Ferromagnetism of Single-Crystalline Cu₂O Induced through Poly(N-vinyl-2-pyrrolidone) Interaction Triggering d-Orbital Alteration

Abstract

Ferromagnetic-like properties of cuprous oxide (Cu 2 O) are induced through its interaction with chemisorbed surfactant poly(N-vinyl-2-pyrrolidone) (PVP), which alters the intrinsic d 10 configuration of Cu ions. Structural and magnetism-related properties of intact Cu 2 O crystals (i-Cu 2 O) and those capped with PVP (c-Cu 2 O) were examined using various analytical instruments. SEM, TEM (corresponding selected area electron diffraction (SAED)), and XRD of i-Cu 2 O and c-Cu 2 O showed cubic and hexagonal shapes of single crystallinity with facets of {200} and {111}, respectively, resulting from the differential growth rates of the original identical crystals along the facets over time. Bulk magnetic susceptibility (χ) of i-Cu 2 O and c-Cu 2 O at room temperature in field-dependent magnetization and the difference in their magnetic moment in temperature-dependent magnetization showed diamagnetic and ferromagnetic properties, respectively. The difference in the fluorescence mode of X-ray absorption near edge structure (XANES) spectra between i-Cu 2 O and c-Cu 2 O, showing no quadruple pre-edge peak for the transition 1s → 3d in Cu(II) ions with d 9 electronic configuration, indicates an orbital alteration on the surface of cCu 2 O caused by an interaction with PVP. Two peaks for c-Cu 2 O at higher binding energies in O 1s X-ray photoelectron spectroscopy may be indicative of the ligand-to-metal charge transfer (LMCT) from O atoms of PVP to Cu ions of Cu 2 O, generating a chemical interaction through coordination bonding. Large hyperfine splitting constants in electron paramagnetic resonance (EPR) spectra of c-Cu 2 O support this interpretation, with septet hyperfine splitting suggestive of Cu−Cu interactions on the surface of c-Cu 2 O via the interaction with O atoms of PVP. These results demonstrate that PVP capping of Cu 2 O crystal (c-Cu 2 O) induces ferromagnetism of Cu(I) ions through coordination with O atoms of chemically adsorbed PVP. This may induce LMCT and Cu−Cu interactions that lead to changes in electronic configurations, deriving the ferromagnetic moments of c-Cu 2 O.

Reducing the Singlet−Triplet Energy Gap by End‐Group π−π Stacking Toward High‐Efficiency Organic Photovoltaics

“…[ 47 ] Note that the energy splitting for singlet and triplet excitons are dominated by Coulombic and exchange terms, respectively, [ 48 ] we envisage that the Δ E ST can be reduced without sacrificing f in dimers or aggregates. [ 49,50 ] As seen in Figure , for the V‐type and J‐type dimers formed by π−π stacking between the end‐groups, the triplet energy splitting is negligible due to the small intermolecular overlap; however, the singlet energy splitting can be very significant, and the lower‐energy state or both splitting states are dipole‐allowed. Consequently, the Δ E ST can be substantially reduced.…”

Cu x O self-assembled mesoporous microspheres with effective surface oxygen vacancy and their room temperature NO2 gas sensing performance

“…3b. As reported, Cu + ions are diamagnetic (3d 10 ) and therefore EPR silent [23]. Cu 2+ ions, on the contrary, have an electron configuration of d 9 and are paramagnetic over a wide range of temperatures [24].…”

“…After NO 2 gas is removed, the resistance returns to the original value due to the re-adsorption of oxygen. The enhanced sensing performance of the virus-like Cu x O SMMs is partly attributed to the heterojunctions formed between Cu 2 O and CuO [23][24][25][26]. Third, the percentage of oxygen vacancy of the virus-like Cu x O SMMs is higher than that of the other Cu x O SMMs.…”

Effects of Cu–Zn phases on electronic properties in ZnO:Cu films

“…Therefore, Cu 2+ were doped into the ZnO films. In addition, another distinct signal appeared at g~2.26 in sample 1125, which corresponds to a Cu 2 O phase . In sample 1150, there was a distinct signal at g~2.46, which corresponds to Cu located at interstitial sites (Cu–Zn phases) .…”