in an embodiment an apparatus for coating a substrate comprises : an array of plasma arcs ; a first plurality of reagent manifolds located upstream of the array of plasma arcs and a second plurality of reagent manifolds located downstream of the array of plasma arcs , each manifold having at least one orifice through which a reagent is ejected into a plasma jet issuing from a respective plasma arc ; and a controller which modulates the flow of reagent to each manifold according to the contours of the substrate and to the substrate position relative to the plasma arcs and the manifolds .