Temperature dependence of nanoscale friction investigated with thermal AFM probes
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1226-II05-02
Temperature dependence of nanoscale friction investigated with thermal AFM probes Christian Greiner1, Jonathan R. Felts2, Zhenting Dai2, William P. King2, and Robert W. Carpick1 1
University of Pennsylvania, Department for Mechanical Engineering and Applied Mechanics, 112 Towne Building, 220 South 33rd St., Philadelphia, PA 19104, USA 2
University of Illinois at Urbana-Champaign, Department of Mechanical Science and Engineering, 242 Mechanical Engineering Building, 1206 W. Green St, Urbana, IL 61801, USA To whom correspondence should be addressed: [email protected]
ABSTRACT 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.
INTRODUCTION The temperature dependence of friction is of increasing interest as it affects energy dissipation, wear, and reliability in a multitude of systems, yet a scientific understanding is lacking (1-6). The motivation to address this problem with atomic force microscopy (AFM) is found in the complex nature of friction processes. When macroscopic objects slide against each other, the contact is not continuous but composted of many asperities. With the extremely sharp tip of an AFM, it is possible to study one of these asperities individually (7, 8). With only one asperity in contact, such experiments allow for more definitive analysis of the basic physical principles and processes governing friction. As only little is known about the temperature dependence of friction, performing tests at different temperatures is of significant scientific interest. For example, to determine the activation energies of dissipation processes in friction, measurements at different temperatures are necessary. Most studies published in this field so far (1, 2, 4, 9, 10), were performed by changing the temperature of the substrate and in ultra high vacuum (UHV), or by changing the temperature of the entire experimental chamber (11). In this contribution, the temperature dependence of single asperity friction was investigated by means of heated AFM cantilevers, thus introducing a new approach to changing the temperature in
nanotribology measurements. A
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