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A thorough understanding of native oxides is essential for designing semiconductor devices. Here, we report a study of the rate and mechanisms of spontaneous oxidation of bulk single crystals of ZrSxSe2–xalloys and MoS2. ZrSxSe2–xalloys oxidize rapidly, and the oxidation rate increases with Se content. Oxidation of basal surfaces is initiated by favorable O2adsorption and proceeds by a mechanism of Zr–O bond switching, that collapses the van der Waals gaps, and is facilitated by progressive redox transitions of the chalcogen. The rate-limiting process is the formation and out-diffusion of SO2. In contrast, MoS2basal surfaces are stable due to unfavorable oxygen adsorption. Our results provide insight and quantitative guidance for designing and processing semiconductor devices based on ZrSxSe2–xand MoS2and identify the atomistic-scale mechanisms of bonding and phase transformations in layered materials with competing anions.

Ab initiomolecular dynamics simulations of shock loading on poly(p-phenylene terephthalamide) (PPTA) reveal stress release mechanisms based on hydrogen bond preserving structural phase transformation (SPT) and planar amorphization. The SPT is triggered by [100] shock-induced coplanarity of phenylene groups and rearrangement of sheet stacking leading to a novel monoclinic phase. Planar amorphization is generated by [010] shock-induced scission of hydrogen bonds leading to disruption of polymer sheets, and trans-to-cisconformational change of polymer chains. In contrast to the latter, the former mechanism preserves the hydrogen bonding and cohesiveness of polymer chains in the identified novel crystalline phase preserving the strength of PPTA. The interplay between hydrogen bond preserving (SPT) and nonpreserving (planar amorphization) shock release mechanisms is critical to understanding the shock performance of aramid fibers.

Detonation processes probed with atomistic details have remained elusive due to highly complex reactions in heterogeneous shock structures. Here, we provide atomistic details of the initial reaction pathways during shock-induced decomposition of 2,4,6-triamino-1,3,5-trinitrobenzene (TATB) crystal using large reactive molecular dynamics simulations based on reactive force fields. Simulation results reveal the existence of three competing intermolecular pathways for the formation of N2. We also observe the formation of large nitrogen- and oxygen-rich carbon aggregates, which delays the release of final reaction products.