Multifrequency Atomic Force Microscopy: Compositional Imaging with Electrostatic Force Measurements

Abstract

We demonstrate that single-pass Kelvin force microscopy (KFM) and dC/dz measurements in different environments expand the compositional imaging with atomic force microscopy. The KFM and dC/dz studies were performed in the intermittent contact mode with force gradient detection of tip-sample electrostatic interactions. Both factors contribute to sensitive measurements of the surface potential and capacitance gradient with nanometer-scale spatial resolution as it was verified on a broad range of materials: metal alloys, polymers, organic layers, and liquid-like objects. For many samples the surface potential and dC/dz variations complement each other in identification of individual components of heterogeneous materials. In situ imaging in different humidity or vapors of various organic solvents further facilitate recognition of the constituents of multicomponent polymer samples due to selective swelling of components.

Single-pass Kelvin force microscopy and dC/dZ measurements in the intermittent contact: applications to polymer materials

“…A true spatial resolution of KFM is often determined as a width of a transition region between locations of different surface potential [ 4 , 12 ]. In a separate paper [ 16 ], we reported the measurements of the potential profile change at the steps of F 14 H 20 self-assemblies on a Si substrate. When the Pt-coated probe was applied the step width was around 20–30 nm – a dimension that is similar to the tip's apex diameter.…”

Sub-surface imaging of carbon nanotube–polymer composites using dynamic AFM methods

“…In this technique, the amplitude of the cantilever oscillation at the second harmonic of electrical excitation yields information regarding the capacitance gradient of the sample (∂C/∂d), which can be related to the local film thickness and dielectric constant. Meanwhile, the phase of the cantilever oscillation at the second harmonic of electrical excitation provides information on dielectric losses in the sample [18,21]. These techniques can be used either in the single-pass mode or in the two-pass mode.…”

Resonant multi-frequency method for Kelvin probe force microscopy in air

“…Generally speaking, for various imaging methods, the way in which the tip interacts with the sample is different, so they do not necessarily measure the same thing. It is known that in multi-frequency AFM [2] the image from the first eigenmode usually reflects the topography while the second one is more sensitive to long-range forces [6] or the sample composition [1,26]. For MF-KPFM and the conventional lift mode KPFM, the employed eigenmodes are different, so it is possible that they reflect or are affected by different tip-sample interactions.…”

“…the CPD, which is just what one intends to measure using KPFM. As demonstrated by Magonov and Alexander, KPFM in different environments can expand the compositional imaging of AFM, which is attributed to the sensitive measurements of surface potential [26]. On the other hand, interference or cross-talk might exist and possibly be different for the two methods, so the tip-sample interaction is not the same and the images might be affected by different aspects of the sample.…”

“…In general, the multi-frequency method can give a good measurement. Besides the multi-frequency EFM [6] and the MF-KPFM, for example, the high-resolution phase image of a multi-frequency AFM is demonstrated to be sensitive to sample composition [1,26], and multi-frequency magnetic force microscopy is capable of separating short-and longrange forces with high spatial resolution [6]. By resonant excitation at high eigenmodes of a cantilever probe, the sensitivity can be improved compared to the non-resonant method, which is commonly used in ambient EFM or KPFM.…”