Helium on planar and nanostructured alkali-metal surfaces

Abstract

We investigate the effects ͑on the wetting characteristics of helium below 3 K͒ of tailoring an alkali-metal surface by incorporating a regular array of nanoscopic indentations. We establish the prewetting line of helium on semi-infinite planar Cs up to 3 K in the frame of a finite-range temperature-dependent density-functional theory, and examine the modifications introduced in the isotherms when the substrate is covered with a periodic lattice of parabolic cavities. We show that, both for the planar and nanostructured surfaces, the unstable regions of the isotherms are stabilized by nucleation of drops and/or bubbles. Results corresponding to nonwettable Cs surfaces are compared with those obtained both for planar and nanopatterned Na substrates, where wetting at zero temperature is instead expected to occur, for a planar surface, preceded by a first-order prewetting transition.

Density functional theory of doped superfluid liquid helium and nanodroplets

“…In particular, the prewetting line and isotherms for helium-Cs adsorbed on nano-patterned surfaces with parabolic cavities were studied by the finite temperature DFT approach. 51,272 The results obtained for Cs surfaces (non-wettable) were compared with the corresponding planar Na (wettable at T = 0) and nano-patterned Na surfaces.…”

“…He on a Na patterned surface 272. The panels show some illustrative equilibrium configurations for different coverages; the panels display the isodensity surfaces drawn at a value which is half the bulk liquid density at T = 0 (ρ 0 = 0.0218Å −3 ).…”

Boundary of prewetting transition of Ar on a Li surface

“…7 In the last few decades, a large number of studies have been carried out to achieve a better understanding of the phenomenon using different theoretical and simulation techniques. [8][9][10][11][12][13][14][15][16][17][18][19][20][21] Although considerable progress has been made, [22][23][24] the exact region in which the prewetting transition for a given system can be found is still in dispute, such as Ar on alkali-metal surfaces. 14,15,20 With a substrate potential of moderate strength, the prewetting transition corresponds to a jump from a thin adsorbed film to a thick adsorbed film at the surface when the pressure P ͑or chemical potential ͒ is below the bulk vaporliquid saturation pressure P sat ͑or chemical potential sat ͒.…”

Size dependence of the contact angle of a nanodrop in a nanocavity: Density functional theory considerations

“…One such theory, the density functional theory (DFT) in a canonical ensemble, was successfully applied to the description of nanodrops on smooth planar solid surfaces as well as to droplike objects (bumps, bridges between walls of nanoslits, etc.) [13][14][15][16][17][18]. In this paper, DFT is employed to examine a nanodrop in a cavity of a solid surface, focusing on the dependence of the contact angle that the nanodrop makes with the wall of the cavity on the size of the drop.…”