Helium in Nanoconfinement: Interplay Between Geometry and Wetting Behavior

Density functional theory of doped superfluid liquid helium and nanodroplets

“…The most recent research employing DFT to study the adsorption of helium samples on various substrates has been reviewed in Ref. 286. The issues addressed in this review include the deposition and spreading of helium droplets on flat alkali metal surfaces; the determination of isotherms; the construction of the phase diagram of helium on such substrates; the adsorption of helium on spherical and cylindrical surfaces; the filling of wedges and the filling/emptying transitions at T = 0 taking place at fixed values of the wedge opening angle; 287 the filling of infinite polygonal pores, and the adsorption on planar surfaces structured with an array of parabolic nanocavities.…”

Helium mediated deposition: Modeling the He−TiO2(110)-(1×1) interaction potential and application to the collision of a helium droplet from density functional calculations

“…The analysis of wetting and spreading properties of quantal fluids (e.g., helium or para-hydrogen films) adsorbed on different substrates has stimulated much experimental and theoretical work during the last years (see, for example, Refs. [1][2][3][4]. Besides obtaining a better microscopic understanding of the fundamental physics upon collision of a quantal fluid with a surface, the fruitful application of helium nanodroplets to the soft-landing deposition of catalytic species (e.g., metallic nano-clusters) immersed within the drop on the surface of different substrates [5][6][7] has provided a renewed impetus for further theoretical works.…”

“…Although this cluster size is much smaller than the average sizes formed through the experimental setup 7 (i.e., nanodroplets with more than 10 6 He atoms), it is considered large enough to provide meaningful physical insight into the process and, at the same time, keeping the computational calculation feasible. Pioneering TDDFT simulations of 4 He nanodroplets interacting with (weakly) attractive alkali metal surfaces were carried out by Giacomazzi et al 1 As far as we are aware, our work represents the first study considering the case of a metal-oxide surface. With a well-depth more than an order of magnitude larger than in the case of alkali metal surfaces (10 vs. 0.6 meV for a Cs surface from Ref.…”

“…Section II provides the details on the construction of the He@TiO 2 (110)-(1×1) potential energy surface, including the analysis of the different potential models, considering the inclusion of long-range dispersion corrections, and testing the validity of the pairwise additive approach in the case of two He atoms interacting with the surface. A very brief outline of the TDDFT method and the analysis of its application to the collision dynamics of a 4 He 300 cluster impinging the He−TiO 2 (110)-(1×1) surface are provided in Sec. III.…”

Hydrodynamical description of long-wavelength density fluctuations of helium in wedges

“…In forthcoming sections I shall focus on sequence ͑b͒ for the average contact angle of helium on planar Cs, c = 36°͑see, i.e., Ref. 19 for a review on experimental data and theoretical computations of c ͒.…”