  Colloids that interact via a short-range attraction serve as the primary
building blocks for a broad range of self-assembled materials. However, one of
the well-known drawbacks to this strategy is that these building blocks rapidly
and readily condense into a metastable colloidal gel. Using computer
simulations, we illustrate how the addition of a small fraction of purely
repulsive self-propelled colloids, a technique referred to as active doping,
can prevent the formation of this metastable gel state and drive the system
toward its thermodynamically favored crystalline target structure. The
simplicity and robust nature of this strategy offers a systematic and generic
pathway to improving the self-assembly of a large number of complex colloidal
structures. We discuss in detail the process by which this feat is accomplished
and provide quantitative metrics for exploiting it to modulate self-assembly.
We provide evidence for the generic nature of this approach by demonstrating
that it remains robust under a number of different anisotropic short-ranged
pair interactions in both two and three dimensions. In addition, we report on a
novel microphase in mixtures of passive and active colloids. For a broad range
of self-propelling velocities, it is possible to stabilize a suspension of
fairly monodisperse finite-size crystallites. Surprisingly, this microphase is
also insensitive to the underlying pair interaction between building blocks.
The active stabilization of these moderately-sized monodisperse clusters is
quite remarkable and should be of great utility in the design of hierarchical
self-assembly strategies. This work further bolsters the notion that active
forces can play a pivotal role in directing colloidal self-assembly.
