www.MaterialsViews.com 1 © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.small-journal.com Dynamics of Gold Nanoparticles on Carbon Nanostructures Driven by van der Waals and Electrostatic Interactions Alessandro La Torre, Maria del Carmen Gimenez-Lopez,* Michael W. Fay, Carlos Herreros Lucas, Paul D. Brown, and Andrei N. Khlobystov 1D and 2D carbon nanostructures, such as carbon nano- tubes and graphene, have attracted a great deal of atten- tion because of their outstanding structural and physical properties. [1,2] Decoration of nanocarbons with metallic nanoparticles (NP) facilitates the incorporating of additional functionalities for exploitation in future electronic, catalytic, and energy storage and conversion applications. [3–6] However, the utilization of composite metal–carbon nanostructures is presently room temperature limited, to preserve the NP size-dependent properties, as adsorbed metal nanoparticles are generally metastable and highly labile. [7,8] In this context, gaining improved understanding of the interactions between metal NP and carbon nanostructures is of paramount impor- tance for controlling the size and position of adsorbed NP, in order to gain full control of the potential functionalities of these hybrid nanostructures. [9] The growth (otherwise termed sintering) of NP on var- ious carbon nanostructures has been extensively studied, [10,11] but only recently has it been possible to shed some light on the key mechanisms involved in the growth of ≈2 nm gold nanoparticles (AuNP) on graphitized carbon nanofibers (GNFs). [12,13] In contrast to carbon nanotubes, GNFs exhibit corrugated interior surfaces dictated by their internal stacked- nanocone structures, with typical step-edge heights of ≈3 nm. The different internal and external surface morphologies DOI: 10.1002/smll.201402807 Nanostructures Dr. A. La Torre, Dr. M. d. C. Gimenez-Lopez, C. H. Lucas, Prof. A. N. Khlobystov School of Chemistry The University of Nottingham University Park, Nottingham, NG7 2RD, UK E-mail: Maria.Gimenez-Lopez@nottingham.ac.uk Dr. M. W. Fay, Prof. A. N. Khlobystov Nottingham Nanoscience and Nanotechnology Centre The University of Nottingham University Park, Nottingham, NG7 2RD, UK Prof. P. D. Brown Division of Materials Mechanics and Structures Department of Mechanical Materials and Manufacturing Engineering Faculty of Engineering The University of Nottingham University Park, Nottingham, NG7 2RD, UK of the GNF ( Figure 1A) provide a unique environment for the study of bonding processes involved in the growth of NP. For example, it has been shown that AuNP adsorbed on the internal surfaces of GNF always grow to the same, con- strained, maximum size of ≈6 nm, while AuNP adsorbed on the atomically smooth graphitic surfaces of the GNF exterior continue their growth to ≈13 nm and beyond (Figure 1A), regardless of the source of energy providing the driving force for growth (i.e., heat or electron beam). [12] Accordingly, it is considered that GNF interior step-edges impose a significant barrier for the migration of AuNP, precluding their growth by coalescence, with Ostwald ripening remaining the only possible growth mechanism. The size of growing AuNP on GNF interior step-edges may also be influenced by electro- static interactions arising from charge transfer between the nanocone graphene stacks and the adsorbed AuNP. Recently, studies on the formation of AuNP on few-layer graphene (FLG) films showed that the strength of electrostatic interac- tion increased with decreasing film thickness for the case of the smallest NP. [14] In view of the complex nature of GNF as a support material for studying AuNP growth, and the dif- ficulty of separating out the effects of electrostatic interaction (i.e., electron transfer from the graphene stack) from struc- tural factors (i.e., the nanocone step-edges), it is recognized that complementary experimental evidence is needed, using simpler model-system carbon support structures, to appraise the relative importance of these competing factors on the nanoscale organization of metallic NP of controlled size. Here, we report on the assembly and growth (induced either by exposure to a high energy electron beam or in situ thermal heating within a transmission electron microscopy (TEM)—in isolation, sequentially, or together) of preformed AuNP on multiwalled carbon nanotubes (MWNT) supported on FLG and amorphous carbon film templates, to appraise the relative importance of van der Waals forces and elec- trostatic interactions, for the creation and stabilization of ordered, linear arrangements of NP. When a 1D cylindrical carbon nanotube is placed on a flat surface, the intersection between the convex surface of the nanotube exterior and the flat surface delineates a 1D channel along the nanotube growth axis (Figure 1B). From a viewpoint of host–guest interaction, this channel could be used to stabilize NP with controlled size. The van der Waals forces acting between NP and the channel are expected to small 2015, DOI: 10.1002/smll.201402807