Study of chromium chalcogenide

众所周知，硫系铬化合物的物理性质取决于组成比例。Crxy(Y=S，Se，Te)在相变点发生相变。在过渡点观察到CrS和CrSe的金属-半导体相变。物理性质与费米能级E_F附近的电子结构有关。本文报道了CrS、CrSe和CrxTe的电子能带结构。在这项研究中，我们介绍了这些系列铬硫化物的电子结构。从Cr位空位和硫族物种对电子结构的影响的角度对态密度进行了比较和讨论。我们在Cr3p-3d激发区进行了共振反光电子能谱测量，得到了导带和未占据的Cr3d部分DOS。结果表明，CrS(x=1)、CrxSe和CrxTe的Cr3DPDO与价带空位几乎无关。随着硫化物从S转变为Se，再转变为Te，Cr3d交换分裂能变大。这一趋势类似于计算的交换分裂能。然而，测量的交换分裂能比计算值要大，在CRS中观察到了金属-半导体的转变。因此，我们用高分辨率的低温光电子能谱测量了低温下在EF附近的CRS的电子结构。Ef附近的光电子能谱强度随着温度的降低而降低。根据测量温度观察到了结构的变化。在CRS中，依赖于电子结构的x也计划测量RIPES。为了研究3d过渡金属离子对电子结构的替代作用，生长了(CrxVi_X)_3Te_4样品，并准备测量DOSS。

It is known that the physical properties of chromium chalcogenides depend on the ratio of composition. Cr_xY (Y=S, Se, Te) show the phase transition at transition point. The metal-semiconductor phase transition is observed for CrS and CrSe at transition point. Physical properties are related with electronic structures near Fermi level E_F. The electronic band-structures of CrS, CrSe and Cr_xTe are reported. In this study, we present the electronic structures in these series of chromium chalcogenides. The density of states (DOSs) are compared and discussed from the view points of the effect of the vacancies at Cr sites and chalcogen species on electronic structures. These DOSs are also compared with the result of the band-structure calculation.We obtained the conduction-band and the unoccupied Cr 3d partial DOSs by resonant inverse photoemission measurements at the Cr 3p-3d excitation region. It can be concluded that the Cr 3d pDOS of CrS (x=1), Cr_xSe and Cr_xTe are almost independent on the vacancies at Cr sites, as similar as those of the valence-band. The Cr 3d exchange splitting energy becomes lager as chalcogen changes from S to Se and further to Te. This tendency is similar to the calculated exchange splitting energies. However, the measured exchange splitting energies are larger than those of calculation.The metal-semiconductor transition is observed in CrS. Therefore, we measured the electronic structure of CrS near EF at low temperatures, with high-resolution and low-temperature photoemission spectrometers. The intensity of photoemission spectra near EF becomes lower as the temperature decreases. A structural change was observed according to the measurement temperature.In CrS, x-dependence on the electronic structures are now also planning to measure the RIPES. In order to study Cr substitutional effect with 3d transition metal ions on the electronic structures, samples of (CrxVi_x)_3Te_4 have been grown, and now are ready to measure DOSs.