Probing Hydrophilic Interface of GaN/Water by Nanoultrasonics
Chih-Chiang Shen1*, Pierre-Adrien Mante1, Vitalyi Gusev2, Jer-Lai Kuo3, Jinn-Kong Sheu4, Chi-Kuang Sun1,5,6
1Department of Electrical Engineering and Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan
2Institut des Molécules et Matériaux du Mans, UMR CNRS 6283, Université du Maine, Le Mans, France
3Institute of Atomic and Molecular Science, Academia Sinica, Taipei, Taiwan
4Institute of Electro-Optical Science and Engineering and Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan, Taiwan
5Molecular Imaging Center, National Taiwan University, Taipei, Taiwan
6Graduate Institute of Biomedical Electronics and Bioinformatics and Center for Optoelectronics Medicine, National Taiwan University, Taipei, Taiwan
* presenting author:Chih-Chiang Shen,
Nanoultrasonics technique was used to investigate the layer structures and viscoelastic characterization of water at the hydrophilic interface with GaN. By measuring the reflection of THz acoustic phonon at a GaN surface with and without water, the spatial distributions of the density, the elasticity and the viscosity of interfacial water are then obtained and the water organization and structure are characterized. The spatial distribution of the density for water at the interface with GaN shows a second maximum near 5 Å, revealing a second ordered layer. According to rheology, the second interfacial layer exhibits viscous modulus being larger to the elastic modulus that is viscous liquid (fluid) behavior (loss factor > 1) compared with that of the fist interfacial layer with elastic solid properties.

Keywords: Nanoultrasonics, Interfacial Water