Preparation And Superconductivity Of Quasi-one-dimensional Mo₂C Single Crystal Nanoribbons

As the information technology based on microelectronics is reaching the physical limits,low-dimensional superconductors have been one of the research hotspots in condensed matter physics due to their novel properties and potential applications.And many kinds of low dimensional superconductors,such as two-dimensional thin films or single crystal flakes,one-dimensional nanostructures and so on,have attracted an extensive attention in recent years.Transition metal carbides are a class of newly emerging low-dimensional superconducting materials.As a typical representative,superconducting Mo2C single crystal flake has been suggested to be an ideal candidate in energy storage,catalysis and microelectronic devices due to its excellent superconductivity,high stability and catalytic activity.In this thesis,we prepared the low-dimensional Mo2C single crystal nanomaterials with different morphologies,and emphatically studied the growth,microstructure and superconducting properties of quasi-one-dimensional(quasi-1D)Mo2C single crystal nanoribbons.Firstly,the Mo2C single crystal nanostructures with different morphologies were synthesized on the Mo/Cu substrates by the chemical vapor deposition(CVD)method.By optimizing the experimental parameters,for example,methane flow rate and growth time,we successfully synthesized quasi-1D Mo2C single crystal nanoribbons with different thicknesses.Secondly,the morphology,microstructure and crystal quality of quasi-1D Mo2C single crystal nanoribbons were characterized with using the electron microscopies,Raman spectroscopy and so on.Thirdly,their low temperature electrical transport properties were measured and the influence of magnetic field on their superconductivity was also discussed.The results indicated that the superconducting transition temperature is about 3.15K at zero field for the quasi-1D Mo2C single crystal nanoribbon with 220nm in thickness.More importantly,its upper critical magnetic field at zero temperature is estimated to be 0.29T,which is far less than its Pauli limit magnetic field(?6T).It suggests that the upper critical magnetic field of quasi-1D Mo2C single crystal nanoribbons should be seriously limited by the enhanced orbital effect.And besides,we also investigated the influence of sample thickness on the superconductivity of quasi-1D Mo2C single crystal nanoribbons.We found that with sample thickness decreasing,the superconductivity is gradually suppressed and the upper critical magnetic field is gradually increased for as-prepared quasi-1D Mo2C single crystal nanoribbons.It may be attributed to the fact that the increase of disorder and the decrease of orbital effect with the decrease of sample thickness for this quasi-1D system.