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Single-walled carbon nanotubes (SWCNTs) containing sp3 defects are a promising class of optoelectronic materials with bright photoluminescence and demonstrated single-photon emission. Using density functional theory simulations, complemented by measurements, we investigate the electronic structure of a series of quantum defects attached to (6,5) SWCNT with the goal of tuning the spin–orbit coupling by introduction of a heavy atom in the defect structure. We characterize the ground state electronic and spin properties of four synthesized and three potential defects on the tube and find that all of the synthesized defects considered introduce a localized midgap defect-centered state containing a single electron, ≈0.2–0.3 eV above the valence band. The spin density is located at the sp3 defect site with negligible spin–orbit coupling even with the presence of a Pd atom. Three additional functional groups were tested via computation to increase spin localization near the metal, thereby increasing spin–orbit coupling. We predict that only the chlorodiphosphanepalladium(II)– [Cl(PH3)2Pd(II)–] defect results in increased spin–orbit splitting of the defect state and the conduction band associated with the pristine-like SWCNT, a measure of the spin–orbit coupling of excited state transitions. This study suggests that for unpassivated sp3 defects in (6,5) SWCNT, forming a direct bond between a heavy atom and the sp3 carbon allows for tuning of spin–orbit coupling.

Functional safety, as addressed in the standard IEC 61508, is a key requirement for a high dependability of controlled systems. In order to guarantee that the function of programmable logic controllers (PLC) complies with given safety specifications, the use of verification has proven to be useful. This contribution builds upon a recently proposed approach to verify PLC programs with time specifications. It starts from a controller design given as sequential function chart (SFC), transforms the SFC into timed automata (TA), and applies model checking to verify (or falsify) functional safety. Since the explicit representation of the cyclic operation mode of PLC can lead to complex TA models, this paper investigates to which extent the cyclic mode can be omitted, to obtain simplified models for which the verification effort is considerably smaller.