https://doi.org/10.1140/epjst/e2009-00953-4
Observation of slowly decreasing molecular oscillations in ultrathin liquid films using X-ray reflectivity
1
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: cjyu@postech.ac.kr
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
