Synthesis of Black Phosphorous and Its Magnetic Properties after Doping

Author:Jiang Xiao Hong

Supervisor:yang shao guang


Degree Year:2019





In recent years,the rising two-dimensional layered materials has been attracted more attention on studying,such as graphene,transition metal sulfides,boron nitride and silene.Due to the zero-band gap of graphene,the low carrier mobility of transition metal sulfides,the extreme instability of silene exposed to air,etc.,the disadvantages of these two-dimensional layered materials limit their application in the field of electronics.It is very important that two-dimensional layered materials with both suitable band gap and high carrier mobility need to be discovered.Black phosphorus is a new type of two-dimensional layered material with a direct band gap and a higher carrier mobility,whose band gap changes with the number of layers.Overcoming the disadvantages that is the short band gap of graphene and the low carrier’s mobility of transition metal sulfide,black phosphorus plays an important role on semiconductor material.Black phosphorus has been limited its further development because of the high market price of black phosphorus,the difficulty in preparation and other problems.which has wide prospects in the fields of energy storage,catalysis.optoelectronics.biomedicine and gas sensors.In this paper,red phosphorus as raw materials,the high-pressure method with a non-toxic,stable and reproducible is served as the preparation of black phosphorus.On the basis of the high-pressure method,black phosphorus nanowires and transition metal doped black phosphorus are prepared,further investigating their magnetic,magnetic transport and gas sensitivity properties.The main contents of research are as follows:(Ⅰ)The high-pressure method of black phosphorus is proposed.The toxic and flammable white phosphorus is substituted by non-toxic and stable red phosphorus that is cheap in the market to prepare the bulk black phosphorus via the high-pressure method with a high-efficiency,stable and high conversion.The relationship between the conversion rate that is from red phosphorus to black phosphorus and temperature,pressure and reaction time is investigated.When the temperature is not lower than 600℃ and the pressure is not lower than 1.5 GPa,the results demonstrate that all red phosphorus is converted into black phosphorus in a short time.The prepared black phosphorus is orthorhombic,with good crystallinity,high purity and lamellar structure,which is characterized by XRD,Raman and SEM.We speculate that in the process of preparing black phosphorus is red phosphorus→white phosphorus(as a molten white phosphorus state)-black phosphorus.Reducing the cost of preparing black phosphorus,the high-pressure method is greatly expected to realize the industrial production of black phosphorus.(Ⅱ)The study on the magnetic properties and transport properties of black phosphorus.Pure black phosphorus is a paramagnetic by magnetic measurements material.The magnetoresistance and Hall resistance are measured by a six-electrode method using a PPMS device.Black phosphorus has a positive nonlinear Hall effect,confirming that black phosphorus is a p-type semiconductor.Magnetoresistance measurement displays that black phosphorus possesses an unsaturated positive magnetoresistance at high temperatures and a saturated negative magnetoresistance at low temperatures.This phenomenon can be explained by classical network models and magnetic polaron models.Meanwhile.we obtain a relationship between carrier concentration and mobility of black phosphorus with temperature the by fitting the conductivity tensors σxx and σxy with the two-band model,which proves that the carrier mobility is much higher than of other 2D materials,like MoS2(Ⅲ)The synthesis of single crystal black phosphorus nanowires.Using red phosphorus as raw material,single crystal black phosphorus nanowires are synthesized with the aid of AAO template.XRD and Raman results show that the synthesized black phosphorus is pure phase.SEM and TEM results display that the synthesized samples possess a linear morphology.HRTEM and SAED measurements demonstrate that the synthesized nanowires are single crystals growing along the<012>direction,confirming that the synthesis of black phosphorus nanowires is<melting-injection-transformation>.Black phosphorus nanowires possess higher response value to NO2,faster adsorption/desorption time and better gas selectivity than bulk black phosphorus at room temperature and dry air,which is attributed to the nanowires with a larger specific surface area.Above all,single crystal black phosphorus nanowires have a good application prospect in the future sensor field.(Ⅳ)The study on transition metal doped black phosphorus and its magnetic properties.Via transition metal phosphide and red phosphorus as raw materials,pure phase black phosphorus doped with transition metals(V,Ti,Cr,Mn,Fe,Co,Ni and Cu)were synthesized by high temperature and high-pressure method.Among them,V,Fe,Co,Ni and Cu doped black phosphorus exhibit paramagnetic.However,Ti,Cr and Mn doped black phosphorus samples exhibit ferromagnetism.From the M-T curve of Cr and Mn doped black phosphorus,the magnetic properties of the sample show a transition from antiferromagnetic to paramagnetic at about 12 K.Also,we can observe a transition from paramagnetic to ferromagnetic at about 100 K.At the same time,there is a transition from ferromagnetic to paramagnetic around 300 K.It can be seen from the M-H curve that Cr and Mn doped black phosphorus still exhibit ferromagnetism at room temperature.The M-T curve of Ti-doped black phosphorus demonstrates a sharp drop around 130-140 K,indicating that this position may be the Curie point of the sample.Furthermore,we analyze the magnetic transport properties of Ti,Cr and Mn doped black phosphorus.The prepared TixP1-x,CrxP1-x and MnxP1-x samples are the semiconductor properties with positive magnetoresistance characteristics at high temperatures and negative magnetoresistance characteristics at low temperatures.Generally speaking,the results show that doped black phosphorus has certain application prospects in the field of spintronics.