One-step vapor-phase synthesis of transparent high refractive index sulfur-containing polymers

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Science Advances  08 Jul 2020:
Vol. 6, no. 28, eabb5320
DOI: 10.1126/sciadv.abb5320
  • Fig. 1 Synthesis of SCP films in vapor phase.

    (A) A schematic illustration of overall sCVD system. (B) SCP synthesis scheme from elemental sulfur and cross-linkable comonomer: (1) elemental sulfur is evaporated from the heated crucible located at the bottom of the sCVD chamber and decomposed to form radicals; (2) the evaporated elemental sulfur is cleaved to shorter linear sulfur diradicals by hot filament; (3) the sulfur diradicals activate the vaporized monomers to propagate the free radical polymerization reaction; and (4) the heavily cross-linked SCP film is deposited on the surface of the substrate. (C) Cross-linkable monomers used in this study for sCVD polymerization: BDDVE, DEGDVE, DDDE (1,11-dodecadiene), DDE (1,9-decadiene), HVDS (hexavinyldisiloxane), V3D3 (1,3,5-trivinyl-1,3,5-trimethylcyclotrisiloxane), and V4D4 (1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane). (D) A scanning electron microscope image of the 1600-nm nanopatterned Si wafer coated conformally with 60-nm-thick SBDDVE film.

  • Fig. 2 Physical properties of sCVD polymers.

    Thermal and structural properties of the SBDDVE: (A) DSC spectra of 60 wt % SBDDVE (blue), 70 wt % SBDDVE (red), and elemental sulfur (black). a.u., arbitrary units. (B) TGA spectra of elemental sulfur (black) and 60 wt % SBDDVE (red). (C) X-ray diffraction (XRD) spectra of elemental sulfur (black) and 60 wt % SBDDVE (red). (D) XRR spectra of 60 wt % SBDDVE film (red) and the corresponding curve fit (black). (E) Atomic force microscopy (AFM) image of the 60 wt % SBDDVE film along with (F) AFM phase image.

  • Fig. 3 Chemical analysis of sCVD SCP films.

    (A) A synthetic scheme of SBDDVE polymerization via sCVD using elemental sulfur. Chemical composition analysis of SBDDVE: (B) FTIR spectra of the elemental sulfur (top), SBDDVE (middle), and BDDVE monomer (bottom). Ether (C─O─C, 1100 cm−1) and vinyl (C═C, 1600 cm−1) peaks found in the monomer moiety are highlighted in blue, and sulfur (S─S, 480 cm−1; C─S, 1080 cm−1) peaks found in the sulfur moiety is highlighted in red. (C) XPS survey scan spectrum of SBDDVE-coated Si wafer and the corresponding (D) XPS C 1s high-resolution scan and its deconvoluted peaks featured with light blue for S─C─O, green for C─O, blue for C─S, and gray for C─C, respectively. (E) XPS S 2p high-resolution scans and its deconvoluted peaks in red for S─S and in blue for C─S. (F) XPS O 1s high-resolution scans and its deconvoluted peak in green for C─O. (G) XPS depth profile analysis of 300-nm-thick SBDDVE film coated on Si wafer.

  • Fig. 4 Optical properties of the sCVD films.

    (A) Transmittance spectra of SBDDVE from sCVD with thickness ranging from 100 nm to 1.8 μm and SDIB from inverse vulcanization with a thickness of 1.0 μm with digital photographs of corresponding films coated on glass slides. (B) Refractive index (n) and extinction coefficient (k) of 500-nm-thick SBDDVE obtained using spectroscopic ellipsometry. (C) The sulfur loading amount (blue; with the fixed process pressure of 1000 mtorr and Ts = 110°C), the chamber pressure (black; with the fixed sulfur amount of 0.1 g and Ts = 110°C), and (D) the substrate temperature (with the fixed sulfur loading amount of 0.5 g and the process pressure of 1000 mtorr). (E) The sulfur weight ratio in SBDDVE calculated from XPS survey scan (black), sulfur rank calculated from XPS survey scan (red dash), and sulfur rank calculated from XPS S 2p high-resolution scan (red solid) with respect to the corresponding refractive index. (F) The average refractive index from 400 to 700 nm versus thickness plot of SBDDVE synthesized by sCVD. Photo credit: Wontae Jang (Korea Advanced Institute of Science and Technology) and Jisung Choi (Kyung Hee University).

  • Fig. 5 Environmental stability of the sCVD films.

    (A) Optical microscopy images of glass coated with SDIB synthesized by inverse vulcanization before (left) and after (right) storage under ambient air for 12 months and SBDDVE film synthesized by sCVD before and after the storage under ambient air for 24 months. (B) Thickness and (C) refractive index of silicon wafer coated with 100-nm-thick SBDDVE polymer film before (black) and after (red) solvent test with water, acetone, toluene, and n-hexane for 2 hours.

Supplementary Materials

  • Supplementary Materials

    One-step vapor-phase synthesis of transparent high refractive index sulfur-containing polymers

    Do Heung Kim, Wontae Jang, Keonwoo Choi, Ji Sung Choi, Jeffrey Pyun, Jeewoo Lim, Kookheon Char, Sung Gap Im

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