Quartz crystal microbalance study of superfluid ⁴He films on gold and porous gold surfaces

The superfluid transition in sub-monolayer ⁴He films was studied using quartz crystal microbalance (QCM). We recently improved the QCM technique by replacing the conventional gold electrodes with porous gold, thus increasing the surface area and therefore sensitivity by 40 times. Simultaneous measurements were taken for QCMs with flat and porous gold electrodes contained within the same copper cell. For both QCMs the superfluid transition temperature was found to be proportional to the ⁴He film thickness. The superfluid transition temperature at each film coverage was greater for porous gold than for flat gold electrodes.