Fabrication and Reliability of ConductiveAFMProbes

Understanding Current Instabilities in Conductive Atomic Force Microscopy

“…However, the kinetics of this degradation process are not presented, i.e., the differences between the 1st and 20th current scans are compared, but the way in which the current signal decays is not analyzed. Furthermore, the degradation process during lateral scans (analyzed in Reference [4]) may not be the same as the one taking place during spectroscopic I-V curves (this work). On one hand, it is expected that lateral scans consume the bulk of the tips faster due to high lateral frictions [4], and they also attach more impurities at the apex collected during the scan, while these phenomena may be minimized in spectroscopic I-V curves.…”

“…Furthermore, the degradation process during lateral scans (analyzed in Reference [4]) may not be the same as the one taking place during spectroscopic I-V curves (this work). On one hand, it is expected that lateral scans consume the bulk of the tips faster due to high lateral frictions [4], and they also attach more impurities at the apex collected during the scan, while these phenomena may be minimized in spectroscopic I-V curves. On the other hand, long sequences of spectroscopic I-V curves may produce faster metallic varnish melting due to the prolonged circulation of high currents [8].…”

“…By comparing Figure 2b and Figure 2c, it can be concluded that the PFTUNA CAFM tip has been degraded. In Reference [4], a complete study regarding the degradation of different CAFM tips has been presented, and it was concluded that the conductivity of the tips could be degraded by metallic varnish melting, by tip apex removal, and by the adhesion of particles. However, the kinetics of this degradation process are not presented, i.e., the differences between the 1st and 20th current scans are compared, but the way in which the current signal decays is not analyzed.…”

“…CAFM uses an ultra-sharp and conductive tip, which is typically made of Si and coated with a thin (<20 nm) metallic layer, located at the end of a cantilever that is put in contact with the sample under test. The radius at the apex ( R TIP ) of metal-coated Si tips ranges from 2 nm to 50 nm, and it allows collecting the currents flowing across single locations of the sample, whose effective areas (namely A eff ) can range between 1 nm 2 and 800 nm 2 [2,4]. One of the main advantages of CAFM is that it allows collecting topographic and current information about the samples simultaneously and independently.…”

“…Despite the tremendous advantages of CAFM in terms of lateral resolution and topography-current correlation, its use still presents a major problem that is still not fully understood: the large current variations observed during the experiments, not only during a single study, but also from one CAFM report to another. The two main sources of current variability are: (i) the degradation of the metallic coating of the CAFM tips [4]. This problem might be minimized (up to a certain degree) by using stable CAFM tips (e.g., solid metallic tips [5]).…”