Zinc sulfide (ZnS) is one of the first semiconductors discovered. It has traditionally shown remarkable versatility and promise for novel fundamental properties and diverse applications. The nanoscale morphologies of ZnS have been proven to be one of the richest among all inorganic semiconductors. In this article, we provide a comprehensive review of the state-of-the-art research activities related to ZnS nanostructures. We begin with a historical background of ZnS, description of its structure, chemical and electronic properties, and its unique advantages in specific potential applications. This is followed by in-detail discussions on the recent progress in the synthesis, analysis of novel properties and potential applications, with the focus on the critical experiments determining the electrical, chemical and physical parameters of the nanostructures, and the interplay between synthetic conditions and nanoscale morphologies. Finally, we highlight the recent achievements regarding the improvement of ZnS novel properties and finding prospective applications, such as field emitters, field effect transistors (FETs), p-type conductors, catalyzators, UV-light sensors, chemical sensors (including gas sensors), biosensors, and nanogenerators. Overall this review presents a systematic investigation of the ‘synthesis-property-application’ triangle for the diverse ZnS nanostructures.

ZnS nanostructures: From synthesis to applications

Physical properties of La-doped NiO sprayed thin films for optoelectronic and sensor applications

In this paper, indium-doped zinc oxide (IZO) films were grown by spray pyrolysis, using zinc acetate and indium acetylacetonate precursors. The focus was on developing a solution recipe based on water as solvent, with only minor acetic acid content, as well as keeping the substrate temperature as low as possible—at 360 °C. The process is therefore environment friendly and energy efficient. Despite the challenging conditions, the resulting IZO films were highly transparent and conductive. Their texture deviates strongly from the (002) texture of ZnO and depends on the indium content, which also influences the resistivity. The latter attains its minimum for an indium concentration of 4 at.% in the solution and decreases for increasing film thickness, reaching the value of (5.0 ± 0.1) × 10−3 Ω cm, mainly due to the increase in carrier mobility. The stability of the resistivity after high dose of UV irradiation was found to increase with the carrier density and the film thickness. Thick, highly doped films show minimal resistivity modification even after a total dose of 12.1 kJ/cm2 UVA/UVB irradiation. Finally, to demonstrate its applicability in devices, the IZO electrode was used for the fabrication of a lead-perovskite absorber solar cell, yielding an energy conversion efficiency of 6% and 910 mV open-circuit voltage.

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Highly transparent and conductive indium-doped zinc oxide films deposited at low substrate temperature by spray pyrolysis from water-based solutions

Effects of potassium incorporation on the structural, optical, vibrational and electrical properties of NiO sprayed thin films for p-type optical windows

Solution-processed nickel oxide films and their liquefied petroleum gas sensing activity

Deposition of p-type NiO films by chemical spray pyrolysis

The ZnS layers morphology, structure, composition, and optical properties were investigated with respect to the precursors (zinc chloride and thiocarbamide, Zn:S) molar ratio in spray solution (1:1, 1:2, and 1:3) and growth temperatures in the range of 400–600 °C. Scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), UV–VIS, and PL spectroscopy were applied to characterize the ZnS layers. Layers obtained at temperatures up to 450 °C are not well crystallized and contain residues originated from undecomposed precursors. ZnS films become crystalline at Ts = 500 °C. Layers grown from 1:1 solution at 550 °C are mixture of ZnS and ZnO phases, whereas at 600 °C layers of ZnO were obtained. Films produced from 1:2 solution at 500–600 °C are of ZnS with a wurtzite structure and Eg of 3.66 eV, but contain traces of ZnO phase when grown at 550 or 600 °C. Appearance of ZnO phase in the films grown from 1:1 and 1:2 solutions is explained by the results of the studies on the formation and decomposition of dichlorobis(thiocarbamide)zinc(II) complex as an intermediate compound formed in the solution of zinc chloride and thiocarbamide. Spraying the solutions with Zn:S = 1:3, which contain more thiocarbamide than required for the complex formation, results in single-phase ZnS layers with wurtzite structure at growth temperatures up to 600 °C. Moreover, ZnS layers obtained from 1:3 solution at 550 °C and higher are composed of highly c-axis oriented ZnS nanorod-like crystals with diameter of ca. 80 nm and length of ca. 300 nm.

Effect of Zn:S molar ratio in solution on the properties of ZnS thin films and the formation of ZnS nanorods by spray pyrolysis

Growth and properties of ZnO films on polymeric substrate by spray pyrolysis method

ZnO:In thin films were deposited by chemical spray pyrolysis from zinc acetate solutions containing 3 at% of InCl3 The films were grown in the temperature region of 400-500 °C using solution spraying rates 06-71 ml/min ZnO:In films were characterized by XRD, Hall and van der Pauw methods The dependence of the film resistivity vs growth temperature is parabolic ZnO:In films with resistivity minimum of 3x10-3 Ωcm can be deposited at 450 °C The solution spraying rate has strong effect on the film resistivity, deposition rates below 3 ml/min result in high resistivities (© 2012 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim)

The effect of growth temperature and spraying rate on the properties of ZnO:In films

Here we demonstrate that highly c-axis oriented vertically aligned hexagonal ZnS nanorod-like crystals have been synthesized via a facile and low-cost spray pyrolysis method. ZnS layers were grown onto soda-lime glass (SGL), glasses covered with transparent conductive oxides (TCOs: ITO and FTO) and silicon wafer substrates using zinc chloride and thiocarbamide precursors solution and air as carrier gas. The effect of main technological parameters on formation and properties of ZnS nanorods are studied. SEM, XRD, PL and UV-VIS were applied to characterize the ZnS layers. Dimensions of the ZnS rods are mainly controlled by the deposition temperature, precursor concentration and substrate type. For instance, rods with d = 80–100 nm and l = 450 nm were obtained using ZnCl2 with c = 0.1 mol/L; whereas rods with d = ca. 80 nm and l = 250 nm were produced from ZnCl2 with c = 0.05 mol/L on glass. According to PL study, such defects as sulphur vacancies (Vs) are present in the ZnS samples, and concentration of Vs decreases with increasing the sulphur amount in solution.



According to UV-VIS, all ZnS layers possess high optical transmittance ca. 80% in the visible spectrum region; the Eg of ZnS is 3.7 eV independent of the deposition conditions, corresponding to wurtzite ZnS. ZnS rods produced at 550 and 580 °C show high haze factor values of ca. 90% at 320–350 nm revealing high light scattering ability. Vertically aligned, uniform in size ZnS rods can be directly grown onto glass, TCO and silicon substrates.

Tarmo Unt

Papers

Deposition of p-type NiO films by chemical spray pyrolysis

Effect of Zn:S molar ratio in solution on the properties of ZnS thin films and the formation of ZnS nanorods by spray pyrolysis

Growth and properties of ZnO films on polymeric substrate by spray pyrolysis method

The effect of growth temperature and spraying rate on the properties of ZnO:In films

Spray pyrolysis deposition and characterization of highly c‐axis oriented hexagonal ZnS nanorod crystals