Optimization of phase contrast in bimodal amplitude modulation AFM

Abstract

SummaryBimodal force microscopy has expanded the capabilities of atomic force microscopy (AFM) by providing high spatial resolution images, compositional contrast and quantitative mapping of material properties without compromising the data acquisition speed. In the first bimodal AFM configuration, an amplitude feedback loop keeps constant the amplitude of the first mode while the observables of the second mode have not feedback restrictions (bimodal AM). Here we study the conditions to enhance the compositional contrast in bimodal AM while imaging heterogeneous materials. The contrast has a maximum by decreasing the amplitude of the second mode. We demonstrate that the roles of the excited modes are asymmetric. The operational range of bimodal AM is maximized when the second mode is free to follow changes in the force. We also study the contrast in trimodal AFM by analyzing the kinetic energy ratios. The phase contrast improves by decreasing the energy of second mode relative to those of the first and third modes.

Opportunities and Challenges for Biosensors and Nanoscale Analytical Tools for Pandemics: COVID-19

“…299,300 Several multifrequency AFM methods have been proposed, however due to their complex physical principle, theoretical development and mechanism of interpretation of data are under more investigation. 299,301 The previous studies of coronaviruses using AFM techniques 302−305 show the significant potential of AFM to image, visualize, and explore the morphological features of the SARS-CoV virus; see Figure 13…”

“…Then, based on the adhesion and mechanical strength of bonds formed between functionalized tip and receptors of the samples, the biological properties can be explored during imaging. , The main challenge of FD-based AFM is the high volume and time of data acquisition . To increase the speed of imaging and reduce the amount of collected data during measurement, high-speed AFM and multifrequency methods are invented. , Several multifrequency AFM methods have been proposed, however due to their complex physical principle, theoretical development and mechanism of interpretation of data are under more investigation. , The previous studies of coronaviruses using AFM techniques − show the significant potential of AFM to image, visualize, and explore the morphological features of the SARS-CoV virus; see Figure as a typical AFM characterization. Generally, visualization/characterization devices are useful as they provide following information: (1) quantify the surface and subsurface properties of the affected cell by COVID-19 in real time; (2) detect multiple dynamic interactions between SARS-CoV2 virus and host cell; and (3) study the mechanism of SARS-CoV2 virus to cross the cellular membrane and deliver its genome inside the host cells and (4) its replication inside cell and characterization of the nucleic acids of SARS-CoV2 virus, to understand how it is condensed and packaged inside capsids.…”

Quantitative analysis of sideband coupling in photoinduced force microscopy

“…The principle of multifrequency AFM is based on the notion that multiple frequency channels can be used simultaneously, opening up the possibility to examine different tip-sample interactions at the same time 2 . By detecting the amplitude and phase of multiple eigenmodes, the experiment can be optimized to detect, for instance, local variations in the contact difference potential [3][4][5] along with local mechanical measurements of material stiffness and damping 6,7 . Another example is photo-induced force microscopy (PiFM), which uses one cantilever eigenmode for registering sample topography and a second mechanical eigenmode for detecting photoinduced forces in the tip-sample junction [8][9][10][11][12][13][14][15][16] .…”

Bulk chemical composition contrast from attractive forces in AFM force spectroscopy

“…Again, these requirements cannot be met by most samples or most AFM setups. However, the principle idea that local attractive forces F attr are specific for the local chemical composition and structure (as shown before by ncAFM [ 15 , 29 ] and NF-DAFM [ 30 ]) can also be utilized for force spectroscopy under ambient conditions.…”