Abstract
We investigate the kinetics of elemental segregation during the synthesis of Cu(In1-x,Ga-x)Se-2 (CIGS) thin films via a rapid thermal growth process. Changes in elemental concentration are mapped rapidly via in situ X-ray fluorescence (XRF) microscopy. In situ XRF enables the quantification of Cu, In, Ga, and Se concentrations with 200 nm spatial resolution over a region of 7 mu m X 7 mu m, large enough to map multiple CIGS grains. Reacting elemental precursor stacks at 500,550, and 600 degrees C, we find that copper is the driving force for alpha-CIGS phase formation at a rate of 17 nmol/cm(2)/min at 500 degrees C. Because of the thermal expansion of the substrate, cluster analysis and classification algorithms were employed to track compositionally similar regions over time and across samples measured at different temperatures. Beyond the direct application of these results for the optimization of CIGS manufacturing, these in situ experiments demonstrate the feasibility of quantitative compositional evaluation at the nanoscale during the synthesis of technologically relevant materials. In combination with advanced analysis methods, this example shows how correlative X-ray microscopy can contribute to the solution of the materials paradigm, relating synthesis to composition and properties at the nanoscale.