No abstract

No abstract

X-ray microscopy is a successful technique with applications in several key fields. Fresnel zone plates (FZPs) have been the optical elements driving its success, especially in the soft X-ray range. However, focusing of hard X-rays via FZPs remains a challenge. It is demonstrated here, that two multilayer type FZPs, delivered from the same multilayer deposit, focus both hard and soft X-rays with high fidelity. The results prove that these lenses can achieve at least 21 nm half-pitch resolution at 1.2 keV demonstrated by direct imaging, and sub-30 nm FWHM (fullpitch) resolution at 7.9 keV, deduced from autocorrelation analysis. Reported FZPs had more than 10% diffraction efficiency near 1.5 keV. ©2014 Optical Society of AmericaOCIS codes: (340.7460) X-ray microscopy; (340.0340) X-ray optics; (340.6720) Synchrotron radiation; (340.7480) X-rays, soft x-rays, extreme ultraviolet (EUV); (050.1965) Diffractive lenses; (220.4241) Nanostructure fabrication. References and links1. J. Vila-Comamala, Y. Pan, J. J. Lombardo, W. M. Harris, W. K. S. Chiu, C. David, and Y. Wang, "Zonedoubled Fresnel zone plates for high-resolution hard X-ray full-field transmission microscopy," J. Synchrotron Radiat. 19(5), 705-709 (2012). 2. E. Zschech, C. Wyon, C. E. Murray, and G. Schneider, "Devices, materials, and processes for nanoelectronics: characterization with advanced x-ray techniques using lab-based and synchrotron radiation sources," Adv. Eng. Mater. 13(8), 811-836 (2011 Schütz, "Fast spin-wave-mediated magnetic vortex core reversal," Phys. Rev. B 86(13), 134426 (2012). 5. J. Kirz and C. Jacobsen, "The history and future of X-ray microscopy," J. Phys. Conf. Ser. 186, 012001 (2009). 6. P. Kirkpatrick and A. V. Baez, "Formation of optical images by X-Rays," J. Opt. Soc. Am. 38(9), 766-774 (1948 International Journal of Optics 31(4), 403-413 (1984). 46. A. A. Michelson, Studies in Optics (Dover Publications, Incorporated, 1995. 47. G. R. Morrison, "Phase contrast and darkfield imaging in x-ray microscopy," Proc. SPIE 1741, 186-193 (1993).

Fresnel zone plates (FZPs) recently showed significant improvement by focusing soft X-rays down to ∼10 nm. In contrast to soft X-rays, generally a very high aspect ratio FZP is needed for efficient focusing of hard X-rays. Therefore, FZPs had limited success in the hard X-ray range owing to difficulties of manufacturing high-aspect-ratio zone plates using conventional techniques. Here, employing a method of fabrication based on atomic layer deposition (ALD) and focused ion beam (FIB) milling, FZPs with very high aspect ratios were prepared. Such multilayer FZPs with outermost zone widths of 10 and 35 nm and aspect ratios of up to 243 were tested for their focusing properties at 8 keV and shown to focus hard X-rays efficiently. This success was enabled by the outstanding layer quality thanks to ALD.Viathe use of FIB for slicing the multilayer structures, desired aspect ratios could be obtained by precisely controlling the thickness. Experimental diffraction efficiencies of multilayer FZPs fabricatedviathis combination reached up to 15.58% at 8 keV. In addition, scanning transmission X-ray microscopy experiments at 1.5 keV were carried out using one of the multilayer FZPs and resolved a 60 nm feature size. Finally, the prospective of different material combinations with various outermost zone widths at 8 and 17 keV is discussed in the light of the coupled wave theory and the thin-grating approximation. Al2O3/Ir is outlined as a promising future material candidate for extremely high resolution with a theoretical efficiency of more than 20% for as small an outermost zone width as 10 nm at 17 keV.

No abstract