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Czochralski grown silicon crystals contain interstitially dissolved oxygen which diffuses on heating to form precipitates of silica. We have examined these precipitates by small angle neutron scattering (SANS) in the Q-range 0.05 Å-1-1. The obtained SANS patterns reveal pronounced anisotropic intensity distributions which resemble the symmetry of the host crystal. The SANS spectra show an anisotropic central peak at Q<0.1 Å-1 due to the single particle shape and a number of weak intensities for larger Q-values. These weak side maxima are considered correlation peaks or quasi-elastic interference peaks. They show, however, an unexpected and distinct temperature dependence: with decreasing temperature below values of 220 K their intensity is lost slowly, but reversibly. At T = 50 K only the central peak from the single-particle scattering remains unchanged. Upon heating, the correlation peaks regain their former value of intensity and Q-position without any evidence of thermal hysteresis.

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ROTAX is a new type of time-of-flight crystal-analyzer spectrometer for inelastic neutron scattering on single crystals. The instrument uses a programmable spinning analyzer to perform scans through a wide range of (Q, ω)-space. The flexibility of ROTAX has been extended by a new type of scan, the ‘linear-Q’ scan. We describe these scans and their preparation for a specific problem. Further we will describe the interpretation of the gathered data and focus on the transformation of the original position and time-of-flight coordinates into the relevant coordinates of reciprocal space and energy transfer. Finally, this will be demonstrated with data from phonons in copper.

ROTAX, a new type of time-of-flight crystal analyser spectrometer for neutron inelastic scattering from single crystals is now installed at ISIS. By utilising its non-uniformly rotating crystal analyser, ROTAX provides a wide variety of time-of-flight scans through (Q, ω) space. A description of the instrument and its software is given as a practical guideline for the use of this novel instrument. Phonon scattering data obtained from a Cu single crystal are presented.

The formation of silicon oxide precipitates from Czochralski grown silicon depends on the time and temperature of the heat treatment as well as on the initial content of interstitially dissolved oxygen. Samples containing between 5×1017 Oi/cm3 and 13×1017 Oi/cm3 have been heated at 750° C for 96 h. SiO2 precipitates of various shape and size have been obtained and investigated by means of small angle neutron scattering (SANS) in the Q-range 0.05 Å-1-1. The obtained SANS patterns reveal a typical anisotropy of their intensity distribution, which splits into a central peak at Q<0.1 Å-1 due to the shape of the individual particles and a number of weak intensities for large Q-values, originating from a correlation between defects, possibly between the precipitates. While these correlation peaks in the SANS patterns are seen best for rather low values of about (5–7)×1017 Oi/cm3 oxygen content, the central peak anisotropy is most pronounced for higher values of ca 10×1017 Oi/cm3. The integrated intensity of the central peak increases with increasing initial oxygen content. For comparison, untreated samples of the same initial oxygen content do not reveal any anisotropic SAN scattering or a broadened central peak beam.

We have continued our investigations on magnetic excitations in the olivine-type silicates with neutron scattering measurements on Co2SiO4. The excitation spectra have been compared with classical spin-wave model calculations. As already reported for Fe2SiO4also the Co-compound shows a strong coupling between magnons and phonons. Further, we could confirm a magnetic pre-ordering above the Néel-temperature of 49 K.

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