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Layered heterostructures based on two-dimensional materials: Interfacial phenomena and device applications
Two-dimensional (2D) materials, such as graphene, h-BN, MoS2, WS2, phosphorene and others, are becoming an increasingly popular field at the interface of materials chemistry and condensed matter physics. These naturally quantum-confined nanomaterials exhibit intriguing physical properties that are not available in their three-dimensional (3D) counterparts. Also, due to the large number of available 2D materials with a broad range of electronic, mechanical and optical characteristics, a simple approach based on stacking different 2D crystals on top of each other provides nearly endless opportunities for engineering of designer heterostructures with custom-tuned properties. However, due to high specific surface area, the interfacial phenomena in 2D materials in general and their heterostructures in particular are extremely important. Since 2D materials are generally impermeable for gases and liquids, they can be used to purposely trap and stabilize molecular layers in 2D heterostructures, thus providing another tool for tuning their properties. ^ In several subprojects of this PhD thesis I studied how interfacial phenomena related to charge impurities, trapped molecular layers and surface adsorbates affect properties of 2D materials and heterostructures. (1) The substrate and interfacial phenomena promote significant device-to-device variability. Utilizing these effects in specially designed graphene-based sensors, we demonstrate a highly selective recognition of analytes of nearly the same chemical nature such as methanol, ethanol and isopropanol. (2) Heterostructures composed of 2D materials on ferroelectric films exhibit unusual hysteresis of electronic properties which does not correspond to ferroelectric hysteresis loop. We propose a measurement technique to probe intrinsic properties of heterostructures and reverse the observed antihysteresis, caused by interfacial phenomena. (3) By altering a molecular layer at the graphene/BaTiO3 interface we dramatically improve the polarization stability and resistive switching of ferroelectric tunnel junctions — heterostructures, composed of two electrodes separated by an ultrathin ferroelectric barrier. (4) Nanosheets of MXenes, a large family of two-dimensional carbides and nitrides, are terminated by various functional groups. We demonstrate that specifically treated interfaces of MXene nanosheets are resistant to ambient conditions. (5) Finally, by modifying the dielectric environment of TiS3, a novel and promising 2D material, we greatly improve electronic characteristics of TiS3 field-effect transistors. ^
Lipatov, Alexey, "Layered heterostructures based on two-dimensional materials: Interfacial phenomena and device applications" (2016). ETD collection for University of Nebraska - Lincoln. AAI10143306.