Abstract
This article focuses on the atomic force microscopy-infrared (AFM-IR) technique and its recent technological developments. Based on the detection of the photothermal sample expansion signal, AFM-IR combines the high spatial resolution of atomic force microscopy with the chemical identification capability of infrared spectroscopy to achieve submicrometric physico-chemical analyses. Since the first publication in 2005, technological improvements have dramatically advanced the capabilities of AFM-IR in terms of spatial and spectral resolution, sensitivity, and fields of applications. The goal of this paper is to provide an overview of these developments and ongoing limitations. We summarize recent progress in AFM-IR implementations based on the major AFM contact, tapping, and peak force tapping modes. Additionally, three new trends are presented, namely, AFM-IR applied to mineral samples, in fluid and a novel, purely surface sensitive AFM-IR configuration, to probe top layers. These trends demonstrate the immense potential of the technique and offer a good insight into the scope of AFM-IR.
Highlights
atomic force microscopy-infrared (AFM-IR) is an Atomic Force Microscopy (AFM) based technique that combines the high spatial resolution of AFM with the chemical identification capability of infrared (IR) spectroscopy
There exist over 250 systems across the world forming a large nano-infrared spectroscopy community, i.e., user base, of at least 2000 people, according to an estimate by Bruker. This community produces about 70% of the publications involving nano-infrared spectroscopy analysis with 65 papers in 2020, which covers a huge diversity of applications as shown by several review papers already published on the AFM-IR technique.[1,2,3,4,5,6,7,8,9]
The principal AFM imaging modes, namely, the contact, tapping, and peak force tapping modes have been implemented in AFM-IR leading to a versatile laboratory tool
Summary
AFM-IR is an Atomic Force Microscopy (AFM) based technique that combines the high spatial resolution of AFM with the chemical identification capability of infrared (IR) spectroscopy. The spatial resolution of such a setup is limited by the diameter of the visible laser spot.[12] The idea of AFM-IR is not to detect the induced photothermal heat but to detect the thermal expansion with an AFM tip, using the high sensitivity of the AFM system to vertical height changes of the sample (tens of picometers) and its excellent lateral resolution (10–20 nm) This first implementation at CLIO was not. Scitation.org/journal/jap a marketable tabletop system as the infrared source was a freeelectron laser but the concept to use the photothermal effect to realize a local absorption measurement with a resolution that goes far beyond the diffraction limit was demonstrated These first results have been the beginning of a constant technical development to increase the performance of this technology.
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