81 research outputs found
Strong Electron Correlation in Cu-doped CaO Nanocolloid
Theoretical prediction of magnetism induced by defects or doping in non-metallic colloids has gained a renewed interests recently. In this work, we investigated the possible appearance of magnetism in Cu doped CaO nanocolloids activated by SPAN-80 in the framework of density functional theory (DFT). Despite of strong antiferromagnetic superexchange interaction between Cu ions, the local magnetic moment of Cu may arise due to attachment of colloidal agent onto the surface of CaO nanocluster. The ferromagnetism attributes to the degeneration of Cu 3d orbitals in CaO crystal fields, the aspects of electron correlation and quantum spin fluctuation. %PACS number: 42.30.R, 42.40.Ht, 42.30.K
Structure and Electrical Properties of the Thin Gold Leaves Fabricated by Vietnam Traditional Laminating Technology
The structure and electrical properties of the thin gold leaves fabricated by Vietnam traditional laminating technology are introduced. The gold leaves are usually created with the average size of 3x3cm, and 200nm thickness, they can easily be broken when handling carelessly. By the measurements of X-ray Diffraction (XRD), and Electron Scanning Microscopy (SEM), the structure and surface morphology were investigated. We have also measured the absorption spectra and determined the resistivity of the samples and found that the gold films possessed the Ca impurities stuck on the surface of the leaves. The conductivity of the films is relatively higher and the absorption maximum is red-shifted in comparison with that of the bulk
Thermal effect on magnetoexciton energy spectra in monolayer transition metal dichalcogenides
It is widely comprehended that temperature may cause phonon-exciton
scattering, enhancing the energy level's linewidth and leading to some spectrum
shifts. However, in the present paper, we suggest a different mechanism that
allows the thermal motion of the exciton's center of mass (c.m.) to affect the
magnetoexciton energies in monolayer dichalcogenides (TMDCs). By the nontrivial
but precise separation of the c.m. motion from an exciton in a monolayer TMDC
with a magnetic field, we obtain an equation for the relative motion containing
a motional Stark term proportional to the c.m. pseudomomentum, related to the
temperature of the exciton gas but neglected in the previous studies. Solving
the Schr\"odinger equation without omitting the motional Stark potential at
room temperature shows approximately a few meV thermal-magnetic shifts in the
exciton energies, significant enough for experimental detection. Moreover, this
thermal effect causes a change in exciton radius and diamagnetic coefficient
and enhances the exciton lifetime as a consequence. Surprisingly, the
thermoinduced motional Stark potential breaks the system's SO(2) symmetry,
conducting new peaks in the exciton absorption spectra at room temperature
besides those of the states. This mechanism could be extended for other
magnetoquasiparticles such as trions and biexcitons.Comment: 8 pages, 4 figures, 3 tables for main manuscript; 20 pages, 6
figures, 6 tables for supplementary. Published on Physical Review
Influence of Reaction Temperature on Optical Property of Mn-Doped ZnS Nanoparticles
The reaction temperature has essential effect on quality of the product synthesized by hydrothermal method. We report here the variation of the optical characteristics of Mn-doped ZnS nanocrystallites prepared by mean of the stated method from Zn(CHCOO).2HO, Mn(CHCOO).4HO and NaSO.5HO as the precursors. The reaction temperature was set to vary from 120\r{}C to 240\r{}C at a constant reaction time of 15 hours. The XRD patterns showed that, for the reaction temperature range from 120 to 160\r{}C, the obtained products possessed a cubic and a wurtzite structure, in which the cubic phase was dominant. At the temperature range from 180 to 240\r{}C, the structures exhibited a cubic phase with the lattice constant increased from 5.41 to 5.43 {\AA}. The photoluminescence spectra showed that with the increase of reaction temperature from 120 to 240\r{}C the intensity of a blue band around 425 - 500 nm (attributed to both Zn, S vacancies) gradually decreased while the intensity of a yellow-orange band at 585 nm (attributed to the TG) - AS) transition of Mn ions) was enhanced and reached maximum at 220\r{}C. The excitation spectra of the 585 nm band recorded at 160\r{}C showed a band at 335 nm which should be assigned to the near band-edge absorption. With increasing temperature to 200-240\r{}C the new bands appeared at 390, 430, 467, 494 nm. The intensity of these bands increased with temperature and achieved the maxima at 220\r{}C. They should be attributed to the absorption transitions of electrons from ground state AS) to excited statesE(D); TD); AG) - E(G); TG) of Mn(3d ions, respectively. The bands at 467, 494 nm only exposed clearly in the absorption spectra at 220\r{}C and 240\r{}C
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