This file Chakraborty_et_al_ReadMe_v1.txt was updated on 2025-03-19 by Rohan D. Chakraborty ------------------- GENERAL INFORMATION ------------------- 1. Title of Dataset: Large Near-Infrared Refractive Index Modulation in Ion-Gel Gated BaSnO3 for Active Metasurfaces 2. Author Information: Principal Investigator Contact Information Name: Vivian E. Ferry Institution: University of Minnesota Address: Department of Chemical Engineering and Materials Science, 421 Washington Ave SE, Minneapolis, Minnesota 55455 Email: veferry@umn.edu ORCID: https://orcid.org/0000-0002-9676-6056 Associate or Co-investigator Contact Information Name: Rohan D. Chakraborty Institution: University of Minnesota Address: Department of Chemical Engineering and Materials Science, 421 Washington Ave SE, Minneapolis, Minnesota 55455 Email: rohanc@umn.edu ORCID: https://orcid.org/0000-0002-5100-885X Associate or Co-investigator Contact Information Name: Chris Leighton Institution: University of Minnesota Address: Department of Chemical Engineering and Materials Science, 421 Washington Ave SE, Minneapolis, Minnesota 55455 Email: leighton@umn.edu ORCID: https://orcid.org/0000-0003-2492-0816 3. Date of data collection (single date, range, approximate date): 20230801 - 20250301 4. Geographic location of data collection (where was data collected?): University of Minnesota - Twin Cities (Minneapolis, MN) 5. Information about funding sources that supported the collection of the data: This work was supported primarily by the National Science Foundation through the University of Minnesota MRSEC under Award Number DMR-2011401. Parts of this work were performed in the Characterization Facility at the University of Minnesota, which receives partial support from NSF through the MRSEC program. Portions of this work were also conducted in the Minnesota Nano Center, which is supported by NSF through the National Nano Coordinated Infrastructure (NNCI) under Award Number ECCS-2025124. -------------------------- SHARING/ACCESS INFORMATION -------------------------- 1. Licenses/restrictions placed on the data: CC0 1.0 Universal 2. Links to publications that cite or use the data: 3. Links to other publicly accessible locations of the data: N/A 4. Links/relationships to ancillary data sets: N/A 5. Was data derived from another source? No 6. Recommended citation for the data: --------------------- DATA & FILE OVERVIEW --------------------- 1. File List A. Filename: Fig1a_v1.csv Short description: Wide-angle X-ray diffraction measurements of as-grown BSO films on SLAO and LSAT substrates B. Filename: Fig2_v1.xlsx Short description: Optical transmittance, spectroscopic ellipsometry, and Hall data of as-grown BSO films at different Hall electron density (n3D) C. Filename: Fig3_v1.xlsx Short description: In-situ Hall measurements during electrolyte gating, and electrostatic/optical modeling of the BSO accumulation layer under electrolyte gating F. Filename: Fig4_v1.xlsx Short description: Finite-difference time-domain optical simulation data of beam steering metasurfaces with BSO 2. Relationship between files: Each file contains a different type of data gathered during this study. These data, when plotted together, comprise the figures presented in the corresponding publication. 3. Additional related data collected that was not included in the current data package: N/A 4. Are there multiple versions of the dataset? N -------------------------- METHODOLOGICAL INFORMATION -------------------------- 1. Description of methods used for collection/generation of data: BSO Film Growth and Structural Characterization: La-doped BaSnO3 (BSO) films were grown on (001)-oriented SrLaAlO4 (SLAO) and (LaAlO3)0.3(Sr2TaAlO6)0.7 (LSAT) substrates using high-pressure-oxygen sputtering. 5 mm × 5 mm × 0.5 mm substrates from MTI were annealed for 15 minutes at 900 °C in 1.9 Torr of ultrapure O2, after which La-doped BSO was sputtered from a 2-inch ceramic La0.02Ba0.98SnO3 target at 38-44 W DC power, resulting in a 1 nm/min growth rate. Films were then cooled to room temperature in 75 Torr of O2. The film in Figure 3 was vacuum annealed post-growth at pressure <10^-6 Torr and 650 °C for 15 min to further boost the Hall electron density (from 1.54 × 10^20 cm-3 to 2.42 × 10^20 cm-3) and mobility (from 33.5 to 42.3 cm^2V^-1s^-1), primarily through microstructural improvements1. Note that BSO films on SLAO and LSAT substrates are subject to very large lattice mismatch. This results in low critical thickness for strain relaxation, which we find promotes rapid strain relaxation with increasing thickness, and higher transport performance. Nevertheless, X-ray diffraction measurements of BSO films show prominent Laue oscillations around the BSO 002 peak (Figure 1a). We fit the oscillation spacings fit to extract film thickness. X-ray diffraction was performed with a Rigaku Smartlab XE diffractometer with a 5-axis goniometer, HyPix-3000 high energy resolution detector, and λ ≈ 1.54 Å (Cu Kα) incident wavelength. We grew BSO films at a wide range of thicknesses (10-70 nm) to access different Hall electron densities (n3D), as n3D and the electronic mobility (µel) increase with thickness due to suppression of compensating charged dislocations and surface/interface depletion. Optical Characterization of BSO Films: Optical transmittance of BSO films on two-side-polished substrates was collected between 350-5000 nm under ambient conditions. Data from 350-2500 nm were collected with an Agilent Cary 7000 UV/Vis/NIR spectrophotometer, where samples were mounted on opaque holders with a 5-mm-diameter opening, matching our substrate size. Data from 2500-5000 nm were collected with a Bruker Hyperion 2000 FTIR microscope with a liquid-N2-cooled MCT detector coupled to a Bruker Invenio-R FTIR spectrometer. All transmittance data were taken with unpolarized light at normal incidence and referenced to the transmittance of air. Spectroscopic ellipsometry was performed on BSO films grown on one-side-polished substrates using a J.A. Woollam VASE instrument from 800-2500 nm and incident angles of 55°, 65°, and 75°. Ellipsometric data from all three angles were fit together to a Drude model. Fabrication and Gating of BSO Electrolyte-Gated Transistors: Electrolyte-gated transistors with BSO were fabricated in a side-gate geometry. Ar+ ion milling through a steel mask defined the gate and channel electrode patterns, then Ti (20 nm)/Au (60 nm) contacts were deposited through a second mask using DC magnetron sputtering. Our ion gel electrolytes were 80 wt % of the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (EMI:TFSI) in 20 wt % of the polymer poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) and were laminated onto devices as detailed previously. Electrolyte gating was performed in a Quantum Design Physical Property Measurement System (PPMS) at 300 K and P < 10^-5 Torr. We used a Keithley 2400 sourcemeter to apply Vg > 0 V to the transistor, inducing additional electron accumulation in the La-doped BSO. At each Vg, four-wire resistance measurements in the van der Pauw geometry were made, followed by a Hall effect measurement with magnetic field sweeps to ±2 T. We used two-channel conduction modeling to isolate the Hall parameters of the accumulation layer from those of the bulk film following the method detailed in our previous work: https://doi.org/10.1103/PhysRevMaterials.3.075001. Finite-Difference Time-Domain Optical Simulations: Finite-difference time-domain (FDTD) simulations of BSO plasmonic metasurfaces were performed using Ansys Lumerical software. The BSO refractive index is taken from this work, the refractive index of Au was taken from literature (https://doi.org/10.1364/AO.37.005271), and the ion gel was modeled as a n = 1.36 dielectric. Experimentally, our ion gel thickness is typically ~10 µm, but we simulated a 10 nm gel here to maintain a nm-scale cavity. We justify this based on recent work showing similar gel electrolyte performance across a wide thickness range spanning 10 nm to ~1 µm (https://doi.org/10.1021/acsami.2c13140). A broadband x-polarized plane wave is injected in the negative z-direction, periodic boundary conditions are used in the x and y directions, and perfectly matched layers were used as boundary conditions in the z-direction. Reflection amplitude/phase spectra were calculated with Lumerical’s “S parameters” analysis group. Beam steering profiles were obtained from far-field transformations of the reflected fields using Lumerical's built-in "farfield3D" function and "farfieldspherical" function. 2. Methods for processing the data: Calculation of Hall Electron Density and Mobility: The Hall electron density (n3D) and mobility (µel) are related by the Drude model: 1/ρ = n3D*e*µel, where ρ is the resistivity and e is the elementary electron charge. The calculation proceeds as follows: -Hall effect measurements, described above, generate a linear plot of Hall resistance (Rhall) vs. magnetic field (Bhall). -The linear Rhall vs. Bhall data are fit to get the slope. n3D is then calculated as n3D = 1/(e*slope*t), where t is the film thickness calculated from X-ray diffraction (described above). - 4-wire resistance measurements are performed with the van der Pauw method. Two resistance measurements (R1 and R2) are performed, representing the two different current-voltage wiring configurations for the 4-wire model. Using R1 and R2, the following van der Pauw equation was numerically solved to obtain the sheet resistance, Rs: exp(-πR1/Rs) + exp(-πR2/Rs) = 1 - Resistivity is calculated as ρ = Rs*t - ρ and n3D are finally put into the Drude model to calculate µel FILL OUT 3. Instrument- or software-specific information needed to interpret the data: N/A 4. Standards and calibration information, if appropriate: N/A 5. Environmental/experimental conditions: See above description of methods. 6. Describe any quality-assurance procedures performed on the data: In Figure 2, all spectroscopic ellipsometry data correspond to fits with an acceptable mean-squared-error (MSE) of 5-10. For the full-wave optical simulations reported in Figure 4, careful convergence testing was performed in order to ensure the accuracy of the simulations. 7. People involved with sample collection, processing, analysis and/or submission: RDC, CL, and VEF conceived of the study, and VEF oversaw its execution. RDC conducted all experiments, electrical/optical simulations, and related analysis for this study, under the guidance of CL and VEF. RDC, CL, and VEF wrote the paper. ----------------------------------------- DATA-SPECIFIC INFORMATION FOR: Fig1a_v1.xlsx ----------------------------------------- 1. Number of variables: 2 2. Number of cases/rows: 2 cases: SLAO substrate, LSAT substrate 3. Variable List A. Name: 2θ Description: 1D vector representing the diffraction angle, in units of degrees. B. Name: Intensity Description: 1D vector representing the diffracted intensity, in arbitrary units (a.u.). ----------------------------------------- DATA-SPECIFIC INFORMATION FOR: Fig2_v1.xlsx ----------------------------------------- 1. Number of variables: 11 2. Number of cases/rows: (a) 6 cases: n3D = 5.22e19 cm^-3, 1.49e20 cm^-3, 1.78e20 cm^-3, 1.98e20 cm^-3, 2.06e20 cm^-3, and 2.46e20 cm^-3 (b,c) 5 cases: n3D = 1.55e20 cm^-3, 1.90e20 cm^-3, 1.99e20 cm^-3, 2.13e20 cm^-3, 2.62e20 cm^-3 (d-f) N/A cases 3. Variable List A. Name: Wavelength Description: 1D vector representing the wavelength of light, in units of nm. B. Name: Transmittance Description: 1D vector representing the optical transmittance, in units of %. C. Name: n Description: 1D vector representing the real part of the complex refractive index, which is unitless. D. Name: k Description: 1D vector representing the imaginary part of the complex refractive index, which is unitless. E. Name: n3D Description: 1D vector representing the carrier density, in units of cm^-3. F. Name: ε_infinity Description: 1D vector representing the high-frequency dielectric constant, which is unitless. G. Name: ω_p Description: 1D vector representing the angular plasma frequency, in units of eV. H. Name: γ Description: 1D vector representing the angular damping frequency, in units of eV. I. Name: m*/m0 Description: 1D vector representing the electron effective mass divided by the elementary mass, which is unitless. J. Name: μel Description: 1D vector representing the electron mobility, in units of cm^2/(Vs). K. Name: μopt Description: 1D vector representing the optical mobility, in units of cm^2/(Vs). ----------------------------------------- DATA-SPECIFIC INFORMATION FOR: Fig3_v1.xlsx ----------------------------------------- 1. Number of variables: 9 2. Number of cases/rows: (a) N/A cases (b) 3 cases: 1 V, 2 V, 3 V (c) N/A cases (d-f) 4 cases: 0 V, 1 V, 2 V, 3 V 3. Variable List A. Name: Vg Description: 1D vector representing the gate voltage, in units of V. B. Name: n3D Description: 1D vector representing the carrier density, in units of cm^-3. C. Name: μel Description: 1D vector representing the electron mobility, in units of cm^2/(Vs). D. Name: z Description: 1D vector representing the film depth, in units of m. E. Name: dA Description: 1D vector representing the accumulation layer thickness, in units of nm. F. Name: Wavelength Description: 1D vector representing the wavelength of light, in units of nm. G. Name: Real Permittivity Description: 1D vector representing the real part of the complex permittivity, which is unitless. H. Name: n Description: 1D vector representing the real part of the complex refractive index, which is unitless. I. Name: k Description: 1D vector representing the imaginary part of the complex refractive index, which is unitless. ----------------------------------------- DATA-SPECIFIC INFORMATION FOR: Fig4_v1.xlsx ----------------------------------------- 1. Number of variables: 7 2. Number of cases/rows: (b,c) 4 cases: 0 V, 1 V, 2 V, 3 V (e) 4 cases: N = 4 antennas, N = 6 antennas, N = 8 antennas, N = 10 antennas (f) N/A cases 3. Variable List A. Name: Wavelength Description: 1D vector representing the wavelength of light, in units of nm. B. Name: Reflectance Description: 1D vector representing the optical reflectance, in units of %. C. Name: Reflection Phase Description: 1D vector representing the reflection phase, in units of degrees. D. Name: Beam Steering Angle Description: 1D vector representing the beam steering angle, in units of degrees. E. Name: Intensity Description: 1D vector representing the beam steering intensity, in arbitrary units (a.u.). F. Name: Absolute Beam Steering Angle Description: 1D vector representing the absolute (±) beam steering angle, in units of degrees. G. Name: Scattering Efficiency Description: 1D vector representing the scattering efficiency, in units of percent. ----------------------------------- Directory Structure ----------------------------------- Chakraborty_et_al_ReadMe_v1.txt Fig1a_v1.xlsx Fig2_v1.xlsx Fig3_v1.xlsx Fig4_v1.xlsx