Engineering Co Vacancies for Tuning Electrical Properties of p-Type Semiconducting Co3O4 Films.

Spinel oxide Co3O4 has attracted more and more attention for energy- and environment-related applications. In order to tune the electrical properties of Co3O4, p-type semiconducting Co3O4 films were fabricated on the Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT), MgAl2O4 (MAO), and SrTiO3 substrates by reactive magnetron sputtering. The Co3O4 film on the MAO substrate exhibits perfect epitaxial growth. However, the Co3O4 film on the PMN-PT substrate presents dislocation defects between the [011] and [112] orientations. The special ferroelectric domain shape surface and phase transition of the PMN-PT substrate induce the higher concentration of Co vacancies in the Co3O4 film, which further reduce the resistivity by several orders of magnitude. The calculated results indicate that introducing Co vacancies can enhance the electrical properties of Co3O4 by building impurity levels near the Fermi level, which is beneficial to form free-moving holes in the valence band. The free-moving holes can also be accumulated/dissipated by the ferroelectric field effect of PMN-PT substrates, leading to upward/downward bending of conduction, valence bands, and low/high-resistance states. This work helps us to tune and improve the electrical properties of Co3O4.

Solution Epitaxy of Halide Perovskite Thin Single Crystals for Stable Transistors.

Halide perovskites hold promise for energy and optoelectronic applications due to their fascinating photophysical properties and facile processing. Among various forms, epitaxial thin single crystals (TSCs) are highly desirable due to their high crystallinity, reduced defects, and easy epitaxial integration with other materials. However, a cost-effective method for obtaining TSCs with perfect epitaxial features remains elusive. Here, we demonstrate a direct epitaxial growth of high-quality all-inorganic perovskite CsPbBr3 TSCs on various substrates through a facile solution process under near-ambient conditions. Structural characterizations reveal a high-quality epitaxy between the obtained perovskite TSCs and substrates, thus leading to efficiently reduced defects. The resultant TSCs display a low trap density (∼1011 cm-3) and a long carrier lifetime (∼10.16 ns). Top-gate/top-contact transistors based on these TSCs exhibit high on/off ratios of over 105, an optimal hole mobility of 3.9 cm2 V-1 s-1, almost hysteresis-free operation, and high stability at room temperature. Such a facile approach for the high-yield production of perovskite epitaxial TSCs will enable a broad range of high-performance electronic applications.

[Applications of AFM in mechanism study of Alzheimer's disease].

Atomic force microscope (AFM) has become a well-established technique for biological sample imaging under physiological conditions. The unique capacity to produce nanometer scale resolution images with simple specimen preparation enables AFM to serve as a powerful tool in neurobiology research. Extensive studies suggest that the conversion of beta-amyloid (Abeta) peptide from soluble forms into fibrillar structure is a key factor in the pathogenesis of Alzheimer's disease (AD). AFM has provided useful insights at all stages of Abeta fibrillization, thus making therapeutic strategy possible. In this brief review, the principles and techniques of AFM and their effects on the pathogenetic study of AD, especially on the study of Abeta and Abeta oligomer are outlined.