We study the strength of the binding of 4d and 5d transition metals on a graphene sheet in the limit of high-coverage using first principles density functional theory. A database of the binding ...energies is presented. Our results show that the elements with low or near-half occupation of the d shell bind strongest to the graphene sheet. We find a transfer of electrons from the transition metal to the graphene sheet; the charge transfer decreases with increasing d shell occupation. Motivated by the strong binding to Hf we also study the binding of graphene to the Hf rich surface of HfO2. The predicted binding energy of −0.18 eV per C atom when coupled with the existing integration of HfO2 into Si-based CMOS devices suggests a new route to integrating graphene with silicon, allowing for an integration of graphene-based nanoelectronic components into existing silicon-based technology.
We study the electron spin resonance (ESR) signal of pristine and potassium doped SWCNTs. We identify signals of a super‐paramagnetic background, a low intensity impurity, and of the conduction ...electron spin resonance (CESR). The latter only appears upon the alkali atom doping. To identify the CESR signal, we critically assess whether it could come from residual graphitic carbon, which we clearly exclude. We give accurate values for the signal intensities and the corresponding concentration of spins and for the g‐factors. The CESR signal intensity allows to determine the density of states on the SWCNT assembly.
Experiments show that the D bands of bundles of single wall carbon nanotubes have a fine structure, apparently consisting of more than one subband. Using the double resonance theory, we calculate for ...the first time the D band for a sample of a given diameter distribution for seven different laser excitation energies in a wide range. In addition, a detailed theoretical explanation for the fine structure of the D band is provided. The calculated results agree well with experiments and show that the main factors in determining the fine structure are an enhanced trigonal warping of the phonon dispersion, the presence of a diameter distribution in the sample, and--most importantly--the resonance from the Van Hove singularities.
A comprehensive theory of electron spin resonance (ESR) for a Luttinger liquid state of correlated metals is presented. The ESR measurables such as the signal intensity and the linewidth are ...calculated in the framework of Luttinger liquid theory with broken spin rotational symmetry as a function of magnetic field and temperature. We obtain a significant temperature dependent homogeneous line broadening which is related to the spin-symmetry breaking and the electron-electron interaction. The result crosses over smoothly to the ESR of itinerant electrons in the noninteracting limit. These findings explain the absence of the long-sought ESR signal of itinerant electrons in single-wall carbon nanotubes when considering realistic experimental conditions.
Recent transport measurements Churchill et al. Nature Phys. 5, 321 (2009) found a surprisingly large, 2-3 orders of magnitude larger than usual (13)C hyperfine coupling (HFC) in (13)C enriched ...single-wall carbon nanotubes. We formulate the theory of the nuclear relaxation time in the framework of the Tomonaga-Luttinger liquid theory to enable the determination of the HFC from recent data by Ihara et al. Europhys. Lett. 90, 17,004 (2010). Though we find that 1/T(1) is orders of magnitude enhanced with respect to a Fermi-liquid behavior, the HFC has its usual, small value. Then, we reexamine the theoretical description used to extract the HFC from transport experiments and show that similar features could be obtained with HFC-independent system parameters.
Albeit difficult to access experimentally, the density of states (DOS) is a key parameter in solid-state systems, which governs several important phenomena including transport, magnetism, thermal, ...and thermoelectric properties. We study DOS in an ensemble of potassium intercalated single-wall carbon nanotubes and show, using electron spin resonance spectroscopy, that a sizable number of electron states are present, which gives rise to a Fermi-liquid behavior in this material. A comparison between theoretical and the experimental DOS indicates that it does not display significant correlation effects, even though the pristine nanotube material shows a Luttinger-liquid behavior. We argue that the carbon nanotube ensemble essentially maps out the whole Brillouin zone of graphene, thus it acts as a model system of biased graphene.
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