ALD Iridium used to fabricate Ultra-high Resolution Fresnel Zone Plates

According to US Department of Energy, Zone-plate microscopes play a crucial role in various critical science areas such as energy storage, catalysis, photovoltaics, energy conversion, and unconventional oil recovery.

• Current microscopes are limited to resolutions of 15-20 nm in the soft X-ray range and 50-70 nm in the hard X-ray range. 
• Pushing resolutions to the 5-10 nm range will have dramatic new impacts on science and technology.

Similar to the double pattering technique used today in the semiconductor industry, scientists at Paul Scherrer Institut in Switzerland employ ALD Iridium  in high aspect ratio structures to increase the resolution of Fresenel Zone Plates beyond the limit of e-beam lithography.

FIB cross section of a line doubled iridium zone plate (Figure from Paul Scherrer Institut)

"To further increase the resolution of Fresnel zone plates beyond the limits of electron-beam lithography, we have developed a novel technique based on the coating of a template structure with a metal layer. The electron-beam written template is coated uniformly with iridium using an atomic layer deposition (ALD) process (see figure 1). As iridium has a much higher x-ray refractive index as the template, we obtain a doubling of the effective zone density and subsequent improvement of the resolution by a factor of two compared to the template structure."

Complete story here: https://www.psi.ch/lmn/ultra-high-resolution-zone-plates