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This work reports a method that uses a KrF excimer laser to enhance the electrical and mechanical properties of amorphous indium tin oxide (ITO) thin films on flexible substrates. Irradiation with nanosecond laser pulses induces thermal crystallization of ITO, and thereby increases the electrical conductivity and flexibility of film deposited on polyethylene terephthalate substrates. The shallow optical (~45 nm) and thermal penetration (~100 nm) of the laser beam confines the thermal effect to within the ITO layer without damaging the substrate. The laser treatment changed the crystallinity of ITO film from amorphous to poly-crystalline; as a result, its electrical-conductivity increased by 20–25%. Moreover, the treatment decreased the critical bending radius to avoid loss of electrical property from 8 mm to 5 mm. The adhesion strength and transparency of the ITO film were not affected significantly by the laser treatment. This work suggests that laser treatment can be an effective tool to enhance the crystallinity, of sputtered ITO thin film, and its electrical and mechanical properties on flexible substrate. [ABSTRACT FROM AUTHOR]

• Pulsed-laser sintering of silver nanoparticles on a flexible substrate is analyzed. • Femtosecond laser sintering is compared with nanosecond laser sintering. • Femtosecond laser sintering yields better conductivity, flexibility and adhesion. • Pulsed laser sintering can occur by inter-particle necking or by full melting. • High-fluence laser irradiation induces balling of molten silver. Pulsed-laser sintering of metal nanoparticles on flexible substrates has attracted increasing attention owing to its potential in direct printing of high-resolution patterns or fabricating flexible devices on thermally weak substrates. However, the physics of pulsed-laser sintering, including the microstructures, properties, and their correlations in different processing regimes, is not yet clearly understood. Especially, the characteristics of ultrafast laser sintering using femtosecond laser pulses without the heat accumulation effect and their comparison with those of nanosecond laser sintering are still unclear. This work analyzed the silver nanoparticle sintering process on polyethylene terephthalate substrates using a KrF nanosecond excimer laser and a Ti: sapphire femtosecond laser. The two laser sources with substantially different pulse widths were compared in terms of the sintering mechanisms, electrical conductivity, flexibility, and adhesion strength of the sintered silver films. Under optimal conditions, femtosecond laser sintering yielded better electrical conductivity and flexibility than nanosecond laser sintering. The nanosecond laser sintering occurred by solid-state diffusion (surface necking) or by full melting of the particles depending on the process condition. On the other hand, the femtosecond laser sintering took place only by inter-particle necking because the polymer substrate was damaged before melting of the particle began. [ABSTRACT FROM AUTHOR]