SKPFM

Scanning Kelvin Probe Force Microscopy (SKPFM)... 

Instrumentation. The experimental procedure for an AFM equipped with a suitably coated tip has been outlined above. In a study of an aluminum alloy AA2024-T3, intermetallic particles and the matrix phase could be separated clearly [98]. The different surface films on these phases could be associated with their corrosion behavior. Inclusions and their corrosive behavior have been studied with a combination of SKPFM and AFM [101]. The effect of chloride-containing solution on corrosion at the matrix and the intermetallic particles was studied with SKPFM, in addition, light scratching with the AFM in the contact mode was applied to study the effect of the mechanical destabilization [102]. The intermetallic particles dissolved immediately after the film on their surface had been destabilized by mechanical abrasion. 

Filiform corrosion on epoxy-coated 1045 carbon steel was investigated with SKPFM [111]. Under coatings of 150 and 300 nm thickness at 93% relative humidity, samples were studied under air. Separation of active anode and cathode locations in the head of the filament could be identified. Microscopic and even submicroscopic aspects of electrochemical delamination have been studied with SKPFM [99]. 

SKPFM Scanning Kelvin probe force microscopy... 

It is also possible to combine AFM with SKP to achieve the capability to map Volta potentials with submicron resolution [90, 120, 121]. The Scanning Kelvin Probe Force Microscope (SKPFM) operates by scanning the topography across a line and then, during a rescan of that line at a fixed distance from the surface. 

A particularly reproducible reference is a nickel surface exposed to deionized water before the measurement [87]. In the absence of further calibration, this is the point of reference. The method cannot be applied in the presence of an electrolyte solution because of the large voltages applied to the tip this would cause Faradaic reactions. Data from measurements of Volta potentials at corroding surfaces could be related to corrosion potentials of the same surface in contact with a solution because the linear correlation has been established before [88]. Nevertheless, studies at air or in the presence of ultrathin electrolyte films (i.e., under conditions frequently encountered in atmospheric corrosion) are possible. The general advantages of SKPFM, in particular the greatly enhanced spatial resolution, in comparison with SKP have been discussed in detail [88]. A critical review of applications of SKPFM focused on corrosion science with particular attention to possible artifacts and a comparison with SKP has been provided [89]. 

Defects at the interface most likely play an important role in the delamination process. Unfortunately, the defects in self-assembled films are mostly nanoscopic and can be studied only with atomic force microscopy (AFM) and STM, which require very time-consuming preparation and limit the flexibility of the experiments. Other operation modes such as scanning Kelvin probe force microscopy (SKPFM) [73] will play an important role in future work [74]. 

Left SKPFM image of AZ91D alloy. Right field emission gun scanning electron microscopy (FEG-SEM) image of the same area. The compositions and Volta potentials of points 1-4 are given in Table 7.5. 

Table 7.5 Compositions and Volta potentials measured by SKPFM (at 40% RH and at 20°C) at points 1-4 in Fig. 7.3.

Yasakau et a/. studied the mechanism of corrosion protection of aluminum alloy 2024-T3 by cerium and lanthanum inhibitors in chloride media using SKPFM,... 

Kelvin Probe Force Microscopy (KPFM or SKPFM) was derived from the development of the atomic force microscope (AFM) al-... 

Figure 5. Relation between the potential measured in air by SKPFM with open-circuit potentials measured in dionized water for different metals (same trend has been found in 0.5 M NaCl) assuming the surface potential of pure Ni as the reference - Reprinted with permission from J. Electrochem. Soc., 145 (1998) 2285 Copyright 1998, The Electrochemical Society.

Nevertheless, the introduction of SKPFM measurements reveals the need to estabhsh galvanic series for microstructures or elements of galvanic couples involved in localized corrosion at the micrometer scale. But the introduction of SKPFM data on numerical simulation seems to be not possible as a large doubt always exists. It justifies the interest to focus on in-situ local microelectro-chemical studies for investigating the cmrent-potential relation in an aqueous solution, i.e., the electrochemical kinetic at the scale of the microstructure. 

Davoodi, A., Pan, J., Leygraf, C., Norgren, S., The role of intermetallic particles in localized corrosion of an aluminum alloy studied by SKPFM and integrated AFM/SECM. J. Electrochem. Soc. 2008, 155, C211. 

Hochstrasser-Kurz, S., Reiss, D., Suter, T., Latkoczy, C., Gunther, D., Virtanen, S., Uggowitzer, P. J., Schmutz, P. ICP-MS, SKPFM, XPS, and microcapillary investigation of the local corrosion mechanisms of WC-Co hard metal. Journal of the Electrochemical Society 2008, 155, C415-C426. 

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