Condensed Matter Journal Club: "Multislice Electron Ptychography on the Uncorrected Microscope"

The development of aberration-corrected electron microscopes allowed for subangstrom resolution imaging in transmission electron microscopes (TEMs) and scanning transmission electron microscopes (STEMs). These aberration-corrected tools are key in understanding atomic structure and properties at atomic resolution. However, the high cost of acquiring, operating, and maintaining aberration-corrected microscopes limits access to subangstrom imaging. Ptychography, a phase-retrieval approach that utilizes convergent-beam electron diffraction (CBED) patterns collected over a set of probe positions to solve for both the object and probe simultaneously. Sub-0.5-angstrom resolution has been demonstrated in twisted 2D materials systems in uncorrected electron microscopes using single-slice electron ptychography. However, single-slice ptychography is incapable of reliably reconstructing samples thicker than a few nanometers, thus significantly limiting the technique to 2D materials. Multislice electron ptychography (MEP) allows for the retrieval of the 3D structure of the sample by dividing the sample into a series of slices. Here, we demonstrate multislice electron ptychography on a commercially available uncorrected electron microscope over a range of materials systems with subangstrom resolution. First, we use MEP on a twisted bilayer WSe2 system with information transfer of 0.48Å in the reconstructed phase image. The 3D information from MEP allows for retrieval of depth resolution as measured by the full-width half-maximum of the atomic intensity along the z-direction of 2nm, comparable to previously reported depth resolutions of experimental MEP of 2–4nm. We then collect a 4D-STEM data set on two additional samples: 5nm SrTiO3 along the [001] direction and 5nm diameter gold nanoparticles mounted on ultrathin 2 nm lacy carbon. In the SrTiO3 sample, we can retrieve the intensity from the O atoms, which, as well as attain lateral resolution of 0.87Å as measured from the information transfer of the FFT. In the gold nanoparticles, we can resolve individual atoms. Furthermore, MEP can correctly identify which slices of the nanoparticles are dominated by the amorphous carbon background. We discuss the implications of thickness and aberrations on the attainable depth resolution in an uncorrected tool, as well as how the phase space for ptychography differs between corrected and uncorrected electron microscopes. These results have potential to broaden the accessibility to subangstrom characterization in three dimensions. 

Progressus microscopiorum electronicorum aberratione correcta imagines resolutionis subangstromicae in microscopiis electronicis transmissionis (TEM) et microscopiis electronicis transmissionis perlustrantibus (STEM) permisit. Haec instrumenta aberratione correcta maximi momenti sunt ad intellegendam structuram et proprietates atomicas ad resolutionem atomicam. Attamen, sumptus altus acquisitionis, operationis, et sustentationis microscopiorum aberratione correctarum accessum ad imagines subangstromicas limitat. Ptychographia, methodus recuperationis phasium quae exemplaria diffractionis electronicae fasciculi convergentis (CBED) collecta per seriem positionum specillorum utitur ad solvendas et obiectum et specillum simul. Resolutio sub 0.5 angstromica demonstrata est in systematibus materiarum 2D contortis in microscopiis electronicis non correctis utens ptychographia electronica unius segmenti. Attamen, ptychographia unius segmenti non potest certo reconstruere exempla crassiora quam pauca nanometra, ita significanter limitans artem ad materias 2D. Ptychographia electronica multis segmentis (MEP) recuperationem structurae 3D speciminis per divisionem speciminis in seriem segmentorum permittit. Hic, ptychographiam electronicam multislicem in microscopio electronico non correcto commercialiter praesto per seriem systematum materialium cum resolutione subangstrom demonstramus. Primo, MEP in systemate WSe2 bi-strato contorto cum translatione informationis 0.48 Å in imagine phasis reconstructa utimur. Informatio 3D ex MEP permittit recuperationem resolutionis profunditatis sicut mensurata per semi-maximum plenae latitudinis intensitatis atomicae secundum directionem z 2 nm, comparabilis resolutionibus profunditatis antea relatis MEP experimentalis 2-4 nm. Deinde collectionem datorum 4D-STEM in duobus exemplaribus additis colligimus: SrTiO3 5 nm secundum directionem [001] et nanoparticulis aureis 5 nm diametri impositis in carbone laceo ultratenui 2 nm. In exemplo SrTiO3, intensitatem ex atomis O recuperare possumus, quae, necnon resolutionem lateralem 0.87 Å consequuntur sicut mensurata est ex translatione informationis FFT. In nanoparticulis aureis, atomos singulos resolvere possumus. Praeterea, MEP recte discernere potest quae segmenta nanoparticularum a fundamento carbonis amorphi dominentur. Implicationes crassitudinis et aberrationum in resolutione profunditatis attingibili in instrumento non correcto discutimus, necnon quomodo spatium phasium pro ptychographia inter microscopia electronica correcta et non correcta differat. Haec eventa potentiam habent ad accessum ad characterizationem subangstrom in tribus dimensionibus amplificandum.