The 3DAP observations were performed using a Cameca Instruments Inc. laser-assisted local electrode 3DAP (LEAP-3000XHR). To reduce the probability of tip fracture during 3DAP evaporation of the atomic layers, we used field evaporation with a laser pulse instead of an electric field pulse. The 3DAP observation conditions were as follows: laser energy of 0.5–0.6 nJ, a laser-pulse repetition rate of 250 kHz, a DC bias voltage of 4–7 kV, and a specimen temperature of 55 K. The DC voltage was automatically controlled to keep a constant evaporation rate of 0.4% at constant energy of the laser pulse. The Ga+-irradiated regions by FIB around the top of the thinned tip were fractured before 3DAP observation at a DC voltage range of 2–4 kV. The computer program IVAS3.6.1 (Cameca Instruments Inc.) was used to analyze the data. Orientations of the screw dislocations were defined with high accuracy on the basis of {111} planes of stacking faults, which were observed while mapping the same atom. Details of the methods were explained in our previous paper [7].
3DAP observation conditions
laser energy
0.5–0.6 nJ
nJ
3DAP observation conditions
laser-pulse repetition rate
250 kHz
kHz
3DAP observation conditions
DC bias voltage
4–7 kV
kV
3DAP observation conditions
specimen temperature
55 K.
K
constant evaporation rate
0.4%
%
3DAP observation
DC voltage
range of 2–4 kV
kV