Shela Aboud

Mercury adsorption on PdAu, PdAg and PdCu alloys

Under specific conditions, sorbent materials such as activated carbon, metal oxides, metal sulfides and pure metals can effectively capture mercury (Hg). Among these materials activated carbon is one of the most widely-used sorbents because of its high removal capacity. Unfortunately, activated carbon can hinder the recycling of particulate matter for concrete manufacturing because it prevents concrete from meeting the freeze-thaw requirements. The use of a sorbent material that can capture Hg efficiently but is also concrete-friendly would allow for the increased sale of waste materials, ultimately oversetting landfill costs. In this work, density functional theory calculations have been used to predict the binding mechanism of Hg on the binary alloys PdAu(111), PdAg(111), PdCu(111) which are potential candidates for concrete-friendly sorbents. Although bulk Pd surfaces are more reactive than bare Au, Ag and Cu surfaces, the addition of small amounts of Au, Ag and Cu alloyed with the Pd acts to increase ...

Investigation of Adsorption Behavior of Mercury on Au(111) from First Principles

The structural and electronic properties of Hg, SO(2), HgS, and HgO adsorption on Au(111) surfaces have been determined using density functional theory with the generalized gradient approximation. The adsorption strength of Hg on Au(111) increases by a factor of 1.3 (from -9.7 to -12.6 kcal/mol) when the number of surface vacancies increases from 0 to 3; however, the adsorption energy decreases with more than three vacancies. In the case of SO(2) adsorption on Au(111), the Au surface atoms are better able to stabilize the SO(2) molecule when they are highly undercoordinated. The SO(2) adsorption stability is enhanced from -0.8 to -9.3 kcal/mol by increasing the number of vacancies from 0 to 14, with the lowest adsorption energy of -10.2 kcal/mol at 8 Au vacancies. Atomic sulfur and oxygen precovered-Au(111) surfaces lower the Hg stability when Hg adsorbs on the top of S and O atoms. However, a cooperative effect between adjacent Hg atoms is observed as the number of S and Hg atoms increases on the perfect Au(111) surface, resulting in an increase in the magnitude of Hg adsorption. Details of the electronic structure properties of the Hg-Au systems are also discussed.

Pseudopotential-based studies of electron transport in graphene and graphene nanoribbons

The theoretical understanding of electron transport in graphene and graphene nanoribbons is reviewed, emphasizing the help provided by atomic pseudopotentials (self-consistent and empirical) in determining not only the band structure but also other fundamental transport parameters such as electron-phonon matrix elements and line-edge roughness scattering. Electron-phonon scattering in suspended graphene sheets, impurity and remote-phonon scattering in supported and gated graphene, electron-phonon and line-edge roughness scattering in armchair-edge nanoribbons are reviewed, keeping in mind the potential use of graphene in devices of the future very large scale integration technology.

Electronic and transport properties of armchair and zigzag sp 3 -hybridized silicane nanoribbons

The electronic and transport properties of sp3-hybridized armchair and zigzag edge silicane nanoribbons have been investigated using nonlocal empirical pseudopotentials and ab-initio calculations. Compared to the armchair graphene nanoribbons, silicane ribbons do no suffer from the chirality dependence of the band gap. Calculated low-field electron mobility and ballistic conductance show a strong edge dependence due to a difference in the effective masses and momentum relaxation rates along the transport direction. Smaller effective masses and momentum relaxation rates in the zigzag edge ribbons results in the electron mobility as much as an order of magnitude larger than the armchair edge ribbons.

Reduction of the normal-superfluid transition temperature in gated bilayer graphene

We show that the normal-superfluid transition in bilayer graphene (BLG) predicted to occur at high temperature is strongly affected not only by the dielectric constants of the insulators, but also by the proximity of ideal metal gates. Even assuming optimistically an unscreened interlayer Coulomb interaction, we find that for a gate-insulator thickness smaller than 2-to-5 nm of equivalent SiO2 thickness, the transition temperature is depressed to the 1 K-1 mK range. Thus, thicker and low-κ gate insulators are required to design transistors exploiting the properties of the superfluid state.

Scaling FETs to (beyond?) 10 nm: From semiclassical to quantum models

We present full-band semi-classical and quantum-mechanical transport models required to study electronic transport in nanometer-scale devices.