Display omitted
•Texturing effects on nanotribological properties and subsurface damage are studied.•Nanoscale friction and wear behaviour of GaN can be regulated by texture parameter.•Nano-texture ...can alleviate dislocation development and reduce subsurface damage.•The m-GaN exhibits lower wear and thicker damage layer compared with the c-GaN.
Surface nanotribological properties and subsurface damage of flat and textured gallium nitride (GaN) substrates during both linear and circular nanoscratching processes are investigated using molecular dynamics simulation. Results show that the surface texture can remarkably reduce not only the surface friction and wear but also the scratching-induced subsurface damage regardless of the tip radius and penetration depth. Tangential force and friction coefficient decreased with an increase in groove width or depth primarily due to the reduced contact area. The effect of texturing on stress distribution can affect the development of dislocation to alleviate the nanoscale material deformation and removal and thereby reduce surface wear and subsurface damage. Increasing tip radius can reduce the friction coefficient and surface wear, but it promotes subsurface damage. By contrast, increasing tip penetration depth can increase the friction, wear, and subsurface damage for flat and textured GaN substrates. Compared with the c-plane, the m-plane GaN substrate exhibits higher friction but lower material wear, and it has a considerably thicker subsurface damage layer due to the difference in their dislocation networks. This work can provide useful insights into the design of GaN-based material with antifriction and wear properties through the surface texturing treatments.
The surface precision and mechanical properties were the bottleneck of laser shock imprinting extensive application in micro/nano manufacturing. In this work, the high-quality and precise nanoscale ...line textures were fabricated on aluminum foil, and the influence of pulse laser energy and laser pre-shock processing on the preparation of nanoscale line textures was also investigated experimentally. The morphology of nanoscale line texture was characterized by scanning electron microscope (SEM) and atomic force microscope (AFM), which obtained the best laser shock imprinting parameter. The microstructure and dislocation changes of laser shock imprinted aluminum foil were analyzed by transmission electron microscope (TEM), which explained the improvement of nanoscale line textured aluminum foil in electrochemical and mechanical properties. The nanotribological properties of nanoscale line textured aluminum foil were characterized by the AFM with sharp probe and SiO2 colloidal probe. The experimental results indicated that nanoscale line textured aluminum foil had the effect of reducing friction and adhesive force between AFM probe and aluminum foil. The laser shock imprinting can fabricate high-accuracy nanoscale line textures on aluminum foil. Compared with the original aluminum foil, the morphology, mechanical properties, electrochemical performance and nanotribological properties of nanoscale line textured aluminum foil were improved.
Display omitted
•Large area and high-quality nanoscale line textures fabricated on aluminum foil by laser shock imprinting.•The mechanical properties and electrochemical performance of nanoscale line textured aluminum foil were greatly improved.•Nanoscale grains and high density dislocation regions were observed in nanoscale line textured aluminum foil.•The nanoscale line textures on aluminum foil can reduce the adhesion and friction force.
Silicone polymeric films were deposited on silicon substrate, and their adhesive and nanomechanical properties were studied. The surface characterization and tribological (wear) behaviour were ...investigated using atomic force microscopy. The surface Gibbs energy was estimated locally, using a special test rig where the contact angle of very small (with a diameter of about 100 μm) sessile drops was measured by processing of the image from a camera. The nanomechanical properties of the films were tested by using Hysitron’s test instruments. Such films seem to be interesting for application on contact surfaces of microgrippers used in assembly processes in micro electro mechanical systems and nanotechnologies.
Graphene is one of the key building blocks for a broad range of flexible/stretchable electronics and has great potential as a solid lubricant in flexible micro/nanoelectromechanical systems, soft ...robot and microfluidic devices due to their excellent electrical, mechanical and tribological properties. The nanotribological properties of graphene on soft elastic substrate were studied using the calibrated atomic force microscopy (AFM). The nanotribological properties of graphene on soft elastic substrate were enhanced by the elastic deformation compared with the hard SiO2/Si substrate. Also the friction force of graphene on soft elastic substrate decreases with the increase of the thickness and shows a sub-linear dependence on the indentation depth. A novel model of the elastic deformation enhancing puckering effect was proposed to explain the nanotribological properties of graphene on soft elastic substrate. The atomic-scale frictional behaviors of graphene on soft elastic substrate confirmed the mechanism of the elastic deformation enhanced puckering effect. These studies can provide a fundamental understanding of graphene as a solid lubricant on soft elastic substrate for graphene-based flexible MEMS/NEMS devices.
Display omitted
Molecular dynamics simulation was performed to study the surface nanotribological behavior and subsurface damage of gallium arsenide (GaAs) substrate coated with monolayer graphene when subjected to ...the scratching action of diamond abrasive. Simulation result shows that the coefficient of friction and wear volume of GaAs/graphene surface are evidently lower than those of the bare GaAs surface for various scratching depths. The material removal of the graphene-coated GaAs workpiece is primarily attributed to compression- and shear-induced plastic deformation of GaAs, whereas abrasive wear is the dominant material-removal mechanism for bare GaAs workpiece. On the contrary, the GaAs workpiece coated with graphene exhibits severe subsurface damage due to the higher stress and that graphene can suppress the stress released within the GaAs workpiece during scratching; hence, the stress has to spread deeply. The scratching-induced slight deformation of graphene occurs when the scratching depth is higher than 15 Å. The deformed graphene induced by scratching is still capable of protecting GaAs substrate to some extent, but its C-C bond is vulnerable to be ruptured at the end of the scratching path due to a scratching-induced bulge structure. Increasing temperature can promote the scratching-induced surface wear and subsurface damage of GaAs workpiece. Monolayer graphene can improve the surface tribological properties of GaAs at each temperature. This work can provide atomic insights into the antifriction and antiwear design for GaAs when graphene is used as a coating.
Display omitted
•Effects of monolayer graphene on scratching properties of GaAs are investigated via MD simulation.•Surface friction and wear are reduced considerably but subsurface damage of GaAs substrate is intensified by graphene.•Monolayer graphene can evidently improve tribological behavior of GaAs substrate over wide temperature range.
The nanohardness (H), reduced elastic modulus (E), and nanotribological properties including nanoscratch and nanowear resistance of tantalum/cobalt (Ta/Co) nanolaminates with varying individual layer ...thickness (h) were systematically studied using a nanoindenter. With decreasing individual layer thickness from 100 nm to 5 nm, the H of the nanolaminates increased gradually and reached a peak of ~7.20 GPa at h = 5 nm, while the E increased gradually with a sudden decrease at h = 25 nm. The critical point of delamination (Pc), coefficient of friction (COF), and post-scratch microstructures of the nanolaminates were assessed via nanoscratch testing. The normal load at Pc was increased gradually with a decrease in h under a ramped load. The post-scratch microstructures after delamination showed clear film chipping/crack formation and propagation of cracks/breakdown of grains at larger h, while no film chipping/cracking/breakdown of grains was observed in the nanolaminate with h = 5 nm. The wear rate of the nanolaminates increased with an increase in applied load irrespective of h and, interestingly, it started decreasing with increasing the numbers of wear cycles and became steady at higher numbers of wear cycles during nanowear tests. The nanolaminate with h = 5 nm showed the lowest wear rate with minimal plastic deformation. Nanoindentation of the worn surfaces of the nanolaminate with h = 5 nm after nanowear testing showed significant work hardening despite its negligible plastic deformation during nanowear tests. Overall, the Ta/Co nanolaminate with individual layer thickness at a few nanometers’ length-scale exhibited high strength and excellent scratch and wear resistance with minimal plastic deformation.
•Nanoindentation and nanotribological behaviors were studied for Ta/Co nanolaminates.•Wear rate decreased with reducing individual layer thickness (h) during nanowear test.•Critical load of delamination increased with decreasing h during nanoscratch test.•Minimal deformation observed at h = 5 nm during both nanoscratch and nanowear tests.•Ta/Co nanolaminate at h = 5 nm exhibited excellent scratch and wear resistance.
Through nanoscratch experiments with a spherical diamond indenter, a contrastive study of the nanotribological properties of Ga- and N-faced gallium nitride (GaN) samples was carried out. ...Nanoindentation results revealed that the elastic modulus of the Ga-faced GaN sample was slightly higher than that of N-faced GaN sample. Particularly, Ga- and N-faced GaN samples exhibited rather different nanotribological properties, and the Ga-faced sample showed a stronger wear resistance. The study indicated that the critical normal load required to cause material removal of N-faced GaN sample was almost two times that of Ga-faced GaN sample. Both Ga- and N-faces exhibited a rather low frictional coefficient at the elastic and elastoplastic stages of material, e.g., ~0.06 for Ga-face and ~0.075 for N-face when scratching under the progressive normal load. Combined with transmission electron microscopy and X-ray photoelectron spectroscopy, we speculated that, except for the intrinsic atomic arrangements attributed to the non-reverse crystallographic symmetry of c-plane wurtzite GaN, the difference of nanotribological properties between Ga- and N-faces may also be related to the preferential formation of a native oxide layer and a slight lattice damage layer on the N-faced GaN surface. This study can enrich the understanding of the nanotribological properties of Ga- and N-polar-faced bulk monocrystalline GaN materials fabricated by the conventional technique.
Display omitted
Frictional and nanomechanical properties of nanostructured polymer surfaces are important to their technological and biomedical applications. In this work, poly(ethylene ...terephthalate) (PET) surfaces with a periodic distribution of well-defined nanopillars were fabricated through an anodization/embossing process. The apparent surface energy of the nanopillared surfaces was evaluated using the Fowkes acid-base approach, and the surface morphology was characterized using scanning electron microscope (SEM) and atomic force microscope (AFM). The normal and lateral forces between a silica microparticle and these surfaces were quantified using colloidal probe atomic force microscopy (CP-AFM). The friction-load relationship followed Amonton’s first law, and the friction coefficient appeared to scale linearly with the nanopillar height. Furthermore, all the nanopillared surfaces showed pronounced frictional instabilities compared to the smooth sliding friction loop on the flat control. Performing the stick–slip amplitude coefficient (SSAC) analysis, we found a correlation between the frictional instabilities and the nanopillars density, pull-off force and work of adhesion. We have summarised the dependence of the nanotribological properties on such nanopillared surfaces on five relevant parameters, i.e. pull-off force fp, Amontons’ friction coefficient μ, RMS roughness Rq, stick–slip amplitude friction coefficient SSAC, and work of adhesion between the substrate and water Wadh in a radar chart. Whilst demonstrating the complexity of the frictional behaviour of nanopillared polymer surfaces, our results show that analyses of multiparametric nanotribological properties of nanostructured surfaces should go beyond classic Amontons’ laws, with the SSAC more representative of the frictional properties compared to the friction coefficient.
The high Brazilian ethnical mixture combined with the country climate conditions make Brazilian hair an uncommon category that is still scarcely studied.
Brazilian hair of types II to V was ...investigated by nanoscratch and nanoindentation techniques. The results were statistically analyzed using ANOVA (p≤0.05 level) and statistical correlation between the measured parameters was studied by linear regression.
Nanoscratch at low loads showed for hair types II and III a pronounced elastic recovery with little damage, while for types IV and V a more plastic and brittle behavior with higher friction in the direction from tip to root was observed. At high loads the tip reached the cortex and elastoplastic deformation, plowing, fracturing and chipping of cuticle cells occurred in all types. Quasi-static nanoindentation yielded average values H=0.22±0.06GPa and E=4.7±0.8GPa. Dynamic nanoindentation showed increasing H and E values when going from types II to V.
The static H and E values of Brazilian hair are consistent with the high Brazilian ethnical mixture. Nanoscratch failure mechanisms can be explained based on the dynamic H and E values. The scratch resistance in the direction from root to tip is associated to the cuticle mechanical properties, but in the opposite direction increased mechanical property values lead to increased damage. The surface friction behavior is determined by roughness of the fibers, however, when the tip goes into the cortex friction decreases due to its softer nature.
•Brazilian hair is an uncommon hair category that is still scarcely studied.•Its mechanical property values are approximately half way between those of Caucasian and African hairs.•The friction effect of the Brazilian hair may be determined by surface topography and roughness.
The fabrication of chemically and mechanically stable monolayers on the surfaces of various inorganic hard materials is crucial to the development of biomedical/electronic devices. In this Article, ...monolayers based on the reactivity of silane, phosphonate, 1-alkene, and 1-alkyne moieties were obtained on the hydroxyl-terminated chromium nitride surface. Their chemical stability and tribology were systematically investigated. The chemical stability of the modified CrN surfaces was tested in aqueous media at 60 °C at pH 3, 7, and 11 and monitored by static water contact angle measurements, X-ray photoelectron spectroscopy (XPS), ellipsometry, and Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS). The tribological properties of the resulting organic monolayers with different end groups (fluorinated or nonfluorinated) were studied using atomic force microscopy (AFM). It was found that the fluorinated monolayers exhibit a dramatic reduction of adhesion and friction force as well as excellent wear resistance compared to those of nonfluorinated coatings and bare CrN substrates. The combination of remarkable chemical stability and superior tribological properties makes these fluorinated monolayers promising candidates for the development of robust high-performance devices.
PDF
