Departamento de Física (FC-DF)
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- A differential mechanical profilometer for thickness measurementPublication . Alves, J. Maia; Brito, M. C.; Serra, J. M.; Vallêra, A. M.A low cost differential profilometer based on standard commercial displacement transducers is fully described. Unlike most common profilometers this device can be used to measure the thickness profile of samples having both surfaces irregular. A sensitivity of about 0.2 mm, independent of the sample thickness is achieved.
- High temperature sound velocity measurement with piezoelectric transducersPublication . Alves, J. Maia; Vallêra, A. M.A technique for high temperature sound velocity measurement using piezoelectric transducers, that avoids the existence of the usual high temperature bond between the sample and the buffer, was developed. This bond is frequently responsible for a large attenuation and distortion of the sound field, with a consequent inaccuracy in the experimental results. This technique was successfully used by the authors to make good quality measurements of sound velocity in iron silicon single crystals from room temperature to T 1000 °C, unlike other authors who report strong attenuation in different regions of this temperature range for similar samples. The furnace, which is only 35 mm wide, allows work under magnetic field and a controlled atmosphere up to 1300 °C.
- Measurement of residual stress in multicrystalline silicon ribbons by a self-calibrating infrared photoelastic methodPublication . Brito, M. C.; Pereira, J. P.; Maia Alves, J.; Serra, J. M.; Vallêra, A. M.This article reports on a method for the measurement of residual stress in multicrystalline silicon ribbons, based on the infrared photoelastic technique. This self-calibrating method allows the in situ determination of the photoelastic coefficients and can thus be used for any crystal orientation. The method was validated by the experimental determination of the photoelastic coefficient of monocrystalline (100) silicon wafers and by comparison with strain measurements using asymmetrical x-ray diffraction. The distribution of residual stress in multicrystalline silicon ribbons was also measured. The results showed strong evidence for tensile stress in the central region and compressive stress near the edges of the ribbons. Both the measured residual stress and the photoelastic coefficient distributions are correlated to grain boundaries