Study On The In Situ Ion Beam System In

An accelerator-TEM interface facility has been established at Wuhan University. The system consists of an H800 TEM linked to a 200kV ion implanter and a 1.7MV tandetron accelerator. Measures were taken to isolate the TEM from mechanical vibration transmitted from the ion beam lines and good resolution was maintained with the TEM machine when operated under high zoom modes during the ion implantation.Nitrogen ions at 115keV were successfully transported from the implanter into the TEM chamber through the interface system, and the ion currents measured at the entrance of the TEM column were between 20 and 180 nA. Structural evolution caused by ion irradiation in Si, GaAs, nanocrystal Ag were observed in situ. The TEM sample could be tilted by 52°and for low energy ion irradiation, real time observation was realized.The in situ observation showed that the critical implant dose for amorphization of Si is 2×1014 cm-2 and it became fully amorphized at 3×1015 cm-2. Amorphization of GaAs started at 1×1014 cm-2, whereas for nanocrystal Ag, the starting dose was 6×1014cm-2. The nuclear material C276 samples implanted with 115keV Ar+ was also studied and dislocation loops with sizes of 3-12 nm were clearly observed after implantation to doses higher than 1×1015 cm-2. The density of the loops increased with the increase in the implant dose and evolution to polycrystalline and amorphous structures were observed at 5×1015cm-2 and 3×1016cm-2, respectively.An in situ RBS/C chamber has been installed on the transport line of the accelerator-TEM interface system. This makes it possible to in situ measure composition and location of impurities in the lattice of the implanted samples. In addition, a 50kV low-energy gaseous ion generator was installed close to the TEM chamber, which facilitates in situ TEM observation of helium bubbles formed in materials by helium implantation.A computer-automated Rutherford backscattering/channeling (RBS/C) system has been developed to provide in situ ion beam analysis. The basic system components are a PC equipped with a multichannel analyzer data acquisition board, motion control hardware including the Panmure stepping motor controller and integrated circuit modules, and a Lab VIEW programmed operating system with associated electronics.