Supporting Information NaSn2As2: An Exfoliatable Layered van der ...
Supporting Information NaSn2As2: An Exfoliatable Layered van der Waals Zintl Phase Maxx Q. Arguilla,‡,1 Jyoti Katoch,‡,2 Kevin Krymowski,3 Nicholas D. Cultrara,1 Jinsong Xu,2 Xiaoxiang Xi,4 Amanda Hanks, 3 Shishi Jiang,1 Richard D. Ross, 1 Roland J. Koch,5 Søren Ulstrup,5 Aaron Bostwick,5 Chris Jozwiak,5 David W. McComb, 3 Eli Rotenberg,5 Jie Shan,4 Wolfgang Windl,3 Roland Kawakami2 and Joshua E. Goldberger*,1 1
Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio
43210-1340, United States 2
Department of Physics, The Ohio State University, Columbus, Ohio 43210-1340, United
States 3
Department of Materials Science and Engineering, The Ohio State University,
Columbus, Ohio 43210-1340, United States 4
Department of Physics, The Pennsylvania State University, University Park,
Pennsylvania 16802-6300, United States
5
Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley,
California 94720, United States
Figure S1. Powder XRD Rietveld refinement results for NaSn2As2 using TOPAS. Table S1. TOPAS Rietveld Refinement parameters for NaSn2As2 Empirical Formula NaSn2As2 Fw 410.253 Space Group R-3m a (Å) 3.99998(10) c (Å) 27.5619(13) Cell Volume (Å3) 381.91(2) T (K) 295 Pattern Range (θ) 5-70 λ (Å) 1.5406 Rwp (%) 4.44 Rp (%) 3.19 Table S2. Atomic coordinates for NaSn2As2 from Rietveld refinement. Atom x y z Occupancy Beq Sn 0 0 0.2095(7) 1 0.72(5) As 0 0 0.4069(1) 1 0.34(7) Na 0 0 0 1 0.41(4) Table S3. Selected bond lengths from the refined NaSn2As2 structure. d (Å) Sn-Sn 3.30 Na-As 3.07 Sn-As 2.69
Figure S2. Verification of the Sn:As stoichiometry in NaSn2As2 measured via X-‐Ray Fluorescence. Red data points correspond to different mixtures of elemental Sn and As to prepare a standard calibration curve.
Figure S3. XPS spectra of the NaSn2As2 crystals after exposure to 4 days in air (green) and after etching the top 1 nm (red) using a Ar+ ion etch, highlighting the a) Na 1s, b) Sn 4d, c) Sn 3d5/2, and d) As 3d peaks.
Figure S4. AFM images and height profiles of mechanically-‐exfoliated NaSn2As2 onto 285 nm SiO2/Si.
Figure S5. Step height analysis of AFM micrographs taken on exfoliated NaSn2As2 flakes with multiple step edges. Step thicknesses were obtained from averaged heights along the horizontal length of each step.
Figure S6. AFM thickness histogram of different step heights obtained from mechanically-‐exfoliated NaSn2As2 showing that cleaved steps always have thicknesses that were multiples of ~0.9 ± 0.2 nm.
Figure S7. UV-‐Vis Spectrum of NaSn2As2 dispersed in various solvents.
Figure S8. AFM images and height profiles of CHP-‐exfoliated NaSn2As2 flakes that were prepared via dropcasting onto 285 nm SiO2/Si.
Figure S9. AFM thickness histogram of 36 different flakes that were prepared via dropcasting CHP-‐exfoliated NaSn2As2 onto 285 nm SiO2/Si.
Figure S10. Representative EDX spectrum of solvent-‐exfoliated NaSn2As2.
Figure S11. HRTEM image of CHP-‐exfoliated NaSn2As2 highlighting long-‐range order based on the (015) lattice fringes. Inset is a fast Fourier transform of the image showing a [2-‐51] zone axis.
Figure S12. XPS spectra of the liquid-‐exfoliated NaSn2As2 flakes after exposure to 1 day (green) and 3 days in air (purple), highlighting the a) Na 1s, b) Sn 3d5/2, and c) As 3d peaks.
Figure S13. Adhesion energy of NaSn2As2 as a function of layer separation. The data for the DFT-‐D2 (plain GGA) calculation are red (blue). The interlayer separation is relative to the equilibrium separation of bulk NaAs2Sn2.
Figure S14. ARPES spectrum of NaSn2As2, collected at 127 eV at 41 K.
Figure S15. HSE band structure of a single layer NaSn2As2 which shows that the metallic character is preserved in isolated layers.
Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio
43210-1340, United States 2
Department of Physics, The Ohio State University, Columbus, Ohio 43210-1340, United
States 3
Department of Materials Science and Engineering, The Ohio State University,
Columbus, Ohio 43210-1340, United States 4
Department of Physics, The Pennsylvania State University, University Park,
Pennsylvania 16802-6300, United States
5
Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley,
California 94720, United States
Figure S1. Powder XRD Rietveld refinement results for NaSn2As2 using TOPAS. Table S1. TOPAS Rietveld Refinement parameters for NaSn2As2 Empirical Formula NaSn2As2 Fw 410.253 Space Group R-3m a (Å) 3.99998(10) c (Å) 27.5619(13) Cell Volume (Å3) 381.91(2) T (K) 295 Pattern Range (θ) 5-70 λ (Å) 1.5406 Rwp (%) 4.44 Rp (%) 3.19 Table S2. Atomic coordinates for NaSn2As2 from Rietveld refinement. Atom x y z Occupancy Beq Sn 0 0 0.2095(7) 1 0.72(5) As 0 0 0.4069(1) 1 0.34(7) Na 0 0 0 1 0.41(4) Table S3. Selected bond lengths from the refined NaSn2As2 structure. d (Å) Sn-Sn 3.30 Na-As 3.07 Sn-As 2.69
Figure S2. Verification of the Sn:As stoichiometry in NaSn2As2 measured via X-‐Ray Fluorescence. Red data points correspond to different mixtures of elemental Sn and As to prepare a standard calibration curve.
Figure S3. XPS spectra of the NaSn2As2 crystals after exposure to 4 days in air (green) and after etching the top 1 nm (red) using a Ar+ ion etch, highlighting the a) Na 1s, b) Sn 4d, c) Sn 3d5/2, and d) As 3d peaks.
Figure S4. AFM images and height profiles of mechanically-‐exfoliated NaSn2As2 onto 285 nm SiO2/Si.
Figure S5. Step height analysis of AFM micrographs taken on exfoliated NaSn2As2 flakes with multiple step edges. Step thicknesses were obtained from averaged heights along the horizontal length of each step.
Figure S6. AFM thickness histogram of different step heights obtained from mechanically-‐exfoliated NaSn2As2 showing that cleaved steps always have thicknesses that were multiples of ~0.9 ± 0.2 nm.
Figure S7. UV-‐Vis Spectrum of NaSn2As2 dispersed in various solvents.
Figure S8. AFM images and height profiles of CHP-‐exfoliated NaSn2As2 flakes that were prepared via dropcasting onto 285 nm SiO2/Si.
Figure S9. AFM thickness histogram of 36 different flakes that were prepared via dropcasting CHP-‐exfoliated NaSn2As2 onto 285 nm SiO2/Si.
Figure S10. Representative EDX spectrum of solvent-‐exfoliated NaSn2As2.
Figure S11. HRTEM image of CHP-‐exfoliated NaSn2As2 highlighting long-‐range order based on the (015) lattice fringes. Inset is a fast Fourier transform of the image showing a [2-‐51] zone axis.
Figure S12. XPS spectra of the liquid-‐exfoliated NaSn2As2 flakes after exposure to 1 day (green) and 3 days in air (purple), highlighting the a) Na 1s, b) Sn 3d5/2, and c) As 3d peaks.
Figure S13. Adhesion energy of NaSn2As2 as a function of layer separation. The data for the DFT-‐D2 (plain GGA) calculation are red (blue). The interlayer separation is relative to the equilibrium separation of bulk NaAs2Sn2.
Figure S14. ARPES spectrum of NaSn2As2, collected at 127 eV at 41 K.
Figure S15. HSE band structure of a single layer NaSn2As2 which shows that the metallic character is preserved in isolated layers.
