Minimization of amorphous layer in Ar+ ion milling for UHR-EM

We present a comprehensive study on the influence of Ar(+) ion milling parameters in the range of low acceleration voltages (0.5-6 kV) and etching angles (3-10(°)) on the quality of standard high resolution Si TEM samples. The quality was assessed by the evaluation of HR-TEM images acquired from real TEM samples considering the thickness of the amorphous layer and the interlocking between crystalline and amorphous parts of the sample created by ion-beam induced amorphization, as well as topographical BSE-SEM investigation of the surface of those TEM samples. Increasing voltage clearly results in increased amorphous layer thickness as well as interlocking. The impact of the etching angle is less significant but still influences the amorphous layer thickness. It has, however, a strong effect on the preparation time, which is inversely correlated to the etching angle. Finally the experimental data were compared to model estimations by TRIM and the Schuhrke-Winterbon approximation, which fitted well to the experimental data for low voltage and angle, but were less accurate for higher voltage and angle. Despite their limitations, the models could reproduce trend and order of magnitude of the data, thus making them a useful tool for estimating the amorphous layer thickness after TEM sample preparation.