Surface Functionalization and Ferromagnetism in 2D van der Waals Materials

Autor: Huey, Warren Lee Beck
Jazyk: angličtina
Rok vydání: 2022
Předmět:
Druh dokumentu: Text
Popis: Two-dimensional materials are a huge field of study owing to the many uses of the materials and the utility they offer in being easily tunable through processes such as functionalization, alloying, and exfoliation. Herein several families of 2D materials will be discussed regarding how altering the base materials can result in the controlled tuning of properties and emergence of new phenomena. One such family of materials are the Xenes. This large family of materials in unique in that a terminal ligand on every atom in the framework is required for stability. The identity of the terminal ligand can be used to control the optical, electrical, and thermal properties of the Xene. Chapter 1 discusses the developed chemical methods used to functionalize Xenes. Additionally, the significant influence of the ligand identity on electronic structure, optical properties, and thermal stability is discussed in detail. The Xene family allows for the systematic exploitation of properties and phenomena resulting from use of surface functionalization with 2D materials.Further exploration of the group 14 graphene analogues Xene materials is examined in Chapter 2. All these analogue materials require surface ligand termination on every atom for stability. In this chapter it is explored how altering the ligand identity can result in nonobvious interactions with other chemical species. Using x-ray diffraction, Fourier transform infrared spectroscopy, and thermal gravimetric analysis it is shown that the reversible intercalation of water occurs in methyl-terminated germanane, GeCH3, but not with hydrogen-terminated germanane, GeH. Molecular dynamics and density functional theory simulations predict that a dative interaction occurs between water and the Ge−C σ* pocket of the Ge framework resulting in local structural distortions. An above bang gap 1.87 eV luminescence with an average lifetime of hundreds of picoseconds is a result of the distortion in the Ge framework. The intercalation of water with GeCH3 and not GeH demonstrates the potential of these materials for separation technologies.Another method of controlling the properties of 2D van der Waals material is through alloying of different metals. This method has proved effective in the development of air-stable, thermally robust, exfoliatable ferromagnets with higher Curie temperatures. Chapter 3 establishes the CrxPt1-xTe2 (x ≤ 0.45) family of magnetic alloys which combines the magnetism of early transition metal Cr with the stability of a late transition metal dichalcogenide PtTe2. Crystals of this alloy series are easily grown from the melt, contain high concentrations of the magnetic element, and are stable in ambient conditions. Both powder and single-crystal x-ray diffraction indicate that Cr readily substitutes on the Pt site and not within the van der Waals space allowing for their exfoliation to the few-layer regime. Cr0.45Pt0.55Te2, the highest Cr-substituted alloy, exhibits ferromagnetism below 220 K with the easy axis along the c-axis as determined by magnetic susceptibility and neutron diffraction measurements. The alloys are metallic with appreciable magnetoresistance below the magnetic transition temperature. The air-stable and exfoliatable nature of the material with its high transition temperature lends itself for use as a building block in 2D devices.
Databáze: Networked Digital Library of Theses & Dissertations