Enhanced stability and direct patterning of quantum dot films via plasma-induced ligand polymerization

Cross-linked quantum dot (QD) films fabricated via plasma-induced ligand polymerization (PILP) are proposed as an effective means of enhancing the air and moisture stability of QD films. The PILP process was performed using Ar plasma in an inductively coupled plasma (ICP) reactor. The analysis of bonding structure using Fourier transform infrared (FT-IR) spectroscopy shows that the C = C–H stretching peak of oleic acid (OA) ligands between 3010 and 3000 cm⁻¹ decreased after Ar plasma treatment, indicating C = C bond cleavage. The optical properties of QD films remained unchanged before and after Ar plasma treatment, as confirmed by photoluminescence (PL) measurements at 520 nm and a photoluminescence quantum yield (PLQY) of approximately 20%. Plasma-treated QD films retained PL intensity with reductions of only 8% in air and 20% in moisture after 350 h, compared to reductions of 59% and 80% for pristine QD films. The surface roughness decreased from 0.582 nm to 0.390 nm after Ar plasma treatment, indicating a smoother film surface with a 33% reduction, as confirmed by atomic force microscopy (AFM). The film thickness decreased from 33.6 nm to 30.4 nm after Ar plasma treatment, as confirmed by scanning electron microscopy (SEM). A stripe pattern with a 50 μm linewidth was achieved by controlling the plasma exposure area with a shadow mask, as verified by fluorescence microscopy (FM).