PLU for adhesion/bonding monitoring

First experimental observation in the PLU experiments on nanometers-thick layer on a substrate, of an oscillation frequency, which is much lower than eigen frequencies of the layer was reported [see ref.]. This frequency was identified as an observation of mass-on-spring oscillation (a motion of a thin metal layer on adhesion bond). Advanced models of the mechanical interfaces were developed to support theoretically the PLU experiments, conducted in different Laboratories in Asia and Europe:

1. by Prof. Chi-Kuang Sun (National Taiwan University) - the generation of CAPs, at frequencies over 1 THz, by depositing a single-layer absorbing material (graphene) on the surface of a transparent substrate [see ref.] (in these experiments the thermal expansion of the adhesion bond was in the origin of thermoelastic contribution to the generated CAP), - probing hydrophilic interface of solid/liquid-water by nanoultrasonics [see ref.]
2. by Prof. Thomas Dekorsy and Dr. Mike Hettich (Konstanz University) - confined viscoelastic polymer nano-layers [see ref. 1, ref. 2], adhesion in Al/Si membranes [see ref. 1, ref. 2] and in rolled-up GaAs/InGaAs multilayer tubes [see ref.],
3. by Prof. Andrey Akimov (Nottingham University) and Dr. Samuel Raetz (Le Mans University) - GHz frequencies elastic coupling of van der Waals nanolayers to the substrate and in the heterostructures [see ref. 1, ref. 2]. The theory supporting the experiments [see ref.], revealed that adhesive coupling of van der Walls layers to periodic nanogratings leads to hybridization of photo-generated GHz flexural waves in the layer with mass-on-spring vibrations.

Very fruitful, for the extraction of quantitative information from the experimental data, were the theories suggested for several PLU experiments on elasticity of an assembly of disordered nanoparticles interacting via either van der Waals – bonded or covalent-bonded in a coating layer [ see ref. ] and on the influence of nanocontacts nature on the mechanical properties of a silica nanoparticle assembly [see ref] which were conducted by Prof. Pascal Ruello and Dr. Gwenaelle Vaudel in the frame of the contracts with French industry.