ABSTRACT
Time resolved pump and probe acoustics and first-principles calculations were employed to assess elastic properties of the TbMnO3perovskite manganite having orthorhombic symmetry. Measuring sound velocities of bulk longitudinal and shear acoustic waves propagating along at least two different directions in the high symmetry planes (100), (010) and (001), provided a powerful mean to selectively determine the six diagonal elastic constantsC11= 227 GPa,C22= 349 GPa,C33= 274 GPa,C44= 71 GPa,C55= 57 GPa,C66= 62 GPa. Among the three remaining off-diagonal ones,C23= 103 GPa was determined with a bissectrice direction. Density functional theory calculations with colinear spin-polarized provided complementary insights on their optical, elastic and magnetoelastic properties.
ABSTRACT
A setup combining surface Brillouin light scattering with a high-temperature chamber has been developed. The temperature of the sample is controlled with a Bühler HDK chamber for optical measurements (maximum temperature of 1600 °C), in controlled atmospheres or high vacuum (10-6 mbar). This setup allows the study of sound velocity of surface acoustic waves and of the elastic constants of opaque thin films and coatings in situ as a function of temperature from surface Brillouin light scattering, by analyzing the backscattered light from the sample at a fixed angle of incidence. In this paper, we will demonstrate the applications of this setup for metallic glass thin films devitrification study and evaluation of high temperature elastic properties of hard nitride coatings. This kind of study using surface acoustic waves is rare, in contrast to those made on transparent bulk materials.
ABSTRACT
The photoelastic response of periodic arrays of stripes attached to the surface of a substrate and illuminated by an ultrashort laser pulse were investigated. The samples were gold arrays on silicon and aluminum arrays either on crystalline quartz or on silicon. The metallic stripes had submicrometer lateral dimensions and the spatial periods ranged from about 1 microm up to 5 microm. The substrate being transparent (quartz) or slightly absorbing (silicon) at the laser wavelength (lambda = 750 nm), a laterally modulated thermal stress is generated near the surface of the substrate when a light pulse illuminates the structure. The studies of vibrations involved by the subsequent relaxation processes show that surface acoustic waves at frequency as high as about 5 GHz are excited with the samples consisting of aluminum stripes. In the case of the aluminum samples with the largest lateral spatial periods (aluminum on quartz), the surface acoustic wave propagates outside the illuminated area. In the case of the gold samples, a normal mode of individual bars is observed instead. Experimental evidence shows that these behaviors are mainly governed both by the lateral spatial period of the structure and by the density of the metal.
