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ACS Nano ; 2021 Jul 13.
Artigo em Inglês | MEDLINE | ID: mdl-34255478


Because of their unique atomic structure, 2D materials are able to create an up-to-date paradigm in fundamental science and technology on the way to engineering the band structure and electronic properties of materials on the nanoscale. One of the simplest methods along this path is the superposition of several 2D nanomaterials while simultaneously specifying the twist angle between adjacent layers (θ), which leads to the emergence of Moiré superlattices. The key challenge in 2D nanoelectronics is to obtain a nanomaterial with numerous Moiré superlattices in addition to a high carrier mobility in a stable and easy-to-fabricate material. Here, we demonstrate the possibility of synthesizing twisted multilayer graphene (tMLG) with a number of monolayers NL = 40-250 and predefined narrow ranges of θ = 3-8°, θ = 11-15°, and θ = 26-30°. A 2D nature of the electron transport is observed in the tMLG, and its carrier mobilities are close to those of twisted bilayer graphene (tBLG) (with θ = 30°) between h-BN layers. We demonstrate an undoubtful presence of numerous Moiré superlattices simultaneously throughout the entire tMLG thickness, while the periods of these superlattices are rather close to each other. This offers a challenge of producing a next generation of devices for nanoelectronics, twistronics, and neuromorphic computing for large data applications.

Ultramicroscopy ; 218: 113083, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32739752


Fracturing microscale constrictions in metallic wires, such as tungsten, platinum, or platinum-iridium, is a common fabrication method used to produce atomically sharp tips for scanning tunneling microscopy (STM), field-emission microscopy and field ion microscopy. Typically, a commercial polycrystalline drawn wire is locally thinned and then fractured by means of a dislocation slip inside the constriction. We examine a special case where a dislocation-free microscale constriction is created and fractured in a single crystal tungsten rod with a long side parallel to the [100] direction. In the absence of dislocations, vacancies become the main defects in the constriction which breaks under the tensile stress of approximately 10 GPa, which is close to the theoretical fracture strength for an ideal monocrystalline tungsten. We propose that the vacancies are removed early in the tensile test by means of deformation annealing, creating a defect-free tungsten constriction which cleaves along the W(100) plane. This approach enables fabrication of new composite STM probes which demonstrate excellent stability, atomic resolution and magnetic contrast that cannot be attained using conventional methods.