The effect of low-temperature uniaxial deformation on the self-trapping-limited mean free path of excitons in a KI–Tl crystal was revealed from x-ray luminescence spectra. The analysis of the dependence of the intensity ratio of the Tl-center emission (2.85 eV) and the luminescence of self-trapped excitons (π-component; 3.3 eV) on the extent of low-temperature deformation showed that in the KI–Tl crystal (3 × 10−3 mol. %) the self-trapping-limited mean free path of excitons is comparable with the distance between Tl atoms (20–27)a under a deformation ε = 2%. As the compression increases to ε ≥ 2%–5%, the mean free path drops to (27-5.35)a. The results of modeling based on the continuum approximation showed that with increasing temperature and the degree of low-temperature deformation the height of the potential barrier for the exciton self-trapping drops, which is consistent with the reduction of the mean free path of excitons in the KI–Tl crystal.
In the framework of the density functional theory and method of nonequilibrium Green functions (DFT [Formula: see text] NEGF), the electric transport properties of the model nanojunction “Graphene–Fullerene C[Formula: see text]–Graphene” were studied. The transmission spectra, the density of states, the current–voltage characteristic (CVC) and the differential conductivity of the nanojunction are determined. The appearance of a feature of the DOS nanotransition is revealed. This is due to the fact that the Lowest Unoccupied Molecular Orbital (LUMO) of C[Formula: see text] becomes closer to the Fermi level of metal substrates than its Highest Occupied Molecular Orbital (HOMO). It is shown that Coulomb stairs associated with the Coulomb blockade effect appear on the CVC of the nanotransition. The same changes are observed on the differential conductivity spectrum in the form of eight distinct peak structures arising with period [Formula: see text][Formula: see text]V. The comparison of the electric transport characteristics of single-fullerene nanodevices with various electrode materials (graphene, gold, platinum) are presented. It was found that the voltage period of Coulomb features [Formula: see text] in a nanodevice with graphene electrodes is less than in nanodevices with platinum and gold electrodes. It was revealed that the considered nanotransition has negative differential conductivity. The results obtained can be useful in calculating promising elements of single-electronics.
The X-ray luminescence spectra at low temperature (90K) uniaxial deformation were researched for KI and KI-Na crystals, that were stored for more than 10 years. The following regularities were observed: firstly, the intensities of the intrinsic emission bands at 3.3 eV ( π ) and 4.1 eV ( σ ) become equal in comparison with freshly grown crystals; and secondly, with an increase in the degree of low-temperature uniaxial deformation, a gradual shift of the emission spectra occurs in two directions: the luminescence maximum at 3.3 eV shifts towards short wavelengths, the final position is fixed at 3.9 eV, which practically merges with σ -luminescence; the radiation maximum at 3.0 eV (Ex-radiation) is shifted toward long wavelengths, the final position which is fixed at 2.8 eV. Thus, low temperature uniaxial deformation leads to the separation of the emission spectra at 3,3 eV( π ) → 3,9 eV and 3.0 eV ( E x ) → 2,8 eV, which are interpreted by the separation of weak → on and weak → strong exciton configurations , respectively.
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