Structural and analytical characterization of Ag(Br,I) nanocrystals by CRYO-AEM techniques

Abstract

The morphology, crystalline and electronic structures and elemental compositions of AgX (X = Br,I) nanocrystals of 20–185 nm in diameter have been evaluated by cryo-energy-filtering transmission electron microscopy (EFTEM)/electron spectroscopic diffraction (ESD)/ electron energy-loss spectroscopy (EELS) and cryo-energy-dispersive X-ray (EDX) analysis in the scanning transmission (STEM) mode. A low-loss fine structure in EEL spectra between 4 and 26 eV was attributed to excitons and plasmons possibly superimposed with interband transitions and many-electron effects. Contrast tuning under energy filtering was used to image electron excitations in the AgX nanoparticles. Intensity oscillations caused by size-confined coupling of surface and volume losses were observed. The real and imaginary parts, ε 1 and ε 2, of dielectric permittivity were determined using Kramers-Kronig relations. The exciton peaks were assigned based on calculations of electronic band structure of AgBr. Combined silver and halide distributions were obtained by electron spectroscopic imaging (three-window method) and by STEM/EDX including high-magnification X-ray mapping of the individual nanocrystals.