Understanding the Atomic-Scale Contrast in Kelvin Probe Force Microscopy

Abstract

A numerical analysis of the origin of the atomic-scale contrast in Kelvin probe force microscopy is presented. Atomistic simulations of the tip-sample interaction force field have been combined with a noncontact atomic force microscope simulator including a Kelvin module. The implementation mimics recent experimental results on the (001) surface of a bulk alkali halide crystal for which simultaneous atomic-scale topographical and contact potential difference contrasts were reported. The local contact potential difference does reflect the periodicity of the ionic crystal, but not the magnitude of its Madelung surface potential. The imaging mechanism relies on the induced polarization of the ions at the tip-surface interface owing to the modulation of the applied bias voltage. Our findings are in excellent agreement with previous theoretical expectations and experimental observations.

Chemical Resolution at Ionic Crystal Surfaces Using Dynamic Atomic Force Microscopy with Metallic Tips

“…[4] for details) broadly agree with the results of previous studies on extended steps at metal surfaces (0:16 À 1 D=step atom [11,12]) and increase with decreasing the coordination of surface atoms [13]. We note that this fundamental property of metal surfaces is difficult to describe within continuum approximations to the tip polarization [14], and remained unaccounted for in some recent models of Kelvin probe microscopy [15].…”

Measuring Electric Field Induced Subpicometer Displacement of Step Edge Ions

“…Unambiguous agreement between experimental results and multiscale theoretical calculations demonstrates that the electrostatic field moves step atoms by subpicometers in different directions. It has been proven how in conventional KPFM the measured signal can be explained with a simple model, where the energy of the system comes mostly from the capacitive quadratic term in V [45] and the contribution from the ion-field coupling gives minor corrections [59]. With this work, both experimentally and theoretically, we show that the torsional mode is insensitive to the capacitor and the measured signal contains only information of the ion-field coupling, demonstrating how the lateral frequency shift is extremely sensitive to subpicometer changes in the ionic positions.…”

Investigating atomic contrast in atomic force microscopy and Kelvin probe force microscopy on ionic systems using functionalized tips

“…Using the force-voltage spectroscopy mode for Kelvin probe force microscopy (KPFM), charge states of single atoms [5], defects [6], and molecules [7] were determined, and submolecular resolution was obtained [8][9][10]. The atomic contrast observed with KPFM [11][12][13][14][15] triggered efforts to explain the underlying contrast mechanism theoretically [16][17][18][19][20]. The most important open questions are: What are the physical properties mapped by AFM and KPFM on the atomic scale, and how can we take advantage of this information?…”