Haiying He

Electronic and thermodynamic properties of β-Ga2O3

Electronic and thermodynamic properties of β-Ga2O3 are investigated in the framework of density functional theory. The equilibrium structural parameters and Debye temperature are obtained through fitting of the energy surface to the equation of state. Analysis of the band structure shows the valence band maximum to be degenerate at Γ and M, whereas the conduction band minimum is predicted to be at Γ. The valence band is almost flat, indicating a rather large effective mass for holes, whereas the calculated electron effective mass comes out to be about 0.12, expressed in units of the free electron mass.

Stacking and electric field effects in atomically thin layers of GaN

Atomically thin layers of nitrides are a subject of interest due to their novel applications. In this paper, we focus on GaN multilayers, investigating their stability and the effects of stacking and electric fields on their electronic properties in the framework of density functional theory. Both bilayers and trilayers prefer a planar configuration rather than a buckled bulk-like configuration. The application of an external perpendicular electric field induces distinct stacking-dependent features in the electronic properties of nitride multilayers: the band gap of a monolayer does not change whereas that of a trilayer is significantly reduced. Such a stacking-dependent tunability of the band gap in the presence of an applied field suggests that multilayer GaN is a good candidate material for next generation devices at the nanoscale.

Highly efficient "Cs8V… superatom-based spin-polarizer

Quantum transport through molecules and the possibility to manipulate spin has generated tremendous excitement. Here, we demonstrate unusual spin transport through a molecule of two Cs8V magnetic superatoms. Calculations based on density functional theory and nonequilibrium Green’s function methods find a much higher current for the spin-down charge carriers relative to the spin-up carriers in the model Au–(Cs8V)–(Cs8V)–Au device system with almost 100% spin polarization, indicating a highly efficient spin polarizer. The new behavior is rooted in strong coupling of the localized magnetic core on V and the itinerant electrons of the Cs shell atoms leading to nearly full spin polarization.

Molecular modeling of water diffusion in amorphous SiC

The diffusion of water in amorphous SiC (a-SiC) was investigated by molecular modeling methods based on density functional theory. It was assumed that the structure of a-SiC at the molecular level can be described by a model that takes into account a distribution of cage structures which consist of SiC units forming n-member rings from a suitable precursor in a chemical vapor deposition process. Electronic structure calculations are then performed to determine the energy barrier that the water molecule encounters when it penetrates through SiC rings of various sizes. It has been found that along its diffusion path through the SiC network the water molecule neither breaks up nor attaches itself to the SiC network and the energy barrier for diffusion depends mainly on the local SiC ring topology.

Mechanism of Electrical Rectification in a Unimolecular Donor-Bridge (π)-Acceptor Diode

We present here the results of theoretical calculations on the electron transport via a donor-bridge (π)-acceptor molecular system. A significant rectification effect is observed. A new transport mechanism involving the electronic structure of the molecular diode will be discussed.

Spin-dependent electron transport along a molecular wire in a metal (probe)-vacuum-molecule-metal system: the effect of the size and the shape of the probe tip

We present the results of a first-principles quantum mechanical study of spin-dependent electron transport along a molecular wire investigating the effects of the size and the shape of the probe tip on the tunneling current. A periodic, gradient-corrected density functional method together with Bardeen, Tersoff and Hamann formalism is employed in this study. The electron tunneling through a self-assembled monolayer of benzene 1,4-dithiol on the Ni(111) substrate is found to be strongly dependent on both shape and size of the probe tip.

Conformation vs voltage gating in a molecular transistor: A first-principles quantum chemical study

The electronic conduction of a novel, three-terminal molecular architecture is studied under the influence of conformational or voltage gating and also when both are simultaneously present. At the ground state configuration, the calculated tunneling current (Id) as a function of external bias (Vds) exhibits typical insulator-semiconductor behaviour. However, a significant increase, by more than an order of magnitude, and a distinct variation in the current are predicted in its operational mode (Vds>;1.5V) when additional non-planarity is induced in the triphenyl chain. The observed conformational gating affects the current via localization/delocalization of the electronic wave function in the conduction channel. As the gate-field is turned on, the transport is affected via “enhancement” or “depletion” mode of a transistor, attributed to the intrinsic dipolar molecular architecture. The current modulation is found to reach its maximum only under exclusive effect of voltage or conformational gating and diminishes when both of them are present.

Electron Transport in Boron Fullerenes

The electron transport properties of B80 fullerene is studied using first-principles density functional theory in conjunction with the Landauer-Biittiker quantum transport formalism. The electron transmission in B80 fullerene is calculated to be much higher than that in C60 fullerene in the Fermi-level region. The enhanced transmission in the B80 fullerene is attributed to its spatially extended charge distribution in delocalized bonds.

Interaction of nanomaterials with biological molecules: Manganese and dopamine

We present here the results of first principles study on the interaction of a Mn13 cluster with a dopamine molecule, an important biomolecule functioning as a neurotransmitter or a neurohormone in the living body. It is found that the dopamine strongly binds to the Mn cluster through co-ordinated covalent bond. This finding confirms the observation of dopamine depletion in the presence of Mn nanoparticles.

Spin-Polarized Electron Transport via a C 60 Molecule

We present here the results of theoretical calculations on the site-dependence of the spin-polarized electron transport in Ni-C60-Ni system. The C60molecule is a realistic candidate for molecular electronic devices, as it is thermodynamically stable and electronically active. Specifically, chemical bonding, and its contribution to transmission function of the Ni-C60-Ni system will be discussed.