Abstract
There is now a significant body of literature which reports that stripes form in the ligand shell of suitably functionalised Au nanoparticles. This stripe morphology has been proposed to strongly affect the physicochemical and biochemical properties of the particles. We critique the published evidence for striped nanoparticles in detail, with a particular focus on the interpretation of scanning tunnelling microscopy (STM) data (as this is the only technique which ostensibly provides direct evidence for the presence of stripes). Through a combination of an exhaustive re-analysis of the original data, in addition to new experimental measurements of a simple control sample comprising entirely unfunctionalised particles, we show that all of the STM evidence for striped nanoparticles published to date can instead be explained by a combination of well-known instrumental artefacts, or by issues with data acquisition/analysis protocols. We also critically re-examine the evidence for the presence of ligand stripes which has been claimed to have been found from transmission electron microscopy, nuclear magnetic resonance spectroscopy, small angle neutron scattering experiments, and computer simulations. Although these data can indeed be interpreted in terms of stripe formation, we show that the reported results can alternatively be explained as arising from a combination of instrumental artefacts and inadequate data analysis techniques.
Highlights
Scanning probe microscopy (SPM) is an exceptionally powerful technique at the core of modern nanoscience
SPM systems operate in a range of environments spanning what might be termed ‘extreme’ conditions — ultrahigh vacuum, low temperatures, and high magnetic fields — to the in vitro application of atomic force microscope (AFM) to study biochemical and biomedical processes [17]
Following a well-established approach [31,32], a C60 monolayer (ML) was formed on the Si(111)-(767) surface to act as a template for the formation of Ag nanoparticles. (This strategy cannot be used to form Au nanoparticles [33], such as those studied by Stellacci et al As feedback ringing and imaging artefacts are entirely independent of the composition of the nanoparticle, our results are applicable to Au nanoparticles.) C60 was first sublimed onto a clean Si(111)-(767) surface, formed using standard flash annealing procedures [34]
Summary
Scanning probe microscopy (SPM) is an exceptionally powerful technique at the core of modern nanoscience. The development of the atomic force microscope (AFM) [9] shortly after the introduction of the STM broadened the applicability of SPM to a much wider variety of substrates — including insulators in particular — and led to the adoption of SPM as a high resolution imaging technique in very many scientific disciplines and sub-fields. SPM systems operate in a range of environments spanning what might be termed ‘extreme’ conditions — ultrahigh vacuum, low temperatures, and high magnetic fields (for example, an STM running at 10 milliKelvin in a field of 15 T has recently been developed [16]) — to the in vitro application of AFM to study biochemical and biomedical processes [17]. A significant number of commercial suppliers provide ‘turn-key’ SPM systems such that the probe microscope has evolved into a standard characterisation tool in the vast majority of nanoscience laboratories
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