Observation by CL and SEM-CL
Fig 7 shows a CL figure of the sample A by a luminoscope, in which orange and green luminescence is observed. Cubic growth sectors are dominated by typeIb and show red and orange fluorescence due to N-V centre, while octahedral growth sectors are dominated by type IaA and show green-yellow fluorescence due to H3 centre. Growth sector boundary of the centre cross is confirmed distinctly by the difference of those luminescence colours. Fig 8a shows a SEM-CL figure of the same sample at the same position. With a luminoscope visible fluorescence can be observed visually as luminescence colour, while with SEM-CL only shows contrast between black and white by the intensity of luminescence. Bright area corresponds to high concentration of defect related to impurity nitrogen and so does darker area to low concentration. The white part on the photo shows higher amount of luminescence that corresponds to cubic growth sector with green-yellow fluorescence in the CL figure of a luminoscope, whereas the black part corresponds to octahedral growth sector of red and orange fluorescence colour with small amount of luminescence.
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| Figure 7: |
A CL figure of the sample A observed by a luminoscope. |
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| Figure 8a: |
A SEM-CL figure of the sample A with a luminescence spectrum at 500nm. |
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Cathodo luminescence spectral analysis confirmed that bright luminescence area corresponds to H3 centre (503nm) and the dark area to N-V centre (575nm and 637nm) (Fig 9a,b). Magnified CL figures of growth sector shown in Fig 8a are observed with two different luminescence spectra, 500nm and 600nm, and they are shown in Fig 8b, c, d and e. The Fig 8b and 8c are CL figures with 500nm luminescence spectre. Centre of the crystal is indistinct, but bright luminescent areas have grown as faces consisting only of smooth {111} with its sector boundaries surrounded by curved surfaces. Linear zonal structure is also observed distinctly due to bright and dark luminescence.
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| Figure 8b,c: |
Zonal structure of smooth {111} growth sector showing strong luminescence (luminescence spectrum at 500nm). |
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On contrary, the CL figures of Fig 8d and 8e that show luminescence spectra of 600nm consist of repetition of steps of very complicated fine zigzag-shaped {111} faces and curved rough {100} faces. In the {100} growth sector, combination with linear {111} faces is observed. These zonal structures prove that the diamond had maintained cube-octahedron that was surrounded by {100} and {111} during its growth, and a shift of supersaturation caused relative delay on the growth speed of {100} faces than {111} faces that made interface configuration unstable, resulted in production of mixed habit growth containing zigzag or curved morphology.
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| Figure 8d,e: |
Growth sector of rough {100} plane show characteristic curved or zigzag pattern, and the whole crystal developed a Mixed habit growth. |
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| Figure 9(a,b): |
Luminescence spectra of the sample A and B on a spectrophotometer attached to a scanning electronic microscope. |
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CL and SEM-CL figures of the sample B are shown in Fig 10 and 11a. Its zonal structure is consists all of sharp straight lines in general, and it shows a centre cross growth form totally different from that of the sample A, although it is also composed of combination of {111} and {100} faces. Other than {111} and {100} faces, some other minor growth sectors such as {110} and {hhk} are observed. A magnified SEM-CL figure shown in Fig 11b reveals that growth faces of {111} and {100} are quite smooth crystal surfaces, which prove that no major variation on growth condition took place during the growth and spiral growth structure has produced on both faces. This growth of the centre cross diamond indicates that the material has grown under condition of high supersaturation (Tolansky and Sunagawa. 1959).
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| Figure 10: |
A CL figure of the sample B. |
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| Figure 11a: |
A SEM-CL figure of the sample B (luminescence spectrum at 500nm). |
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| Figure 11b: |
Growth faces of both {111} and {100} show smooth crystal surface. |
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