Quartz Crystals with Rough Surfaces

Quartz Crystals with Rough Surfaces Operating in Liquids 

The surface profile may be specified by a single valued function z = (R) of the lateral coordinates R that defines a local height of the surface with respect to a reference plane (z = 0). The latter is chosen so that the 

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In order to stress the multiscale nature of roughness, the profile function can be written as the sum of the functions that characterize the profile of the specific scale i  

For the calculation of the response of the QCM, the height-height pan-correlation function is needed [80]. When rough structures having different 

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Quartz Crystals with Rough Surfaces Operating in Liquids. 130... 

To mimic the PG electrode surface for QCM measurements of layers adsorbed on the gold-quartz resonators, we first chemisorb a mixed monolayer of mercaptopropionic acid/mercaptopropanol. This layer is represented by the first point in Fig. 2, labeled MPA. The second layer is PDDA. Quartz crystal microbalance frequency decreasing in a roughly linear fashion and at regular intervals for the multiple adsorption steps demonstrates repeatable adsorption for the two DNA/en-zyme films. Relative precision of layer formation on multiple resonators within 15% can be achieved. Film thicknesses and component weights in Table 1 were obtained by analyzing the QCM data with Eqs. 1 and 2. 

Admittedly, some of the amazing simplicity of quartz crystal resonators is lost once the surfaces are covered with electrodes and the crystal is inserted into a holder. In this chapter, we mostly stick to an ideahstic view and describe the modeling as if there were none of these complications. We do not touch upon compressional waves [24,25], effects of varying temperature or stress [26,27], anharmonic side bands [23], roughness [28,29], bubbles and slip [30], or effects of a variable dielectric environment [31,32]. 

Abstract In this chapter we discuss the results of theoretical and experimental studies of the structure and dynamics at solid-liquid interfaces employing the quartz crystal microbalance (QCM). Various models for the mechanical contact between the oscillating quartz crystal and the liquid are described, and theoretical predictions are compared with the experimental results. Special attention is paid to consideration of the influence of slippage and surface roughness on the QCM response at the solid-liquid interface. The main question, which we would like to answer in this chapter, is what information on... 

An important part of modern experimental surface science and electrochemistry has been performed on single-crystal electrodes. In contrast, the metal deposited on the surface of the quartz resonator always has a rough surface and at best a preferred crystal orientation. Studies with a QCM having a true single crystal surface have not yet been reported. Making a thin (about 1 xm) stable single-crystal metal layer on the surface of quartz seems to be an insurmountable problem. 

In order for both mass and heat-flow sensors to operate, the thin-film sample must adhere to the top surface of the QCM and be of uniform thickness. The mechanical behaviour of films on the quartz microbalance has been modeled by Kanazawa(12), who examined the amplitude of the shear displacement in the quartz crystal and in the overlying film for several cases. For a 1 volt peak RF applied voltage typical of the Stanford Research Systems oscillator driver, the amplitude of the shear wave of a bare crystal is 132 nm. Mecca [29] has calculated the inertial acceleration at the centre of a similar quartz resonator, and finds that it is roughly 10 g, where g is the gravitational constant. At these extremely high accelerations, powder or polycrystalline samples do not follow the transverse motion of the QCM surface and cannot be used without being physically bound to the surface with a thin adhesive layer. 

When acting as a microbalance, it is sometimes stated that the change in resonant frequency is an absolute measure of the change in mass loading, namely that this device does not require calibration. This statement is only partially true, and one is well advised to calibrate the QCM. Admittedly, the constant C in Eq. (1) can be calculated from the fundamental properties of the quartz crystal, as given by the Sauerbrey equation [see Eq. (9)]. However, for this constant to be applicable for the determination of the added mass, several implicit assumptions must be made. Primarily, it must be assumed that the mass distribution on the surface is uniform. It must also be borne in mind that the Sauerbrey equation only applies to thin films, such that the thickness of the film is small compared to the thickness of the crystal itself. In addition, the EQCM can operate as a true microbalance only if, in the course of the process being studied, the nature of the interface—its roughness, the density and viscosity of the solution adjacent to it, and the structure of the solvent in contact with it—is kept constant. 

Deposition and corrosion of Cu thin layers from an aqueous sulfate-based electrolyte were studied in situ with an AFM-EQCM system by Bund et al. [66]. The shift of the resonance frequency and of the damping of the quartz crystal (EQCM), on one side, and the evolution of surface roughness (AFM), on the other side, could be thus monitored simultaneously. No disturbance of the AFM response by the oscUlating quartz or vice versa was observed in this study. The authors proved that a quantitative separation of internal (information given by EQCM) and external friction (which is the roughness contribution, obtained by AFM) of the solid materials is possible by combining AFM and EQCM techniques. 

Many techniques have been developed to characterize the properties of the SEI layer on the anodes, such as X-ray photoelectron spectroscopy (XPS), EELS and selected area electron diffraction (SAED) " as well as FTIR and HRTEM. Most of these techniques provide ex situ information on both the elechonic and crystalline stmctural variations of the electrode. Electrochemical impedance spectroscopy (EIS) and electrochemical quartz crystal microbalance (ECQCM) can provide in situ information of macro-scale properties of the SEI layers. Reflectance FTIR techniques and atomic force microscopy (AFM) have been used in situ to study the surface of metal lithium and electrochemically nonactive electrodes, such as Pt, Au and Ni as well. Nevertheless, it is still difficult to study rough electrode surfaces of composite materials in lithium ion batteries with these techniques. In addition, none of the above techniques, except for FTIR spectroscopy, can provide structural information at the molecular levels. 

The piezoelectric quartz crystal resonators modified with oligonucleotide probes were used for detection of HCV in serum by Skladal et al. [66]. The gold electrodes on either rough or smooth surface crystals were modified with a self-assembled monolayer of cystamine. After activation with glutaraldehyde, either avidin or streptavidin were immobilized and used for attachment of biotinylated DNA probes (four different sequences). 

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