ELECTRONIC PROPERTY OF NA-DOPED EPITAXIAL GRAPHENES ON SIC

The electronic property of epitaxial graphenes with Na adsorption or intercalation is studied with the use of pseudopotential density functional method. It is found that the charge transfer and the Na binding energy show strong coverage dependence. Calculated energetics shows that Na prefers the intercalation between the buffer and top graphene layers to the adsorption on top graphene layer. The buffer layer is inert to Na adsorption on top graphene layer but it is charged when Na atoms are intercalated. This indicates that the conduction of epitaxial graphenes can be affected significantly by Na intercalation.X1119sciescopu

SELF-ASSEMBLED METAL ATOM CHAINS ON GRAPHENE NANORIBBONS

Electronic and magnetic properties of alkali and alkaline-earth metal doped graphene nanoribbons (GNRs) are studied by the pseudopotential density functional method. Strong site dependence is observed in metal adsorption on GNRs, and the adsorbed metal atoms are found to spontaneously form atomic chains in a particular form of GNRs. Such doped GNRs exhibit intriguing magnetic properties such as hysteresis and spin compensation as metal atoms switch from one edge to another at alternating gate voltages. Our study shows that the metal atoms can be used as reagents that can identify the edge atomic structures of GNRs and also as gate-driven spin valves that control the spin current in GNRs.X1170sciescopu

Effects of Strain on Electronic Properties of Graphene

We present first-principles calculations of electronic properties of graphene under uniaxial and isotropic strains, respectively. The semi-metallic nature is shown to persist up to a very large uniaxial strain of 30% except a very narrow strain range where a tiny energy gap opens. As the uniaxial strain increases along a certain direction, the Fermi velocity parallel to it decreases quickly and vanishes eventually, whereas the Fermi velocity perpendicular to it increases by as much as 25%. Thus, the low energy properties with small uniaxial strains can be described by the generalized Weyl's equation while massless and massive electrons coexist with large ones. The work function is also predicted to increase substantially as both the uniaxial and isotropic strain increases. Hence, the homogeneous strain in graphene can be regarded as the effective electronic scalar potential.Comment: 4 pages, 6 figures; Published versio

Ultimately short ballistic vertical graphene Josephson junctions

Much efforts have been made for the realization of hybrid Josephson junctions incorporating various materials for the fundamental studies of exotic physical phenomena as well as the applications to superconducting quantum devices. Nonetheless, the efforts have been hindered by the diffusive nature of the conducting channels and interfaces. To overcome the obstacles, we vertically sandwiched a cleaved graphene monoatomic layer as the normal-conducting spacer between superconducting electrodes. The atomically thin single-crystalline graphene layer serves as an ultimately short conducting channel, with highly transparent interfaces with superconductors. In particular, we show the strong Josephson coupling reaching the theoretical limit, the convex-shaped temperature dependence of the Josephson critical current and the exceptionally skewed phase dependence of the Josephson current; all demonstrate the bona fide short and ballistic Josephson nature. This vertical stacking scheme for extremely thin transparent spacers would open a new pathway for exploring the exotic coherence phenomena occurring on an atomic scale.open113435sciescopu

To Be Almost Like White: The Case of Soon Ja Du

This is a case study of Korean Americans’ prejudiced attitudes toward African Americans. To discuss this attitudes, I chose to examine the case of People of the State of California v. Soon Ja Du. On the morning of March 16, 1991, Latasha Harlins, a fifteen-year-old African American high school girl was shot in the back of the head by Soon Ja Du, a fifty-one-year-old Korean liquor and grocery store owner after a fight. This fight started by Soon Ja falsely accusing Latasha of shoplifting. In many ways, Soon Ja Du’s negative attitudes represent a typical Korean American’s prejudice

Proximity-induced giant spin-orbit interaction in epitaxial graphene on topological insulator

Heterostructures of Dirac materials such as graphene and topological insulators provide interesting platforms to explore exotic quantum states of electrons in solids. Here we study the electronic structure of graphene-Sb2Te3 heterostructure using density functional theory and tight-binding methods. We show that the epitaxial graphene on Sb2Te3 turns into quantum spin-Hall phase due to its proximity to the topological insulating Sb2Te3. It is found that the epitaxial graphene develops a giant spin-orbit gap of about ~20 meV, which is about three orders of magnitude larger than that of pristine graphene. We discuss the origin of such enhancement of the spin-orbit interaction and possible outcomes of the spin-Hall phase in graphene

Antioxidant properties of guava fruit : comparison with some local fruits

Two varieties of guava fruit were analyzed for total phenol contents, ascorbic acid contents and antioxidant activities. The antioxidant activities were assessed based on the ability of the fruit extracts in 50% ethanol to scavenge DPPH, reduce Fe(III) to Fe(II) and to bind to Fe(II) ion. The results were compared to several other local fruits as well as orange. It was found that the guava fruit contains relatively high amounts of antioxidant. It also has high primary, but low secondary antioxidant potential. Storage at 4oC has the effect of increasing ascorbic acid content, and the non-peeled fruit has higher total phenol and ascorbic acid contents compared to the peeled fruit. The length and width of the seedy guava were also monitored over a period of 17 weeks to define specific stages of fruit ripening