Electronic Structures and Spectroscopic Signatures of Noble-Gas-Doped Nanodiamonds.

Fluorescent nanodiamonds, that is, those containing optically active defects, have attracted interest for their ability to be used as qubits; for in vivo imaging; and as sensors for spin, stress, and temperature. One of the most commonly studied nanodiamond color centers is the nitrogen vacancy. However, there is strong interest in discovering other impurity centers that provide localized midband gap transitions. Noble gas atoms have garnered attention since they have been discovered within nanodiamonds produced through high-pressure-high-temperature laser-heated diamond anvil cell synthesis methods, where they are commonly used as hydrostatic pressure media. Noble gas atoms that exist in macrosized natural or synthetic diamonds have been shown to be able to form color centers. This research uses ab initio density functional theory and cluster models to systematically study the localized electronic structure for group VIII impurities of nanodiamond, including helium, neon, argon, krypton, and xenon. An in-depth examination of the interaction between the noble gas atom and diamond lattice has been carried out. The changes to the vibrational and UV/vis absorption spectra have been analyzed. It was determined that the energetically preferred geometry is dependent on the atom size. Most noble gas defects are stabilized within the nanodiamond lattice and exist in tetrahedral interstitial positions, except for the largest noble gas studied in this work, Xe, which was determined to prefer a substitutional configuration. Both Kr and Xe are expected to be able to manifest visible/near-IR optical responses when included in the diamond lattice.

Kinetically Corrected Monte Carlo-Molecular Dynamics Simulations of Solid Electrolyte Interphase Growth.

We present a kinetic approach to the Monte Carlo-molecular dynamics (MC-MD) method for simulating reactive liquids using nonreactive force fields. A graphical reaction representation allows definition of reactions of arbitrary complexity, including their local solvation environment. Reaction probabilities and molecular dynamics (MD) simulation times are derived from ab initio calculations. Detailed validation is followed by studying the development of the solid electrolyte interphase (SEI) in lithium-ion batteries. We reproduce the experimentally observed two-layered structure on graphite, with an inorganic layer close to the anode and an outer organic layer. This structure develops via a near-shore aggregation mechanism.