Gigahertz longitudinal acoustic phonons originating from ultrafast ligand field transitions in hematite thin films

The creation and propagation of longitudinal acoustic phonons （LAPs） in high quality hematite thin films （α-Fe203） epitaxially grown on different substrates （BaTiO3, SrTiO3, and LaAlO3） are investigated using the femtosecond pump- probe technique. Transient reflection measurements （AR/R） indicate the photo-excited electron dynamics, and the initial decay less than 1 ps and the slow decay of -500 ps are attributed to the electron-LO phonon coupling and electron-hole nonradiative recombination, respectively. LAPs in α-Fe2O3 film can be created by ultrafast excitation of the ligand field state, such as the ligand field transitions under 800-nm excitation as well as the ligand to metal charge-transfer with 400- nm excitation. The strain modulations of the sound velocity and the out-of-plane elastic properties are demonstrated in α-Fe2O3 film on different substrates.

Negative dependence of surface magnetocrystalline anisotropy energy on film thickness in Co_(33)Fe_(67) alloy

In this work, the magnetocrystalline anisotropy energy(MAE) on the surface of FeCoalloy film is extracted from x-ray magnetic linear dichroism(XMLD) experiments. The result indicates that the surface MAE value is negatively correlated with thickness. Through spectrum calculations and analysis, we find that besides the thickness effect, another principal possible cause may be the shape anisotropy resulting from the presence of interface roughness. These two factors lead to different electron structures on the fermi surface with different exchange fields, which produces different spin–orbit interaction anisotropies.

Influence of Ga^(3+) on Photoluminescence of Ce^(3+)

The electro optical characteristics of SrS∶Ce and SrGa 2S 4∶Ce as two kinds of hopeful blue TFEL phosphors have been intensively investigated. The color purity of SrGa 2S 4∶Ce is better than that of SrS∶Ce. In this paper, the influence of Ga 3+ on photoluminescence (PL) characteristics of Ce 3+ is first reported. Ga 2S 3 was doped into SrS, then sintered. The emission spectra shift obviously towards short wavelength range with increase of Ga 3+ concentration. At the same time, the relative intensity of the excitation peaks corresponding to the interband absorption of SrS reduces, and the excitation efficiency corresponding to the transition from the ground state to the excited state of Ce 3+ ion increases. The ligand field around Ce 3+ is changed by doped Ga 3+ . The ionicity of the substituted become stronger and Ce 3+ -Ce 3+ interaction become weaker. These are favorite to blue emission.

Effect of O–O bonds on p-type conductivity in Ag-doped ZnO twin grain boundaries

Based on density functional theory, first-principles calculation is applied to study the electronic properties of undoped and Ag-doped Zn O-Σ7（123^-0） twin grain boundaries（GBs）. The calculated result indicates that the twin GBs can facilitate the formation and aggregation of Ag substitution at Zn sites（AgZn） due to the strain release. Meanwhile, some twin GBs can also lower the ionization energy of AgZn. The density of state shows that the O–O bonds in GBs play a key role in the formation of a shallow acceptor energy level. When AgZnbonds with one O atom in the O–O bond, the antibonding state of the O–O bond becomes partially occupied. As a result, a weak spin splitting occurs in the antibonding state, which causes a shallow empty energy level above the valence band maximum. Further, the model can be applied to explain the origin of p-type conductivity in Ag-doped Zn O.

Bonding Characteristics and Magnetic Coupling Interactions in One-dimensional α′-NaV_2O_5

The spin-polarized generalized gradient approximation（GGA）＋U approach was employed to study the bonding characteristics and magnetic coupling interactions in room-temperature phase α＇-NaV2O5. The calculated resuits indicate that the Vdry orbital is split off from other 3d orbitals in the VO5 pyramidal ligand field. The Vdry orbitals are hybridized strongly with the Opx/py orbitals, forming a V--O--V π bond in the ab plane. The ligand field effect together with the intra-atomic exchange splitting results in the insulating behavior. With the aid of Noodleman＇s bro- ken symmetry methods, the magnetic exchange constant was derived from mapping the relative energies onto the Heisenberg model. The antiferromagnetic（AFM） exchange energy, d, along the chain was calculated to be -593 K in good agreement with the experimental data.