• Tribology and Lubricants
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• v.28 no.2
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• pp.62-69
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• 2012

Atomic force microscopy (AFM) has been widely utilized as a versatile tool not only for imaging surfaces but also for understanding nano-scale interfacial phenomena. By measuring the responses of the photo detector due to bending and torsion of the cantilever, which are caused by the interactions between the probe and the sample surface, various interfacial phenomena and properties can be explored. One of the challenges faced by AFM researchers originates in the physics of measuring the small forces that act between the probe of a force sensing cantilever and the sample. To understand the interactions between the probe and the sample quantitatively, the force calibration is essential. In this work, the procedures used to calibrate AFM instrumentation for nano-scale force measurement in normal and lateral directions are reviewed.

• Advanced Composite Materials
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• v.17 no.2
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• pp.101-110
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• 2008

Metal nanohoneycomb structures were fabricated by E-beam evaporation and a two-step anodization process in phosphoric acid. Their tribological properties of adhesion and friction were investigated by AFM in relation to the pore size of the nanohoneycomb structures. Variations of the adhesive force are not found with pore size, but formation of the pore greatly reduces the adhesive force compared to the absence of pore structure. The coefficient of friction increased nonlinearly with pore size, due to surface undulation around the pore. Tribological properties do not differ greatly between the original nanohoneycomb structure and the metal nanohoneycomb structure.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.4
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• pp.369-374
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• 2009

In micro/nano-scale contacts in MEMS and NEMS, capillary and van der Waals forces generated around contacting micro-asperities significantly influence the performance of concerning device as they are closely related to adhesion and stiction of interacting surfaces. In this regard, it is of prime importance to accurately estimate the magnitude of surface forces so that an optimal solution for reducing friction and adhesion of micro/nano-surfaces may be obtained We introduced an effective method to calculate these surface forces based on topography information obtained from an atomic force microscope. This method was used to calculate surface forces generated in the contact interface formed between diamond-like carbon coating and $Si_3N_4$ ball. This method is shown to effectively demonstrate the influence of capillary force in the contact area, especially in humid atmosphere.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.167-168
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• 2002

In this study, the effects of oxide layer formed on the wear tracks of TiN coated silicon wafer on friction characteristics were investigated. Silicon wafer was used for the substrate of coated disk specimens, which were prepared by depositing TiN coating with $1\;{\mu}m$ in coating thickness. AISI 52100 steel balls were used for the counterpart. The tests were performed both in air for forming oxide layer on the wear track and in nitrogen to avoid oxidation. This paper reports characterization of the oxide layer effects on friction characteristics using X-ray diffraction (XRD). scanning electron microscopy (SEM) and friction force microscope (FFM).

• Ceramist
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• v.22 no.4
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• pp.381-392
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• 2019

Recently, demands for lithium-ion batteries (LIB) in various fields are increasing. In particular, understanding of the reaction mechanism occurring at the electrode-electrolyte surface/interface is significant for the development of advanced LIBs. Meanwhile, research and development of LIBs highly requires a new specific characterization approach. For example, atomic force microscopy (AFM) has been utilized to the LIB research field for various purposes such as investigation of topography, electrochemical reactions, ion transport phenomena, and measurement of surface potential at high resolution. Advances in the AFM analysis have made it possible to inspect various material properties such as surface friction and Young's modulus. Therefore, this technique is expected to be a powerful method in the LIB research field. Here, we review and discuss ways to apply AFM to LIB studies.

• The korean journal of orthodontics
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• v.49 no.1
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• pp.12-20
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• 2019

Objective: The aim of this study was to analyze the surface composition, roughness, and relative friction of metal clips from various ceramic self-ligating brackets. Methods: Six kinds of brackets were examined. The control group (mC) consisted of interactive metal self-ligating brackets while the experimental group (CC, EC, MA, QK, and WA) consisted of interactive ceramic self-ligating brackets. Atomic force microscopy-lateral force microscopy and scanning electron microscopy-energy-dispersive X-ray spectroscopy were used to analyze the surface of each bracket clip. Results: All the clips in the experimental groups were coated with rhodium except for the QK clip. The results showed that the QK clip had the lowest average roughness on the outer surface, followed by the MA, EC, WA, and CC clips. However, the CC clip had the lowest average roughness on the inner surface, followed by the QK, WA, MA, and EC clips. The QK clip also had the lowest relative friction on the outer surface, followed by the MA, EC, CC, and WA clips. Likewise, the CC clip had the lowest relative friction on the inner surface, followed by the QK, WA, MA, and EC clips. Conclusions: The surface roughness and relative friction of the rhodium-coated clips were generally higher than those of the uncoated clips.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.159-159
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• 2013

Atomically thin graphene is the ideal model system for studying nanoscale friction due to its intrinsic two-dimensional anisotropy. Furthermore, modulating its tribological properties could be an important milestone for graphene-based micro and nano-mechanical devices. Here, we report that the tribological properties can be easily altered via simple chemical modifications of the graphene surface. Friction force microscopy measurements show that hydrogenated, fluorinated, and oxidized graphenes exhibit, 2-, 6-, and 7-fold enhanced nanoscale friction on their surfaces, respectively, compared to pristine graphene. The measured nanoscale friction should be associated with the adhesive and elastic properties of the chemically modified graphenes. Density functional theory calculations suggest that, while the adhesive properties of chemically modified graphenes are marginally reduced down to ~30%, the out-of-plane elastic properties are drastically increased up to 800%. Based on these findings, we propose that nanoscale friction on graphene surfaces is characteristically different from that on conventional solid surfaces; stiffer graphene exhibits higher friction, whereas a stiffer three-dimensional solid generally exhibits lower friction. The unusual friction mechanics of graphene is attributed to the intrinsic mechanical anisotropy of graphene, which is inherently stiff in plane, but remarkably flexible out of plane. The out-of-plane flexibility can be modulated up to an order of magnitude by chemical treatmentof the graphene surface. The correlation between the measured nanoscale friction and the calculated out-of-plane flexibility suggests that the frictional energy in graphene is mainly dissipated through the out-of-plane vibrations, or the flexural phonons of graphene.

• Tribology and Lubricants
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• v.35 no.4
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• pp.199-205
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• 2019

Two-dimensional materials such as graphene, h-BN, and $MoS_2$ have attracted increased interest as solid lubricant and protective coating layer for nanoscale devices owing to their superior mechanical properties and low friction characteristics. In this work, the frictional properties of single-layer graphene, h-BN, and $MoS_2$ are experimentally investigated under various normal forces using atomic force microscope (AFM) tips with a spherical and flat end, with the aim to gain a better understanding of frictional behaviors. The nonlinear relationship between friction and normal force friction was clearly observed for single-layer graphene, h-BN, $MoS_2$ specimens slid against the spherical and flat AFM tips. The results also indicate that single-layer graphene, h-BN, $MoS_2$ exhibit low frictional properties (e.g., friction coefficient below 0.1 under 70~100 nN normal force). In particular, graphene is found to be superior to h-BN and $MoS_2$ in terms of frictional properties. However, the friction of single-layer graphene, h-BN, $MoS_2$ against the flat tip is larger than that against the spherical tip, which may be attributed to the relatively large adhesion. Furthermore, it is shown that the fluctuation of friction is more significant for the flat tip than the spherical tip. The resutls of this study may be helpful to elucidate the feasibility of using two-dimensional materials as solid lubricant and protective coating layer for nanoscale devices.

• Applied Science and Convergence Technology
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• v.23 no.5
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• pp.240-247
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• 2014

Modelling and measurements of normal and lateral stiffness for atomic force microscopy (AFM) are presented in this work. Important issues, such as element discretisation, stiffness calibration, and deflection angle are explored using the finite element (FE) model. Elements with various dimension ratios are investigated and comparisons with several mathematical models are reported to verify the accuracy of the model. Investigation of the deflection angle of a cantilever is also shown. Moreover, AFM force measurement experiments with conical and colloid probe tips are demonstrated. The relationships between force and displacement, required for stiffness measurement, in normal and lateral directions are acquired for the conical tip and the limitations of the colloid probe tip are highlighted.

• Tribology and Lubricants
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• v.37 no.5
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• pp.179-188
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• 2021

Reputed for their low friction coefficient and wear protection effect, diamond-like carbon (DLC) materials are considered amongst the most important lubricant coatings for tribological applications. In this framework, this investigation aims to elucidate the effect of a few operating parameters, such as applied stress and sliding amplitude on the friction lifetime of DLC coatings. Fretting wear tests are conducted using a 12.7 mm radius counterpart of 52100 steel balls slid against a substrate of the same material coated with a 2 ㎛ thickness DLC. Approximately, 5 to 57 N force is applied, generating a maximum Hertzian contact pressure of 430 to 662 MPa, corresponding to the applied force. The coefficient of friction (CoF) generates three regimes, first a running-in period regime, followed by a steady-state evolution regime, and finally a progressive increase of the CoF reaching the steel CoF value, as an indicator of reaching the substrate. To track the wear scenario, interrupted tests are performed with analysis combining scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), 3D profilometer and micro-Raman spectroscopy. The results show two endurance values: one characterizing the coating failure (Nc₁), and the other (Nc₂) indicating the friction failure which is situated where the CoF reaches a threshold value of μ_th = 0.3 in the third regime. The Archard energy density factor is used to determine the two endurance values (Nc₁, Nc₂). Based on this approach, a master curve is established delimitating both the coating and the friction endurances.