| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016) | |
| Thin Films | Tuesday Sessions |
| Session TF-TuP |
| Session: | Thin Films Poster Session |
| Presenter: | Koichiro Yamakawa, Gakushuin University, Japan |
| Authors: | K. Yamakawa, Gakushuin University, Japan A. Ishibashi, Gakushuin University, Japan I. Arakawa, Gakushuin University, Japan |
| Correspondent: | Click to Email |
Field and co-workers recently reported that the strong electric field, whose strength may exceed 108 V/m, exists in a vacuum-deposited film of dipolar molecules and attributed it to the spontaneous alignment of the molecular axes [1-4]. They have utilized two experimental techniques: the direct measurement of the electrostatic potential at the film surface for N2O [1] and reflection-absorption infrared spectroscopy for N2O and CO [2-4]. In the latter method, the infrared absorption band due to the intramolecular stretching vibration split into two peaks owing to the coupling with phonons in the film, so that the temperature dependence of the split was attributed to the intense electric field. In order to judge the validity of their argument, one needs experimental data obtained by other techniques as well as theoretical models to explain the mechanism where such thermodynamically unstable film structure is realized simply after vapor deposition onto a cold substrate. In the present study, we directly determine the strength of the electric field in CO films using induced infrared absorption due to H2.
A sample chamber equipped with a liquid-helium continuous-flow cryostat was in the ultra-high vacuum condition after baking at 373 K for 24 hours. The substrate was a gold plate mechanically fixed on a copper block placed at the end of the cryostat. Temperatures of the substrate were measured with a silicon diode. We prepared two kinds of samples on the substrate maintained at 5 K; I) CO and H2 were premixed in a gas handling with the molar ratio of CO/ H2 = 10 and were deposited; II) We condensed two gasses alternatively through different variable leak valves to form their periodic films, where the thickness of each CO (H2) film was ~40 (1) monolayer. Fourier transform infrared spectroscopy was performed with a HgCdTe detector in the reflection configuration.
For both the kinds of samples, infrared spectra showed a strong absorption peak at 2142 cm-1 due to the CO stretch along with satellite features at 2047 and 2092 cm-1. In addition, weak absorption peaks were found in the H2 stretch region. We will give detailed assignment of these peaks and will determine the strength of the electric field in each film from the infrared absorption intensity of the H2 stretch. Temperature dependence of the field strength will be also discussed.
[1] R. Balog et al., Phys. Rev. Lett. 102, 073003 (2009).
[2] J. Lasne et al., Phys. Chem. Chem. Phys. 17, 20971 (2015).
[3] J. Lasne et al., Phys. Chem. Chem. Phys. 17, 30177 (2015).
[4] A. Rosu-Finsen et al., Phys. Chem. Chem. Phys. 18, 5159 (2016).