Effect of Noise on Determining Ultrathin-Film Parameters from QCM-D Data with the Viscoelastic Model

Abstract

Quartz crystal microbalance with dissipation monitoring (QCMD) is a well-established technique for studying soft films. It can provide gravimetric as well as nongravimetric information about a film, such as its thickness and mechanical properties. The interpretation of sets of overtone-normalized frequency shifts, Δf/n, and overtone-normalized shifts in half-bandwidth, ΔΓ/n, provided by QCMD relies on a model that, in general, contains five independent parameters that are needed to describe film thickness and frequency-dependent viscoelastic properties. Here, we examine how noise inherent in experimental data affects the determination of these parameters. There are certain conditions where noise prevents the reliable determination of film thickness and the loss tangent. On the other hand, we show that there are conditions where it is possible to determine all five parameters. We relate these conditions to the mathematical properties of the model in terms of simple conceptual diagrams that can help users understand the model’s behavior. Finally, we present new open source software for QCMD data analysis written in Python, PyQTM.

Modeling Nonlinear Dynamics of Functionalization Layers: Enhancing Gas Sensor Sensitivity for Piezoelectrically Driven Microcantilever

“…The first resonance mode offers a prominent response spectrum, easing fit with the measured response, despite the findings that it produces insufficient energy trapping, 81 with irregularities and erratic behavior in prominence. 82 By tuning the values of G′ and G″, the theoretical response curve can be shifted and the profile adjusted (refer to Figure 5) for the resonances as defined from the BVD impedance response spectrum 83 in both curves to coincide in shape and position. Series resonance is used because its value is related to the mechanical properties of the resonator, thereby providing information on the coating of the QCM.…”

“…The measured impedance response was used to estimate G f , in a custom MATLAB script by plotting the measured impedance response curves for the first resonance mode alongside the theoretically calculated ones. The first resonance mode offers a prominent response spectrum, easing fit with the measured response, despite the findings that it produces insufficient energy trapping, with irregularities and erratic behavior in prominence . By tuning the values of G′ and G″ , the theoretical response curve can be shifted and the profile adjusted (refer to Figure ) for the resonances as defined from the BVD impedance response spectrum in both curves to coincide in shape and position.…”

Influence of titanium nanoscale surface roughness on fibrinogen and albumin protein adsorption kinetics and platelet responses

“…Evaluation of protein adsorption on nanostructured titanium-coated QCM sensors was conducted using a QSense ® Analyzer E4 Auto QCM-D system (Biolin Scientific, Sweden), and data were analyzed with both QSense ® Dfind software (v. 1.2.1) (Biolin Scientific AB, Sweden) 30 and a free software package, QTM (Diethelm Johannsmann, TU Clausthal, Germany), 31 to determine the adsorbed protein layer thickness, mass density, and viscoelastic properties. A description of the QTM software is found in the Supplementary Materials.…”

“…30 Due to the dissipative nature of the surface-adsorbed proteins tested in this study, viscoelastic modeling was chosen as the approach to analyze the QCM-D data. Measurements of the shifts in frequency (Δf ) and dissipation (ΔD) acquired during the QCM-D experiments were fitted with Dfind 36 and QTM software 31 to a viscoelastic model utilizing small load approximation approaches to determine the values of adsorbed protein layer thickness, mass density, and viscoelastic properties. 20,23,25 This approach utilizes multiple harmonics of the quartz crystal sensor resonance frequency, considering the frequency shifts of the resonator and the energy dissipated by the adsorption of soft matter on the sensor surface.…”

Stiffness of Contacts between Adsorbed Particles and the Surface of a QCM‐D Inferred from the Adsorption Kinetics and a Frequency‐Domain Lattice Boltzmann Simulation

“…For planar layers with a thickness much below the wavelength of sound (a few nanometers for soft adsorbates), the viscoelastic parameters of the layer (such as the shear modulus G = G ʹ + i G ʹʹ or the shear compliance, J = 1/ G = J ʹ – i J ʹʹ) can be derived from the set of parameters {Δ f / n , ΔΓ/ n }, even including an estimate of their dependence on frequency. [ 20 ] No such analytical models exist for structured samples. These require a numerical simulation, which predicts Δ f / n and ΔΓ/ n from the geometry and the viscoelastic parameters in the different domains.…”