We investigated the role of trace amounts of solvent additives in the performance improvement of all-polymer blend solar cells, composed of poly­(3-hexylthiophene) (P3HT) as the donor and a naphthalene diimide-based copolymer (P­(NDI2OD-T2)) as the acceptor, by photoconductive atomic force microscopy (PC-AFM). Nanoscale observation of the evolution of the photocurrent generation and distribution demonstrates that the addition of 0.5 vol % 1,8-diiodooctane (nonaromatic additive) and 1-chloronaphthalene (aromatic additive) has a negligible effect on the scale of phase segregation but leads to an increase in photocurrent owing to an increase in the charge transport efficiency, which is achieved by increasing the ordering of P3HT with extended interchain conjugation. In particular, the formation of a pathway that transports photogenerated charge carriers is found to be critical for increasing the photocurrent in the device. The PC-AFM characterization elucidates the interplay between the additive-mediated microstructures of the polymer:polymer blends and their local and macroscopic device performances.

Aluminum nitride is a promising substrate material for AlGaN-based UV-LED. In order to develop a robust growth processing route for AlN single crystals, fundamental studies of solution growth experiments using Ni-Al alloy melts as a new solution system were performed. Al can be stably kept in solution the Ni-Al liquid even at high temperature; in addition, the driving force of the AlN formation reaction from solution can be controlled by solution composition and temperature. To investigate AlN crystal growth behavior we developed an in situ observation system using an electromagnetic levitation technique. AlN formation behavior, including nucleation and growth, was quantitatively analyzed by an image processing pipeline. The nucleation rate of AlN decreased with increasing growth temperature and decreasing aluminum composition. In addition, hexagonal c-axis oriented AlN crystal successfully grew on the levitated Ni-40 mol%Al droplet reacted at low driving force (1960 K), on the other hand, AlN crystal with dendritic morphology appeared on the sample with higher driving force (Ni-50 mol%Al, 1960 K). Thus, the nucleation rate and crystal morphology were dominated by the driving force of the AlN formation reaction. K E Y W O R D S aluminum nitride, crystal growth, nucleation, thermodynamicsThis is an open access article under the terms of the Creat ive Commo ns Attri bution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. How to cite this article: Adachi M, Hamaya S, Yamagata Y, et al. In-situ observation of AlN formation from Ni-Al solution using an electromagnetic levitation technique. J Am Ceram Soc.

Ni-Al alloys are good candidates for the fabrication high-efficiency gas turbine blades. The Ni-Al system is also important as a solution for AlN crystal growth. To accurately model the casting process for turbine blade fabrication and design solution growth techniques for AlN, the thermophysical properties of the liquid alloy are required. In this study, the normal spectral emissivity of Ni-Al liquid alloys was measured using the electromagnetic levitation technique under a static magnetic field. Both the melting temperature of Cu and the eutectic temperature of the Ni-C system were used as fixed temperature points for spectrometer calibration to obtain the radiance of liquid Ni-Al alloys. The composition dependence of the normal spectral emissivity of liquid Ni-Al alloys had a maximum at ~40-50 mol%Al-Ni. The Ni-Al binary system had a stable intermetallic compound of NiAl with a melting temperature of 1 911 K. The short range chemical ordering could be attributed to strong bonding between Ni and Al atoms, which affected the scattering cross section of the conduction electrons even in the liquid state; hence, the normal spectral emissivity had a maximum at ~40-50 mol%Al-Ni.

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