Effect of temperature on the (100) surface features of type Ib and type IIa large single crystal diamonds

Abstract

In this paper, by choosing FeNiMnCo alloy as a catalyst and the (100) face of a seed crystal as the growth face, high quality type Ib and type IIa large diamond single crystals (diameter about 3-4 mm) can be successfully synthesized using temperature gradient method, at 5.6 GPa pressure and different temperatures between 1250-1340 ℃. To control the diamond crystal morphology, the growth temperature should be adjusted. Then the morphology of the synthesized large diamonds is plate-like at low temperatures, tower-like at medium temperatures, and spire tower-like at high temperatures. For the same crystal morphology, the synthetic temperature of type IIa diamond single crystals is about 30 ℃ higher than that of type Ib. The central and angularity regions of the top (100) surface, for the synthesized samples of type Ib and type IIa large diamond single crystals at different temperatures, are examined by laser Raman microscope respectively. It is found that the black lines of the type Ib and type IIa large diamond single crystals become dimmed and dense on the same top surface from center to the edge. It is indicated that the priority growth mechanism is in the angularity regions, compared with the central regions. Namely the solute of carbon is primarily precipitated in the angularity regions of the (100) surface. With increasing synthesis temperature, the black lines on the top surface (100) of type Ib diamond single crystals become gradually denser, and the characteristics of the lines are transformed from irregular distribution to typical dendritic distribution. The reason of the above results is that the rate of carbon deposition (the growth rate of diamond crystal), which is along the direction of the diamond crystal [100], will gradually rise as the synthesis temperature of the crystal is increased. The characteristics of the lines on the top surfaces (100) of type IIa large diamond single crystals, which are synthesized under different temperatures, are similar to that of type Ib. However, the lines on the top (100) surface of type IIa diamonds are not so obvious and denser than that of type Ib diamonds at different synthesis temperatures. Similar characteristics of lines on the top (100) surface of both types of diamond single crystals can be explained by the axis and radial growth rate variation at different temperatures. These different characteristics of the lines are due to the fact that the growth rate of type IIa diamonds is slower than that of type Ib diamonds, and the nitrogen concentrations in type IIa diamonds are lower than those of type Ib diamonds. Finally, the full width at half maximum (5.554 cm-1) of the tower-like type IIa diamond is narrower than that (5.842 cm-1) of tower-like type Ib diamond from the test of Raman spectra. It is shown that the quality of type IIa diamond single crystals is better than that of type Ib.