Practical Method to Limit Tip–Sample Contact Stress and Prevent Wear in Amplitude Modulation Atomic Force Microscopy

Abstract

Amplitude modulation atomic force microscopy (AM-AFM) is one of the most popular AFM modes because of the reduced tip-sample interaction, compared to contact mode AFM, and the ability to acquire high-resolution images while interrogating the sample's material composition through phase imaging. Despite the reduced tip-sample interaction, tip and sample wear can occur through gradual atomic scale processes that can significantly accumulate due to the high frequency of the tip-sample interaction and through high intermittent contact stresses. Starting from existing analytical formulations, we introduce a method for selecting an appropriate probe and free oscillation amplitude that avoids exceeding a critical contact stress to minimize tip/sample damage. The approach is presented for the case of both a Hertzian- and a Derjaguin-Müller-Toporov-like tip-sample contact. Stress maps and related simplified formulas are provided that enable one to determine allowable free oscillation amplitudes to stay below a target contact stress for given cantilever and sample parameters (combined into a single "cantilever-sample constant" that we introduce). Experimental results show how sharp silicon tips, either uncoated or coated with diamond-like carbon and silicon nitride, interacting with a hard and wear-resistant sample (ultrananocrystalline diamond) can be preserved while attaining high-quality AM-AFM images by using our proposed scheme. We also show that using our analysis to select parameters that exceed the target contact stress indeed leads to significant tip wear. This method provides AM-AFM users with a better understanding of contact stresses and enables selection of AM-AFM cantilevers and experimental parameters that preserve the tip for long periods of use and prevents the sample from damage.

High-speed AFM for 1x node metrology and inspection: Does it damage the features?

“…The results will be discussed in the next section. It was verified that our calculations gave the same results as reported in literature as a function of, amongst others, amplitude set-point, surface elasticity, and cantilever stiffness [6][7][8] Error! Reference source not found.Error!…”

“…Only somewhere between 10 8 and 10 9 taps damage will occur [6]. Especially on soft materials like biological material, the stress can be very high without ever causing damage [7].…”

Fast, quantitative and high resolution mapping of viscoelastic properties with bimodal AFM

“…Its value must be known in order to determine the nanomechanical properties of the sample with the bimodal AM-FM method. Several methods have been proposed to determine the tip radius, ranging from electron microscopy images 63 to the in situ characterization by AFM. 64 The first approach is time consuming and, more often than not, implies the irreversible damage of the tip, in particular for sharp tips.…”

Combining TEM, AFM, and Profilometry for Quantitative Topography Characterization Across All Scales

“…This was alleviated using the wear-mitigation strategies described in Ref. 60 . In subsequent testing, the values of free-air amplitude and amplitude ratio were kept in the range of 37 -49 nm and 0.15 -0.3, respectively.…”