The microscopic properties of the inner surface of the cavities of Anopore and Nuclepore membranes are investigated with scanning electron microscopy (SEM), nitrogen adsorption isotherms, and deuterium nuclear magnetic resonance (2H‐NMR). Useful information about the cavity orientation and morphology, and internal surface area is obtained. Analysis of SEM photographs yields estimates of the surface area and the porosity of these membranes which complements the adsorption results. The orientation of liquid crystals permeated in the cavities of Anopore and Nuclepore membranes is probed with the 2H‐NMR technique. It is found that the orientation of the liquid crystal molecules is governed by the confining volume and surface conditions. The 2H‐NMR spectral line shape of the confined liquid crystal also provides information on the substrate morphology and roughness that is consistent with SEM and adsorption experiments.

Characterization of the cylindrical cavities of Anopore and Nuclepore membranes

$^{2}\mathrm{H}$ NMR of a liquid crystal confined to submicron cylindrical cavities, in a 17 K interval above the nematic-isotropic transition, reveals a weakly orientationally ordered molecular layer at the cavity wall governed by local interactions. The order (${\mathit{S}}_{0}$=0.02) is temperature independent so that a partial wetting is realized with no prewetting transition expected. A molecular exchange rate between the surface layer and the bulk is measured to be \ensuremath{\sim}${10}^{3}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. The coherence length measuring the order penetrating further into the cavity is described by \ensuremath{\alpha}=0.4 and ${\ensuremath{\xi}}_{0}$=0.6 nm.

Ordering and self-diffusion in the first molecular layer at a liquid-crystal-polymer interface.

Finite-size scaling of He 4 at the superfluid transition

We have studied the superfluid response of 3He-4He mixture films adsorbed onto porous gold for a wide range of 3He and 4He coverages, focusing on submonolayer superfluidity. At T = 0, 3He appears to float on top of 4He and can be viewed as a second substrate that induces its own inert layer. Depending on the 4He content, the zero-temperature superfluid mass and the superfluid onset temperature either saturate or vanish with the addition of 3He. The T = 0 superfluid-insulator phase boundary, which can be described by a simple function, is found in the 3He-4He coverage plane.

Effect of 3He on submonolayer superfluidity.

Nuclear-magnetic-resonance measurements of the magnetization of $^{3}\mathrm{He}$ on thin $^{3}\mathrm{\ensuremath{-}}^{4}$He mixture films show discrete structure as a function of $^{3}\mathrm{He}$ coverage over the range 0.0055\ensuremath{\le}${d}_{3}$\ensuremath{\le}4 layers at a $^{4}\mathrm{He}$ coverage of 44 \ensuremath{\mu}mol/${\mathrm{m}}^{2}$ for 30\ensuremath{\le}T\ensuremath{\le}250 mK in a weakly polarizing 2-T field. A steplike doubling of the magnetization at ${d}_{3}$\ensuremath{\approxeq}0.8 layers and a second less pronounced step at ${d}_{3}$\ensuremath{\approxeq}1.5 layers are ascribed to the population of higher energy levels which evolve as the $^{3}\mathrm{He}$ thickens. The magnetization as a function of temperature near the first step is fit by a two-level model with an energy gap ${e}_{12}$\ensuremath{\approxeq}1.8 K at the step.

NMR observation of steps in the magnetization of 3He in thin 3He-4He mixture films.

We report measurements and analysis of the heat capacity of /sup 3/He in films of /sup 4/He. The data span a range of /sup 3/He coverage from 0.03 to 1 atomic layer and /sup 4/He film thickness from 10 to 45 A. We find that for cases where the /sup 3/He remains homogeneously spread out over the surface of the film, it acts like a two-dimensional gas of Fermi quasiparticles. To analyze our data, we use a model whereby the /sup 3/He retains its two-dimensional degree of freedom along the surface, but is quantized in its motion perpendicular to the surface. For thin films, up to about 25 A, a single excited state within the film is necessary to describe the data satisfactorily. For the thickest films, several excited states become necessary. Equivalently, in this case, one may assume a continuous three-dimensional spectrum. The results of our analysis show that the /sup 3/He on these films behaves quite differently from /sup 3/He at the surface of bulk /sup 4/He. The surface effective mass and excitation energy are functions of coverage and /sup 4/He thickness. This suggests that the /sup 3/He is highly interacting with the strength of the interaction beingmore » controlled by the thickness of the /sup 4/He. For the thinnest films we find that the excitation energy has a minimum as a function of coverage, at about 0.2 layer.« less

/sup 3/He in /sup 4/He films: Homogeneous two-dimensional behavior

Binding of 3 He in 4 He films

Measurements and analysis of heat capacity for /sup 3/He in /sup 4/He films at temperatures below 350 mK are reported. The data show that /sup 3/He is less bound to the free surface of the /sup 4/He film than to the bulk /sup 4/He surface, and that it has a larger effective mass. Both of these parameters depend on /sup 3/He surface coverage. The /sup 3/He dissolved within the film behaves as a two-dimensional system for sufficiently thin /sup 4/He films.

Two-dimensional /sup 3/He in /sup 4/He films

We present the results of various measurements we have made to characterize Nuclepore filters. These include nitrogen and helium adsorption isotherms, heat capacity and SEM studies of pore size distribution and pore density.

Some properties of Nuclepore filters

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Papers

/sup 3/He in /sup 4/He films: Homogeneous two-dimensional behavior

Binding of 3 He in 4 He films

Two-dimensional /sup 3/He in /sup 4/He films

Some properties of Nuclepore filters