FIM tips in SPM: Apex orientation and temperature considerations on atom transfer and diffusion

Abstract

Atoms transferred to W(111) and W(110) tip apices from the Au(111) surface during tunneling and approach to mechanical contact experiments in STM are characterized in FIM at room temperature and at 158 K. The different activation energies for diffusion on the (111) and (110) tip planes and the experiment temperature are shown to be important factors controlling the extent of changes to the atomic structure of the tip. W(111) tips are much better suited to scanning probe studies which require the characterization of an atomically defined tip and subsequent verification of its integrity in FIM. The statistics of the observed spikes in the tunneling current when the tips are approached to Au(111) are interpreted using a simple model of adatoms diffusing through the STM junction.

Transient adhesion and conductance phenomena in initial nanoscale mechanical contacts between dissimilar metals

“…The conductance and adhesion behavior is in good quantitative agreement between the two experiments with tips of similar radii, although the second experiment begins with an initially lower conductance and adhesion. It is difficult to say whether this deviation is statistically significantdefining an initial condition for the tips is hindered by the fact that their approach to tunneling proximity with the substrate allows for the transfer of material to the tip [9,20], though we have attempted to minimize this effect as described in the Experimental Methods section. Any discrepancies in the duration of tunneling or feedback conditions could result in a different initial condition of the tip apex, altered by material transfer.…”

“…One particularly intriguing feature about the transient behavior is that it takes a substantial number of mechanical contacts between the tip apex and gold surface to reach steady state. We hypothesize that it takes repeated indentations to reach equilibrium values conductance and adhesion because the transferred gold atoms rapidly diffuse away from the tip apex at room temperature [20]. After many indentations, however, a sufficient reservoir of gold may be established on the tip such that the behavior becomes repeatable.…”

“…This contact area makes up a small fraction of the tip hemisphere which has been cleaned by field evaporation. Our observations of transferred atoms from Au(111) surfaces to W(111) FIM tips at 298 K and 158 K show that activation energies for diffusion over the tip surface are low enough to permit complete rearrangement of the atoms over all visible regions of the tip (in FIM) at room temperature, but the diffusion is frozen out at 158 K [20]. This justifies our assumption that the transferred atoms can redistribute themselves by surface diffusion between indentations at room temperature.…”

Fabrication of nano ion–electron sources and nano-probes by local electron bombardment

“…This makes single atom tips (SATs) ideal for low energy electron microscopy that would enable the characterization of biological molecules or fragile nano structures with minimal risk. Nanotips with a well-defined shape of nano or atomic scales are also crucial for manipulating and characterizing molecules and nano objects in scanning probe microscope (SPM) [9][10][11][12][13][14][15][16][17][18][19]. Furthermore, in multi-probe SPM, multiple probes are needed to be brought in close vicinity to form physical contacts with nano objects [20,21].…”

Artificial-intelligence-driven scanning probe microscopy

“…Previous studies have aimed to improve imaging efficiency, e.g., by linking probe morphology and image quality, via analytical simulations 10 , inverse imaging of the probe through sample features [11][12][13] , or probe characterization/manipulation (field ion microscopy 14 ). These approaches can suppress the need for heuristic probe conditioning.…”