Author : Yizhou Yang
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (135 download)
Book Synopsis Electronic and Magnetic Properties of Double Metal MXenes by : Yizhou Yang
Download or read book Electronic and Magnetic Properties of Double Metal MXenes written by Yizhou Yang and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: MXene are a rapidly-expanding family of 2D transition metal carbides and nitrides with chemical formula of Mn+1XnTx where M is one or more early transition metals, X is carbon or/and nitrogen, and Tx represents surface species. The freedom allowed within the chemical composition of MXenes is an enabling factor in their wide range of applications such as supercapacitors, EMI shielding, catalysts, and water deionization. This dissertation presents an investigation into their fundamental electronic properties with emphasis on understanding how the M-site affects the MXene electronic behavior in three different types of double-M MXenes. The first type is the out-of-plane ordered double-M MXenes M'2M"C2Tx. The contributions of surface (M' site) and sub-surface (M" site) Ti atoms to the electronic structure of four Ti-based MXenes (Ti2CTx, Ti3C2Tx, Cr2TiC2Tx, and Mo2TiC2Tx) is studied using soft x-ray absorption spectroscopy, revealing minimal changes in the spectral features between the parent MAX phase and its MXene counterpart when no surface Ti atoms are present in the MXene, such as Mo2TiC2Tx and Cr2TiC2Tx. In contrast, for MXenes with surface Ti atoms, here Ti3C2Tx and Ti2CTx, the Ti L-edge spectra are significantly modified compared to their parent MAX phase compounds. The second type is solid solution MXene TiyNb2-yCTx where Ti and Nb randomly occupy the M site. To understand the intrinsic and extrinsic contributions to the macroscopic electronic transport properties, a systematic study controlling compositional and structural parameters was conducted within the solid solution TiyNb2-yCTx system. In particular, I investigate the different roles played by M-site composition, flake size and d-spacing on macroscopic transport. Hard x-ray photoemission spectroscopy and ellipsometry were employed to identify changes to electronic structure induced by the M-site alloying. A statistical analysis of measured transport data was used to find the dependence, correlation, and p-value for the low- and room-temperature conductivities and effective carrier mobility as a function of the compositional and structural contributions. The results provide guidance for designing and engineering MXenes with increased conductivities. The third type is secondary metal incorporated Ti3C2Tx, M-Ti3C2Tx. Ni and Co are incorporated into delaminated Ti3C2Tx by mixing dilute NiCl2 or CoCl2 solutions with delaminated Ti3C2Tx solutions. The ratio of Ni:Ti = 0.024 and Co:Ti = 0.071 is determined by nano x-ray fluorescence (XRF). The incorporated Ni and Co are uniformly distributed in the sample as imaged by nano XRF. DC magnetization measurements confirm that as-synthesized delaminated Ti3C2Tx is paramagnetic with a low susceptibility of 2.0 × 10-7 emg/g⋅Oe. The room temperature magnetic susceptibility for Ni-Ti3C2 is 10 times larger than d-Ti3C2, and Co-Ti3C2 is 100 times larger than the d-Ti3C2. The work provides a straightforward means of enhancing magnetic responses of MXenes using post-synthesis incorporation of magnetic transition metals.
