Quantitative Measurement of Interfacial Adhesion of CVD Grown Bilayer WS on Various Substrates.

The interfacial adhesion between transition metal dichalcogenides (TMDs) and the growth substrate significantly influences the employment of flakes in various applications. Most previous studies have focused on MoS and graphene, particularly their interaction with SiO/Si substrates. In this work, the adhesion strength of CVD-grown bilayer WS is directly measured using the nano scratch technique on three different substrates-Sapphire, SiO/Si, and fused quartz.

Graphene Mitigates Nanoscale Tribochemical Wear of Silica Glass in Water.

Despite the ubiquitous use of glasses, their simultaneous susceptibility toward scratch-induced defects and atmospheric hydration deteriorates their mechanical and chemical durability. Here, it is demonstrated that the deposition of a few-layer graphene provides unprecedented wear resistance to silica glass in aqueous conditions. To this extent, nanoscale scratch tests are carried out on graphene-glass surfaces via contact-mode atomic force microscopy with chemically inert and reactive tips.

Anisotropic Stick-Slip Frictional Surfaces via Titania Nanorod Patterning.

Nanoscale or microscale surface texturing is an effective technique to tailor the tribological properties between two surfaces that are rubbed against each other. In order to achieve the desired frictional properties by a patterned surface, one needs an in-depth understanding of the underlying mechanisms. Here, we demonstrate anisotropic stick-slip friction achieved via a nanotextured surface of tilted titania nanorods (TiNRs).

Transforming friction: unveiling sliding-induced phase transitions in CVD-grown WS monolayers under single-asperity sliding nanocontacts.

Transition metal dichalcogenides (TMDs) exhibit diverse properties across different phases, making them promising materials for various engineering applications. In the present work, we employed a comprehensive approach, combining experimental investigations and computational simulations to elucidate the remarkable tunable frictional characteristics of chemical vapor deposition (CVD) grown WS monolayers through the sliding-induced transitions between the 1H and 1T' phases. Our atomic force microscopy (AFM) measurements reveal a significant contrast in friction between the two phases, with the 1H phase displaying higher friction (∼52%) than the 1T' phase.

Recent Advancements in Understanding of Growth and Properties of Antiwear Tribofilms Derived from Zinc Dialkyl Dithiophosphate Additives under Nanoscale Sliding Contacts.

Zinc dialkyl dithiophosphate (ZDDP) is a key antiwear additive in lubricants that forms robust phosphate glass-based tribofilms to mitigate wear on rubbing surfaces. The quest to unravel the enigma of these antiwear film formations on sliding surfaces has persisted as an enduring mystery, despite nearly a century of fervent research. This paper presents a comprehensive review of nanotribological investigations, centering on the tribochemical decomposition of ZDDP antiwear additives.

Superlubricity and Stress-Shielding of Graphene Enables Ultra Scratch-Resistant Glasses.

Glasses, when subjected to scratch loading, incur damages affecting their optical and mechanical integrity. Here, it is demonstrated that silica glasses protected with mechanically exfoliated few-layer graphene sheets can exhibit remarkable improvement in scratch resistance. To this extent, the friction and wear characteristics of silica glasses with exfoliated graphene using atomic force microscopy (AFM) are explored.

Multi-Functional Applications of H-Glass Embedded with Stable Plasmonic Gold Nanoislands.

Metal nanoparticles (MNPs) are synthesized using various techniques on diverse substrates that significantly impact their properties. However, among the substrate materials investigated, the major challenge is the stability of MNPs due to their poor adhesion to the substrate. Herein, it is demonstrated how a newly developed H-glass can concurrently stabilize plasmonic gold nanoislands (GNIs) and offer multifunctional applications.

Nanoscale friction and wear behavior of a CVD-grown aged WS monolayer: the role of wrinkles and surface chemistry.

Friction reduction by transition metal dichalcogenide (TMD) monolayers is well documented; however, wrinkle formation on the surface of TMDs takes place due to strain relaxation over time and leads to the deterioration of the tribological properties at a small scale. Herein, we report the role of wrinkles on the wear behavior of a chemical vapor deposition (CVD) grown aged WS monolayer and the comparison with wrinkle-free regions. Atomic force microscopy (AFM) was utilized to perform load-dependent experiments, and we noticed that the wear initiated near wrinkles resulted in the disintegration of the monolayer.

Benefit of coconut-based hair oil via hair porosity quantification.

Objective: The present study is intended to characterize the surfactant damage suffered by the hair cortex in routine washing and the mechanistic effect of Coconut Based Hair Oils (CBHO) to mitigate the damage.

Methods: Surfactants which diffuse into the hair structure solubilize protein moieties, leading to an increase in porosity and internal surface area as well as the pore volume. The changes in hair pores occurring in the hair cortex are measured by nitrogen sorption method in line with the Brunauer-Emmett-Teller (BET) theory.

Looking through glass: Knowledge discovery from materials science literature using natural language processing.

Most of the knowledge in materials science literature is in the form of unstructured data such as text and images. Here, we present a framework employing natural language processing, which automates text and image comprehension and precision knowledge extraction from inorganic glasses' literature. The abstracts are automatically categorized using latent Dirichlet allocation (LDA) to classify and search semantically linked publications.

Linear Aging Behavior at Short Timescales in Nanoscale Contacts.

Nanoscale silica-silica contacts were recently found to exhibit logarithmic aging for times ranging from 0.1 to 100 s, consistent with the macroscopic rate and state friction laws and several other aging processes. Nanoscale aging in this system is attributed to progressive formation of interfacial siloxane bonds between surface silanol groups.

Memory Distance for Interfacial Chemical Bond-Induced Friction at the Nanoscale.

Macroscale rate and state friction (RSF) laws include a memory distance, , which is considered to be the distance required for a population of frictional contacts to renew itself slip, counteracting the effects of aging in slow or static contact. This concept connects static friction and kinetic friction. Here, we use atomic force microscopy to study interfacial chemical bond-induced kinetic friction and the memory distance at the nanoscale for single silica-silica nanocontacts.

Stick-Slip Instabilities for Interfacial Chemical Bond-Induced Friction at the Nanoscale.

Earthquakes are generally caused by unstable stick-slip motion of faults. This stick-slip phenomenon, along with other frictional properties of materials at the macroscale, is well-described by empirical rate and state friction (RSF) laws. Here we study stick-slip behavior for nanoscale single-asperity silica-silica contacts in atomic force microscopy experiments.

Load and Time Dependence of Interfacial Chemical Bond-Induced Friction at the Nanoscale.

Rate and state friction (RSF) laws are widely used empirical relationships that describe the macroscale frictional behavior of a broad range of materials, including rocks found in the seismogenic zone of Earth's crust. A fundamental aspect of the RSF laws is frictional "aging," where friction increases with the time of stationary contact due to asperity creep and/or interfacial strengthening. Recent atomic force microscope (AFM) experiments and simulations found that nanoscale silica contacts exhibit aging due to the progressive formation of interfacial chemical bonds.

Dynamic shear force microscopy of viscosity in nanometer-confined hexadecane layers.

Hexadecane exhibits pronounced molecular layering upon confinement to gaps of a few nanometer width which is discussed for its role in boundary lubrication. We have probed the mechanical properties of the confined layers with the help of an atomic force microscope, by quasi-static normal force measurements and by analyzing the lateral tip motion of a magnetically actuated torsional cantilever oscillation. The molecular layering is modeled by a oscillatory force curve and the tip approach is simulated assuming thermal equilibrium correlations in the liquid.

Nano-rheology of hydrogels using direct drive force modulation atomic force microscopy.

We present a magnetic force-based direct drive modulation method to measure local nano-rheological properties of soft materials across a broad frequency range (10 Hz to 2 kHz) using colloid-attached atomic force microscope (AFM) probes in liquid. The direct drive method enables artefact-free measurements over several decades of excitation frequency, and avoids the need to evaluate medium-induced hydrodynamic drag effects. The method was applied to measure the local mechanical properties of polyacrylamide hydrogels.

Atomic force microscopy on plasma membranes from Xenopus laevis oocytes containing human aquaporin 4.

Atomic force microscopy (AFM) is a unique tool for imaging membrane proteins in near-native environment (embedded in a membrane and in buffer solution) at ~1 nm spatial resolution. It has been most successful on membrane proteins reconstituted in 2D crystals and on some specialized and densely packed native membranes. Here, we report on AFM imaging of purified plasma membranes from Xenopus laevis oocytes, a commonly used system for the heterologous expression of membrane proteins.

Quantized friction across ionic liquid thin films.

Ionic liquids - salts in the liquid state under ambient conditions - are of great interest as precision lubricants. Ionic liquids form layered structures at surfaces, yet it is not clear how this nano-structure relates to their lubrication properties. We measured the friction force between atomically smooth solid surfaces across ionic liquid films of controlled thickness in terms of the number of ion layers.

Impact of van der Waals interactions on single asperity friction.

Single asperity measurements on Si wafers with variable SiO(2) layer thickness, yet identical roughness, revealed the influence of van der Waals (vdW) interactions on friction: on thin (1 nm) SiO(2) layers, higher friction and jump-off forces were observed as compared to thick (150 nm) SiO(2) layers. The vdW interactions were additionally controlled by a set of silanized Si wafers, exhibiting the same trend. The experimental results demonstrate the influence of the subsurface material and are quantitatively described by combining calculations of interactions of the involved materials and the Derjaguin-Müller-Toporov model.

Monolayer to Bilayer Structural Transition in Confined Pyrrolidinium-Based Ionic Liquids.

Ionic liquids can be intricately nanostructured in the bulk and at interfaces resulting from a delicate interplay between interionic and surface forces. Here we report the structuring of a series of dialkylpyrrolidinium-based ionic liquids induced by confinement. The ionic liquids containing cations with shorter alkyl chain substituents form alternating cation-anion monolayer structures on confinement to a thin film, whereas a cation with a longer alkyl chain substituent leads to bilayer formation.

Ageing of a microscopic sliding gold contact at low temperatures.

Nanometer-scale friction measurements on a Au(111) surface have been performed at temperatures between 30 and 300 K by means of atomic force microscopy. Stable stick slip with atomic periodicity is observed at all temperatures, showing only weak dependence on temperature between 300 and 170 K. Below 170 K, friction increases with time and a distortion of the stick-slip characteristic is observed.

Self-assembly in the electrical double layer of ionic liquids.

We have studied the structure of two ionic liquids confined between negatively charged mica sheets. Both liquids exhibit interfacial layering, however the repeat distance is dramatically different for the two liquids. Our results suggest a transition from alternating cation-anion monolayers to tail-to-tail cation bilayers when the length of the cation hydrocarbon chain is increased.

Molecular order and disorder in the frictional response of alkanethiol self-assembled monolayers.

Molecular processes in the frictional response of an alkanethiol monolayer, self-assembled on a Au(111) surface, are studied by means of high-resolution friction force microscopy in ultrahigh vacuum. With increasing load, three regimes are observed on defect-free domains of the monolayer: smooth sliding with negligible friction, regular molecular stick-slip motion with increasing friction, and the onset of wear in the monolayer. Molecular contrast in the lateral force is found for inequivalent molecules within the unit cell of the c(4 × 2) superstructure.

Switching atomic friction by electrochemical oxidation.

Friction between the sliding tip of an atomic force microscope and a gold surface changes dramatically upon electrochemical oxidation of the gold surface. Atomic-scale variations of the lateral force reveal details of the friction mechanisms. Stick-slip motion with atomic periodicity on perfect Au(111) terraces exhibits extremely low friction and almost no dependence on load.

Template-assisted patterning of nanoscale self-assembled monolayer arrays on surfaces.

We report a general, simple, and inexpensive approach to pattern features of self-assembled monolayers (SAMs) on silicon and gold surfaces using porous anodic alumina films as templates. The SAM patterns, with feature sizes down to 30 nm and densities higher than 10(10)/cm(2), can be prepared over large areas (>5 cm(2)). The feature dimensions can be tuned by controlling the alumina template structure.