Shimin Hou

First-principles calculation of the conductance of a single 4,4 bipyridine molecule.

The conductance of a single 4,4 bipyridine (44BPD) molecule connected to two gold electrodes is calculated using a density functional theory based Green function method. The atomic geometry of such a molecular junction is constructed from the optimized structure of a gold trimer-44BPD-gold trimer complex. Resonant conduction is the main feature of its transport properties. The magnitude of the transmission coefficient at the Fermi level is determined to be T = 1.01 × 10(-2), which is in excellent agreement with the experimental value. The dependence of the transmission on the Au-N bond length and the torsion angle is also discussed.

Solution-processable, low-voltage, and high-performance monolayer field-effect transistors with aqueous stability and high sensitivity.

Low-voltage, low-cost, high-performance monolayer field-effect transistors are demonstrated, which comprise a densely packed, long-range ordered monolayer spin-coated from core-cladding liquid-crystalline pentathiophenes and a solution-processed high-k HfO2 -based nanoscale gate dielectric. These monolayer field-effect transistors are light-sensitive and are able to function as reporters to convert analyte binding events into electrical signals with ultrahigh sensitivity (≈10 ppb).

An efficient nonequilibrium Green’s function formalism combined with density functional theory approach for calculating electron transport properties of molecular devices with quasi-one-dimensional electrodes

An efficient self-consistent approach combining the nonequilibrium Greens function formalism with density functional theory is developed to calculate electron transport properties of molecular devices with quasi-one-dimensional (1D) electrodes. Two problems associated with the low dimensionality of the 1D electrodes, i.e., the nonequilibrium state and the uncertain boundary conditions for the electrostatic potential, are circumvented by introducing the reflectionless boundary conditions at the electrode-contact interfaces and the zero electric field boundary conditions at the electrode-molecule interfaces. Three prototypical systems, respectively, an ideal ballistic conductor, a high resistance tunnel junction, and a molecular device, are investigated to illustrate the accuracy and efficiency of our approach.

Analysis on the contribution of molecular orbitals to the conductance of molecular electronic devices

We present a theoretical approach which allows one to extract the orbital contribution to the conductance of molecular electronic devices. This is achieved by calculating the scattering wave functions after the Hamiltonian matrix of the extended molecule is obtained from a self-consistent calculation that combines the nonequilibrium Greens function formalism with density functional theory employing a finite basis of local atomic orbitals. As an example, the contribution of molecular orbitals to the conductance of a model system consisting of a 4,4-bipyridine molecule connected to two semi-infinite gold monatomic chains is explored, illustrating the capability of our approach.

An accurate and efficient self-consistent approach for calculating electron transport through molecular electronic devices: including the corrections of electrodes

A self-consistent ab initio approach for calculating electron transport through molecular electronic devices is developed. It is based on density functional theory (DFT) calculations and the Greens function technique employing a finite basis of local orbitals. The device is rigorously separated into the extended molecule region and the electrode region. In the DFT part calculating the Hamiltonian matrix of the extended molecule from its density matrix, the electrostatic correction induced by electrodes and the exchange?correlation correction due to the spatial diffuseness of localized basis functions are included. Our approach is efficient and accurate, with a controllable error to deal with such open systems. A one-dimensional infinite gold monatomic chain, whose electronic structure can be known from conventional DFT calculations with periodic boundary conditions (PBCs), is employed to validate the accuracy of our approach. With both corrections, our result for the gold chain at equilibrium is in excellent agreement with the PBC DFT result. We find that, for the gold chain, the exchange?correlation correction is more significant than the electrostatic correction.

Solution‐Crystallized Organic Semiconductors with High Carrier Mobility and Air Stability

Molecular engineering and chemical self-assembly are combined with materials fabrication to achieve air-stable solution-processable oligothiophene-based field-effect transistors with mobilities up to 6.2 cm(2) V-1 s(-1), which ranks as the highest among oliogthiophene- based semiconducting materials.

The spin filter effect of iron-cyclopentadienyl multidecker clusters: the role of the electrode band structure and the coupling strength

We present a theoretical study of spin transport in a series of organometallic iron-cyclopentadienyl, Fe(n)Cp(n+1), multidecker clusters sandwiched between either gold or platinum electrodes. Ab initio modeling is performed by combining the non-equilibrium Greens function formalism with spin density functional theory. Due to the intrinsic bonding nature, the low-bias conductance of the Fe(n)Cp(n+1) clusters contacted to gold electrodes is relatively small even for strong cluster-electrode coupling. However, a nearly 100% spin polarization of the transmitted electrons can be achieved for the Fe(n)Cp(n+1) (n>2) clusters. In contrast, the Fe(n)Cp(n+1) (n>2) clusters attached to platinum electrodes through Pt adatoms not only can act as nearly perfect spin filters but also show a much larger transmission around the Fermi level, demonstrating their promising applications in future molecular spintronics.

Fractal structure in the silver oxide thin film

Abstract The first two steps of the preparation of Ag–O–Cs photocathodes are the deposition of silver films and their oxidation with the glow discharge method. The fractal structure and texture structure in the silver oxide thin film have been characterized by transmission electron microscopy (TEM). The Hausdorf dimension D of the fractal structure is calculated to be 1.80±0.01. The formation mechanism of the fractal structure is also discussed.

Tuning the Magneto-Transport Properties of Nickel−Cyclopentadienyl Multidecker Clusters by Molecule−Electrode Coupling Manipulation

Spin transport in a series of organometallic multidecker clusters made of alternating nickel atoms and cyclopentadienyl (Cp) rings is investigated by using first-principles quantum transport simulations. The magnetic moment of finite NinCp(n+1) clusters in the gas phase is a periodic function of the number of NiCp monomers, n, regardless of the cluster termination and despite the fact that the band structure of the infinite [NiCp]infinity chain is nonmagnetic. In contrast, when the clusters are sandwiched between gold electrodes, their spin polarization is found to strongly depend on the molecule-electrode coupling. On the one hand, a substantial magnetic moment and a large spin polarization can be detected for NiCp2 and Ni4Cp5 with both weak and modest molecule-electrode coupling. On the other hand, when the coupling of the clusters is strong and mediated by Ni adatoms, the spin polarization of all NinCp(n+1) (n = 1-4) clusters is destroyed, although their low-bias conductance is large. This demonstrates that the magnetism and the spin-transport properties of fragile molecular magnets, such as NinCp(n+1), can be tuned in a controllable way by changing the contact geometry.

First-principles calculation on the conductance of a single 1,4-diisocyanatobenzene molecule with single-walled carbon nanotubes as the electrodes

The conductance of a single 1,4-diisocyanatobenzene molecule sandwiched between two single-walled carbon nanotube (SWCNT) electrodes are studied using a fully self-consistent ab initio approach which combines nonequilibrium Greens function formalism with density functional theory calculations. Several metallic zigzag and armchair SWCNTs with different diameters are used as electrodes; dangling bonds at their open ends are terminated with hydrogen atoms. Within the energy range of a few eV of the Fermi energy, all the SWCNT electrodes couple strongly only with the frontier molecular orbitals that are related to nonlocal pi bonds. Although the chirality of SWCNT electrodes has significant influences on this coupling and thus the molecular conductance, the diameter of electrodes, the distance, and the torsion angle between electrodes have only minor influences on the conductance, showing the advantage of using SWCNTs as the electrodes for molecular electronic devices.