Nanofriction Mechanisms Derived from the Dependence of Friction on Load and Sliding Velocity from Air to UHV on Hydrophilic Silicon

Opitz, Andreas; Ahmed, S.I.-U.; Scherge, Matthias; Schaefer, J.A.

doi:10.1007/s11249-005-8550-1

Cited by 12 publications

(15 citation statements)

References 19 publications

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“…Bound-mobile lubrication couples the stability of a bound layer with the mobility of a liquid or liquid-like layer in order to provide both good frictional properties as well as good durability. [24][25][26][27][28][29][30] The frictional behavior of contacting surfaces containing functional groups that can form hydrogen bonds is complex and depends on a number of factors, including the length and flexibility of the chains that attach the hydrogen bond forming groups to the surface, 31,32 the surface coverage and separation of the chains, 19,23,33,34 temperature, 35 pH, 36 surface disorder, 19 sliding velocity, 20 etc. The frictional properties of self-assembled monolayers of alkanethiol molecules on gold surfaces containing COOH-terminal groups have been studied experimentally and compared to the properties of alkanethiol molecules containing CH 3 -terminal groups; at zero-load hydrogen bonds formed in the COOH-terminated monolayers results in friction forces ∼17 times higher than those for monolayers with CH 3 -terminal groups.…”

Section: Introductionmentioning

confidence: 99%

Examining the frictional forces between mixed hydrophobic – hydrophilic alkylsilane monolayers

Rivera

Jennings

McCabe

2012

The Journal of Chemical Physics

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Monolayers presenting methyl-terminated (hydrophobic) and hydroxyl-terminated (hydrophilic) surfaces on silica have been studied by molecular dynamics simulation and the effects of hydrogen bonding, chain length, and chain mixing on the frictional properties determined. The hydroxyl-terminated monolayers were found to show large adhesion zones as a result of strong interfacial interlayer hydrogen bonds; the interfacial sliding forces observed in the hydroxyl-terminated monolayers being one order of magnitude higher than the interfacial forces for the hydrophobic surfaces at the characteristic point of zero-load. Mixed hydroxyl- and methyl-terminated monolayers of equal length were found to exhibit intermediate shear stress values between those observed for pure monolayers, with the magnitude of the shear stress depending on the surface content of the hydroxyl-terminated chains. For mixed monolayers of unequal chain lengths, at high loads a maximum in the magnitude of the shear stress as a function of the length of the methyl-terminated chain was observed due to the creation of a buffer zone between the hydroxyl-terminated chains that produces strong hydrogen-bonding interactions. The effect of a constant normal load or constant separation simulation ensemble on the results has also been studied and in general found to have minimal influence on the observed behavior, although some differences are observed for the shear stress at intermediate normal loads due to the formation of stronger hydrogen bond networks at constant load compared to constant separation.

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Section: Introductionmentioning

confidence: 99%

Examining the frictional forces between mixed hydrophobic – hydrophilic alkylsilane monolayers

Rivera

Jennings

McCabe

2012

The Journal of Chemical Physics

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“…The accompanying grey bar shows the uncertainty of the measurement, which is smaller then the symbols in range (c). The used normal load is F L =60 nN by a scanning velocity v=300 nm/s and moving distance of s=300 nm[10].…”

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confidence: 99%

A comparative investigation of thickness measurements of ultra-thin water films by scanning probe techniques

Opitz

Scherge

Ahmed

et al. 2007

Journal of Applied Physics

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The reliable operation of micro- and nanomechanical devices necessitates a precise knowledge of the water film thickness present on the surfaces of these devices with accuracy in the nanometer range. In this work, the thickness of an ultra-thin water film was measured by distance tunneling spectroscopy and distance dynamic force spectroscopy during desorption in an ultra-high vacuum system, from about 2.5 nm up to complete desorption at 10-8 mbar. The tunneling current and the amplitude of vibration and the normal force were detected as a function of the probe-sample distance. In these experiments, a direct comparison of both methods was possible. It was determined that dynamic force spectroscopy provides the most accurate values. The previously reported tunneling spectroscopy, which requires the application of significantly high voltages generally leads to values that are 25 times higher than values determined by dynamic force spectroscopy

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“…The idea of a dominance of capillary forces at ambient pressures was also proposed by Opitz el al. (32,33) as well as other authors (34,35).…”

Section: Velocity Dependencementioning

confidence: 59%

Temperature Dependence of Nanoscale Friction Investigated with Thermal AFM Probes

et al. 2009

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Measurements of nanoscale friction between silicon AFM tips featuring an in-situ solid state heater and silicon substrates (both with native oxide) were performed. The temperature of the heater was varied between room temperature and approximately 650 °C. For these temperatures and the silicon substrate, the temperatures at the point of contact are estimated to range from room temperature to approximately 120±20 °C. Experiments were carried out in ambient atmosphere (˜30% relative humidity) and under dry nitrogen. Tests under constant load revealed that in the presence of ambient, friction increased with heater temperature whereas it did not change in dry nitrogen. For experiments carried out for different tip velocities (40 to 7800 nm/s), friction decreased with velocity in ambient and did not change in dry nitrogen. Both trends can be explained by thermally-assisted formation of capillary bridges between tip and substrate and the kinetics of capillary condensation under ambient conditions.

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Nanofriction Mechanisms Derived from the Dependence of Friction on Load and Sliding Velocity from Air to UHV on Hydrophilic Silicon

Cited by 12 publications

References 19 publications

Examining the frictional forces between mixed hydrophobic – hydrophilic alkylsilane monolayers

Examining the frictional forces between mixed hydrophobic – hydrophilic alkylsilane monolayers

A comparative investigation of thickness measurements of ultra-thin water films by scanning probe techniques

Temperature Dependence of Nanoscale Friction Investigated with Thermal AFM Probes

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