Π-GISANS: probing lateral structures with a fan shaped beam

Abstract

We have performed grazing incidence neutron small angle scattering using a fan shaped incident beam focused along one dimension. This allows significantly reduced counting times for measurements of lateral correlations parallel to an interface or in a thin film where limited depth resolution is required. We resolve the structure factor of iron inclusions in aluminium oxide and show that the ordering of silica particles deposited on a silicon substrate depends on their size. We report hexagonal packing for 50 nm but not for 200 nm silica spheres deposited by a modified Langmuir-Schaefer method on a silicon substrate. For the 200 nm particles we extract the particles shape from the form factor. Moreover, we report dense packing of the particles spread on a free water surface. We name this method π-GISANS to highlight that it differs from GISANS as it gives lateral information while averaging the in-depth structure.

Figure 1

Sketch of the focusing and collimation systems of the instrument Super ADAM.

Figure 2

Sketch of the scattering geometry for one-dimensional (π-GISANS) studies.

Figure 3

π-GISANS data taken on Super ADAM with a sample of a porous aluminum oxide film with the pores filled with iron. The left panel depicts the image on the PSD of Super ADAM with the individual monochromator crystals well visible. The center panel depicts a zoom into the detector image to highlight the internal structure of the wire detector. The panel on the right hand side depicts the vertically integrated data revealing Bragg scattering from the iron arranged in a hexagonal lattice.

Figure 4

π-GISANS data taken on Super ADAM with silica particles, of size 200 nm (a), 100 nm (b) and 50 nm (c, d), deposited on a silicon wafer and shown as red circles. The grey open circles symbolise a measurement performed with a bare silicon substrate. The solid black lines represent simulations of the form (a, b, c) and structure factor (d) of the particles.

Figure 5

π-GISANS data taken on Super ADAM for 100 nm silica particles self-organised on a D₂O surface. The panel to the left depicts the raw 2D-detector image with the regions of interest for the signal and background indicated. The panel to the right is the same data but vertically integrated over the respective regions of interest. The GISANS signal minus the background is plotted versus Q_y on a linear scale.