Controllable Growth And Application Of Iron-Based Oxygen Compounds For Two-Dimensional Magnetic Materials

Graphene,as a representative of two-dimensional materials,has a broad application prospect in optoelectronics,magnetism and many other fields because of its unique electronic structure and excellent physical and chemical properties.In recent years,the research on two-dimensional magnetic materials has developed rapidly,but there are still many problems to be solved.First,it is known that two-dimensional magnetic materials suffers from poor stability and can not exist stably in the air environment for a long time.Secondly,although there are many studies on two-dimensional magnetic materials,many of which are predicted to be magnetic through theory,but only a few materials have been experimentally prepared.At present,it is still difficult to prepare two-dimensional magnetic materials.To solve the problem of difficult preparation,a general chemical vapor deposition（CVD）method is designed in this paper,which uses iodide as the source,and utilizing the easy sublimation property of iodide to realize the controllable and rapid preparation of iron-based oxy-compound two-dimensional materials.It is found that the samples have good crystal quality and room temperature ferromagnetism from the test.The emergence of these room temperature ferromagnetic materials is the necessary condition for the practical use of two-dimensional magnetic materials.The method of preparing two-dimensional materials using iodide as a source can be applied to the preparation of more two-dimensional magnetic materials.The main research contents are as follows:（1）Controllable growth of two-dimensional Fe₃O₄ and application of mid-infrared laser mode locking.Aiming at the difficulty in the preparation of two-dimensional magnetic materials,a low-pressure space-confined CVD method was designed to achieve controllable two-dimensional Fe₃O₄ nanosheets on mica,sapphire and magnesium oxide substrates using ferrous iodide as the iron source.The prepared Fe₃O₄nanosheets are non-layered materials,but the lateral size of the sample can reach 45μm and the thickness can be kept within 5 nm by adjusting the experimental method,which is close to the thickness of only a few atomic layers.The samples have high crystal quality and stability through various tests such as Raman and XPS.The experiment also found that the laser damage threshold of Fe₃O₄ can be increased by more than 3times through Mn doping,and it has stronger thermodynamic stability.Pure Fe₃O₄ and Mn-doped Fe₃O₄ are made into saturable absorbers and applied to the mid-infrared 2.8μm optical path,showing stable Q-switched pulses.The optical path using Fe₃O₄ as the saturable absorber has a stable Q-switched pulse of up to 112 m W output,while the Mn-doped sample exhibited an average output power as high as 774 m W.（2）Through the research and analysis of the preparation method of Fe₃O₄,the controllable preparation of two-dimensional Fe S,Fe Se and Fe Te nanosheets was realized by the same CVD method using ferrous iodide as the source.The two-dimensional Fe S nanosheets are prepared in the experiment for the first time,the lateral size can reach more than 100μm and have room temperature ferromagnetism.The prepared Fe Se nanosheets are transformed into two structures of square and hexagonal phases.The experiment also realizes the controllable preparation of the two samples by controlling the temperature.As a non-layered material,the hexagonal fese has a thickness of 4nm and a transverse dimension of 10μm,and the hexagonal fese has room temperature ferromagnetism in the experiment,Fe Te nanosheets with square and triangular morphologies are also prepared.The controllable preparation of samples with two morphologies was also realized by controlling the temperature,the triangular Fe Te nanosheets were found to have room temperature ferromagnetism through testing.The experimental results show that these two-dimensional magnetic materials can be easily and simply prepared by using iodide as the source,which has the characteristics of simple experimental method,controllable process and fast growth rate.