Speaker
Description
Hydrogen adsorption and absorption at solid surfaces is a prototype surface reaction, where fundamental concepts of gas-surface interaction are embodied. As such, hydrogen interaction with solid surfaces has been extensively studied in the surface science community [1]. To investigate the behavior of hydrogen at surfaces, our group has developed nuclear reaction analysis (NRA), which allows us to quantitatively measure the H depth distribution and H location in materials [2], and resonance-enhanced multiphoton ionization combined with atomic/molecular hydrogen beams, which allows us to detect the internal quantum states of hydrogen including the spin and ro-vibrational motion [3]. With these techniques, we have studied molecular physisorption, dissociative adsorption, and diffusion into the bulk of hydrogen on various metals such as Pd, V, Fe and Ti and metal oxides such as TiO2, CeO2 and perovskite oxides.
Palladium and Vanadium are typical H-absorbing metals. We demonstrate the hydrogen diffusion across the Pd surface can be controlled by molecular cap and surface alloy formation [4]. By applying low-energy hydrogen ions, furthermore, metastable hydride states were formed in the near-surface region of Pd and V films. The resistance of the films was found to change as the films relax from the metastable states to stable states. By measuring the time evolution of the film resistance, the diffusion of H in the films were analyzed, which revealed a crossover from a classical thermal regime to a quantum regime [5]. Even if the substrate does not absorb hydrogen exothermically, hydrogen ions penetrate the surface and migrate into the near-surface region causing heavy H doping. The depth distribution measured by NRA was consistent with SRIM simulations. As observed by photoemission spectroscopy and transport measurements, it is shown that hydrogen acts as an electron donor for most metal oxides including TiO2 and SrTiO3 [6]. From the depth profile of H, the diffusion coefficient in TiO2 is analyzed.
- K. Fukutani et al., Chem. Rec. 17, 233 (2017).
- M. Wilde and K. Fukutani, Surf. Sci. Rep. 69 (2014) 196; T. Ozawa et al., Nat. Commun. 15, 9558 (2024).
- H. Ueta et al., Front. Chem. 11, 1258035 (2023); Y. Nagaya et al., J. Chem. Phys. 155, 194201 (2021).
- S. Ogura et al., J. Phys. Chem. C 117 (2013) 9366; K. Namba et al., PNAS 115, 7896 (2018).
- T. Ozawa et al., J. Phys. Chem. Solids 185, 111741 (2024).
- Y. Ohashi et al., J. Phys. Chem. C 123, 10319 (2019); N. Nagatsuka et al., J. Chem. Phys. 152, 074708 (2020); G.C. Lim et al., J. Am. Chem. Soc. 146, 32013 (2024).
