Sensitivity-enhanced atomic force acoustic microscopy with concentrated-mass cantilevers

Abstract

Atomic force acoustic microscopy (AFAM) provides nanometre resolution images reflecting sample elasticity and a possible technique for measuring the elastic modulus of thin films and extremely narrow areas. In AFAM, the resonant frequency of a micro-cantilever equipped with a sensor tip measures the contact stiffness between tip and sample. In the case of stiff samples like metals and ceramics, AFAM exhibits significantly low sensitivity, i.e., the resonant frequency is insensitive to the contact stiffness. The proposed concentrated-mass (CM) cantilever offers a smart solution to the problem without trade-offs. The present study discusses schemes for imaging elastic heterogeneity and evaluating elastic modulus in the case of CM cantilevers. The present experiment employed a flat tip with a metallic coating, namely a Ti/Pt thin film. The adhesive strength and ductility of the coating resulted in a prolonged lifetime. Images of a Ti sheet sample acquired with so-called slope detection clearly revealed nano-grains and slip bands, which would be unachievable by topographic images. The flat tip ensures a constant contact area, rendering contact stiffness independent of the magnitude of the contact force and tip–sample adhesion force, and significantly simplifying evaluation of the elastic modulus.

Measuring the Size Dependence of Young's Modulus Using Force Modulation Atomic Force Microscopy

“…Therefore, much research has been ongoing in instrument development, careful calibration, and models. [49][50][51][52][53] In AFM measurements of Young's modulus, a modulation signal is introduced to the sample while the cantilever's response is monitored by recording the responsive amplitude and phase. 14,44 The spectrum of responsive amplitude versus driving frequency can also be acquired.…”

Atomic force microscopy cantilever simulation by finite element methods for quantitative atomic force acoustic microscopy measurements

“…21,22 Hitherto was a constant contact area assumed but it has been proven that it changes during each AFAM measurement. 16 Similar results were reported by Passeri et al 23 by supposing that for normal loads higher than a critical value the cantilever tip acts as a flat punch indenting a plain surface.…”

Acoustic Scanning Probe Microscopy: An Overview

“…In this case, higher flexural modes can be used. Alternatively, a smart solution to such a limitation consists in using concentrated mass cantilevers that are obtained by depositing a particle of hundreds of nanograms on the cantilever backside in proximity to the tip [50].…”

“…Moreover, the mechanical properties of the coatings are generally unknown, thus undermining the reliability of the measurements unless they are contextually characterized in the A-SPM experiment as described below. Finally, a strategy going in the opposite direction and applicable when high lateral resolution is not needed consists in intentionally flattening standard tips or tips coated with materials that easily undergo plastic deformations, which increases the stability during measurements as the relatively wide contact area ensures low stress at the tip-sample interface [50,90].…”