Applied Surface Science 333 (2015) 244–253 Contents lists available at ScienceDirect Applied Surface Science journal h om epa ge: www.elsevier.com/locate/apsusc Study of NBE emission enhancement with an absence of DL emission from ZnO nanorods through controlled growth on ultra-thin Ag films Anil Kumar Pal, D. Bharathi Mohan ∗ Department of Physics, School of Physical, Chemical and Applied Sciences, Pondicherry University, Pondicherry 605014, India a r t i c l e i n f o Article history: Received 9 December 2014 Received in revised form 21 January 2015 Accepted 2 February 2015 Available online 9 February 2015 Keywords: ZnO/Ag hybrid structure X-ray diffraction Scanning electron microscopy Raman Spectroscopy Coupled surface plasmon resonance and exciton bands Enhanced near band edge emission a b s t r a c t ZnO nanorods (NRs) exhibiting enhanced ultra-violet near band edge (UV-NBE) emission without a broad visible deep level (DL) emission has been investigated on catalytically grown ZnO/Ag hybrid nanostruc- ture. The hybrid structure is fabricated in two steps, (1) Thermal evaporation of ultra-thin catalytic layer of Ag with mass thickness ∼1 nm on glass substrate followed by annealing process from 50 to 250 ◦ C and (2) vertical growth of ZnO NRs by hydrothermal reaction process on all Ag films. The surface properties of Ag layer such as particle size, inter-particle distance, particles number density, surface roughness and surface coverage area were altered through annealing process. Annealing at 100 ◦ C modifies Ag from quasi-amorphous to nanocrystalline leading to high density growth and high aspect ratio of ZnO NRs where as a random and less density growth was realized at 250 ◦ C due to increase of both particle size and inter-particles distance in Ag layer. X-ray diffraction reveals a predominant growth of (0 0 2) plane at 100 ◦ C confirming the formation of wurtzite phase of ZnO NRs with highest texture coefficient of 2.35. Raman spectra verify the chemical structure of ZnO with very good crystallinity. Absorption spectra demonstrates the overlapping of surface plasmon resonance (SPR) and exciton bands up to 200 ◦ C while the excitonic absorption band is resolved at above 200 ◦ C because of the red shift in SPR due to change in surface properties of Ag layer. At 250 ◦ C, a broad optical absorption spectra from 300 to 800 nm attributed to the dominant properties of SPR and exciton. Besides acting as a catalyst, Ag interlayer enhances the NBE emission at above 200 ◦ C through electrons transfer from Ag to ZnO which is quite possible because of the direct contact between them, explained by giving energy band diagram. The morphology is such that there is an increase in passage for light interaction due to less density and random growth of ZnO NRs leading to increase light scattering over absorption of Ag interlayer. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Surface plasmon enhanced semiconductor/metal hybrid nano- structures as well as composites have been widely utilized to enhance the luminescence of light-emitting materials and other optoelectronic devices [1–5]. Okamoto et al. have reported a strong enhancement of light emission from InGaN/GaN thorough the energy transfer between quantum wells and SPs which lead to a new class of very bright and highly efficient light emitting diodes (LEDs) [2]. This large emission enhancement is obtained through increasing the density of states and the spontaneous emission rate in the semiconductor by surface plasmons (SPs). Recently, a momentous deep UV emission enhancement of AlGaN through ∗ Corresponding author. Tel.: +91 4132654786. E-mail addresses: d.bharathimohan@gmail.com, dhanabharathi@yahoo.com (D. Bharathi Mohan). SP-exciton coupling process was demonstrated by Yin et el. by introducing Al NPs [3]. Emission enhancement through SP-exciton coupling was also employed for ZnO films. Three fold emission enhancement was obtained for band gap emission of ZnO while defect emission was quenched by Ag interlayer island film [4]. The emission enhancement from ZnO depends on the morphol- ogy (size and shape) and the surface roughness of noble metal inter-layer which plays a most significant role for the match- ing of SPs to emission band energies [5]. Recently, ZnO based NRs have attracted much attention towards potential applications such as nanoscale electronic, light emitting diodes, field emission devices, chemical sensors and energy conversion devices due to their remarkable physical and chemical properties [6–9]. Several synthesis methods have been established for 1D ZnO nanomaterials growth such as physical vapour deposition, chemical vapour depo- sition, pulsed laser deposition and various wet chemistry methods [10–15]. Among all, hydrothermal method is an economical route which has the merit of fabricating vertically aligned ZnO NRs arrays http://dx.doi.org/10.1016/j.apsusc.2015.02.015 0169-4332/© 2015 Elsevier B.V. All rights reserved.