title: Precision and accuracy in film stiffness measurement by Brillouin spectroscopy.
abstract: The interest in the measurement of the elastic properties of thin films is witnessed by a number of new techniques being proposed. However, the precision of results is seldom assessed in detail. Brillouin spectroscopy (BS) is an established optical, contactless, non-destructive technique, which provides a full elastic characterization of bulk materials and thin films. In the present work, the whole process of measurement of the elastic moduli by BS is critically analyzed: experimental setup, data recording, calibration, and calculation of the elastic moduli. It is shown that combining BS with ellipsometry a fully optical characterization can be obtained. The key factors affecting uncertainty of the results are identified and discussed. A procedure is proposed to discriminate factors affecting the precision from those affecting the accuracy. By the characterization of a model transparent material, silica in bulk and film form, it is demonstrated that both precision and accuracy of the elastic moduli measured by BS can reach 1% range, qualifying BS as a reference technique.
authors.affiliation: Energy Department and NEMAS Center, Politecnico di Milano, Via Ponzio 34∕3, 20133 Milano, Italy.
authors.forename: M G
authors.initials: MG
authors.lastname: Beghi
authors.forename: F
authors.initials: F
authors.lastname: Di Fonzo
authors.forename: S
authors.initials: S
authors.lastname: Pietralunga
authors.forename: C
authors.initials: C
authors.lastname: Ubaldi
authors.forename: C E
authors.initials: CE
authors.lastname: Bottani