New Workfl ows
Figure 4 : Final thinning and polishing. (a) Sample during thinning process. (b) Finished sample after low-energy polishing at 5 keV.
Workflow design . The recipe for this semi-automated TEM sample preparation workflow was created using a visual scripting framework that enables automation of a wide range of instrument control commands and imaging tasks. The user can record customized sample preparation routines that can be saved as recipes for repetitive use. The integration of the automation software with a nanomanipu- lator (Thermo Scientific EasyLift) enables the user to easily and automatically lift the sample from the bulk material and smoothly transfer it to a TEM grid for further preparation. The design priorities for the workflow include: • Minimizing user interaction: whenever possible the microscope automatically sets the system conditions required for each recipe step.
• Requesting user input only when interaction is required for a critical recipe step.
• Permitting the user to abort the recipe at any time. • Attaching concise descriptions for each recipe step. T e workfl ow is essentially a sequence of three sub-processes: protection of the region of interest (ROI) and chunk milling; in-situ liſt -out; and fi nal thinning, including low-energy polishing (5 kV). Using the guided workfl ow, an operator can create samples that yield reliable and reproducible results and ultimately permit
2018 January •
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Figure 5 : High-angle annular dark-fi eld (HAADF) STEM images of AlGaN/ GaN/AlN multilayer collected at 300 keV using a Themis probe-corrected TEM. (a) is a survey image of the device, and (b) shows atomic columns containing Ga atoms.
confi dent conclusions about the real structure, morphology, and composition of the material being analyzed in the TEM.
Results
AlGaN/GaN/AlN Multilayer Specimen . Al x Ga 1-x N has been studied extensively in the past several years because of this material’s ability to be used as an electron blocking layer in light-emitting diode heterostructures and as an active layer in potential ultraviolet-emitting optoelectronic devices [ 7 ]. T ere
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