Search

The rich physical properties unveiled in a plethora of transition and rare-earth metal oxides have been attributed to the intricate interplays between the orbital, charge, and spin degrees of freedom. Among them, rare-earth manganites (RMnO3) have been attracting tremendous attention owing to the ionic size-induced lattice distortion dictated by the Goldschmidt tolerance factor and the substantial Jahn–Teller distortion unique to Mn3+ ions, which evidently have resulted in a variety of emergent characteristics in electronic, magnetic, and orbital ordering. In this work, we deliberately engineered the orientation of a series of orthorhombic YMnO3 (o-YMO) films grown on SrTiO3(100) [STO(100)] and SrTiO3(110) [STO(110)] substrates by means of pulsed laser deposition. The x-ray diffraction (XRD) and reciprocal space mapping revealed that o-YMO/STO(100) is c-axis-oriented and o-YMO/STO(110) is a-axis-oriented, respectively. The XRD ϕ-scans further indicate that both films have excellent in-plane crystallinity, allowing the exploration of anisotropies along the respective crystallographic orientations. Indeed, the x-ray absorption linear dichroism spectroscopy taken along the respective crystallographic orientations evidently exhibited substantial anisotropy. Theoretical fitting with configuration interaction cluster calculations suggests that the d 3 z 2 − r 2 orbitals are parallel to YMO[001]/(100), leading to stronger electron scattering along the c-axis. Independent polarization-dependent Δ R/R spectra obtained using the femtosecond pump–probe method exhibited substantial anisotropic behaviors in carrier relaxation dynamics when probing along different crystallographic orientations, presumably due to orbital ordering anisotropies. [ABSTRACT FROM AUTHOR]

Biopolymers such as carrageenan or collagen can be used as carriers for loading a drug to enhance a drug’s bioavailability. In this work, allopurinol was loaded on a carrageenan/collagen blend and the carrageenan/collagen/allopurinol (CCA) biocomposite films were prepared using the ionic gelation method combined with the 3D printing method using carrageenan/collagen/allopurinol gel as a 3D printing ink material. The advantages of the 3D printing method are the ease in shaping the design of films and the ease in controlling the thickness of films. The results of infrared (IR) spectroscopy and field emission scanning electron microscopy (FESEM) analyses showed that the CCA biocomposite films have a regular structure, and the functional groups of components in the biocomposites can interact with each other. After 30 minutes of immersion in distilled water and pH buffer solution, the biocomposite films swelled and disintegrated. The carrageenan/collagen blend can control the release of allopurinol in simulated body fluids. In addition, the drug release kinetic models reflecting the release process of allopurinol from CCA biocomposite films in simulated body fluids have also been calculated.

The origin of insulating ferromagnetism in epitaxial LaCoO3 films under tensile strain remains elusive despite extensive research efforts are devoted. Surprisingly, the spin state of its Co ions, the main parameter of its ferromagnetism, is still to be determined. Here, the spin state in epitaxial LaCoO3 thin films is systematically investigated to clarify the mechanism of strain‐induced ferromagnetism using element‐specific X‐ray absorption spectroscopy and dichroism. Combining with the configuration interaction cluster calculations, it is unambiguously demonstrated that Co3+ in LaCoO3 films under compressive strain (on LaAlO3 substrate) is practically a low‐spin state, whereas Co3+ in LaCoO3 films under tensile strain (on SrTiO3 substrate) have mixed high‐spin and low‐spin states with a ratio close to 1:3. From the identification of this spin state ratio, it is inferred that the dark strips observed by high‐resolution scanning transmission electron microscopy indicate the position of Co3+ high‐spin state, i.e., an observation of a spin state disproportionation in tensile‐strained LaCoO3 films. This consequently explains the nature of ferromagnetism in LaCoO3 films. The study highlights the importance of spin state degrees of freedom, along with thin‐film strain engineering, in creating new physical properties that do not exist in bulk materials. [ABSTRACT FROM AUTHOR]

This work reports molecular beam epitaxy (MBE) of two-dimensional (2D) GaSe1−xTex ternary alloys that have recently attracted a lot of interest in physics for prospective electronics and optoelectronics even though they face crucial challenges in their epitaxial technology. Disregarding a distinction in crystal phase symmetry of two end-terminals, i.e., hexagonal-GaSe (h-GaSe) and monoclinic-GaTe (m-GaTe), the majority of hexagonal-GaSe1−xTex (h-GaSe1−xTex) phase on a GaN/sapphire platform is guaranteed under our specific growth conditions without a visible sign of phase transition. We have also proposed extracting the Te composition of the ternary alloy via the experimental in-plane lattice constant, which is consistent with those indicated from energy dispersion X-ray data. Fascinatingly, the experimental and predictable band emission versus Te content displays a continuous redshift from 1.78 eV (h-GaSe) to 1.25 eV (h-GaSe0.4Te0.6) then a reversible blueshift to 1.46 eV (h-GaTe). Importantly, benefiting from the presence of Te incorporated atoms, the photoresponse performance of the hexagonal ternary alloy has greatly enhanced in comparison to the h-GaSe binary in terms of photocurrent density (up to 1250 nA cm−2 for h-GaSe0.65Te0.35 at only 300 mV bias). Overall, the results pave a way for phase/physical engineering of the alloys through the MBE process and realizing self-powered wafer-scale photodetectors based on 2D Ga-based monochalcogenide epitaxial thin films. [ABSTRACT FROM AUTHOR]

The magneto-structural coupling of BiFeO3 (BFO)–CoFe2O4 (CFO)/LaAlO3 (LAO) heteroepitaxy with various lateral sizes of CFO pillars embedded in a BFO matrix was investigated. A structural phase transformation of the BFO matrix was observed when the pillar size of CFO was increased to exceed 200 nm. Such structural transformation led to modification of magneto-elastic coupling behavior and magnetic anisotropy in the BFO–CFO/LAO system. The flexibility of tuning the pillar size of CFO, and hence, the strain and interfacial effect on the multiferroic system have significant application implications in these functional oxide nanocomposites. [ABSTRACT FROM AUTHOR]