Wai-Ning Mei

Sub-10 nm Gate Length Graphene Transistors: Operating at Terahertz Frequencies with Current Saturation

Radio-frequency application of graphene transistors is attracting much recent attention due to the high carrier mobility of graphene. The measured intrinsic cut-off frequency (fT) of graphene transistor generally increases with the reduced gate length (Lgate) till Lgate = 40 nm, and the maximum measured fT has reached 300 GHz. Using ab initio quantum transport simulation, we reveal for the first time that fT of a graphene transistor still increases with the reduced Lgate when Lgate scales down to a few nm and reaches astonishing a few tens of THz. We observe a clear drain current saturation when a band gap is opened in graphene, with the maximum intrinsic voltage gain increased by a factor of 20. Our simulation strongly suggests it is possible to design a graphene transistor with an extraordinary high fT and drain current saturation by continuously shortening Lgate and opening a band gap.

Interfacial Properties of Bilayer and Trilayer Graphene on Metal Substrates

One popular approach to prepare graphene is to grow them on transition metal substrates via chemical vapor deposition. By using the density functional theory with dispersion correction, we systematically investigate for the first time the interfacial properties of bilayer (BLG) and trilayer graphene (TLG) on metal substrates. Three categories of interfacial structures are revealed. The adsorption of B(T)LG on Al, Ag, Cu, Au, and Pt substrates is a weak physisorption, but a band gap can be opened. The adsorption of B(T)LG on Ti, Ni, and Co substrates is a strong chemisorption, and a stacking-insensitive band gap is opened for the two uncontacted layers of TLG. The adsorption of B(T)LG on Pd substrate is a weaker chemisorption, with a band gap opened for the uncontacted layers. This fundamental study also helps for B(T)LG device study due to inevitable graphene/metal contact.

Resonant Photoemission Observations and DFT Study of s–d Hybridization in Catalytically Active Gold Clusters on Ceria Nanorods

Gold clusters have garnered intense interest because of their unusual catalytic activities towards chemical reactions of industrial importance. Electronic structures of oxide supported gold clusters can provide critical clues to the mechanisms for their catalytic activity. Gold atoms possess an electronic configuration of [Xe] 4f145d106s1. However, both relativistic effects and 5d band upshift of gold clusters result in a theoretically expected hybridization of the 5d and 6s orbitals. These s-d hybridized orbitals are expected to, essentially, increase the number of free d states (or d holes) available for bonding with incoming reactant molecules, thus lowering the transition state energy and promoting the reactions.

The surface states of lithium tetraborate

The different low index surface terminations of lithium tetraborate, Li(2)B(4)O(7), are dominated by electronic states that fall within the band gap of the projection of the bulk states. As a pyroelectric material, lithium tetraborate, Li(2)B(4)O(7), is a wide band gap dielectric, yet the (110) surface has a much smaller band gap because of occupied surface states that fall at binding energies between the valence band maximum and the Fermi level. The (100) surface is dominated, however, by unoccupied surface states that also fall in the gap between the conduction band minimum and the valence band maximum, but at binding energies just below the conduction band minimum. These very different types of surface states are consistent with the assignment of occupied surface states to states that are observed near the Fermi level in photoemission studies of Li(2)B(4)O(7)(110). The unoccupied surface states are also seen to be consistent with the inverse photoemission spectra of Li(2)B(4)O(7)(100). Clearly, the different surface terminations of lithium tetraborate yield very different types of surface electronic states.

SEARCHING FOR ELECTRICAL PROPERTIES, PHENOMENA AND MECHANISMS IN THE CONSTRUCTION AND FUNCTION OF CHROMOSOMES

Our studies reveal previously unidentified electrical properties of chromosomes: (1) chromosomes are amazingly similar in construction and function to electrical transformers; (2) chromosomes possess in their construction and function, components similar to those of electric generators, conductors, condensers, switches, and other components of electrical circuits; (3) chromosomes demonstrate in nano-scale level electromagnetic interactions, resonance, fusion and other phenomena similar to those described by equations in classical physics. These electrical properties and phenomena provide a possible explanation for unclear and poorly understood mechanisms in clinical genetics including: (a) electrically based mechanisms responsible for breaks, translocations, fusions, and other chromosomal abnormalities associated with cancer, intellectual disability, infertility, pregnancy loss, Down syndrome, and other genetic disorders; (b) electrically based mechanisms involved in crossing over, non-disjunction and other events during meiosis and mitosis; (c) mechanisms demonstrating heterochromatin to be electrically active and genetically important.