Osiris

Thin foils (cross-sectional) of the memory devices around the floating gates were cut by using a focused ion beam system (USA, FIB, FEI Expida1265) and milled with an ultralow current, and the microstructure was observed by using a transmission electron microscope (Netherlands, TEM, FEI Osiris). The depth profile of elemental compositions along the floating gates for understanding the distribution of dopants was determined by using a secondary ion mass spectrometer (France, SIMS, AMETEK ims-6f). The sheet resistance (R_s) of the floating gates, programing threshold voltage (V_th) and erasing voltage (V_er) were measured by using a WAT system (USA, Keysight, 4082F). The charge simulation of the floating gates was performed by the TCAD (Technology Computer-Aided Design).

Drops of boron nitride and graphene inks were dispensed on holey carbon TEM grids and then analysed in a FEI Osiris operating in bright field mode at 80 kV. A FEI Helios dual beam Focus Ion Beam/Field Emission Gun—Scanning Electron Microscope (FIB/FEG-SEM) was employed to prepare lamellae for STEM imaging and analysis. The same microscope was used for slice and view imaging. EDX data were acquired using a FEI Osiris TEM equipped with a high-brightness Schottky X-FEG gun and a Bruker Super-X EDX system composed of four silicon drift detectors, each ~30 mm² in area and arranged symmetrically around the optical axis to achieve a collection solid angle of 0.9 sr. The windowless design of the detector allows qualitative mapping of light elements. Spectrum images were acquired with an acceleration voltage of 80 kV, a spatial sampling of 10 nm pixel⁻¹ and 100 ms pixel⁻¹ dwell time. We employed multivariate analysis to localise EDX signals from compounds by applying a statistical analysis algorithm (non-negative matrix factorisation—NMF—in this case)^{78 (link)} to the EDX dataset, comprising several thousand spectra, and identifying correlations between spectral features. Data were acquired with Tecnai Imaging and Analysis (TIA) and analysed within Hyperspy⁷⁹ , an open source analysis tool-kit where statistical analysis algorithms such as NMF, are implemented.

Lamellae for TEM analysis were prepared using a FEI Helios Nanolab focused ion beam/scanning electron microscope (FIB/SEM). A 2-μm-thick capping layer was deposited to protect the film. Scanning transmission electron microscopy-High-Angle Annular Dark Field images and energy-dispersed X-ray maps were acquired on a FEI Osiris (200 kV acceleration voltage) equipped with a high-brightness field emission gun (X-FEG) and a Bruker Super-X detector.

STEM-EELS data were acquired using an FEI Osiris equipped with an X-FEG electron source and operated at 80 kV. The beam convergence was 11.0 mrad. EELS was acquired on a Gatan Enfinium spectrometer with a dispersion of 0.25 eV per channel. A 2.5 mm entrance aperture was selected, defining a collection semiangle of 17.9 mrad. Spectra were acquired in dualEELS mode with an exposure time of 0.2 s for core ionization signals and 0.0001 s for the zero loss peak and plasmon loss energies. For ADF tilt-series data, images were acquired every 3° from 70° to −52° for the particle aggregate in Figs 1 and 3 and from 69° to −72° for the particle aggregate in Fig. 4.

The crystallinity, interface, strain status, and the Si-Ge intermixing of individual Ge island were studied by a FEI Osiris (operated at 200 kV) transmission electron microscopy (TEM) system equipped with components for scanning TEM (STEM) and energy-dispersive X-ray spectroscopy (EDX) measurements. High resolution TEM (HRTEM) measurements were also performed using the FEI TITAN 80–300 Berlin Holography specially operated at 300 kV.