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Nanoelectronic devices integrated with functional complex oxides have drawn much attention in recent years. However, due to material and processing compatibility issues, integrating functional complex oxides with Si-based devices is challenging, and success has been limited. As an example, the Bi3Fe2Mn2Ox(BFMO) supercell system, a single-phase layered oxide made by compositing BiFeO3and BiMnO3, has been studied for much of the past decade for its unusual layered Aurivillius structure and magnetic and ferroelectric properties. However, most of the BFMO thin film growth has been demonstrated on single-crystal oxide substrates such as SrTiO3and LaAlO3. In this work, we demonstrate that the BFMO layered supercell phase can be integrated on Si with high epitaxial quality using a buffer stack of TiN/SrTiO3/CeO2. Further understanding of the strain-controlled growth of the BFMO supercell phase has allowed such Si integration. Microstructure, magnetic, ferroelectric, and optical properties of the BFMO films on Si have been characterized and compared with those of BFMO on SrTiO3single-crystal substrates, demonstrating comparable epitaxial quality and physical properties. Integrating multiferroic BFMO oxides on Si demonstrates the potential of layered supercell oxides in practical device applications such as ferroelectric field effect transistors.

VO2has shown great promise for sensors, smart windows, and energy storage devices, because of its drastic semiconductor-to-metal transition (SMT) near 340 K coupled with a structural transition. To push its application toward room-temperature, effective transition temperature (Tc) tuning in VO2is desired. In this study, tailorable SMT characteristics in VO2films have been achieved by the electrochemical intercalation of foreign ions (e.g., Li ions). By controlling the relative potential with respect to Li/Li+during the intercalation process, Tcof VO2can be effectively and systematically tuned in the window from 326.7 to 340.8 K. The effective Tctuning could be attributed to the observed strain and lattice distortion and the change of the charge carrier density in VO2introduced by the intercalation process. This demonstration opens up a new approach in tuning the VO2phase transition toward room-temperature device applications and enables future real-time phase change property tuning.

Pancake bonding between partially oxidized tetramethyltetrathiafulvalene (TMTTF) moieties was examined via X-ray structural, spectral, and magnetic susceptibility measurements of the salts comprising mono- and dicationic trimers, together with the computational analysis of their trimeric and dimeric associations. The salt with hexabromocarborane anions contained isolated dicationic (TMTTF)32+trimers, in which charge was residing mainly on the side moieties (rotated by 26° relative to the central TMTTF). Magnetic measurements revealed singlet ground states of these trimers with the antiferromagnetic coupling of 2J= −630 cm–1. The salt with dodecamethylcarborane comprised TMTTF stacks consisting of distinct monocationic (TMTTF)3+•trimers with monomers shifted relative to each other along their main axes. The central TMTTF moiety in these trimers carried the largest fraction of charge, and intertrimer (TMTTF)3+•antiferromagnetic coupling was 2J= −290 cm–1. A computational analysis demonstrated strong multicenter π-bonding within mono- and dicationic trimers. While a weakly covalent component was critical to the formation and properties of these complexes, the variation of their binding energies was related mainly to the interplay between electrostatic interaction between monomers and dispersion. Specifically, an electrostatic repulsion between cationic monomeric moieties in the dicationic trimers was close to that in the corresponding (TMTTF)22+dimers, but the dispersion energy in the former was roughly twice that in the dimers. As a result, the (TMTTF)32+trimers are thermodynamically stable in the gas and condensed phases─in contrast to the dicationic dimers, which are stable only if electrostatic repulsion is attenuated by the polar solvent and/or compensated by interaction with counterions in the solid state. Also, the weaker electrostatic repulsion between monomers in the monocationic trimers and dimers led to the higher stabilities of such complexes as compared to their dicationic analogues.

The origin of the second, faster relaxation process in Mn₁₂ molecules has been identified as a different relative orientation of the Jahn–Teller elongation axes of the Mn^III ions, which we have termed ‘Jahn–Teller isomerism’.