DOI: 10.6078/d17675
title: In Situ Transmission Electron Microscopy Data of Dislocations in Imperfectly Attached PbTe Nanocrystal Pairs

description: Dataset containing high resolution transmission electron microscopy data
 of imperfectly attached PbTe nanocrystals.  The data contains
 High Resolution TEM timeseries of images showing the annealing of of well
 defined b=a/2[110] edge dislocations in PbTe nanocrystal pairs viewed down
 the&lt;001&gt; zone axis.  Depending on the attachment
 facets of the particles, the dislocations anneal out at different
 rates.  In addition we performed geometric phase analysis on the
 images to visualize the strain fields surrounding the dislocation
 cores.  The raw image series, as well as drift corrected image
 series and all strain and rotation maps from geometric phase analysis are
 included in this dataset.  Further overlays of dislocation
 positions determined by geometric phase analysis overlaid on raw images
 are included to show the validity of dislocaiton tracking. Simple scripts
 used to analyze dislocation positions and overlay strain fields with TEM
 images for visualization and are included in this
 dataset.  
description: <b>Nanocrystal synthesis</b>: PbTe nanocrystals
 were synthesized based on modified methods from Zhu et.
 al.<sup>73</sup> 1.0 M TOP-Te was prepared by dissolving
 tellurium shot in TOP in an argon glovebox (&lt;1 ppm
 O<sub>2</sub> and H<sub>2</sub>O) at room
 temperature for ~36 hours.  Next, 900 mg PbO, 7.56 g OA, 16 g ODE were
 loaded in a 3-neck round bottom flask and heated under vacuum on a Schlenk
 line at 100C for 1 hour to complex lead oleate and dry the solution.  The
 flask was refilled with argon (ultrapure &lt;1ppm
 O<sub>2</sub>) 3X and heated to 120°C. 2 ml of the 1.0 M
 TOP-Te solution was injected and the nanocrystals were allowed to grow for
 10 min at 120 °C.  The reaction was quenched by quickly cooling to room
 temperature using a water bath.  The nanocrystals were cannula transferred
 to a Schlenk flask and transferred to an argon glovebox.  The nanocrystals
 were washed 3X by precipitating them with excess acetone, centrifuging and
 dissolving the resulting pellet in toluene.  The sample were stored in an
 argon glovebox.  It was found that pristine unoxidized surfaces were
 necessary for ligand displacement mediated attachment. <b>TEM
 sample preparation</b>: Graphene coated TEM grids were prepared by
 direct transfer of 3-5 layer graphene onto holey quatifoil TEM
 grids.<sup>74</sup>  PbTe particles sandwiched between
 graphene sheets where prepared based on modified methods for making
 graphene veils and sandwitches.<sup>75</sup> Briefly, in a
 glovebox a small droplet of dilute PbTe nanocrystals in toluene was
 dropped on a graphene coated TEM grid and the droplet was allowed to dry.
 A second graphene coated TEM grid was placed on top and a droplet of
 toluene or orthodichlobenzene (ODCB) was placed on the sandwich.  This
 assembly was covered with a glass dish and the solvent was allowed to
 slowly evaporate for several hours to seal the sample between the
 graphene.  The sample was taken out of the glovebox and quickly (~3min)
 transferred to the TEM column. <b>TEM
 imaging</b>: TEM imaging was performed on a FEI Tecnai T20 S-TWIN
 TEM operating at 200kV with a LaB<sub>6</sub> filament. 
 Images were taken near Scherzer focus which resulted in dark atom contrast
 for this crystal thickness.  Timeseries of TEM images were collected with
 a Gatan Orius SC200 using a custom digital micrograph script with full
 2048x2048 pixel readout, at a nominal magnification of 400kX resulting in
 a pixel resolution of 0.13Å/pixel, an exposure time of 1s, and a readout
 time of 1.4s yielding a framerate of 0.4 fps.  Since the defect dynamics
 were beam initiated, care was taken to minimize electron dose prior to
 imaging. Searching was performed with a spread beam, then once a suitable
 defective nanoparticle was found, a custom Digital Micrograph script was
 used to condense the beam to reproducibly return to the same dose rate
 within a session for each movie acquisition. We estimate a dose rate of
 ~4000 e<sup>-</sup>/Å<sup>2</sup>s was used for
 all data collected. <strong>Image
 Analysis</strong>: The movies were drift corrected using a cross
 correlation method using the raw images as inputs and manually checked and
 corrected where necessary (Stack Alignment, Dave Mitchell's
 DigitalMicrograph™ Scripting Website,  http://www.dmscripting.com/stack_alignment.html). The geometric phase analysis (GPA) and all other analysis was performed with the raw but drift corrected unrotated images from our CCD camera to avoid introducing artifacts. Geometric phase analysis was performed using the GPA tool contained in the FRWRtools plugin (https://www.physics.hu-berlin.de/en/sem/software/software_frwrtools)  for Gatan Digital Micrograph.  The (200) and (020) peaks were used for analysis with a reference lattice with a and b parameters of 3.09Å with a 90° angle between the two, a resolution of 0.7 nm and a smoothing of 0.6 with a symmetric strain matrix.
description: See readme files in the dataset