Huxian Zhao

Structural, electronic and magnetic properties of AgnFe clusters (n ? 15): local magnetic moment interacting with delocalized electrons

The size-dependent electronic, structural and magnetic properties of AgnFe (n ≤ 15) clusters have been investigated by using the density functional theory (DFT) within the generalized gradient approximation. The starting structures were generated from empirical genetic algorithm simulations. The most stable structures were then selected from a number of structural isomers based on the results of the further DFT calculations. The atom prefers to stay at the centre of the clusters. The 2D to 3D transition occurs at n = 6. The magnetic properties and the geometric structures are strongly correlated. For , the total magnetic moment of the cluster is quenched. The reason is similar to the Kondo effect in bulk metal. Also, is considered to be very stable according to the 18-electron counting rule.

Double-stage soft x-ray laser pumped by multiple pulses applied in grazing incidence

In this paper we report on results obtained with a compact double-stage molybdenum x-ray laser (XRL), operated with a total pump energy of 600 mJ. The two gain regions were pumped using the double-pulse grazing incidence pumping technique, which includes travelling wave excitation for both the seed- and the amplifier-target. In addition, the influence of an additional pre-pulse has been studied. Seeded XRL operation has been demonstrated in both schemes, resulting in XRL pulses with a divergence of 2 × 2 mrad. The peak brilliance of the amplified XRL of 4 × 10^23 photons/s/mm2/mrad2 in 5 × 10^−5 relative bandwidth was more than two orders of magnitude larger compared to the original seed pulses. The presented experimental concept provides an alternative approach to the currently more common use of high-order harmonic pulses as a seed source, well suited for applications like laser spectroscopy of highly-charged ions at a storage ring.

The structural and electronic properties of amorphous HgCdTe from first-principles calculations

Amorphous mercury cadmium telluride (a-MCT) model structures, with x being 0.125 and 0.25, are obtained from first-principles calculations. We generate initial structures by computation alchemy method. It is found that most atoms in the network of amorphous structures tend to be fourfold and form tetrahedral structures, implying that the chemical ordered continuous random network with some coordination defects is the ideal structure for a-MCT. The electronic structure is also concerned. The gap is found to be 0.30 and 0.26 eV for a-Hg0.875Cd0.125Te and a-Hg0.75Cd0.25Te model structures, independent of the composition. By comparing with the properties of crystalline MCT with the same composition, we observe a blue-shift of energy band gap. The localization of tail states and its atomic origin are also discussed.

Interaction between AsHg and v Hg in Arsenic-Doped Hg1-x Cd x Te

Arsenic-related defect complexes have been proven responsible for the charge-compensation effects in arsenic-doped Hg1−xCdxTe, but the underlying mechanism is still unclear. In this study, we systematically investigated the interaction between arsenic donor (AsHg) and mercury vacancy (VHg) versus the AsHg–VHg separation in arsenic-doped Hg1−xCdxTe using first-principles calculations. A new long-range interaction between AsHg and VHg is found, and the related binding energies and electronic structures are calculated to reveal its coupling mechanism. Our results show that VHg can increase the distortion of the lattice collaboratively with AsHg due to the different characteristics of AsHg and VHg in distorting the lattice. The relaxational enhancement as well as the electrical compensation of the AsHg donor is weakened as VHg moves away from AsHg, and the underlying mechanism is revealed. In addition, a set of defect levels in the band gap generated from the donor–acceptor interaction are also shown, and the origin of these levels is explored. The results of this work are important for theoretically explaining the characteristics of complicated defect levels found in experiments.

High pressure phase transitions and depressurization amorphization of Bi2Fe4O9

High pressure structural behavior of Bi2Fe4O9 has been studied by in situ angular-dispersive X-ray diffraction (ADXD) measurements up to 51.3 GPa. Two phase transitions have been observed at 7.6 and 22.6 GPa, respectively. A second high pressure structure (HP2) involving the tripling of lattice parameter c has been identified. An unusual amorphization occurs after releasing pressure. The high pressure phase transitions can be understood in terms of the increase in the coordination number of Fe3+ ion. The depressurization amorphization results from the appearance of the metastable HP2 and its collapse after releasing pressure. The results extend our understanding of pressure-induced amorphization.

Ab initio investigation of the structural and electronic properties of amorphous HgTe

We present the structure and electronic properties of amorphous mercury telluride obtained from first-principle calculations. The initial configuration of amorphous mercury telluride is created by computation alchemy. According to different exchange–correlation functions in our calculations, we establish two 256-atom models. The topology of both models is analyzed in terms of radial and bond angle distributions. It is found that both the Te and the Hg atoms tend to be fourfold, but with a wrong bond rate of about 10%. The fraction of threefold and fivefold atoms also shows that there are a significant number of dangling and floating bonds in our models. The electronic properties are also obtained. It is indicated that there is a bandgap in amorphous HgTe, in contrast to the zero bandgap for crystalline HgTe. The structures of the band tail and defect states are also discussed.

Electronic properties of hgte within different structures

We present the results of a density functional theory study of high-pressure structures of HgTe up to bcc structure, which is the highest-pressure structure that has been fully characterized in experiments in the compounds. We investigated the different structures of HgTe and studied the semimetal → semiconductor → conductor transition in detail. We found, in the mechanism for the semimetal → semiconductor transition, the local structure plays a very important role. Change in local structure leads to the change in hybridization of bonding, sp3 →sp3d2 and led to the change from semiconductor to conductor. In addition, we focused on the special transition of semimetal → semiconductor. The tiny change of bond angle reduces the p–d repulsion interaction in the compound and a band gap is open up, which indicates the semiconductor property.