The analytical relations between particles and probe trajectories in atomic force microscope nanomanipulation

Exploring the Challenges of Characterising Surface Topography of Polymer-Nanoparticle Composites

Nanomechanical testing plays a crucial role in evaluating surfaces containing nanoparticles. Testing verifies surface performance concerning their intended function and detects any potential shortcomings in operational standards. Recognising that nanostructured surfaces are not always straightforward or uniform is essential. The chemical composition and morphology of these surfaces determine the end-point functionality. This can entail a layered surface using materials in contrast to each other that may require further modification after nanomechanical testing to pass performance and quality standards. Nanomechanical analysis of a structured surface consisting of a poly-methyl oxazoline film base functionalised with colloidal gold nanoparticles was demonstrated using an atomic force microscope (AFM). AFM nanomechanical testing investigated the overall substrate architecture's topographical, friction, adhesion, and wear parameters. Limitations towards its potential operation as a biomaterial were also addressed. This was demonstrated by using the AFM cantilever to apply various forces and break the bonds between the polymer film and gold nanoparticles. The AFM instrument offers an insight to the behaviour of low-modulus surface against a higher-modulus nanoparticle. This paper details the bonding and reaction limitations between these materials on the application of an externally applied force. The application of this interaction is highly scrutinised to highlight the potential limitations of a functionalised surface. These findings highlight the importance of conducting comprehensive nanomechanical testing to address concerns related to fabricating intricate biomaterial surfaces featuring nanostructures.

Frictional behavior of one-dimensional materials: an experimental perspective

The frictional behavior of one-dimensional (1D) materials, including nanotubes, nanowires, and nanofibers, significantly influences the efficient fabrication, functionality, and reliability of innovative devices integrating 1D components. Such devices comprise piezoelectric and triboelectric nanogenerators, biosensing and implantable devices, along with biomimetic adhesives based on 1D arrays. This review compiles and critically assesses recent experimental techniques for exploring the frictional behavior of 1D materials. Specifically, it underscores various measurement methods and technologies employing atomic force microscopy, electron microscopy, and optical microscopy nanomanipulation. The emphasis is on their primary applications and challenges in measuring and characterizing the frictional behavior of 1D materials. Additionally, we discuss key accomplishments over the past two decades in comprehending the frictional behaviors of 1D materials, with a focus on factors such as materials combination, interface roughness, environmental humidity, and non-uniformity. Finally, we offer a brief perspective on ongoing challenges and future directions, encompassing the systematic investigation of the testing environment and conditions, as well as the modification of surface friction through surface alterations.

Oligo(3-methoxythiophene)s as Water-Soluble Dyes for Highly Lustrous Gold- and Bronze-like Metal-Effect Coatings and Printings

To overcome various shortcomings associated with commercial metal-effect gloss paints containing metal flakes, we examine possible candidates to be used as novel organic-only metal-effect dyes for both paints and inks. Recently, one of the authors developed a potential candidate (ClO₄ ^--doped oligo(3-methoxythiophene)), but the required solvent was not industrially acceptable and the cured paint displayed low glossiness. Herein, we synthesized and characterized Cl^--doped oligo(3-methoxythiophene) dyes that were water-soluble and displayed a highly lustrous gold- and bronze-like hue upon curing. Additionally, we found that films derived from these oligomers form extremely regular and compact edge-on lamella crystallites through self-organization; these films also display a highly glossy metallic appearance due to the extremely high optical constants of the crystallites. These as-prepared films were easily soluble in water, but we also found that the films become insoluble in water upon dehydration, making industrial implementation feasible.

Influence of contact aging on nanoparticle friction kinetics

One of the oldest concepts in tribology is stick-slip dynamics, where a disruptive sequence of stick and slip phases determine the overall resistance in sliding friction. While the mechanical energy dissipates in the sudden slip phase, the stick phase has been shown to be characterized by contact strengthening mechanisms, also termed contact aging. We present experiments of sliding nanoparticles, where friction is measured as a function of sliding velocity and interface temperature. The resulting complex interdependence is in good agreement with Monte Carlo simulations, in which the energy barrier for contact breaking increases logarithmically with time, at a rate governed by thermal activation.

Manipulation of nanoparticles of different shapes inside a scanning electron microscope

In this work polyhedron-like gold and sphere-like silver nanoparticles (NPs) were manipulated on an oxidized Si substrate to study the dependence of the static friction and the contact area on the particle geometry. Measurements were performed inside a scanning electron microscope (SEM) that was equipped with a high-precision XYZ-nanomanipulator. To register the occurring forces a quartz tuning fork (QTF) with a glued sharp probe was used. Contact areas and static friction forces were calculated by using different models and compared with the experimentally measured force. The effect of NP morphology on the nanoscale friction is discussed.

Exploring the retention properties of CaF2 nanoparticles as possible additives for dental care application with tapping-mode atomic force microscope in liquid

Amplitude-modulation atomic force microscopy (AM-AFM) is used to determine the retention properties of CaF2 nanoparticles adsorbed on mica and on tooth enamel in liquid. From the phase-lag of the forced cantilever oscillation the local energy dissipation at the detachment point of the nanoparticle was determined. This enabled us to compare different as-synthesized CaF2 nanoparticles that vary in shape, size and surface structure. CaF2 nanoparticles are candidates for additives in dental care products as they could serve as fluorine-releasing containers preventing caries during a cariogenic acid attack on the teeth. We show that the adherence of the nanoparticles is increased on the enamel substrate compared to mica, independently of the substrate roughness, morphology and size of the particles.

Controlled AFM manipulation of small nanoparticles and assembly of hybrid nanostructures

We demonstrate controlled manipulation of semiconductor and metallic nanoparticles (NPs) with 5-15 nm diameters and assemble these NPs into hybrid structures. The manipulation is accomplished under ambient environment using a commercial atomic force microscope (AFM). There are particular difficulties associated with manipulating NPs this small. In addition to spatial drift, the shape of an asymmetric AFM tip has to be taken into account in order to understand the intended and actual manipulation results. Furthermore, small NPs often attach to the tip via electrostatic interaction and modify the effective tip shape. We suggest a method for detaching the NPs by performing a pseudo-manipulation step. Finally, we show by example the ability to assemble these small NPs into prototypical hybrid nanostructures with well-defined composition and geometry.

Manipulation of gold colloidal nanoparticles with atomic force microscopy in dynamic mode: influence of particle-substrate chemistry and morphology, and of operating conditions

One key component in the assembly of nanoparticles is their precise positioning to enable the creation of new complex nano-objects. Controlling the nanoscale interactions is crucial for the prediction and understanding of the behaviour of nanoparticles (NPs) during their assembly. In the present work, we have manipulated bare and functionalized gold nanoparticles on flat and patterned silicon and silicon coated substrates with dynamic atomic force microscopy (AFM). Under ambient conditions, the particles adhere to silicon until a critical drive amplitude is reached by oscillations of the probing tip. Beyond that threshold, the particles start to follow different directions, depending on their geometry, size and adhesion to the substrate. Higher and respectively, lower mobility was observed when the gold particles were coated with methyl (-CH(3)) and hydroxyl (-OH) terminated thiol groups. This major result suggests that the adhesion of the particles to the substrate is strongly reduced by the presence of hydrophobic interfaces. The influence of critical parameters on the manipulation was investigated and discussed viz. the shape, size and grafting of the NPs, as well as the surface chemistry and the patterning of the substrate, and finally the operating conditions (temperature, humidity and scan velocity). Whereas the operating conditions and substrate structure are shown to have a strong effect on the mobility of the particles, we did not find any differences when manipulating ordered vs random distributed particles.

A collisional model for AFM manipulation of rigid nanoparticles

The trajectories of differently shaped nanoparticles manipulated by atomic force microscopy are related to the scan path of the probing tip. The direction of motion of the nanoparticles is essentially fixed by the distance b between consecutive scan lines. Well-defined formulas are obtained in the case of rigid nanospheres and nanowires. Numeric results are provided for symmetric nanostars. As a result, orienting the fast scan direction perpendicular to the desired direction of motion and reducing b well below the linear size of the particles turns out to be an efficient way to control the nanomanipulation process.

Controlled manipulation of rigid nanorods by atomic force microscopy

The motion of rigid nanorods caused by the normal vibrations of a nanotip rastering a flat surface is described within an original collisional model. Provided that the friction between the nanorods and the surface is sufficiently high, the direction of motion and the orientation of the nanorods are determined by two pairs of differential equations. In the limiting case of thin nanowires, the direction of motion is precisely related to the length of the nanowire, the tip radius and the density of the scan lines. At the same time the wire oscillates perpendicularly to this direction in a characteristic wobbling motion. Similar conclusions approximately hold also when the rod thickness is not negligible (compared to its length), as shown by a comparison between numerical solutions of our model and measurements on gold nanorods manipulated on a silicon oxide surface. Our results open the path to understanding and controlling the manipulation of arbitrarily shaped nanoparticles.