TiO2 nanotubes constitute very promising nanomaterials for water decontamination by the removal of cations. We combined a range of experimental techniques from structural analyses to measurements of ...the properties of aqueous suspensions of nanotubes, with (i) continuous solvent modeling and (ii) quantum DFT-based simulations to assess the adsorption of Cs+ on TiO2 nanotubes and to predict the separation of metal ions. The methodology is set to be operable under realistic conditions, which, in this case, include the presence of CO2 that needs to be treated as a substantial contaminant, both in experiments and in models. The mesoscopic model, based on the Poisson–Boltzmann equation and surface adsorption equilibrium, predicts that H+ ions are the charge-determining species, while Cs+ ions are in the diffuse layer of the outer surface with a significant contribution only at high concentrations and high pH. The effect of the size of nanotubes in terms of the polydispersity and the distribution of the inner and outer radii is shown to be a third-order effect that is very small when the nanotube layer is not very thick (ranging from 1 to 2 nm). Besides, DFT-based molecular dynamics simulations demonstrate that, for protonation, the one-site and successive association assumption is correct, while, for Cs+ adsorption, the size of the cation is important and the adsorption sites should be carefully defined.
In the work we highlight the structural features of 2D perovskite cuprates (tilted CuO6 octahedra with different orientation with respect to spacer rocksalt layers), where sources of charge and spin ...inhomogeneity can be hidden. We used the impurity Anderson model with the Jahn-Teller(JT) local cells to show the charge inhomogeneity arises at any low doping concentration x, but disappears when the doping level exceeds threshold concentration xc, and the smaller the magnitudes xc, the larger the area of regions with JT pseudo effect. It is expected that spontaneous chiral symmetry breaking in the dynamic JT state of the stripe CuO2 layer as a whole can lead to the appearance of the goldstone phonon mode. As consequence, the giant thermal Hall effect could be observed in the 2D perovskite cuprates with CuO6 octahedra, rather than with CuO4 squares, e.g. in the Tl-based n layer cuprates or cuprates based on infinite-layer CaCuO2 structure.
•Jahn-Teller (JT) pseudo effect in 2D perovskite cuprates with charge inhomogeneity.•Dependence of JT distortion on a hole delocalization. Threshold hole concentration.•Phase diagram: JT distortion on the Coulomb and JT interactions.•In what perovskite materials can charge inhomogeneity be observed.•Chiral symmetry breaking in the dynamic JT state. Conclusions can be verified.
The coexistence of superconductivity and charge inhomogeneity was observed in many cuprate superconductors. The relationship between those two is still controversial. Similarly, in the graphene ...sheets of the intercalated graphitic superconductor CaC 6, the charge inhomogeneity was also observed. We simulate such a system by constructing the Hubbard model on the honeycomb lattice with charge inhomogeneity imposed by force. Utilizing the finite-temperature determinant quantum Monte Carlo algorithm, we examine the relationship between the superconducting pairing and the charge inhomogeneity. An optimal charge inhomogeneity for the d+i d-wave pairing is found. While for other artificial charge inhomogeneities, the d+i d-wave pairing is monotonically suppressed. The possible π-phase shift induced by charge inhomogeneity is also examined.
Kelvin probe microscopy in ultrahigh vacuum is used to image the local electrostatic potential fluctuations above hexagonal boron nitride (h-BN) and SiO2, common substrates for graphene. Results are ...compared to a model of randomly distributed charges in a two-dimensional (2D) plane. For SiO2, the results are well modeled by 2D charge densities ranging from 0.24 to 2.7 × 1011 cm–2, while h-BN displays potential fluctuations 1–2 orders of magnitude lower than SiO2, consistent with the improvement in charge carrier mobility for graphene on h-BN compared to SiO2. Electron beam exposure of SiO2 increases the charge density fluctuations, creating long-lived metastable charge populations of ∼2 × 1011 cm–2 at room temperature, which can be reversed by heating.
Scattering mechanisms in graphene are critical to understanding the limits of signal-to-noise ratios of unsuspended graphene devices. Here we present the four-probe low-frequency noise (1/f) ...characteristics in back-gated single layer graphene (SLG) and bilayer graphene (BLG) samples. Contrary to the expected noise increase with the resistance, the noise for SLG decreases near the Dirac point, possibly due to the effects of the spatial charge inhomogeneity. For BLG, a similar noise reduction near the Dirac point is observed, but with a different gate dependence of its noise behavior. Some possible reasons for the different noise behavior between SLG and BLG are discussed.
Twisted bilayer graphene (tBLG) provides an opportunity to control the optoelectronic properties of graphene owing to the relative orientation (θ)-induced van Hove singularities (vHs). However, how ...different environments affect vHs behaviors of various tBLGs and their Raman resonance window is not clear. A study of the optical vHs properties of tBLGs on a quartz substrate, prepared by chemical vapor deposition, was carried out using simultaneous reflection and Raman imaging techniques according to the presence of ubiquitous residual amorphous carbon (RAC). The results show that the presence of RAC exhibits a narrower vHs peak width and resonance Raman windows of tBLG as compared to that without RAC, due to the absence of charge-inhomogeneous interactions from bare substrate. In addition, the background-subtracted vHs peak reflectances from various θ values at a specific laser energy are proportional to the measured G-band enhancement factor (GEF). The comparison reveals the detailed optical and Raman resonance windows of various tBLGs in both environments. Extension of the approach to twisted fewlayer graphenes reveals the different vHs peak behaviors including broadening, intensification, and splitting governed by θ-, along with layer number-dependent band structure hybridization.
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The self-gravitational instability of partially ionized dusty plasma with radiative effects of electrons and ions, dust polarization force, and dust charge fluctuation has been studied. Using basic ...sets of fluid equations for ion, electron, neutral, and dust components, a general dispersion relation is derived. In the dynamics of dust charge, an equilibrium dust charge inhomogeneity along with the dust charge fluctuation is also considered. It is found that the presence of radiative cooling of ions and electrons, polarization force, and dust charge fluctuation significantly affects the criterion as well as the growth rate of self-gravitational instability while the dust charge inhomogeneity and dust-neutral collisions affect only the growth rate of instability. The outcomes of this paper are useful in dusty molecular clouds.
63Cu nuclear quadrupole resonance (NQR) experiments were preformed on six Nd-doped La
2−
x
Sr
x
CuO
4 samples. The NQR spectra show a systematic evolution with various Nd and/or Sr doping, except for ...La
1.48Nd
0.4Sr
0.12CuO
4. A completely different NQR spectrum was observed for the sample, which is similar to that for undoped insulator La
2CuO
4. It is speculated that a static stripe phase on the NQR time scale μs may be responsible for the anomalous spectrum.
Lattice effects in cuprates Egami, T.
Physica. C, Superconductivity,
09/2007, Letnik:
460-462, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
We describe the fine details of the dependence of the dispersion of the Cu–O bond-stretching phonon in YBa2Cu3O6+x on temperature and composition, recently determined by inelastic neutron scattering. ...The results suggest the presence of a localized phonon mode above the pseudogap temperature, which softens at lower temperatures. Its implications and possible role in the mechanism of high-temperature superconductivity are discussed.
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