Research ArticleMATERIALS SCIENCE

Antimony thin films demonstrate programmable optical nonlinearity

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Science Advances  01 Jan 2021:
Vol. 7, no. 1, eabd7097
DOI: 10.1126/sciadv.abd7097
  • Fig. 1 Thickness dependence on optical and structural properties of Sb.

    (A and B) The spectra (from ultraviolet to near infrared) of the refractive index na (A) and extinction ratio ka (B) of thin-film Sb with different thicknesses (tSb) as deposited on silicon wafers measured by spectroscopic ellipsometry. (C and D) The spectra of nc (C) and kc (D) of the same Sb samples in (A) and (B) after annealing on a hot plate (270°C for 10 min). (E and F) The absolute change of refractive index |Δn| (|ncna|) (E) and extinction ratio |Δk| (|kcka|) (F) of Sb upon annealing, calculated from (A) and (C) and (B) and (D), respectively. (G) Raman spectra of annealed Sb films with different tSb. Eg and A1g vibration modes are denoted by the dashed lines. Typical vibration modes F2g and Ag of Sb2O3 are illustrated by the circles. The Raman spectrum intensity of 3-nm Sb (purple) has been enlarged by two times for clarification. a.u., arbitrary units.

  • Fig. 2 TEM characterization of Sb.

    (A) TEM image of a 5-nm-thick Sb layer as deposited has an amorphous structure. (B) Selected-area (344 nm diameter) electron diffraction (SAED) of the as-deposited Sb, corresponding to the sample in (A). (C) TEM image of the same Sb sample in (A) after thermal annealing. (D) SAED (200-nm-diameter region) of the annealed Sb sample in (B) has formed diffraction spots from crystalline planes. Two patterns, corresponding to the zone axis of [001] (white) and [100] (cyan), are overlapped. Miller indices of crystal planes with high symmetry are labeled. The arrows show merged diffraction spots coming from different planes. (E) TEM image of the annealed Sb with visible crystalline planes along the [120] direction. Inset: Fourier transform of the whole image showing reflections (120) with an interplane spacing (d) of 2.2 Å. (F) The hexagonal unit cell of the rhombohedral crystalline structure of Sb. The red lines show the primitive rhombohedral unit cell. a and c are the measured crystal constants in the hexagonal unit cell.

  • Fig. 3 Switchable reflective stacks using ultrathin-film Sb.

    (A) Structure of reflective display based on phase-change Sb sandwiched between two ITO layers (ITO/Sb/ITO) on top of a Pt mirror. The phase-change Sb layer can be switched from amorphous to crystalline through thermal annealing. (B) Optical images show typical display samples with different thicknesses (tITO) of the bottom ITO layer, while Sb and the top ITO are fixed at 5 and 15 nm, respectively. The samples have an amorphous (top row) and a crystalline (bottom row) Sb layer. (C and D) Measured (C) and simulated (D) reflection spectra of samples corresponding to (B). Each measured spectrum curve was normalized to the peak of the corresponding simulated curve.

  • Fig. 4 Electro-optical switching of Sb using conductive AFM.

    (A) Schematic of the electrical switching of Sb using CAFM. The Sb film is sandwiched between two ITO layers above a Pt mirror. The conductive probe of the CAFM is biased using a DC voltage (VB) while contacting or scanning the Sb sample. The Pt substrate is grounded via a resistor RS (3 kilohms) to limit the current (IS) passing through the probe and the sample. (B) Static measurement of IS while sweeping VB on the probe that is in contact with different locations of the sample. Inset: Histogram distribution of the threshold voltage Vth of the switching during voltage sweeping. (C to E) Original grayscale (8-bit, 256 × 256) images used to modulate VB. (C) is from Marco Schmidt’s standard test images database, (D) is reproduced from the logo of the University of Oxford, and (E) is from the University of Southern California-Signal and Image Processing Institute (USC-SIPI) Image Database. (F) The optical image of the Sb sample switched by CAFM, corresponding to the image in (C). The Sb sample structure is 15-nm ITO/5-nm Sb/100-nm ITO/Pt (from top to bottom layer). (G and H) The optical image of the Sb sample switched by CAFM, corresponding to the images in (D) and (E), respectively. The Sb sample structure is 15-nm ITO/3-nm Sb/50-nm ITO/Pt. (I to L), Optical images show zoomed-in regions of the switched areas: blue (I), orange (J), green (K), and red (L) boxes in (H).

  • Fig. 5 Ultrafast optical switching of Sb.

    (A) Schematic of optical switching of Sb using femtosecond laser. LED, light-emitting diode; CCD, charge-coupled device; NA, numerical aperture. (B) Optical image shows amorphized regions (blue disks) using single laser pulse (200 fs) with increasing energy Ep (from bottom to top). (C) Large area switching of the c-Sb sample (c-Sb background) through single femtosecond pulse (200 fs, Ep = 0.56 nJ) while raster scanning the sample (moving speed, 500 μm/s). a-Sb1 and a-Sb2 are switched areas with different sizes. (D) Recrystallization (c-Sb1) of the amorphized region a-Sb1 in (C) with multiple femtosecond pulses (200 fs, Ep = 29 pJ, 80 MHz) while translating the sample at 200 μm/s. (E) Reflection spectra of different locations of the sample in (D). (F) The stability of the amorphized region by femtosecond laser switching. Optical images show the amorphized region after different aging times in ambient conditions at RT. The Sb sample used is 15-nm ITO/3-nm Sb/50-nm ITO/Pt.

Supplementary Materials

  • Supplementary Materials

    Antimony thin films demonstrate programmable optical nonlinearity

    Zengguang Cheng, Tara Milne, Patrick Salter, Judy S. Kim, Samuel Humphrey, Martin Booth, Harish Bhaskaran

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