Nanoparticle particle interactions

The composite films containing metal or semiconductor (M/SC) nanoparticles in various dielectric matrices, draw much attention in connection with fundamental scientific problems and technological applications [1-3]. Specific properties of such films are determined by both individual characteristics of immobilized nanoparticles and interaction of particles with a matrix. Moreover, the new important effects caused by interaction between M/SC nanoparticles appear in composite films at the high M/SC contents [2,3]. 

During the formation of nanoparticles, surfactants interact with the surfaces of the particles in a dynamic equilibrium process. On the contrary, ligands that are chemisorbed to the surface of the particle are less prone to desorption compared to physisorbed ones. A first consequence of a low desorption rate is that particles do not grow rapidly after nucleation. As an example, when thiols are chemisorbed to AuNPs particle sizes are typically limited to <5 nm. In contrast, the majority of surfactants used to stabilize nanoparticles associate with the surface of particles through van der Waals or other weak interactions, allowing the preparation of larger particles. The first report of thiol-stabilized AuNPs appeared in 1993 by Giersig and Mulvaney.145... 

Lamprecht B, Schider G, Lechner RT et al (2000) Metal nanoparticle gratings influence of dipolar particle interaction on the particle resonance. Phys Rev Lett 84 4721 724... 

It is noted that the optical properties of nanoparticles are generally assumed to be sufficiently dispersed and that they may be treated as isolated. However, in most practical situations, particle interactions are important, and sometimes, they are dominant. 

Systems of randomly oriented magnetic nanoparticles randomly dispersed in a supporting medium or matrix and that interact via dipole-dipole forces (last subsection) are systems having several energetically equivalent supermoment orientational states, at given temperatures and applied fields. As such, it is relevant to compare their magnetic behaviors with both the observed behaviors of canonical SG systems (dilute magnetic alloys such as MnCu) and the theoretical predictions from overly simple SG models. This has lead to a productive examination of the effects of dipolar and other inter-particle interactions in synthetic nanoparticle model systems that is reviewed below. Hopefully, this will in turn motivate the development of more realistic theoretical models of disordered dipolar systems. 

As a result of magnetic inter-particle interactions, each nanoparticle will feel a net local interaction field that can be modelled by a time-dependent local applied field, Hint(t). If the time variation of the local interaction field is either very fast or very slow compared to the relevant characteristic times (e.g., i) of the particle, then Hi t(t) can in turn be modelled as a static local field, that will, of course, depend on temperature and macroscopic applied field. The distributions of particle positions, orientations, and supermoments will determine the distribution of local interaction fields. These interaction fields are present in zero applied field and dramatically affect the behaviors of the individual nanoparticles and, consequently, of the sample as a whole. They achieve this in two important ways. First, they change the equilibrium magnetic properties of the sample, giving rise, for example, to superferromagnetic ordering or interaction Curie-Weiss behaviors (see below). Second, and possibly more importantly, they affect dynamic response, via their influence on SP dwell times. 

The main points are that there are at least two characteristic microscopic dwell times, at the level of a single nanoparticle, that they are field dependent, and that they are distributed, at the level of the sample, by two mechanisms via the distributions of particle properties (Eb, ps) and via the distribution of interaction fields Such is the added complexity due to inter-particle interactions. 

Main recent developments in magnetic nanoparticle systems Measurements on single magnetic nanoparticles Synthetic model systems ofmagnetic nanoparticles Inter-particle interactions and collective behavior Noteworthy attempts at dealing with nanoparticle complexity Interpreting the Mossbauer spectra of nanoparticle systems Needed areas of development... 

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