Solvent-Engineered Stress in Nanoscale Materials?

Abstract

Nanoscale materials are frequently coated with surface stabilisation layers during growth that prevent flocculation in solution and facilitate processing technologies such ink-jet device printing. Here, we show that few-nanometer thick stabilisation layers typically used swell in the presence of certain solvents and impart significant stresses into the nanomaterial that remains even after the solvent has evaporated. Solvent-swelling of the surface layer dramatically enhances nanomaterial-substrate adhesion via the collapse of the stabilisation layer during solvent evaporation, preventing stress relaxation. We demonstrate stress modulation of Ag, Au and Si nanowires functionalised with surface polymers and surfactant layers and detect strain levels of between 0.1% and 0.6% using AFM mechanical measurement and Raman spectroscopy. Dry-transferred nanowires exhibit poor adhesion and show no evidence of incorporated stress but become stressed immediately following solvent exposure. Strain engineering is demonstrated by coating nanowires with few nanometer thick solvent-responsive polymer layers.