Magnetoresistance Effect of Black Phosphorus.

1.从尽可能减少化学杂质和安全处理有毒白色磷的角度出发，对全封闭铋熔剂法制备黑磷单晶进行了改进。在该方法中，红色P到白色P的转化和黑色P单晶的生长在抽真空的石英玻璃装置中进行，而不破坏真空。对针状晶体的部分晶体形貌进行了观察和晶体学分析.在-10K以下，黑P针状晶体的电导率与lobT有关，负磁电阻与logH有关。负磁电阻具有显著的角度依赖性，H的角度依赖性大，H//的角度依赖性小。结果表明，在黑P针状晶中，特别是在黑P针状晶中，会产生二维安德森局域化，这种局域化受到温度、磁场和电场的抑制，并且黑P的霍尔系数由类空穴的正号变为类电子的负号。这表明在针状晶体上会形成表面反型层.利用从头算方法计算了黑P的能带。结果表明，除了有效质量外，在能带、态密度、反射谱、静态介电常数、等离子体频率等方面，计算结果与实验结果符合较好。还进行了加压下的能带计算。结果表明，计算结果与实验结果一致，表明黑P具有窄的直接允许跃迁带隙和层状结构，在红外探测器和新型插层化合物方面具有潜在的应用价值。

1. An all-closed bismuth-flux method for preparing black P single crystals was improved from the point of view that chemical impurities will be reduced as much as possible and poisonous white P must be handled safely. In the method, the conversion of red P to white P and the growth of black P single crystals were performed in an evacuated quartz-glass apparatus without breaking the vacuum. Some crystal morphologies for needle-like crystals were observed and analyzed crystallographically.2. We have found that the needle crystals of black P show the lobT dependence of the conductivity and the logH dependence of the negative magnetoresistance ( vs H) below -10K. The negative magnetoresistance has a remarkable angular dependence of large for H and small got H//. These results show that two-dimensional Anderson localization is caused particularly in the black-P needle ceystals and the localization is suppressed by temperarure, magnetic field and electric field.It is also found that a Hall coefficient of black P is reversed from a hole-like plus sign to an electron-like minus sign. This suggests that a surface inversion-layer will be formed on the needle crystal.3. The energy band calculation of black P based on an ab-initio norm-conserving pseudopotential was presented. It has been that the results are in better agreement with experimental results regarding the energy band, density of states, reflectance spectra, static dielectric constant, plasma frequency, except for effective masses. The energy band calculation under pressure was also performed. It has been found that the results are in good agreement with the experimental results of structural properties and pressure dependencies of energy gap and TAy phonon frequency.Theoretical and experimental results of black P such as a narrow and direct-allowed-transition band-gap and a layered structure suggest that black P has a potential use to an infrared detector and new intercalation compounds.