Mechanochemically induced sulfur doping in ZnO via oxygen vacancy formation

Abstract

Surface defects of ZnO nanoparticles were induced via mechanical stressing using a Turbula shaker mixer and a planetary ball mill, and the possibilities for surface modification and functionalization of the ZnO nanoparticles were exemplified by sulfur doping of activated ZnO. Raman spectroscopy reveals that the formation of oxygen vacancies (V) does not only occur under high stressing conditions in a planetary ball mill but even upon rather 'mild stressing' in the shaker mixer. The temporal evolution of the vacancy concentration in ZnO stressed under different conditions can be described by a model that accounts for stress number and vacancy diffusion with diffusion coefficients of V of 3.7 × 10 m s and 2.4 × 10 m s for stressing in the shaker and the planetary ball mill, respectively. The thickness of the V layer was estimated to be about 1 nm. Thiourea was mixed with defective ZnO particles, and then heated at various temperatures for sulfur-doping. A linear relationship between the amount of induced V and the level of sulfur doping was found. Remarkably, mechanical activation is indispensable in order to control the level of sulfur doping quantitatively. High-angle annular dark field scanning transmission electron microscopy (HAADF STEM) observations with energy dispersive X-ray spectroscopy (EDX) analysis clearly revealed that the doped sulfur atoms are concentrated at the particle surface. Thus, ZnO (core)/ZnS (shell) structures are obtained easily via mechanochemical activation and subsequent thermal treatment.

ZnO/ZnS (hetero)structures: ab initio investigations of polytypic behavior of mixed ZnO and ZnS compounds

“…This similarity is demonstrated not only on theoretical grounds by the polytype calculations presented here, but also by many experimental observations, such as the existence of wurtzite and sphalerite modifications in both ZnO and ZnS, which are in agreement with the calculations presented in this study. In support of this claim, we would also like to mention recent investigations that suggest the occurrence of theoretically proposed (Zafar et al, 2014;Luo et al, 2017;Goclon & Meyer, 2013;Iversen & Spencer, 2013), synthesized (Skinner & Barton, 1960;Patil et al, 2010;Chen et al, 2008;Shen et al, 2005;Homm et al, 2010;Wang et al, 2015) and natural (Š rot et al, 2003) polymorphs of ZnO intergrown with ZnS, as well as the great amount of research that has been performed on ZnO/ZnS heterostructures and heterojunctions (Wang et al, 2002;Yan & Xue, 2006;Hu et al, 2011;Jia et al, 2013;Sadollahkhani et al, 2014;Daiko et al, 2017;Giri et al, 2014;Tarish et al, 2017;Lu et al, 2009;Tian et al, 2014;Zhu et al, 2008 Sukkabot, 2017;Flores et al, 2018). Taken together, these are strong indications that the synthesis of at least some of the predicted mixed ZnO/ZnS compounds/modifications presented in this study should be possible.…”

“…One might also suggest other synthesis methods employed in ZnO/ZnS compounds, such as, e.g. precipitation (Skinner & Barton, 1960), mechanochemistry (Patil et al, 2010;Daiko et al, 2017), molecular beam epitaxy (Homm et al, 2010;He et al, 2012), sol-gel synthesis (Raleaooa et al, 2017;Baranowska-Korczyc et al, 2017), atomic layer deposition (Ö zgü r et al, 2005;Logar et al, 2009), or the hydrothermal method (Zhang et al, 2015). Finally, a synthesis employing one of the methods used in related AB compounds (Morkoç et al, 1994;Andrievski, 2009;Wang et al, 2008) could be attempted; in particular, recent experiments show that it is possible to control the polytypes of GeH, a representative two-dimensional material (Cultrara et al, 2018), which suggests a possible use of polytypes in the synthesis process of the ZnO/ ZnS heterostructures and heterojunctions (Wang et al, 2002;Yan & Xue, 2006;Hu et al, 2011;Jia et al, 2013;Sadollahkhani et al, 2014;Daiko et al, 2017;Giri et al, 2014;Tarish et al, 2017;Lu et al, 2009;Tian et al, 2014;Zhu et al, 2008;Chen et al, 2010;Xitao et al, 2014).…”

“…Recently, studies of ZnO/ZnS heterostructures and heterojunctions with various morphologies have been reported (Wang et al, 2002;Yan & Xue, 2006;Hu et al, 2011;Jia et al, 2013;Sadollahkhani et al, 2014;Daiko et al, 2017). These investigations mostly observe core/shell-structured materials, which usually show improved physical and chemical properties for biosensors, electronics, magnetism, optics, catalysis, mechanics and electrochemistry (Giri et al, 2014;Tarish et al, 2017;Lu et al, 2009;Tian et al, 2014;Zhu et al, 2008;Chen et al, 2010;Xitao et al, 2014).…”

Defect Restoration of Low‐Temperature Sol‐Gel‐Derived ZnO via Sulfur Doping for Advancing Polymeric Schottky Photodiodes

“…However, ZnO thin films derived via the sol‐gel method have more unreacted organic residuals and other chemical defects than those derived via other high‐temperature methods such as magnetron sputtering, spray pyrolysis, or molecular beam epitaxy . Therefore, various surface treatment methods have been developed to decrease the surface defects of solution‐processed ZnO and realize high‐performance organic diodes . The representative examples introduce nanoparticle ZnO doped with thiophene, sulfur, or Cs in colloid phases, which result in enhanced organic photovoltaic performances as the electron transport layer.…”

“…Therefore, various surface treatment methods have been developed to decrease the surface defects of solution‐processed ZnO and realize high‐performance organic diodes . The representative examples introduce nanoparticle ZnO doped with thiophene, sulfur, or Cs in colloid phases, which result in enhanced organic photovoltaic performances as the electron transport layer. In these cases of using doped nanoparticle, however, the issues related with electrically inert surface ligands still exist and therefore, defects generated during solidification may still exist.…”