Nanomechanical analysis of materials using photothermal off-resonance actuation

J.D. Adams, H. Gunstheimer, G. Fläschner, B. Hoogenboom
Nanosurf AG,
Switzerland

Keywords: atomic force microscopy, nanomechanics, photothermal actuation, off-resonance techniques, biomaterials

Summary:

Multifunctional imaging, in which additional sample characteristics such as sample stiffness or adhesiveness may be obtained alongside topographic information, is a general trend in Atomic Force Microscopy (AFM). However, most existing methods for obtaining reliable mechanical characteristics of the sample are rather slow in operation or in accessible frequency range, limiting their use in creating spatial maps of mechanical characteristics or in probing higher-frequency sample characteristics. A primary source of this speed limit is the piezo scanner used to modulate the tip-sample distance during measurement. In contrast, direct cantilever actuation methods, such as photothermal actuation, provide the benefit of moving a much smaller mass. The resulting higher actuation bandwidths of photothermal actuation compared with piezo scanner-based motion enable new approaches for using the AFM in nanomechanical characterization. In this work, we will present an overview of new developments and methods for nanomechanical sample characterization using photothermal cantilever actuation at off-resonance frequencies. Although off-resonance imaging techniques have gained popularity in recent years due to their robustness, simplicity, and the ability to simultaneously characterize sample mechanical properties, they have been limited in their speed of operation. Photothermal actuation provides an avenue towards overcoming this limit. We will present applications towards rapid spatial characterization of sample mechanical properties as well as measurement of frequency-dependent sample characteristics of soft materials such as mammalian cells over a frequency range of up to tens of kilohertz. Such technology enables researchers to measure both fast molecular processes, as well as slow, more global dynamics of cells, and potentially unlock new insights into the cellular-level workings of living systems.