Real-Time Visualization of Solid-Phase Ion Migration Kinetics on Nanowire Monolayer

Janus Helical Ribbon Structure of Ordered Nanowire Films for Flexible Solar Thermoelectric Devices

Solar thermoelectric devices play a significant role in addressing the problem of global warming, owing to their unique features of converting both waste heat and solar energy directly into electricity. Herein, a flexible 3D Janus helical ribbon architecture is designed, starting from well-aligned tellurium (Te) nanowire film, using an in situ redox process reacting with Ag⁺ and Cu²⁺ resulting in n-type, p-type, and photothermal sides in one film. Remarkably, the device shows all-day electricity generation and large temperature gradient by coupling the cold side with a passive radiative cooling technique and the hot side with a selective solar absorption technique, showing a temperature gradient of 29.5 K, which is much higher than previously reported devices under a low solar radiation of only 614 W m^-2 . Especially, the device can still generate electricity even at night. The present strategy offers a new way for heat management by efficiently utilizing solar energy and the cold of the universe.

Self-Assembly of Nanowires: From Dynamic Monitoring to Precision Control

ConspectusNatural biomaterials often show ordered nanowire structures (ONWS) which display unique structural color or superior mechanical performance. Meanwhile, plenty of modern nanodevices with ONWS have flourished with activities focused on both basic and applied research. Manipulating synthetic nanowire (NW) from a disordered state to a hierarchically ordered structure via various assembly strategies brings about intriguing and exotic chemical/physical properties. In the past decades, many methods have been developed to assemble NWs and fabricate organized architectures, such as Langmuir-Blodgett interfacial assembly, spin-coating assembly, fluid-flow-induced assembly, and ice-template assembly. Nevertheless, for practical applications, large-scale and high-efficiency assembly strategies toward precise controlled architectures are largely limited by the lack understanding of assembly mechanisms. Especially, the manipulation principles and driving forces behind the state-of-art assembly strategies are still unclear. Besides, the lesser research attention on dynamic kinetics also impedes the revelation of the NW self-assembly mechanism. With the emergence of advanced in situ techniques, such as synchrotron-based X-ray techniques and in situ transmission electron microscopy (TEM), the dynamic monitoring of NW behavior in many practical environments becomes possible. In addition, the alignment direction and the stacking manner of NW film are of significance to the final performance. There is a lack of connection between the properties of one-dimensional nanoscale building blocks and the functionalities of the macro-assembly structures. To this end, dynamic monitoring is highly desired, which enables the precision modulation of NW assembly structure, leading to the discovery or prediction of new structures, novel properties, and performance optimization.In this Account, we aim to uncover the underlying kinetics of NW assembly or local reaction and mass transportation processes, as well as to build a solid connection from individual NWs to NW assembly structures with enhanced properties and eventually to macroscopic materials application. We first review the recent progress in state-of-art NW assembly strategies for diverse aligned structures according to the manipulation principle and the driving forces. To systematically review the NW self-assembly strategies, we categorize these strategies into three states: NWs on the liquid interface via surface tension, NW assembly in liquid via solution-shearing flow field, and NW assembly at the solid interval via physical repulsive force. Then, we introduce the existing advanced characterization techniques, including synchrotron-based X-ray scattering and in situ TEM, to dynamically monitor the intermediate states of the NW assembly and transport processes. The comprehensive understanding of this thermodynamic and kinetic mechanism facilitates the rational design, large scale, and high-efficiency fabrication of NW assemblies, thus promoting their applications in tailored optical-electrical electronics, smart electrochromic devices, electrocatalysis, structural materials, and chiral photonic crystals.

Tailoring atomic diffusion for in situ fabrication of different heterostructures

Atomic diffusion has been recognized as a particularly powerful tool in the synthesis of heterostructures. However, controlled atomic diffusion is very difficult to achieve in the fabrication of individual nanostructures. Here, an electrically driven in situ solid-solid diffusion reaction inside a TEM is reported for the controlled fabrication of two different hetero-nanostructures in the Ag-Te system. Remarkably, the morphology and structure of the as-formed heterostructures are strongly dependent on the path of atomic diffusion. Our experiments revealed that the surface diffusion of Te atoms to Ag nanowires leads to a core-shell structure, while the bulk diffusion of Ag atoms give rise to a Ag₂Te-Te segmented heterostructure. Heat released by Joule heating caused the surface diffusion process to be replaced by bulk diffusion and thereby determined the structure of the final product. Our experimental results provide an insight into solid-state diffusion reactions under an electric field and also propose a new process for the fabrication of complex nanostructures.

Atomic diffusion is a powerful tool for the synthesis of heterostructures, even though controlled atomic diffusion is difficult to achieve. Here, the authors control solid-solid atomic diffusion between an Ag nanowire and a Te nanowire, producing 1D heterostructures by applying an electrical bias inside a TEM.

Single-Particle Imaging of Anion Exchange Reactions in Cuprous Oxide

Ion exchange is a predominant and flexible route to tailor the composition and crystal structure of various materials. In situ monitoring of the ion exchange process at the single-particle level is critical to better understand the reaction mechanism and engineer high-performance materials. We report herein a dark-field imaging approach to in situ investigate the anion exchange reactions between individual Cu₂O microparticles and S^2- or Cl^- assisted by the hydrolysis of Sn⁴⁺, which are visualized by directly observing the color change of single Cu₂O microparticles. The variation of the scattering intensity is applied for quantitative analysis of anion exchange kinetics, revealing that this reaction process is dependent on the morphology, size, environmental pH, and reactant concentration. We directly observe that the corners of Cu₂O are the preferential exchange sites, and the reaction activity is surface dependent. Moreover, the reaction rate constant and diffusion coefficient are estimated to be 1.1 × 10^-2 s^-1 and 9.4 × 10^-11 cm²/s. Furthermore, a single-particle colorimetric assay is also fabricated for visual detection of S^2-.

Necklace-like ultrathin silver telluride nanowire films and their reversible structural phase transition

Ultrathin necklace-like Ag2Te nanowires with a diameter of 10 nm and a length of several micrometers are fabricated by a simple solution-based process at low temperature, and the Ag2Te nanowire films are fabricated by a Langmuir-Blodgett technique. A reversible structural phase transition of the nanowire films obtained can be observed, and in addition is also reflected by the electrical properties.