New Workfl ows
Figure 6 : X-ray element maps of specimen area in Figure 5a collected at 300 keV using a SuperX detector on a Themis probe-corrected TEM. The image at the left is a STEM HAADF image followed by the Ga map, Al map, N map, and a composite map of Ga and Al maps. From these maps the features in the STEM image can be determined: bright regions are GaN, gray regions are GaAlN, and dark regions are AlN.
have been many attempts to produce both n-type and p-type conductivity thin fi lms with mole fractions of x in the range of 0.35–0.6, but growth is challenging because of the high stress state of the fi lms [ 8 ].
In this example, interfacial stress within the mulilayer stack is examined by TEM for a given mole fraction to understand how growth conditions aff ect the thin fi lms. T e sample was prepared on a T ermo Scientifi c Helios G4 FX DualBeam FIB-SEM. Step 1: Protection of ROI and chunk milling. In a fi rst step, the user interactively confi gures the lamella dimensions and milling conditions for the sample to be created. Aſt er locating the area of interest, the system automatically mills fi ducial markers that will be used for accurate visual end-pointing during the fi nal thinning stages of the workfl ow (note the patterned cross next to the lamella site in Figure 1 . Next, the user selects the fi ducial marker to determine the position of the deposition layer that protects the chunk sample during the milling process ( Figure 1a ). Aſt er the system automatically deposits the protective layer, the user selects the fi ducial marker for bulk milling of the chunk at high beam current. T e system automatically completes the bulk milling step
and cleans up sputtered material redeposited on sample surface near the milling site ( Figure 1b ). T e stage is tilted so the chunk can be separated from the bulk sample in the undercut step. Step 2: In-situ liſt -out To ensure that the sample is at the eucentric position and coincident with the beam position, the user is prompted to select the fi ducial marker with the SEM image and then the FIB image to align the stage for liſt -out. T is position will be used as a reference for the liſt -out process and helps the user to safely operate the nanomanipulator. Next, the user selects the probe tip of the nanomanipular in the SEM image and aligns it in X and Y directions. T e user is then prompted to select the probe tip in the FIB image to align the Z direction and lower the probe in two steps. T e probe has thus been accurately positioned with respect to the sample with only three point-and-click movements. Aſt er accurately aligning the probe tip of the nanomanipulator, the user is prompted to confi rm the position of the welding pattern that will attach the chunk to the probe tip, and the system executes the attachment procedure ( Figure 2a ). Prior to in-situ liſt -out, small crosses are patterned onto the top of the TEM section to assist with fi nal thinning of the section. Next, the user confi rms the position of the right-side cut pattern to prepare the chunk to be released from the bulk. T e system then cuts the chunk free from the bulk and extracts it to a safe position ( Figure 2b ).
Figure 7 : HAADF STEM and spectra at 300 keV from two areas of the X-ray spectrum image. Raw spectral data from the GaN area (red) and the AlN area (blue box) indicate the identity of these phases.
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Step 3: Grid attachment T e user is asked to move the stage to bring a 3-millimeter TEM grid into position, and the user selects the correct chunk attachment location on the grid in a series of prompts identifying the position with the SEM and FIB that ensures the grid is at the eucentric and beam coincident position. In order to attach the chunk sample to the TEM grid, the user selects the position of the
www.microscopy-today.com • 2018 January
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