Versatile X-ray reflector extension setup for grazing-incidence experiments at SAXS facilities for liquid surface study

Abstract

Existing beamlines for in situ grazing-incidence small-angle scattering on liquids are either limited in angular range or incompatible with the large sample-detector distance required for submicrometre resolution. We present a low-cost, easily assembled beam-tilting extension for synchrotron-based ultra-small-angle X-ray scattering (USAXS) facilities, enabling grazing-incidence and transmitted scattering (GIUSAXS, GTUSAXS) studies on liquid surfaces. The setup is compatible with standard USAXS beamlines and requires only ∼0.5 m of additional space at the sample stage. It allows X-ray beam incidence angles of up to ∼0.6° at the liquid surface, equal to twice the angle of incidence on a reflector and below its critical angle of typical materials (e.g. silicon, germanium, etc.), and provides access to a q-range of approximately 0.003-0.5 nm^-1. The system was tested at P03 beamline (DESY) using polystyrene nanoparticles (∼197 nm) self-assembled at the air/water interface. The recorded GIUSAXS and GTSAXS patterns revealed features characteristic of near-surface hexagonally ordered monolayers and multilayer assemblies, validating the system's resolution and sensitivity. The proposed scheme enables selective depth profiling and expands the research capabilities of existing small-angle X-ray scattering synchrotron facilities for in situ studyies of submicrometre nanostructured objects at liquid surfaces under grazing-incidence geometry, while remaining fully compatible with complementary techniques such as grazing-incidence wide-angle scattering and total reflection X-ray fluorescence.

Keywords: GISAXS; GTSAXS; X-ray reflector; beam tilting; colloid; grazing-incidence X-ray scattering; grazing-incidence small-angle X-ray scattering; liquid interface; liquid surface.

Figure 1

Schematic representation of the reflector and sample assembly combination for the USAXS setup. The reflector is positioned on a specialized holder mounted on a hexapod with six degrees of freedom. The Teflon liquid trough is mounted on the sample stage with the possibility of adjusting the horizontal position of the trough, as well as adjusting the air/liquid interface level in height and moving the sample perpendicular to the beam axis.

Figure 2

(a) Sketch of the reflector holder. The main (lower) part of the holder is designed for mounting the reflector plate at the top above the slot, reflective side down. The upper part is designed for soft pressing of the reflector by plastic screws to the main part of the holder. (b) Silicon reflector at final assembly, mounted on the hexapod in the experimental hutch.

Figure 3

(a) General view of the setup with the realized scheme of tilting the X-ray beam onto a liquid surface for the USAXS study inside the experimental hutch EH1 of the P03 station at the PETRA III synchrotron (DESY, Hamburg, Germany). (b) The reflector assembly was placed on the hexapod and the sample assembly was placed on the Huber sample stage (side view). Propagation directions of a collimated monochromatic X-ray beam focused on the reflector. The vertical axes of the reflector and the sample are shown by yellow dashed-dotted lines.

Figure 4

The geometry of the three different steps of the beam tilting procedure with the beam axes, main reflecting blocks and corresponding scattering image at the detector: (a) initial direct beam, (b) beam tilted by the reflector, and (c) transmitted and reflected beam from the liquid interface.

Figure 5

AFM 3D image of the PPS colloid agglomerate, transferred from the air/water interface after the X-ray experiment.

Figure 6

The PPS assembly under the air/water interface model and incident/reflected and transmitted X-ray beam (a), and 2D GISAXS/GTSAXS diffraction image (b)

Figure 7

(a) Horizontal line cut I(q_y) at q_z = 0.145 nm⁻¹. (b) Vertical line cut I(q_z) at q_y = 0.0335 nm⁻¹.

Figure 8

IsGISAXS simulation of representative GIUSAXS scattering patterns of 200 nm polystyrene nanoparticles self-assembled in a 2D-hexagonal lattice directly floating (a) on top and (b) below the air/water interface. The corresponding scattering intensity, scattering vectors as scale bars, and scattering geometry are indicated.