Laser-based guided ultrasonic waves: from macroscopic properties to nanoscopic models
Event details
| Date | 07.05.2013 |
| Hour | 13:15 › 14:15 |
| Speaker |
Prof. Dr. Peter Hess Bio : Prof. Dr. Peter Hess is professor (retired) of Physical Chemistry at University of Heidelberg since 1980. Previously, he studied for a diploma in chemistry at the Karlsruhe Institute of Technology (KIT) and for a PhD thesis on “Physical adsorption processes” (1968) and then for the habilitation thesis on “Energy transfer processes in gases” (1972) at Ruprecht-Karls-University in Heidelberg. From 1974 he was research fellow at the Department of Chemistry, University of California (Berkely, USA) and after 1980, he was regularly visiting scientist at Almaden Research Laboratories, IBM, San Jose, California, USA for shorter time periods. He has been active in several research field. (1) Laser-based photoacoustics in gases: chemical relaxation and trace gas analysis. (2) Laser-based surface acoustic waves (SAWs) and wedge waves (WWs): all-optical nondestructive evaluation (NDE), linear and nonlinear elastic constants and mechanical properties of superhard materials, nonlinear behavior and fracture strength of solids and solitary surface waves. (3) Laser-induced desorption, ablation, and surface processing: time-of-flight mass spectrometry of specific surface reactions induced by pulsed laser irradiation and measurement of the thermal stability of surface end groups and functionalizations. (4) Silicon surface spectroscopy and chemistry: in situ and real-time diagnostics of surface reactions (e.g. functionalization, oxidation) on silicon with monolayer resolution (FTIR spectroscopy, IR-UV spectroscopic ellipsometry), and atomic force microscopy (AFM). He produced about 300 publications in scientific journals, one worldwide and one European patent on functionalization and processing of silicon surfaces. He was editor or co-editor of 6 books (Springer 1987, 1989; Elsevier 1995, 1999; SPIE 1997, 2000), chairman or co-chairman of ten international conferences. |
| Location | |
| Category | Conferences - Seminars |
Abstract : Current progress in laser ultrasonics employing guided elastic waves is reviewed [1]. Excitation and detection of linear and nonlinear ultrasonic waves by a laser pump-probe setup will be described. This includes ultrasound in three-dimensional (3D) bulk waveguides such as rods or rails, two-dimensional (2D) surface acoustic wave (SAW) pulses, traveling along surfaces and penetrating only about one wavelength deep into the solid, and one-dimensional (1D) wedge waves (WWs), propagating at the apex of a wedge with the elastic energy remaining at the tip of the edge. The emerging field of laser-based excitation and detection of linear and nonlinear WWs and their potential applications will be discussed in detail [2]. The dependence of dispersion and diffraction of ultrasound on the geometry of the system and dimension of wave propagation is considered with respect to the degree of nonlinearity that can be achieved by pulsed laser excitation of elastic waves. Note that with short laser pulses of nanosecond to femtosecond duration a localized desintegration of solids into electrons and ions (plasma) and, as a consequence, efficient formation of steep shocks with gigapascal to terapascal pressure can be achieved by the resulting confined micro-explosions.
Recent applications of linear guided ultrasonic waves (3D to 1D) in nondestructive evaluation (NDE) will be presented. Novel developments in the use of guided bulk waves to monitor flaws in rails, for example, as well as the problems connected with this approach will be discussed. Another important application is the characterization of real partially closed surface-breaking cracks by linear SAW pulses, since failure usually starts at the surface. One-dimensional WWs provide new possibilities for sensitive evaluation of defects or cracks at the apex of wedges, e.g., in cutting tools or turbine blades. On the other hand, linear WWs recently were also applied in sensor devices and in actuators such as ultrasonic motors or streaming in fluidics.
Strongly nonlinear SAW and WW pulses developing shock fronts during propagation due to nonlinearity could be realized experimentally. Shocked SAW pulses were used to measure the fracture strength of single-crystal silicon for selected crystallographic planes and directions. The measured well-defined critical fracture stresses can be compared directly with ab initio calculations if theoretical strengths for these particular configurations are available. With the experimental and theoretical information it is possible to describe the tensile bond-breaking process along the weakest Si{111} cleavage plane on the basis of the Griffith approach. This model introduces a characteristic length scale in the nanometer range. The length scale is identified with the distance between the (111) planes in the ideal crystal lattice in the case of the theoretical strength and the size of the largest defect at the surface in the real crystal, where nucleation of the surface-breaking crack with lowest critical fracture stress takes place. On the basis of the normalized model the defect size can be estimated. The critical fracture stress measured for shock waves propagating along the Si{111} cleavage plane in the <11-2> direction was 4 GPa, while the corresponding theoretical stress for tensile opening of the perfect lattice is 22 GPa. These values point to a defect size of about 9 nm at the surface of the silicon specimen that is responsible for impulsive failure. Thus, this method allows the determination of the effective strength of real materials and the size of the defect responsible for failure. The latter essentially depends on the manufacturing process (“engineering strength”).
[1] P. Hess, A. M. Lomonosov, A. P. Mayer, Ultrasonics, to be published
[2] A. M. Lomonosov, P. Hess, A. P. Mayer, Appl. Phys. Lett. 101, 031904-1-4 (2012).
Recent applications of linear guided ultrasonic waves (3D to 1D) in nondestructive evaluation (NDE) will be presented. Novel developments in the use of guided bulk waves to monitor flaws in rails, for example, as well as the problems connected with this approach will be discussed. Another important application is the characterization of real partially closed surface-breaking cracks by linear SAW pulses, since failure usually starts at the surface. One-dimensional WWs provide new possibilities for sensitive evaluation of defects or cracks at the apex of wedges, e.g., in cutting tools or turbine blades. On the other hand, linear WWs recently were also applied in sensor devices and in actuators such as ultrasonic motors or streaming in fluidics.
Strongly nonlinear SAW and WW pulses developing shock fronts during propagation due to nonlinearity could be realized experimentally. Shocked SAW pulses were used to measure the fracture strength of single-crystal silicon for selected crystallographic planes and directions. The measured well-defined critical fracture stresses can be compared directly with ab initio calculations if theoretical strengths for these particular configurations are available. With the experimental and theoretical information it is possible to describe the tensile bond-breaking process along the weakest Si{111} cleavage plane on the basis of the Griffith approach. This model introduces a characteristic length scale in the nanometer range. The length scale is identified with the distance between the (111) planes in the ideal crystal lattice in the case of the theoretical strength and the size of the largest defect at the surface in the real crystal, where nucleation of the surface-breaking crack with lowest critical fracture stress takes place. On the basis of the normalized model the defect size can be estimated. The critical fracture stress measured for shock waves propagating along the Si{111} cleavage plane in the <11-2> direction was 4 GPa, while the corresponding theoretical stress for tensile opening of the perfect lattice is 22 GPa. These values point to a defect size of about 9 nm at the surface of the silicon specimen that is responsible for impulsive failure. Thus, this method allows the determination of the effective strength of real materials and the size of the defect responsible for failure. The latter essentially depends on the manufacturing process (“engineering strength”).
[1] P. Hess, A. M. Lomonosov, A. P. Mayer, Ultrasonics, to be published
[2] A. M. Lomonosov, P. Hess, A. P. Mayer, Appl. Phys. Lett. 101, 031904-1-4 (2012).
Practical information
- General public
- Free
Organizer
- IGM
Contact
- Géraldine Palaj