Quartz crystal resonator

Goubaidoulline, L, Vidrich, G., and Johannsmann, D., Organic vapor sensing with ionic liquids entrapped in alumina nanopores on quartz crystal resonators. Anal. Chem., 77,615-619,2005. 

A Acoustically active area of the quartz crystal resonator... 

Fig. 5 Mass change, under FIA conditions, of the MIP film (imprinted with L-aspartic acid) due to injection of a 10-mM sample of L-aspartic acid or D-aspartic acid into the KC1-HC1 carrier solution (pH = 1.6). The MIP film was deposited on a gold-coated quartz crystal resonator held at a constant potential of —0.4 V (adapted from [148])...

Fucassi F et al (2001) Characterisation of small molecule binding to DNA using a quartz crystal resonant sensor. Chem Commun 841-842... 

Since the early work of Kanazawa [1] and Bruckenstein in 1985 [2], quartz crystal resonators have been used for more than 12 years in contact with liquids to assess changes in mass during electrochemical surface processes. Extensive use of the electrochemical quartz crystal microbalance (EQCM) has been done in the study of electrode processes with change of mass simultaneous to charge transfer. 

Figure 12.4 depicts a typical admittance parametric plot for the quartz crystal resonator. Note that the effect of the static capacitance C0 in the parallel branch is to shift the admittance circle upward by resonance frequency top which now depends on C0, in addition to the series resonance frequency to, = 2irfa. Changes in the resonance frequency are related to changes in the equivalent inductance L and broadening of the admittance curve near resonance (decrease in the circle diameter l/R in Fig. 12.4) are related to equivalent resistance R. 

Oyama and Tatsuma measured the resonant frequency and resonant resistance of quartz crystal resonators coated with several redox active polymers [58-60], DNA [61] and tungsten oxide [62]. 

As the readers may see, quartz crystal resonator (QCR) sensors are out of the content of this chapter because their fundamentals are far from spectrometric aspects. These acoustic devices, especially applied in direct contact to an aqueous liquid, are commonly known as quartz crystal microbalance (QCM) [104] and used to convert a mass ora mass accumulation on the surface of the quartz crystal or, almost equivalent, the thickness or a thickness increase of a foreign layer on the crystal surface, into a frequency shift — a decrease in the ultrasonic frequency — then converted into an electrical signal. This unspecific response can be made selective, even specific, in the case of QCM immunosensors [105]. Despite non-gravimetric contributions have been attributed to the QCR response, such as the effect of single-film viscoelasticity [106], these contributions are also showed by a shift of the fixed US frequency applied to the resonator so, the spectrum of the system under study is never obtained and the methods developed with the help of these devices cannot be considered spectrometric. Recent studies on acoustic properties of living cells on the sub-second timescale have involved both a QCM and an impedance analyser thus susceptance and conductance spectra are obtained by the latter [107]. 

Srikhirin, X, Laschitsch, A., Neher, D., and johannsmann, D. Light-induced softening of azobenzene dye-doped polymer films probed with quartz crystal resonators. Appl. Phys. Lett. 2000, 77, pp. 963-965. 

Multilayer films were fabricated directly on one side of preliminary cleaned in a piranha solution quartz crystal resonators with gold working surface having the basic oscillation frequency of 5 MHz. The resonators were covered with a PEI/PSS layer if needed. The adsorption of PEI and PSS was carried out from 1 mg/mL polyelectrolyte solutions. Each adsorption step was followed by washing the resonator with the film in distilled water to remove an excess polyelectrolyte. 

Figure 2. Frequency shift upon HRP/PSS alternate adsorption from the aqueous solution on a (PEI/PSS>2-covered quartz crystal resonator.

In conclusion, the QCM-technique has been applied to study the process of a HRP layer formation on a PEI/PSS coated quartz crystal resonator from enzyme aqueous solutions. It has been shown, that adsorption of HRP can be described by the Freundlich and Langmuir equations. 

Another resonant-frequency thermometer is the quartz crystal resonator (Benjaminson and Rowland, 1972), which, if the crystal is properly cut, is quite linear from about 190 to 525 K. Although this thermometer has excellent resolution, it does exhibit hysteresis and drift. The principle of quartz crystal thermometry is based on the temperature dependence of the piezoelectric resonant frequency of a quartz crystal wafer of a given dimension. The angle of cut of the quartz crystal is selected to give as nearly a linear and yet sensitive correspondence between resonant frequency and temperature as possible. This angle of cut is referred to as an LC (linear coefficient) cut. The temperature sensitivity of the quartz crystal thermometer is about 1000 Hz/°C. 

Piezoelectric Quartz Crystal Resonators Applied for Immunosensing and Affinity Interaction Studies... 

Fig. 1. Piezoelectric quartz crystal resonator (left, photo of the optically polished smooth crystal) and schematic description (right). The crystal shown (part no. 151620-10) is produced by International Crystal Manufacturing, see Note 1.

Direct detection biosensors utilize direct measurement of the biological interaction. Such detectors typically measure physical changes (e.g., changes in optical, mechanical, or electrical properties) induced by the biological interaction, and they do not require labeling (i.e., label free) for detection. Direct biosensors can also be used in an indirect mode, typically to increase their sensitivity. Direct detection systems include optical-based systems (most common being surface plasmon resonance) and mechanical systems such as quartz crystal resonators. 

Abstract Oscillators are the standard interface circuits for quartz crystal resonator sensors. When applying these sensors in gases a large set of circuits is available, which can be adapted to particular applications. In liquid applications viscous damping accompanied by a significant loss in the Q factor of the resonator requires specific solutions. We summarize major design rules and discuss approved solutions. We especially address the series resonance frequency and motional resistance determination and parallel capacitance compensation. We furthermore introduce recent developments in network analysis and impulse excitation technique for more sophisticated applications. Impedance analysis especially allows a more complete characterization of the sensor and can nowadays be... 

Keywords Quartz crystals Resonance frequencies Oscillators Network analysis... 

Quartz crystal microbalance Quartz crystal resonator Resistance... 

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 performance of oscillators depends essentially on the stabihty of the acoustic device [7-9] no matter if working as electromechanical resonator or delay line. Because of its extraordinary importance we will concentrate further on resonators, namely quartz crystal resonators. However, the analysis is descriptive also for other piezoelectric materials and partly for delay line elements as well. 

In its original application as timing reference, special care has been taken to minimize the perturbations on frequency of the selected mode of vibration caused by unavoidable variations in the environment, first of all temperature and acceleration. The breakthrough of quartz crystal resonators in timekeeping is very much correlated to the existence of a specific crysfal cuf, at which the device resonance frequency provides a zero temperature coefficient of frequency at 25 °C and a remarkable temperature stability around room... 

When applying quartz crystal resonators outside Sauerbrey s limitations in the so-called non-gravimetric regime, material properties come into play. The electrical admittance (impedance) of the coated quartz crystal gives access to the determination of material properties of the coating. The crystal cut can again be used for optimization of the sensor performance. If mechanical stability is an issue (e.g., lateral stress induced during the experiment) BT-cut crystals are favorable. 

Fig. 12 Characteristic resonance frequencies of quartz crystal resonators, shown in the locus of impedance, Z = R+jX (a), and admittance, Y = G+jB (b). is the parallel resonant frequency/p at Umax, O is the parallel resonant frequency/a at X = 0, O is the parallel resonant frequency/ at 2 max, i Ih series resonance frequency/s at Gmax, is the series resonant frequency/r at = 0, and is the series resonant frequency/m...

The quartz crystal microbalance (QCM) is a well-known tool to measure film thicknesses in the nanometer range [1-3]. It is difficult to imagine a device which is simpler than a quartz crystal resonator, and simphcity is one of the principal advantages of the QCM. A QCM is a disk of crystalline quartz. The disk displays acoustic resonances like any other three-dimensional body. As a resonator, it distinguishes itself from other resonators by a number of features ... 

The classical sensing application of quartz crystal resonators is microgravimetry [1,5]. Many commercial instruments are around. These devices exploit the Sauerbrey relation (Eq. 28). For thin films, the resonance frequency is—by and large—inversely proportional to the total thickness of the plate. The latter increases when a film is deposited onto the crystal surface. Monolayer sensitivity is easily reached. Flowever, when the film thickness increases, viscoelastic effects come into play, as was for instance recognized by Lu and Lewis, who derived a refined version of the Sauerbrey equation [6]. These authors mainly intended to improve the microweighing procedure. Actually measuring viscoelastic properties with the QCM was not a major issue... 

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]. 

The most popular BAW resonator is the QCM. The name QCM correctly suggests that its main use is microgravimetry. However, many researchers who use quartz resonators for other purposes have continued to call the quartz crystal resonator QCM . We will follow this usage and call all quartz crystal resonators QCMs. Actually, the term balance makes sense even for... 

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