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Solvents enable growth of phase-pure two-dimensional perovskites without dissolving three-dimensional perovskite substrates. 

The discovery and control of new phases of matter is a central endeavour in materials research. The emergence of atomically thin 2D materials, such as transition-metal dichalcogenides and monochalcogenides, has allowed the study of diffusive, displacive and quantum phase transitions in 2D. In this Review, we discuss the thermodynamic and kinetic features of 2D phase transitions arising from dimensionality confinement, elasticity, electrostatics, defects and chemistry unique to 2D materials. We highlight polymorphic, ferroic and high-temperature diffusive phase changes, and examine the technological potential of controlled 2D phase transitions. Finally, we give an outlook to future opportunities in the study and applications of 2D phase transitions, and identify key challenges that remain to be addressed. 

Abstract We propose a data and knowledge driven approach for SPECT by combining a classical iterative algorithm of SPECT with a convolutional neural network.The classical iterative algorithm, such as ART and ML-EM, is employed to provide the model knowledge of SPECT.A modified U-net is then connected to exploit further features of reconstructed images and data sinograms of SPECT.We provide mathematical formulations for the architecture of the proposed networks.The networks are trained by supervised learning using the technique of mini-batch optimization.We apply the trained networks to the problems of simulated lung perfusion imaging and simulated myocardial perfusion imaging, and numerical results demonstrate their effectiveness of reconstructing source images from noisy data measurements. 

Polymeric semiconductors are crucial candidates for the construction of next‐generation flexible and printable electronic devices. By virtue of the successful preparation of monodispersed colloidal solution in orthogonal solvent, poly(3‐hexylthiophene) (P3HT) nanofibers are developed into versatile building blocks for nanoelectronics and their compatibilities are verified with photolithographic lift‐off technology. Then, the joint efforts from both the bottom‐up hierarchical self‐assembly and top‐down self‐alignment technology have led to the realization of lateral asymmetric heterojunctions with resolution better than 1 µm. As a result, planar photovoltaic devices incorporatingN,Nʹ‐dioctyl‐3,4,9,10‐perylenedicarboximide and P3HT supramolecular nanowires as active components are constructed with the cathode‐to‐anode distance being tuned from ≈0.1 to 1–2 µm. Based on such a novel device configuration, an interesting phenomenon of channel‐length‐dependent photovoltaic efficiency is observed for the first time, strongly suggesting the impact of near‐field light intensity on the performance of nanophotonic devices.