Ptychographic Imaging of Branched Colloidal Nanocrystals Embedded in Free-Standing Thick Polystyrene Films

Abstract

Research on composite materials is facing, among others, the challenging task of incorporating nanocrystals, and their superstructures, in polymer matrices. Electron microscopy can typically image nanometre-scale structures embedded in thin polymer films, but not in films that are micron size thick. Here, X-ray Ptychography was used to visualize, with a resolution of a few tens of nanometers, how CdSe/CdS octapod-shaped nanocrystals self-assemble in polystyrene films of 24 ± 4 μm, providing a unique means for non-destructive investigation of nanoparticles distribution and organization in thick polymer films.

Materials characterization by synchrotron x-ray microprobes and nanoprobes

“…PCDI has no limitation on the sample extension and therefore it has been largely applied: it was adopted for label-free cell tomography (Nam et al, 2013) to inspect local strain fields or lattice defects and plastic deformation with nanoscale probes (Godard et al, 2011;Takahashi et al, 2013), and for in situ and operando studies on planar devices (Hruszkewycz et al, 2013). Figure 21 reports on the PCDI imaging of composite materials, made of 25 μm thick polystyrene (PS) films embedding CdSe/CdS octapodshaped nanocrystals (De Caro et al, 2016). The question here is to image the exact architecture of the nanocrystals, i.e., to discriminate between linear chains, such as those found for the as-deposited nanocrystals [ Fig.…”

X-ray ptychographic mode of self-assembled CdSe/CdS octapod-shaped nanocrystals in thick polymers

“…The set of X-ray ptychography data was collected at the cSAXS beamline of the Swiss Light Source, at the Paul Scherrer Institut in Villigen, Switzerland. The most relevant technical details are as follows (De Caro et al, 2016): the experiments were conducted with an X-ray beam of 6.2 keV (wavelength = 0.2 nm) using Fresnel zone plate primary optics with a diameter of 200 mm, deposited on a 200 nm-thick silicon nitride membrane, with an outermost zone width and a thickness of 50 and 500 nm, respectively. A 50 mm focal distance and a 50 mm depth of focus were established, and a piezoelectric stage was used for positioning the samples with nanometre resolution for the ptychography scans.…”

“…The expected aperiodic network of the octapods also rules out any traditional scattering technique (SAXS/GISAXS). Indeed, GISAXS data were collected and the diffraction patterns were interpreted as the scattering of the octapod shape only, or were useful only in the case of periodic assembly of octapods without any polymeric matrix (De Caro et al, 2016).…”

X-ray Diffraction: A Powerful Technique for the Multiple-Length-Scale Structural Analysis of Nanomaterials

“…Here, polystyrene (PS) free standing films containing CdSe/CdS nanocrystals were studied with coherent X-rays at the cSAXS beamline of the Swiss Light Source (SLS, Villigen, Switzerland) [73]. A practical application of coherent X-rays is described in Figure 11.…”

“…A practical application of coherent X-rays is described in Figure 11. Here, polystyrene (PS) free standing films containing CdSe/CdS nanocrystals were studied with coherent X-rays at the cSAXS beamline of the Swiss Light Source (SLS, Villigen, Switzerland) [73]. Figure 11a shows the TEM image of a single octapod standing on a carbon-coated Cu grid with four pods.…”