Enabling Nano-Scale TKD Mapping in Immersion/UHR Mode of Certain FE-SEMs

See Every Detail in your Nanostructured Sample

The recent massive adoption of nanotechnology has triggered a race for the highest resolution in Scanning Electron Microscopy (SEM). One approach for achieving the ultimate spatial resolution uses a Magnetic Immersion Lens. Previously, the use of an immersion lens made orientation mapping impossible. This is because the magnetic field created by the lens interferes with the Transmission Kikuchi Pattern (TKP) collection and analysis process. The interference has two major components:

The scattered electrons are constrained within a narrow space around the optical axis of the SEM (see TKP "with field" below).
The Kikuchi patterns are distorted, rotated and shifted by the magnetic field.

First, the Kikuchi signal is reduced to a region expanding up to 10 mm from the optical axis of the SEM. This containment of electrons around the optical axis means that very few scattered electrons will reach a standard EBSD detector which typically places its phosphor screen at distances greater than 15 mm from the optical axis of the SEM. On-axis TKD technique enabled by OPTIMUS 2 solves this issue by capturing the Kikuchi patterns from around the SEM optical axis.

Second, the heavy distortions created by the magnetic field’s presence in the TKPs, render impossible an accurate band detection. To correct the distortions and compensate for the rotations and shifts in the TKPs, we have developed a new software feature (patent pending) called ESPRIT FIL TKD (Full Immersion Lens TKD). The feature is easy to calibrate and has been fully integrated in the automatic map acquisition process of ESPRIT 2 software.

The combination of FIL TKD feature with on-axis TKD makes possible accurate orientation mapping using high-end FE-SEMs while operating in their ultra-high resolution mode, i.e. with the immersion lens active.

Fig. 1a: Non-corrected Transmission Kikuchi Pattern (TKP) acquired using on-axis TKD geometry in the presence of the magnetic field

Fig. 1b: TKP from Fig.1 (left) after correction using FIL-TKD

Fig. 1c: For comparison with Fig.1 (center) - TKP acquired from the same grain but without magnetic field, i.e. immersion lens was inactive

The end result or benefit of this unique combination of HW & SW options is clearly visible in the TKD results shown in Fig. 2 (*). The Pattern Quality maps (left) demonstrate qualitatively that the physical spatial resolution is far better when activating the immersion lens (much sharper features). Grains/features finer than 10 nm can be clearly seen in the orientation map acquired with the immersion lens active.

Contact an expert Learn more about QUANTAX EBSD

Fig. 2: Raw on-axis TKD maps of the same region acquired from a 20 nm Au thin film without magnetic field, a.k.a. analytical mode (top) and with magnetic field a.k.a. ultra-high-resolution mode (bottom). Both maps were acquired using the same parameters for probe current, accelerating voltage, TKD detector settings and step size of 3 nm. The scale bar represents 100 nm. No data cleaning was applied to the orientation maps. Results are courtesy of Alice Da Silva Fanta from DTU Nanolab in Denmark.

_{(*) The results presented here should be taken qualitatively and not as a resolution specification of our TKD solution and/or that of a certain brand of SEMs. The difference in TKD map resolution and indexing quality between immersion and non-immersion modes of relevant SEMs may vary depending on the model and/or make as well as the room environment, e.g. temperature, ground vibrations, acoustics, etc.}