Recent advances in hybrid measurement methods based on atomic force microscopy and surface sensitive measurement techniques

Abstract

AFM was proposed in the 1990s as a tool to determine the topography at a sub-micrometer level. Since then AFM proved to be a valuable tool in material science and physical chemistry. Soon after successful application of AFM, it was employed for biological applications. The success of AFM can be ascribed to the high sensitivity, versatility, and resolution (1000 times higher resolution compared to optical microscopy). However, it intrinsically lacks amongst others chemical sensitivity. These limitations of AFM can be overcome by coupling it to orthogonal (complementary) optical (i.e. microscopy techniques) or non-optical techniques (i.e. Kelvin method). Such combinations are capable to garner information on morphological and mechanical properties of a sample together with fluorescence, spectroscopic (IR/Raman/fluorescence), electric, temperature or conductivity. Recently, advances in microscopy and super-resolution techniques enable the collection of even more than 2 measurands. Furthermore, new combinations, such as the photothermal-induced resonance (PTIR), a combination of IR spectroscopy and AFM, and scanning near-field ellipsometry microscopy (SNEM), a combination of ellipsometry and AFM, are actively researched, widening the adoptability of orthogonal combinations relying on AFM, while researchers devote tremendous effort to enhance established hybrid methods, such as tip-enhanced Raman spectroscopy (TERS). Here, we introduce hybrid measurement techniques, relying on AFM and complementary techniques. The main focus of these hybrid techniques is on the combination with optical techniques as there has been much progress in the past few years and we can contribute our expertise in this field. For each combination, the working principle is explained briefly and applications of such combinations are pointed out. Finally, a short comprehension is given with basic information on resolution and field of application of all major combinations. We envision that this review is helpful to those confronted with combined measurements for the first time, for experienced researchers, needing quick access to recent literature as it may convey new ideas for problems in analysis, as well as for researchers, who develop novel combined methods.