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Horizontal Attenuated Total Reflectance Fourier Transform Infrared and X-ray Photoelectron Spectroscopy Measurements of Water Adsorption on Oxidized Tin(II) Sulfide (SnS) Surfaces
Journal article   Peer reviewed

Horizontal Attenuated Total Reflectance Fourier Transform Infrared and X-ray Photoelectron Spectroscopy Measurements of Water Adsorption on Oxidized Tin(II) Sulfide (SnS) Surfaces

Courtney D Hatch, Matthew J Christie, Robert M Weingold, Chia-Ming WU, David M Cwiertny and Jonas Baltrusaitis
Journal of physical chemistry. C, Vol.117(1), pp.472-482
2013
DOI: 10.1021/jp310726t

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Abstract

Tin(II) sulfide (SnS) is considered to be a promising optoelectronic material due to its narrow band gap, strong optical absorption, low cost and nontoxic and chemically inert characteristics. As an inherently stable compound, SnS surfaces are expected to be hydrophobic by nature. However, exposure of pristine SnS surfaces to air inevitably leads to surface oxidation which can affect the mineral’s dissolution, reactivity, optical and electronic properties as well as hydrophobicity. In the present study, water adsorption measurements on oxidized SnS thin films were performed using horizontal attenuated total reflection Fourier transform infrared (HATR-FTIR) spectroscopy. X-ray photoelectron spectroscopy (XPS) analysis allowed for characterization of the SnS surface composition before water vapor exposure and identification of any changes that occurred to the surface after water vapor exposure. XPS results are consistent with water adsorption occurring on SnS surfaces containing hydroxyl and carbonate groups. Additionally, XPS analysis showed that exposure of SnS to water vapor resulted in no significant changes to the original surface composition. Quantitative water adsorption measurements using HATR-FTIR spectroscopy show that the oxidized SnS surface exhibits a slightly hydrophilic nature, demonstrating multilayer water adsorption at high relative humidity (RH) values. Experimental water adsorption data were fit using the Brunauer–Emmett–Teller (BET) and Freundlich adsorption models. From these model fits, details of monolayer water adsorption and the water adsorption mechanisms were extracted to provide a better understanding of gas/surface adsorption on oxidized SnS surfaces. Results suggest that water adsorption on SnS powder occurs in three distinct regimes, including sub-monolayer water adsorption up to monolayer coverage at 13% RH, followed by filling of mesopores (13–76% RH) and finally multilayer water adsorption (>76% RH) via filling of macropores. This study represents the first report of in situ water adsorption measurements on SnS as a function of relative humidity, illustrating how oxidized surface species can alter the hydrophobic nature of SnS surfaces.
 Applied Sciences Physics Condensed matter: electronic structure, electrical, magnetic, and optical properties Condensed matter: structure, mechanical and thermal properties Electron states and collective excitations in thin films, multilayers, quantum wells, mesoscopic and nanoscale systems Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures Electronics Exact sciences and technology Fullerenes and related materials Molecular electronics, nanoelectronics Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices Solid surfaces and solid-solid interfaces Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties) Visible and ultraviolet spectra

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