Localization of the phantom force induced by the tunneling current

Abstract

The phantom force is an apparently repulsive force, which can dominate the atomic contrast of an AFM image when a tunneling current is present. We described this effect with a simple resistive model, in which the tunneling current causes a voltage drop at the sample area underneath the probe tip. Because tunneling is a highly local process, the areal current density is quite high, which leads to an appreciable local voltage drop that in turn changes the electrostatic attraction between tip and sample. However, Si(111)-7×7 has a metallic surface state and it might be proposed that electrons should instead propagate along the surface state, as through a thin metal film on a semiconducting surface, before propagating into the bulk. In this paper, we first measure the phantom force on a sample that displays a metallic surface state [here, Si(111)-7×7] using tips with various radii. If the metallic surface state would lead to a constant electrostatic potential on the surface, we would expect a direct dependence of the phantom force with tip radius. In a second set of experiments, we study H/Si(100), a surface that does not have a metallic surface state. We conclude that a metallic surface state does not suppress the phantom force, but that the local resistance R s has a strong effect on the magnitude of the phantom force.

The effect of sample resistivity on Kelvin probe force microscopy

“…Ohmic resistive drops have been used to explain energy shifts in tunneling spectroscopy 14 and there is increasing evidence that they can be dominated by local effects near the tip-sample junction. 3,15 While our initial explanation described the voltage drop only within the sample, this voltage drop can also occur in the tip, as demonstrated in Ref. 15.…”

“…We have recently reported upon a Phantom force that can dominate AFM images, in which attractive surface features can appear relatively repulsive. 2,3 In this letter, we describe the effect of the Phantom force upon KPFM.…”

Atomic species recognition on oxide surfaces using low temperature scanning probe microscopy

“…Consequently, KPFM or STM experiments can be performed simultaneously to completely separate the potential or electrical density information from the topography. [37][38][39]…”

Frequency shift, damping, and tunneling current coupling with quartz tuning forks in noncontact atomic force microscopy

“…A.Weymouth et al evoked a repulsive phantom force on samples with limited conductivity such as semi-conductors (SC) 25,29 . A year after, T.Wutscher et al extended the frame of that model and proved that a metallic surface state did not prevent the phantom force from occurring 30 . This result went along with the work by M.Baykara et al on the conductive oxidized Cu(100) surface, where a strong topography-feedbackinduced coupling on ∆f upon constant-current imaging was reported 31 .…”

“…Although refs. [26,30] yet pointed out the electronic coupling was weak, a new design of probe was proposed wherein I t is collected by means of a thin insulated wire glued at the QTF prong's end 26,29,[32][33][34] . This design was a valuable technical solution to lower the coupling and became a commercial standard, as well known as the qPlus sensor.…”