One-dimensional silicon nanoribbons (SiNRs) have the potential applying to future electronics devices because its compatibility with current silicon-based electronics devices and the theoretical outstanding electronic properties such as size-dependent band gap. Here, with the deposition of Si on Ag(111) surface, we have grown SiNRs. We investigate SiNRs on Ag(111) with a combination of scanning tunneling microscopy(STM), atomic force microscopy(AFM) and density functional theory (DFT) calculations. We obtained the atomic resolution STM and AFM images, which reveal that SiNRs have the same width and align along the equivalent orientations of Ag(111). The main body of SiNRs was found symmetric about the long axes of ribbons, but the terminals of SiNRs break the symmetry. The observations indicate that SiNRs are stable under room temperature. In order to determine the detailed atomic structure of SiNRs, based on the STM and AFM observations, we performed the DFT calculations. The calculation results reveal the buckled single-layer structure of SiNRs, which agrees well with the experimental results.
Understanding the function of real materials in heterogeneous system, such as magnetic domain and metallographic structure, has been a outstanding issue in materials science. Thus the development of a consistent and fast analysis method that consider the defects, roughness, crystal sizes, etc. is utmost important. Here we are developing a machine learning-based formula that can treats the microscopic morphology and describes the macroscopic properties based on the energy of the system. One interesting application is to describe the coercivity based on the structure and micromagnetic properties. The Landau free energy theory is very hard to be implemented in complex applications due to the pinning de-pinning process of the domain walls. Thus, the development of pseudo free energy that considers the metallography structure is necessary to describe the physics in inhomogeneous polycrystalline systems.
There are a lot of electron-beam based techniques in surface analysis, and each of them has its own characteristics, but they also have, at least, one characteristics in common, the information about the target sample is obtained through the analysis of identified signal data. These techniques generally are inefficient for quantitative purpose because only the signal data contribute to the conclusions, while other detected data, the overwhelming majority of measured data, have been completely disregarded as undesirable background data. Therefore, there is a need for a universal method that could extract meaningful information from background data. In this talk, we proposed a data-driven analysis method to extract meaningful information from the background signal and to propose an important breakthrough for the next generation surface analysis. The unique feature of this method is to use the combinations of a large number of spectral groups measured by intentionally changing a plurality of experimental conditions, to describe the background data, instead of interpreting individual spectrum in terms of physically meaningful parameters.
We present a study on the adsorption of corrosion inhibitors, anti-wear additives and friction modifiers from a synthetic and a mineral base oil on metal (Fe2O3) surfaces. In order to obtain quantitative and spatial data during the adsorption process we set up a combined quartz crystal microbalance (QCM-D) and confocal scanning laser microscope (CLSM). In addition to QCM-D and CLSM, also a UHV-tribometer was used to study the performance of gas phase deposited additives films without environmental interferences. In combination with macroscopic performance tests using a “ball-on-three-plates-tribometer” and corrosion tests, the adsorption, the morphology and the mechanical properties of the additives were correlated with their performance.
Friction is one of the most familiar physical phenomena to us. The behavior of friction has been studied since ancient times. Recently new experimental techniques, such as vacuum technology, friction force microscopy (FFM), and surface force measurement devices, enable us the stydy of atomic scale friction and have been ushering in a new era in friction research. Some researchers have been trying to explain macro-scale friction from such microscopic phenomena. The largest scale frictional phenomenon on Earth is earthquakes. However, the research on the connection between micro- and macro-friction has not been sufficiently successful yet. In this talk, I would like to introduce the physics behind friction phenomena from the nanoscale to the macroscale, as well as various applications.
Superlubricity, where the friction vanishes or significantly small, is of great interest in friction and it has been realized at the nanoscale in the piconewtons, but not yet at the macroscale. We demonstrate the macroscopic superlubricity is realized using a superlubric pillar array. The superlubricity of piconewtons appearing at a single silicon nanopillar is a novel type, which is quite different from the structural superlubricity studied so far and enables the macroscopic superlubricity. The conditions at which the macroscopic superlubricity appears are summarized using the friction coefficient and the viscous friction coefficient. This work clarifies the factor that controls fiction at the macroscopic scale.
Molecular mechanisms of lubrication have been studied by high resolution atomic force microscopy (AFM). We will report on two different material system, which exhibit fascinating lubrication properties at the nanometer scale. Graphene is the two-dimensional building block of graphite, a well-known solid lubricant. We will report how friction and the molecular structure of a liquid lubricant oil change at the steel interface due to the presence of graphene. Ionic liquids are promising materials for lubrication, given their viscosity, low vapor pressure, and electric conductivity. When confined to the nanometer-scale gaps, the structure of ionic liquids becomes ordered in molecular layers. Normal forces oscillate when closing the gap between the confining surfaces. We introduce magnetically actuated dynamic shear force microscopy as a method to measure the shear viscosity of confined ionic liquids.
The Stribeck curve is a fundamental concept to characterize the shear behavior in the entire range of lubrication, including hydrodynamic, mixed, and boundary lubrication regime. This concept covers both rheological and tribological aspects, and is widely used to grasp the shear behavior of many practical systems. However, the Stribeck curve has at least two quantitative problems: (i) baseless assumption that the effect of increasing sliding velocity on lubricant film thickness (and resulting friction force) is quantitatively equivalent to that of decreasing load; and (ii) the viscosity of lubricant is regarded as constant, which is incorrect. The surface forces apparatus (SFA) is very suitable to approach this issue; the SFA enables the direct measurement of film thickness using optical technique simultaneously with friction measurements, and boundary lubrication is quantitatively described using effective viscosity. According to this approach, bulk rheological properties and thin film tribological properties have been quantitatively connected, which leads to the updated Stribeck curve for smooth surfaces.