Calculation of Positron Annihilation Lifetime in Diamond Doped with B, Cr, Mo, Ti, W, Zr

Metal-matrix diamond composites have been extensively applied and studied, but vacancies, doping, and other defects caused by the pretreatment of the diamond surface significantly impact the interface performance between the metal base and diamond. Although techniques like transmission electron microscopy and spectroscopy analysis have been utilized for defect detection, they present certain limitations. Calculating the positron annihilation lifetime in diamond provides an accurate assessment of interface defects in the diamond. This study uses first-principles calculation methods, adopting various positron annihilation algorithms and enhancement factors, to compute the positron annihilation lifetime in ideal diamond crystals, single vacancies, and when doped with B, Cr, Mo, Ti, W, and Zr. The results, obtained using local density functional in combination with Boronski & Nieminen algorithms and RPA restriction as annihilation enhancement factors, indicate that the computed positron annihilation lifetime of diamond is 119.87ps, aligning closely with literature experimental results. Furthermore, after doping B, Cr, Mo, Ti, W, and Zr atoms in diamond (doping concentration of 1.6at%), the positron annihilation lifetime changed from a single vacancy 119.87ps to 148.57, 156.82, 119.05, 116.5, 117.62, and 115.74ps respectively. This implies that defects due to doped atoms in diamond alter its positron annihilation lifetime, with the impact varying according to the different atoms doped. Based on the calculated electron density in diamond vacancies and doped atom areas, it was discovered that doping atoms did not cause severe distortion in the diamond lattice. However, after doping B and Cr atoms, a significant increase in positron annihilation lifetime was noted. The primary reason is the relatively low positron affinity of B and Cr atoms, resulting in an extended positron residence time in the vacancy, thereby increasing the annihilation lifetime. Overall, vacancies and doped atom defects in diamond will cause changes in its positron annihilation lifetime, and the above conclusions provide crucial theoretical references for detecting and identifying interface defects caused by doping treatment on the diamond surface during the preparation of metal-matrix diamond composites.