Quartz crystal balance

Figure 5.5 shows the variation of the pore size distribution as a function of cycles of surface-modification-based N2 adsorption isotherms. The pore size decreases with the modification cycle number. The reduction of the mesopore size for each cycle should be about twice the single-layer thickness. Accordingly, the effective singlelayer thickness is about 6 to 7 A based on the above BET measurements. This value is close to those estimated from the frequency changes of a quartz crystal balance for ultrathin fihns prepared by the surface sol-gel process on 2-D substrates." " ... 

Figure 11.30 Schematic of a quartz crystal microbalance dissolution monitor. The mass of the quartz crystal balance controls the frequency of the oscillating circuit. The change in the total mass of the crystal as the resist film coated on it dissolves is linearly related to the oscillating frequency, which is monitored with the frequency counter. The dissolution rate of the resist is thus monitored by measuring the change in frequency of the oscillator with time as the resist film dissolves. (Adapted from Ref. 153.)...

The wet disks are immediately immersed into the vapor of refluxing isopropanol. Once they reach the reflux temperature, as noted by a reduction in the rate of alcohol condensation on the disks, they are removed into the room air where they rapidly become dry and slowly cool to room temperature. At this point, the disks are individually weighed to the nearest 0.1 mg. The disks are then loaded into a metal tray with large circular regions on their bottom faces exposed and the tray placed in the load lock of a vacuum chamber. The load lock is pumped to about 10 torr and then the tray is translated into the chamber and the load lock sealed off from the chamber. The chamber is pumped to about 10 torr with a cryopump. The major residual gas is water from the rotatable rubber seal used between the evacuated space in the chamber and the water flow path into and out of the rotatable copper crucible mentioned below. Titanium vapor is sublimed from a Ti ingot by bombardment with about 8 keV electrons while the periphery of the ingot is cooled by sparse physical contacts with the water-cooled copper crucible in which it rests. The Ti vapor condenses in the line of sight from the source onto the exposed bottoms of the disks. The thickness of the deposited titanium, is monitored by a calibrated quartz crystal balance close to the quartz disks. Typically (iji 5 x 10 cm. 

Piezoelectric transducers The formation of antigen—antibody complexes impHes an increase of mass as compared with the antigen or the antibody alone that is detected with piezoelectric devices, such as a quartz crystal balance or a cantilever. 

Metal-solution interface, quantum mechanical calculations for (Kripsonsov), 174 Metal-water affinity, 177 Micro-balance, quartz crystal, 578 Microwave circuit, 446 for Faraday rotation, 454 Microwave conductivity... 

Quantum chemical calculations, 172 Quantum chemical method, calculations of the adsorption of water by, 172 Quantum mechanical calculations for the metal-solution interface (Kripsonsov), 174 and water adsorption, 76 Quartz crystal micro-balance, used for electronically conducting polymer formation, 578... 

The quartz balance uses a thin quartz crystal, a few hundred /xm thick, with thin, vapor-deposited gold films on the two sides. Such a crystal has a fundamental mode for shear waves with a frequency in the 1-15 MHz region, which can be excited by application of a corresponding alternating voltage on the two electrodes. The resonance frequency is very sensitive to small mass changes of the system. One... 

An application of an electrochemical quartz crystal microbalance (EQCM) in the study of the A11/HCIO4 system shows that even at a potential about 0.5 V more negative than the onset of AuO formation (the so-called preoxide region), the resonant frequency of the Au-covered quartz crystal decreases as that of the surface mass increases. A comparison of a voltammogram with the potential dependence of the micro-balance frequency for an Au electrode is shown in Figs. 6a and 6b. 

Fig. 8.10 Mode of operation of the quartz micro balance (left schematic). Right A dendrimer as guest-selective host compound (selector) for coating of the quartz crystal oscillator. Red Selector layer green various analyte components...

In this paper we present a brief topical account of the kinetic possibilities and limitations of the EQCM. Extensive review chapters with theoretical aspects of the quartz crystal micro-balance have been written by Buttry and Ward [3-5] and the reader is referred to them for a more detailed discussion. 

The quartz crystal micro-balance (QCM), the most extensively studied shear mode AT-cut quartz resonator, is comprised of a thin slice of quartz single crystal with two metal electrodes deposited on both faces of the crystal. These excitation electrodes generate a transverse shear wave across the thickness of the crystal that propagates into the film immobilized onto the crystal surface. When the over-layer is non-rigidly coupled to the... 

The rotatable reactor can also be used for reactions in fluids having suitably low (< 10"3 Torr) vapor pressure. In this mode, metal atoms are evaporated upwards into the cold liquid, which is spun as a thin band on the inner surface of the flask. Reactions with dissolved polymers can then be studied. Specially designed electron gun sources can be operated, without static discharge, under these potentially high organic vapor pressure conditions (6). Run-to-nin reproducibility is obtained by monitoring the metal atom deposition rate with a quartz crystal mass balance (thickness monitor). 

Hence, the study of the different adsorption modes of oxygen is an interesting way to bring a deeper understanding of ORR mechanism on a catalyst. The Electrochemieal Quartz Crystal Miero-balance (EQCM) is a partieularly convenient analytieal method to study adsorption - desorption of species on a eatalyst smfaee. 

In either case, the resultant negative charge generated by electron accumulation at the internal surfaces has to be balanced by cations (from the electrolyte phase) for charge compensation. Such ion insertion reactions have been studied using techniques such as voltammetry, reflectance or absorption spectroscopy, chronoamper-ometry and electrochemical quartz-crystal microgravimetry [329, 332-336]. Both aqueous and aprotic electrolytes have been deployed for these studies. 

The simplest balance mechanism, readily adaptable to decomposition studies, is that based on measurement of the extension of a quartz spiral spring. Quartz crystal microbalances can be used for very sensitive measurements [84] (e.g. on single crystals) but the temperature range is limited. 

Quartz crystal micro balance shows promise in its applications for chemical sensing. A proper and selective coating on the surface of a QCM can be used to selectively absorb a chemical species. The mass of the absorbed species, even in very minute quantity, can be used to quantify the species present. It is an effective means for chemical sensing under appropriate circumstance. 

Smith, A.L., Shirazi, H.M., and Mulligan, S.R. Water sorption isotherms and enthalpies of water sorption by lysozyme using the quartz crystal micro-balance/Heat-conduction calorimeter, Biochim. Biophys. Acta — Protein Struct. Mol. Enzymol., 1594,150, 2002. 

In the gravimetric method, the adsorbent (usually in the form of powder) is placed into a bulb, which is mounted on a sensitive balance and the bulb is then evacuated. Next, the weight increase of the adsorbent solid as a function of the absorptive gas pressure is monitored at constant temperature. More recently, the quartz crystal microbalance (QCM) technique has been applied this is very sensitive to mass increases. Quartz is a piezoelectric material and the thin crystal can be excited to oscillate in a traverse shear mode at its resonance frequency when a.c. voltage is applied across the metal (usually gold) electrodes, which are layered on two faces of the crystal. When the mass on the crystal increases upon adsorption, its resonance frequency decreases. The increase in the mass is calculated from the reduction in resonance frequency. On the other hand, adsorption on single flat surfaces can also be measured by ellipsometry, which measures the film thickness of transparent films optically using the difference between light reflection from bare and adsorbed surfaces. 

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... 

Other types of balances using quartz crystals have been described also (48). 

Most chemists and materials scientists are not aware that an alternative gravimetric technology has been available for decades that provides sensitivities at least 3 orders of magnitude lower than mechanical balances, using a piezoelectric sensor that is rugged, inexpensive, and operates at high frequencies relatively immune to vibrations the quartz crystal microbalance. The purpose of this chapter is to describe the capabilities and limitations of the quartz crystal microbalance and to discuss its uses in thermal analysis and calorimetry. 

V. Tsionsky [28] Is the quartz crystal microbalance really a microbalancel For one thing, it should rightly be called a nano-balance, considering that the sensitivity of modern-day devices is on the order of 1-2 ng/cm and could be pushed further, if necessary. More importantly, calling it a balance implies that the Sauerbrey... 

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