This file README.txt was updated on 2021-10-11 by Wyatt Curtis Suggested Citation: Curtis, Wyatt, A; Flannigan, David J. (2021). Simulation data supporting Toward A-fs-meV Resolution in Electron Microscopy: Systematic Simulation of the Temporal Spread of Single-Electron Packets. Retrieved from the Data Repository for the University of Minnesota, https://doi.org/10.13020/91yh-x581. ------------------- GENERAL INFORMATION ------------------- Title of Dataset: Simulation data supporting "Toward A-fs-meV Resolution in Electron Microscopy: Systematic Simulation of the Temporal Spread of Single-Electron Packets" Author Information: Principal Investigator Contact Information Name: Wyatt Curtis Institution: University of Minnesota Address: Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, United States Email: curti477@umn.edu ORCID: Associate or Co-investigator Contact information Name: David J. Flannigan Institution: University of Minnesota Ultrafast Electron Microscopy Lab Address: Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, United States Email: flan0076@umn.edu ORCID: https://orcid.org/0000-0002-1829-1868 Date Published:2021-10-11 Date of data collection (single date, range, approximate date): 2021-05-01 through 2021-07-13 Geographic location of data collection: University of Minnesota Information about funding sources that supported the collection of the data: This research was supported by a grant from the National Science Foundation through MRSEC award DMR-1420013. -------------------------- SHARING/ACCESS INFORMATION -------------------------- Recommended citation for the data: 1. Licenses/restrictions placed on the data: CC0 1.0 Universal http://creativecommons.org/publicdomain/zero/1.0/ 2. Links to publications that cite or use the data: W. A. Curtis and D. Flannigan, Phys. Chem. Chem. Phys., 2021, DOI: 10.1039/D1CP03518E. https://pubs.rsc.org/en/content/articlelanding/2021/cp/d1cp03518e 3. Links to other publicly accessible locations of the data: 4. Links/relationships to ancillary data sets: 5. Was data derived from another source? --------------------- DATA & FILE OVERVIEW --------------------- Under each top-level file or folder, add description of the data, file formats, software required to open, and any other information (e.g., conditions, filenaming, etc.) to help understand, explain, and navigate the files. 1. File List A. Filename: "figure 1" Short description: Folder containing text files from Figure 1. Datasets are titled as follows: f1_X.XXeVspectrum.txt f1 -> indicates this dataset is from figure 1 X.XXeVspectrum -> indicates this data refers to the photoelectron spectrum for excitation with X.XXeV photons Datasets contains two columns. - "E" refers to the photoelectron energy in units of eV. - "Counts" refers to the normalized probability of emission of an electron with the given energy. B. Filename: "figure 2" Short description: Folder containing text files from Figure 2. Datasets are titled as follows: f2_PANEL_X.XXeV.txt f2 -> indicates this dataset is from figure 2 PANEL -> indicates which panel this data refers (upper/lower) X.XXeV -> indicates this data refers to the electron packet with energy of X.XXeV Datasets contains two columns: - "Photoemission Spot-Size" is in units of meters. - "stdt (tau_electron/2.355)" is the temporal standard deviation of the electron packet in seconds. C. Filename: "figure 3" Short description: Folder containing text files from Figure 3. Datasets are titled as follows: f3_X.XXeV.txt f3 -> indicates this dataset is from figure 3 X.XXeV -> indicates this data refers to the electron packet with energy of X.XXeV. Datasets contains two columns: - "theta" refers to the angle of emission of electrons in radians. - "relative arrival time" is in units of seconds. D. Filename: "figure 4" Short description: Folder containing text files from Figure 4. Datasets are titled as follows: f4_X.Xmm.txt f4 -> indicates this dataset is from figure 4 X.Xmm -> indicates this data refers to the simulation performed with Wehnelt aperture of X.Xmm. Datasets contains two columns: - "Photoemission Spot-Size" is in units of meters. - "stdt (tau_electron/2.355)" is the temporal standard deviation of the electron packet in seconds. E. Filename: "figure 5" Short description: Folder containing text files from Figure 5. Datasets are titled as follows: f5_PANEL_X.XXeV.txt f5 -> indicates this dataset is from figure 5 PANEL -> indicates which panel this data refers (upper/lower) X.XXeV -> indicates this data refers to the simulation conducted with photoemission with X.XXeV photons. Datasets contains two columns: - "Photoemission Spot-Size" is in units of meters. - "stdt (tau_electron/2.355)" is the temporal standard deviation of the electron packet in seconds. F. Filename: "figure 6" Short description: Folder containing text files from Figure 6. Datasets are titled as follows: f6PANEL_XXfs.txt f5 -> indicates this dataset is from figure 6 PANEL -> indicates which panel this data refers (a-d) XXfs -> indicates this data refers to the simulation conducted with XXfs (FWHM) laser pulse durations. For panels "a" and "c" datasets contain two columns: - "Photoemission Spot-Size" is in units of meters. - "stdt (tau_electron/2.355)" is the temporal standard deviation of the electron packet in seconds. For panels "b" and "d" datasets contain four columns: - "Photoemission Spot-Size" is in units of meters. - "tau_el - tau_el,50fs" is the linear fit to the difference in temporal durations between the current dataset and the 50fs dataset in units of seconds. - "lower confidence limit" is the lower 95% confidence limit for the linear fit in units of seconds. - "upper confidence limit" is the upper 95% confidence limit for the linear fit in units of seconds. G. Filename: "figure 7" Short description: Folder containing text files from Figure 7. Datasets are titled as follows: f7_XXum.txt f7 -> indicates this dataset is from figure 7 XXum -> indicates this data refers to the simulation conducted with a flat LaB6 photocathode with a diameter of XX microns. Datasets contains two columns: - "Photoemission Spot-Size" is in units of meters. - "stdt (tau_electron/2.355)" is the temporal standard deviation of the electron packet in seconds. 2. Relationship between files: 3. Additional related data collected that was not included in the current data package: 4. Are there multiple versions of the dataset? No -------------------------- METHODOLOGICAL INFORMATION -------------------------- 1. Description of methods used for collection/generation of data: General Particle Tracer (GPT, Pulsar Physics) was used to map particle trajectories through the electron gun and the electrostatic accelerator of a Thermo Fisher/FEI Tecnai Femto UEM (Fig. 1a).63 To reduce computation time, simulations of n = 50,000 non-interacting electrons simultaneously generated from the cathode were performed. In the gun region, a series of dynodes comprise the accelerator and raise the electron energy to 200 keV. Once fully accelerated, the beam impinges upon an X-ray aperture, which here is the final element of the simulated electron gun. Two-dimensional, cylindrically-symmetric electrostatic field maps were calculated for the specific architecture and dimensions of the Tecnai Femto UEM (base instrument is Tecnai T20 G2)(a) using Poisson Superfish.62 In UEM mode, the electron gun consists of an unbiased Wehnelt triode with an aperture of diameter DW and a truncated LaB6 cathode with an emitting surface of diameter Dtip and a work function of  = 2.4 eV. The aperture can be variably positioned relative to the emitting surface at a distance Ztip in the Wehnelt assembly. Here, a fixed Ztip of 0.35 mm was used, as previous simulations of the Tecnai Femto indicated that this is the optimal position for maximizing electron collection efficiency in single-electron mode for DW = 0.7 mm.55 Further, a fixed Ztip was used in order to specifically study the effects of photoemission spot size (i.e., assumed to be the fwhm size of the laser spot on the LaB6 surface) and DW on τelectron. As with previous simulations on minimally-modified TEMs for ultrafast operation,55 the effects of emission spot size and DW are of interest because they are readily adjustable and tunable. Single-electron packets were approximated by generating a set of non-interacting particles having momentum distributions and spatial coordinates specific to the photoemission characteristics under consideration. This approximates a series of single-electron photoemission events. Note the distinction between photoemission spot size and Dtip, which manifests in the emission probability (P) for a Gaussian laser-spot spatial profile (Fig. 1b). Further, LaB6 shank emission was not considered, as the laser spot can be trained entirely on the flat cathode surface.54,58 This is experimentally achieved by encircling the LaB6 with a high  material such that hv <  and by simply focusing the laser-spot size such that it is smaller than Dtip.1,8,58 The probability of photoemission (P) was varied as the cosine of the initial emission angle, θ [i.e., P(θ) = cos(θ)] (Fig. 1c).55,64 Note that different approaches to treating the angular photoemission distribution in UEM and ultrafast electron diffraction (UED) simulations have been adopted. One common approach is to assume a uniform distribution of photoemission probabilities within the hemisphere subtended by the photocathode emitting surface.57,59,65 Compared to the cos(θ) approach, uniformly-distributed trajectories will produce photoelectron packets with increased temporal distortions due to the larger fraction of off-axis emission events. Only the cos(θ) distribution was employed here. Following this, the product of the Lorentz factor () and the normalized relativistic velocity () was used as the momentum factor () to initialize the GPT simulations. Initial photoelectron kinetic-energy distributions were modeled as calculated transmission coefficients for free electrons encountering a step potential (Fig. 1d). Photoemission was approximated by shifting the Fermi-Dirac distribution by the amount of the incident photon energy hv; the three photon energies studied here (2.41, 3.61, and 4.81 eV) are harmonics (2nd – 4th, respectively) of the UEM laser system at Minnesota (Yb:KGW, hvfundamental = 1.2 eV). Note that this approach is an approximation for near-threshold photoemission from the surface of LaB6.66 All reported single-electron-packet properties are those that are present 2.5 ns after photoemission. This ensured that all packets were fully increased to 200 keV and had reached the X-ray aperture, regardless of initial trajectory. Finally, electron (single-electron temporal distribution for n individual, integrated non-interacting particles) was calculated by dividing the root-mean-square longitudinal packet length by the average longitudinal velocity. 2. Methods for processing the data: Data was exported directly to Origin for figure generation. For the columns refering to the temporal standard deviation of the electron packet, the y-axis was scaled to display the temporal full-width at half-maximum. 3. Instrument- or software-specific information needed to interpret the data: 4. Standards and calibration information, if appropriate: 5. Environmental/experimental conditions: 6. Describe any quality-assurance procedures performed on the data: Electrostatic field maps were verified with Erik Kieft at Thermo Fisher Scientific. 7. People involved with sample collection, processing, analysis and/or submission: ----------------------------------- Directory Structure ----------------------------------- | +---Data Files.zip | | +---figure 1 | | | f1_2.41eVspectrum.txt | | | f1_3.61eVspectrum.txt | | | f1_4.81eVspectrum.txt | | | | | +---figure 2 | | | f2_lower_0.1eV.txt | | | f2_lower_1.76eV.txt | | | f2_lower_2.4eV.txt | | | f2_upper_0.1eV.txt | | | f2_upper_1.76eV.txt | | | f2_upper_2.4eV.txt | | | | | +---figure 3 | | | f3_0.1eV.txt | | | f3_1.76eV.txt | | | f3_2.4eV.txt | | | | | +---figure 4 | | | f4_0.7mm.txt | | | f4_0.8mm.txt | | | f4_0.9mm.txt | | | f4_1.0mm.txt | | | f4_1.1mm.txt | | | f4_1.2mm.txt | | | | | +---figure 5 | | | f5_lower_2.41eV.txt | | | f5_lower_3.61eV.txt | | | f5_lower_4.81eV.txt | | | f5_upper_2.41eV.txt | | | f5_upper_3.61eV.txt | | | f5_upper_4.81eV.txt | | | | | +---figure 6 | | | f6a_100fs.txt | | | f6a_150fs.txt | | | f6a_200fs.txt | | | f6a_250fs.txt | | | f6a_300fs.txt | | | f6a_50fs.txt | | | f6b_100fs.txt | | | f6b_150fs.txt | | | f6b_200fs.txt | | | f6b_250fs.txt | | | f6b_300fs.txt | | | f6c_100fs.txt | | | f6c_150fs.txt | | | f6c_200fs.txt | | | f6c_250fs.txt | | | f6c_300fs.txt | | | f6c_50fs.txt | | | f6d_100fs.txt | | | f6d_150fs.txt | | | f6d_200fs.txt | | | f6d_250fs.txt | | | f6d_300fs.txt | | | | | \---figure 7 | | f7_100um.txt | | f7_16um.txt | | f7_180um.txt | | f7_50um.txt