The Transmission X-ray Microscopy (TXM) Beamline at High Energy Photon Source

Abstract

A zone-plate-based full-field transmission X-ray microscopy (TXM) beamline has been successfully constructed and commissioned at ID30 of the High Energy Photon Source (HEPS). Based on extensive commissioning and optimization, the beamline now achieves the best spatial resolution of approximately 16 nm, which is derived from extrapolation of Fourier ring correlation (FRC) and radial power spectrum density (RPSD) analyses of imaging results of the Siemens star pattern whose finest directly resolved feature is 25 nm. This beamline is designed to provide full-field transmission imaging, absorption edge imaging, and X-ray absorption near-edge structure (XANES) imaging, revealing the 2D/3D distribution of structures, elements, and chemical valence states, respectively. To meet the stringent illumination requirements of zone-plate imaging, three key strategies were implemented: (i) selection of the red-shift radiation from the undulator source to obtain hollow-cone illumination by exploiting the ultralow emittance of the HEPS storage ring; (ii) a two-stage focusing scheme, comprising a toroidal mirror in the beamline and a beam-shaping condenser (BSC) at the end-station to achieve the illumination angle dictated by the numerical aperture of the zone plate; and (iii) a dedicated BSC design to provide a suitable imaging field of view (FOV) while delivering the required beam divergence magnification. Commissioning results confirm that the beamline specifications meet the design targets. The beamline’s capability for nanoscale structural imaging and XANES imaging is demonstrated through performance measurements and preliminary experiments, as presented in this work.