Liyan Zhu

Formation and electronic properties of hydrogenated few layer graphene

Motivated by the controversial experimental conclusions on the affinity of few layer graphenes (FLGs) towards hydrogen plasma, we systematically investigate the hydrogenation of FLGs within the framework of density functional theory. The approaching hydrogen atoms from both sides of an FLG induce a structural transition from a layered structure into a hydrogen passivated thin diamond film (HP-TDF). The very low transition barrier of FLG hydrogenation indicates the feasibility of FLG hydrogenation through the proposed mechanism. The increasing formation energy with the thickness of FLGs implies that hydrogenation of single layer graphene is easier than that of FLG, which is in agreement with most experimental observations. Moreover, the electronic properties of HP-TDFs and the hydrogenated bilayer graphene ribbons are also studied.

Edge-passivation induced half-metallicity of zigzag zinc oxide nanoribbons

The electronic and magnetic properties of zigzag zinc oxide (ZnO) nanoribbons with or without hydrogen passivation are investigated using ab initio calculations. The ribbon is found to be half-metallic ferromagnet when edge zinc atoms are passivated only. Moreover, the half-metallicity only emerges in the ribbons with relatively large width. Besides, the half-metallic ferromagnet can also be achieved when the passivatator H is replaced by CH3 or NH2. These diverse electronic and magnetic properties might open ZnO materials great possibility in future spintronics.

Fluorination induced half metallicity in two-dimensional few zinc oxide layers

We systematically explore the stability, bonding characteristics, and electronic and magnetic properties of two-dimensional (2D) few zinc oxide layers (few-ZnOLs) with or without fluorination by using density functional theory approach. The pristine few-ZnOLs favor stable planar hexagonal structures, which stem from their unique bonding characteristics: The intralayer Zn-O interaction is dominated by covalent bonding while the interaction between layers is weak ionic bonding. Furthermore, we demonstrate that fluorination from one side turns the planar few-ZnOLs back to the wurtzitelike corrugated structure, which enhances the stability of the 2D ZnO films. The fluorinated few-ZnOLs are ferromagnets with magnetic moments as high as 0.84, 0.87, 0.89, and 0.72 mu(B) per unit cell for the number of layers of N=1, 2, 3, and 4, respectively. Most interestingly, the fluorination can also turn few-ZnOLs from semiconductor into half metallicity with a half-metal gap up to 0.56 eV. These excellent electronic and magnetic properties may open 2D ZnO based materials great opportunity in future spintronics.

Ab Initio Study on Mixed Inorganic/Organic Ligand Sandwich Clusters: BzTMC60, TM = Sc−Co

We have systematically investigated mixed inorganic/organic ligand sandwich clusters comprised of 3d transition metal (TM) atoms with C(60) and benzene (Bz) molecules, BzTMC(60), by using all electron density functional theory. We found the bonding type between TM and C(60) in the ground state evolves from eta(6) (TM = Sc-Cr) to eta(5) (TM = Mn) and then to eta(2) (TM = Fe, Co) with increasing number of d electrons of TM. The BzTMC(60) clusters (TM = Sc-Co) are of high stability through ionic-covalent interactions. The BzCrC(60) cluster has the lowest binding energy due to its largest spin-flip energy and the weakest ionic bonding interaction between the CrBz unit and C(60). With the exception of BzTiC(60) being triplet, all the BzTMC(60) clusters energetically prefer the lowest available spin states, e.g., the ground spin state is either a singlet (with an even number of electrons) or a doublet (with an odd number of electrons). Moreover, the magnetic properties of BzTMC(60) show clear dependence to the bond type between TM and C(60), and the eta(5)-ligand configurations tend to be in high spin states.

Gold nanotube encapsulation enhanced magnetic properties of transition metal monoatomic chains: An ab initio study.

The magnetic properties of gold nanotubes encapsulated transition metal (TM, TM=Co and Mn) and monoatomic chains (TM@Au) are studied using first-principles density functional calculations. The TM chains are significantly stabilized by the gold nanotube coating. TM-TM distance-dependent ferromagnetic-antiferromagnetic phase transition in TM@Au is observed and can be understood by Ruderman-Kittel-Kasuya-Yosida (RKKY) model. The magnetocrystalline anisotropy energies of the TM@Au tubes are dramatically enhanced by one order of magnitude compared to those of free TM chains. Furthermore, the stronger interaction between Mn chain and gold nanotube even switches the easy magnetization axis along the tube.

Structural and Magnetic Properties of 3d Transition‐Metal‐Atom Adsorption on Perfect and Defective Graphene: A Density Functional Theory Study

We systematically investigate the interactions and magnetic properties of a series of 3d transition-metal (TM; Sc-Ni) atoms adsorbed on perfect graphene (G6), and on defective graphene with a single pentagon (G5), a single heptagon (G7), or a pentagon-heptagon pair (G57) by means of spin-polarized density functional calculations. The TM atoms tend to adsorb at hollow sites of the perfect and defective graphene, except for G6Cr, G5Cr, and G5Ni. The binding energies of TMs on defective graphene are remarkably enhanced and show a V-shape, with G(N)Cr and G(N)Mn having the lowest binding energies. Furthermore, complicated element- and defect-dependent magnetic behavior is observed in G(N)TM. Particularly, the magnetic moments of G(N)TM linearly increase by about 1 μB and follow a hierarchy of G7TM<G57TM<G5TM as the TM varies from Sc to Mn, and the magnetic moments begin to decrease afterward; by choosing different types of defects, the magnetic moments can be tuned over a broad range, for example, from 3 to 6 μB for G(N)Cr. The intriguing element- and defect-dependent magnetic behavior is further understood from electron- and back-donation mechanisms.

Stability and electronic structure of hydrogen passivated few atomic layer silicon films : a theoretical exploration

The stability, electronic, and optical properties of two dimensional hydrogenated few atomic layer silicon (H-FLSi) are systematically studied with density functional theory calculations. The formation energy of H-FLSi decreases with increasing layer thickness and approaches zero at the thickness of double layer, suggesting that this material is energetically favorable and thus its experimentally synthesizing is feasible. Its bandgap decreases with the increase of the thickness and eventually approaches the value of bulk silicon. More interestingly, the bandgap of hydrogenated silicon films can be tuned by external electric field and even becomes metal. Importantly, the light absorption threshold and absorption peak of the H-Si mono- and bilayer locate in different energy regions and both move toward higher energy region as compared with those of the bulk silicon.

The Great Reduction of a Carbon Nanotube's Mechanical Performance by a Few Topological Defects.

It is widely believed that carbon nanotubes (CNTs) can be employed to produce superstrong materials with tensile strengths of up to 50 GPa. Numerous efforts have, however, led to CNT fibers with maximum strengths of only a few GPa. Here we report that, due to different mechanical responses to the tensile loading of disclination topological defects in the CNT walls, a few of these topological defects are able to greatly decrease the strength of the CNTs, by up to an order of magnitude. This study reveals that even nearly perfect CNTs cannot be used to build exceptionally strong materials, and therefore synthesizing flawless CNTs is essential for utilizing the ideal strength of CNTs.

Structures and magnetism of multinuclear vanadium-pentacene sandwich clusters and their 1D molecular wires

Two types of multinuclear sandwich clusters, (V(3))(n)Pen(n+1), (V(4))(n)Pen(n+1) (Pen = Pentacene; n = 1, 2), and their corresponding infinite one-dimensional (1D) molecular wires ([V(3)Pen](∞), [V(4)Pen](∞)) are investigated theoretically, especially on their magnetic coupling mechanism. These sandwich clusters and molecular wires are found to be of high stability and exhibit intriguing magnetic properties. The intra-layered V atoms in (V(3))(n)Pen(n+1) clusters prefer antiferromagnetic (AFM) coupling, while they can be either ferromagnetic (FM) or AFM coupling in (V(4))(n)Pen(n+1) depending on the intra-layered V-V distances via direct exchange or superexchange mechanism. The inter-layered V atoms favor FM coupling in (V(3))(2)Pen(3), whereas they are AFM coupled in (V(4))(2)Pen(3). Such magnetic behaviors are the consequence of the competition between direct exchange and superexchange interactions among inter-layered V atoms. In contrast, the 1D molecular wires, [V(3)Pen](∞) and [V(4)Pen](∞), appear to be FM metallic with ultra high magnetic moments of 6.8 and 4.0 μ(B) per unit cell respectively, suggesting that they can be served as good candidates for molecular magnets.

Facile preparation of surfactant-free Au NPs/RGO/Ni foam for degradation of 4-nitrophenol and detection of hydrogen peroxide

The application of Au nanoparticles (Au NPs) often requires surface modification with chemical surfactants, which dramatically reduce the surface activity and increase the chemical contamination and cost of Au NPs. In this research, we have developed a novel Au NPs/reduced graphene oxide/Ni foam hybrid (Au NPs/RGO/NiF) by in situ reduction through ascorbic acid and replacement reaction. This method is green, facile and efficient. The Au NPs are free of chemical surfactants and are homogeneously distributed on the surface of the RGO/NiF. The as-prepared Au NPs/RGO/NiF hybrid is uniform, stable and exhibits not only a high reduction efficiency for the reduction of 4-nitrophenol with a catalytic kinetic constant of up to 0.46 min-1 (0.15 cm3 catalysis) but also a sensitive and selective detection of H2O2 with a detection limit of ∼1.60 μM.