Evidence for shallow implantation during the growth of bismuth nanocrystals by pulsed laser deposition

The implantation of bismuth during pulsed laser deposition (PLD) has been directly observed and investigated. Bi was deposited on amorphous aluminum oxide (Al2O3) and the laser energy density on the Bi target was varied by one order of magnitude (0.4 to 5 J cm−2). Cross-sectional transmission electron micrographs reveal that, for laser energy densities above 2 J cm−2, in addition to the formation of Bi nanocrystals, there is a dark and apparently continuous layer in the Al2O3 underneath them. From previous velocity measurements, the kinetic energy of the Bi species in the plume generated at laser energy densities above 2 J cm−2 has been estimated to be around 200 eV, which gives a calculated implantation range of 1.8 nm in Al2O3. This is in good agreement with the position of the Bi-rich layer.