Quartz Crystal Microbalance Resonance Research Articles

Evidence for the Existence of a “Liquid-Like Layer” between a Metal Electrode and a Frozen Aqueous Electrolyte

The quartz-crystal microbalance (QCM) was used to study premelting at the ice/gold and the frozen electrolyte/gold interfaces. It was shown that in a certain range of temperature, below the melting point, (i) the resonance of the QCM is readily detectable (at temperatures lower than this temperature range the QCM did not show any resonance), (ii) the parameters of the resonance depend on temperature, and (iii) the shape of the resonance is very different from that observed for the QCM in contact with liquids. The observed phenomena were ascribed to the existence of a liquid-like layer (LLL) between ice or frozen electrolyte and the gold surface. It was shown that for the frozen electrolyte/gold interface the parameters of the QCM resonance depend on potential. The latter, in turn, shows that the properties of the LLL could be controlled by the electrochemical potential of the metal/electrolyte interface.

Steady state and transient QCM solutions at the metal ∣ solution interface

The quartz crystal microbalance (QCM) is seeing a rapid increase in new applications and new instrumentation techniques. It is increasingly evident that this sensor provides not only mass data, but can provide information relative to the mechanical properties of deposited films as well. Determining film properties from the measured electrical properties of the QCM resonator requires a modeling of the effects of the film on the electrical behavior of the resonator. We show that the complete electro-mechanical model can provide descriptions of the effects of film properties on resonator behavior in a number of formats to include not only the standard steady-state behavior, but also the transient responses used in a recent new measurement technique. The use of a single model for all techniques will permit comparisons among the results.

Characterization Of SnO2 Nanoparticles Deposited Via Layer-by-Layer Self Assembly And Investigation Of Their Sensing Properties

ABSTRACTA technique of Layer-by-Layer (LbL) self-assembly is used to deposit SnO2 nanoparticles on Quartz Crystal Microbalance (QCM) resonators, and on glass substrates which the authors believe has not been previously reported. Characterization of self-assembled SnO2 layers has been performed using QCM, Scanning Electron Microscopy (SEM), and Zeta Potential analysis.We have successfully deposited SnO2 nanoparticles on QCM resonator using self-assembly technique. LbL self-assembly is a method of organization of ultra-thin films by interlayer electrostatic attraction. The thickness and mass of the self-assembled layers can be characterized by the frequency shift obtained using the QCM and empirical equations relating change in frequency with mass and thickness of deposited layers. The deposition of SnO2 nanolayers exhibited a linear reproducibility and the process of self-assembly was independent of the residence time of QCM resonator in the SnO2 nanoparticle colloidal solution. High resolution SEM analysis reveals that the SnO2 nanoparticle layers are uniformly deposited across the entire substrate. Electrical characterization was performed on SnO2 nanoparticle layers self-assembled on glass substrates which were patterned for two point (current-voltage) IV characteristic measurements. Two classes of samples were used. One sample was self-assembled glass substrate patterned with electrical contacts and calcined (baked at 350°C for one hour) to eliminate interlayered polyions and the other sample was not calcined. Results revealed that the calcined samples demonstrated linear ohmic behavior but the uncalcined showed some spurious points which we believe are due to the polyion layers.Characterization of the self-assembled SnO2 nanoparticles is being carried out with the intention of fabricating a high-selectivity μ-gas sensor. A test chamber has been fabricated and results of resistance behavior of the sensor with variation in temperature have been presented.The sensor can find applications in high selectivity sensing of chemical, industrial, domestic, and hazardous environments. After further research and development, this μ-gas sensors could be made generic to sense a variety of gases and employed for integrated on-chip product analysis in multiple chemical microsystem applications.

Multistep Adsorption of Perfluoropolyether Hard-Disk Lubricants onto Amorphous Carbon Substrates from Solution

We have used a quartz crystal microbalance (QCM) to study the solution-phase adsorption of the perfluoropolyether lubricants Fomblin ZDOL and Demnum SA from perfluorohexane and perfluorobutylmethyl ether onto model carbon-coated hard-disk surfaces. The validity of the QCM results and the applicability of the well-known Sauerbrey equation have been verified through combined QCM and surface plasmon resonance experiments. The adsorption isotherms are relatively simple and exhibit a Langmuir-like behavior. However, the plateau region is sometimes ill-defined, and the adsorption process is strongly dependent on the history of the system. The adsorbed mass at a particular concentration shows a pronounced dependence on the equilibration time between successive concentration changes, even though the adsorption kinetics appears to have equilibrated. In the first few seconds, the adsorption process is diffusion limited, with the adsorbed mass quickly increasing to a maximum before decaying to the equilibrium value....

On the measurement of thin liquid overlayers with the quartz-crystal microbalance

We present a simple model that predicts the changes in resonance frequency and dissipation factor for a quartz-crystal microbalance (QCM) when it is coated with a viscous film that may or may not slip on the crystal. In this context, the validity of the Sauerbrey equation (change in resonance frequency α change in applied mass) is discussed. The Sauerbrey equation gives an accurate estimate of the film thickness, t f, only if (i) the film is thin compared to the shear-wave penetration depth, δ, into the liquid, i.e., t f ⪡ δ, and (ii) the film does not slide on the QCM electrode (s). We have shown that by measuring both the QCM resonance frequency and the dissipation factor simultaneously, the thickness range over which t f can be measured accurately can be extended to about 2δ for non-slipping films. If the film slips, which we have only observed for molecularly thin films, changes in dissipation factor can be used to calculate the coefficient of friction between the film and the substrate. We also show the usefulness of measuring the dissipation factor of the QCM when studying solid to liquid phase transitions.