One challenge in the production of nanometer-sized objects with given properties is to control their growth at a macroscopic scale in situ and in real time. A dedicated ultrahigh-vacuum grazing-incidence small-angle x-ray scattering setup has been developed, yielding high sensitivity and dynamics. Its capabilities to derive the average particle shape and size and the film growth mode and ordering and to probe both surfaces and buried interfaces are illustrated for two prototypical cases: the model catalyst Pd/MgO(100) and the self-organized Co/Au(111) system. A wide range of technologically important systems can potentially be investigated in various gaseous environments.

The present paper focuses on the analysis of grazing incidence small-angle x-ray scattering (GISAXS) of islands on a substrate. Getting accurate morphological parameters relevant for the elaboration process, i.e., growth curves, island equilibrium shape, and interfacial energy, implies a quantitative data analysis. The emphasis is put on the island form factor, i.e., the Fourier transform of the island shape. It is shown that the island shape and size can be obtained through the island symmetry, the presence of island facets, the asymptotic behavior at high momentum transfer for large polydispersity, and the zeros or minima of the intensity for small polydispersity. The specificity brought by the grazing incidence scattering geometry is highlighted by a careful comparison between the Born approximation and the more accurate distorted wave Born approximation. The interplay between the form factor and the interference function is all the more important in the total scattering intensity when incoherent diffuse scattering comes into play at small momentum transfer for disordered systems. Getting rid of these interpretation difficulties requires accurate measurements of the scattered intensity far in the reciprocal space. This analysis methodology is illustrated through recently acquired GISAXS patterns during the in situ molecular beam epitaxy of Pd nanoislands on MgO(001) single crystals for different thicknesses and temperatures. The morphological parameters obtained agree very well with subsequent transmission electron microscopy-results. Finally, GISAXS diffuse scattering has been shown, originating from the growth-coalescence process and from the size dependence of the island capture area.

This paper compares the capability of surface differential reflectivity spectroscopy (SDRS) and grazing incidence small angle x-ray scattering (GISAXS) to characterize in situ, “at a glance,” a collection of nanoclusters by statistically defining the geometry of an average particle (diameter, height, and interparticle distance). SDRS and GISAXS are run simultaneously on Ag/MgO(001) films during their growth. They are shown to lead to consistent values of the morphological parameters, with a particular good agreement about the aspect ratio (height/diameter) which, thanks to the basic physics underlying the two measurements, is determined in both cases. By modeling silver particles by truncated spheres, close estimates of the wetting angle and of the adhesion energy are derived ($0.75\pm 0.08\text{J}{\text{m}}^{-2}$ for SDRS and $0.85\pm 0.20\text{J}{\text{m}}^{-2}$ for GISAXS). This demonstrates that the very flexible laboratory SDRS can be used to study the growth of a film in a similar way as the well-documented small angle x-ray scattering provided it is analyzed in an appropriate framework.

The growth of Ag/MgO(001) was investigated at three temperatures, 300, 540, and 640 K, in situ, in ultrahigh vacuum, by grazing incidence small angle x-ray scattering (GISAXS). The samples prepared at 300 and 540 K were also examined ex situ by transmission electron microscopy (TEM). Nucleation, growth, and coalescence are studied via the evolution of the average particle diameter, height, interparticle distance, and size distributions. Power laws are given. Size-spacing correlations are evidenced by TEM and GISAXS. A heterogeneous nucleation of silver on the defects $\left[\left(7.5\pm 1.5\right)\times {10}^{12}\text{defects}{\text{cm}}^{-2}\right]$ of the MgO surface is evidenced. Above a silver coverage of approximately 2 nm, a dynamic coalescence regime takes place involving diffusion of the islands. A value of $0.76\pm 0.1\text{J}{\text{m}}^{-2}$ for the Ag/MgO(001) adhesion energy is derived by using a Wulff-Kaishew construction from the particle shape obtained by GISAXS. The diffusion energy of Ag on MgO(001) is estimated to be $0.05\pm 0.02\text{eV}/\text{atom}$ via kinetic Monte Carlo simulations of the growth stage.