Monitoring quartz crystal

Quartz, since it is a piezoelectric and not a ferroelectric, has no hysteresis loss when it oscillates, thus quartz crystal oscillators are widely used as frequency control devices in radios, computers, and watches. Since the frequency is a function of the mass of the crystal, they can serve as deposition monitors (quartz crystal microbalances) with sensitivities of less than 1 ng. By functionalizing the surface to absorb specific gases, they can also act as chemical sensors. The temperature sensitivity of a quartz crystal oscillator can be minimized by choosing the cut of the crystal relative to the optical axis, which is necessary for its use as a frequency standard. On the other hand, a cut can be chosen to maximize the frequency dependence on temperature and quartz crystal thermometers with millikelvin resolution are available. 

Acoustic Wave Sensors. Another emerging physical transduction technique involves the use of acoustic waves to detect the accumulation of species in or on a chemically sensitive film. This technique originated with the use of quartz resonators excited into thickness-shear resonance to monitor vacuum deposition of metals (11). The device is operated in an oscillator configuration. Changes in resonant frequency are simply related to the areal mass density accumulated on the crystal face. These sensors, often referred to as quartz crystal microbalances (QCMs), have been coated with chemically sensitive films to produce gas and vapor detectors (12), and have been operated in solution as Hquid-phase microbalances (13). A dual QCM that has one smooth surface and one textured surface can be used to measure both the density and viscosity of many Hquids in real time (14). 

Fig. 11. Photograph of the four-electrode, vacuum flange and dual, quartz crystal, microbalance assembly, (A) side view, and (B) front view, used for mixed Cr atom. Mo atom matrix depositions with simultaneous monitoring of the individual metal flows. (The resolution of the microbalance is 10 g) (113).

In the case of Ni(OH)2 and conductive polymer electrodes, solvent and anions intercalate into the electrode at anodic potentials. Electrochemical quartz crystal microbalance (EQCM) is a useful technique for monitoring the ingress and egress of solvent and anions in these materials. 

In the measurement technique, which has been used on D3 for many years, the ratio of the time spent counting with the cryoflipper in (+) or (-) mode is controlled by a quartz crystal controlled oscillator with a highly stable output frequency / of 1 MHz. There are two scalers to count the detector pulses (+ and - states), a single monitor scaler and a single time scaler used to end the measurement when the total time is reached (precision of 1 ms). 

I. Vikholm, W.M. Albers, H. Valimaki, and H. Helle, In situ quartz crystal microbalance monitoring of Fab-fragment binding to hnker lipids in a phosphatidylcholine monolayer matrix application to immunosensors. Thin Solid Films 327, 643-646 (1998). 

Fig. 2 (a) Edwards E308 evaporator. One quartz-crystal thickness monitor is pointed towards the Au source to monitor Au vapor deposition on chamber walls the other monitors Au deposited through the shadow mask atop the organic layer. In the cold Au deposition, a small amount of Ar gas is added to the chamber to cool the Au atoms to room temperature before they physisorb atop the cryocooled organic monolayer, (b) Geometry of an Au I monolayer I Au pad sandwich, with electrical connections made using a Ga/In eutectic... 

C, is a cylindrical glass vessel with a volume of 450 cm. The piezometer contains the solution and 330 gms of Hg. The top of the piezometer is fitted with a Taper joint for filling. A precision bore capillary, E, (2mm in diameter) is fitted to the bottom of the piezometer. The piezometer is suspended (6) in a brass or stainless steel pressure vessel, H. A glass boiler tube, J, encloses the upper portion of the capillary. The pressure vessel is filled with ethylene glycol which serves as a thermal and pressure medium. The entire apparatus is submerged in a constant temperature bath controlled to 0.001 C. The temperature inside the pressure vessel is monitored with a Hewlett-Packard quartz crystal thermometer (to determine when thermal equilibrium is reached after compression and decompression). 

Niwa et al. [297] prepared a mixed SAM from dithiols on gold which partly bears a dithiocarbamate group. The RAFT-SIP of methacrylic acid was monitored by in situ quartz crystal microbalance. The polymerization rate depended strongly on the composition of the SAM. 

X. Bi and K. Yang, On-line monitoring imidacloprid and thiacloprid in celery juice using quartz crystal microbalance, Anal. Chem., 81, 527-532 (2009). 

Acoustic Wave Analysis of the Operation of Quartz Crystal Film Thickness Monitors. 

Fig. 2.5. Quartz crystal monitor response when a silicon surface, previously exposed to a high dosage of CF ions, is subjected to 500 eV O2 ion bombardment. The regions of this curve are dominated by the following phenomena ...

Piezoelectric hygrometers (Fig. 6.S6) These consist of a quartz crystal with a hygroscopic coating (Fig. 6.S60 and Section 6.3.3). Two crystals are usually employed and the wet gas (sample) and dry gas (reference) are passed over them alternately (normally every 30s—Fig. 6.566). The crystals absorb and desorb. The difference in angular frequency Am is proportional to the concentration of water vapour by volume. Capable of high precision. Can monitor moisture contents of the order of 1 to 3000 ppm by volume. Usually measures up to dewpoint of 310 K. Fast response but expensive. Sample must be dean to avoid contamination of the crystals. Complex sampling system. Suitable for on-line use. 

Since evaporation is done in vacuum the mean free path of the molecules is long and they move practically in straight lines to condense onto the substrate, which is placed at an appropriate position. Typically amorphous or polycrystalline layers of some 10 nm thickness are produced by this technique. To get a crystalline surface the sample is usually annealed during or after evaporation. The film thickness is usually monitored by a quartz crystal microbalance. 

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. 

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