• Tribology and Lubricants
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• 제18권4호
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• pp.267-272
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• 2002

Nano adhesion between SPM(scanning probe microscope) tips and DDPO$_4$(octadecylphosphoric acid ester.) and ODPO$_4$(octadecylphosphoric acid ester) SAM(self-assembled monolayer.) was experimentally studied. Tests were performed to measure the nano adhesion and friction in both AFM(atomic force microscope) and LFM(lateral force microscope) modes with the applied normal load. DDPO$_4$ and ODPO$_4$ SAM were formed on Ti and TiOx surfaces. Ti and TiOx were coated on the Si wafer by ion sputtering. Adhesion and friction of DDPO$_4$ and ODPO$_4$ SAM surfaces were compared with those of OTS(octadecyltrichlorosilane) SAM and DLC surfaces. DDPO$_4$ and ODPO$_4$ SAM converted the Ti and TiOx surfaces to be hydrophobic. When the surface was hydrophobic, the adhesion and friction forces were found lower than those of bare surfaces. Work of adhesion was also discussed to explain how the surface was converted into hydrophobic Results also showed that tribological characteristics of DDPO$_4$ and ODPO$_4$ SAM had good properties in the adhesion, friction, wetting angle and work of adhesion. DDPO$_4$ and ODPO$_4$ SAM could be one of the candidates for the bio-MEMS elements.

• KSTLE International Journal
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• 제6권2호
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• pp.33-38
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• 2005

Submicron-scale patterns made of polymethyl methacrylate (PMMA) were fabricated on silicon-wafer using a capillarity-directed soft lithographic technique. Polyurethane acrylate (PUA) stamps (Master molds) were used to fabricate the patterns. Patterns with three different aspect ratios were fabricated by varying the holding time. The patterns fabricated were the negative replica of the master mold. The patterns so obtained were investigated for their adhesion and friction properties at nano-scale using AFM. Friction tests were conducted in the range of 0-80 nN. Glass (Borosilicate) balls of diameter 1.25 mm mounted on cantilever (Contact Mode type NPS) were used as tips. Further, micro-friction tests were performed using a ball-on-flat type micro-tribe tester, under reciprocating motion, using a soda lime ball (1 mm diameter) under a normal load of 3,000 mN. All experiments were conducted at ambient temperature ($24{\pm}1^{\circ}C$) and relative humidity ($45{\pm}5\%$). Results showed that the patterned samples exhibited superior tribological properties when compared to the silicon wafer and non-patterned sample (PMMA thin film) both at the nano and micro-scales, owing to their increased hydrophobicity and reduced real area of contact. In the case of patterns it was observed that their morphology (shape factor and size factor) was decisive in defining the real area of contact.

• Tribology and Lubricants
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• 제39권3호
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• pp.111-117
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• 2023

This paper presents an experimental investigation of the tribological characteristics of PTFE composites filled with nano CuO particles under low sliding speed and load. All the specimens were prepared by sintering. Before sintering, the mixture of PTFE powder and CuO particles were mixed by a high-speed mixer using CuO volume fractions of 0.2 vol. % and 5 vol. %. Each mixture was sintered at 350 ℃ for 30 min on the steel disk. We conducted ball-on-disk sliding test an hour using a steel ball against PTFE composites, including pure PTFE. The load and sliding speed used was 2 N and 0.01 m/s, respectively. Adding nano CuO particles increases the friction coefficient because of the abrasiveness of hard nano CuO particles. The highest coefficient of frictions was obtained from 5 vol. % CuO. Conversely, the lowest wear of the composites was obtained from the 5 vol. % CuO nanocomposite. This study reveals that the addition of nano CuO particles can lower the wear of PTFE, despite an increase in the coefficient of friction. However, the coefficient friction is still moderate compared to other engineering polymers. In addition, the amount of CuO nano particles has to be optimized to reduce friction and wear at the same time.

• Tribology and Lubricants
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• 제15권1호
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• pp.52-58
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• 1999

Nano-indentation and nano-scratch tests were peformed to assess the mechanical and tribological properties of the coating on a commercially available thin-film magnetic recording disk. Surface topography and roughness of the disk was studied using atomic force microscopy. The hardness and elastic modulus data show a peak at an indentation depth equivalent to the thickness of carbon overcoat, indicating strong influence of the coatin $g_strate interaction and the coating surface roughness on the measurements. The variations of surface roughness data were analysed statistically based on the normal probability distribution theories and Weibull cumulative probability theories.es.

• KSTLE International Journal
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• 제9권1_2호
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• pp.10-12
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• 2008

Silicon micro-patterns were fabricated on Si (100) wafers using photolithography and DRIE (Deep Reactive Ion Etching) fabrication techniques. The patterned shapes included micro-pillars and micro-channels. After the fabrication of the patterns, the patterned surfaces were chemically modified by coating Z-DOL (perfluoropolyether, PFPE) thin films. The surfaces were then evaluated for their micro-friction behavior in comparison with those of bare Si (100) flat, Z-DOL coated Si (100) flat and uncoated Si patterns. Experimental results showed that the chemically treated (Z-DOL coated) patterned surfaces exhibited the lowest values of coefficient of friction when compared to the rest of the test materials. The results indicate that a combination of both the topographical and chemical modification is very effective in reducing the friction property. Combined surface treatments such as these could be useful for tribological applications in miniaturized devices such as Micro/Nano-Electro-Mechanical-Systems (MEMS/NEMS).

• Tribology and Lubricants
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• 제17권4호
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• pp.276-282
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• 2001

Nano adhesion between SPM (scanning probe microscope) tips and 075 (octadecyltrichlorosilane) SAM (self-assembled monolayer) was experimentally studied. Tests were performed to measure the nano adhesion and friction in both AFM(atomic force microscope) and LFM(lateral force microscope) modes in various conditions of relative humidity. OTS SAM was formed on Si-wafer (100) surfaces, and Si$_3$N$_4$ tips of different radius of curvature were used. When the surface was hydrophobic, the adhesion and friction forces were found lower than those of bare Si-wafer. Results also showed that micro-adhesion force increased as the relative humidity and the tip radius of curvature increased. The main parameter for affecting the micro-adhesion was found absorbed humidity on the contact surface. These results were discussed with the JKR model and a capillary force caused by absorbed water.

• Tribology and Lubricants
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• 제24권5호
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• pp.264-268
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• 2008

A large number of additives have been used with the efforts of improving the performance of lubricants used along with the development of internal combustion engine. In this study, nano-sized graphite was used as liquid-lubricant additive. In order to disperse graphite into oil, we esterified the nano-carbon manufactured by our company with various types of alcohol. After measuring the anti-wear in accordance with the types of alcohol and added concentration, it has been found that its anti-wear/friction decrease has been improved in case of adding 0.1% of the sample composed with C12/14 mixed alcohol & hexadecanol.

• Tribology and Lubricants
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• 제20권5호
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• pp.237-244
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• 2004

Micro/nano tribological characteristics of PTFE coating films were experimentally studied. PTFE (polytetrafluoroethylene) modified polyethylene and low molecular weight PTFE were used as a coating materials. These films were deposited on Si-wafer (100) by IBAD (ion beam assisted deposition) method. The Ar ion beam sputtering was performed to change the surface topography of films using a hollow cathode ion gun under different Ar ion dose conditions in a vacuum chamber. Micro/nano tribological characteristics, water wetting angles and roughness were measured with a micro tribotester, SPM (scanning probe microscope), contact anglemeter and profilometer, respectively. The durability of the films were measured with macro tribotester. Results showed that the PTFE coating surfaces were converted to hydrophobic. The water contact angle of coated surfaces and surface roughness increased with the coating thickness. Adhesion and friction in micro and nano scale were governed by magnitude of normal load in soft material such as PTFE films. As the increase of sputtering time on low molecular weight PTFE films, the surface roughness was increased and nano adhesion and friction were decreased. The nano tribological characteristics of surfaces are mainly improved by chemical modification such as PTFE coating and given a synergy effect by the physical modification such as topographic modification.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.11-12
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• 2002

Tribology research is constantly changing focus as new drivers for the research emerge. They include new industrial needs and barriers to performance, new possibilities brought about by new observation and modeling tools, and new people with different backgrounds. We outline the changes in basic academic tribology research over the past 15-20 years, as it is reflected in the research portfolio of the US National Science Foundation. While independent tribology programs may be a thing of the past there is a clear tendency for tribology research to continue as part of other activites, such as nano- and biotechnology and computational materials research.

• KSTLE International Journal
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• 제7권1호
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• pp.5-9
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• 2006

The main principle of two widely used methods which were proposed by Ruan and Bhushan, and by Ogletree and Carpick are introduced. Experiments were conducted using the two methods to measure friction force between AFM probe and silicon sample quantitatively. To characterize the frictional properties, the conversion factors of the two methods by which lateral electronic signal is converted into actual friction force were calculated. The experimental results show that that the conversion factors were extraordinarily different from each other. Further research should be done to identity the reasons for these differences.