Helios g3 uc

A 100 × 100 µm² Si₃N₄ membrane with a thickness of 50 nm was used as a base for the mask fabrication. After coating it with 50 nm of copper (thermal evaporation) from the backside to support charge dissipation during the structuring process, a focused Ga⁺ ion beam (FEI Helios G3 UC, 30 keV, 80 pA) was scanned over the Si₃N₄ surface to etch the desired aperture through the membrane and the copper layer. For this purpose, a black and white bitmap was used to define the structure consisting of 1024 × 1024 pixels with a pitch of 12 nm by toggling the exposure time between 0 and 200 µs for black and white pixels, respectively. The writing was done within a single pass. Afterward, additional 220 nm of copper were deposited on the backside to achieve a final absorber thickness of 270 nm Cu + 50 nm Si₃N₄. Finally, the aperture shape was confirmed using STEM.

The cross-sectional transmission electron microscopy (TEM) samples, and cross-sections for scanning electron microscopy (SEM) imaging were prepared with a FEI Helios G3 UC focused ion beam scanning electron microscope (FIB-SEM). Both the cross-sectional TEM lamellae and cross-sections were prepared using 30 keV Ga⁺ ion beam and different beam currents (9 nA to 40 pA). Secondary electron (SE) images of the cross-sections were taken under low keV (2 keV) electron beam and high-resolution immersion mode using a through lens detector (TLD). To prevent charging during the FIB-SEM study, the sample was coated with a thin layer of carbon by means of a carbon thread evaporator. A FEI Talos F200X TEM equipped with a four-quadrant silicon drift detector system for energy dispersive X-Ray spectroscopy [Super-X(FEI)] system was used for taking high angle annular dark field (HAADF) images and to perform EDS analysis on 10 µm × 100 nm lamellae. Spectrum images (SI) were acquired using a 1 nA beam current and dwell time of 10 µs per pixel. Resolution was 512 × 512 pixels with a pixel size of 766 pm. To get a better signal-to-noise ratio integrated intensities of over 1000 drift corrected SI were used.

Metamaterial emitters with W and HfO₂ thin films were fabricated on 5 × 5 mm² single crystalline sapphire substrates ([1–102] orientation) by radio frequency and direct current magnetron sputtering at a rate of 0.2 and 0.09 nm s⁻¹, respectively. All the layers are grown sequentially at argon (99.99999%) gas pressure of 2 × 10⁻³ mbar. The W and HfO₂ sputtering targets with 99.95% purity were purchased from Sindlhauser Materials. Cross-sectional SEM images of the emitter structures were prepared using a focused-ion beam (FIB, FEI Helios G3 UC) operating at 30 keV. The secondary electron images were taken under low kV (2 kV) and high-resolution immersion mode using a through lens detector (TLD).