ZnS Nanopowders and ZnS/Ag 2 S Heteronanostructures: Synthesis and Properties
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ZnS Nanopowders and ZnS/Ag2S Heteronanostructures: Synthesis and Properties S. I. Sadovnikova, *, A. V. Ishchenkob, and I. A. Weinsteinb aInstitute bUral
of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, Yekaterinburg, 620990 Russia Federal University named after the first President of Russia B.N. Yeltsin, Yekaterinburg, 620002 Russia *e-mail: [email protected] Received February 19, 2020; revised March 23, 2020; accepted April 27, 2020
Abstract—Zinc sulfide ZnS nanopowders were prepared by chemical deposition from aqueous solutions of zinc nitrate and sodium sulfide in the presence of sodium citrate or Trilon B. ZnS/Ag2S heteronanostructures were prepared by two-step chemical codeposition of zinc and silver sulfides. The prepared ZnS nanopowders had average particle sizes ranging from 2 to 10 nm depending on the reagent concentration ratio in the batch. The nanoparticle sizes in the thus-prepared heteronanostructures were 8–10 nm. The diffuse reflectance spectra of nanostructured ZnS and ZnS/Ag2S heteronanostructures were measured. The bandgap width Eg in the studied sulfide nanostructures was assessed based on an examination of the measured optical absorption spectra. As the nanoparticle size decreased from 10 to 2 nm, the Eg in ZnS nanopowders increased in the range 3.59–3.72 eV. The increasing Ag2S percentage in ZnS/Ag2S heteronanostructures leads to narrowing of the bandgap. Pulsed cathodoluminescence (PCL) spectra were recorded. The luminescence characteristics of ZnS and ZnS/Ag2S depend on the preparation method and nanoparticle morphology. Keywords: zinc sulfide, silver sulfide, chemical deposition, optical absorption, bandgap DOI: 10.1134/S0036023620090144
INTRODUCTION Zinc sulfide ZnS and silver sulfide Ag2S are highly demanded compound semiconductors [1–8]. They are used in ultrasound amplifiers and detectors, infrared sensors, lasers, phosphors, solar cells, LEDs, photochemical cells, infrared detectors, catalysts, resistance switches, and non-volatile memory devices [9–13]. The low-temperature cubic α-ZnS phase (space group F 43m ) has the zinc blende or sphalerite ZnS (type В3) cubic structure, and is stable at temperatures below 1290 K. At 1293 K low-temperature cubic zinc sulfide converts to the high-temperature hexagonal phase β-ZnS (space group P63mc) with the wurtzite structure. At the standard temperature and pressure, bulk zinc sulfide is a wide-gap semiconductor. The bandgap Eg of cubic α-ZnS is 3.50–3.76 eV; that of hexagonal β-ZnS is 3.74–3.91 eV [7]. The exciton diameter in bulk zinc sulfide is 4.8–5.2 nm [7]. Silver sulfide Ag2S has three polymorphs. The lowtemperature semiconductor phase, acanthite α-Ag2S with a monoclinic (space group P21/c) structure, exists below 450 K; body-centered cubic (space group Im3 m) superionic argentite β-Ag2S exists at temperatures in the range 452–859 K; and high-temperature face-centered cubic (space group Fm3 m) γ-Ag2S is
stable in the range from 860 K to the melting temperature.
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