  We use path-integral Monte Carlo (PIMC) to study the effects of adding a
long-range repulsive Coulomb interaction to the usual Van der Waals interaction
between two atoms of a submonolayer quantum film such as helium on graphite or
a pure two-dimensional superfluid. Such interactions frustrate or compete with
the natural tendency of the system for phase separation namely to form a
macroscopic liquid or solid phase. We find that as a function of the relative
strength of the long-range repulsion, surface coverage and temperature, the
system undergoes a series of transformations, including a triangular
Wigner-like crystal of clusters, a charge stripe-ordered phase and a fluid
phase. The goal of these studies is to understand the role of quantum
fluctuations when such competing interactions appear together with formation of
preexisting electron pairs as might be the case in cuprate superconductors.
