Mapping Contact Potential Differences with Noncontact Atomic Force Microscope Using Resonance Frequency Shift versus Sample Bias Voltage Curves

Abstract

We have measured cantilever resonance frequency versus sample bias voltage and generated frequency vs bias ( f–V) curves using an ultrahigh-vacuum noncontact atomic force microscope (UHV NC-AFM). Using the f–V data, we calculated the contact potential difference (CPD) between the tip and the sample. These CPD measurements were compared with those that were directly observed with a scanning Kelvin probe force microscope (SKPM) on the same atomically resolved area of the sample using a UHV-AFM. The CPD values obtained by both methods were similar, however, it was difficult to obtain CPD values that agreed precisely on the atomic scale.

Atomic-scale electric capacitive change detected with a charge amplifier installed in a non-contact atomic force microscope

“…To synthesize the time-varying input signal, caused by scanning over the areas with different V CPD , we used the values of V CPD in literature for Si(111)-7 × 7. 6,[20][21][22][23][24] A typical result is shown in Fig. 4 for the values reported by Kitamura et al; 6) the local V CPD was approximately −0.13 V on Si adatoms and approximately −0.09 V on the other regions.…”

“…6,[20][21][22][23][24] A typical result is shown in Fig. 4 for the values reported by Kitamura et al; 6) the local V CPD was approximately −0.13 V on Si adatoms and approximately −0.09 V on the other regions. 6) Here the difference between the two values of local V CPD is significant for the CA when the tip scans across the regions, though the absolute values of local V CPD often change owing to the change in the local work function of the tip apex.…”

“…In KPFM, the tip and sample are modeled as a capacitor, taking into account their CPD. KPFM measurements have been performed on metals, semiconductors, oxides, ionic crystals, and atoms or molecules adsorbed on solid substrates, [6][7][8][9][10][11][12] and the local electric dipoles and charge transfers have been investigated.…”

Measuring and Tuning the Potential Landscape of Electrostatically Defined Quantum Dots in Graphene

“…At each location, after disabling the tip height feedback, we tuned V s until the electrostatic force on the tip was minimized,that is, until the applied voltage exactly compensated for the LCPD. The force minimum was determined by recording the bias-dependent frequency shift of the tip and performing a parabolic fit to the resulting curve as shown in Figure c. ,− This fitting procedure was repeated at many points across the surface to achieve at least 14 nm resolution. In general, the surface potential U ( r ) is offset from the measured LCPD by a constant value determined by the work function of the tip, which is unknown and geometry dependent.…”