## 4 Summary and Outlook  
By means of various X-ray diffraction and scattering experiments, we have shown that the characterization of the film formation and film growth, and especially to follow the crystallization, is feasible in real time, thus adding the important dimension to the fundamental understanding of the evolution of the film micro structure. Furthermore, these techniques were used to study the crystallization dependence of the deposition process and the growth on SiO\({}_{2}\) substrate material. It is observed that the whole evolution from nucleation, diffusion adsorption and grain growth to the crystallization can be observed during all stages of thin film growth as well as quantitatively as qualitatively using the prototypical showcase of BaTiO\({}_{3}\). Investigations of various parameters of the deposition process and their influence on the crystallization such as surface structure and deposition temperature was also performed and will be published elsewhere. A logical next step would be a in situ study of the deposition and crystallization using the thin film pair distribution function analysis (tfPDF) [21].  
[PERSON] has conceived the experiment. The experiment was performed by [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and U.K. The data was analyzed by [PERSON] The original draft was written by [PERSON] with dedicated contributions by [PERSON] and U.K. All authors have read and agreed to the published version of the manuscript.  
SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76 SF00515. We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at P03 at PETRA III. M.I. acknowledges funding from the Volkswagen Foundation within a [PERSON].  
Raw data were generated at PETRA III at DESY, Hamburg, large scale facility. Derived data supporting the findings of this study are available from the corresponding author upon reasonable request.  
The authors gratefully acknowledge [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] and the FS-EC group. Because of their work and efforts the sputtering unit is operational. We further thank [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] from the FS-PE group and the Aarhus University for fruitful discussions and help during the beam time at P03. For help in creating the graphic Figure 1. we are indebted to [PERSON].  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.  
Figure 8: Schematic of the BaTiO\({}_{3}\) thin film evolution over time above the crystallization temperature. Showing, as described in detail in the text, the early formation (nucleation, diffusion, adsorption and grain growth) towards the crystallization inside the amorphous clusters, towards the growing poly-crystalline cluster grow, up to the poly-crystalline final thin film grow with on coming amorphous BaTiO\({}_{3}\).