Quartz crystal microbalance principle

Such approximation is valid when the thickness of the polymeric layer is small compared to die thickness of die crystal, and the measured frequency change is small with respect to the resonant frequency of the unloaded crystal. Mass changes up to 0.05% of die crystal mass commonly meet this approximation. In die absence of molecular specificity, EQCM cannot be used for molecular-level characterization of surfaces. Electrochemical quartz crystal microbalance devices also hold promise for the task of affinity-based chemical sensing, as they allow simultaneous measurements of both tile mass and die current. The principles and capabilities of EQCM have been reviewed (67,68). The combination of EQCM widi scanning electrochemical microscopy has also been reported recently for studying die dissolution and etching of various thin films (69). The recent development of a multichannel quartz crystal microbalance (70), based on arrays of resonators, should further enhance die scope and power of EQCM. 

Ward, M. D., Principles and applications of the electrochemical quartz crystal microbalance, in Physical Electrochemistry, I. Rubenstein, Ed., Marcel Dekker, New York, 1995, p. 293. 

We first experimented with the Quartz Crystal Microbalance (QCM) in order to measure the ablation rate in 1987 (12). The only technique used before was the stylus profilometer which revealed enough accuracy for etch rate of the order of 0.1 pm, but was unable to probe the region of the ablation threshold where the etch rate is expressed in a few A/pulse. Polymer surfaces are easily damaged by the probe tip and the meaning of these measurements are often questionable. Scanning electron microscopy (21) and more recently interferometry (22) were also used. The principle of the QCM was demonstrated in 1957 by Sauerbrey (22) and the technique was developed in thin film chemistiy. analytical and physical chemistry (24). The equipment used in this work is described in previous publications (25). When connected to an appropriate oscillating circuit, the basic vibration frequency (FQ) of the crystal is 5 MHz. When a film covers one of the electrodes, a negative shift <5F, proportional to its mass, is induced ... 

Figure 9.11 Working principle of a quartz crystal microbalance.

First, the underlying principles upon which bulk acoustic wave (BAW) devices operate are described. When a voltage is applied to a piezoelectric crystal, several fundamental wave modes are obtained, namely, longitudinal, lateral and torsional, as well as various harmonics. Depending on the way in which the crystal is cut, one of these principal modes will predominate. In practice, the high-frequency thickness shear mode is often chosen since it is the most sensitive to mass changes. Figure 3.4 schematically illustrates the structure of a bulk acoustic wave device, i.e. the quartz crystal microbalance. 

Fig. 6.10 The principle of the quartz crystal microbalance gold surface modification (left) and analyte detection by frequency modulation (right)... 

There has been remarkable progress in the development and application of the quartz crystal microbalance (QCM) principle in sensitive devices for the detection and concentration measurement of specific molecules in gaseous and liquid media [1]. Since the behavior of quartz crystal resonator (QCR) sensors in gases is similar to quartz crystals technically used as frequency standards, a large set of circuit configurations is available, whose known properties can merely be adapted to particular applications [2-5]. In many cases quartz crystals used in electronic circuitry, sometimes even from mass production, are employed. 

The practical application of this measurement principle is the QCM-D technique (quartz crystal microbalance with dissipation monitoring), patented by Q-Sense [55]. The QCM-D technique extracts frequency, /, and dissipation, D = Rs/ coLs), or the respective changes A/ and AD (see Chap. 12 in this volume). 

Quartz Crystal Microbalance (QCM) sensors detect changes in mass adsorption at an interface and may represent an alternative sensor technology for the study of biospecific interactions in real-time [78], The operating principle of these sensors is based on changes of frequency in acoustic shear waves in the substrate of the sensor. When the QCM system is used in piezoelectric detection mode, the resulting frequency will shift in direct proportion to molecular mass adsorbed at the surface of the sensor [79]. 

Although quartz-crystal microbalances are not a new invention, they have not been used extensively in thermoanal5 ical investigations. In Chapter 5, Alan Smith provides a historical backgroimd to quartz-crystal microbalances and describes the principles of their operation, before... 

The first subdiscipline of chemistry in which the QCM was widely applied was electrochemistry. In 1992 Buttry and Ward published a review entitled Measurement of interfacial processes at electrode surfaces with the electrochemical quartz crystal microbalance , with 133 references [8]. This is the most widely cited paper on quartz crystal microbalances. After presenting the basic principles of AT-cut quartz resonators, the authors discuss the experimental aspects and relation of electrochemical parameters to QCM frequency changes. In their review of the investigation of thin films, they discuss electrodeposition of metals, dissolution of metal films, electrovalency measurements of anion adsorption, hydrogen absorption in metal films, bubble formation, and self-assembled monolayers. The review concludes with a brief section on redox and conducting polymer films. 

Buttry DA (1991) Applieations of the quartz crystal microbalance to electrochemistry. In Bard AJ (ed) Electroanalytical chemistry, vol 17, Marcel Dekker, New York, p 1 Ward MD (1995) Principles and applications of the electrochemical quartz crystal microbalance. In Rubinstein I (ed) Physical electrochemistry. Marcel Dekker, pp 293-338 Buck RP, Lindner E, Kutner W, Inzelt G (2004) Pure Appl Chem 76 1139 Hepel M (1999) Electrode-solution interface studied with electrochemical quartz crystal nanobalance. In Wieczkowski A (ed) Interlacial electrochemistry. Marcel Dekker, New York Barbero CA (2005) Phys Chem Chem Phys 7 1885... 

Mecca VM (2005) From quartz crystal microbalance to fundamental principles of mass measurements. Artal Lett 38 753-767 Bucur RV, Carlsson J-O, Mecea VM (1996) Quartz-crystal mass sensors with glued foil electrodes. Sens Actuators B 37 91-95 Bucur RV, Mecea VM, Carlsson J-O (2003) EQCM with air-gap excitation electrode. Calibration tests with copper and oxygen coatings. Electrochim Acta 48 3431-3438 Mecea V, Bucur RV (1979) The mechanism of the interaction of thin films with resonating quartz crystal substrates the energy transfer model. Thin Solid Films 60 73-84 Mecea V, Bucur RV, Indrea E (1989) On the possibility of thin film structure study with a quartz crystal microbalance. Thin Solid Films 171 367-375... 

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