Helical etch channels in quartz
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Helical etch channels in quartz John Ballatoa) and Richard E. Riman Department of Ceramic and Materials Engineering, Rutgers, The State University of New Jersey, 607 Taylor Road, Piscataway, New Jersey 08854-8065
John R. Vigb) and Sally M. Laffey U.S. Army Communications – Electronics Command, AMSEL-RD-C2–CS, Fort Monmouth, NJ 07703-5603 (Received 2 June 1997; accepted 1 April 1998)
Helical etch channels were found to form in a-quartz when treated with anhydrous HF vapor at 400 ±C. Both hydrogen and fluorine species were determined to play an important role in helix formation. Crystal orientation, quartz source, etch channel density, and surface pretreatments had no influence. Helix formation was altogether arrested when water was present in the etch vapor. The genesis of the helices remains unknown.
I. INTRODUCTION
The piezoelectric effect was discovered by the brothers Curie in 1880. It largely remained a curiosity until the 1920s when its presence in quartz was used to realize crystal resonators.1 This permitted the field of frequency control to move from astronomical references to hand-held standards of greater accuracy and stability.2 Today, frequency control products based on piezoelectric crystal resonators (of which quartz is almost exclusively employed) include watches, clocks, telephones, radar, computers, as well as a full gamut of other communication, navigational, and consumer electronic devices. Further indications as to the importance of these devices lie in their market values. Two exemplifying illustrations are quartz crystals for timekeeping (currently 1.2 billion $yyear market)3 and cellular communications (50–60 billion $yyear globally by the year 2000).4 On the basis of the vast utility of quartz, it has become among the most well-characterized materials known, both in terms of property-value accuracy and depth of scientific investigation. The processing of quartz crystals prior to utilization in the aforementioned devices generally requires an etching step for the purposes of removing surface damage produced by the preceding steps, such as cutting, lapping, and polishing. Etching has been studied extensively for more than 100 years.5–15 The etchants are aqueous-based, including ammonium bifluoride, hydrofluoric acid, and ammonium fluoride-HF solutions. In addition to removing material from the surfaces, the aqueous etchants produce etch channels9,11,12,15 that are linear and anisotropic with respect to the crystallographic First presented at the 1996 IEEE International Frequency Control Symposium, June 5 – 7, 1996, Honolulu, Hawaii. a) Presently at the Department of Ceramic and Materials Engineering, Olin Hall, Box 340907, Clemson, South Carolina 29634-0907. b) Author to whom correspondence should be addressed. 3144
http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 11, Nov 1998
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axes, as shown in Fig. 1. After a few micrometers are removed from the surfaces, the etch channels becomes clearly visible at magnifi
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