Induced Superconducting Transition in Ultra-Thin Iron-Selenide Films by a Mg-Coating Process.

Binary Iron selenide (FeSe) thin films have been widely studied for years to unveil the high temperature superconductivity in iron-based superconductors. However, the origin of superconducting transition in this unconventional system is still under debate and worth deep investigations. In the present work, the transition from insulator to superconductor was achieved in non-superconducting FeSe ultrathin films (~8 nm) grown on calcium fluoride substrates via a simple in-situ Mg-coating by a pulsed laser deposition technique. The Mg-coated FeSe film with an optimized amount of Mg exhibited a superconducting critical temperature as 9.7 K and an upper critical field as 30.9 T. Through systematic characterizations on phase identification, carrier transport behavior and high-resolution microstructural features, the revival of superconductivity in FeSe ultrathin films is mostly attributed to the highly crystallized FeSe and extra electron doping received from external Mg-coating process. Although the top few FeSe layers are incorporated with Mg, most FeSe layers are intact and protected by a stable magnesium oxide layer. This work provides a new strategy to induce superconductivity in FeSe films with non-superconducting behavior, which might contribute to a more comprehensive understanding of iron-based superconductivity and the benefit to downstream applications such as magnetic resonance imaging, high-field magnets and electrical cables.

Vacancy engineering of Cu2-xSe nanoparticles with tunable LSPR and magnetism for dual-modal imaging guided photothermal therapy of cancer.

The vacancies in the semiconductor nanocrystals not only induce unique properties, but also provide spaces for engineering them with multifunctions by the introduction of other elements. Herein, the vacancy of Cu2-xSe nanoparticles was tuned by doping with magnetic ferric ions (Fe3+) at room temperature, and the position and intensity of the near-infrared localized surface plasmon resonance (LSPR) in the resultant nanostructure can be finely controlled by altering the feeding amount of Fe3+ ions. The results of the density-functional theory (DFT) calculations show that both doping and replacement reactions are favourable. Owing to its tunable near-infrared absorption and magnetic property, the obtained hybrid nanostructure was demonstrated to be a novel nanotheranostic agent for effective deep-tissue photoacoustic imaging, magnetic resonance imaging, and photothermal therapy of cancer.

Ultrasmall Magnetic CuFeSe2 Ternary Nanocrystals for Multimodal Imaging Guided Photothermal Therapy of Cancer.

Nanoscale ternary chalcogenides have attracted intense research interest due to their wealth of tunable properties and diverse applications in energy and environmental and biomedical fields. In this article, ultrasmall magnetic CuFeSe2 ternary nanocrystals (<5.0 nm) were fabricated in the presence of thiol-functionalized poly(methacrylic acid) by an environmentally friendly aqueous method under ambient conditions. The small band gap and the existence of intermediate bands lead to a broad NIR absorbance in the range of 500-1100 nm and high photothermal conversion efficiency (82%) of CuFeSe2 nanocrystals. The resultant CuFeSe2 nanocrystals show superparamagnetism and effective attenuation for X-rays. In addition, they also exhibit excellent water solubility, colloidal stability, biocompatibility, and multifunctional groups. These properties enable them to be an ideal nanotheranostic agent for multimodal imaging [e.g., photoacoustic imaging (PAI), magnetic resonance imaging (MRI), computed tomography (CT) imaging] guided photothermal therapy of cancer.