Understanding Current Instabilities in Conductive Atomic Force Microscopy

Abstract

Conductive atomic force microscopy (CAFM) is one of the most powerful techniques in studying the electrical properties of various materials at the nanoscale. However, understanding current fluctuations within one study (due to degradation of the probe tips) and from one study to another (due to the use of probe tips with different characteristics), are still two major problems that may drive CAFM researchers to extract wrong conclusions. In this manuscript, these two issues are statistically analyzed by collecting experimental CAFM data and processing them using two different computational models. Our study indicates that: (i) before their complete degradation, CAFM tips show a stable state with degraded conductance, which is difficult to detect and it requires CAFM tip conductivity characterization before and after the CAFM experiments; and (ii) CAFM tips with low spring constants may unavoidably lead to the presence of a ~1.2 nm thick water film at the tip/sample junction, even if the maximum contact force allowed by the setup is applied. These two phenomena can easily drive CAFM users to overestimate the properties of the samples under test (e.g., oxide thickness). Our study can help researchers to better understand the current shifts that were observed during their CAFM experiments, as well as which probe tip to use and how it degrades. Ultimately, this work may contribute to enhancing the reliability of CAFM investigations.

Interfacial Synthesis of Layer-Oriented 2D Conjugated Metal–Organic Framework Films toward Directional Charge Transport

“…Again, this technique was chosen to prevent short currents from being measured. Voltages of 1, 2, 3, and 4 V were applied to the tip, and the resulting local current in the contact area of ∼100 nm 2 (ref ) was recorded simultaneously with the film topography (Figure S20). To estimate an upper value for the conductivity, only the highest positions within a scan were evaluated.…”

Microscopic Characterization of Poly(Sulfur Nitride)

“…The TUNA Current image (Figure 6b) is also showing a remarkably similar behavior (more bright contrast along the fiber direction). Since several factors influence the conductivity such as tip size and geometry, surface roughness, applied force between tip and sample, and formation of a thin water layer on the sample, [ 34 ] it is difficult to draw simple conclusions from these measurements. A more detailed estimation is therefore done by measuring I – V curves at different spots of the crystal.…”

Insights into dynamic sliding contacts from conductive atomic force microscopy

“…7,[16][17][18][19] However, some of these studies showed that, for very small contacts ($50 nm or less), the expected current-contact area relationship does not always hold true. 16,17,20,21 One explanation for this lack of correlation is that trace contamination of the contact can inhibit conduction 22 such that the magnitude of the electrical current does not reect the size of the contact. 16,20 Certain environmental conditions (e.g.…”

“…16,17,20,21 One explanation for this lack of correlation is that trace contamination of the contact can inhibit conduction 22 such that the magnitude of the electrical current does not reect the size of the contact. 16,20 Certain environmental conditions (e.g. ambient conditions in which a water meniscus can form in the contact) can also break the correlation between current and contact area for nanoscale contacts.…”