A novel experimental approach for nanostructure analysis: simultaneous small-angle X-ray and neutron scattering

Abstract

Exploiting small-angle X-ray and neutron scattering (SAXS/SANS) on the same sample volume at the same time provides complementary nanoscale structural information in two different contrast situations. Unlike an independent experimental approach, the truly combined SAXS/SANS experimental approach ensures the exactness of the probed samples, particularly for in situ studies. Here, an advanced portable SAXS system that is dimensionally suitable for installation in the D22 zone of ILL is introduced. The SAXS apparatus is based on a Rigaku switchable copper/molybdenum microfocus rotating-anode X-ray generator and a DECTRIS detector with a changeable sample-to-detector distance of up to 1.6 m in a vacuum chamber. A case study is presented to demonstrate the uniqueness of the newly established method. Temporal structural rearrangements of both the organic stabilizing agent and organically capped gold colloidal particles during gold nanoparticle growth are simultaneously probed, enabling the immediate acquisition of correlated structural information. The new nano-analytical method will open the way for real-time investigations of a wide range of innovative nanomaterials and will enable comprehensive in situ studies on biological systems. The potential development of a fully automated SAXS/SANS system with a common control environment and additional sample environments, permitting a continual and efficient operation of the system by ILL users, is also introduced.

Keywords: SANS; SAS; SAXS; nanomaterials; small-angle X-ray scattering; small-angle neutron scattering.

Figure 1

(a) Photograph of the portable SAXS instrument for simultaneous SAXS/SANS measurements at D22–ILL. (b) Six-axis goniometer for correct sample alignment with respect to both X-ray and neutron beams. (c) EIGER R 1M detector with three degrees of freedom to move inside the vacuum chamber. (d) The central hub for easy and smooth plug-and-play operation, including power supplies, cooling water and ethernet cable. All system components are enclosed within a single heavy-duty metal non-magnetic chassis.

Figure 2

(a) Center and (b) off-center accessible q ranges at different SDDs for both Cu Kα and Mo Kα radiation. When the direct beam is on the detector’s active area (center position), q _min (the smallest scattering angle) is assumed to be at a value of 4 × FWHM of direct beam intensity. For the off-center configuration, scaled representations of the detector vacuum tube (black semicircle) and detector active area (yellow rectangles) for two different SDDs (523 and 1613 mm) are shown. The blue (Cu Kα) and red (Mo Kα) semicircles represent scattering rings at different accessible q values (nm⁻¹) and their relative positions on the detector’s active area.

Figure 3

(a) Photograph of the SAXS instrument installed at the D22 instrument (ILL) for simultaneous SAXS/SANS experiment. (b) A sample at an angle of 45° relative to both orthogonal neutron and X-ray beams. Lead shielding can be seen (1) on the front of the detector vacuum chamber, (2) along the neutron collimation and (3) on the side of the vacuum chamber of the X-ray detector. The red and yellow arrows indicate the directions of the X-ray and neutron beams, respectively.

Figure 4

2D SAXS patterns of silver behenate (Agbh) at three different SDDs of (a) 1613 mm, (b) 802 mm and (c) 523 mm, indicating a SAXS q range between 0.04 and 4.4 nm⁻¹. (d) Azimuthally averaged SAXS data of Agbh showing overlapping data along the three employed SDDs.

Figure 5

(a) Azimuthally averaged SAXS data of the empty cell (EC, black), a 1 mm-thick water layer (red) sandwiched between two mica windows (cell), the detector dark noise (green) and a sample of platelet-shaped tripalmitin nanocrystals (TP NCs) in water (blue) collected at SDD = 1613 mm. The 1D SAXS profiles of (b) platelet-shaped tripalmitin nanocrystals and (c) colloidal silica NPs (Ludox TM50; average size = 26 ± 2 nm) collected at different SDDs. Data were plotted and overlapped over different q ranges on an absolute scale. The insets are the corresponding 2D SAXS patterns.

Figure 6

1D SAXS profiles calculated from the 2D detector images of silica NPs (100 nm) recorded with an open (red; simultaneous SAXS/SANS mode) and a closed (blue; standalone SAXS mode) neutron shutter for different neutron collimation lengths and X-ray sample-to-detector (SD_xray) distances. Owing to the reduced neutron flux, the radiation background is insignificant on the X-ray detector for (a) a long collimation length, while for (b) intermediate and (c) short collimation lengths significant background radiation is observed for q > 0.31 nm⁻¹. The intensity is plotted as an intensity normalized to the direct beam intensity with no background radiation subtraction for comparison purposes.

Figure 7

1D SANS profiles of 100 nm silica NPs collected at two different sample angles. The scattering profile corrected by multiplying each data point of the sample measured at a 45° angle by 1 mm × 2^1/2 is perfectly coincident with that collected at a 90° angle.

Figure 8

Time evolution of (a) SAXS and (b) SANS 1D profiles during the in situ reduction process of a gold solution at 308 K. Insets show 2D (a) SAXS and (b) SANS patterns during hydroquinone synthesis of Au NPs. (c) Rod-like Au particle radius and length as a function of reaction time, as revealed from the SAXS data fitting. The inset in (c) is a TEM image of the Au particles, with average radius and length of about 8 and 60 nm, respectively; the scale bar is 100 nm. (d) The exponential volume fraction decay of the CTAB micelles with time, as obtained from SANS data fitting.