Z.Z. Zhu

The Effects of AlF3 Coating on the Performance of Li [ Li0.2Mn0.54Ni0.13Co0.13 ] O2 Positive Electrode Material for Lithium-Ion Battery

National Basic Research Program of China (973 Program) [2007CB209702]; National Natural Science Foundation of China (NNSFC) [20433060, 20473068, 29925310]

Energetics of local clusters in Cu64.5Zr35.5 metallic liquid and glass

Correlation between the cluster energy and its population and dynamics can provide a better understanding of the complicated energy landscape of disordered metallic systems. We propose a method to analyze the cluster energy distribution for different kinds of short-range order (local clusters) in liquid and glass systems. By applying this analysis to an interesting and important glass forming system— Cu 64.5 Zr 35.5 we observe a direct correlation between the energy and dynamics of the cluster in this realistic glass-forming system. This study suggests that dynamic arrest originates from the environment-dependent energetics of local clusters.

Structural properties and energetics of Li2FeSiO4 polymorphs and their delithiated products from first-principles

Structural properties, thermodynamic stability and delithiation process for Li(2)FeSiO(4) polymorphs are investigated by using density functional theory (DFT) within the DFT + U framework. Three Li(2)FeSiO(4) polymorphs crystallizing in space group Pmn2(1), P2(1)/n, and Pmnb have been considered. The investigations demonstrate that the strong Si-O bonds remain almost unchanged during the lithiation-delithiation process for all the polymorphs, which contribute significantly to the structural stability. On the other hand, the differences in local environment around FeO(4) tetrahedra will be translated into varying degrees of distortion, which shows a significant influence on the structural stability and average voltages. The average voltages obtained here are in good agreement with the experimental values. Furthermore, the possibility of extracting more than one lithium ions per formula unit from Li(2)FeSiO(4) of P2(1)/n is also discussed.

Adsorption of alkali, alkaline-earth, simple and 3d transition metal, and nonmetal atoms on monolayer MoS2

Single adsorption of different atoms on pristine two-dimensional monolayer MoS2 have been systematically investigated by using density functional calculations with van der Waals correction. The adatoms cover alkali metals, alkaline earth metals, main group metal, 3d-transition metals, coinage metal and nonmetal atoms. Depending on the adatom type, metallic, semimetallic or semiconducting behavior can be found in direct bandgap monolayer MoS2. Additionally, local or long-range magnetic moments of two-dimensional MoS2 sheet can also attained through the adsorption. The detailed atomic-scale knowledge of single adsorption on MoS2 monolayer is important not only for the sake of a theoretical understanding, but also device level deposition technological application.

Band gap control and transformation of monolayer-MoS2-based hetero-bilayers

The study of heterostructured bilayer systems is an essential prerequisite for developing two-dimensional nano-electronic devices. Using ab initio density functional theory calculations, we investigated the atomic and electronic properties of hetero-bilayers composed of silicene and germanene layers with the MoS2 monolayer. Our results show that both silicene–MoS2 and germanene–MoS2 hetero-bilayers are direct band gap semiconductors. The band gaps of silicene and germanene in hetero-bilayers are opened due to the sublattice symmetry breaking induced by the introduction of the MoS2 monolayer, indicating that the MoS2 monolayer makes a good complement to silicene and germanene. Moreover, tunable band gaps in silicene and germanene can be realized by changing the interlayer distance or employing in-plane compressing/stretching. Especially, through compressing or stretching, germanene–MoS2 bilayers realize a transformation from an indirect band gap semiconductor to a direct band gap semiconductor, while the silicene–MoS2 bilayers can retain the direct band gaps. Our results in this work provide a new method for designing MoS2-based nanodevices with controllable band gaps.

Electronic structures of solids made of C20 clusters

By performing first-principles calculations based on the density functional theory, we have investigated the optimized structures, cohesive energies and electronic properties of crystalline solids made of C20 clusters. A very interesting result is found from the optimized diamond structure made of C20’s, where the dimered C20 clusters, i.e., (C20)2 dimmers, are formed. Such (C20)2 dimers are then condensed by weak van der Waals interaction between them, leading to the formation of a molecular solid. We also found that one-dimensional molecular solid could be formed when C20 clusters are head to head. Results on C20 clusters arranged in the two-dimensional graphene structure and in fcc structure both show that there are significant coalescences of neighboring C20 fullerenes, leading to metallic characters for both the graphene and fcc structures.

Electronic properties of a new structured Sin/O superlattice

Silicon is a material which dominants the semiconductor industry and has a well-established processing technology based on it. However, silicon has an indirect-bandgap and is not efficient in light emitting. This limits its applications in optoelectronics. In this paper, we proposed a new structural model for the silicon-based superlattice, i.e., the Sin/O one. The model consists of alternating films of n-layers of Si and a monolayer of oxygen along z-direction, together with a surface cell of Si(001) (2×1) reconstruction in the x-y plane. The importance of employing such a Si(001) (2×1) reconstruction is that all the electrons at interface can be strongly bonded. Our results showed interesting electronic properties, e.g., the band folding and large band gap of bulk Si, when the thickness of the silicon layers was increased (but still thin). Our structure might also offer other interesting properties.

Conduction-band-edge variations of pseudomorphic Si1-x-yGexCy alloys on (110) Si and Ge substrates

Abstract The trends of the conduction band minima with the alloy compositions for the pseudomorphic Si 1−x−y Ge x C y alloys grown on (110) Si and Ge substrates are investigated theoretically with the use of the ab initio pseudopotential method and the virtual-crystal approximation. It is found that the minimum energy gaps are all indirect and not monotonically dependent on the compositions in some cases. In the case of the tensile and compressive strains, the minimum energy gap decreases and increases, respectively, as the C fraction increases and the Ge fraction is constant. Our result is in good agreement with other theoretical results for the Si 1−x Ge x system.