Nanocrystalline Ag2S on polydiacetylene Langmuir films

Silver sulfide (Ag2S) nanocrystals were prepared in ambient conditions by exposing crystalline polydiacetylene (PDA) Langmuir films at the air-AgNO3 solution interface to H2S gas. The deposited nanocrystals were studied by atomic force microscopy (AFM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), fast Fourier transform (FFT) analysis of HRTEM images, ultrahigh-resolution scanning electron microscopy (UHR-SEM), and X-ray powder diffraction (XRD). PDA Langmuir films played a dominant role in controlling the size and lateral arrangement of the chemically deposited Ag2S nanocrystals. Two distinct nanocrystal populations were obtained: small nanocrystals of ca. 8 nm in diameter arranged along the strands on the PDA film, and larger Ag2S nanocrystals of ca. 50 nm were formed in the voids between the PDA domains. The concentration of the Ag+ ions in the subphase controlled the nanocrystal film morphology and surface coverage. The linearly arranged nanocrystals were not crystallographically oriented with respect to the PDA film template, as opposed to PbS and CdS (divalent metal ion sulfides) that were previously shown to be oriented along the conjugated direction of the PDA film.