Diffusion-Induced Thickness Thinning of Spin-Coated Films in Crystalline Grain Boundaries: A Process of Amorphization

Complex molecular-level interactions of receptor molecules with semiconducting channels are often engineered to achieve higher sensitivity. However, integrating receptors in the sensor's semiconducting channel introduces deformation in crystallinity leading to poor device performance. In this work, the authors have shown how the growth of a peptide-based receptor molecule in the grain boundaries of pentacene semiconducting films can be controlled to maintain crystallinity with better integration. Pentacene has a bulk and a thin-film crystallographic phases with approximate to 5.8% higher lattice constant. As the receptor molecules diffuse into the grain boundaries, they systematically start impairing the thin-film crystalline phase to bulk depending on the amount of mass transport, ushering to a complete amorphization at higher doses of diffusion. A statistical analysis of rough surfaces has been conducted to study the evolution of thin-film morphology, which is connected to the diffusion of the spin-coated film. Besides, a thickness thinning of the spin-coated film is observed due to diffusion-related mass transport into grain boundaries, which has been explained with a new thickness thinning rate equation. The damage in the crystalline quality is confirmed qualitatively with residual compressive strain developed due to the diffusion of molecules into grain boundaries.