Nanocrystals are fundamental to modern science and technology. Mastery over the shape of a nanocrystal enables control of its properties and enhancement of its usefulness for a given application. Our aim is to present a comprehensive review of current research activities that center on the shape-controlled synthesis of metal nanocrystals. We begin with a brief introduction to nucleation and growth within the context of metal nanocrystal synthesis, followed by a discussion of the possible shapes that a metal nanocrystal might take under different conditions. We then focus on a variety of experimental parameters that have been explored to manipulate the nucleation and growth of metal nanocrystals in solution-phase syntheses in an effort to generate specific shapes. We then elaborate on these approaches by selecting examples in which there is already reasonable understanding for the observed shape control or at least the protocols have proven to be reproducible and controllable. Finally, we highlight a number of applications that have been enabled and/or enhanced by the shape-controlled synthesis of metal nanocrystals. We conclude this article with personal perspectives on the directions toward which future research in this field might take.

Shape‐Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics?

The special mechanical properties of nanoparticles allow for novel applications in many fields, e.g., surface engineering, tribology and nanomanufacturing/nanofabrication. In this review, the basic physics of the relevant interfacial forces to nanoparticles and the main measuring techniques are briefly introduced first. Then, the theories and important results of the mechanical properties between nanoparticles or the nanoparticles acting on a surface, e.g., hardness, elastic modulus, adhesion and friction, as well as movement laws are surveyed. Afterwards, several of the main applications of nanoparticles as a result of their special mechanical properties, including lubricant additives, nanoparticles in nanomanufacturing and nanoparticle reinforced composite coating, are introduced. A brief summary and the future outlook are also given in the final part. (Some figures may appear in colour only in the online journal)

https://iopscience.iop.org/article/10.1088/0022-3727/47/1/013001/pdf

Mechanical properties of nanoparticles: basics and applications

The physics of sliding friction is gaining impulse from nanoscale and mesoscale experiments, simulations, and theoretical modeling This Colloquium reviews some recent developments in modeling and in atomistic simulation of friction, covering open-ended directions, unconventional nanofrictional systems, and unsolved problems

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Colloquium : Modeling friction: from nanoscale to mesoscale

Nanokristalle sind von grundlegender Bedeutung in der modernen Wissenschaft und Technologie. Die Eigenschaften eines Nanokristalls lassen sich uber seine Form beeinflussen und auf eine bestimmte Anwendung hin zuschneiden. Ziel dieses Aufsatzes ist es, einen umfassenden Uberblick uber den aktuellen Stand der Forschung auf dem Gebiet der formkontrollierten Synthese von Metallnanokristallen zu geben. Nach einer kurzen Einleitung uber die Prinzipien von Kristallkeimbildung und -wachstum diskutieren wir einzelne Arten von Nanokristallformen und betrachten verschiedene experimentelle Parameter, uber die die Keimbildung und das Wachstum von Metallnanokristallen in der Losungssynthese gezielt manipuliert werden kann. Wir erlautern diese Methoden anhand von Beispielen, wo zumindest ein Grundverstandnis fur die beobachtete Formkontrolle vorhanden ist. Schlieslich stellen wir Anwendungen vor, bei denen die Formkontrolle von Metallnanokristallen ein entscheidender Faktor ist, und beenden den Aufsatz mit einem personlichen Ausblick auf kunftig zu erwartende Entwicklungen auf diesem Gebiet.

Formkontrolle bei der Synthese von Metallnanokristallen: einfache Chemie, komplexe Physik?

This review article aims to provide an updated and comprehensive description on the development of atomic force microscopy (AFM) nanolithography for structuring and fabrication at the nanometer scale. The many AFM nanolithographic techniques are classified into two general groups of force-assisted and bias-assisted nanolithography on the basis of their mechanistic and operational principles. Force-assisted AFM nanolithography includes mechanical indentation and plowing, thermomechanical writing, manipulation and dip-pen nanolithography. Bias-assisted AFM nanolithography encompasses probe anodic oxidation, field evaporation, electrochemical deposition and modification, electrical cutting and nicking, electrostatic deformation and electrohydrodynamic nanofluidic motion, nanoexplosion and shock wave generation, and charge deposition and manipulation. The experimental procedures, pattern formation mechanisms, characteristics, and functionality of nanostructures and nanodevices fabricated by AFM nanolithography are reviewed. The capabilities of AFM nanolithography in patterning a large family of materials ranging from single atoms and molecules to large biological networks are presented. Emphasis is given to AFM nanolithographic techniques such as dip-pen nanolithography, probe anodic oxidation, etc. due to the rapid progress and wide applications of these techniques.

Nanoscale materials patterning and engineering by atomic force microscopy nanolithography

One of the most fundamental questions in tribology concerns the area dependence of friction at the nanoscale. Here, experiments are presented where the frictional resistance of nanoparticles is measured by pushing them with the tip of an atomic force microscope. We find two coexisting frictional states: While some particles show finite friction increasing linearly with the interface areas of up to $310\text{ }000\text{ }\text{ }{\mathrm{nm}}^{2}$, other particles assume a state of frictionless sliding. The results further suggest a link between the degree of surface contamination and the occurrence of this duality.

Frictional duality observed during nanoparticle sliding.

Antimony nanoparticles grown on highly oriented pyrolytic graphite and molybdenum disulfide were used as a model system to investigate the contact-area dependence of frictional forces. This system allows one to accurately determine both the interface structure and the effective contact area. Controlled translation of the antimony nanoparticles (areas between 10 000 and $110\phantom{\rule{0.2em}{0ex}}000\phantom{\rule{0.3em}{0ex}}{\mathrm{nm}}^{2}$) was induced by the action of the oscillating tip in a dynamic force microscope. During manipulation, the power dissipated due to tip-sample interactions was recorded. We found that the threshold value of the power dissipation needed for translation depends linearly on the contact area between the antimony particles and the substrate. Assuming a linear relationship between dissipated power and frictional forces implies a direct proportionality between friction and contact area. Particles about $10\phantom{\rule{0.2em}{0ex}}000\phantom{\rule{0.3em}{0ex}}{\mathrm{nm}}^{2}$ in size, however, were found to show dissipation close to zero. To explain the observed behavior, we suggest that structural lubricity might be the reason for the low dissipation in the small particles, while elastic multistabilities might dominate energy dissipation in the larger particles.

Contact-area dependence of frictional forces: Moving adsorbed antimony nanoparticles

Nanometer scale metallic particles have been manipulated on an atomically flat graphite surface by atomic force microscopy techniques and quantitative information on interfacial friction was extracted from the lateral manipulation of these nanoparticles. Similar to conventional friction force microscopy, the particle-surface interfacial friction was extracted from the torsional signal of the cantilever during the particle pushing process. As a model system, we chose antimony particles with diameters between 50 and 500nm grown on a highly oriented pyrolytic graphite substrate. Three different manipulation strategies have been developed, which either enable the defined manipulation of individual nanoparticles or can be utilized to gather data on a larger number of particles found within a particular scan area, allowing for fast and statistically significant data collection. While the manipulation strategies are demonstrated here for operation under vacuum conditions, extensive testing indicated that the proposed methods are likewise suited for ambient environments. Since these techniques can be applied to a large variety of chemically and structurally different material combinations as well as a large range of particle sizes, our results indicate a viable route to solve many recent issues in the field of nanoscale friction, such as the influence of contact size and interface crystallinity.

Interfacial friction obtained by lateral manipulation of nanoparticles using atomic force microscopy techniques

We report on the application of a home-built scanning force microscope for translation and in-plane rotation of nanometer-sized latex spheres by dynamic surface modification (DSM). This technique is based on the incrementof the amplitude of the oscillating voltage applied at the dither piezo that drives the cantilever vibrations in the dynamic mode of scanning force microscopy. Thus, it is easily possible to switch between the imaging mode and DSM mode, enabling the direct manipulation of nanostructures under ambient conditions with high precision. The main advantage of our technique compared to earlier methods is that it operates with an active feedback loop, allowing a steady manipulation of nanostructures independent of the surface corrugation or sample tilt. Such controlled translations of latex spheres enable us in addition to study their properties regarding friction, adhesion, and cohesion. By translating latex spheres of different sizes (radii between 50 and 110 nm), it was found that the force needed to move a particle depends on its dimensions. Finally, the lateral translation of an intentionally marked sphere gives evidence that sliding is preferred over rolling.

Controlled translational manipulation of small latex spheres by dynamic force microscopy

The spontaneous formation of complex interfacial patterns from thermally deposited Sb4 clusters on HOPG is controlled by the deposition conditions (i.e., coverage and deposition rate) at constant t...

Claudia Ritter

Papers

Frictional duality observed during nanoparticle sliding.

Contact-area dependence of frictional forces: Moving adsorbed antimony nanoparticles

Interfacial friction obtained by lateral manipulation of nanoparticles using atomic force microscopy techniques

Controlled translational manipulation of small latex spheres by dynamic force microscopy

Crystallization of antimony nanoparticles: Pattern formation and fractal growth