Observation of slowly decreasing molecular oscillations in ultrathin liquid films using X-ray reflectivity
Department of Physics, Soongsil University, Seoul, 156-743, Korea
2 Pohang Accelerator Laboratory, San31, Hyoja-Dong, Nam-Gu, Pohang, Gyeongbuk, 790-784, Korea
3 Department of Physics, Hanyang University, 17 Haengdang-Dong, Sungdong-Ku, Seoul, 33-791, South Korea
Corresponding author: email@example.com
We studied ~0.5 μm and 30–80 Å thick films of a normal dielectric liquid, tetrakis(2-ethylhexoxy)silane (TEHOS), at temperature range 228–286 K, deposited onto silicon (111) substrate with native oxide using X-ray reflectivity. TEHOS is spherical with size ~10 Å, non-polar, non-reactive, and non-entangling; TEHOS has been reported to show interfacial layering at room temperature and surface layering at 0.23 Tc (Tc≈ 950 K). For films m thick, the reflectivity data did not change significantly as a function of temperature; for films 30–80 Å thick, the reflectivity data did change. The data could be fitted with an electron density model composed of a minimum necessary number of Gaussians and a uniform density layer with error-function broadened interfaces. When the film thickness is 60–80 Å below 246 K, we found that the interface and the surface layering coexist but do not overlap. When the film thickness is 30–40 Å below 277 K, they overlap and the electron density profile shows slowly decreasing molecular oscillations at the air-liquid interface.
© EDP Sciences, Springer-Verlag, 2009