Insertion of guest atoms and ions into the crystal structure of layered materials can be used to tune properties and create entirely new materials, but the presence of guest species can also affect the transformation mechanisms and stability of materials under different environments. Here, we reveal the nanoscale evolution of Bi 2 Te 3 crystals containing intercalated Cu atoms. The results show that the presence of Cu affects thermal stability and transformation pathways, with important implications for electronic and thermoelectric applications.
Layered metal chalcogenide materials, such as MoS2 and Bi2Te3, have found important applications as 2D materials in emerging electronic devices. To create nanoscale layered chalcogenide materials with precisely controlled structures and properties, it is critical to understand and control how they evolve and transform under various conditions. This Minireview presents an overview of recent research focused on using in situ characterization to understand the atomic‐scale details of transformations during growth, under exposure to reactive chemical and thermal environments, and on interfacing with other materials. These efforts have used techniques including in situ transmission electron microscopy (TEM), X‐ray spectroscopy, and optical methods to understand nanoscale transformations. These in situ studies have provided a substantially improved understanding of transformation mechanisms in layered chalcogenide materials, which is an important step toward the use of these interesting materials in a variety of electronic and electrochemical devices.
It is critical to understand the transformation mechanisms in layered metal chalcogenides to enable controlled synthesis and processing. Here, we develop an alumina encapsulation layer-based in situ transmission electron microscopy (TEM) setup that enables the investigation of melting, crystallization, and alloying of nanoscale bismuth telluride platelets while limiting sublimation in the high-vacuum TEM environment. Heating alumina-encapsulated platelets to 700 °C in situ resulted in melting that initiated at edge planes and proceeded via the movement of a sharp interface. The encapsulated melt was then cooled to induce solidification, with individual nuclei growing to form single crystals with the same basal plane orientation as the original platelet and nonequilibrium crystal shapes imposed by the encapsulation layer. Finally, heating platelets in the presence of antimony caused alloying and lattice strain, along with heterogeneous phase formation. These findings provide new insight into important transformation processes in layered metal chalcogenide materials.
Electrodeposition of metals with controlled crystallography and grain structure is critical for applications including batteries, electronic circuit fabrication, and industrial coating processes. For metal-anode-based batteries in particular, it is important to understand how the electrode surface affects the crystallography of electrodeposited metals. Graphene and other 2D materials have recently been shown to exhibit strong effects on metal crystallography during electrodeposition, but it is unclear the extent to which graphene is affecting epitaxy, and further understanding of the 3D metal/2D material interface is crucial for advancing interfacial electrodeposition control. In this work, we study the influence of graphene and the underlying Cu substrate on the crystal structure and morphology of electrodeposited metals. Based on extensive electrochemical testing and electron backscatter diffraction (EBSD), we find that the orientation of the substrate underneath graphene (usually copper) exerts a controlling crystallographic influence on the electrodeposited metal overlayer, rather than the graphene layer itself. Further transmission electron microscopy (TEM) and Raman spectroscopy investigations are used to probe the nature of the interface and the graphene layer. These findings are important because they show that graphene can potentially be used as an interlayer to enable high-quality remote epitaxy between a variety of metals that normally exhibit inhibited epitaxy because of surface oxide layers.
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