High-speed x-ray reflectometry for characterization of thin film growth at high deposition rates

We present a high-throughput, real-time study of PTCDI- <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msub> <a:mi mathvariant="normal">C</a:mi> <a:mn>8</a:mn> </a:msub> </a:math> thin film growth using quick x-ray reflectivity (qXRR) with 12 ms time resolution, combined with machine learning-based analysis. qXRR enables monitoring of vacuum deposition at growth rates from 1 to <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:mn>30</c:mn> <c:mspace width="0.16em"/> <c:mo>Å</c:mo> <c:mo>/</c:mo> <c:mi mathvariant="normal">s</c:mi> </c:mrow> </c:math> , accessing a previously unexplored regime in molecular beam deposition. To efficiently analyze the resulting <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"> <f:mrow> <f:mo>∼</f:mo> <f:mn>20</f:mn> <f:mspace width="0.16em"/> <f:mn>000</f:mn> </f:mrow> </f:math> reflectivity curves, we employ a convolutional neural network trained on a physics-informed multilayer model. This approach robustly extracts key structural parameters—including thickness, roughness, and crystalline versus amorphous content—from noisy data. We quantify interface roughness as a function of both film thickness and growth rate, identifying rapid roughening with a scaling exponent of <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"> <h:mrow> <h:mi>β</h:mi> <h:mo>=</h:mo> <h:mn>0.62</h:mn> </h:mrow> </h:math> with film thickness and a secondary scaling exponent of <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"> <i:mrow> <i:mi>γ</i:mi> <i:mo>=</i:mo> <i:mn>0.21</i:mn> </i:mrow> </i:math> with growth rate. Additionally, we observe a reduction in the coherently ordered film thickness and a rise in amorphous content at higher deposition rates. These results demonstrate that combining qXRR with machine learning provides quantitative access to fast kinetic growth processes, offering a powerful tool for characterization and morphological control in organic thin film fabrication.