Friction traced to the single atom

Abstract

Friction is caused by dissipative lateral forces that act between macroscopic objects. An improved understanding of friction is therefore expected from measurements of dissipative lateral forces acting between individual atoms. Here we establish atomic resolution of both conservative and dissipative forces by lateral force microscopy, presenting the resolution of atomic defects. The interaction between a single-tip atom that is oscillated parallel to an Si (111)

Bidirectional quantitative force gradient microscopy

“…Rotation of the force sensor by 90°leads to the pendulum or shear force configuration. Giessibl et al used this geometry to perform lateral force gradient and friction measurements at the atomic scale [15]. MFM based on the pendulum geometry is sensitive to lateral force derivatives of magnetostatic interactions [16,17].…”

“…Equation (15) leads to a relation between the x-component and the z-component of the field gradient:…”

Probing the shape of atoms in real space

“…Monitoring the dissipative component allows one to assess if tip and sample atoms are deflected strongly from their equilibrium positions. 19 The STM images are recorded in the topographic mode, where the average tunneling current ͑averaged over a time of approximately 30 oscillation cycles͒ is kept constant by adjusting the z position of the tip accordingly. For an exponentially decaying tunneling current I(z)ϭI 0 exp(Ϫ2 z), the average tunneling current I av is smaller than the peak tunneling current I pk with I av /I pk Ϸ(2 A) Ϫ0.5 .…”

“…The damping signal did not show significant variations within the adatom image, which proves that a hysteretic lateral jump of the adatom or the tip atom, which possibly could have explained the sharp atomic peaks, did not occur. 19 In theory, fluctuations of the cantilevers amplitude could explain modulations in topography. However, the oscillation amplitude was kept constant by an amplitude control circuit and monitored, ruling out amplitude fluctuations as a source of the measured atom shapes.…”

Stability considerations and implementation of cantilevers allowing dynamic force microscopy with optimal resolution: the qPlus sensor

“…• to allow lateral force detection [25]. (3) Quartz, the material of the tuning forks is far superior to silicon with respect to frequency stability.…”