Surface Review and Letters

Tribological issues between friction pair are fundamental problems for minimized devices because of their higher surface-to-volume ratio. Micro/nanotexturing is an effective technique to reduce actual contact area between contact pair at the nanoscale. Micro/nanotexture made a great impact on the frictional behavior of textured surfaces. This paper summarizes the recent advancements in the field of frictional behavior of micro/nanotextured surfaces, which are based on solid surface contact in atmosphere environment, especially focusing on the factors influencing the frictional behavior: Surface property, texturing density, texturing height, texturing structure and size of contact pair (atomic force microscope (AFM) tip) and texturing structures. Summarizing the effects of these factors on the frictional behavior is helpful for the understanding and designing of the surfaces in sliding micro/nanoelectromechanical systems (MEMS/NEMS). Controlling and reducing the friction force in moving mechanical systems is very important for the performance and reliability of nanosystems, which contribute to a sustainable future.

We have investigated the field evaporation of grounded arsenic (As) doped silicon (Si) clusters composed of 52 atoms with density functional theory (DFT) to mimic Si nano structures of hundreds of nanometers long standing on a substrate. Six cluster structures with different As doping concentrations and dopant locations are studied. The critical evaporation electric fields are found to be lower for clusters with higher doping concentrations and doping sites closer to the surface. We attribute the difference to the difference in binding energies corresponding to the different As-doping concentrations and to the doping locations. Our theoretical study could shed light on the stability of nano apexes under high electric field.

LaTiO₃ films were prepared at room temperature, 60, 140 and 220°C using a thermal vapor deposition technique with an electronic beam gun to investigate the relationship between deposition temperatures and the optical properties of the samples. In the ellipsometric analysis, the corresponding refractive indexes were 1.8993, 1.9123, 1.9197 and 1.9283 at a wavelength of 1064 nm. At the same time, extremely low absorption characteristics of all the samples presented in the visible and IR regions. With the same high-energy testing laser of 200 mJ (about 40 J/cm²) at a wavelength of 1064 nm and a pulse width of 10 ns, the laser-induced damage threshold (LIDT) of the LaTiO₃ samples prepared at different temperatures were 15.5, 16.7, 18.5 and 18.2 J/cm², respectively. This shows that a higher LIDT may be obtained at higher deposition temperatures.

The structural, electronic and magnetic properties of monolayer WS₂ doped with single Mn atom, MnX₃ and MnX₆ clusters (X = N, O and F) are investigated using first principles approach. Monolayer WS₂ doped with single Mn atom displays a spin gapless semiconducting character. WS₂ embedded with MnX₃ and MnX₆ presents rich electronic and magnetic properties. For example, monolayer WS₂ incorporated with MnF₃ exhibits a half-metallic nature. The substitutions of impurities introduce magnetism except MnN₃. The calculation results demonstrate that monolayer WS₂ is a promising material for spintronic device when doped with MnX_m.

In this paper, composite carbon nanotubes (C-CNTs); single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs) are synthesized using an ultrasonic nebulizer in a large quartz tube for photovoltaic device fabrication in poly-3-octyl-thiophene (P3OT)/n-Si heterojunction solar cells. We found that the device fabricated with C-CNTs shows much better photovoltaic performance than that of a device without C-CNTs. The device with C-CNTs shows open-circuit voltage (V_oc) of 0.454 V, a short circuit current density (J_sc) of 12.792 mA/cm², fill factor (FF) of 0.361 and power conversion efficiency of 2.098 %. Here, we proposed that SWCNTs and MWCNTs provide efficient percolation paths for both electron and hole transportation to opposite electrodes and leading to the suppression of charge carrier recombination, thereby increasing the photovoltaic device performance.

The crystallization of calcium carbonate (CaCO₃) in soil controlled by natural organic material was considered a very important reason to enhance the property of ancient Chinese organic Sanhetu (COS), but how the organic material affected the crystallization of CaCO₃ in COS is still unclear. In this paper, a natural organic material (sticky rice, SR) and a synthetic organic material (anionic polyacrylamide, APAM) were selected as additives to investigate their effect on the crystallization of CaCO₃. The experimental results showed that the morphology and size of CaCO₃ crystals could be affected by the concentration of additives and reaction time, while only the size of CaCO₃ crystals could be affected by the concentration of reactant. Although the morphology and size of CaCO₃ crystals varied greatly with the variation of additive concentration, reactant concentration and reaction time, the polymorph of CaCO₃ crystals were always calcite, according to SEM/EDX, XRD and FTIR analyses. This study may help us to better understand the mechanism of the influence of organic materials on CaCO₃ crystallization and properties of COS.

This study investigates the effects of sliding ratio on the tribological response of the contact between the teeth of a metal/polymer gear in the regions close to the pitch point. For this purpose, a new twin-disc test rig was developed on the basis of two discs of different diameters rotating one above the other at the same angular speed. Two different materials were used: non-alloyed structural steel (C45) and polyamide (PA66). The effect of the slip ratio (4%, 12%, 20% and 28%) was studied at a constant pressure of 34 MPa and a constant angular speed of 300 rpm. In addition, the contact conditions were controlled with measurements of the two discs surface temperatures. The results indicate that the wear and the friction are closely related to the contact temperature generated by the sliding phenomenon. At low slip ratio (4% and 12%), the coefficient of friction and the temperature are characterized by a quasi-linear increase with time, and the wear increases slowly. At higher slip ratio (20% and 28%), the coefficient of friction and the temperature presents a steady state, and the wear increases dramatically. During the test, a film of transferred PA66 is formed on the steel surface causing the development of adhesive interactions between the contacting discs which increase the friction coefficient and the contact temperature. The high thermal conductivity of steel as compared to that of the polymer can reduce enormously the contact temperature generated by the sliding process.

The reliability and performance of precision mechanical components that experience sliding under contact depend heavily on the friction and wear characteristics at the sliding interface. In order to improve the reliability of the sliding interface, there is a need to predict, measure and monitor any physical interactions at the head–disk interface (HDI). In the present work, the basic tribological characteristics of HDI were analyzed. The HDI during start–stop and constant speed operation using acoustic emission (AE) were studied. The Fast Fourier Transform (FFT) analysis of the AE signal was used to understand the interaction between the AE signal and the state of contact. In addition, we developed laser textured (LT) disk and the contact start–stop (CSS) tests were performed to investigate the effect of dimples on the stiction performance of the HDI. Furthermore, numerical analysis between the slider and disk surface pressure were performed using the boundary coordinate system and divergence formulation for the nonlinear Reynold's equation solution.

Different electroless Ni–P coatings were deposited on open-cell aluminum foams at various bath pH. The effect of bath pH on the morphology, structure, components, phases and corrosion resistance of the Ni–P coating was studied by scanning electron microscopy (SEM), confocal laser scanning microscope (CLSM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), immersion test and electrochemical polarization measurement, respectively. The experimental results show that the bath pH not only changed the reactivity of the bath, but also had a influence on the microstructure and anticorrosive property of electroless Ni–P coating. The high pH bath raises the thickness of Ni–P coating but decreases the content of phosphorus element in the Ni–P coating. The corrosion resistance of the coated aluminum foams increases when the bath pH rises.

The capillary pressure is one of the crucial parameters in many science and engineering applications such as composite materials, interface science, chemical engineering, oil exploration, etc. The drop/bubble formation and its mechanisms that affect the permeability of porous media have steadily attracted much attention in the past. When a drop/bubble moves from a larger capillary to a smaller one, it is often obstructed by an additional pressure difference caused by the capillary force. In this paper, a comprehensive model is derived for the capillary pressure difference when a drop/bubble flows through a constricted capillary, i.e. a geometrically constricted passage with an abrupt change in radius. The proposed model is expressed as a function of the smaller capillary radius, pore-throat ratio, contact angle, surface tension and length of the drop/bubble in the smaller capillary. The model predictions are compared with the available experimental data, and good agreement is found between them.

Using density functional theory calculations with van der Waals corrections, we have investigated the stability and electronic properties of monolayer hexagonal boron nitride (hBN) on the Ni(111) surface. We have found that hBN can bind either strongly (chemisorption) or weakly to the substrate with metallic or insulating properties, respectively. While the more stable configuration is the chemisorbed structure, many weakly bound (physisorbed) states can be realized via growth around an hBN nucleus trapped in an off-registry position. This finding provides an explanation for seemingly contradictory sets of reports on the configuration of hBN on Ni(111).

Surface contamination usually occurs during welding processing and it affects the welds quality largely. However, the formation of such contaminants has seldom been studied. Effort was made to study the contaminants caused by metal inert gas (MIG) welding and tungsten inert gas (TIG) welding processes of aluminum alloy, respectively. SEM, FTIR and XPS analysis was carried out to investigate the microstructure as well as surface chemistry. These contaminants were found to be mainly consisting of Al₂O₃, MgO, carbide and chromium complexes. The difference of contaminants between MIG and TIG welds was further examined. In addition, method to minimize these contaminants was proposed.