ZnS nanoparticle decorated ZnO nanowall network: investigation through electron microscopy and secondary ion mass spectrometry Sayan Bayan,* Biswarup Satpati and Purushottam Chakraborty We report on the fabrication of ZnO nanowall networks decorated with ZnS nanostructures on aluminum substrates using simple chemical route. The structural features and elemental constituents of the ZnS/ZnO heterostructure systems have been extensively studied using electron microscopy and energy dispersive X-ray spectroscopy. The light emission characteristics of the bare and heterostructured systems have been analyzed using room temperature photoluminescence spectroscopy. The decoration of ZnS nanostructures over ZnO nanowalls has been evidenced through secondary ion mass spectrometry (SIMS). The ‘matrix effect’ has been found to be prominent during SIMS analysis of the bare and heterostructured nanowalls indicating the presence of ZnS phase over ZnO surface. ‘MCs + -SIMS’ has been employed to suppress the matrix effect and is found to be potentially effective in making a semi-quantitative estimation of Zn and O surface–atom concentrations in both systems. The luminescence responses of the ZnS/ZnO heterostructures have been found to be strongly dependent on the extent of ZnS phase over ZnO. The higher luminescence responses in ZnS/ZnO heterostructures fabricated with smaller ZnS nanoparticles have been explained in terms of a mechanism of charge-carrier transfer from ZnS to ZnO. Copyright © 2014 John Wiley & Sons, Ltd. Keywords: semiconductors; nanowalls; scanning and transmission electron microscopy; secondary ion mass spectrometry Introduction Semiconducting nanostructured materials have gained immense importance in recent years owing to their potential application for the next generation optoelectronic devices. [1–3] Among different semiconducting nanostructures, zinc oxide (ZnO)-based and zinc sulfide (ZnS)-based systems hold promise for the appli- cation in diverse electronic and photonic devices. [3–5] Both ZnO and ZnS being wide band gap semiconductors (E ZnO ~ 3.37 eV and E ZnS ~ 3.7 eV at 300 K) have been proven to be excellent materials for the fabrication of prototype light emitting and detecting devices in the ultraviolet (UV) region of the electro- magnetic spectrum. [3–5] Again, the presence of various native defects makes the systems suitable for the luminescent devices in the visible region. [6,7] With the rapid development in the fabrication and processing techniques, it has been possible to fabricate a rich variety of nanoscale structures in both systems. Apart from the conventional nanostructures, fabrication of nanoscaled wall-like structures of ZnO and ZnS is often reported in the literature. [8–10] In contrast to the usual nanoparticle and nanorod structures, the higher surface area of the nanowall structures makes the latter a promising candidate for efficient solar cell and sensing applications. [8] On the other hand, decoration of nanostructures with other materials is a prolific approach to obtain heterostructured system. Using the appropriate external materials for the heterostructure, the properties of the host material can be tuned to the desired requirement. In order to modify various optoelec- tronic properties of the system, decoration of the ZnO nanorod surfaces with quantum dots, metal nanoparticles, polymers, and so on has often been realized. [11–14] However, reports on the fab- rication of heterostructures through decoration of ZnO nanowall surfaces with ZnS nanostructures are missing in the existing liter- ature. Here, we report on the chemical synthesis of ZnS/ZnO heterostructure-based nanowalls and their extensive character- izations using electron microscopy and secondary ion mass spectrometry (SIMS). The surface chemical analysis of such nanowall-based heterostructures using SIMS is a unique ap- proach in the present work. Finally, the luminescence responses of the two types of systems have been investigated highlighting the role of ZnS nanostructures in modifying the luminescence feature of the ZnO nanowalls. Experimental details Prior to the growth of ZnO nanowalls on metallic aluminum sub- strates, commercially available Al substrates were repeatedly cleaned in deionized water and acetone under ultrasonic agitation. The cleaned Al substrates were immersed in a growth solution of deionized water containing equimolar solution of zinc nitrate hexahydrate (ZNT) [Zn(NO 3 ) 2 .6H 2 O] and hexamethylene- tetramine (HMT) [(CH 2 ) 6 N 4 ] in 90 ml, under constant stirring for 2 h at ~50 °C. After the completion of the growth process, white * Correspondence to: S. Bayan, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata-700064, India. E-mail: sayan.bayan@gmail.com Saha Institute of Nuclear Physics, Kolkata 700064, India Surf. Interface Anal. (2014) Copyright © 2014 John Wiley & Sons, Ltd. Research article Received: 28 March 2014 Revised: 19 May 2014 Accepted: 5 July 2014 Published online in Wiley Online Library (wileyonlinelibrary.com) DOI 10.1002/sia.5642