IOP PUBLISHING NANOTECHNOLOGY Nanotechnology 20 (2009) 095707 (6pp) doi:10.1088/0957-4484/20/9/095707 The photoluminescent lifetime of polyelectrolytes in thin films formed via layer by layer self-assembly Roseanne S Reilly, Ciar´ an A Smyth, Yury P Rakovich and Eithne M McCabe School of Physics, Trinity College Dublin, Dublin 2, Republic of Ireland E-mail: reillyrs@tcd.ie Received 10 December 2008 Published 11 February 2009 Online at stacks.iop.org/Nano/20/095707 Abstract We present results on luminescence lifetime studies of thin multilayer films of polyelectrolyte molecules produced via layer by layer (LbL) electrostatic assembly. We found that, in contrast to common assumptions, LbL films show measurable photoluminescent lifetimes with an average value of 6 ns. Scanning fluorescence lifetime imaging microscopy studies combined with steady-state photoluminescence measurements imply that this lifetime may be due to aggregation of polyelectrolyte molecules during preparation of LbL films. This conclusion has been further confirmed by atomic force microscopy (AFM). AFM images clearly show the presence of 100–200 nm high aggregates on the surface of these films. This aggregation of polyelectrolyte molecules contributes significantly to the experimentally detected luminescence decays of any light-emitting samples attached to LbL film, especially in a single molecule detection regime. To demonstrate this effect we compare photoluminescence lifetime results for CdTe quantum dots deposited on the surface of LbL polyelectrolyte films. (Some figures in this article are in colour only in the electronic version) 1. Introduction The layer by layer (LbL) deposition technique by electrostatic self-assembly is an extremely popular technique that allows for the fabrication of ultra thin films with monolayer control [1]. This notion of adsorbing particles onto solid substrates via a LbL deposition technique was introduced by Iler in the mid 1960s [2]. Decher and co-workers extended Iler’s work to a combination of linear polycations and polyanions in the early 1990s [3]. Other groups later adapted the LbL technique to include inorganic nanoparticles, biomolecules and dyes in polyelectrolyte (PE) multilayer assemblies [4–6]. The above studies work all focused on employing macroscopic, two- dimensional, charged surfaces as the substrates for adsorption. The thin film structures are built up by the sequential adsorption of a polyanion and a polycation [3]. In this work poly(diallyldimethylammoniumchloride) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS) acted as the polyanion and polycation respectively. The LbL electrostatic technique has proven to be a versatile and flexible tool when applied to controlling nanoscale dimensions, with nanometre resolution. It is often used as a method to fabricate controlled spacer layers within samples [7, 8] and as a method to create uniform monolayers of quantum dots (QDs). Their popularity when used in this context is due to the availability of optically transparent PEs as well as the high level of control of the multilayer structures they yield [1, 9]. The LbL method is thus often used in conjunction with investigating electrostatically assembled charged luminescent quantum dots as it allows a uniform monolayer of QDs do be deposited and their properties investigated. Kulakovich et al reports on a photoluminescence (PL) signal for 19 bilayers of PE that was comparable to that of zero layers within experimental error [10]. However, very little is published about the significance of the PE multilayers to the radiative emission lifetime of the samples. Previously it has been assumed that their contribution is negligible [10], or even nonexistent [11]. It has been assumed that the only contributing factor was scattered light with a lifetime of the order of 250 ps. However, here we present results which show 0957-4484/09/095707+06$30.00 © 2009 IOP Publishing Ltd Printed in the UK 1