Applications of the Quartz Crystal Microbalance

The most common commercial use of the QCM is as a thickness gauge in thin-layer technology. When used to monitor the thickness of a metal film during physical or chemical vapor deposition, it acts very closely as a nanobalance, providing a real-time measurement of the thickness. Indeed, devices sold for this purpose are usually calibrated in units of thickness (having a dilferent scale for each metal, of course), and claim a sensitivity of less than 0.1 nm, which imphes a sensitivity of less than a monolayer. 

The other common application of the QCM is as a nano-sensor proper, made sensitive to one gas or another by suitable surface treatment. Selecting the suitable coating on the electrodes of the QCM can determine selectivity and enhance sensitivity. It is not our purpose to discuss sensors in the present review. It should only be pointed out that any such sensor would have to be calibrated, since the Sauerbrey equation would not be expected to apply quantitatively. 

It was not initially obvious that the quartz crystal resonator would operate in liquids until this was proven experimentally [9,10]. The term associated with the influence of the viscosity and density of liquid in Eq. (2) can be written [11] as 

Since the product of y/ifp in liquids is about two orders of magnitude higher than in gases at ambient pressure, the crystal is heavily loaded when transferred from the gas phase into a liquid. 

Once the door had been opened to its use in liquids, the potential of the QCM for interfacial electrochemistry was obvious, and the EQCM became popular. 

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The first application of the quartz crystal microbalance in electrochemistry came with the work of Bruckenstein and Shay (1985) who proved that the Sauerbrey equation could still be applied to a quartz wafer one side of which was covered with electrolyte. Although they were able to establish that an electrolyte layer several hundred angstroms thick moved essentially with the quartz surface, they also showed that the thickness of this layer remained constant with potential so any change in frequency could be attributed to surface film formation. The authors showed that it was possible to take simultaneous measurements of the in situ frequency change accompanying electrolysis at a working electrode (comprising one of the electrical contacts to the crystal) as a function of the applied potential or current. They coined the acronym EQCM (electrochemical quartz crystal microbalance) for the technique. 

Refs. [i] Lu C, CzandernaAW (eds) (1984) Applications of piezoelectric quartz crystal microbalances. Elsevier New York [ii] Buttry DA (1991) Applications of the quartz crystal microbalance to electrochemistry. In Bard AJ (ed) Electro analytical chemistry, vol. 17. Marcel Dekker, New York, pp 1-85 [Hi] Buck RP, Lindner E, Kutner W, Inzelt G (2004) Pure Appl Chem 76 1139 [iv] Sauerbrey G (1959) Z Phys 155 206 [v] Buttry DA, WardMD (1992) Chem Rev 92 1355 [vi] O Sullivan CK, Guil-bault (1999) Biosens Bioelectron 14 663 [vii] Bacskai J, Lang G, Inzelt G (1991) J Electroanal Chem 319 55... 

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. 

QCMs have been used as film-thickness monitors in vacuum deposition of metals and inorganic solids since the 1970s. The monograph by Lu and Czandema [35], while over 20 years old, is still a very good summary of early applications of the quartz crystal microbalance in physics and engineering, as well as applications as thickness monitors in the vacuum deposition industry. Well before the fiill... 

J. Tian, Comparative Solubility Studies of C60 and C60- Piperazine and Applications of the Quartz Crystal Microbalance/Heat Conduction Calorimeter, PhD Thesis, Drexel University, Philadelphia, 2002. 

Buttry DA (1991) Applications of the quartz crystal microbalance to electrochemistry. In Bard AJ (ed) Electroanalytical chemistry, vol 17. Marcel Dekker, New York, pp 1-85... 

Buttry DA (1991) Applications of the quartz crystal microbalance to electrochemistry. In ... 

Applications of the Quartz Crystal Microbalance to Electrochemistry, Daniel A. Buttry... 

Bund A (2004) Application of the quartz crystal microbalance for the investigation of nanotribological process. J Solid State Electrochem 8 182-186... 

Deakin MR, Buttry DA (1989) Electrocheanical applications of the quartz crystal microbalance. Anal Chem 61(20) 1147A-1154A... 

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