Magnetoresistance Effect of Black Phosphorus.

1.从尽可能减少化学杂质和安全处理有毒白磷的角度出发，对全封闭铋熔剂法制备黑磷单晶进行了改进。在不破坏真空的情况下，在真空石英玻璃装置中实现了红磷到白磷的转化和黑磷单晶的生长。对针状晶体的一些晶体形态进行了观察和晶体学分析。我们发现，在-10K以下，黑色P的针状晶体表现出导电性的lobT特性和负磁电阻(VS H)的Logh特性。负磁电阻具有大的H和小的GET H//的角度依赖关系。这些结果表明，二维Anderson局域化是在Black-P针状晶体中产生的，这种局域化受到温度、磁场和电场的抑制，并且发现Black P的霍尔系数从类空穴的正号反转到类电子的负号。这表明针状晶体上会形成一层表面反转层。提出了基于从头算范数守恒赝势的能带计算方法。结果表明，除有效质量外，在能带、态密度、反射光谱、静态介电常数、等离子体频率等方面与实验结果吻合较好。还进行了压力下的能带计算。理论和实验结果表明，黑色P具有窄的、允许直接跃迁的带隙和层状结构，在红外探测器和新型插层化合物方面具有潜在的应用前景。

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.