Atomic structural characterization of multiple quantum wells by aberration-corrected STEM

Summary form only given. Resolving and identifying the structure and composition of atoms in a solid material at atomic resolution has been a long-standing goal of analytical microscopy. Controlling crystalline interfaces at the atomic scale is now actively being research in the broader range of materials science and device engineering fields. However, the atomic resolution of electron optics instrument was limited by the unavoidable aberration. Aberration corrected scanning transmission electron microscope (STEM) equipped with electron energy loss spectrometer (EELS) and energy distribution spectrometer (EDS) has proved most effective in measuring not only image of atom arrangement, but also the chemical composition. High resolution power provides much improved sensitivity to atomic arrangements at defects and interfaces, down to the atomic level. The epitaxial multiple quantum wells (MQWs) were grown by ultra-high vacuum chemical vapor deposition (UHV-CVD) on a single crystalline SiGe/Si (111) substrate. Aberration corrected scanning transmittance electron microscopy equipped the high bright electron gun, high angle annular dark field (HAADF) detector, and EDS was used to analysis the atomic structure of MQWs interface. The defocus (C1) and aberration coefficients of electronic optics system such as astigmatism (A1, A2, A3, A5), coma (B2, B4), spherical aberration (C3, C5), and star aberration (S3) were corrected preciously by changing the convergence angle of electron beam probe (18 and 25 mrad) [1-2]. It was found that the distance between dumbbell Si and Ge atoms is around 0.136 nm which directly measured by the HRSTEM HAADF image. The corresponding FFT shows the point resolution was around 0.78 Å (subÅ). In addition, the interfacial layer was composed of silicon atoms, which connected coherently with the epitaxial SiGe/Si MQWs. This interfacial layer contained a few atomic percent of Ge, the atoms of which had been diffused from the high quality crystalline Si0.81Ge0.19 layer. Furthermore, the atoms can be quantitatively counted; their relative position in chemical composition could be direct visualizing determined. The experimental results also demonstrated that complementary atomic-resolution EDS line-scan signal in HRSTEM HAADF image(Fig. 1 (a). The HAADF image of light element N atom also observed directely by using aberration-corrected STEM at atomic resolution as shown in Fig. 1 (b).These results provide an effective approach to investigate structural chemical in real space.