Combined characterization of composite tabular silver halide microcrystals by cryo-EFTEM/EELS and cryo-STEM/EDX techniques

Abstract

The combination of 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) and scanning (SEM) modes was applied for the characterization of composite tabular Ag(Br,I) microcrystals. 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. The contrast tuning under the energy‐filtering in the low‐loss region was used to image the crystal morphology, defect structure (random dislocations and {111―} stacking faults) and bend and edge contours as well as electron excitations in the microcrystals. Sharp extra reflections at commensurate positions in between the main Bragg reflections and diffuse honeycomb contours in ESD patterns of the microcrystals taken near the [111] zone were assigned to the number of defects in the shell region parallel to the grain edges and polyhedral clusters of interstitial silver cations, respectively. The imaginary part of the energy‐loss function, Im (‐1/ϵ), and the real and imaginary parts, ϵ1and ϵ2, of the dielectric permittivity were determined by means of a Kramers‐Kronig analysis. An assignment of exciton peaks based on calculations of electronic band structure of silver bromide is proposed. Inner‐shell excitation bands of silver halide were detected in line with EDX‐analyses. The energy‐loss near‐edge structure (ELNES) of the AgM4,5‐edge governed by spin‐orbital splitting between the 3d3/2‐ and 3d5/2‐states has been evaluated. Combined silver and halide distributions were obtained by a three‐window method (EFTEM) and by EDX/STEM including area mapping and line profiling of iodide. Microsc. Res. Tech. 42:108–122, 1998. © 1998 Wiley‐Liss, Inc.

Bending Contours in Silver Nanoprisms

“…An alternative source of contrast variation in nanoparticles are the so-called "bending contours", which have been reported for several types of nanoparticles and nanowires, 18 as well as in silver halide microcrystals. 19 On the other hand, authors reporting the electron diffraction analysis of gold and silver nanoprisms 8,10,20,21 have consistently found 1/3{422} spots, forbidden for a pure fcc structure (see Supporting Information, Figure S1). The presence of such forbidden spots has been assigned either to the presence of twin planes, 8,20,21 to the presence of stacking faults lying parallel to the (111) surfaces and extending across the entire nanoprisms, 22 or to a hexagonal-like monolayer on the nanoprism faces, which would slightly distort the (111) planes of the pure fcc cubic structure.…”

“…During TEM observation, these dislocation networks would be seen as band-shaped contrast variations. An alternative source of contrast variation in nanoparticles are the so-called “bending contours”, which have been reported for several types of nanoparticles and nanowires, as well as in silver halide microcrystals …”

Synthesis of Curved CuIn1–xGax(S1–ySey)2 Nanocrystals and Complete Characterization of Their Diffraction Contrast Effects

“…Although, bend contours are an artefact in TEM imaging, they provide invaluable information into the crystal structure and morphology of nanomaterials. Bend contours have previously been observed in single metal (i.e., Ag, Au, and Pt) nanocrystals, − as well as silver halide microcrystals that most commonly form in the cubic crystal structure . They have also been observed in binary nanocrystal systems with hexagonal crystal structures, specifically in ZnS − and SnO 2 nanoribbons, , SnS 2 nanoplates, and CdSe nanosaws .…”

“…Ag, Au, Pt) nanocrystals, [38][39][40] as well as silver halide microcrystals that most commonly form in the cubic crystal structure. 41 They have also been observed in binary nanocrystal systems, specifically in ZnS [42][43][44] and SnO2 nanoribbons, 45,46 SnS2 nanoplates 47 and CdSe nanosaws 48 with hexagonal crystal structures. To the best of our knowledge, this is the first observation of bend contours in a complex copper chalcogenide nanocrystal system, as well as the first report of CuIn1-xGax(S1-ySey)2 (x = y = 0.5) (CIGSSe) semiconductor nanocrystals crystallizing in the hexagonal wurtzite phase.…”