Quartz crystal, sources

FIGURE 3.3 Overtone and spurious frequency response of a quartz crystal. (Source Frerking, M.E. 1978. Crystal... 

In an attempt to stimulate onshore production of synthetic quartz and piezoelectric devices in the 1970s, Brazil imposed an embargo on exports and ultimately raised the price several-fold for small quartz crystals used as the starting material for quartz growth. However, sources of suitable pure quartz were located in the United States and Canada, including vein and pegmatic deposits (1). Synthetic processes compatible with the natural U.S. quartz starting material from a variety of sources were developed, and U.S. production became relatively independent of imports (1). 

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... 

The line width of the X-ray source is on the order of 1 eV for A1 or Mg Ka sources but can be reduced to better than about 0.3 eV with the use of a monochromator. A monochromator contains a quartz crystal which is positioned at the correct Bragg angle for A1 Ka radiation. The monochromator narrows this line significantly and focuses it onto the sample. It also cuts out all unwanted X-ray satellites and background radiation. An important advantage of using a monochromator is that heat and secondary electrons generated by the X-ray source cannot reach the sample. 

Acoustic waves. The microbalance is generally based on quartz crystals which are mechanically distorted when subjected to an electrical potential. The source is usually an alternating frequency in the MHz region and will be perturbed by minor changes at... 

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). 

The graywacke and quartzite cobbles used for tool making were probably obtained locally from the storm beaches immediately below the coastal sites. Conversely, chert or quartz crystals have not been found on coastal beaches or adjacent regions, despite intensive survey. Although potential chert-bearing calcareous sediments are located inland, no source is known to exist in this region of southern Portugal (5). 

Finally, real-time bulk measurements include an approach in which the frequency of an oscillator such as a quartz crystal is altered as mass is deposited on the oscillating element. Surrogate measurements are also employed, such as inference of mass concentration from the decreasing transmission of electrons from a beta source to a detector as mass is deposited on an intervening substrate (see Gebhart, 1993, for a review). 

In addition, other potential sources of variability were considered. For example, the sensor surface may potentially differently adsorb deposited polymers. Flowever, the inert nature of quartz crystal and gold sensor electrode,36 with respect to the employed solvents and polymers, resulted in no detectable irreversible adsorption of polymers to the sensor surface as measured by the recovery of the sensor baseline after washing-off deposited polymers. Thus, the sensors were completely reusable because the solvents and dissolved polymers did not chemically interact with the quartz crystal and gold electrodes of the sensor. 

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