Quartz crystal microbalance shift

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 ... 

Another tool used to study friction on the molecular scale is the quartz crystal microbalance (QCM) introduced in Section 9.4.1. The QCM has been used to monitor the adsorption of thin films on surfaces via the induced frequency shift [385], In the years since 1986, Krim and coworkers could show that the slippage of adsorbed layers on the QCM leads to a damping of the oscillator [472], This damping is reflected as a decrease in the quality factor Q of the oscillator. From the change in Q, a characteristic time constant rs, the so-called slip-time, can be derived. This corresponds to the time for the moving object s speed to fall to 1 /e, i.e. 

This is the correct name for most popular mass sensors, although they are better known as Quartz Crystal Microbalances (QCMs). A piezoelectric crystal vibrating in its resonance mode is a harmonic oscillator. For microgravimetric applications, it is necessary to develop quantitative relationships between the relative shift of the resonant frequency and the added mass. In the following derivation, the added mass is treated as added thickness of the oscillator, which makes the derivation more intuitively accessible. 

Fig. 2 Quartz crystal microbalance frequency shifts for cycles of alternate myoglobin/ds-DNA and cytochrome P450cam/ds-DNA adsorption on gold resonators coated with mixed mono-layers of mercaptoproionic acid/mercaptopropanol as first layer and PDDA as second layer. DNA was from salmon testes (ST) and calf thymus (CT). Average values are shown for five replicates of [Mb/ST ds-DNA] (0) and four replicates of [cyt P450cam/ST ds-DNA] ( ) films. (From Ref. [15] with permission. Copyright American Chemical Society.)...

Quartz Crystal Microbalance. The shift Av (Hz) from the natural resonant frequency of the "unloaded" quartz v0 (Hz it depends on the "cut" of the quartz crystal) as molecules are adsorbed onto the crystal can be used to measure small increase of mass Am (g). The Sauerbrey95 equation (1959) is... 

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]. 

The quartz crystal microbalance (QCM) is a very sensitive technique allowing measurements of mass changes in the nanogram range. " Under high vacuum conditions, the attachment to the quartz crystal surface of a foreign layer of mass dm yields a frequency shift Sfrn which follows the Sauerbrey equation... 

Shifts of the resonance frequency of a quartz crystal microbalance in micro-gravimetric sensors (Richter et al. 2004b)... 

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]. 

The most effective method to measure the adsorbed mass is the quartz crystal microbalance (QCMB). This method goes back to the work of Sauerbrey. ° The apphcation of this method is based on the following equation relating the shift A/of the resonance frequency /o of a quartz crystal to the change of the mass of the crystal Am divided by A (area)... 

Figure 4.17 Shift and change of the resonance frequency of a quartz crystal microbalance, real part of the admittance versus frequency, /q, Wq, resonance frequency and full width at half maximum (FWHM) of the initial gold electrode,/j, w, resonance frequency and FWHM of a gold electrode after formation of a rigid and smooth surface film (no damping), resonance frequency and FWHM of a gold electrode after formation of a viscoelestic and/or rough surface film (strong damping).

Water Sorption. A laboratory-constructed piezoelectric apparatus (quartz crystal microbalance) was used to measure water sorption in the polymer films. The AT-cut quartz crystal with gold electrodes (Hokuto Electronics) had a resonance frequency of 10.000 MHz. With this crystal, a frequency shift of 1 Hz corresponded to a mass change of 0.58 ng. The frequency change is linearly related to the mass sorbed on the quartz plate (5,9). 

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