Flexible humidity sensors composed of graphite-like carbon micro-pinecone arrays

Abstract

We have prepared flexible graphite-like carbon humidity sensors at room temperature in air. Self-organized carbon micro-pinecone (CMP) arrays consisting of stacks of very thin nanosheets with thicknesses below 5–10 nm and arranged in a pinecone shape were fabricated by KrF laser irradiation of flexible polyimide sheets containing SiO₂ nanoparticles of approximately 5 nm in diameter. The Raman spectrum of CMP showed two clear bands, at 1350 cm⁻¹ (D) and 1598 cm⁻¹ (G), indicating a typical graphite-like carbon structure. Temperature simulation of photothermal heating during KrF laser irradiation of the polyimide substrate containing a single SiO₂ nanoparticle suggested that the areas surrounding the SiO₂ nanoparticle experience a much higher photothermal heating effect than other areas, leading to preferential combustion of carbon near the nanoparticles. This modulation of the photothermal heating temperature is likely strongly related to CMP formation. The obtained CMP arrays showed high sensitivity for humidity when decorated with surface noble metal nanoparticles and Pt-decorated CMP in particular showed very good response and high sensitivity.