II. The growth of gold films on rocksalt in high vacuum-growth model

Evidence of a ZnCr2Se4 Spinel Inclusion at the Core of a Cr-Doped ZnSe Quantum Dot

“…In fact, of the AB 2 X 4 structures that are known for Cr(III) ion incorporation into II−VI semiconductor, Cr(III) shows the greatest thermodynamic potential for occupation of O h sites. 27 Further stabilization of the center is achieved by the favorable ionic radius of Cr(III) (0.755 Å) which can fit into O h site formed by Zn ion vacancy, whereas Cr(II) has a much larger radius of 0.94 Å. While it might be anticipated that the formation of Cr(III) is surprising, due to better charge balance for Cr(II), observation of a change in oxidation state for a doped metal ion is observed reflecting the formation of a thermodynamically more stable oxidation for Cu(I):CdSe and Eu(III):CdSe QDs.…”

“…The incorporation of Cr(III) ions as a pair into the ZnSe lattice forms the initial cell of a spinel phase of the form ACr 2 X 4 (A = Cd, Zn; X = S, Se). 27 Such a structure is supported by the only available spinel phase diagram (CdCr 2 Se 4 ) where a solid solution is formed for Cd to Cr ratios below 64%. In this range it is observed that a peritectoid reaction leads to the CdCr 2 Se 4 spinel precipitating out of the metal chalcogenide crystal below 885 °C due to low solubility in the phase.…”

“…The d 3 configuration has a lowest-lying half-filled t 2g orbital, inducing greater thermodynamic stability for the Cr(III) center. In fact, of the AB 2 X 4 structures that are known for Cr(III) ion incorporation into II–VI semiconductor, Cr(III) shows the greatest thermodynamic potential for occupation of O h sites . Further stabilization of the center is achieved by the favorable ionic radius of Cr(III) (0.755 Å) which can fit into O h site formed by Zn ion vacancy, whereas Cr(II) has a much larger radius of 0.94 Å.…”

“…Of the three oxidation states, the Cr(III) oxidation state is preferred due to its one-half-filled t 2g level and has been shown to be naturally introduced into octahedral (O h ) sites formed by ion vacancies that charge compensate the lattice in the otherwise tetrahedral coordination environment observed in II−VI semiconductors (ZnS, ZnSe, CdS, CdSe). 27 Synthesis of the Cr(III)-doped II−VI semiconductor occurs via a peritectoid decomposition reaction leading to formation of a AB 2 X 4 spinel structure by the group II metal occupying the tetrahedral (T d ) site (A site) and the Cr(III) ion occupying the O h site (B site). 28 The spinel phase is a singularity in the phase diagram and does form as a precipitated inclusion due to its low solubility in the II−VI lattice over a wide range of Cr to metal ion ratios.…”

“…In Cr-doped II–VI semiconductors, the incorporation of Cr(I), , Cr(II), , and Cr(III) , have been reported by solid-state synthesis. Of the three oxidation states, the Cr(III) oxidation state is preferred due to its one-half-filled t 2g level and has been shown to be naturally introduced into octahedral ( O h ) sites formed by ion vacancies that charge compensate the lattice in the otherwise tetrahedral coordination environment observed in II–VI semiconductors (ZnS, ZnSe, CdS, CdSe) . Synthesis of the Cr(III)-doped II–VI semiconductor occurs via a peritectoid decomposition reaction leading to formation of a AB 2 X 4 spinel structure by the group II metal occupying the tetrahedral ( T d ) site (A site) and the Cr(III) ion occupying the O h site (B site) .…”