearly at x ≤ 0.37. In Raman spectra, peak positions of A ( [ABSTRACT FROM AUTHOR]

Thin films of nitrogen-doped cuprous oxide (Cu2O:N) have been deposited by means of direct-current and radio-frequency sputtering using a metallic copper target and a mixture of argon, oxygen, and nitrogen for generating the plasma. The doping with nitrogen appears to significantly increase the electrical conductivity of the films. All samples exhibit a temperature-activated transport behavior. It is shown that the activation energy decreases proportionally to the reciprocal distance between nitrogen atoms, which indicates that a constant fraction of nitrogen is most likely substitutionally incorporated on oxygen site in the Cu2O lattice and acts as an acceptor. Nevertheless, Raman measurements suggest that molecular nitrogen can also be found in the samples, bound at different sites inside the bulk and at the surface. [ABSTRACT FROM AUTHOR]

Polarized Raman spectra of the epitaxial Ba0.4Sr0.6TiO3 film grown on MgO substrate with thickness of 600 nm were studied in a broad temperature range of 80-600 K and the phase transition from paraelectric to tetragonal ferroelectric phase was observed at about 500 K. This critical temperature is substantially higher than that calculated from the lattice-mismatch strain theory. In addition, the predicted from the theory low-temperature orthorhombic and rhombohedral phases were not observed. We ascribe the strengthening of the tetragonal ferroelectric phase to the effect of the interface-induced build-in electric field resulted from the interface-accumulated charges. [ABSTRACT FROM AUTHOR]

In this article, we report a comparative analysis of various spectroscopic studies including low-temperature ( [ABSTRACT FROM AUTHOR]

The phonon structure of the silver sulfide Ag2S was investigated, experimentally using Raman spectroscopy, and theoretically using the density-functional perturbation theory for the first time. Seven Raman-active modes were observed and identified at 23, 39, 42, 44, 62, 65, and 243 cm−1. Symmetry assignments of all the vibrational modes were derived from considerations of point group symmetry. The phonon band structure and the relative Raman intensities were also investigated by ab initio calculations and compared with the experimental data. The temperature, laser power, and illumination time dependencies of frequency, linewidth, and intensity of the Raman-active modes are discussed. In the Raman spectra at higher frequencies 1300-1700 cm−1, additional broad Raman modes observed in all samples at higher laser powers 8-10 mW were ascribed to luminescence from β-Ag2S. The phonon and Raman spectra of the β-Ag2S provide a useful insight into the β-Ag2S → α-Ag2S phase transition. Finally, calculated infrared vibrational mode frequencies were compared with measured infrared mode frequencies. [ABSTRACT FROM AUTHOR]

Phase-change materials (PCM) show remarkable property-contrast from amorphous to crystalline phase that forms the basis for high-speed non-volatile memory device applications. Despite understanding the local structure and physical properties of these phases, a systematic study on the phase-change behavior is essential. Here, we used in situ UV-Vis-NIR spectroscopic measurements to study a systematic evolution of optical band gap ( Eg) and the local disorder described by Tauc parameter ( B), for the temperatures from 90 to 480 K on amorphous and cubic phases of Ge1Sb4Te7 thin films. It has been found that the Eg of amorphous phase decreases with increasing temperature from 90 to 400 K, while the disorder as exemplified by B, increases owing to thermal vibrations. At 420 K, a rapid decrease in the Eg from 0.47 to 0.33 eV and also a sharp reduction of ∼13% in the value of B1/2 is observed evidencing the signature of amorphous-to-cubic phase transition. Furthermore, the hexagonal phase is more disordered compared to cubic phase. The Raman results are consistent with optical measurements, which indicate that the degree of disorder reduces from amorphous to cubic phase, while hexagonal phase with an increased disorder is attributed to elongated bonds. [ABSTRACT FROM AUTHOR]

In this work, the analysis of both experimental and theoretical angular dispersion of the Raman frequencies of the optical polar phonons in LiNbO3 (LN) single crystal has been determined with the emphasis of the determination without ambiguity of a new and complete set of the normal mode assignments that clarify long-standing debates. The coherency of such couple assignments is assessed by the computed oscillator strengths that are revealed to be in satisfactory agreement with others on the one hand and by the comparison with the oblique frequencies measured from the compilation of the Raman spectra acquired under different geometrical configurations in the 90° scheme on the other hand. Finally, the directional behavior of the quasinormal vectors has been established and discussed with regard to the symmetry mixing of modes or the mode with oblique polarization. [ABSTRACT FROM AUTHOR]

Undoped and Ba-doped ZnO nanoparticles were successfully synthesized using microwave hydrothermal method. The influence of Barium concentration on physical and optical properties of ZnO nanoparticles was investigated. X-Ray Diffraction (XRD) analysis revealed that the synthesized ZnO nanoparticles are polycrystalline with hexagonal wurtzite crystal structure and their average crystallite sizes are found to vary from 20 to 21.5 nm in diameter. The SEM images showed that surface morphology of the samples was influenced by the presence of Ba impurities. Ultraviolet and green emission bands around 415 and 603 nm, respectively were observed in photoluminescence spectra for all samples. The FTIR spectra indicated the presence of the distinct characteristic absorption peak at 489 cm−1 for Zn-O stretching modes. Raman spectra exhibited the presence of an intense peak around 437 cm−1 followed by a peak around 586 cm−1 in the higher wave number region. [ABSTRACT FROM AUTHOR]

In our study, we sandwiched fullerenes C70 in between two layers of isotopically labeled graphene and studied this heterostructure by atomic force microscopy and by Raman spectroscopy. Isotope labeling was used to distinguish between the top and the bottom graphene layers in the measured Raman spectra. We analyzed the Raman maps of isotopically labeled graphene-fullerene heterostructures and described the effect of the fullerenes on graphene layers. Apart from the peak parameters obtained directly from fitting the principal Raman modes of graphene, we evaluated strain and doping in both layers employing a correlation analysis of the positions of the G and the 2D bands. Our results show that the top layer is less doped and contains less sub-micron charge inhomogeneities than the bottom layer. [ABSTRACT FROM AUTHOR]

Using Raman spectral-mapping, we investigated in situ temperature dependence (100-300 K) of strain and doping of isotopically labelled double-layer graphene, which allows us to simultaneously and independently follow the strain and doping in both layers of the double layer. We find that the strain in both layers of the double-layer graphene is almost the same and becomes larger when the temperature is decreased. The bottom graphene layer, in contact with the Si/SiO2 substrate has a stronger doping than the top graphene layer which is in contact with the graphene bottom layer. We also observed that the spatial distribution of the temperature-induced strain and doping is not homogeneously distributed within the substrate. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDs) have recently attracted attention due to their interesting electronic and optical properties. Fabrication of these materials in a reliable and facile method is important for future applications, as are methods to characterize material quality. Here we present the chemical vapor deposition of MoSe2 monolayer and few layer crystals. These results show the practicality of using chemical vapor deposition to reliably fabricate these materials. Low frequency Raman spectra and mapping of shear and layer breathing modes of MoSe2 are presented for the first time. We correlate the behavior of these modes with layer number in the materials. The usefulness of low frequency Raman mapping to probe the symmetry, quality, and monolayer presence in CVD grown 2D materials is emphasized. Raman map of maximum intensity position for low wavenumber shear and layer breathing modes of MoSe2. [ABSTRACT FROM AUTHOR]

We report on strong interference effects on the ratio of the integrated intensities of the Raman 2D- and G-mode features (herein denoted [ABSTRACT FROM AUTHOR]

X-ray transmission windows for the low energy range, especially between 0.1 and 1 keV have been designed and fabricated based on graphenic carbon (GC) with an integrated silicon frame. A hexagonal and a bar grid support structure design have been evaluated. The bar grid design offers higher X-ray transmission and better visible light rejection than polymer-based windows, and allows vacuum encapsulation of silicon drift detectors (SDD). The high mechanical resilience of graphenic carbon is demonstrated by pressure cycle tests, yielding over 10 million cycles without damage. The data are complemented by bulge tests to determine a Young's modulus for graphenic carbon of approximately 130 GPa. Additional finite-element simulation and Raman studies reveal that the mechanical stress is not homogeneously distributed, but reaches a maximum near the anchoring points of the free standing graphenic carbon membrane. The cross-section of a vacuum encapsulated silicon drift detector (SDD) in (a) shows the highly transparent X-ray transmission window that is integrated into the top of a TO8 housing. The photograph (b) shows a prototype TO8 detector module with a graphenic carbon low-energy transmission window with an hexagonal support grid structure. [ABSTRACT FROM AUTHOR]

Recent experimental results based on Raman spectroscopy and mass spectroscopy showed that an appropriate heat treatment of small diameter carbon nanotubes filled with ferrocene molecules results in the formation of hydrocarbon molecules. However, the exact nature of these molecules is still unknown. In order to find possible candidates, we performed density functional theory calculations of the structure, electronic transition energies, and Raman spectrum for a large set of hydrocarbon molecules, including oligoenes and polyaromatic hydrocarbons. To follow the effect of deuteration in the Raman spectra we varied the mass of hydrogen atom from 1 to 2 by 0.1 steps. With increasing mass, the position of the lines red shifted as expected. However, in some rare occasions, the intensity of the red shifted line dramatically decreased and at the same time, an originally weak line gained large intensity at a nearby higher frequency. This can be interpreted in an experiment as an apparent blue shift. From a comparison of the calculations with experiments, based on molecular weight, excitation energy, and Raman spectrum (for both hydrogenated and deuterated forms) either quaterrylene (dimer of perylene) or the dimer of the 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) is the most likely product of the heat treatment. [ABSTRACT FROM AUTHOR]

We have performed a thorough characterization of 1.4 nm-diameter single-walled carbon nanotubes (SWCNTs) separated according to their metallicity by optical absorption (OAS), X-ray photoelectron (XPS), ultraviolet photoelectron (UPS), and multifrequency Raman spectroscopy. The OAS, XPS, and UPS data prove a high purity ( [ABSTRACT FROM AUTHOR]

Here, we overview Raman spectroscopy of graphene and transition-metal dichalcogenides as a function of laser excitation energy [ABSTRACT FROM AUTHOR]

We performed resonance Raman spectroscopy on HiPCO-produced single-walled carbon nanotubes in the spectral region of 846 and [ABSTRACT FROM AUTHOR]

The frequency axis of Fig. 3 is corrected. [ABSTRACT FROM AUTHOR]

We performed a thorough multifrequency Raman spectroscopy study to access the entire spread of all traces of chirality species and confirm the absence of metallic species in metallicity and single chirality sorted single-walled carbon nanotubes. On the bulk scale the diameters of all detectable species fall within 1.43 nm [ABSTRACT FROM AUTHOR]

Chemical vapor deposition (CVD) of graphene onto Cu substrates is a very promising approach for large-scale production. When dealing with Cu thin films instead of foils, there are additional problems related to the stability of the film at high temperatures. We show that the film rupture and agglomeration can be prevented by monitoring in-situ dewetting dynamics of the catalytist. We investigated the possibility to perform CVD of graphene onto Cu films, 200 nm thick, at low-pressure conditions, with ethanol or methane as C precursors. Same recipes applied on Cu foils lead to worse results highlighting the important role played by the substrate thickness to achieve a high catalytic activity. The influence on the deposition quality of parameters such as time, temperature and hydrogen flow is then discussed. [ABSTRACT FROM AUTHOR]

We present electrochemical Raman measurements on energy transfer complexes formed by combining single-walled carbon nanotubes and dye molecules. The presence of the dye molecules in the proximity of the nanotubes impacts the nanotubes' charging behavior, leading to changes in the position of the charge neutrality point and the maximum achievable doping strength. We compare these results to spectra acquired in solution and determine the corresponding Fermi energy shifts, which are found to be similar in the energy transfer complexes and a reference sample. Our results have implications for the photoluminescence enhancement/quenching previously observed in these energy transfer complexes. Electrochemical G-mode Raman spectra at a gate voltage of −1.1 V showing much larger doping strength for the reference sample than for the energy transfer complexes, as seen in the higher-frequency and narrower peak. [ABSTRACT FROM AUTHOR]

We examine the influence of nuclear spins on the performance of optically induced rotations of single electron spins in semiconductor quantum dots. We consider Raman-type optical transitions between electron spin states and take into account the additional effect of the Overhauser field. We calculate average fidelities of rotations around characteristic axes in the presence of nuclear spins analytically with perturbation theory up to second order in the Overhauser field. Moreover, we calculate the fidelity using numerical averaging over the nuclear field distribution, including arbitrary orders of the hyperfine interaction. [ABSTRACT FROM AUTHOR]

Amorphous silicon carbonitride (a-SiC xN y) thin films deposited on the SiO2 substrates by reactive magnetron sputtering was studied by Raman and electron paramagnetic resonance (EPR) spectroscopy. Raman analysis indicates the presence of C-N, Si-N, C-C bonds in a-SiC xN y films. Three EPR signals were revealed in a-SiC xN y/SiO2. One of them with g = 2.0033 was attributed to the carbon-dangling bonds (CDB). Based on the lineshape and linewidth, the EPR signal was attributed to the unpaired electron delocalized over sp2 carbon cluster. With the increase of nitrogen (N) content, the spin density of CDB significantly increases. From the temperature dependence of the linewidth and integral intensity of the CDB EPR signal, it was concluded that the antiferromagnetic ordering occurs in spin system. The antiferromagnetic exchange constant between CDBs was found to be J = −32 K. The second EPR signal having g = 2.009 was attributed to the interface defect representing threefold-coordinated Si dangling bond, which may appear due to the formation of the oxidized Si on the film surface. The third EPR signal with g = 2.05 was tentatively attributed to the trapped holes at Si atom near Si/SiO2 interface. The N incorporation in a-SiC x/SiO2 has no effect on the spin density of both interface defects. [ABSTRACT FROM AUTHOR]

The optical properties of LiNbO3 crystals doped with iron at mol% between 0.015 and 0.1 were studied by optical absorption and Raman spectroscopies. The long wavelength tail below the fundamental absorption band is modeled by Urbach exponent assumed to be due to the tunneling of charged carriers through potential energy barrier bent by micro-electric field. We presume that non-uniform local charge distribution creates micro-electric field. Temperature dependence of the Fe2+ absorption band is reported over the range from 100 to 250 K. The Fe2+ absorption band at around 2.58 eV is red shifted at a rate of 4 × 10−5 eV K−1 as the temperature increases. We conclude that Li deficiency increases with iron, which sit on Li sites. [ABSTRACT FROM AUTHOR]

Using the two types of the finite-temperature ( T) local-field corrections, namely, the Singwi-Tosi-Land-Sjölander (STLS) and Hubbard (H) approximations, we investigate the exchange-correlation (XC) and T effects on plasmons (PLs) in strongly-correlated two-dimensional electron systems with ultralow density. In a density-parameter range of [ABSTRACT FROM AUTHOR]

The preparation of continous three-dimensional carbon foam composed of a few-layer graphene film decorated with carbon nanowalls standing perpendicular to its surface is presented. The synthesis is done by the direct-current PECVD method using nickel foam as a catalyst substrate. Variable curvature of the surface of the Ni foam causes a variation in electric field during the dcPECVD synthesis, which results in forming the foam of hybrid carbon structures. The material was characterized by scanning electron microscope images and by Raman spectra. The effect of plasma penetration depth on growth of carbon nanowalls is also discussed. Macropores and nanopores coexisting in the structure might offer new functionalities particularly for charge storage applications. [ABSTRACT FROM AUTHOR]

The two-dimensional sp2-bonded material hexagonal boron nitride (h-BN) has unique electronic, thermal, mechanical, and chemical properties. It has recently found use as an ideal substrate for graphene-based electronic devices. We here describe synthesis of mono- to few-layer h-BN films using low pressure chemical vapor deposition (LPCVD) from borazine, with nickel, copper and platinum employed as catalytic substrates, and transfer of some of these films using a non-polymer method. Characterization of the films via Raman spectroscopy and transmission electron microscopy (TEM) is performed. Chemical vapor deposition synthesis of hexagonal boron nitride from borazine using metallic substrates. [ABSTRACT FROM AUTHOR]

We investigate the stacking-order dependence of the double-resonant LO-ZO [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) can be used as nanoreactors due to their unique hollow nanostructures. In order to prepare linear carbon chains inside CNTs, eDIPS single-wall carbon nanotubes were annealed at high temperatures from 1300 to 1500 [ABSTRACT FROM AUTHOR]