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As a branch of laser powder bed fusion, selective laser sintering (SLS) with femtosecond (fs) lasers and metal nanoparticles (NPs) can achieve high precision and dense submicron features with reduced residual stress, due to the extremely short pulse duration. Successful sintering of metal NPs with fs laser is challenging due to the ablation caused by hot electron effects. In this study, a double-pulse sintering strategy with a pair of time- delayed fs-laser pulses is proposed for controlling the electron temperature while still maintaining a high enough lattice temperature. We demonstrate that when delay time is slightly longer than the electron-phonon coupling time of Cu NPs, the ablation area was drastically reduced and the power window for successful sintering was extended by about two times. Simultaneously, the heat-affected zone can be reduced by 66% (area). This new strategy can be adopted for all the SLS processes with fs laser and unlock the power of SLS with fs lasers for future applications. 

A general method is developed for removal of native nonpolar oleate ligands from colloidal metal oxide nanocrystals of varying morphologies and compositions. Ligand stripping occurs by phase transfer into potassium hydroxide solution, yielding stable aqueous dispersions with little nanocrystal aggregation and without significant changes to the nanomaterials’ physical or chemical properties. This method enables facile fabrication of conductive films of ligand-free nanocrystals.