This ReadMe.txt file was updated on 2025-10-31 by Louis G Corcoran Recommended citation for the data: Corcoran, Louis G; Monzo, Ellen M; Onuoha, Chinomso E; Varshney, Shivasheesh; Lee, Hanseung; Fretham, Chris; Jalan, Bharat; McCormick, Alon V; Penn, R. Lee. (2025). Data for "Electron Microscopy Transfer System to Protect Atmosphere-sensitive Materials for Scanning Electron Microscopy Characterization”. Retrieved from the Data Repository for the University of Minnesota (DRUM); https://doi.org/10.13020/0s3h-wm31 ------------------- GENERAL INFORMATION ------------------- Title of Dataset: Data for Electron Microscopy Transfer System to Protect Atmosphere-sensitive Materials for Scanning Electron Microscopy Characterization Author Information: Author Contact: Alon V. McCormick (mccormic@umn.edu) Name: Louis G. Corcoran Institution: University of Minnesota Twin Cities Email: corco104@umn.edu ORCID: 0000-0003-3061-8808 Name: Ellen Monzo Institution: University of Minnesota Twin Cities Email: monzo003@umn.edu ORCID: 0000-0002-6675-568X Name: Chinomso E. Onuoha Institution: University of Minnesota Twin Cities Email: onuoh010@umn.edu ORCID: 0000-0003-4156-4649 Name: Shivasheesh Varshney Institution: University of Minnesota Twin Cities Email: varsh022@umn.edu ORCID: 0000-0001-9496-0456 Name: Han Seung Lee Institution: University of Minnesota Twin Cities Email: cfac-sem@umn.edu ORCID: 000-0002-0411-2400 Name: Chris Fretham Institution: University of Minnesota Twin Cities Name: Bharat Jalan Institution: University of Minnesota Twin Cities Email: bjalan@umn.edu ORCID: 0000-0002-7940-0490 Name: Alon V. McCormick Institution: University of Minnesota Twin Cities Email: mccormic@umn.edu ORCID: 0000-0002-8885-1330 Name: R. Lee Penn Institution: University of Minnesota Twin Cities Email: rleepenn@umn.edu ORCID: 0000-0002-9610-9507 Date of data collection: 2022 - 2024 Geographic location of data collection: University of Minnesota; Lab Space of Prof. R. Lee Penn, Prof. Alon V. McCormick, Prof. Bharat Jalan, and the Characterization Facility. Information about funding sources that supported the collection of the data:This research was made possible by the University of Minnesota Industry Partnership for Research in Interfacial and Materials Engineering (IPRIME) through the Nanostructural Materials and Processes (NMP) program. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from the NSF through the MRSEC (Award Number DMR-2011401) and the NNCI (Award Number ECCS-2025124) programs. The Hitachi SU8320 cryo-SEM and cryospecimen preparation system were provided by NSF MRI DMR-1229263. S.V. and B.J. were supported by the U.S. Department of Energy through DE-SC0020211 and the Center for Programmable Energy Catalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences at the University of Minnesota, under Award No. DE-SC0023464. C.O and A.M were supported in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under award no. DE-AR0000804; in part by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Advanced Manufacturing Office Award Number DE-EE0007888; in part by the Office of the Vice President for Research, University of Minnesota; and in part by University of Minnesota West Central Research and Outreach Center through the State of Minnesota Renewable Development Account. Overview of this data (abstract): This data was collected to provide evidence for the successful ability of a novel scanning electron microscopy sample preparation method to protect highly atmosphere- and/or moisture-sensitive materials from undesired exposure to atmosphere. Initial proof-of-concept experiments were conducted with highly hygroscopic MgCl2 material exposed to controlled humidity environments and qualitative (photographs) and quantitative data (x-ray diffraction) were collected to compare samples that were prepared (1) with the use of the sample protection/preparation method (2) with no protections provided. Following this, hygroscopic BaO thin films were synthesized and prepared with the outlined method and characterized via scanning electron microscopy to demonstrate the functional application of the preparation technique. -------------------------- SHARING/ACCESS INFORMATION -------------------------- 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: "Electron Microscopy Transfer System to Protect Atmosphere-sensitive Materials for Scanning Electron Microscopy”, submitted to Microscopy Research and Technique 3. Was data derived from another source? No 4. Terms of Use: Data Repository for the U of Minnesota (DRUM): By using these files, users agree to the Terms of Use. https://conservancy.umn.edu/pages/policies/#drum-terms-of-use --------------------- 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. Folder List A. Folder name: RHEED and BaO Growth Short description: Folder contains an Excel file of the raw RHEED (reflection high energy electron diffraction) data as well as the RHEED image after growth. File Names: 1. BaO_AfterGrowth_90C-20p5_[100] Image (PNG File) 2. RHEED-intensity (Excel worksheet) B. Folder name: Salt Humidity Chamber Images Short description: Folder contains qualitative data (photographs) associated with MgCl2 proof-of-concept experiments. Photographs taken of protected and exposed samples after various timepoints in the humidity box (as outlined in the “Description of methods” section below) File Names: 1. 5min_Exposed (.jpg) 2. 5min_Protected (.jpg) 3. 15min_Exposed (.jpg) 4. 15min_Protected (.jpg) 5. 30min_Exposed (.jpg) 6. 30min_Protected (.jpg) 7. 60min_Exposed (.jpg) 8. 60min_Protected (.jpg) 9. 180min_Exposed (.jpg) 10. 180min_Protected (.jpg) 11. 180min_Weighboat_Exposed (.jpg) 12. ExampleGlassSlide+SaltPrep (.jpg) 13. StubsPreparedinGloveBox (.jpg) 14. ReadMe.txt C. Folder name: SEM+EDX Data Short description: Contains SEM micrographs and EDX data collected for BaO exposed and protected samples for both Pt-coated and non-coated samples File Names: Folder 1. BaO_exposed (Word Document) 2. BaO_exposed_analyzer (Word Document) 3. Barium Oxide-exposed_0001 (Tiff file for image and .txt for metadata) 4. Barium Oxide-exposed_0002 (Tiff file for image and .txt for metadata) 5. Barium Oxide-exposed_0003 (Tiff file for image and .txt for metadata) 6. Barium Oxide-exposed_0004 (Tiff file for image and .txt for metadata) 7. Barium Oxide-exposed_0005 (Tiff file for image and .txt for metadata) 8. Barium Oxide-exposed_0006 (Tiff file for image and .txt for metadata) 9. Barium Oxide-exposed_0007 (Tiff file for image and .txt for metadata) 10. Barium Oxide-exposed_0008 (Tiff file for image and .txt for metadata) 11. Barium Oxide-exposed_0009 (Tiff file for image and .txt for metadata) 12. Barium Oxide-exposed_0010 (Tiff file for image and .txt for metadata) 13. Barium Oxide-exposed_0011 (Tiff file for image and .txt for metadata) 14. ReadMe.txt File Names: Folder 1. BaO (Word Document) 2. Barium Oxide_not exposed_0001 (Tiff file for image and .txt for metadata) 3. Barium Oxide_not exposed_0002 (Tiff file for image and .txt for metadata) 4. Barium Oxide_not exposed_0003 (Tiff file for image and .txt for metadata) 5. Barium Oxide_not exposed_0004 (Tiff file for image and .txt for metadata) 6. Barium Oxide_not exposed_0005 (Tiff file for image and .txt for metadata) 7. Barium Oxide_not exposed_0006 (Tiff file for image and .txt for metadata) 8. Barium Oxide_not exposed_0007 (Tiff file for image and .txt for metadata) 9. Barium Oxide_not exposed_0008 (Tiff file for image and .txt for metadata) 10. Barium Oxide_not exposed_0009 (Tiff file for image and .txt for metadata) 11. Barium Oxide_not exposed_0010 (Tiff file for image and .txt for metadata) 12. Barium Oxide_not exposed_0011 (Tiff file for image and .txt for metadata) 13. Barium Oxide_not exposed_0012 (Tiff file for image and .txt for metadata) 14. Barium Oxide_not exposed_0013 (Tiff file for image and .txt for metadata) 15. ReadMe.txt File Names: Folder 1. BaO analyzer (Word Document) 2. BaO (Word Document) 3. Barium Oxide_not exposed_0001 (Tiff file for image and .txt for metadata) 4. Barium Oxide_not exposed_0002 (Tiff file for image and .txt for metadata) 5. Barium Oxide_not exposed_0003 (Tiff file for image and .txt for metadata) 6. Barium Oxide_not exposed_0004 (Tiff file for image and .txt for metadata) 7. Barium Oxide_not exposed_0005 (Tiff file for image and .txt for metadata) 8. Barium Oxide_not exposed_0006 (Tiff file for image and .txt for metadata) 9. Barium Oxide_not exposed_0007 (Tiff file for image and .txt for metadata) 10. Barium Oxide_not exposed_0008 (Tiff file for image and .txt for metadata) 11. ReadMe.txt File Names: Folder 1. BaO-24 hrs exposed_20_RH_0001 (Tiff file for image and .txt for metadata) 2. BaO-24 hrs exposed_20_RH_0002 (Tiff file for image and .txt for metadata) 3. BaO-24 hrs exposed_20_RH_0003 (Tiff file for image and .txt for metadata) 4. BaO-24 hrs exposed_20_RH_0004 (Tiff file for image and .txt for metadata) 5. BaO-24 hrs exposed_20_RH_0005 (Tiff file for image and .txt for metadata) 6. BaO-24 hrs exposed_20_RH_0006 (Tiff file for image and .txt for metadata) 7. BaO-24 hrs exposed_20_RH_0007 (Tiff file for image and .txt for metadata) 8. BaO-24 hrs exposed_20_RH_0008 (Tiff file for image and .txt for metadata) 9. BaO-24 hrs exposed_20_RH_0009 (Tiff file for image and .txt for metadata) 10. BaO-24 hrs exposed_20_RH_0010 (Tiff file for image and .txt for metadata) 11. BaO-24 hrs exposed_20_RH_0011 (Tiff file for image and .txt for metadata) 12. ReadMe.txt D. Folder name: XRD Data Files Short description: XRD data files for reference crystal structures and sample files File Names: 1. MgCl2_data (Powerpoint file of compiled raw data) File Names: Folder Nested Folder 1: <2min Air + 3&6hr HB Data> Folder. Note: Each file includes .ASC, Microsoft Excel, and .xrdml file version unless otherwise specified. In the top row of each spreadsheet (column I1 or J1) a cell is presented with the maximum background corrected intensity found in column E. This value [in cell I1 or J1] is utilized for all of the Normalized intensities found in column F of these spreadsheets and selecting any data point within this column will highlight the values use in calculating the normalized intensity. 1. 20221201_3hrHB_Spinner, 10-70, 105s, 52min_1 2. 20221201_6hrHB_Spinner, 10-70, 105s, 52min_1 3. 20221201_air3minsample_Spinner, 10-70, 105s, 52min_1 4. 20221202_EMM_Background-3siwafers_Spinner, 10-70, 105s, 52min_1 5. ReadMe.txt Nested Folder 2: Folder. Note: Each file includes .ASC, Microsoft Excel, and .xrdml file version unless otherwise specified. 1. 20221007_Air-5Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1 2. 20221007_Air-15Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1 3. 20221007_Air-30Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1 4. 20221007_Air-60Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1 5. 20221007_Burrito-5Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1 6. 20221007_Burrito-15Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1 7. 20221007_Burrito-30Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1 8. 20221007_Burrito-60Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1 9. 20221007_Burrito-180Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1 10. 20221012_Dr-MgCl2#2_Standard_Spinner, 10-70, 105s, 52min_1 11. Background-3siwafers_Spinner, 10-70, 105s, 52min_1 12. ReadMe.txt File Names: Folder 1. MgCl2_4H2O_&2H2O_&1H2O_kd5011sup1 (CIF file) 2. MgCl2_4H2O_262265-ICSD Profile (.txt and Microsoft Excel) 3. MgCl2_4H2O_CCDC_1719928 (CIF File) 4. MgCl2_6H2O_sm_isp_SD1100275-published_cell Profile (.txt and Micro. Excel) 5. MgCl2_8H2O Profile (.txt and Microsoft Excel) 6. MgCl2_8H2O_CCDC_966251 (CIF File) 7. MgCl2_10H2O_high pressure_ps5038sup1 (CIF File) 8. MgCl2_12H2O Profile (.txt and Microsoft Excel) 9. MgCl2_12H2O_CCDC_966248 (CIF File) 10. MgCl2_no hydrate_01-089-1567 (.txt and Microsoft Excel) 11. MgCl2-2H2O_Sugimoto_2007 (Microsoft Excel and .xye file) 12. MgCl2-4H2O Profile_Sugimoto_2007 (.txt and Microsoft Excel) 13. MgCl2-H2O Profile_Sugimoto_2007 (.txt and Microsoft Excel) 14. MgCl2x6H2O_sd_1100275 (CIF File) 15. Mgi2_hydrates_actacryst_2013 (PDF) 16. Mgi2_hydrates_actacryst_2013 (.txt and Microsoft Excel) 4. Are there multiple versions of the dataset? No -------------------------- METHODOLOGICAL INFORMATION -------------------------- 1. Description of methods used for collection/generation of data: 1. MgCl2 Proof-of-Concept Experiments: 1. MgCl2 Preparation MgCl2 was placed in a borosilicate scintillation vial capped with aluminum foil and purified in a vacuum oven. The sample was placed in the oven at room temperature and heated to 235 °C at a pressure of ~1.3 kPa for at least 15 hours before turning the oven off. While under vacuum, the oven was allowed to cool to 50 °C or below before releasing the vacuum and extracting the scintillation vial. Upon extraction, the vial was immediately capped, wrapped in parafilm, and moved into a vacuum desiccator for later use. A small mass of this sample was reserved as a standard (“MgCl2 Standard”) and was not manipulated further. 2. Sample Preparation for Characterization MgCl2 was removed from the vacuum desiccator and the cap removed. Immediately after removing the cap, the vial and cap were placed in the antechamber of a dry glovebox, and the vacuum was pulled for 4 minutes before refilling the antechamber with N2 gas; once the pressure in the antechamber reached 0 in Hg, vacuum was again pulled for four minutes. This process was repeated for four cycles before the sample was moved into the glovebox. The following materials were also transferred to the glovebox: 10 plastic weigh boats, 5 glass microscope slides (cleaned with methanol and a kimwipe and dried in a glassware oven at 50 °C for 5-10 minutes) with carbon tape affixed to all four edges, loosely folded aluminum foil, a small pair of scissors, and six metal rectangle stubs with dimensions ~1 cm2 × 1 mm thick (one side of each metal stub was covered with carbon tape with the backing kept on). 3. Glass Slide and Weigh Boat Preparation In the glovebox, 0.15 g of MgCl2 was massed on a tared plastic weigh boat for sample preparation; 10 such samples were prepared in succession. For the first five, the MgCl2 was transferred to one of the glass slides (the tape backing was removed prior to salt transfer) and spread evenly across the slide in a thin layer with a cleaned metal spatula. A rectangular strip of aluminum foil, slightly larger than the dimensions of the whole glass slide, was then cut with the scissors and applied to the tape over the MgCl2 sample with a clean foil surface covering the sample (taking care to press the foil firmly and evenly across the tape edges surrounding the sample using a metal tweezers and a flexible, rounded metal spatula). 4. Metal Stub Preparation - MgCl2 After removing the carbon tape backing from the stub, enough MgCl2 to lightly cover ~75% of the carbon tape when pressed/spread into the tape, was transferred to the center of the carbon tape with a metal spatula and spread thinly. A strip of foil slightly larger than the metal surface was then cut and applied over the sample. The edges of the foil were then crimped on the tape edges surrounding the sample using a metal tweezers and a flexible, rounded metal spatula (taking care not to rip the foil protecting the sample). 5. Controlled Humidity Experiments A 1L beaker with DI water was placed in a sealed plexiglass box (100 × 70 × 55 cm3 L × W × H) with a small gasketed door. A glass gas dispersion tube (ASTM 10 -20 μL) with air flowing through it was placed inside the beaker; after several hours, the internal RH was measured at 90%+ with a Fisherbrand Traceable digital thermometer (hereafter this will be referred to as the humidity box (HB)). Following this, the samples prepared in the glovebox were taken out and placed in theHB and the door was closed; the process for the samples prepared on metal stubs will be discussed first. The samples prepared on the small metal stubs were used to collect qualitative proof-of-concept data. The salt used to prepare these samples could not be characterized via XRD due to the small volume of MgCl2 used and its subsequent adhesion to carbon tape. Instead, the experiments detailed herein were conducted to visualize the effectiveness of sample protection and/or extent of hydration for MgCl2 loadings that would be consistent with SEM characterization. Before placing the stubs in the HB, the foil pouch on one stub was opened with a razor blade to expose the salt to air; this stub was used as the control stub (CS). Following this, all 6 stubs were then transferred into the HB and stubs were taken out in succession at 5-, 15-, 30-, 60-, and 180-minute timepoints, with the CS taken out at each time point for comparison. Note, during the subsequent sample extraction from the HB the humidity did fluctuate but never fell below 84% RH. Following extraction, the foil pouch was cut open, and an image was taken of both the protected salt sample and that of the CS with a cell phone camera. The CS was then placed back in the HB and extracted at each subsequent timepoint to collect a comparison image. The MgCl2 samples prepared on protected glass slides and weigh boats were immediately transferred to the HB upon removal from the glovebox. One of each sample was taken out of the HB at the following timepoints: 5-, 15-, 30-, 60-, and 180-minutes. At each time point, the two samples were transferred to a labeled 20 mL scintillation vial (dried at 50 °C prior) that was then sealed with a cap wrapped in parafilm before storing in a vacuum desiccator. To transfer the sample from weigh boats, a cleaned metal spatula was used. For samples on the microscope slides, a razor blade was used to cut the foil into a “v” shape and remove the carbon tape from one end of the slide. A clean metal spatula was then used to scrape the salt into the vial. After all samples were extracted from the HB, nine sample vials were transferred to the glovebox (the weigh boat sample exposed to high humidity for 180 minutes had become a liquid brine, which was unsuitable for the glovebox). To do so, samples were all uncapped and placed in the antechamber of the glove box. Vacuum was immediately pulled for four minutes and cycled with N2 gas. Following this, vacuum was then pulled for two minutes and cycled with N2 gas; three iterations of this shorter cycle were completed. The samples were then brought into the glovebox and immediately capped and wrapped in parafilm. These samples, along with one control MgCl2 standard (stored in the glovebox during HB experiments) were used for the X-ray diffraction experiments discussed below. Glass-slide samples prepared in this way were also utilized for mass-gain experiments to provide further evidence for the effectiveness of the protection protocol. 6. Powder X-ray diffraction To quantify the effectiveness of the sample protection method, direct comparisons were made between the XRD patterns of 1) the control sample (“MgCl2 standard”) and the protected MgCl2 samples, 2) the control sample (“MgCl2 standard”) and the exposed MgCl2 samples, and 3) the protected and exposed samples across all 5 timepoints. To prepare each sample for XRD, a sample holder equipped with a plastic dome (to protect the sample; Anton Paar) was transferred into the glovebox with three well-fitting, zero background Si (Si (510) zero background insert) sample wafers already placed in the sample stage. These components were cycled into the box using the 4, 2, 2, 2 - minute vacuum and nitrogen cycling method described above. Once in the glovebox, enough material from a given sample was transferred with a spatula to the stage to provide a uniform deposit on the Si wafer (enough sample such that the sample height appeared visually level with the well on the sample holder). Following this, the plastic dome was affixed to the sample stage using the tools included in the kit. The entire apparatus was immediately extracted from the box and loaded onto a spinning sample stage apparatus (PANalytical Reflection Transmission Spinner PW3064) in the XRD instrument (PANalytical X’Pert Pro), and the X-ray diffraction pattern was collected. Diffraction patterns were collected using Co Kα radiation (λ = 1.79 Å), using operating conditions of 45 kV and 40 mA. Patterns were collected from 10 to 70 °2θ using an effective dwell time of 105 seconds per step and a step size of 0.0167 °2θ for a total scan length of 51.5 minutes. The scan time was selected to require less than one hour to ensure that the domed sample holder maintained a sufficient air- and moisture-free environment for the duration of the measurement. A powder X-ray diffraction pattern of the domed XRD sample holder along with the three Si background wafers (no sample) was also collected using the same program. Powder XRD diffraction patterns were simulated from crystallographic information files for MgCl2·H2O, MgCl2·2H2O, MgCl2·4H2O, MgCl2·6H2O, MgCl2·8H2O, and MgCl2·12H2O using CrystalDiffract 6 or Mercury 4.1.3 software. These simulated powder patterns were compared against experimental data. Powder X-ray diffraction file MgCl2 01-089-1567 was also used as reference. Experimental powder XRD patterns displayed a broad amorphous peak centered at ~20.6 °2θ due to the plastic dome of the sample holder. To correct for this, the intensity recorded at each °2θ value for the plastic dome was subtracted from each corresponding data point in the experimental patterns. The slight downturn in the baseline of experimental patterns at low °2θ is an artifact of the point-by-point baseline correction. B. BaO Thin Film Synthesis Thin films of BaO grown by MBE were used to further probe the efficacy of the sample preservation method. Epitaxial single crystalline 100 nm BaO thin film was grown by MBE by co-deposition of Barium (Ba) and oxygen plasma on Nb-doped SrTiO3 (001) single crystal substrate (CrysTec GmbH). Two samples were loaded together for the growth of the primary test sample and a reference sample. 99.99% purity Barium source was supplied using an elemental effusion cell operated at the cell temperature of 563 ˚C, giving the beam equivalent pressure (BEP) of 7.89 × 10-8 Torr. Oxygen plasma at 250 W at an oxygen pressure of 5 × 10–6 Torr was used to clean the substrate prior to growth for 25 minutes. The substrate was maintained at a temperature of 600 ˚C for the growth of BaO film. During growth, reflection high energy electron diffraction (RHEED; Staib Instruments) was used to monitor thin film growth. After growth, the sample was transferred into the load lock chamber which has a base pressure of 5 × 10–9 Torr. To take out the sample from vacuum, an atmospheric controlled glovebox filled with N2 was connected with the load lock chamber. The load lock was vented with N2 and the sample was taken out in an N2 glass container attached to the load lock chamber. The samples were then transported in a desiccator to an N2 glovebox where they were prepared for scanning electron microscopy characterization. C. BaO Sample Preparation for Characterization via Scanning Electron Microscopy The BaO-containing desiccator was first placed in the antechamber of a N2 glovebox along with carbon tape, aluminum foil (which had been dried in a vacuum oven at 150 °C for 1 hour) and two metal stubs (1 cm x 1 cm x 1 mm). Vacuum was then pulled to evacuate ambient air and moisture in the chamber until the vacuum pressure was below -30 in Hg vacuum. The antechamber was then filled with N2 gas (ultrahigh purity) to a pressure of 0 in Hg vacuum before transferring the desiccator into the glovebox. The moisture level inside the glovebox was < 21 ppm. A double-sided carbon tape was then fixed onto the metal stub making sure to cover all four edges. After removing the carbon tape backing from the stub, the BaO sample was placed on the center of the tape and pressed lightly. A strip of aluminum foil, slightly larger in area than the metal surface, was then cut and applied over the sample. Using metal tweezers, the edges of the foil surrounding the sample were pressed on the tape to ensure a tight seal. During sealing, care was taken (1) not to rip the foil and (2) to leave enough room above the sample to prevent it from puncturing the foil. While in the N2 glovebox, samples were placed in a sealed plastic container that was transferred back into the desiccator; the entire desiccator assembly was transported to the characterization facility. Two BaO sample sets were prepared in this manner; one sample was not sputter coated while the second was coated with 2 nm platinum to demonstrate the ability to sputter coat samples with this method. Both samples were characterized using SEM before and after exposure to controlled humidity. D. Scanning Electron Microscopy At the SEM station, the plastic container containing the BaO sample was removed from the desiccator and transferred into an in-house fabricated plexiglass box that was placed over the sample loading station of a Leica vacuum cryo manipulation system (Leica EM VCM). To purge the box, a continuous flow of N2 gas was maintained using an integrated port. The measured relative humidity in the plexiglass box was 14%. In the box, the sample stub was then removed from the sealed plastic container and mounted onto the Leica cryo-SEM sample mount. The mounted sample was then transferred into a Leica EM ACE600 high vacuum sputter coater using a Leica vacuum cryo transfer system (Leica EM VCT500) via the exchange ports on the VCM and ACE600. A knife attached via a sealed port in the ACE600 was then used to cut open the foil pouch and expose the sample. After opening the foil pouch with the knife, the non-coated BaO sample was transferred to the SEM (Hitachi SU8230) with the VCT500 for surface characterization. This Hitachi SU8230 microscope is equipped with an energy dispersive X-ray Spectroscopy (EDS) detector (Oxford Instruments X-max 80N) which was used to perform elemental analysis on the sample (15 kV accelerating voltage, ~15 mm working distance). Lastly, standard micrographs were collected at an accelerating voltage of 1 kV, an emission current of 4000 – 10000 nA, and a working distance of 5- or 10-mm. Following characterization, the BaO sample was then extracted from the SEM and exposed to 100% relative humidity for 5 minutes; humidity was controlled with the use of a VITROBOT (ThermoFisher Mark IV system). This exposed sample was then brought back into the SEM to observe sample degradation and collect EDS data. 2. Methods for processing the data: Processing methods are outlined in the “Description of Methods” section. 3. Instrument- or software-specific information needed to interpret the data: All instruments have been outlined in the “Description of Methods” section. Data has been provided with software-specific (e.g., .xrdml files) and universal (e.g. txt) formats and should be plottable with excel or google sheets. .xrdml files would require Panalytical X’Pert Highscore Plus software. 4. Standards and calibration information, if appropriate: Standards and subsequent XRD diffraction patterns were outlined in the “Description of Methods” section. 5. Environmental/experimental conditions: Relevant environmental conditions for data collection are detailed in the “Description of Methods” section. 6. Describe any quality-assurance procedures performed on the data: N/A 7. People involved with sample collection, processing, analysis and/or submission: Louis G. Corcoran, Ellen Monzo, Chinomso E. Onuoha, Shivasheesh Varshney, Han Seung Lee, Chris Fretham, Bharat Jalan, Alon V. McCormick, and R, Lee Penn ----------------------------------------- DATA-SPECIFIC INFORMATION: ----------------------------------------- 1) Folder ReadMe: 1. Xmin_Exposed: Sample image of the exposed sample taken after "X" minutes in the Humidity Box. 2. Xmin_Protected: Sample image of the protected sample after "X" minutes in the humidity box; aluminum foil pouch was cut immediately upon removal from the box and the image was taken immediately afterwards. 3. Sample images are included in Figure 3 in the main text. 2) Folder ReadMe: Naming Scheme for folders: Sample Name _ Exposure condition _ Relative Humidity (if applicable)_Sputter Coating Results (if Applicable) 1. Barium Oxide_exposed 100_RH 5 min_no Pt: Barium oxide sample exposed to 100% RH for 5 minutes; no sputter coating. 2. Barium Oxide_not exposed 14_RH_no Pt: Barium oxide sample protected in the aluminum foil pouch on a small metal sample stub; relative humidity on day of characterization was 14% RH; no sputter coating 3. Barium Oxide_not exposed 14_RH_2.12 nm Pt: BaO sample protected in he aluminum foil pouch on a small metal sample stub; relative humidity on day of characterization was 14% RH; 2.12 nm of Pt on surface as a result of sputter coating 4. Exposed over night (24 hrs) center_Pt coated sample: This is sample imaged in folder (3) that was taken out of the SEM chamber and exposed to environmental conditions for 24 hrs before being brought back into the SEM for additional characterization; sample was sputter coated originally with 2.12 nm Pt 3) > Barium Oxide_exposed 100_RH-5min_no Pt> Folder ReadMe 1. The text files are the metadata for sample characterization associated with the tiff file of the same name 2. BaO_Exposed word document includes SEM-EDX images 3. BaO_Exposed_analyzer includes SEM-EDX data. 4) > Barium Oxide_not exposed 14_RH_2.12 nm Pt> Folder ReadMe 1. The text files are the metadata for sample characterization associated with the tiff file of the same name. 2. BaO word document contains SEM-EDX images and data. 5) > Barium Oxide_not exposed 14_RH-no Pt> Folder ReadMe 1. The text files are the metadata for sample characterization associated with the tiff file of the same name. 2. BaO word document contains SEM-EDX images and data. 3. "BaO analyzer" word document contains SEM-EDX data relevant to exposed sample (5 min at 100% RH). 6) > exposed over night (24 hrs) center_Pt coated sample> Folder ReadMe 1. Relative humidity on the day the exposed sample was brought back into the SEM (after exposing to ambient conditions for 24 hrs) was 20%. 2. The text files are the characterization metadata of the tiff files with the same name. 7) >Raw Data Files>>3min Air + 3&6hrHB Data> Folder ReadMe 1. Background pattern in this folder was utilized as the background subtraction for all data in this folder. 2. Excel spreadsheets include raw data from diffractograms produced via the instrument software; sample files with the same name correspond to the same diffraction pattern. 8) >Raw Data Files>>/Exposed&ProtectedData> Folder ReadMe 1. Background pattern in this folder was utilized as the background subtraction for all data in this folder. 2. "Burrito" in the naming scheme refers to samples that were "protected" when placed in the humidity box for the denoted time. 3. "Air" in the naming scheme refers to samples that were fully exposed (i.e., not protected) when placed in the humidity box for the denoted time. 4. Excel spreadsheets include raw data from diffractograms produced via the instrument software; sample files with the same name correspond to the same diffraction pattern. ---------------------------------- DATA TREE ---------------------------------- | ReadMe_Electron Microscopy Transfer System_Penn2025.txt | +---RHEED and BaO Growth.zip | \---RHEED and BaO Growth | BaO_AfterGrowth_90C_20p5_[100] Image.png | RHEED-intensity.xlsx | +---Salt Humidity Chamber Images.zip | \---Salt Humidity Chamber Images | 15min_Exposed.jpg | 15min_Protected.jpg | 180min_Exposed.jpg | 180min_Protected.jpg | 180min_weighboat_Exposed.jpg | 20221006_125915.jpg | 30min_Exposed.jpg | 30min_Protected.jpg | 5min_Exposed(Additional).jpg | 5min_Exposed.jpg | 5min_Protected.jpg | 60min_Exposed.jpg | 60min_Protected.jpg | ExampleGlassSlide+SaltPrep (Refer to Figure 1A1-3).jpg | ReadMe.txt | StubsPreparedinGloveBox.jpg | +---SEM+EDX Data | \---SEM+EDX Data.zip | | ReadMe.txt | | | +---Barium Oxide_exposed 100_RH 5 min_no Pt | | BaO_exposed.docx | | BaO_exposed_analyzer.docx | | Barium Oxide_exposed_0001.tif | | Barium Oxide_exposed_0001.txt | | Barium Oxide_exposed_0002.tif | | Barium Oxide_exposed_0002.txt | | Barium Oxide_exposed_0003.tif | | Barium Oxide_exposed_0003.txt | | Barium Oxide_exposed_0004.tif | | Barium Oxide_exposed_0004.txt | | Barium Oxide_exposed_0005.tif | | Barium Oxide_exposed_0005.txt | | Barium Oxide_exposed_0006.tif | | Barium Oxide_exposed_0006.txt | | Barium Oxide_exposed_0007.tif | | Barium Oxide_exposed_0007.txt | | Barium Oxide_exposed_0008.tif | | Barium Oxide_exposed_0008.txt | | Barium Oxide_exposed_0009.tif | | Barium Oxide_exposed_0009.txt | | Barium Oxide_exposed_0010.tif | | Barium Oxide_exposed_0010.txt | | Barium Oxide_exposed_0011.tif | | Barium Oxide_exposed_0011.txt | | ReadMe.txt | | | +---Barium Oxide_not exposed 14_RH_2.13 nm Pt | | BaO.docx | | Barium Oxide_not exposed_0001.tif | | Barium Oxide_not exposed_0001.txt | | Barium Oxide_not exposed_0002.tif | | Barium Oxide_not exposed_0002.txt | | Barium Oxide_not exposed_0003.tif | | Barium Oxide_not exposed_0003.txt | | Barium Oxide_not exposed_0004.tif | | Barium Oxide_not exposed_0004.txt | | Barium Oxide_not exposed_0005.tif | | Barium Oxide_not exposed_0005.txt | | Barium Oxide_not exposed_0006.tif | | Barium Oxide_not exposed_0006.txt | | Barium Oxide_not exposed_0007.tif | | Barium Oxide_not exposed_0007.txt | | Barium Oxide_not exposed_0008.tif | | Barium Oxide_not exposed_0008.txt | | Barium Oxide_not exposed_0009.tif | | Barium Oxide_not exposed_0009.txt | | Barium Oxide_not exposed_0010.tif | | Barium Oxide_not exposed_0010.txt | | Barium Oxide_not exposed_0011.tif | | Barium Oxide_not exposed_0011.txt | | Barium Oxide_not exposed_0012.tif | | Barium Oxide_not exposed_0012.txt | | Barium Oxide_not exposed_0013.tif | | Barium Oxide_not exposed_0013.txt | | ReadMe.txt | | | +---Barium Oxide_not exposed 14_RH_no Pt | | BaO analyzer.docx | | BaO.docx | | Barium Oxide_not exposed_0001.tif | | Barium Oxide_not exposed_0001.txt | | Barium Oxide_not exposed_0002.tif | | Barium Oxide_not exposed_0002.txt | | Barium Oxide_not exposed_0003.tif | | Barium Oxide_not exposed_0003.txt | | Barium Oxide_not exposed_0004.tif | | Barium Oxide_not exposed_0004.txt | | Barium Oxide_not exposed_0005.tif | | Barium Oxide_not exposed_0005.txt | | Barium Oxide_not exposed_0006.tif | | Barium Oxide_not exposed_0006.txt | | Barium Oxide_not exposed_0007.tif | | Barium Oxide_not exposed_0007.txt | | Barium Oxide_not exposed_0008.tif | | Barium Oxide_not exposed_0008.txt | | ReadMe.txt | | | \---exposed over night (24 hrs) center_ Pt coated sample | BaO_24 hrs exposed 20_RH_0001.tif | BaO_24 hrs exposed 20_RH_0001.txt | BaO_24 hrs exposed 20_RH_0002.tif | BaO_24 hrs exposed 20_RH_0002.txt | BaO_24 hrs exposed 20_RH_0003.tif | BaO_24 hrs exposed 20_RH_0003.txt | BaO_24 hrs exposed 20_RH_0004.tif | BaO_24 hrs exposed 20_RH_0004.txt | BaO_24 hrs exposed 20_RH_0005.tif | BaO_24 hrs exposed 20_RH_0005.txt | BaO_24 hrs exposed 20_RH_0006.tif | BaO_24 hrs exposed 20_RH_0006.txt | BaO_24 hrs exposed 20_RH_0007.tif | BaO_24 hrs exposed 20_RH_0007.txt | BaO_24 hrs exposed 20_RH_0008.tif | BaO_24 hrs exposed 20_RH_0008.txt | BaO_24 hrs exposed 20_RH_0009.tif | BaO_24 hrs exposed 20_RH_0009.txt | BaO_24 hrs exposed 20_RH_0010.tif | BaO_24 hrs exposed 20_RH_0010.txt | BaO_24 hrs exposed 20_RH_0011.tif | BaO_24 hrs exposed 20_RH_0011.txt | ReadMe.txt | \---XRD Data Files.zip \---XRD Data Files | MgCl2_data.pptx | +---Raw Data Files | +---3min Air + 3&6hrHB Data | | 20221201_3hrHB_Spinner, 10-70, 105s, 52min_1.ASC | | 20221201_3hrHB_Spinner, 10-70, 105s, 52min_1.xlsx | | 20221201_3hrHB_Spinner, 10-70, 105s, 52min_1.xrdml | | 20221201_6hrHB_Spinner, 10-70, 105s, 52min_1.ASC | | 20221201_6hrHB_Spinner, 10-70, 105s, 52min_1.xlsx | | 20221201_6hrHB_Spinner, 10-70, 105s, 52min_1.xrdml | | 20221201_air3minsample_Spinner, 10-70, 105s, 52min_1.ASC | | 20221201_air3minsample_Spinner, 10-70, 105s, 52min_1.xlsx | | 20221201_air3minsample_Spinner, 10-70, 105s, 52min_1.xrdml | | 20221202_EMM_Background-3siwafers_Spinner, 10-70, 105s, 52min_1.ASC | | 20221202_EMM_Background-3siwafers_Spinner, 10-70, 105s, 52min_1.xlsx | | 20221202_EMM_Background-3siwafers_Spinner, 10-70, 105s, 52min_1.xrdml | | ReadMe.txt | | | \---Exposed&ProtectedData | 20221007_Air-15Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.ASC | 20221007_Air-15Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.xlsx | 20221007_Air-15Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.xrdml | 20221007_Air-30Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.ASC | 20221007_Air-30Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.xlsx | 20221007_Air-30Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.xrdml | 20221007_Air-5Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.ASC | 20221007_Air-5Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.xlsx | 20221007_Air-5Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.xrdml | 20221007_Air-60Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.ASC | 20221007_Air-60Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.xlsx | 20221007_Air-60Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.xrdml | 20221007_Burrito-15Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.ASC | 20221007_Burrito-15Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.xlsx | 20221007_Burrito-15Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.xrdml | 20221007_Burrito-180Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.ASC | 20221007_Burrito-180Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.xlsx | 20221007_Burrito-180Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.xrdml | 20221007_Burrito-30Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.ASC | 20221007_Burrito-30Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.xlsx | 20221007_Burrito-30Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.xrdml | 20221007_Burrito-5Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.ASC | 20221007_Burrito-5Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.xlsx | 20221007_Burrito-5Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.xrdml | 20221007_Burrito-60Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.ASC | 20221007_Burrito-60Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.xlsx | 20221007_Burrito-60Min-MgCl2#2_Spinner, 10-70, 105s, 52min_1.xrdml | 20221012_Dr-MgCl2#2_Standard_Spinner, 10-70, 105s, 52min_1.ASC | 20221012_Dr-MgCl2#2_Standard_Spinner, 10-70, 105s, 52min_1.xlsx | 20221012_Dr-MgCl2#2_Standard_Spinner, 10-70, 105s, 52min_1.xrdml | Background-3siwafers_Spinner, 10-70, 105s, 52min_1.ASC | Background-3siwafers_Spinner, 10-70, 105s, 52min_1.xlsx | Background-3siwafers_Spinner, 10-70, 105s, 52min_1.xrdml | ReadMe.txt | \---Reference crystal structures MgCl2-2H2O_Sugimoto_2007.xlsx MgCl2-2H2O_Sugimoto_2007.xye MgCl2-4H2O Profile_Sugimoto_2007.txt MgCl2-4H2O Profile_Sugimoto_2007.xlsx MgCl2-H2O Profile_Sugimoto_2007.txt MgCl2-H2O Profile_Sugimoto_2007.xlsx MgCl2x6H2O_sd_1100275.cif MgCl2_10H2O_high pressure_ps5038sup1.cif MgCl2_12H2O Profile.txt MgCl2_12H2O Profile.xlsx MgCl2_12H2O_CCDC_966248.cif MgCl2_4H2O_&2H2O_&1H2O_kd5011sup1.cif MgCl2_4H2O_262265-ICSD Profile.txt MgCl2_4H2O_262265-ICSD Profile.xlsx MgCl2_4H2O_CCDC_1719928.cif MgCl2_6H2O_sm_isp_SD1100275-published_cell Profile.txt MgCl2_6H2O_sm_isp_SD1100275-published_cell Profile.xlsx MgCl2_8H2O Profile.txt MgCl2_8H2O Profile.xlsx MgCl2_8H2O_CCDC_966251.cif MgCl2_no hydrate_01-089-1567.txt MgCl2_no hydrate_01-089-1567.xlsx mgi2_hydrates_actacryst_2013.pdf MgO_00-045-0946.txt MgO_00-045-0946.xlsx