On the selective decoration of facets in metallic nanoparticles
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s work presents key modeling aspects that are central to the manipulation of the decoration of metallic nanoparticles by a thin shell of a metal of different chemical nature. The concept of underpotential deposition is generalized to nanoparticles. An all-atom model, taking into account many-body interactions by means of the embedded atom potential, was used to represent nanoparticles of different sizes and atomic adsorbates on them. A full set of state-of-the-art computer simulations are performed for a model system, showing that selective decoration of facets is possible. The trends observed in the present work are in good qualitative agreement with experimental data reported very recently.
I. INTRODUCTION
The study of nanomaterials has been the subject of a huge number of researches during the last two decades. Because of their large surface-to-volume ratio, metal and semiconducting nanoparticles (NPs) in general have properties that depend heavily on their sizes and shapes. The problem of the control of their size and shape has been the subject of several reviews and books and so far it is an open issue, being one of the highly topical research fields in the current literature.1–5 Thus, it is not strange that the development of precise in situ synthesis methods of NPs with different sizes and shapes has become an area of intensive research. The growth of NPs from atomic or molecular precursors, such as inorganic salts, complex species, or organometallic compounds appears as one of the most promising methodology to produce NPs.1–5 Strong reducing agents, like borohydride, are often used to produce NPs due to their ability to quickly induce the nucleation stage.1,6,7 However, the resulting size distribution is widespread, because nucleation and growth take place simultaneously.2,5,8,9 Using wet chemical methods, a proper control over NP sizes and shapes has been achieved in some experiments using NPs as seeds.10–27 This type of growth is an example of heterogeneous nucleation. The initial nucleation stage, that is, the appearance of small clusters in the bulk of the solution, is practically absent in this methodology. In a seed-mediated growth experiment, preexisting NPs (called seeds) are immersed in a growth bath where the growth process only occurs on the surface of the seed-NPs. This growth, involving a lower activation barrier than a)
Address all correspondence to this author. e-mail: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2012.132 J. Mater. Res., Vol. 27, No. 14, Jul 28, 2012
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homogeneous nucleation, usually uses milder conditions (i.e. weak reducing agents, like ascorbic acid), thus allowing for a more precise tuning of the final NP size.1,2 In the particular case of an electrochemical experiment, precise potential control has enabled the deposition of a thin shell of dimensions comparable to those of a monolayer, and even of fractions of it on the surface of NPs.10,28 This is possible thro
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