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Addition energies in semiconductor quantum dots: Role of electron-electron interaction  [PDF]
Massimo Rontani,Fausto Rossi,Franca Manghi,Elisa Molinari
Physics , 1997, DOI: 10.1063/1.120933
Abstract: We show that the addition spectra of semiconductor quantum dots in the presence of magnetic field can be studied through a theoretical scheme that allows an accurate and practical treatment of the single particle states and electron-electron interaction up to large numbers of electrons. The calculated addition spectra exhibit the typical structures of Hund-like shell filling, and account for recent experimental findings. A full three dimensional description of Coulomb interaction is found to be essential for predicting the conductance characteristics of few-electron semiconductor structures.
Multiple charging of InAs/GaAs quantum dots by electrons or holes: addition energies and ground-state configurations  [PDF]
Lixin He,Alex Zunger
Physics , 2005, DOI: 10.1103/PhysRevB.73.115324
Abstract: Atomistic pseudopotential plus configuration interaction calculations of the energy needed to charge dots by either electrons or holes are described, and contrasted with the widely used, but highly simplified two-dimensional parabolic effective mass approximation (2D-EMA). Substantial discrepancies are found, especially for holes, regarding the stable electronic configuration and filling sequence which defies both Hund's rule and the Aufbau principle.
Knowledge Emergence in Scientific Communication: From "Fullerenes" to "Nanotubes"  [PDF]
Diana Lucio-Arias,Loet Leydesdorff
Physics , 2009,
Abstract: This article explores the emergence of knowledge from scientific discoveries and their effects on the structure of scientific communication. Network analysis is applied to understand this emergence institutionally as changes in the journals; semantically, as changes in the codification of meaning in terms of words; and cognitively as the new knowledge becomes the emergent foundation of further developments. The discovery of fullerenes in 1985 is analyzed as the scientific discovery that triggered a process which led to research in nanotubes.
Octagraphene as a Versatile Carbon Atomic Sheet for Novel Nanotubes, Unconventional Fullerenes and Hydrogen Storage  [PDF]
Xian-Lei Sheng,Hui-Juan Cui,Fei Ye,Qing-Bo Yan,Qing-Rong Zheng,Gang Su
Physics , 2012, DOI: 10.1063/1.4757410
Abstract: We study a versatile structurally favorable periodic $sp^2$-bonded carbon atomic planar sheet with $C_{4v}$ symmetry by means of the first-principles calculations. This carbon allotrope is composed of carbon octagons and squares with two bond lengths and is thus dubbed as octagraphene. It is a semimetal with the Fermi surface consisting of one hole and one electron pocket, whose low-energy physics can be well described by a tight-binding model of $\pi$-electrons. Its Young's modulus, breaking strength and Poisson's ratio are obtained to be 306 $N/m$, 34.4 $N/m$ and 0.13, respectively, which are close to those of graphene. The novel sawtooth and armchair carbon nanotubes as well as unconventional fullerenes can also be constructed from octagraphene. It is found that the Ti-absorbed octagraphene can be allowed for hydrogen storage with capacity around 7.76 wt%.
Doping of zigzag carbon nanotubes through the encapsulation of small fullerenes  [PDF]
K. S. Troche,V. R. Coluci,R. Rurali,D. S. Galv?o
Physics , 2006,
Abstract: In this work we investigated the encapsulation of C$_20$ and C$_30$ fullerenes into semiconducting carbon nanotubes to study the possibility of bandgap engineering in such systems. Classical molecular dynamics simulations coupled to tight-binding calculations were used to determine the conformational and electronic properties of carbon nanotube supercells containing up to 12 fullerenes. We have observed that C$_20$ fullerenes behave similarly to a p-type dopant while C$_30$ ones work as n-type ones. For larger diameter nanotubes, where fullerene patterns start to differ from the linear arrangements (peapods), the doping features are preserved for both fullerenes, but local disorder plays an important role and significantly alters the electronic structure. The combined incorporation of both fullerene types (hybrid encapsulation) into the same nanotube leads to a behavior similar to that found in electronic junctions in Silicon-based electronic devices. These aspects can be exploited in the design of nanoelectronic devices using semiconducting carbon nanotubes.
Hydrogen-induced disintegration of fullerenes and nanotubes: An ab initio study  [PDF]
Savas Berber,David Tomanek
Physics , 2009, DOI: 10.1103/PhysRevB.80.075427
Abstract: We use ab initio density functional calculations to study hydrogen-induced disintegration of single- and multi-wall carbon fullerenes and nanotubes. Our results indicate that hydrogen atoms preferentially chemisorb along lines in sp2 bonded carbon nanostructures, locally weakening the carbon bonds and releasing stress. For particular structural arrangements, hydrogen helps to relieve the accumulated stress by inducing step-wise local cleavage leading to disintegration of the outermost wall.
Shapes and energies of icosahedral fullerenes: Onset of ridge sharpening transition  [PDF]
A. Siber
Physics , 2006, DOI: 10.1140/epjb/e2006-00375-6
Abstract: Shapes and energies of icosahedral fullerenes are studied on an atomically detailed level. The numerical results based on the effective binary carbon-carbon potential are related to the theory of elasticity of crystalline membranes with disclinations. Depending on fullerene size, three regimes are clearly identified, each of them characterized by different geometrical properties of the fullerene shape. For extremely large fullerenes (more than about 500000 atoms), transition of fullerene shapes to their asymptotic limit is detected, in agreement with previous predictions based on generic elastic description of icosahedral shells. Quantum effects related to delocalized electrons on the fullerene surface are discussed and a simple model introduced to study such effects suggests that the transition survives even in more general circumstances.
Magnetic fullerenes inside single-wall carbon nanotubes  [PDF]
F. Simon,H. Kuzmany,B. Nafradi,T. Feher,L. Forro,F. Fulop,A. Janossy,L. Korecz,A. Rockenbauer,F. Hauke,A. Hirsch
Physics , 2006, DOI: 10.1103/PhysRevLett.97.136801
Abstract: C59N magnetic fullerenes were formed inside single-wall carbon nanotubes by vacuum annealing functionalized C59N molecules encapsulated inside the tubes. A hindered, anisotropic rotation of C59N was deduced from the temperature dependence of the electron spin resonance spectra near room temperature. Shortening of spin-lattice relaxation time, T_1, of C59N indicates a reversible charge transfer toward the host nanotubes above $\sim 350$ K. Bound C59N-C60 heterodimers are formed at lower temperatures when C60 is co-encapsulated with the functionalized C59N. In the 10-300 K range, T_1 of the heterodimer shows a relaxation dominated by the conduction electrons on the nanotubes.
Spin-orbit coupling in curved graphene, fullerenes, nanotubes, and nanotube caps  [PDF]
D. Huertas-Hernando,F. Guinea,A. Brataas
Physics , 2006, DOI: 10.1103/PhysRevB.74.155426
Abstract: A continuum model for the effective spin orbit interaction in graphene is derived from a tight-binding model which includes the $\pi$ and $\sigma$ bands. We analyze the combined effects of the intra-atomic spin-orbit coupling, curvature, and applied electric field, using perturbation theory. We recover the effective spin-orbit Hamiltonian derived recently from group theoretical arguments by Kane and Mele. We find, for flat graphene, that the intrinsic spin-orbit coupling $\Hi \propto \Delta^ 2$ and the Rashba coupling due to a perpendicular electric field ${\cal E}$, $\Delta_{\cal E} \propto \Delta$, where $\Delta$ is the intra-atomic spin-orbit coupling constant for carbon. Moreover we show that local curvature of the graphene sheet induces an extra spin-orbit coupling term $\Delta_{\rm curv} \propto \Delta$. For the values of $\cal E$ and curvature profile reported in actual samples of graphene, we find that $\Hi < \Delta_{\cal E} \lesssim \Delta_{\rm curv}$. The effect of spin-orbit coupling on derived materials of graphene, like fullerenes, nanotubes, and nanotube caps, is also studied. For fullerenes, only $\Hi$ is important. Both for nanotubes and nanotube caps $\Delta_{\rm curv}$ is in the order of a few Kelvins. We reproduce the known appearance of a gap and spin-splitting in the energy spectrum of nanotubes due to the spin-orbit coupling. For nanotube caps, spin-orbit coupling causes spin-splitting of the localized states at the cap, which could allow spin-dependent field-effect emission.
Exciton binding energies in carbon nanotubes from two-photon photoluminescence  [PDF]
J. Maultzsch,R. Pomraenke,S. Reich,E. Chang,D. Prezzi,A. Ruini,E. Molinari,M. S. Strano,C. Thomsen,C. Lienau
Physics , 2005, DOI: 10.1103/PhysRevB.72.241402
Abstract: One- and two-photon luminescence excitation spectroscopy showed a series of distinct excitonic states in single-walled carbon nanotubes. The energy splitting between one- and two-photon-active exciton states of different wavefunction symmetry is the fingerprint of excitonic interactions in carbon nanotubes. We determine exciton binding energies of 0.3-0.4 eV for different nanotubes with diameters between 0.7 and 0.9 nm. Our results, which are supported by ab-initio calculations of the linear and non-linear optical spectra, prove that the elementary optical excitations of carbon nanotubes are strongly Coulomb-correlated, quasi-one dimensionally confined electron-hole pairs, stable even at room temperature. This alters our microscopic understanding of both the electronic structure and the Coulomb interactions in carbon nanotubes, and has direct impact on the optical and transport properties of novel nanotube devices.
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