Heat-Treatment-Induced Compositional Evolution and Magnetic State Transition in Magnetic Chalcogenide Semiconductor GeFeTe without Structural Phase Change

Control of magnetic properties in diluted magnetic semiconductors (DMSs) using external stimuli is a prerequisite for many spintronic applications. Fe-doped chalcogenide semiconductors are promising candidate materials for future spintronic devices since they offer the possibility of magnetic switching by their fast and reversible transition between amorphous and crystalline phases. However, for many proposed applications, magnetic manipulation in crystalline DMSs without a structural change is highly desirable. Thus, the ability to externally control the magnetism of magnetic chalcogenide semiconductors without structural phase change is of significance to enhance their application potential. Here we find that the annealing process could induce an antiferromagnetic (AFM)–ferromagnetic (FM) transition in magnetic chalcogenide semiconductor GeFeTe epilayers without deteriorating the crystal structure. The impact of heat treatment on magnetization in Ge_1–<i>x</i>Fe_<i>x</i>Te film depends on Fe concentration. The present data indicate that the AFM–FM transition originates from the evolution of Fe phase composition. This study gives an insight into the correlation between Fe phase composition, electronic structure, and magnetism in GeFeTe thin films

Strain-Engineering of Band Gaps in Piezoelectric Boron Nitride Nanoribbons

Two-dimensional atomic sheets such as graphene and boron nitride monolayers represent a new class of nanostructured materials for a variety of applications. However, the intrinsic electronic structure of graphene and h-BN atomic sheets limits their direct application in electronic devices. By first-principles density functional theory calculations we demonstrate that band gap of zigzag BN nanoribbons can be significantly tuned under uniaxial tensile strain. The unexpected sensitivity of band gap results from reduced orbital hybridization upon elastic strain. Furthermore, sizable dipole moment and piezoelectric effect are found in these ribbons owing to structural asymmetry and hydrogen passivation. This will offer new opportunities to optimize two-dimensional nanoribbons for applications such as electronic, piezoelectric, photovoltaic, and opto-electronic devices

Hydrogenated Oxygen-Deficient Blue Anatase as Anode for High-Performance Lithium Batteries

Blue oxygen-deficient nanoparticles of anatase TiO₂ (H-TiO₂) are synthesized using a modified hydrogenation process. Scanning electron microscope and transmission electron microscope images clearly demonstrate the evident change of the TiO₂ morphology, from 60 nm rectangular nanosheets to much smaller round or oval nanoparticles of ∼17 nm, after this hydrogenation treatment. Importantly, electron paramagnetic resonance and positronium annihilation lifetime spectroscopy confirm that plentiful oxygen vacancies accompanied by Ti³⁺ are created in the hydrogenated samples with a controllable concentration by altering hydrogenation temperature. Experiments and theory calculations demonstrate that the well-balanced Li⁺/e^– transportation from a synergetic effect between Ti³⁺/oxygen vacancy and reduced size promises the optimal H-TiO₂ sample a high specific capacity, as well as greatly enhanced cycling stability and rate performance in comparison with the other TiO₂