Multiscan 4D-STEM datasets on molecular crystals: biotin and Ni(dppf)Cl2

<p>This repository contains data from scanning nanobeam electron diffraction experiments acquired using the 4D Camera installed on the double-aberration-corrected TEAM 0.5 instrument at NCEM.&nbsp;</p> <p>Before data acquisition, the incident beam current was reduced to the detection threshold of the fluorescent screen ammeter (&lt;40 pA) by using the monochromator focus as a continuously adjustable gun lens. Beam flux was estimated from previous reference measurements using a Faraday cup and an ammeter under similar conditions.</p> <p>A near-parallel probe was formed by using a custom 10 &mu;m C2 aperture (Norcada) to access a range of narrow (&lt;0.1 mrad) semiconvergence angles. Using a custom DigitalMicrograph script, multiscan 4D-STEM data were acquired with the 4D Camera operating at 87000 frames per second. As an illustrative example, each biotin dataset is comprised of 512&times;512 probe positions and 576&times;576 detector pixels, resulting in 174 GB of raw data per scan. These raw data were counted and reduced to a sparse, linear-index-encoded electron event representation (EER) in HDF5 format on the NERSC supercomputer, Perlmutter, using the open-source software package <a href="https://github.com/OpenChemistry/stempy">stempy</a>. These <a href="https://stempy.readthedocs.io/en/latest/StempyH5Format.html">sparse HDF5 files</a> can be interactively viewed using our open-source python-based software, <a href="https://github.com/ercius/DuSC_explorer/">DuSC Explorer</a>.</p> <p>Each directory contains a time series of several consecutive 4D-STEM scans acquired on the same molecular crystal (25 for biotin, 300 for Ni(dppf)Cl2), alongside a sequence of simultaneously acquired HAADF images.</p> <p>Experimental parameters for biotin:</p> <table> <tbody> <tr> <td>Accelerating voltage</td> <td>300 kV</td> </tr> <tr> <td>Semiconvergence angle</td> <td>0.07 mrad</td> </tr> <tr> <td>Scan dimensions</td> <td>512&times;512</td> </tr> <tr> <td>Real-space step size</td> <td>9.22 nm</td> </tr> <tr> <td>Estimated probe size (FWHM)</td> <td>14.4 nm</td> </tr> <tr> <td>Total illuminated area</td> <td>11.2 &mu;m^2</td> </tr> <tr> <td>Estimated fluence per probe position</td> <td>0.15 e- &Aring;^(-2)</td> </tr> <tr> <td>Total size of raw data</td> <td>4350 GB</td> </tr> <tr> <td>Total size of sparsified data</td> <td>2.18 GB</td> </tr> </tbody> </table> <p>&nbsp;</p> <p>Experimental parameters for Ni(dppf)Cl2:</p> <table> <tbody> <tr> <td>Accelerating voltage</td> <td>200 kV</td> </tr> <tr> <td>Semiconvergence angle</td> <td>0.07 mrad</td> </tr> <tr> <td>Scan dimensions</td> <td>256&times;256</td> </tr> <tr> <td>Real-space step size</td> <td>15.1 nm</td> </tr> <tr> <td>Estimated probe size (FWHM)</td> <td>18.4 nm</td> </tr> <tr> <td>Total illuminated area</td> <td>7.55 &mu;m^2</td> </tr> <tr> <td>Estimated fluence per probe position</td> <td>1.5 e- &Aring;^(-2)</td> </tr> <tr> <td>Total size of raw data</td> <td>13200 GB</td> </tr> <tr> <td>Total size of sparsified data</td> <td>9.93 GB</td> </tr> </tbody> </table> <p>&nbsp;</p>