Second harmonic generation (SHG) imaging can be used to visualize unique biological phenomena, but currently available dyes limit its application owing to the strong fluorescent signals that they generate together with SHG. Here we report the first non-fluorescent and membrane potential-sensitive SHG-active organic dye Ap3. Ap3 is photostable and generates SH signals at the plasma membrane with virtually no fluorescent signals, in sharp contrast to the previously used fluorescent dye FM4-64. When tested in neurons, Ap3-SHG shows linear membrane potential sensitivity and fast responses to action potentials, and also shows significantly reduced photodamage compared with FM4-64. The SHG-specific nature of Ap3 allows simultaneous and completely independent imaging of SHG signals and fluorescent signals from various reporter molecules, including markers of cellular organelles and intracellular calcium. Therefore, this SHG-specific dye enables true multimodal two-photon imaging in biological samples.

We demonstrate local crystal structure analysis based on annular dark-field (ADF) imaging in scanning transmission electron microscopy (STEM). Using a stabilized STEM instrument and customized software, we first realize high accuracy of elemental discrimination and atom-position determination with a 10-pm-order accuracy, which can reveal major cation displacements associated with a variety of material properties, e.g. ferroelectricity and colossal magnetoresistivity. A-site ordered/disordered perovskite manganites Tb(0.5)Ba(0.5)MnO(3) are analysed; A-site ordering and a Mn-site displacement of 12 pm are detected in each specific atomic column. This method can be applied to practical and advanced materials, e.g. strongly correlated electron materials.

We have synthesized A-site ordered (AO)-and A-site disordered (AD)-Y 1/4 Sr 3/4 CoO 3−δ (YSCO) with various oxygen deficiency δ, and have made a comparative study of the structural and physical properties. We have found that A-site (Y/Sr) ordering produces the unconventional oxygen-vacancy ordered (OO) structure, and that the magnetic and transport properties of both AO-and AD-YSCO strongly depend on the oxygen-vacancy (or excess oxygen) ordering pattern. AO-YSCO with a stoichiometric δ of 0.5 has the unconventional OO structure reflecting Y/Sr ordering pattern. With decreasing δ from 0.5, the overall averaged OO structure is essentially unchanged except for an increase of occupancy ratio for the oxygen-vacant sites. At δ = 0.34, excess oxygen atoms are ordered to form a novel superstructure, which is significant for the room-temperature ferromagnetism of AO-YSCO. In AD-YSCO, on the other hand, the quite different OO structure, which is of a brownmillerite-type, is found only in the vicinity of δ = 0.5.

We have succeeded in preparing A-site ordered and disordered Y1∕4Sr3∕4CoO3−δ with various oxygen deficiencies δ, and have made a comparative study of their structural and physical properties. In the A-site ordered structure, oxygen vacancies order, and δ=0.34 sample shows a weak ferromagnetic transition beyond 300K. On the other hand, in the A-site disordered structure, no oxygen-vacancy ordering is observed, and δ=0.16 sample shows a ferromagnetic metallic transition around 150K. A-site disordering destroys the orderings of oxygen vacancies and orbitals, leading to the strong modification of the electronic phases.

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