Controlling the growth of DNTT thin film on Au substrates by surface roughness, SAM-functionalization, and temperature

HQ Li and WT Wang and WK Li and W Zhang and YJ Cheng and SY Xiong, INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 253, 127574 (2025).

DOI: 10.1016/j.ijheatmasstransfer.2025.127574

Understanding and controlling the vapor-phase deposition and growth processes of conjugated organic molecules are essential for improving the film quality and device performance of organic thin-film transistors (OTFTs). In this study, we systematically investigate the early-stage growth dynamics of dinaphtho2,3-b:2 ',3 '-fthieno3,2-b thiophene (DNTT) thin film on rough Au substrates functionalized with self- assembled monolayers (SAMs) using molecular dynamics simulations. Our investigation focuses on the effects of substrate surface roughness, SAM functionalization, and temperature on the molecular stacking orientation and film morphology. The results show that hydrophilic SAM(-COOH)-functionalized substrates can consistently form high-quality upright DNTT films, except when the substrate channels are too shallow. In contrast, hydrophobic SAM(-CH3)-functionalized substrates require smaller sizes, narrower gaps, and sufficient channel depths to achieve similar film quality. Free energy calculations highlight the importance of surface roughness and SAM functionalization in driving the formation and reorientation of DNTT molecules. Specifically, larger free energy differences between protruding areas and channel intersections on SAM(-COOH)-functionalized substrates facilitate faster seed nucleus formation and upright film growth. Additionally, higher temperatures promote molecular reorientation, but excessively high temperatures can disrupt molecular ordering and reduce film quality. These findings provide valuable theoretical insights for the fabrication of high- performance OTFTs.

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