Confocal Raman spectroscopy has emerged as a major, versatile workhorse for the non-invasive characterization of graphene. Although it is successfully used to determine the number of layers, the ...quality of edges, and the effects of strain, doping and disorder, the nature of the experimentally observed broadening of the most prominent Raman 2D line has remained unclear. Here we show that the observed 2D line width contains valuable information on strain variations in graphene on length scales far below the laser spot size, that is, on the nanometre-scale. This finding is highly relevant as it has been shown recently that such nanometre-scaled strain variations limit the carrier mobility in high-quality graphene devices. Consequently, the 2D line width is a good and easily accessible quantity for classifying the crystalline quality, nanometre-scale flatness as well as local electronic properties of graphene, all important for future scientific and industrial applications.
A model is developed to explain a hysteresis observed experimentally in nanotube field-effect transistors. The model explains the hysteresis through trapping of electrons in an oxide layer. The ...Fowler-Nordheim tunneling mechanism is held responsible for the electron injection. The influence of different parameters such as the sweeping rate or the range of the gate voltage on the hysteresis is studied and compared with experimental results.
Intraconnects, as-grown single-walled carbon nanotubes bridging two metal electrodes, were investigated as gated structures. We show that even with a seemingly “ohmic” contact at zero gate voltage ...one observes negative differential resistance (NDR) at nonzero gate bias. Large differential photo conductance (DPC) was associated with the NDR effect raising hopes for the fabrication of novel high-speed optoelectronic devices.
The electronic properties of carbon nanotubes (NTs) in a uniform transverse field are investigated within a single orbital tight-binding (TB) model. For doped nanotubes, the dielectric function is ...found to depend not only on symmetry of the tube, but also on radius and Fermi level position. Band gap opening/closing is predicted for zigzag tubes, while it is found that armchair tubes always remain metallic, which is explained by the symmetry in their configuration. The bandstructures for both types are considerably modified when the field strength is large enough to mix neighboring subbands.
► Spontaneous decay of an emitter coupled to a system of carbon nanotubes is studied. ► Presence of carbon nanotubes substantially enhances emitter decay rate. ► Emitter decay rate spectra contain ...pronounced resonance lines. ► Resonance frequencies depend on the carbon nanotube length. ► Resonance frequencies depend on the relative permittivity of surrounding medium.
After devising an integral-equation formalism to study the spontaneous decay rate of an emitter coupled to an array of three identical and parallel SWNTs, the half spaces containing the emitter and the SWNTs being occupied by homogeneous materials of different relative permittivities, and the electric dipole moment of the emitter as well as all SWNTs aligned normal to the bimaterial interface, we found that the presence of SWNTs substantially enhances the spontaneous decay rate. The spectrum of the decay rate contains closely spaced sub-resonances, which arise from the propagation of surface plasmon–polariton waves on the SWNTs. The sub-resonance frequencies decrease with the increase of the relative permittivity of the material surrounding the SWNT and come closer to each other as the inter-SWNT distance decreases.
The book describes the state of the art in fundamental, applied and device physics of nanotubes, including fabrication, manipulation and characterization for device applications; optics of nanotubes; ...transport and electromechanical devices and fundamentals of theory for applications. This information is critical to the field of nanoscience since nanotubes have the potential to become a very significant electronic material for decades to come. The book will benefit allreaders interested in the application of nanotubes, either in their theoretical foundations or in newly developed characterization tools that may enable practical device fabrication.
The electronic structure and dielectric screening of finite-length armchair carbon nanotubes are studied in view of their technical applications. For this purpose, a self-consistent tight-binding ...method, which captures the periodic oscillation pattern of the finite band gap as a function of tube length, is applied. We find the parallel screening constant ε∥ to grow nearly linearly with the length L and to show little dependence on the band gap. In contrast, the perpendicular screening constant ε⊥ is strongly related to the band gap and converges for L > 10R (radius) to its bulk value. Our description is employed to study the wall polarization in a short (6,6) nanotube filled with six water molecules, a situation that arises with technical uses of carbon nanotubes as channels.
A unified approach to the analysis of the mechanisms that lead to the edge reconstruction of graphite and growth of a variety of non-planar graphitic structures, such as nanotubes, is suggested. ...Transmission electron microscopy (TEM) shows that nano-arches are formed on the edge planes of natural and synthetic graphite, as well as graphite polyhedral crystals, which are built of graphene sheets; this makes the edge reconstruction of graphite different from the surface reconstruction of other crystals. A theoretical study of edge zipping in graphite and formation of tubular carbon structures has been performed using an integrated approach combining molecular dynamics simulation and analytical continual energetics modeling. The suggested theoretical framework describes the formation of curved surfaces in a wide range of dimensions, which is a general feature of the growth of layered materials. Layered materials isostructural to graphite, such as hexagonal BN, demonstrate similar edge structures and also form nanotubes. Thus, the ability of materials to form arches as a result of edge reconstruction points out to their ability to form nanotubes and vice versa. TEM studies of graphite and hexagonal boron nitride provide experimental verification of our analytical model.
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