Preparation And Characterization Of Two-Dimensional Layered Van Der Waals Materials

Materials are the material basis for human survival and development,and the development of human history and civilization is inseparable from the development of materials.Two-dimensional materials have developed rapidly since the advent of graphene in 2004.Up to now,there are about 700 kinds of two-dimensional materials that have been experimentally or theoretically verified to exist stably.Thanks to their unique structural characteristics,many excellent physical properties,and a huge potential market,Two-dimensional materials have attracted the research interest of many researchers.In addition,2D layered materials can be assembled together in a specific order by van der Waals forces,forming van der Waals heterojunctions.Since van der Waals heterojunctions do not rely on chemical bonds,there is no lattice matching problem.By cleverly stacking two-dimensional materials with different properties together,various new functional devices can be designed.However,the premise and basis for realizing all this work is to first master the preparation methods of different two-dimensional materials and understand their unique physical properties through appropriate characterization methods,so as to realize "the best use of materials".In this article,the preparation and physical property characterization of several typical two-dimensional layered van der Waals materials are mainly studied.The main contents are as follows:1.We have studied the method of growing hexagonal boron nitride crystals by the co-solvent method,and successively tried different combinations of binary alloys(Fe-Cr,Fe-Cu,Co-Cr)as co-solvents,and also studied binary alloys.Effects of different ratios between alloys on crystal quality and size.During the experiment,we also tried to use boron nitride powder as a raw material,and found that it was not suitable for the growth of hexagonal boron nitride crystals,and the possible reasons were analyzed.In addition,we also observed the triangular crystal habit of hBN crystals during the experiment,and explained the reason for the appearance of the triangular crystal shape through analysis.2.We have done related research on the controllable preparation of two-dimensional Bi2O2Se crystals by chemical vapor deposition.We first built a set of vapor deposition systems that meet the growth conditions of vapor deposition,and then expounded the relevant theoretical basis.Then we used the ionic layered material fluorophlogopite as the substrate and Bi2Se3 and Bi2O3 as the source materials to realize the chemical vapor deposition growth of the two-dimensional ionic layered material Bi2O2Se crystal.Finally,the single-variable principle was adopted,and the growth conditions were optimized by adjusting the growth parameters,and the stable preparation of two-dimensional Bi2O2Se crystals was realized.3.We studied the magnetic properties of a series of Ru1-xCrxCl3 single crystals with different Cr doping ratios.It is found that Cr doping increases the interlayer distance monotonically.More importantly,with Cr doping,the long-range AFM order is suppressed gradually,accompanied with a possible SG state appearing in Ru1-xCrxCl3 single crystals when x>0.039.Such an SG state persists even at very high Cr doping level(x=0.761).Such behavior originates from the introduction of FM interaction by Cr3+ ions,which leads to the competition of AFM and FM interactions in the doped samples.The highest SG transition temperature emerges when the sign of Curie-Weiss temperature is changed at x=0.418,where the competition between the AFM and FM interactions should be strongest.In addition,the effective moment of Ru1-xCrxCl3 single crystal increases with Cr doping because of the larger magnetic moment of Cr3+ ion than the low-spin state Ru3+ ion.