Showing papers by "Mildred S. Dresselhaus published in 2014"
TL;DR: The thinnest semiconductor, molybdenum disulfide (MoS2) monolayer, exhibits promising prospects in the applications of optoelectronics and valleytronics and is found that an optimized concentration of seed molecules is helpful for the nucleation of the MoS2.
Abstract: The thinnest semiconductor, molybdenum disulfide (MoS2) monolayer, exhibits promising prospects in the applications of optoelectronics and valleytronics. A uniform and highly crystalline MoS2 monolayer in a large area is highly desirable for both fundamental studies and substantial applications. Here, utilizing various aromatic molecules as seeding promoters, a large-area, highly crystalline, and uniform MoS2 monolayer was achieved with chemical vapor deposition (CVD) at a relatively low growth temperature (650 °C). The dependence of the growth results on the seed concentration and on the use of different seeding promoters is further investigated. It is also found that an optimized concentration of seed molecules is helpful for the nucleation of the MoS2. The newly identified seed molecules can be easily deposited on various substrates and allows the direct growth of monolayer MoS2 on Au, hexagonal boron nitride (h-BN), and graphene to achieve various hybrid structures.
643 citations
TL;DR: These findings are helpful to better understand the tightly bound exciton properties in strongly quantum-confined systems and provide a simple approach to the selective and separate generation of excitons or trions with potential applications in excitonic interconnects and valleytronics.
Abstract: Photoluminescence (PL) properties of single-layer MoS2 are indicated to have strong correlations with the surrounding dielectric environment. Blue shifts of up to 40 meV of exciton or trion PL peaks were observed as a function of the dielectric constant of the environment. These results can be explained by the dielectric screening effect of the Coulomb potential; based on this, a scaling relationship was developed with the extracted electronic band gap and exciton and trion binding energies in good agreement with theoretical estimations. It was also observed that the trion/exciton intensity ratio can be tuned by at least 1 order of magnitude with different dielectric environments. Our findings are helpful to better understand the tightly bound exciton properties in strongly quantum-confined systems and provide a simple approach to the selective and separate generation of excitons or trions with potential applications in excitonic interconnects and valleytronics.
531 citations
TL;DR: H-BN and MoS2 are identified as two different types of 2D materials with potential for use as Raman enhancement substrates and both charge transfer and dipole-dipole coupling may occur, although weaker in magnitude, forMoS2.
Abstract: Realizing Raman enhancement on a flat surface has become increasingly attractive after the discovery of graphene-enhanced Raman scattering (GERS). Two-dimensional (2D) layered materials, exhibiting a flat surface without dangling bonds, were thought to be strong candidates for both fundamental studies of this Raman enhancement effect and its extension to meet practical applications requirements. Here, we study the Raman enhancement effect on graphene, hexagonal boron nitride (h-BN), and molybdenum disulfide (MoS2), by using the copper phthalocyanine (CuPc) molecule as a probe. This molecule can sit on these layered materials in a face-on configuration. However, it is found that the Raman enhancement effect, which is observable on graphene, hBN, and MoS2, has different enhancement factors for the different vibrational modes of CuPc, depending strongly on the surfaces. Higher-frequency phonon modes of CuPc (such as those at 1342, 1452, 1531 cm–1) are enhanced more strongly on graphene than that on h-BN, whi...
435 citations
TL;DR: Two-dimensional molybdenum disulfide (MoS2) is a promising material for optoelectronic devices due to its strong photoluminescence emission, and a tunability of the interlayer coupling of bilayer MoS2 is revealed.
Abstract: Two-dimensional molybdenum disulfide (MoS2) is a promising material for optoelectronic devices due to its strong photoluminescence emission. In this work, the photoluminescence of twisted bilayer MoS2 is investigated, revealing a tunability of the interlayer coupling of bilayer MoS2. It is found that the photoluminescence intensity ratio of the trion and exciton reaches its maximum value for the twisted angle 0° or 60°, while for the twisted angle 30° or 90° the situation is the opposite. This is mainly attributed to the change of the trion binding energy. The first-principles density functional theory analysis further confirms the change of the interlayer coupling with the twisted angle, which interprets our experimental results.
211 citations
TL;DR: In this article, a thorough group theory study of the symmetry aspects relevant to optical and spectroscopic analysis, for the most common polytypes of transition metal dichalcogenides (TMDCs), as a function of the number of layers, is presented.
Abstract: Transition metal dichalcogenides (TMDCs) have emerged as a new two-dimensional material's field since the monolayer and few-layer limits show different properties when compared to each other and to their respective bulk materials. For example, in some cases when the bulk material is exfoliated down to a monolayer, an indirect-to-direct band gap in the visible range is observed. The number of layers $N$ ($N$ even or odd) drives changes in space-group symmetry that are reflected in the optical properties. The understanding of the space-group symmetry as a function of the number of layers is therefore important for the correct interpretation of the experimental data. Here we present a thorough group theory study of the symmetry aspects relevant to optical and spectroscopic analysis, for the most common polytypes of TMDCs, i.e., $2Ha$, $2Hc$ and $1T$, as a function of the number of layers. Real space symmetries, the group of the wave vectors, the relevance of inversion symmetry, irreducible representations of the vibrational modes, optical activity, and Raman tensors are discussed.
156 citations
Journal Article•
TL;DR: In this paper, a thorough group theory study of the symmetry aspects relevant to optical and spectroscopic analysis, for the most common polytypes of transition metal dichalcogenides, i.e., 2 Ha, 2 Hc and 1T, is presented.
Abstract: Transition metal dichalcogenides (TMDCs) have emerged as a new two-dimensional material’s field since the monolayer and few-layer limits show different properties when compared to each other and to their respective bulk materials. For example, in some cases when the bulk material is exfoliated down to a monolayer, an indirect-to-direct band gap in the visible range is observed. The number of layers N (N even or odd) drives changes in space-group symmetry that are reflected in the optical properties. The understanding of the space-group symmetry as a function of the number of layers is therefore important for the correct interpretation of the experimental data. Here we present a thorough group theory study of the symmetry aspects relevant to optical and spectroscopic analysis, for the most common polytypes of TMDCs, i.e., 2 Ha ,2 Hc and 1T ,a s af unction of the number of layers. Real space symmetries, the group of the wave vectors, the relevance of inversion symmetry, irreducible representations of the vibrational modes, optical activity, and Raman tensors are discussed.
118 citations
TL;DR: It is observed that the asymmetric growth environment of a Cu enclosure can yield a much higher bilayer coverage on the outside surface as compared to the bilayer growth on a flat Cu foil, where both sides are exposed to the same growth environment.
Abstract: In this work, we investigated the growth mechanisms of bilayer graphene on the outside surface of Cu enclosures at low pressures. We observed that the asymmetric growth environment of a Cu enclosure can yield a much higher (up to 100%) bilayer coverage on the outside surface as compared to the bilayer growth on a flat Cu foil, where both sides are exposed to the same growth environment. By simultaneously examining the graphene films grown on both the outside and inside surfaces of the Cu enclosure, we find that carbon can diffuse from the inside surface to the outside via exposed copper regions on the inside surface. The kinetics of this process are examined by coupling the asymmetric growth between the two surfaces through a carbon diffusion model. Finally, using these results, we show that the coverage of bilayer graphene can be tuned simply by changing the thickness of the Cu foil, further confirming our model of carbon delivery through the Cu foil.
110 citations
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01 Jan 2014
TL;DR: Experimental Manifestation of Berry Phase and Probing Dirac Fermions in Graphene by Scanning Tunneling Microscopy and Spectroscopy as discussed by the authors, the Competition between Interactions and Disorder.
Abstract: Experimental Manifestation of Berry Phase.- Probing Dirac Fermions in Graphene by Scanning Tunneling Microscopy and Spectroscopy.- Electron and Phonon Transport in Graphene in and out of the Bulk.- Optical Magneto-Spectroscopy of Graphene-Based Systems.- Graphene Constrictions.- Electronic Structure of Monolayer and Multilayer Graphene.- Graphene - Topological Properties, Chiral Symmetry and their Manipulation.- Aspects of the Fractional Quantum Hall Effect in Graphene.- Symmetry Breaking in Graphene Quantum Hall Regime - the Competition between Interactions and Disorder.- Weak Localization and Spin-Orbit Coupling in Monolayer and Bilayer Graphene.
95 citations
TL;DR: The studies indicate that this method for nanowire hydrogels/aerogels production is not only economical but greatly augmented their applications in environmental, catalysis, sensing, absorption, energy storage, and beyond.
Abstract: Creating inorganic nanowire hydrogels/aerogels using various materials and inexpensive means remains an outstanding challenge despite their importance for many applications. Here, we present a facile methodology to enable highly porous inorganic nanowire hydrogel/aerogel production on a large scale and at low cost. The hydrogels/aerogels are obtained from in situ hydrothermal synthesis of one-dimensional (1D) nanowires that directly form a cross-linking network during the synthesis process. Such a method not only offers great simplicity but also allows the interconnecting nanowires to have much longer length. The longer length offers aerogels with remarkable porosity and surface area extremely low densities (as low as 2.9 mg/cm3), are mechanically robust, and can have superelasticity by tuning the synthesis conditions. The nanowires in the hydrogels/aerogels serve both as structural support and active sites, for example, for catalysis or absorption. In this work, we have found that the as-grown hydrogels ...
92 citations
TL;DR: In this article, the stability of pure-carbon-rich edges and/or heteroatom-decorated edges, and their effect on the electrochemical performance remain largely unexplored.
Abstract: Chemically doped graphene has been actively investigated as an electrode material for achieving high-performance electrochemical systems. However, the stability of pure-carbon-rich edges and/or heteroatom-decorated edges, and their effect on the electrochemical performance remain largely unexplored. We found that in a high temperature thermal doping process, the functionalized graphene edges were structurally stable at 1200 °C, whereas the edges at 1500 °C were unstable and coalesced into loops through covalent bond formation between adjacent graphene edges. Interestingly, boron and nitrogen co-doped graphene prepared at 1200 °C showed the largest capacitance in both acidic and alkaline media due to the presence of the BNO moieties along the edge sites. The doped material also showed the best rate capability due to the largely enhanced electrical conductivity originating from the substitutionally doped boron and nitrogen atoms. Our findings regarding the stability of heteroatom-decorated edges without loop formation can now be utilized as a guideline for maximizing the electrochemical activity of graphene in various electrochemical systems.
90 citations
TL;DR: In this paper, the lattice thermal conductivity of Bi, Sb, and Bi-Sb alloys is calculated using first principles, and the relative contributions from phonons and electrons to the total thermal conductivities as a function of temperature are estimated.
Abstract: Using first principles, we calculate the lattice thermal conductivity of Bi, Sb, and Bi-Sb alloys, which are of great importance for thermoelectric and thermomagnetic cooling applications. Our calculation reveals that the ninth-neighbor harmonic and anharmonic force constants are significant; accordingly, they largely affect the lattice thermal conductivity. Several features of the thermal transport in these materials are studied: (1) the relative contributions from phonons and electrons to the total thermal conductivity as a function of temperature are estimated by comparing the calculated lattice thermal conductivity to the measured total thermal conductivity, (2) the anisotropy of the lattice thermal conductivity is calculated and compared to that of the electronic contribution in Bi, and (3) the phonon mean free path distributions, which are useful for developing nanostructures to reduce the lattice thermal conductivity, are calculated. The phonon mean free paths are found to range from 10 to 100 nm for Bi at 100 K.
TL;DR: In this article, the structural and mechanical properties of two-dimensional (2D) materials by using first-principles density functional theory calculations were reported, and the buckled single-layer silicene could transit to planar hexagonal silicenes at a critical tensile strain of 0.20.
Abstract: Here, we report the structural and mechanical properties of several two-dimensional (2-D) materials by using first-principles density functional theory calculations. We find that the buckled single-layer silicene could transit to planar hexagonal silicene at a critical tensile strain of 0.20. Phonon dispersion analysis suggests that the planar hexagonal silicene under tension is stable. The Poisson's ratio of silicene and MoS2 shows strong anisotropy: it increases while stretched in the zigzag direction, but decreases when strained in the armchair direction. When stretched in the zigzag direction, the Poisson's ratio of silicene could reach 0.62.
TL;DR: In this paper, a third-order perturbation theory was proposed to describe the chemical surfaceenhanced Raman spectroscopy of molecules interacting with two-dimensional (2D) surfaces such as an ideal 2D metal and graphene.
Abstract: We propose a third-order time-dependent perturbation theory approach to describe the chemical surfaceenhanced Raman spectroscopy of molecules interacting with two-dimensional (2D) surfaces such as an ideal 2D metal and graphene, which are both 2D metallic monolayers. A detailed analysis is performed for all the possible scattering processes involving both electrons and holes and considering the different time orderings for the electron-photon and electron-phonon interactions. We show that for ideal 2D metals a surface enhancement of the Raman scattering is possible if the Fermi energy of the surface is near the energy of either the HOMO or the LUMO states of the molecule and that a maximum enhancement is obtained when the Fermi energy matches the energy of either the HOMO or the LUMO energies plus or minus the phonon energy. The graphene-enhanced Raman spectroscopy effect is then explained as a particular case of a 2D surface, on which the density of electronic states is not constant, but increases linearly with the energy measured from the charge neutrality point. In the case of graphene, the Raman enhancement can occur for any value of the Fermi energy between the HOMO and LUMO states of the molecule. The proposed model allows for a formal approach for calculating the Raman intensity of molecules interacting with different 2D materials.
TL;DR: This work experimentally investigates the structural interactions between graphene and transition metals such as palladium (Pd) and titanium (Ti), which have been confirmed by density functional simulations and shows that a surface induced p-d hybridization occurs between atomic carbon and titanium orbitals.
Abstract: Carbon-based materials such as graphene sheets and carbon nanotubes have inspired a broad range of applications ranging from high-speed flexible electronics all the way to ultrastrong membranes. However, many of these applications are limited by the complex interactions between carbon-based materials and metals. In this work, we experimentally investigate the structural interactions between graphene and transition metals such as palladium (Pd) and titanium (Ti), which have been confirmed by density functional simulations. We find that the adsorption of titanium on graphene is more energetically favorable than in the case of most metals, and density functional theory shows that a surface induced p-d hybridization occurs between atomic carbon and titanium orbitals. This strong affinity between the two materials results in a short-range ordered crystalline deposition on top of graphene as well as chemical modifications to graphene as seen by Raman and X-ray photoemission spectroscopy (XPS). This induced hybridization is interface-specific and has major consequences for contacting graphene-nanoelectronic devices as well as applications toward metal-induced chemical functionalization of graphene.
TL;DR: Double walled carbon nanotubes (DWCNTs) are considered an ideal model for studying the coupling interactions between different concentric shells in multi-walled CNTs as discussed by the authors.
Abstract: Double walled carbon nanotubes (DWCNTs) are considered an ideal model for studying the coupling interactions between different concentric shells in multi-walled CNTs. Due to their intrinsic coaxial structures they are mechanically, thermally, and structurally more stable than single walled CNTs. Geometrically, owing to the buffer-like function of the outer tubes in DWCNTs, the inner tubes exhibit exciting transport and optical properties that lend them promise in the fabrication of field-effect transistors, stable field emitters, and lithium ion batteries. In addition, by utilizing the outer tube chemistry, DWCNTs can be useful for anchoring semiconducting quantum dots and also as effective multifunctional fillers in producing tough, conductive transparent polymer films. The inner tubes meanwhile preserve their excitonic transitions. This article reviews the synthesis of DWCNTs, their electronic structure, transport, and mechanical properties, and their potential uses.
TL;DR: In this article, the up-to-date achievements on electronic properties of nanostructured Bi1−xSbx, and points out future directions for scientific research in this field.
Abstract: Bismuth antimony (Bi1−xSbx) is one of the most important materials systems for fundamental materials science, condensed matter physics, low temperature thermoelectrics, infrared applications, and beyond. The bulk materials have been studied for many decades. Recently, nanoscience and nanotechnology has been introduced to this materials system, which has brought much more interest and attention for both research and applications. The present article reviews the up-to-date achievements on electronic properties of nanostructured Bi1−xSbx, and points out future directions for scientific research in this field.
TL;DR: In this paper, a polarization-difference technique is used to suppress the fluorescence background by subtracting two spectra collected using different excitation laser polarizations, and enhancement factors are obtained ranging between 1.7 and 5.6 for the four Raman modes of R6G at 611, 1,183, 1361, and 1,647 cm−1 under resonant excitation by a 514.5 nm laser.
Abstract: Graphene substrates have recently been found to generate Raman enhancement. Systematic studies using different Raman probes have been implemented, but one of the most commonly used Raman probes, rhodamine 6G (R6G), has yielded controversial results for the enhancement effect on graphene. Indeed, the Raman enhancement factor of R6G induced by graphene has never been measured directly under resonant excitation because of the presence of intense fluorescence backgrounds. In this study, a polarization-difference technique is used to suppress the fluorescence background by subtracting two spectra collected using different excitation laser polarizations. As a result, enhancement factors are obtained ranging between 1.7 and 5.6 for the four Raman modes of R6G at 611, 1,183, 1,361, and 1,647 cm−1 under resonant excitation by a 514.5 nm laser. By comparing these results with the results obtained under non-resonant excitation (632.8 nm) and pre-resonant excitation (593 nm), the enhancement can be attributed to static chemical enhancement (CHEM) and tuning of the molecular resonance. Density functional theory simulations reveal that the orbital energies and densities for R6G are modified by graphene dots.
TL;DR: It is explained how the surroundings of the nanotubes in a multiwalled system influence their radial breathing modes, and metallic innermost tubes, when compared to their semiconducting counterparts, clearly show weaker intertube interactions.
Abstract: Resonant Raman spectroscopy studies are performed to access information about the intertube interactions and wall-to-wall distances in double- and triple-walled carbon nanotubes. Here, we explain how the surroundings of the nanotubes in a multiwalled system influence their radial breathing modes. Of particular interest, the innermost tubes in double- and triple-walled carbon nanotube systems are shown to be significantly shielded from environmental interactions, except for those coming from the intertube interaction with their own respective host tubes. From a comparison of the Raman results for bundled as well as individual fullerene-peapod-derived double- and triple-walled carbon nanotubes, we observe that metallic innermost tubes, when compared to their semiconducting counterparts, clearly show weaker intertube interactions. Additionally, we discuss a correlation between the wall-to-wall distances and the frequency upshifts of the radial breathing modes observed for the innermost tubes in individual do...
TL;DR: It is proposed that, in switching to a resistive state, the nanotube oxidizes by extracting oxygen from the substrate, and this switching event occurs at ~600 °C, the temperature associated with the oxidation of nanotubes.
Abstract: The integration of carbon nanotubes with silicon is important for their incorporation into next-generation nano-electronics. Here, the authors demonstrate a non-volatile switch that utilizes carbon nanotube networks to electrically contact a conductive nano-crystal silicon filament in silica.
Patent•
27 Aug 2014TL;DR: In this article, a metal dichalcogenide layer is produced on a transfer substrate by seeding F 16 CuPc molecules on a surface of a growth substrate, growing a layer {e.g., a monolayer} via chemical vapor deposition on the growth substrate surface.
Abstract: A metal dichalcogenide layer is produced on a transfer substrate by seeding F 16 CuPc molecules on a surface of a growth substrate, growing a layer {e.g., a monolayer) of a metal dichalcogenide via chemical vapor deposition on the growth substrate surface seeded with F 16 CuPc molecules, and contacting the F 16 CuPc- molecule and metal-dichalcogenide coated growth substrate with a composition that releases the metal dichalcogenide from the growth substrate.
TL;DR: In this paper, a defect engineering strategy for improving the intrinsic electrical conductivity of nanotube assemblies by thermally incorporating a large number of boron atoms into substitutional positions within the hexagonal framework of the tubes is presented.
Abstract: Carbon nanotubes have shown great potential as conductive fillers in various composites, macro-assembled fibers, and transparent conductive films due to their superior electrical conductivity. Here, we present an effective defect engineering strategy for improving the intrinsic electrical conductivity of nanotube assemblies by thermally incorporating a large number of boron atoms into substitutional positions within the hexagonal framework of the tubes. It was confirmed that the defects introduced after vacuum ultraviolet and nitrogen plasma treatments facilitate the incorporation of a large number of boron atoms (ca. 0.496 atomic %) occupying the trigonal sites on the tube sidewalls during the boron doping process, thus eventually increasing the electrical conductivity of the carbon nanotube film. Our approach provides a potential solution for the industrial use of macro-structured nanotube assemblies, where properties, such as high electrical conductance, high transparency, and lightweight, are extremel...
Journal Article•
TL;DR: In this paper, two dominant Raman vibrational modes in the low frequency range of 100-200 cm(1) in misoriented few-layer graphene on a SiO2/Si substrate are identified.
Abstract: Stacking disorder will significantly modify the optical properties and interlayer coupling stretch of few-layer graphene. Here, we report the observation of the Raman breathing modes in the low-frequency range of 100-200 cm(-1) in misoriented few-layer graphene on a SiO2/Si substrate. Two dominant Raman modes are identified. The one at similar to 120 cm(-1) is assigned as the E-g + ZO' combination mode of the in-plane shear and the out-of-plane interlayer optical phonon breathing modes. Another peak at similar to 182 cm(-1) is identified as the overtone mode 2ZO'. The appearance of these Raman modes for different twist angles indicates that stacking disorder in few-layer graphene significantly alters the Raman feature, especially for those combination modes containing the interlayer breathing mode. Further investigation shows that the two Raman vibrational modes (similar to 120 and similar to 182 cm(-1)) are strongly coupled to the excitation laser energy, but their frequencies are independent of the number of graphene layers before folding. The present work provides a sensitive way to study the phonon dispersion, electron-phonon interaction, and electronic band structure of misoriented graphene layers.
TL;DR: In this article, an analytical study of the double resonant Raman scattering process in graphene, responsible for the D and ${\mathrm{D}}^{\ensuremath{'}}$ features in the Raman spectra is presented.
Abstract: An analytical study is presented of the double resonant Raman scattering process in graphene, responsible for the D and ${\mathrm{D}}^{\ensuremath{'}}$ features in the Raman spectra. This work yields analytical expressions for the D and ${\mathrm{D}}^{\ensuremath{'}}$ integrated Raman intensities that explicitly show the dependencies on laser energy, defect concentration, and electronic lifetime. Good agreement is obtained between the analytical results and experimental measurements on samples with increasing defect concentrations and at various laser excitation energies. The use of Raman spectroscopy to identify the nature of defects is discussed. Comparison between the models for the edge-induced and the disorder-induced D-band intensity suggests that edges or grain boundaries can be distinguished from disorder by the different dependence of their Raman intensity on laser excitation energy. Similarly, the type of disorder can potentially be identified not only by the intensity ratio ${I}_{\mathrm{D}}/{I}_{{\mathrm{D}}^{\ensuremath{'}}}$, but also by its laser energy dependence. Also discussed is a quantitative analysis of quantum interference effects of the graphene wave functions, which determine the most important phonon wave vectors and scattering processes responsible for the D and ${\mathrm{D}}^{\ensuremath{'}}$ bands.
TL;DR: This re-engineering of carbon bonds evolves via a coalescence-induced reconfiguration of sp(2) hybridization, terminates with negligible introduction of defects and demonstrates remarkable reproducibility, reflecting a potential step forward for large-scale engineering of nanocarbon allotropes and their junctions.
Abstract: Inter-allotropic transformation of carbon is of immense fundamental and technological interest, but requires extreme conditions. Here, the authors report a method to transform single-walled carbon nanotubes into other carbon structures with high reproducibility by controlling alternating-voltage pulses.
Journal Article•
TL;DR: Rodriguez-Nieva et al. as mentioned in this paper, E. B. Barros, R. Saito, and M. S. Dresselhaus proposed a method to solve the problem of computational complexity in physics.
Abstract: J. F. Rodriguez-Nieva,1 E. B. Barros,1,2 R. Saito,3 and M. S. Dresselhaus1,4 1Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA 2Departamento de Fisica, Universidade Federal do Ceara, Fortaleza, Ceara 60455-760, Brazil 3Department of Physics, Tohoku University, Sendai 980-8578, Japan 4Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA (Received 6 May 2014; revised manuscript received 29 August 2014; published 3 December 2014)
01 Jan 2014
TL;DR: In this paper, the properties of nano-carbon based materials are discussed in relation to the electrical and thermal conductivities of various nano carbon based materials, and the similarities and differences observed in the transport properties of an isolated single layer graphene out of the bulk (SLG), or a few layers of graphene out-of-the bulk (FLG), supported or suspended, and those of a single (stage-1) or more (stage n, where n=2,3,…) of these carbon layer planes sandwiched between planes formed by other chemical species, as is
Abstract: Carbon atoms have the unique capability of associating with each other in different ways at the macro- and nanoscopic scales to form various architectures, some of them being unique. Following the discovery of fullerenes, these last twenty-five years witnessed the discovery of some new forms of carbon atom associations leading to a large diversity of nanocarbons with fascinating properties. As regards bulk carbons, the decade preceding the discovery of fullerenes paved the way for finding some physical properties which were found later to be displayed in these new nano entities. This mainly concerns the semiclassical and, more particularly, the quantum aspects of two-dimensional (2D) electronic transport and the behavior of phonons in low-dimensional materials. These effects are discussed here in relation to the electrical and thermal conductivities of various nano-carbon based materials. This chapter also reflects the obvious similarities and differences observed in the transport properties of an isolated single layer graphene out of the bulk (SLG), or a few layers of graphene out of the bulk (FLG), supported or suspended, and those of a single (stage-1) or more (stage-n, where n=2,3,…) of these carbon layer planes sandwiched between planes formed by other chemical species, as is the case for macroscopic graphite intercalation compounds (GICs), and more particularly quasi 2D acceptor compounds (GACs), or even, in some cases, pristine highly oriented pyrolytic graphite (HOPG).
01 Jan 2014
TL;DR: In this paper, the optical properties of carbon nanotubes are discussed from a theoretical point of view using Raman spectroscopy and other optical techniques for measuring electronic and phonon properties and the electron-phonon interaction.
Abstract: The optical properties of carbon nanotubes are overviewed. In carbon nanotubes, the exciton properties are essential for describing the optical processes since many special properties of the excitons, such as dark excitons or environmental effects, affect the physics of nanotubes in essential ways. Raman spectroscopy and other optical techniques for measuring electronic and phonon properties and the electron–phonon interaction are discussed in this chapter mainly from a theoretical point of view.
TL;DR: In this paper, a brief historical review about how graphene logically fits into the nanoscience field from my own perspective in contrast to the actual history of graphene is given, and a brief review of the history of the development of graphene can be found.
Abstract: I start this perspectives article with a brief historical review about how graphene logically fits into the nanoscience field from my own perspective in contrast to the actual history of graphene r...
TL;DR: In this article, the effect of texturing in polycrystalline bismuth thin films was investigated using magneto-resistance measurements, and it was shown that the anisotropic conduction is a result of the large electron effective mass anisotropy.
Abstract: We use magneto-resistance measurements to investigate the effect of texturing in polycrystalline bismuth thin films. Electrical current in bismuth films with texturing such that all grains are oriented with the trigonal axis normal to the film plane is found to flow in an isotropic manner. By contrast, bismuth films with no texture such that not all grains have the same crystallographic orientation exhibit anisotropic current flow, giving rise to preferential current flow pathways in each grain depending on its orientation. Extraction of the mobility and the phase coherence length in both types of films indicates that carrier scattering is not responsible for the observed anisotropic conduction. Evidence from control experiments on antimony thin films suggests that the anisotropy is a result of bismuth's large electron effective mass anisotropy.