Novel method for measuring nanofriction by atomic force microscope

Abstract

The authors describe a novel approach to the measurement of nanofriction, and demonstrate the application of the method by measurement of the coefficient of friction for diamondlike carbon ͑DLC͒ on DLC, Si on DLC, and Si on Si surfaces. The technique employs an atomic force microscope in a mode in which the tip moves only in the z ͑vertical͒ direction and the sample surface is sloped. As the tip moves vertically on the sloped surface, lateral tip slipping occurs, allowing the cantilever vertical deflection and the frictional ͑lateral͒ force to be monitored as a function of tip vertical deflection. The advantage of the approach is that cantilever calibration to obtain its spring constants is not necessary. Using this method, the authors have measured friction coefficients, for load range 0 Ͻ L Ͻ 6 N, of 0.047Ϯ 0.002 for Si on Si, 0.0173Ϯ 0.0009 for Si on DLC, and 0.0080Ϯ 0.0005 for DLC on DLC. For load range 9 Ͻ L Ͻ 13 N, the DLC on DLC coefficient of friction increased to 0.051Ϯ 0.003.

A compact torsional reference device for easy, accurate and traceable AFM piconewton calibration

“…Most of the force-distance curves recorded exhibit different kinds of artefacts including jumps in the contact region of the curve (most likely due to pick-up of low-frequency mechanical noise given that the device has a mechanical resonance at 20 Hz), hysteresis, differences between the trace and retrace slopes, and nonlinearity of the top part of the retrace, all of which have been linked to friction in cantilever-on-cantilever measurements [38], as well as intervals showing different slopes inside the same contact region which suggest changes in the friction coefficient as the tip slides along the surface. The most common are the friction-related artefacts which are associated with deviations of the trace and retrace slopes from the frictionless slope [39,40,38]. The amount of hysteresis and difference between the slopes varies strongly between measurements suggesting that the friction coefficient has large local variations.…”

Comportamento mecânico dos tribofilmes formados pela aditivação de MoDTC e ZDDP em motores a etanol.

“…Neste cenário, a Figura 3-11 exemplifica uma caracterização de uma superfície contendo tribofilme de MoDTC via AFM, no modo de força lateral. Este modo de operação é capaz de mapear uma superfície quanto à tendência de torção do cantiléver, gerando uma imagem (posições dadas por uma matriz x-y) com contraste em relação a este estímulo mecânico (armazenado como variável z), que pode ser a posteriori correlacionado com a força de atrito (SALVADORI et al, 2008). Nesta imagem, as regiões escuras tendem a "torcer" o cantiléver com magnitude mais reduzida, sendo, portanto, atribuídas a regiões com propriedades de baixo atrito.…”