On-axis Transmission Kikuchi Diffraction in SEM

Brief history

OPTIMUS TKD detector head

First proposed in 2012⁽¹⁾, Transmission Kikuchi Diffraction (TKD) in SEM, also known as t-EBSD, has quickly become an established technique due to its spatial resolution being at least one order of magnitude better than that of standard EBSD. The technique requires an electron transparent sample placed horizontally or slightly tilted, i.e. normal or close to normal to the electron beam, and a standard EBSD detector positioned so that it captures a Kikuchi pattern from below the sample plane.

Patented TKD sample holder

Recognizing the potential of this technique, Bruker started a collaboration with a team of researchers from Lorraine University in Metz, France, to address the limitations related to the non-ideal sample-detector geometry. This collaboration proved the principle for a new sample-detector geometry known as “on-axis TKD”⁽²⁾ which later resulted in the launch of OPTIMUS™ TKD detector head. The new detector head features a horizontal screen that can be inserted directly beneath the electron transparent sample with the optical axis of the SEM intersecting the screen center, thus the name “on-axis” TKD. This configuration has the advantage of capturing the Kikuchi patterns where signal yield is strongest and with minimized gnomonic projection induced distortions.

The OPTIMUS™ TKD detector head

Since its launch in 2015, OPTIMUS^TM TKD is the only commercial solution enabling on-axis TKD in the SEM and it has positioned itself as the leading TKD solution due its capabilities.

Unmatched performance
Low probe current requirements - OPTIMUS^TM TKD enables orientation and phase mapping with nanometer scale spatial resolution at hundreds of points per second using not more than 2nA probe current and with excellent data integrity or indexing quality.

Spatial resolution - With a spatial resolution of at least 2 nm (when using a high-end FE-SEM), OPTIMUS^TM TKD reveals in high detail features smaller than 10 nm and sometimes features even smaller than 5 nm (see application examples below).

Easy to use
OPTIMUS™ TKD detector head can be used interchangeably with the standard detector head on all Bruker e^-Flash EBSD detectors, giving easy access to both EBSD and TKD using the same detector. Depending on the measurement requirements e.g. spatial resolution, trained users can switch between TKD and EBSD analysis in 10-15 minutes. OPTIMUS^TM TKD works perfectly in combination with our patented TKD sample holder (EP 2824448 A1).

Raw/unprocessed orientation map from a 20 nm Au film (left) and zoomed-in area containing annealing twins ~4 nm wide. Important parameters: 30 kV EHT, 2 nA probe current, 1.5 nm steps, 11.5% zero solutions, 320 fps speed, 6:31min measurement time. Sample is courtesy of Alice Da Silva Fanta from DTU Nanolab in Copenhagen, Denmark.

Integrated ARGUS for DF & BF like imaging

To maximize performance and analysis success, OPTIMUS TKD was designed with a built-in ARGUS™ imaging system. Its high quality and high sensitivity solid state detectors give the user the option to acquire brilliant Dark and Bright Field like images with nanometer resolution at speeds of up to 125k points/sec. While being just qualitative information, these images reveal important microstructure details like: orientation and phase contrast, dislocations and stacking faults or, in certain cases, even residual strain.

False color Bright Field like (left) and Dark Field like (right) images acquired from 20nm Au film and respectively PtNi nanoparticles held together by polymer ligand

Simultaneous TKD/EDS measurements

One of Bruker’s QUANTAX EDS/EBSD system most appreciated features is its advanced integration of the two techniques. The excellent integration is of course available also for electron transparent samples and is especially powerful when combining the e^-Flash^FS and the unique XFlash^® FlatQUAD EDS detector. The two detectors provide unrivaled data quality, spatial resolution & throughput and work flawlessly with our patented TKD sample holder and the newly released X-ray mask.

TKD phase map after offline phase identification and EDS assisted reanalysis (left), patented TKD sample holder retrofitted with X-ray mask (top-right) and XFlash FlatQUAD EDS detector (bottom-right). Important parameters: 30 kV EHT, 6.7 nA probe current, 10 nm steps, 272 pps speed, 1.5 Mcps ICR, 1 Mcps OCR, <3000 counts per spectrum/pixel.