Effects of phosphorus with Mn3P2 as additive on diamonds growth along (100) surface
In this study, diamond crystals were synthesized via temperature gradient method at 5.6 GPa and 1230-1245 ℃ by adding Mn3P2 dopant and FeNi solvent catalyst. Experimental results show that Mn3P2 shifted the V-shape growth region move to up and right by influencing the catalytic properties. The scanning electron microscope (SEM) photographs of diamonds synthesized at 1245 ℃ reveal that there are many dendritic structures in the (100) surfaces. The diamond crystals quality can be improved when the Mn3P2 additive is less than 6 wt% at 1245 ℃, but it would be seriously damaged when Mn3P2 is heavily doped. The pits and uneven layered structures appeared on diamond surfaces when the additive arrived 12 wt% at 1245 ℃. The Fourier Transform infrared spectroscopy (FTIR) spectra reveal that Mn3P2 additive increases the N content of the crystal and N is present in the diamond crystal in the form of a “C” center. It is worth noting that phosphorus can be doped into diamond crystals by additive Mn3P2 and other impurities in diamonds are mostly C-N and C-O forms by X-ray photoelectron spectroscopy (XPS) test. The phosphorus in the sample crystals mainly formed the C-P bonds with carbon and a smaller amount of phosphorus formed the P-O bonds with oxygen. It can be shown from the test results of the electrical properties by Van der Pauw method that diamond crystals with Mn3P2 doped at 1245 ℃, whose resistivity are 0.516×106 ~ 9.729×106 Ω•cm and Hall coefficient is negative, belong to n-type semiconductor.