Towards a 2D nonperiodic Solid

We report on an experimental study of the two-dimensional phase behavior of colloidal dumbbells (dimers) trapped at a water-oil interface. The dimers are made out of $1.0\,\mu {\rm m}$ silica microspheres that are fused together at a point. The water-oil interface is very slightly concave so that the dimers are gently compressed by gravity towards the center of interface. The spheres form a stable dense state after a few days. The pair correlation function of single spheres exhibits order on a length scale of about 10 particle diameters. We report on the translational and orientational order of the dumbbells as a function of particle density.