This paper describes a rational strategy to obtain self-assembled two-dimensional (2D) nanocrystals with definite and uniform thickness from a series of molecular Janus particles based on molecular nanoparticles (MNPs). MNPs are 3D framework with rigid shapes. Three different types of MNPs based on derivatives of polyhedral oligomeric silsesquioxane (POSS), [60]fullerene (C60), and Lindqvist-type polyoxometalate (POM) are used as building blocks to construct these amphiphilic molecular Janus particles by covalently connecting hydrophobic crystalline BPOSS with a charged hydrophilic MNP. The formation of 2D nanocrystals with an exact thickness of double layers of molecules is driven by directional crystallization of the BPOSS MNP and controlled by various factors such as solvent polarity, number of counterions, and sizes of the MNPs. Strong solvating interactions of the ionic MNPs in polar solvents (e.g., acetonitrile and dimethylformamide) are crucial to provide repulsive interactions between the charged outlying ionic MNPs and suppress further aggregation along the layer normal direction. The number of counterions per molecule plays a major role in determining the self-assembled morphologies. Size matching of the hydrophobic and ionic MNPs is another critical factor in the formation of 2D nanocrystals. Self-assembly of rationally designed molecular Janus particles provides a unique "bottom-up" strategy to engineer 2D nanostructures.

In this study, MAPbBr3 single crystal (MSC) p‐n perovskite homojunction photodiode and n‐p‐n phototriode are successfully fabricated through controlled incorporation of Bi3+ ions in solution. Optoelectronic analysis reveals that the photodiode shows typical photovoltaic behavior and the best photovoltaic performance can be achieved when the n‐type MSC is grown in 0.3% Bi3+ feed solution. The as‐assembled p‐n MSC photovoltaic detector displays obvious sensitivity to 520 nm illumination, with a high responsivity of up to 0.62 A W‐1 and a specific detectivity of 2.16 × 1012 Jones, which surpass many those of MSC photodetectors previously reported. Further performance optimization can be realized by constructing an n‐p‐n phototriode using the same growth method. The photocurrent magnification rate of the as‐fabricated n‐p‐n phototriode can reach a maximum value of 2.9 × 103. Meanwhile, a higher responsivity of 14.47 A W‐1, specific detectivity of 4.67 × 1013 Jones, and an external quantum efficiency of up to 3.46 × 103 are achieved under an emitter–collector bias of 8 V. These results confirm that the present p‐n and n‐p‐n MSC homojunctions are promising device configurations, which may find potential application in future optoelectronic devices and systems.

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In this paper, bulk-quantity tin-doped indium oxide nanowires were successfully synthesized by direct thermal evaporation of a mixture of In and SnO powders in air at 920°C. Such nanowires have a uniform shape and single crystalline cubic bixbite structure, with the diameters varying from 100 to 200 nm and lengths in the range of tens to hundreds of micrometres. The growth process of these ternary oxide nanowires can be interpreted by a self-catalytic vapour–liquid–solid growth mechanism. This approach to synthesizing ternary oxides should be readily extensible to preparing other multinary oxide nanowires, such as Cd2SnO4, Zn–Sn–In–O, Ga–In–Sn–O, Cd–In–Sn–O and Zn–Sn–Cd–O nanowires or nanobelts.

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In this study, we present a simple ultraviolet (UV) light photodiode by transferring a layer of graphene film on single-crystal ZnO substrate. The as-fabricated heterojunction exhibited typical rectifying behavior, with a Schottky barrier height of 0.623 eV. Further optoelectronic characterization revealed that the graphene-ZnO Schottky junction photodiode displayed obvious sensitivity to 365-nm light illumination with good reproducibility. The responsivity and photoconductive gain were estimated to be 3×104 A/W and 105, respectively, which were much higher than other ZnO nanostructure-based devices. In addition, it was found that the on/off ratio of the present device can be considerably improved from 2.09 to 12.1, when the device was passivated by a layer of AlOx film. These results suggest that the present simply structured graphene-ZnO UV photodiode may find potential application in future optoelectronic devices.

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