SuperSTEM 1
SuperSTEM1 is based on the Cambridge VG HB 501 dedicated STEM and has a Nion Mark II Quadrupole-Octupole corrector retrofitted within the column. Electron-optic aberrations upto 3rd order are corrected. The instrument provides bright-field (BF) and high angle annular dark-field (HAADF) imaging at ~1 Å spatial resolution. Electron energy loss spectroscopy (EELS) is carried out using an UHV ENFINA spectrometer with ~0.3 eV energy resolution.
We are in the process of developing a silicon drift detector for energy dispersive X-ray (EDX) spectroscopy as well as an ex-situ gas reaction cell which would enable the sample to be transferred directly into the pole piece without a vacuum break.
Microscope parameters:
- 100 kV operating voltage (cold FEG emitter)
- 24 mrad probe semi-convergence angle after aberration correction
- 70- 210 mrad HAADF semi-convergence angles
- EELS collection semi-angles of 19, 8 and 5 mrad
SuperSTEM2 is a Nion UltraSTEM™ 100 which was specifically designed for the aberration corrected era. It is the first instrument to correct upto 5th order electron-optic aberrations. It consists of 3 condenser lenses which enables the source demagnification to be varied without producing any thermal drift (unlike the old VG microscopes). This provides the flexibility to form a 2 Å sized probe with >0.5 nA current for rapid EELS mapping at atomic spatial resolution. The post-field of the objective lens has also been optimised for efficient coupling with the EELS spectrometer. There is also a parallel illumination for spot nano-diffraction patterns as well as CTEM- style parallel imaging.
Microscope parameters:
- 100 kV operating voltage (cold FEG emitter)
- 3 condenser lenses which allow source magnification (i.e. the probe current) to be varied, and the probe convergence to be adjusted from highly convergent to parallel-illumination
- C3/C5 corrector (quadrupole-octupole design) which allows all aberrations up to and including to C5,6 to be nulled or kept very small
- Ultrastable x, y, z sample stage with smallest mechanical steps of about 1 nm and stability of the order of 0.1 nm per minute
- Computer-controlled sample exchange system that can be controlled remotely
- Sample magazine that holds up to 5 sample holders in the microscope vacuum
