Research ArticleChemistry

Fluorinated h-BN as a magnetic semiconductor

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Science Advances  14 Jul 2017:
Vol. 3, no. 7, e1700842
DOI: 10.1126/sciadv.1700842
  • Fig. 1 Synthesis and characterization of fluorinated boron nitride.

    (A) The schematic of the method used for the fluorination of h-BN is outlined. The bulk h-BN is dispersed in DMF, and Nafion is added to it. The mixture is heated in an autoclave at 200°C for 12 hours. (B) The deconvoluted XPS spectrum of B 1s peak shows two peaks, one corresponding to B-N bonding in h-BN and the other low intensity peak at higher energy corresponds to B-F bonding. (C) Deconvoluted XPS spectrum of N 1s peak also shows two peaks corresponding to N-B and N-F. (D) The IR spectra showing the broad B-N-B bending vibrations in h-BN and F-BN. In F-BN, the F-B peaks can be clearly seen interspersed with the broad B-N peak. (E) XRD showing the most intense peaks in h-BN and F-BN. (F) Raman spectra shows the E2g peak in h-BN and the shifted peak, which appears in F-BN. (G) Low-magnification bright-field TEM image of the thin F-BN sheets and the diffraction pattern of 001 orientation (inset) confirms the hexagonal structure.

  • Fig. 2 Electronic properties and band structure of fluorinated boron nitride.

    (A) Variation of bandgap calculated from the UV-vis absorption measurements with the percentage of fluorine doping. The bandgap was calculated from the absorbance measurements using Tauc plot. (B) Variation of deconvoluted PL spectra according to the percentage of fluorine doping. Each PL spectrum was deconvoluted into three peaks, namely, A, B, and C. (C) I-V curve obtained from two-probe measurements conducted on a device fabricated on fluorinated boron nitride (F-BN) on a silicon substrate with SiO2 coating. The inset shows an optical image of the device. (D) Magnetotransport measurements as a function of temperature at zero field, low field, and at high field. The inset shows the negative magnetoresistance at two different temperatures. (E and F) Band structures and density of states with atomic contribution obtained by spin-polarized calculations for F-BN sheets having (E) 6.25% and (F) 12.5% F concentrations. (G) Change in bandgap (Eg) as a function of F concentrations calculated from DFT calculations. Inset shows variation in defect level and valence band maximum (VBM) and conduction band minimum (CBM) from doping above 5%, where defect level is seen.

  • Fig. 3 Unconventional magnetic properties of fluorinated boron nitride.

    (A) The room temperature hysteresis curve of F-BN with 8.1% fluorine. (B) The experimentally observed temperature-dependent susceptibility fitted with the Curie’s law. The measurement was performed at an applied dc field of 500 Oe. (C) The susceptibility variation with temperature obtained on zero field cooling (ZFC) and field cooling (FC) after subtracting the diamagnetic background. (D) The real part of the ac susceptibility against temperature for measurements at 75 and 750 Hz at an ac field of 2 Oe. The freezing temperature (Tf) is marked.

  • Fig. 4 DFT calculations of the magnetic moment for various configurations.

    The energy difference between different magnetic solutions marked by I to VII for different F concentrations and their corresponding nonmagnetic states. I, II, IV, and VI; III and V; and VII are FM, AFM, and ferrimagnetic solutions, respectively. The total magnetic moment [MB)] for different magnetic states is also shown in the same plot by orange diamonds, whereas axis is marked on the right side. The spin-up and spin-down densities are colored purple and yellow, respectively. The isosurface value of 0.002 e/A3 is fixed for spin-density plots. The magnetic moment is localized to the nearest six N atoms of the region, where three F atoms (red color sphere) are attached to three B atoms, and one F atom is attached in the opposite site with N atom in the middle of hexagon (as shown by dotted blue line). II (IV) and III (V) are FM and AFM solutions of the 4 × 4 × 1 (8 × 8 × 1) supercell (shown in orange dotted line) corresponding to 12.5% F concentration. VII is the FM solution of the 4 × 4 × 1 supercell corresponding to 15.625%. I and VI are not displayed because these have the same structure as II but with 9.375 and 12.5% F.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/7/e1700842/DC1

    section S1. Synthesis

    section S2. 19F NMR analysis

    section S3. Structural characterizations

    section S4. Bandgap calculations

    section S5. Photoluminescence spectra

    section S6. Magnetic measurements

    section S7. Computational methodology

    fig. S1. Structural characterizations of plasma-fluorinated boron nitride.

    fig. S2. XPS spectrum of highly fluorinated boron nitride.

    fig. S3. 19F MAS spectra (376.3-MHz) of F-BN with MAS rate of 12 and 10 kHz.

    fig. S4. Electron microscope images of the fluorinated boron nitride sheets.

    fig. S5. Tauc plot for the various doping of h-BN sheets.

    fig. S6. Emission spectra for the different doping concentrations of the fluorine in boron nitride nanosheets on excitation at 280 nm.

    fig. S7. Control measurements of the blank cuvette.

    fig. S8. ac magnetic measurements.

    fig. S9. Structures of fluorinated BN sheets.

    fig. S10. Alignment of band edges and band-decomposed charge density.

    fig. S11. Band structure and density of states of F-BN.

    fig. S12. Charge accumulation and depletion of F-BN.

    table S1. Literature of 19F chemical shifts of B-F and N-F.

    table S2. Literature of 19F chemical shifts of FNXY and F2NXY.

    table S3. Literature of 19F chemical shifts of FBXY and F2BXY.

    References (3657)

  • Supplementary Materials

    This PDF file includes:

    • section S1. Synthesis
    • section S2. 19F NMR analysis
    • section S3. Structural characterizations
    • section S4. Bandgap calculations
    • section S5. Photoluminescence spectra
    • section S6. Magnetic measurements
    • section S7. Computational methodology
    • fig. S1. Structural characterizations of plasma-fluorinated boron nitride.
    • fig. S2. XPS spectrum of highly fluorinated boron nitride.
    • fig. S3. 19F MAS spectra (376.3-MHz) of F-BN with MAS rate of 12 and 10 kHz.
    • fig. S4. Electron microscope images of the fluorinated boron nitride sheets.
    • fig. S5. Tauc plot for the various doping of h-BN sheets.
    • fig. S6. Emission spectra for the different doping concentrations of the fluorine in boron nitride nanosheets on excitation at 280 nm.
    • fig. S7. Control measurements of the blank cuvette.
    • fig. S8. ac magnetic measurements.
    • fig. S9. Structures of fluorinated BN sheets.
    • fig. S10. Alignment of band edges and band-decomposed charge density.
    • fig. S11. Band structure and density of states of F-BN.
    • fig. S12. Charge accumulation and depletion of F-BN.
    • table S1. Literature of 19F chemical shifts of B-F and N-F.
    • table S2. Literature of 19F chemical shifts of FNXY and F2NXY.
    • table S3. Literature of 19F chemical shifts of FBXY and F2BXY.
    • References (3657)

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