Visualization of Diamond Nucleation and Growth from Energetic Species

The mystery of diamond nucleation by energetic species is resolved via a special deposition scheme. The evolution of the precursor material for diamond nucleation and the development of the nanodiamond crystallites are visualized by high resolution electron microscopy and other spectroscopies. The diamond precipitation and growth are explained in terms of our recently proposed mechanism [Science 297, 1531 (2002)]: (i) precipitation of $s{p}^3$ clusters a small fraction of which are perfect diamond; (ii) growth of diamond crystallites by preferential displacement of amorphous carbon atoms leaving diamond atoms intact. This general scheme is applicable to other materials such as cubic boron nitride.

Figure 1

Low-magnification cross-sectional TEM image of the film. A layered structure consisting of five layers with increasing density (deduced from the darkening of each layer with respect to the previous one) is observed on the Si substrate. The marking Diamond of the utmost layer denotes the nucleation layer (a diamond/graphitic carbon composite).

Figure 2

Small area electron diffraction (SAED) pattern of the different layers of the film in Fig. 1. (a) Interface between Si substrate and layer 1. (b) Layer 3. (c) Layer 4. (d) Layer 5. Layers 1–4 are graphitic with an oriented structure (only partial rings). The relative orientation of the rings with respect to the Si indicates the graphitic basal planes are perpendicular to the Si surface. The rings in layer 5 are diamond rings which indicate preferred orientation (they are more intense in certain directions with symmetry similar to that of the cubic diamond lattice).

Figure 3

Cross-sectional high-resolution TEM (HRTEM) imaging of the five layers of the film in Fig. 1. (a) Interface between Si substrate and layer 1. (b) Layer 1. (c) Layer 4. (d) Layer 5. The graphitic fringes are perpendicular to the Si surface. The films look denser as the layer develops from one to 4. Layer 5 shows 2–5 nm diamond crystallites embedded in a graphitic matrix. The marked region in $d$ is enlarged to show the crystallites more clearly.

Figure 4

Electron energy loss spectroscopy taken in the different layers in a cross-sectional sample. The first three layers are graphitic, the forth indicates an intermediate structure, and the fifth indicates a diamond structure.

Figure 5

X-ray reflectivity (XRR) measurements of the density of films with different thickness corresponding to the layers indicated in the cross-sectional image of Fig. 1. The density increases from $2.4–2.5\mathrm{g}/{\mathrm{c}\mathrm{m}}^3$ in layers 1 and 2, to 2.6 in layer 3, 2.8 in layer 4, and 3 in the diamond layer. The XRR data of polycrystalline diamond films (with two different thickness values) produced by regular hot filament CVD is given for comparison

Figure 6

SIMS depth profile of the H concentration of the film shown in Fig. 1. The hydrogen concentration is small in layers 1 and 2, increases in layer 3, and reaches a maximum in layers 4 and 5.