Single magnetic 3dN adatoms on surfaces – Proper outlook on compatibility of orthorhombic zero-field splitting parameters and their relationships with magnetic anisotropy quantities

Tuning Properties of Partially Reduced Graphene Oxide Fibers upon Calcium Doping

The arrangement of two-dimensional graphene oxide sheets has been shown to influence physico-chemical properties of the final bulk structures. In particular, various graphene oxide microfibers remain of high interest in electronic applications due to their wire-like thin shapes and the ease of hydrothermal fabrication. In this research, we induced the internal ordering of graphene oxide flakes during typical hydrothermal fabrication via doping with Calcium ions (~6 wt.%) from the capillaries. The Ca2+ ions allowed for better graphene oxide flake connections formation during the hydrogelation and further modified the magnetic and electric properties of structures compared to previously studied aerogels. Moreover, we observed the unique pseudo-porous fiber structure and flakes connections perpendicular to the long fiber axis. Pulsed electron paramagnetic resonance (EPR) and conductivity measurements confirmed the denser flake ordering compared to previously studied aerogels. These studies ultimately suggest that doping graphene oxide with Ca2+ (or other) ions during hydrothermal methods could be used to better control the internal architecture and thus tune the properties of the formed structures.

Unraveling Origins of EPR Spectrum in Graphene Oxide Quantum Dots

Carbon nanostructures are utilized in a plethora of applications ranging from biomedicine to electronics. Particularly interesting are carbon nanostructured quantum dots that can be simultaneously used for bimodal therapies with both targeting and imaging capabilities. Here, magnetic and optical properties of graphene oxide quantum dots (GOQDs) prepared by the top-down technique from graphene oxide and obtained using the Hummers' method were studied. Graphene oxide was ultra-sonicated, boiled in HNO3, ultra-centrifuged, and finally filtrated, reaching a mean flake size of ~30 nm with quantum dot properties. Flake size distributions were obtained from scanning electron microscopy (SEM) images after consecutive preparation steps. Energy-dispersive X-ray (EDX) confirmed that GOQDs were still oxidized after the fabrication procedure. Magnetic and photoluminescence measurements performed on the obtained GOQDs revealed their paramagnetic behavior and broad range optical photoluminescence around 500 nm, with magnetic moments of 2.41 µB. Finally, electron paramagnetic resonance (EPR) was used to separate the unforeseen contributions and typically not taken into account metal contaminations, and radicals from carbon defects. This study contributes to a better understanding of magnetic properties of carbon nanostructures, which could in the future be used for the design of multimodal imaging agents.

Importance of the fourth-rank zero field splitting parameters for Fe2+ (S = 2) adatoms on the CuN/Cu(100) surface evidenced by their determination based on DFT and experimental data

Equations allow to determine 2nd- and 4th-rank ZFSPs (B_k^q) based on spin energy levels (λi) at B = 0. This method is applied to Fe²⁺ (S = 2) adatoms on CuN/Cu(100) surface using DFT and experimental data. Relative importance of ZFSPs is analyzed.