Selective diffusion of gold nanodots on nanopatterned substrates realized by self-assembly of diblock copolymers
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E. Rimini Università di Catania, Dipartimento di Fisica, Catania, Italy
S. Lombardo Consiglio Nazionale delle Ricerche, Istituto per la Microelettronica e Microsistemi, Zona Industriale, 95121 Catania, Italy (Received 19 May 2010; accepted 15 July 2010)
We investigated a simple and low-cost route for the formation of metallic nanodots on Si substrates ordered in size and position and laterally isolated by SiO2. The method was based on a two-step process: (i) the formation of a nanopattern of ordered cylindrical pores on oxidized Si substrates through self-assembly of diblock copolymers, and successive oxide dry etching down to the Si; (ii) the deposition of gold nanodots and thermal diffusion over the nanopatterned oxide substrates. After diffusion, the nanodot density outside the nanopores was found to decrease, and most of the nanodots were found to saturate the nanopores. The process was followed in situ by transmission electron microscopy (TEM) and ex situ by scanning electron microscopy (SEM) analysis for different thermal budgets. This patterned substrate can be used for catalyst mediated growth, for example, through vapor-liquid-solid (VLS), of nanowires for the formation of absorber materials in novel photovoltaic architectures. I. INTRODUCTION
Silicon nanowires have recently been proposed as basic building blocks for high efficiency PV cells, because they relax the constraints on the quality of the silicon material and on the amount of semiconductor required for efficient light absorption.1 On the other hand, metallic dots grafted on the nanowire surface can produce localized plasmonic modes to enhance light absorption by the semiconductor and further boost PV efficiency.2,3 These two concepts can be integrated in PV production if low cost technologies for Si nanowire and metallic dot synthesis, among the large range of available approaches, are identified, with the target of reducing cost with maximum performance. Two of the most proposed approaches for the synthesis of the Si nanowires are based on vapor-liquid-solid (VLS) growth4–11 or on solid-liquid-solid (SLS) growth.12,13 In both these methods, metallic nanoparticles are deposited randomly on an Si substrate and work as catalyst seeds for the nucleation of the Si phase from the vapor source, in the first case, and from the substrate source, in the second case. During the growth, in both cases however, some lateral diffusion of the metallic dots on the substrate can produce a coalescence of the metal nanoseeds, thus increasing the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2010.19 240
J. Mater. Res., Vol. 26, No. 2, Jan 28, 2011
http://journals.cambridge.org
Downloaded: 16 Mar 2015
disorder level in the template substrate, and producing a final forest-like material. There are several low-cost methods present in the literature for producing ordered templates for nanowire growth, but the final catalyst seed density is usually lower than 1 109 cm 2, or not directly compatible with standard semico
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