Surface Layering Near Room Temperature in a Nonmetallic Liquid

Oscillatory density profiles (layers) have been observed at the free surfaces of many liquid metals at and above room temperature [1]. A surface-layered state has been previously reported only in one dielectric liquid, tetrakis(2-ethylhexoxy)silane (TEHOS), and only at lower temperatures [2]. We have used x-ray reflectivity to study a molecular liquid, pentaphenyl trimethyl trisiloxane. Below T$\sim $ 267K (well above the freezing point for this liquid), density oscillations appear at the surface. This liquid has a higher $T_{c}$ ($\sim $1200K) than TEHOS ($\sim $950K), so that layers appear at $T/T_{c} \quad \approx $ 0.2 in both cases. Our results indicate that surface order is a universal phenomenon in both metallic and dielectric liquids, and that the underlying physics is likely to be the same since layers always appear at T$<\sim $0$.$2$T_{c}$ as theoretically predicted [3] \\[3pt] REFERENCES: \\[0pt] [1]. e.g. O. M. Magnussen \textit{et al}., Phys. Rev. Lett. \textbf{74}, 4444 (1995) \\[0pt] [2]. H. Mo et al. \textit{Phys. Rev. Lett.} \textbf{96}, 096107 (2006); \textit{Phys. Rev. B} 76, 024206 (2007) \\[0pt] [3]. e.g. E. Chac\'{o}n et al., Phys. Rev. Lett. \textbf{87}, 166101 (2001)