Measurements of the mechanical Q of single-crystal silicon at low temperatures

Abstract

Measurements of the mechanical quality factor Q in a single crystal of silicon vs. temperature have been made. A value of 2x lO 9 has been measured at T=3.5K.We have been studying large dielectric and semiconductor single crystals as possible gravitational wave detectors. 1 These detectors are frequently cylinders instrumented to detect vibrations of the first longitudinal mode. One of the important desirable properties is a high mechanical quality factor Q. With an ideal transducer the sensitivity to gravitational waves is proportional to Q. The inverse quality factor Q-1 is a direct measure of the dominant mechanism of the attenuation of first sound. Measurements of Q are frequently the best way to gather information concerning the various internal loss mechanisms of a substance. In the region of very high Q (low loss) this sometimes is the only easy method. We report here on measurements on a large single crystal of silicon whose Q values exceed 10 9.The crystal was manufactured by Monsanto by the zero-dislocation Czochralski process in the form of a cylinder (diameter 10.6 cm, length 22.9 cm, mass 4.9 kg), with the [111] axis parallel to the cylinder axis. The ends were polished by the University of Rochester Institute of Optics personnel to better than one wavelength of light. The barrel of the crystal, somewhat wavy from the crystal growing process, was left in this state so that its edge deviates from straightness by -1 mm. The crystal is a p-type

Optical absorption of ion-beam sputtered amorphous silicon coatings

“…The presently used test-mass material fused silica becomes unsuitable at low temperatures due to high mechanical loss and thus high thermal displacement noise [5]. A promising replacement material with low mechanical loss at cryogenic temperatures is crystalline silicon (cSi) [6,7]. cSi has several other interesting properties including zero crossings of the thermal expansion coefficient at 120 K and 20 K resulting in low thermo-elastic noise [8,9] and a low optical absorption at the telecommunication wavelength of 1550 nm [10,11].…”

Low temperature study of loss mechanisms of mechanical oscillators

“…Experiments are underway to improve Q by minimizing the impact of metal films. A better low temperature Q (1 × 10 9 ) has been reported by McGuigan et al [16] on a suspended silicon cylinder. Although their geometry is unapplicable to MEMS, it certainly encourages improvement efforts.…”

High index top layer for multimaterial coatings

“…Crystalline silicon (cSi) is a potential candidate material due to its low mechanical loss [23,26], low optical absorption [27,28], and various industrial applications providing large scale substrates. The mechanical loss of cSi at 20 K can be as low as 3×10 −7 .…”