Sumeet C. Pandey

QDB: a new database of plasma chemistries and reactions

One of the most challenging and recurring problems when modeling plasmas is the lack of data on the key atomic and molecular reactions that drive plasma processes. Even when there are data for some reactions, complete and validated datasets of chemistries are rarely available. This hinders research on plasma processes and curbs development of industrial applications. The QDB project aims to address this problem by providing a platform for provision, exchange, and validation of chemistry datasets. A new data model developed for QDB is presented. QDB collates published data on both electron scattering and heavy-particle reactions. These data are formed into reaction sets, which are then validated against experimental data where possible. This process produces both complete chemistry sets and identifies key reactions that are currently unreported in the literature. Gaps in the datasets can be filled using established theoretical methods. Initial validated chemistry sets for SF 6 /CF 4 /O 2 and SF 6 /CF 4 /N 2 /H 2 are presented as examples.

Cu impurity in insulators and in metal-insulator-metal structures: Implications for resistance-switching random access memories

We present numerical results from atomistic simulations of Cu in SiO2 and Al2O3, with an emphasis on the thermodynamic, kinetic, and electronic properties. The calculated properties of Cu impurity at various concentrations (9.91 × 1020 cm−3 and 3.41 × 1022 cm−3) in bulk oxides are presented. The metal-insulator interfaces result in up to a ∼4 eV reduction in the formation energies relative to the crystalline bulk. Additionally, the importance of Cu-Cu interaction in lowering the chemical potential is introduced. These concepts are then discussed in the context of formation and stability of localized conductive paths in resistance-switching Random Access Memories (RRAM-M). The electronic density of states and non-equilibrium transmission through these localized paths are studied, confirming conduction by showing three orders of magnitude increase in the electron transmission. The dynamic behavior of the conductive paths is investigated with atomistic drift-diffusion calculations. Finally, the paper conclud...

The electrical resistivity of rough thin films: A model based on electron reflection at discrete step edges

The effect of the surface roughness on the electrical resistivity of metallic thin films is described by electron reflection at discrete step edges. A Landauer formalism for incoherent scattering leads to a parameter-free expression for the resistivity contribution from surface mound-valley undulations that is additive to the resistivity associated with bulk and surface scattering. In the classical limit where the electron reflection probability matches the ratio of the step height h divided by the film thickness d, the additional resistivity Δρ =  3/2/(g0d) × ω/ξ, where g0 is the specific ballistic conductance and ω/ξ is the ratio of the root-mean-square surface roughness divided by the lateral correlation length of the surface morphology. First-principles non-equilibrium Greens function density functional theory transport simulations on 1-nm-thick Cu(001) layers validate the model, confirming that the electron reflection probability is equal to h/d and that the incoherent formalism matches the coherent...

Theoretical Study of Magnetic Damping and Anisotropy of Fe/Pd (001) Superlattice

The material properties, magnetic damping and anisotropy, which are critical to spin-transfer-torque magnetic random access memory device performance, are theoretically explored for Fe/Pd superlattices deposited in the (001) orientation. Various superlattice geometries at different Fe and Pd layer thicknesses show perpendicular anisotropy. With the inclusion of the shape anisotropy, thin-film structures with an effective anisotropy of 1.4 × 107 erg/cm3 have been observed. The damping is enhanced due to the broken symmetry at the Pd interface. This interfacial contribution increases when more Pd monolayers are deposited in the superlattice. The superlattice damping is relatively smaller than damping (α) in the L10 phase FePd. The optimized superlattices are 3Fe/3Pd or 3Fe/2Pd: these multilayers have sufficient energy barriers (~1 eV) to maintain thermal stability in very small devices, yet the switching currents are low (<;5 × 106 A/cm2) and, thus, expected to lower the energy consumption.