Amorphization and graphitization of single-crystal diamond — A transmission electron microscopy study

a r t i c l e i n f o The amorphization and graphitization of single-crystal diamond by ion implantation were explored using transmission electron microscopy (TEM). The effect of ion implantation and annealing on the microstructure was studied in (100) diamond substrates Si + implanted at 1 MeV. At a dose of 1 × 10 15 cm − 2, implants done at 77 K showed a damage layer that evolves into amorphous pockets upon annealing at 1350 °C for 24 h whereas room temperature implants (303 K) recovered to the original defect free state upon annealing. Increasing the dose to 7 × 10 15 Si + /cm 2 at 303 K created an amorphous-carbon layer 570 ± 20 nm thick. Using a buried marker layer, it was possible to determine that the swelling associated with the amorphization process was 150 nm. From this it was calculated that the layer while obviously less dense than crystalline diamond was still 15% more dense than graphite. Electron diffraction is consistent with the as-implanted structure consisting of amorphous carbon. Upon annealing, further swelling occurs, and full graphitization is achieved between 1 and 24 h at 1350 °C as determined by both the density and electron diffraction analysis. No solid phase epitaxial recrystallization of diamond is observed. The graphite showed a preferred crystal orientation with the (002)g//(022)d. Comparison with Monte Carlo simulations suggests the critical displacement threshold for amorphization of diamond is approximately 6 ± 2 × 10 22 vacancies/cm 3. Diamond, in many crystallographic forms but especially single-crystal diamond, is gaining academic and industrial interest [1–3]. Relative to silicon (Si), diamond exhibits a significantly higher thermal conductivity (~1000× greater), a higher hole and electron mobility (3800 cm 2 /Vs vs 450 for holes and 4500 vs 1500 for electrons), and diamond holds great promise for high frequency and MEMS devices. Ion implantation of single-crystal diamond is of great interest to the micro-electrical-mechanical systems (MEMS) community for creating new single-crystal diamond devices [4,5]. Amorphization and/or graphitization of diamond via implantation is used to enable etching of sacrificial layers for diamond MEMS processing [6,7]. Even though ion implantation into single-crystal diamond has been studied for decades, [8,9] cross-sectional transmission electron microscopy (XTEM) studies of the effect of ion implantation exist [10] but are rare, due to the difficulty in making XTEM samples [11]. There are key questions surrounding the evolution of ion-implantation damage in …