In situ study of the precursor conversion reactions during solventless synthesis of Co ₉ S ₈ , Ni ₃ S ₂ , Co and Ni nanowires

Synthesis of Co9S8, Ni3S2, Co and Ni nanowires by solventless thermolysis of a mixture of metal(ii) acetate and cysteine in vacuum is reported. The simple precursor system enables the nanowire phase to be tuned from pure metal (Co or Ni) to metal sulfide (Co9S8, Ni3S2) by varying the relative concentration of the metal(ii) acetate. The growth environment facilitates new insights through in situ characterization using field-emission scanning electron microscopy (FESEM) and thermogravimetric analysis with gas chromatography-mass spectrometry (TGA-GC-MS). Direct observation by FESEM shows the temperature at which nanowire growth occurs and suggests adatoms are incorporated into the base of the growing nanowire. TGA-GC-MS reveals the rates of precursor decomposition and identity of the volatilized ligand fragments during heat-up and at the nanowire growth temperature. Our results constitute a new approach for the selective fabrication of high quality Co9S8 and Ni3S2 nanowires and more importantly provides new understanding of precursor decomposition reactions that support symmetry-breaking growth in nanocrystals by heat-up synthesis.